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Instead of hot rolling and cold rolling followed by annealing, strip casting is a more economic and environmentally friendly way to produce transformation-induced plasticity (TRIP) steels. According to industrial practice of strip casting, rapid cooling in this work was achieved using a dip tester, and a Gleeble 3500 thermo-mechanical simulator was used to carry out the processing route. A typical microstructure of TRIP steels, which included ~0.55 fraction of polygonal ferrite with bainite, retained austenite and martensite, was obtained. The effects of deformation (0.41 reduction) above non-recrystallisation temperature, isothermal bainite transformation temperature and the size of second phase region on microstructure and mechanical properties were studied. The steel isothermally transformed at 400 °C had the best combination of ultimate tensile strength (UTS) and total elongation (TE), whether deformation was applied or not. The deformation resulted in the improvement of mechanical properties after holding at 400 °C: the UTS increased from 590 to 696 MPa and TE decreased from 0.27 only to 0.26. It was predominantly ascribed to grain size refinement and dislocation strengthening. The studied TRIP steel had comparable mechanical properties with TRIP 690 produced commercially.

Instead of hot rolling and cold rolling followed by annealing, strip casting is a more economic and environmentally friendly way to produce transformation-induced plasticity (TRIP) steels. According to industrial practice of strip casting, rapid cooling in this work was achieved using a dip tester, and a Gleeble 3500 thermo-mechanical simulator was used to carry out the processing route. A typical microstructure of TRIP steels, which included ~0.55 fraction of polygonal ferrite with bainite, retained austenite and martensite, was obtained. The effects of deformation (0.41 reduction) above non-recrystallisation temperature, isothermal bainite transformation temperature and the size of second phase region on microstructure and mechanical properties were studied. The steel isothermally transformed at 400 °C had the best combination of ultimate tensile strength (UTS) and total elongation (TE), whether deformation was applied or not. The deformation resulted in the improvement of mechanical properties after holding at 400 °C: the UTS increased from 590 to 696 MPa and TE decreased from 0.27 only to 0.26. It was predominantly ascribed to grain size refinement and dislocation strengthening. The studied TRIP steel had comparable mechanical properties with TRIP 690 produced commercially.

The effect of thermomechanical treatment on sliding wear of high-Cr cast iron was studied. Due to the inherent embrittlement of high-Cr cast iron, the bimetallic composites, in which the cast iron was cladded by low carbon steel, were prepared to conduct plastic deformation in the temperature range of 950-1150 °C with the strain rate of 0.001 s-1. The wear properties of the as-cast high-Cr cast iron and the bimetallic composites were compared using pin-on-disc type sliding wear tests. Experimental results demonstrated that the brittle cast iron was severely deformed with crack free at high temperatures in the form of bimetallic composites. The thermomechanical treatments not only rotated the carbide orientation with ∼90, but also increased the volume fraction of carbide. Because the long axes of carbide rods were parallel to the worn surface and the higher volume fraction of carbide provided a better protection for the ferrous matrices, the bimetallic composites bonding at 1050 and 1150 °C had a better wear resistance than the as-cast high-Cr cast iron. However, the wear resistance of the bimetallic composite bonding at 950 °C was inferior to the as-cast high-Cr cast iron due to the higher volume fraction of carbide void accelerating the wear rate on both carbide and ferrous matrix.

A hot compression bonding process was developed to prepare a novel laminated composite consisting of high-Cr cast iron (HCCI) as the inner layer and low carbon steel (LCS) as the outer layers on a Gleeble 3500 thermomechanical simulator at a temperature of 950 °C and a strain rate of 0.001 S-1. Interfacial bond quality and hot deformation behaviour of the laminate were studied by microstructural characterisation and mechanical tests. Experimental results show that the metallurgical bond between the constituent metals was achieved under the proposed bonding conditions without discernible defects and the formation of interlayer or intermetallic layer along the interface. The interfacial bond quality is excellent since no deterioration occurred around the interface which was deformed by Vickers indentation and compression test at room temperature with parallel loading to the interface. After well cladding by the LCS, the brittle HCCI can be severely deformed (about 57 % of reduction) at high temperature with crack-free. This significant improvement should be attributed to the decrease of crack sensitivity due to stress relief by soft claddings and enhanced flow property of the HCCI by simultaneous deformation with the LCS.

The effect of thermomechanical treatment on sliding wear of high-Cr cast iron was studied. Due to the inherent embrittlement of high-Cr cast iron, the bimetallic composites, in which the cast iron was cladded by low carbon steel, were prepared to conduct plastic deformation in the temperature range of 950-1150 °C with the strain rate of 0.001 s-1. The wear properties of the as-cast high-Cr cast iron and the bimetallic composites were compared using pin-on-disc type sliding wear tests. Experimental results demonstrated that the brittle cast iron was severely deformed with crack free at high temperatures in the form of bimetallic composites. The thermomechanical treatments not only rotated the carbide orientation with ∼90, but also increased the volume fraction of carbide. Because the long axes of carbide rods were parallel to the worn surface and the higher volume fraction of carbide provided a better protection for the ferrous matrices, the bimetallic composites bonding at 1050 and 1150 °C had a better wear resistance than the as-cast high-Cr cast iron. However, the wear resistance of the bimetallic composite bonding at 950 °C was inferior to the as-cast high-Cr cast iron due to the higher volume fraction of carbide void accelerating the wear rate on both carbide and ferrous matrix.

A hot compression bonding process was developed to prepare a novel laminated composite consisting of high-Cr cast iron (HCCI) as the inner layer and low carbon steel (LCS) as the outer layers on a Gleeble 3500 thermomechanical simulator at a temperature of 950 °C and a strain rate of 0.001 S-1. Interfacial bond quality and hot deformation behaviour of the laminate were studied by microstructural characterisation and mechanical tests. Experimental results show that the metallurgical bond between the constituent metals was achieved under the proposed bonding conditions without discernible defects and the formation of interlayer or intermetallic layer along the interface. The interfacial bond quality is excellent since no deterioration occurred around the interface which was deformed by Vickers indentation and compression test at room temperature with parallel loading to the interface. After well cladding by the LCS, the brittle HCCI can be severely deformed (about 57 % of reduction) at high temperature with crack-free. This significant improvement should be attributed to the decrease of crack sensitivity due to stress relief by soft claddings and enhanced flow property of the HCCI by simultaneous deformation with the LCS.

The effect of thermomechanical treatment on sliding wear of high-Cr cast iron was studied. Due to the inherent embrittlement of high-Cr cast iron, the bimetallic composites, in which the cast iron was cladded by low carbon steel, were prepared to conduct plastic deformation in the temperature range of 950-1150 °C with the strain rate of 0.001 s-1. The wear properties of the as-cast high-Cr cast iron and the bimetallic composites were compared using pin-on-disc type sliding wear tests. Experimental results demonstrated that the brittle cast iron was severely deformed with crack free at high temperatures in the form of bimetallic composites. The thermomechanical treatments not only rotated the carbide orientation with ∼90, but also increased the volume fraction of carbide. Because the long axes of carbide rods were parallel to the worn surface and the higher volume fraction of carbide provided a better protection for the ferrous matrices, the bimetallic composites bonding at 1050 and 1150 °C had a better wear resistance than the as-cast high-Cr cast iron. However, the wear resistance of the bimetallic composite bonding at 950 °C was inferior to the as-cast high-Cr cast iron due to the higher volume fraction of carbide void accelerating the wear rate on both carbide and ferrous matrix.

A hot compression bonding process was developed to prepare a novel laminated composite consisting of high-Cr cast iron (HCCI) as the inner layer and low carbon steel (LCS) as the outer layers on a Gleeble 3500 thermomechanical simulator at a temperature of 950 °C and a strain rate of 0.001 S-1. Interfacial bond quality and hot deformation behaviour of the laminate were studied by microstructural characterisation and mechanical tests. Experimental results show that the metallurgical bond between the constituent metals was achieved under the proposed bonding conditions without discernible defects and the formation of interlayer or intermetallic layer along the interface. The interfacial bond quality is excellent since no deterioration occurred around the interface which was deformed by Vickers indentation and compression test at room temperature with parallel loading to the interface. After well cladding by the LCS, the brittle HCCI can be severely deformed (about 57 % of reduction) at high temperature with crack-free. This significant improvement should be attributed to the decrease of crack sensitivity due to stress relief by soft claddings and enhanced flow property of the HCCI by simultaneous deformation with the LCS.

A hot compression bonding process was developed to prepare a novel laminated composite consisting of high-Cr cast iron (HCCI) as the inner layer and low carbon steel (LCS) as the outer layers on a Gleeble 3500 thermomechanical simulator at a temperature of 950 °C and a strain rate of 0.001 S-1. Interfacial bond quality and hot deformation behaviour of the laminate were studied by microstructural characterisation and mechanical tests. Experimental results show that the metallurgical bond between the constituent metals was achieved under the proposed bonding conditions without discernible defects and the formation of interlayer or intermetallic layer along the interface. The interfacial bond quality is excellent since no deterioration occurred around the interface which was deformed by Vickers indentation and compression test at room temperature with parallel loading to the interface. After well cladding by the LCS, the brittle HCCI can be severely deformed (about 57 % of reduction) at high temperature with crack-free. This significant improvement should be attributed to the decrease of crack sensitivity due to stress relief by soft claddings and enhanced flow property of the HCCI by simultaneous deformation with the LCS.

The effect of thermomechanical treatment on sliding wear of high-Cr cast iron was studied. Due to the inherent embrittlement of high-Cr cast iron, the bimetallic composites, in which the cast iron was cladded by low carbon steel, were prepared to conduct plastic deformation in the temperature range of 950-1150 °C with the strain rate of 0.001 s-1. The wear properties of the as-cast high-Cr cast iron and the bimetallic composites were compared using pin-on-disc type sliding wear tests. Experimental results demonstrated that the brittle cast iron was severely deformed with crack free at high temperatures in the form of bimetallic composites. The thermomechanical treatments not only rotated the carbide orientation with ∼90, but also increased the volume fraction of carbide. Because the long axes of carbide rods were parallel to the worn surface and the higher volume fraction of carbide provided a better protection for the ferrous matrices, the bimetallic composites bonding at 1050 and 1150 °C had a better wear resistance than the as-cast high-Cr cast iron. However, the wear resistance of the bimetallic composite bonding at 950 °C was inferior to the as-cast high-Cr cast iron due to the higher volume fraction of carbide void accelerating the wear rate on both carbide and ferrous matrix.

During solidification of steel, dendrite nucleation and growth leads to the segregation of alloying elements in the inter-dendritic regions. The dendrite arms are low in carbon while alloying elements segregate to the inter-dendritic regions. During subsequent hot-rolling, this variation in alloying element content leads to the formation of regions of high and low solute content, which in turn, leads to the formation of microstructural banding during heat treatment. In the present study, the respective mechanical properties of these dendritic and inter-dendritic regions were studied in medium carbon steel in order to investigate the rotation of dendrites during hot rolling.

The objective of this study is to develop a hot diffusion-compression bonding process for cladding low carbon steel (LCS) to high chromium cast iron (HCCI) in solid-state. The influence of temperature (950-1150 degrees C) and strain rate (0.001-1 s (1)) on microstructure, hardness and bond strength of the HCCI/LCS bimetal were investigated. The interface microstructure reveals that the unbonded region can only be found for 950 degrees C due to lack of diffusion, while the intergrowth between the constituent metals occurred at and above 1100 degrees C. When bonding temperature increases to 1150 degrees C, a carbide-free zone was observed near the interface on the HCCI layer, and the thickness of the zone decreases with an increase of bonding strain rate. These evolutions indicate that the bond quality was improved by raising temperature and reducing strain rate due to the increase of element diffusion. The hot compression process of the bonding treatment not only changes the carbide orientation of the HCCI, but also increases the volume fraction of Cr-carbide. Based on the microstructural examinations and mechanical tests, the optimum bonding temperature and bonding strain rate are determined to be 1150 degrees C and 0.001 s (1), respectively.

Austenite grain growth does not only play an important role in determining the mechanical properties of steel, but certain surface defects encountered in the continuous casting industry have also been attributed to the formation of large austenite grains. Earlier research has seen innovative experimentation, the development of metallographic techniques to determine austenite grain size and the building of mathematical models to simulate the conditions pertaining to austenite grain growth during the continuous casting of steel. Oscillation marks and depressions in the meniscus region of the continuously casting mold lead to retarded cooling of the strand surface, which in turn results in the formation of coarse austenite grains, but little is known about the mechanism and rate of formation of these large austenite grains. Relevant earlier research will be briefly reviewed to put into context our recent in situ observations of the delta-ferrite to austenite phase transition. We have confirmed earlier evidence that very large delta-ferrite grains are formed very quickly in the single-phase region and that these large delta-ferrite grains are transformed to large austenite grains at low cooling rates. At the higher cooling rates relevant to the early stages of the solidification of steel in a continuously cast mold, delta-ferrite transforms to austenite by an apparently massive type of transformation mechanism. Large austenite grains then form very quickly from this massive type of microstructure and on further cooling, austenite transforms to thin ferrite allotriomorphs on austenite grain boundaries, followed by Widmanstätten plate growth, with almost no regard to the cooling rate. This observation is important because it is now well established that the presence of a thin ferrite film on austenite grain boundaries is the main cause of reduction in hot ductility. Moreover, this reduction in ductility is exacerbated by the presence of large austenite grains.

During solidification of steel, dendrite nucleation and growth leads to the segregation of alloying elements in the inter-dendritic regions. The dendrite arms are low in carbon while alloying elements segregate to the inter-dendritic regions. During subsequent hot-rolling, this variation in alloying element content leads to the formation of regions of high and low solute content, which in turn, leads to the formation of microstructural banding during heat treatment. In the present study, the respective mechanical properties of these dendritic and inter-dendritic regions were studied in medium carbon steel in order to investigate the rotation of dendrites during hot rolling.

Austenite grain growth does not only play an important role in determining the mechanical properties of steel, but certain surface defects encountered in the continuous casting industry have also been attributed to the formation of large austenite grains. Earlier research has seen innovative experimentation, the development of metallographic techniques to determine austenite grain size and the building of mathematical models to simulate the conditions pertaining to austenite grain growth during the continuous casting of steel. Oscillation marks and depressions in the meniscus region of the continuously casting mold lead to retarded cooling of the strand surface, which in turn results in the formation of coarse austenite grains, but little is known about the mechanism and rate of formation of these large austenite grains. Relevant earlier research will be briefly reviewed to put into context our recent in situ observations of the delta-ferrite to austenite phase transition. We have confirmed earlier evidence that very large delta-ferrite grains are formed very quickly in the single-phase region and that these large delta-ferrite grains are transformed to large austenite grains at low cooling rates. At the higher cooling rates relevant to the early stages of the solidification of steel in a continuously cast mold, delta-ferrite transforms to austenite by an apparently massive type of transformation mechanism. Large austenite grains then form very quickly from this massive type of microstructure and on further cooling, austenite transforms to thin ferrite allotriomorphs on austenite grain boundaries, followed by Widmanstätten plate growth, with almost no regard to the cooling rate. This observation is important because it is now well established that the presence of a thin ferrite film on austenite grain boundaries is the main cause of reduction in hot ductility. Moreover, this reduction in ductility is exacerbated by the presence of large austenite grains.

The objective of this study is to develop a hot diffusion-compression bonding process for cladding low carbon steel (LCS) to high chromium cast iron (HCCI) in solid-state. The influence of temperature (950-1150 degrees C) and strain rate (0.001-1 s (1)) on microstructure, hardness and bond strength of the HCCI/LCS bimetal were investigated. The interface microstructure reveals that the unbonded region can only be found for 950 degrees C due to lack of diffusion, while the intergrowth between the constituent metals occurred at and above 1100 degrees C. When bonding temperature increases to 1150 degrees C, a carbide-free zone was observed near the interface on the HCCI layer, and the thickness of the zone decreases with an increase of bonding strain rate. These evolutions indicate that the bond quality was improved by raising temperature and reducing strain rate due to the increase of element diffusion. The hot compression process of the bonding treatment not only changes the carbide orientation of the HCCI, but also increases the volume fraction of Cr-carbide. Based on the microstructural examinations and mechanical tests, the optimum bonding temperature and bonding strain rate are determined to be 1150 degrees C and 0.001 s (1), respectively.

During solidification of steel, dendrite nucleation and growth leads to the segregation of alloying elements in the inter-dendritic regions. The dendrite arms are low in carbon while alloying elements segregate to the inter-dendritic regions. During subsequent hot-rolling, this variation in alloying element content leads to the formation of regions of high and low solute content, which in turn, leads to the formation of microstructural banding during heat treatment. In the present study, the respective mechanical properties of these dendritic and inter-dendritic regions were studied in medium carbon steel in order to investigate the rotation of dendrites during hot rolling.

Austenite grain growth does not only play an important role in determining the mechanical properties of steel, but certain surface defects encountered in the continuous casting industry have also been attributed to the formation of large austenite grains. Earlier research has seen innovative experimentation, the development of metallographic techniques to determine austenite grain size and the building of mathematical models to simulate the conditions pertaining to austenite grain growth during the continuous casting of steel. Oscillation marks and depressions in the meniscus region of the continuously casting mold lead to retarded cooling of the strand surface, which in turn results in the formation of coarse austenite grains, but little is known about the mechanism and rate of formation of these large austenite grains. Relevant earlier research will be briefly reviewed to put into context our recent in situ observations of the delta-ferrite to austenite phase transition. We have confirmed earlier evidence that very large delta-ferrite grains are formed very quickly in the single-phase region and that these large delta-ferrite grains are transformed to large austenite grains at low cooling rates. At the higher cooling rates relevant to the early stages of the solidification of steel in a continuously cast mold, delta-ferrite transforms to austenite by an apparently massive type of transformation mechanism. Large austenite grains then form very quickly from this massive type of microstructure and on further cooling, austenite transforms to thin ferrite allotriomorphs on austenite grain boundaries, followed by Widmanstätten plate growth, with almost no regard to the cooling rate. This observation is important because it is now well established that the presence of a thin ferrite film on austenite grain boundaries is the main cause of reduction in hot ductility. Moreover, this reduction in ductility is exacerbated by the presence of large austenite grains.

The objective of this study is to develop a hot diffusion-compression bonding process for cladding low carbon steel (LCS) to high chromium cast iron (HCCI) in solid-state. The influence of temperature (950-1150 degrees C) and strain rate (0.001-1 s (1)) on microstructure, hardness and bond strength of the HCCI/LCS bimetal were investigated. The interface microstructure reveals that the unbonded region can only be found for 950 degrees C due to lack of diffusion, while the intergrowth between the constituent metals occurred at and above 1100 degrees C. When bonding temperature increases to 1150 degrees C, a carbide-free zone was observed near the interface on the HCCI layer, and the thickness of the zone decreases with an increase of bonding strain rate. These evolutions indicate that the bond quality was improved by raising temperature and reducing strain rate due to the increase of element diffusion. The hot compression process of the bonding treatment not only changes the carbide orientation of the HCCI, but also increases the volume fraction of Cr-carbide. Based on the microstructural examinations and mechanical tests, the optimum bonding temperature and bonding strain rate are determined to be 1150 degrees C and 0.001 s (1), respectively.

During solidification of steel, dendrite nucleation and growth leads to the segregation of alloying elements in the inter-dendritic regions. The dendrite arms are low in carbon while alloying elements segregate to the inter-dendritic regions. During subsequent hot-rolling, this variation in alloying element content leads to the formation of regions of high and low solute content, which in turn, leads to the formation of microstructural banding during heat treatment. In the present study, the respective mechanical properties of these dendritic and inter-dendritic regions were studied in medium carbon steel in order to investigate the rotation of dendrites during hot rolling.

Austenite grain growth does not only play an important role in determining the mechanical properties of steel, but certain surface defects encountered in the continuous casting industry have also been attributed to the formation of large austenite grains. Earlier research has seen innovative experimentation, the development of metallographic techniques to determine austenite grain size and the building of mathematical models to simulate the conditions pertaining to austenite grain growth during the continuous casting of steel. Oscillation marks and depressions in the meniscus region of the continuously casting mold lead to retarded cooling of the strand surface, which in turn results in the formation of coarse austenite grains, but little is known about the mechanism and rate of formation of these large austenite grains. Relevant earlier research will be briefly reviewed to put into context our recent in situ observations of the delta-ferrite to austenite phase transition. We have confirmed earlier evidence that very large delta-ferrite grains are formed very quickly in the single-phase region and that these large delta-ferrite grains are transformed to large austenite grains at low cooling rates. At the higher cooling rates relevant to the early stages of the solidification of steel in a continuously cast mold, delta-ferrite transforms to austenite by an apparently massive type of transformation mechanism. Large austenite grains then form very quickly from this massive type of microstructure and on further cooling, austenite transforms to thin ferrite allotriomorphs on austenite grain boundaries, followed by Widmanstätten plate growth, with almost no regard to the cooling rate. This observation is important because it is now well established that the presence of a thin ferrite film on austenite grain boundaries is the main cause of reduction in hot ductility. Moreover, this reduction in ductility is exacerbated by the presence of large austenite grains.

The objective of this study is to develop a hot diffusion-compression bonding process for cladding low carbon steel (LCS) to high chromium cast iron (HCCI) in solid-state. The influence of temperature (950-1150 degrees C) and strain rate (0.001-1 s (1)) on microstructure, hardness and bond strength of the HCCI/LCS bimetal were investigated. The interface microstructure reveals that the unbonded region can only be found for 950 degrees C due to lack of diffusion, while the intergrowth between the constituent metals occurred at and above 1100 degrees C. When bonding temperature increases to 1150 degrees C, a carbide-free zone was observed near the interface on the HCCI layer, and the thickness of the zone decreases with an increase of bonding strain rate. These evolutions indicate that the bond quality was improved by raising temperature and reducing strain rate due to the increase of element diffusion. The hot compression process of the bonding treatment not only changes the carbide orientation of the HCCI, but also increases the volume fraction of Cr-carbide. Based on the microstructural examinations and mechanical tests, the optimum bonding temperature and bonding strain rate are determined to be 1150 degrees C and 0.001 s (1), respectively.

This investigation attempts to improve the wear resistance of low chromium white cast iron (LCCI) by thermomechanical treatment. The thermomechanical treatment of the brittle LCCI with crack-free was successfully carried out by bonding it with a ductile low carbon steel firstly. Afterwards the dry sliding wear behavior of as-cast (LCCI-A) and thermomechanically processed (LCCI-B) samples was studied using a pin-on-disc apparatus under different test conditions. The microstructural examination shows that the refined supercooled austenite and plenty of secondary carbides in LCCI-B replaced the original microstructure of martensite and retained austenite with network carbide in LCCI-A. This significant evolution is beneficial to form and stabilise the oxide layer on the substrate, which makes the oxidational wear rather than abrasive wear or delamination dominating the wear process so that the improvement of the wear resistance of LCCI was achieved by hot working.

The effects of thermal and thermomechanical treatments on sliding wear of graphite crystallised white cast iron (GWCI) were studied. Due to the inherent embrittlement of GWCI, a laminated metal in which the GWCI is cladded by low carbon steel was prepared for this study. Three cylindrical samples (GWCI-A, GWCI-B and GWCI-C) were machined from the same laminate. GWCI-A was kept in as-cast state while GWCI-B and GWCI-C underwent the thermal and thermomechanical treatments, respectively. The pin-on-disc type sliding wear tests were performed on the GWCI layers at room temperature. The microstructures and wear mechanisms were analysed by optical microscope, scanning electron microscope and the Vickers hardness test. Experimental results demonstrated that the GWCI, after laminating with ductile steel, can be deformed at high temperature with crack-free. The thermomechanical treatment produced a finer microstructure and crushed primary carbides in GWCI-C. Both GWCI-B and GWCI-C displayed plenty of secondary carbides in supercooled austenitic matrix, which was more favourable to squeeze the graphite and form the oxide layers than the matrix of martensite plus retained austenite in GWCI-A. The wear resistance of GWCI-C was superior to that of GWCI-A and GWCI-B because the oxidational wear rather than delamination dominated the sliding wear process.

As limited results were reported in terms of the evolution of sliding friction with growth of oxide layer in thickness during running-in, a pin-on-disc wear test was carried out in this study. 4.8Ni-1.Cr cast iron as core layer and low carbon steel as outer layers, were thermo-mechanically processed via three different routes. For samples with lower hardness due to their predominantly austenitic or martensite retarded matrices, we found that initially rapid increase of thickness of oxide layer continually lowers the sliding friction. However, after the oxide layer was beyond a certain thickness, the sliding friction began to increase consecutively. After a fluctuation of friction caused by the break-down of oxide, a mild equilibrium wear with roughly constant friction followed.

Interface adhesion between cast iron substrate and oxide layer formed during dry unidirectional sliding wear was studied by using thermo-mechanically processed 4.8Ni-1.5Cr cast iron. The purpose of the present work is to reveal the difference of the adhesion behaviour between martensitic matrix with a higher hardness and austenitic matrix with low hardness. The 4.8Ni-1.5Cr alloy was sandwiched as a middle layer with low carbon steel as outer layers and thermo-mechanically processed via (1) hot rolling (HR), (2) hot rolling and heat treatment (HT), and (3) hot rolling, heat treatment and hot compression (HC), respectively. The applied normal loads were 20 and 40. N, and the sliding speeds were 45 and 78. mm/s in sliding wear test. The durations of the wear test were 2 and 7. min, respectively for different testing rounds. It was found that the wear after running-in was always mild under the conditions of 20. N and 45. mm/s or 20. N and 78. mm/s for all the tested samples. Prior to the transition into mild oxidational wear, negative displacements of pins were observed for HT and HC samples when the applied load was raised to 40. N at the sliding speed of 78. mm/s. No similar response was observed for HR sample under the same testing condition. The possible mechanisms for the negative displacement of pin in the test are discussed in terms of the microstructure and phases of the testing samples. The effect of the hardness of the substrate on the growth and integrity of the oxide film formed during the sliding and the interface adhesion between the oxide film and substrate are also discussed. © 2012 Elsevier B.V.

Quantitative investigation is made on the elemental segregation in different zones of a heavy microalloyed cast steel by energy dispersive X-ray spectroscopy. It is demonstrated that C shows serious segregation tendency than that of Mn and Si, and the degree of C segregation in the surface zone is higher than that in the central zone. C enrichment is generally observed at both dendrite arm and grain boundaries, and more C segregation at dendrite arm boundary in contrast to that at grain boundary is found in this steel. The distribution of C concentration shows a decreased trend from root to tip along the dendrite arm boundary. The C concentration at trigeminal boundary intersection shows higher level than that at other position of the grain boundaries.

In the present work, the effects of hot forging and post-forging heat treatment on the impact fracture toughness and tensile properties of a microalloyed cast steel were investigated. Mechanical tests were used to evaluate the room temperature impact fracture toughness and tensile properties of the steel. The resulting microstructures were analysed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The extraction replica technology was used to investigate the characterisation of complex precipitates formed during heat treatment. The obtained results showed that the coarse-grained microstructure of the forged specimen was significantly refined after post-forging heat treatment. Presence of complex precipitates had a favourable effect on the formation of refined austenite grains, and consequently refined final microstructure. Hot forging was beneficial to enhance the impact fracture toughness and tensile properties of the microalloyed cast steel. After 920 °C-treatment followed by air cooling, the impact energy of the forged specimen was significantly increased from 19.3 to 208.3 J, and further enhancement in tensile properties was obtained. The enhanced impact fracture toughness and tensile properties of the microalloyed cast steel after hot forging and post-forging heat treatment were closely related to the refined and homogenised ferritic–pearlitic microstructure.

In the present work, detailed studies were made on the optimization of microstructure and mechanical properties of a low-carbon microalloyed cast steel through control of heat treatment conditions. Specimens were austenitized at temperatures ranging from 950 to 1200 °C for 2 h followed by different cooling methods (furnace, air and water). For analyzing the effect of holding time on mechanical properties, some cast specimens were austenitized at 1100 °C for different times followed by furnace cooling. After heat treatment, mechanical tests were employed to evaluate the room temperature Charpy impact and tensile properties. The characterization of complex precipitates formed during heat treatment process was investigated by using analytical electron microscopy. The results show that dissolution of vanadium-containing precipitates plays an important role in the abnormal growth of austenite grains at 1150 °C. Further growth in austenite grains at 1200 °C is caused by the dissolution of Ti-containing particles and the reduction of the amount of precipitates. Correct selection of the austenitizing temperature, holding time and cooling method is very important to improve the mechanical properties of the steel. Heat treatment at 1100 °C for 2 h followed by furnace cooling leads to the best combination of excellent Charpy impact and tensile properties.

In the present work, detailed studies were made on the optimization of microstructure and mechanical properties of a low-carbon microalloyed cast steel through control of heat treatment conditions. Specimens were austenitized at temperatures ranging from 950 to 1200 °C for 2 h followed by different cooling methods (furnace, air and water). For analyzing the effect of holding time on mechanical properties, some cast specimens were austenitized at 1100 °C for different times followed by furnace cooling. After heat treatment, mechanical tests were employed to evaluate the room temperature Charpy impact and tensile properties. The characterization of complex precipitates formed during heat treatment process was investigated by using analytical electron microscopy. The results show that dissolution of vanadium-containing precipitates plays an important role in the abnormal growth of austenite grains at 1150 °C. Further growth in austenite grains at 1200 °C is caused by the dissolution of Ti-containing particles and the reduction of the amount of precipitates. Correct selection of the austenitizing temperature, holding time and cooling method is very important to improve the mechanical properties of the steel. Heat treatment at 1100 °C for 2 h followed by furnace cooling leads to the best combination of excellent Charpy impact and tensile properties.

In the present work, the effects of hot forging and post-forging heat treatment on the impact fracture toughness and tensile properties of a microalloyed cast steel were investigated. Mechanical tests were used to evaluate the room temperature impact fracture toughness and tensile properties of the steel. The resulting microstructures were analysed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The extraction replica technology was used to investigate the characterisation of complex precipitates formed during heat treatment. The obtained results showed that the coarse-grained microstructure of the forged specimen was significantly refined after post-forging heat treatment. Presence of complex precipitates had a favourable effect on the formation of refined austenite grains, and consequently refined final microstructure. Hot forging was beneficial to enhance the impact fracture toughness and tensile properties of the microalloyed cast steel. After 920 °C-treatment followed by air cooling, the impact energy of the forged specimen was significantly increased from 19.3 to 208.3 J, and further enhancement in tensile properties was obtained. The enhanced impact fracture toughness and tensile properties of the microalloyed cast steel after hot forging and post-forging heat treatment were closely related to the refined and homogenised ferritic–pearlitic microstructure.

As limited results were reported in terms of the evolution of sliding friction with growth of oxide layer in thickness during running-in, a pin-on-disc wear test was carried out in this study. 4.8Ni-1.Cr cast iron as core layer and low carbon steel as outer layers, were thermo-mechanically processed via three different routes. For samples with lower hardness due to their predominantly austenitic or martensite retarded matrices, we found that initially rapid increase of thickness of oxide layer continually lowers the sliding friction. However, after the oxide layer was beyond a certain thickness, the sliding friction began to increase consecutively. After a fluctuation of friction caused by the break-down of oxide, a mild equilibrium wear with roughly constant friction followed.

Quantitative investigation is made on the elemental segregation in different zones of a heavy microalloyed cast steel by energy dispersive X-ray spectroscopy. It is demonstrated that C shows serious segregation tendency than that of Mn and Si, and the degree of C segregation in the surface zone is higher than that in the central zone. C enrichment is generally observed at both dendrite arm and grain boundaries, and more C segregation at dendrite arm boundary in contrast to that at grain boundary is found in this steel. The distribution of C concentration shows a decreased trend from root to tip along the dendrite arm boundary. The C concentration at trigeminal boundary intersection shows higher level than that at other position of the grain boundaries.

Interface adhesion between cast iron substrate and oxide layer formed during dry unidirectional sliding wear was studied by using thermo-mechanically processed 4.8Ni-1.5Cr cast iron. The purpose of the present work is to reveal the difference of the adhesion behaviour between martensitic matrix with a higher hardness and austenitic matrix with low hardness. The 4.8Ni-1.5Cr alloy was sandwiched as a middle layer with low carbon steel as outer layers and thermo-mechanically processed via (1) hot rolling (HR), (2) hot rolling and heat treatment (HT), and (3) hot rolling, heat treatment and hot compression (HC), respectively. The applied normal loads were 20 and 40. N, and the sliding speeds were 45 and 78. mm/s in sliding wear test. The durations of the wear test were 2 and 7. min, respectively for different testing rounds. It was found that the wear after running-in was always mild under the conditions of 20. N and 45. mm/s or 20. N and 78. mm/s for all the tested samples. Prior to the transition into mild oxidational wear, negative displacements of pins were observed for HT and HC samples when the applied load was raised to 40. N at the sliding speed of 78. mm/s. No similar response was observed for HR sample under the same testing condition. The possible mechanisms for the negative displacement of pin in the test are discussed in terms of the microstructure and phases of the testing samples. The effect of the hardness of the substrate on the growth and integrity of the oxide film formed during the sliding and the interface adhesion between the oxide film and substrate are also discussed. © 2012 Elsevier B.V.

As limited results were reported in terms of the evolution of sliding friction with growth of oxide layer in thickness during running-in, a pin-on-disc wear test was carried out in this study. 4.8Ni-1.Cr cast iron as core layer and low carbon steel as outer layers, were thermo-mechanically processed via three different routes. For samples with lower hardness due to their predominantly austenitic or martensite retarded matrices, we found that initially rapid increase of thickness of oxide layer continually lowers the sliding friction. However, after the oxide layer was beyond a certain thickness, the sliding friction began to increase consecutively. After a fluctuation of friction caused by the break-down of oxide, a mild equilibrium wear with roughly constant friction followed.

In the present work, detailed studies were made on the optimization of microstructure and mechanical properties of a low-carbon microalloyed cast steel through control of heat treatment conditions. Specimens were austenitized at temperatures ranging from 950 to 1200 °C for 2 h followed by different cooling methods (furnace, air and water). For analyzing the effect of holding time on mechanical properties, some cast specimens were austenitized at 1100 °C for different times followed by furnace cooling. After heat treatment, mechanical tests were employed to evaluate the room temperature Charpy impact and tensile properties. The characterization of complex precipitates formed during heat treatment process was investigated by using analytical electron microscopy. The results show that dissolution of vanadium-containing precipitates plays an important role in the abnormal growth of austenite grains at 1150 °C. Further growth in austenite grains at 1200 °C is caused by the dissolution of Ti-containing particles and the reduction of the amount of precipitates. Correct selection of the austenitizing temperature, holding time and cooling method is very important to improve the mechanical properties of the steel. Heat treatment at 1100 °C for 2 h followed by furnace cooling leads to the best combination of excellent Charpy impact and tensile properties.

In the present work, the effects of hot forging and post-forging heat treatment on the impact fracture toughness and tensile properties of a microalloyed cast steel were investigated. Mechanical tests were used to evaluate the room temperature impact fracture toughness and tensile properties of the steel. The resulting microstructures were analysed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The extraction replica technology was used to investigate the characterisation of complex precipitates formed during heat treatment. The obtained results showed that the coarse-grained microstructure of the forged specimen was significantly refined after post-forging heat treatment. Presence of complex precipitates had a favourable effect on the formation of refined austenite grains, and consequently refined final microstructure. Hot forging was beneficial to enhance the impact fracture toughness and tensile properties of the microalloyed cast steel. After 920 °C-treatment followed by air cooling, the impact energy of the forged specimen was significantly increased from 19.3 to 208.3 J, and further enhancement in tensile properties was obtained. The enhanced impact fracture toughness and tensile properties of the microalloyed cast steel after hot forging and post-forging heat treatment were closely related to the refined and homogenised ferritic–pearlitic microstructure.

Interface adhesion between cast iron substrate and oxide layer formed during dry unidirectional sliding wear was studied by using thermo-mechanically processed 4.8Ni-1.5Cr cast iron. The purpose of the present work is to reveal the difference of the adhesion behaviour between martensitic matrix with a higher hardness and austenitic matrix with low hardness. The 4.8Ni-1.5Cr alloy was sandwiched as a middle layer with low carbon steel as outer layers and thermo-mechanically processed via (1) hot rolling (HR), (2) hot rolling and heat treatment (HT), and (3) hot rolling, heat treatment and hot compression (HC), respectively. The applied normal loads were 20 and 40. N, and the sliding speeds were 45 and 78. mm/s in sliding wear test. The durations of the wear test were 2 and 7. min, respectively for different testing rounds. It was found that the wear after running-in was always mild under the conditions of 20. N and 45. mm/s or 20. N and 78. mm/s for all the tested samples. Prior to the transition into mild oxidational wear, negative displacements of pins were observed for HT and HC samples when the applied load was raised to 40. N at the sliding speed of 78. mm/s. No similar response was observed for HR sample under the same testing condition. The possible mechanisms for the negative displacement of pin in the test are discussed in terms of the microstructure and phases of the testing samples. The effect of the hardness of the substrate on the growth and integrity of the oxide film formed during the sliding and the interface adhesion between the oxide film and substrate are also discussed. © 2012 Elsevier B.V.

Quantitative investigation is made on the elemental segregation in different zones of a heavy microalloyed cast steel by energy dispersive X-ray spectroscopy. It is demonstrated that C shows serious segregation tendency than that of Mn and Si, and the degree of C segregation in the surface zone is higher than that in the central zone. C enrichment is generally observed at both dendrite arm and grain boundaries, and more C segregation at dendrite arm boundary in contrast to that at grain boundary is found in this steel. The distribution of C concentration shows a decreased trend from root to tip along the dendrite arm boundary. The C concentration at trigeminal boundary intersection shows higher level than that at other position of the grain boundaries.

As limited results were reported in terms of the evolution of sliding friction with growth of oxide layer in thickness during running-in, a pin-on-disc wear test was carried out in this study. 4.8Ni-1.Cr cast iron as core layer and low carbon steel as outer layers, were thermo-mechanically processed via three different routes. For samples with lower hardness due to their predominantly austenitic or martensite retarded matrices, we found that initially rapid increase of thickness of oxide layer continually lowers the sliding friction. However, after the oxide layer was beyond a certain thickness, the sliding friction began to increase consecutively. After a fluctuation of friction caused by the break-down of oxide, a mild equilibrium wear with roughly constant friction followed.

In the present work, detailed studies were made on the optimization of microstructure and mechanical properties of a low-carbon microalloyed cast steel through control of heat treatment conditions. Specimens were austenitized at temperatures ranging from 950 to 1200 °C for 2 h followed by different cooling methods (furnace, air and water). For analyzing the effect of holding time on mechanical properties, some cast specimens were austenitized at 1100 °C for different times followed by furnace cooling. After heat treatment, mechanical tests were employed to evaluate the room temperature Charpy impact and tensile properties. The characterization of complex precipitates formed during heat treatment process was investigated by using analytical electron microscopy. The results show that dissolution of vanadium-containing precipitates plays an important role in the abnormal growth of austenite grains at 1150 °C. Further growth in austenite grains at 1200 °C is caused by the dissolution of Ti-containing particles and the reduction of the amount of precipitates. Correct selection of the austenitizing temperature, holding time and cooling method is very important to improve the mechanical properties of the steel. Heat treatment at 1100 °C for 2 h followed by furnace cooling leads to the best combination of excellent Charpy impact and tensile properties.

In the present work, the effects of hot forging and post-forging heat treatment on the impact fracture toughness and tensile properties of a microalloyed cast steel were investigated. Mechanical tests were used to evaluate the room temperature impact fracture toughness and tensile properties of the steel. The resulting microstructures were analysed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The extraction replica technology was used to investigate the characterisation of complex precipitates formed during heat treatment. The obtained results showed that the coarse-grained microstructure of the forged specimen was significantly refined after post-forging heat treatment. Presence of complex precipitates had a favourable effect on the formation of refined austenite grains, and consequently refined final microstructure. Hot forging was beneficial to enhance the impact fracture toughness and tensile properties of the microalloyed cast steel. After 920 °C-treatment followed by air cooling, the impact energy of the forged specimen was significantly increased from 19.3 to 208.3 J, and further enhancement in tensile properties was obtained. The enhanced impact fracture toughness and tensile properties of the microalloyed cast steel after hot forging and post-forging heat treatment were closely related to the refined and homogenised ferritic–pearlitic microstructure.

This investigation attempts to improve the wear resistance of low chromium white cast iron (LCCI) by thermomechanical treatment. The thermomechanical treatment of the brittle LCCI with crack-free was successfully carried out by bonding it with a ductile low carbon steel firstly. Afterwards the dry sliding wear behavior of as-cast (LCCI-A) and thermomechanically processed (LCCI-B) samples was studied using a pin-on-disc apparatus under different test conditions. The microstructural examination shows that the refined supercooled austenite and plenty of secondary carbides in LCCI-B replaced the original microstructure of martensite and retained austenite with network carbide in LCCI-A. This significant evolution is beneficial to form and stabilise the oxide layer on the substrate, which makes the oxidational wear rather than abrasive wear or delamination dominating the wear process so that the improvement of the wear resistance of LCCI was achieved by hot working.

The effects of thermal and thermomechanical treatments on sliding wear of graphite crystallised white cast iron (GWCI) were studied. Due to the inherent embrittlement of GWCI, a laminated metal in which the GWCI is cladded by low carbon steel was prepared for this study. Three cylindrical samples (GWCI-A, GWCI-B and GWCI-C) were machined from the same laminate. GWCI-A was kept in as-cast state while GWCI-B and GWCI-C underwent the thermal and thermomechanical treatments, respectively. The pin-on-disc type sliding wear tests were performed on the GWCI layers at room temperature. The microstructures and wear mechanisms were analysed by optical microscope, scanning electron microscope and the Vickers hardness test. Experimental results demonstrated that the GWCI, after laminating with ductile steel, can be deformed at high temperature with crack-free. The thermomechanical treatment produced a finer microstructure and crushed primary carbides in GWCI-C. Both GWCI-B and GWCI-C displayed plenty of secondary carbides in supercooled austenitic matrix, which was more favourable to squeeze the graphite and form the oxide layers than the matrix of martensite plus retained austenite in GWCI-A. The wear resistance of GWCI-C was superior to that of GWCI-A and GWCI-B because the oxidational wear rather than delamination dominated the sliding wear process.

Quantitative investigation is made on the elemental segregation in different zones of a heavy microalloyed cast steel by energy dispersive X-ray spectroscopy. It is demonstrated that C shows serious segregation tendency than that of Mn and Si, and the degree of C segregation in the surface zone is higher than that in the central zone. C enrichment is generally observed at both dendrite arm and grain boundaries, and more C segregation at dendrite arm boundary in contrast to that at grain boundary is found in this steel. The distribution of C concentration shows a decreased trend from root to tip along the dendrite arm boundary. The C concentration at trigeminal boundary intersection shows higher level than that at other position of the grain boundaries.

Interface adhesion between cast iron substrate and oxide layer formed during dry unidirectional sliding wear was studied by using thermo-mechanically processed 4.8Ni-1.5Cr cast iron. The purpose of the present work is to reveal the difference of the adhesion behaviour between martensitic matrix with a higher hardness and austenitic matrix with low hardness. The 4.8Ni-1.5Cr alloy was sandwiched as a middle layer with low carbon steel as outer layers and thermo-mechanically processed via (1) hot rolling (HR), (2) hot rolling and heat treatment (HT), and (3) hot rolling, heat treatment and hot compression (HC), respectively. The applied normal loads were 20 and 40. N, and the sliding speeds were 45 and 78. mm/s in sliding wear test. The durations of the wear test were 2 and 7. min, respectively for different testing rounds. It was found that the wear after running-in was always mild under the conditions of 20. N and 45. mm/s or 20. N and 78. mm/s for all the tested samples. Prior to the transition into mild oxidational wear, negative displacements of pins were observed for HT and HC samples when the applied load was raised to 40. N at the sliding speed of 78. mm/s. No similar response was observed for HR sample under the same testing condition. The possible mechanisms for the negative displacement of pin in the test are discussed in terms of the microstructure and phases of the testing samples. The effect of the hardness of the substrate on the growth and integrity of the oxide film formed during the sliding and the interface adhesion between the oxide film and substrate are also discussed. © 2012 Elsevier B.V.

Intermetallic TiAl alloys are a class of innovative high-temperature materials which are developed to replace the substantially denser Ni-base alloys in low-pressure turbine blades of jet engines. By streamlining the production process of these parts, a substantial decrease in production costs can be achieved. To this end, a profound knowledge of the microstructural processes occurring during hot deformation is a prerequisite. To investigate the microstructural development during forming operations, cast and extruded as well as only cast specimens were hot-deformed and the microstructural development investigated in-situ by means of a novel diffraction method. This powder diffraction method utilizes the behavior of individual reflection spots on the Debye-Scherrer rings for deriving the materials response to the deformation imposed. It was found that the behavior of the two specimens is rather similar, although the starting microstructures show pronounced differences.

A cast iron/low carbon steel sandwich-structured bimetal fabricated through composite casting, followed by hot rolling and hot compression (40% reduction) in a vacuum, and water quenched using Gleeble 3500 thermomechanical simulator. The microstructure of a predominantly martensitic structure is transferred to a matrix with an amount of austenite. The measured results show that the macro-hardness is significantly lower due to the evolution of matrix. A considerable amount of secondary carbides were precipitated from the matrix. This study also shows that a significant difference in the value of coefficient of friction (COF) at the end when hot rolling (HR) was tested under three sets of sliding wear conditions, while those for hot rolling and heat treatment (HT) tends to be merged. An increased wear resistance of interfacial zone is expectable.

Intermetallic TiAl alloys are a class of innovative high-temperature materials which are developed to replace the substantially denser Ni-base alloys in low-pressure turbine blades of jet engines. By streamlining the production process of these parts, a substantial decrease in production costs can be achieved. To this end, a profound knowledge of the microstructural processes occurring during hot deformation is a prerequisite. To investigate the microstructural development during forming operations, cast and extruded as well as only cast specimens were hot-deformed and the microstructural development investigated in-situ by means of a novel diffraction method. This powder diffraction method utilizes the behavior of individual reflection spots on the Debye-Scherrer rings for deriving the materials response to the deformation imposed. It was found that the behavior of the two specimens is rather similar, although the starting microstructures show pronounced differences.

Intermetallic TiAl alloys are a class of innovative high-temperature materials which are developed to replace the substantially denser Ni-base alloys in low-pressure turbine blades of jet engines. By streamlining the production process of these parts, a substantial decrease in production costs can be achieved. To this end, a profound knowledge of the microstructural processes occurring during hot deformation is a prerequisite. To investigate the microstructural development during forming operations, cast and extruded as well as only cast specimens were hot-deformed and the microstructural development investigated in-situ by means of a novel diffraction method. This powder diffraction method utilizes the behavior of individual reflection spots on the Debye-Scherrer rings for deriving the materials response to the deformation imposed. It was found that the behavior of the two specimens is rather similar, although the starting microstructures show pronounced differences.