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The 1045 steel with lamellar spacing of pearlite in nanometer was prepared by aluminothermic reaction casting and annealed at 873 K (600°C) with different time. Microstructures of steels were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). Tensile properties of the steels were measured. The results showed that the lamellar spacing of the pearlite increased with the annealing time. It was found that the microstructure of steels consisted of nanocrystalline-ferrite matrix and laminar pearlite phase. The average grain sizes of the ferrite were 26.9, 27.0, 26.1, and 34.9 nm for the cast steel and samples annealed for 2, 4, and 6 h, respectively. As the annealing time increased, the volume fraction of the pearlite almost remained constant, while the laminar spacing of pearlite increased from 146 to 300 nm. The tensile and yield strength varied slightly; the elongation obviously improved. After annealing for 4 h, the elongation increased to be 33%, which was the reported highest value for the steel up to now and about twice of the conventional 1045 steel. [ABSTRACT FROM AUTHOR]

Microstructures and mechanical properties of 316L stainless steels with dual phases austenite prepared by an aluminothermic reaction casting were explored. It is found that the steels consist of nano- and micro-crystalline austenite phases, a little δ ferrite and contaminations. Before and after annealing at 1073 K and 1273 K (800 °C and 1000 °C), average grain sizes of the nanocrystalline austenite phase are about 32, 31, 38 nm, respectively. Tensile strength increases first from 371 to 640 MPa and then decreases to 454 MPa. However, elongation ratio increases gradually from 16 to 23 and then 31 pct after annealing. The results illustrate that the steel after annealing at 1073 K (800 °C) has better properties, also indicating that combination of dual nano- and micro-crystalline austenite phase is conductive to improving tensile properties of materials. [ABSTRACT FROM AUTHOR]

The microstructures of 304 stainless steels with different amounts of nanocrystalline and microcrystalline austenite prepared by an aluminothermic reaction casting, without and with annealing at 1073?K for 8?h, have been investigated by X-ray diffraction, an electron probe micro-analyser, a transmission electron microscope and a scanning electron microscope. The steels, both without and with annealing, consisted of different dual nanocrystalline and microcrystalline austenite combinations and a little nanocrystalline ? ferrite, while the average grain size of the nanocrystalline austenite increased from 19 to 26?nm and volume fraction of the microcrystalline austenite increased from 17 to 30% after annealing. The tensile strength of the steel was dramatically increased from 500 to 1000?MPa and the tensile elongation ratio increased from 8 to 12% after annealing. However, the tensile strength was decreased to 600?MPa and the tensile elongation ratio increased from 12 to 22% after an annealing at 1273?K. The combination of dual nanocrystalline and microcrystalline austenite obtained after the annealing at 1073?K results in the best tensile properties. [ABSTRACT FROM AUTHOR]

Abstract: Microstructure and mechanical properties of bulk nanocrystalline Fe3Al based alloy with 5wt.% Cu prepared by aluminothermic reaction before and after annealed at 873, 1073 and 1273K for 8h were investigated. Microstructures of the alloy before and after the annealing consisted of a Fe–Al–Cu matrix, a little Al2O3 sphere and Fe3AlC x fiber phases. The matrix of the alloy before the annealing was composed a nanocrystalline phase with disordered bcc crystal structure and a little amorphous phase. The amorphous phase disappeared after the annealing and Fe3Al phase with ordered DO3 structure appeared in the alloy after annealed at 1073 and 1273K in the matrix of the alloy. Size of the Fe3AlC x fiber phase increased with the annealing temperature. The alloy after the annealing had better plasticity, higher yield strength than that of the alloy before the annealing, and the alloy after annealed at 1273K had the highest yield strength. [Copyright &y& Elsevier]

Abstract: Bulk nanocrystalline Fe3Al based materials containing 5, 10 and 15wt.% Mn element were prepared by aluminothermic reaction. The materials were analyzed by X-ray diffraction (XRD), transmission electron microscope (TEM) and electron probe microanalyzer (EPMA). Compressive behavior and hardness of the materials were investigated. It shows that all of the three materials consist of nanocrystalline matrix and a little contamination phases. The nanocrystalline matrix phases are solid solutions composed of Fe, Al and Mn elements. The nanocrystalline matrix phases of the materials containing 5 and 10wt.% Mn have disordered solid solution of bcc crystal structure and that of the material containing 15wt.% Mn has ordered DO3 crystal structure. Average grain size of the nanocrystalline matrix phases dramatically decreases at first and then increases a little with content of Mn and that of the material containing 10wt.% Mn is the smallest. The material containing 10wt.% Mn does not fracture in the compression and exhibits good plasticity, the yield strength and hardness increases at first and then decreases with content of Mn and those of the material containing 10wt.% Mn are the highest. [Copyright &y& Elsevier]

Abstract: Nano-eutectic bulk 1080 carbon steel was prepared on glass and copper substrates by an aluminothermic reaction casting. The microstructure of the steel was analyzed by an optical microscope, transmission electron microscopy, an electron probe micro-analyzer, a scanning electron microscope and X-ray diffraction. Results show that the microstructure of the steel consisted of a little cementite and lamellar eutectic pearlite. Average lamellar spacing of the pearlite prepared on copper and glass substrates was about 230nm and 219nm, respectively. Volume fraction of the pearlite of the two steels was about 95%. Hardness of the steel was about 229 and 270HV. Tensile strength was about 610 and 641MPa and tensile elongation was about 15% and 8%. Compressive strength was about 1043 and 1144MPa. Compared with the steel prepared on copper substrate, the steel prepared on glass substrate had smaller lamellar spacing of the pearlite phase and higher strength, and low ductility due to the smaller spacing. [Copyright &y& Elsevier]

Abstract: Large dimensional bulk nanocrystalline based Fe–Al–Cr alloys with 5, 10 and 15wt.% Cr which were about 200mm in diameter and 10mm in thickness was prepared by an aluminothermic reaction casting method. Microstructures of the alloys were investigated by scanning electron microscope (SEM) attached with energy dispersive spectrometer (EDS) and electron backscattered diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscope (TEM). Compressive properties of the alloys were tested. The results show that the alloys were consisted of a Fe–Al–Cr nanocrystalline matrix with the grain size in a range of 15–18nm and a precipitated Cr7C3 phase which dispersed homogeneously in the matrix. The content of Cr dissolved in the nanocrystalline matrix, volume fraction and morphology of the Cr7C3 phase varied with the increasing of Cr element added in the alloys. Compressive strength of the alloys was in a range of 1100–1200MPa. The alloy with 10wt.% Cr had the highest yield strength of about 1048MPa, while the alloy with 15wt.% Cr had the lowest yield strength of about 911MPa. The alloys showed considerable ductility and best plastic deformation capability for that of 15wt.% Cr. [Copyright &y& Elsevier]

Abstract: A white cast iron with nano-eutectic microstructure was prepared by an aluminothermic reaction casting. Microstructures of the cast iron were investigated by optical microscope (OM), electron probe micro-analyzer (EPMA), scanning electron microscope (SEM) and X-ray diffraction (XRD). Mechanical properties of the cast iron were tested. The results showed that the cast iron consisted of pearlite and cementite phases. Lamellar spacing of the pearlite phase was in a range of 110–275nm and much smaller than that of the Ni-Hard 2 cast iron. Hardness of the cast iron was 552Hv, tensile strength was 383MPa, total elongation was 3% and compressive strength was 2224MPa. Tensile strength and hardness of the cast iron was same to Ni-Hard 2 cast iron, besides the ductility was much better than that of the Ni-Hard 2 cast iron which is much expensive than the cast iron. [Copyright &y& Elsevier]

Abstract: Bulk nanocrystalline Fe3Al based materials with 5, 10 and 15wt.% Cr were prepared by aluminothermic reaction, in which melts were superheated about 1500K before solidification. Microstructures of the materials were investigated by optical microscope, electron probe microscope, X-ray diffraction and transmission electron microscope. It was shown that microstructure of the materials consist of nanocrystalline matrix phase, which was composed of Fe, Al and Cr elements, and a small amount of contamination. The nanocrystalline phase was disordered bcc structure, and which did not change with Cr content. Average grain sizes of the nanocrystalline phase of the materials with 5, 10 and 15wt.% Cr were 33, 21 and 37nm, respectively. Compressive properties and hardness of the materials were tested. It indicated that the materials had a considerable plastic deformation and were not fractured in compression. Yield strength of the materials were about three times higher but hardness were a little lower than those of Fe3Al material with coarsen grain. The hardness and yield strength of the materials varied slightly with Cr content and that of the material with 10wt.% Cr was slightly lower. Average grain sizes of the materials decreased and texture changes appeared after the compression. [Copyright &y& Elsevier]