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Investigations of microstructural and hardness gradients in the heat-affected zone (HAZ) of quenched and tempered (Q&T) steels have indicated that peak hardness does not occur in the grain-coarsened heat-affected zone (GCHAZ) adjacent to the fusion boundary, which is typical of ferritic steels, but corresponds more closely to the grain-refined region (GRHAZ). This phenomenon, the displaced hardness peak (DHP) effect, is considered to arise when the hardenability of the steel is high enough to result in the same microstructure in the GC and GR heat-affected zones, except for significant refinement of the microstructure of the GRHAZ, which increases the hardness and strength above those of the GCHAZ. The current paper concentrates on the effect of grain size on hardness in the HAZ of a boron-containing low-carbon martensitic steel subjected to bead-on-plate welding. Thermal simulation experiments were used to clarify the relationship between prior austenite grain size and the hardness gradients in the actual HAZ. The simulation work demonstrated that peak hardness in simulation samples occurred in regions of lower austenite grain size, supporting the proposed origin of the DHP effect in actual welds. Implications regarding hydrogen-induced cold cracking (HICC) susceptibility of the GRHAZ are discussed.

Investigations of microstructural and hardness gradients in the heat-affected zone (HAZ) of quenched and tempered (Q&T) steels have indicated that peak hardness does not occur in the grain-coarsened heat-affected zone (GCHAZ) adjacent to the fusion boundary, which is typical of ferritic steels, but corresponds more closely to the grain-refined region (GRHAZ). This phenomenon, the displaced hardness peak (DHP) effect, is considered to arise when the hardenability of the steel is high enough to result in the same microstructure in the GC and GR heat-affected zones, except for significant refinement of the microstructure of the GRHAZ, which increases the hardness and strength above those of the GCHAZ. The current paper concentrates on the effect of grain size on hardness in the HAZ of a boron-containing low-carbon martensitic steel subjected to bead-on-plate welding. Thermal simulation experiments were used to clarify the relationship between prior austenite grain size and the hardness gradients in the actual HAZ. The simulation work demonstrated that peak hardness in simulation samples occurred in regions of lower austenite grain size, supporting the proposed origin of the DHP effect in actual welds. Implications regarding hydrogen-induced cold cracking (HICC) susceptibility of the GRHAZ are discussed.

Investigations of microstructural and hardness gradients in the heat-affected zone (HAZ) of quenched and tempered (Q&T) steels have indicated that peak hardness does not occur in the grain-coarsened heat-affected zone (GCHAZ) adjacent to the fusion boundary, which is typical of ferritic steels, but corresponds more closely to the grain-refined region (GRHAZ). This phenomenon, the displaced hardness peak (DHP) effect, is considered to arise when the hardenability of the steel is high enough to result in the same microstructure in the GC and GR heat-affected zones, except for significant refinement of the microstructure of the GRHAZ, which increases the hardness and strength above those of the GCHAZ. The current paper concentrates on the effect of grain size on hardness in the HAZ of a boron-containing low-carbon martensitic steel subjected to bead-on-plate welding. Thermal simulation experiments were used to clarify the relationship between prior austenite grain size and the hardness gradients in the actual HAZ. The simulation work demonstrated that peak hardness in simulation samples occurred in regions of lower austenite grain size, supporting the proposed origin of the DHP effect in actual welds. Implications regarding hydrogen-induced cold cracking (HICC) susceptibility of the GRHAZ are discussed.

Investigations of microstructural and hardness gradients in the heat-affected zone (HAZ) of quenched and tempered (Q&T) steels have indicated that peak hardness does not occur in the grain-coarsened heat-affected zone (GCHAZ) adjacent to the fusion boundary, which is typical of ferritic steels, but corresponds more closely to the grain-refined region (GRHAZ). This phenomenon, the displaced hardness peak (DHP) effect, is considered to arise when the hardenability of the steel is high enough to result in the same microstructure in the GC and GR heat-affected zones, except for significant refinement of the microstructure of the GRHAZ, which increases the hardness and strength above those of the GCHAZ. The current paper concentrates on the effect of grain size on hardness in the HAZ of a boron-containing low-carbon martensitic steel subjected to bead-on-plate welding. Thermal simulation experiments were used to clarify the relationship between prior austenite grain size and the hardness gradients in the actual HAZ. The simulation work demonstrated that peak hardness in simulation samples occurred in regions of lower austenite grain size, supporting the proposed origin of the DHP effect in actual welds. Implications regarding hydrogen-induced cold cracking (HICC) susceptibility of the GRHAZ are discussed.

This is the first transmission Kikuchi diffraction (TKD) study to report the indexing of nano-sized cementite as distinct structures and its orientation relationship with the body-centered cubic matrix in a quenched and tempered steel. Crystallographic analysis via TKD and selected area diffraction returned the well-known Bagaryatskii and Isaichev orientation relationships. However, the indexing of nano-sized cementite via TKD was sensitive to the thickness of the electron transparent region such that TEM remains the most precise method to characterise such precipitates.

A systematic study has been carried out on the electronic band structure and density of states, crystal structures, thermoelectric properties, and hardness of the Cu2-xSe system with and without Te2− or I− substitutions for Se2−. Density functional theory calculations indicate that stoichiometric Cu2Se is a zero-gap material, and copper-deficient Cu1.875Se is a p-type conductor. Te2- substitution increases the total density of states at the Fermi level, whereas, the I− substitution leads to the reduction of the total and partial density of states for both Se and Cu. Highly dense undoped, Te-doped, and I-doped Cu2-xSe bulks have been fabricated by a melt-quenching method which only takes a few minutes. Rietveld refinements of the X-ray diffraction patterns reveal that the unit cells are expanded after doping. All the fabricated bulks are p-type conductors in accordance with band structure calculations, and they all have figure of merit, zT, values over or close to 1.0 at T = 973 K, except for the Cu2-xTe0.16Se0.84. Furthermore, the hardness is distinctly improved by the doping approach, with a maximum value of ca. 0.66 GPa for the Cu2-xTe0.16Se0.84, which is higher than those of polycrystalline Bi2Te3 and PbTe bulks.

Practical applications of the high temperature thermoelectric materials developed so far are partially obstructed by the costly and complicated fabrication process. In this work, we put forward two additional important properties for thermoelectric materials, high crystal symmetry and congruent melting. We propose that the recently discovered thermoelectric material Cu2-xSe, with figure of merit, zT, over 1.5 at T of ~ 1000 K, should meet these requirements, based on our analysis of its crystal structure and the Cu-Se binary phase diagram. We found that its excellent thermoelectric performance is intrinsic, and less dependent on grain size, while highly dense samples can be easily fabricated by a melt-quenching approach. Our results reveal that the melt-quenched samples and single crystals exhibit almost the same superior thermoelectric performance, with zT as high as 1.7-1.8 at T of ~973 K. Our findings not only provide a cheap and fast fabrication method for highly dense Cu2-xSe bulks with superior thermoelectric performance, paving the way for possible commercialization of Cu2-xSe as an outstanding component in practical thermoelectric modules, but also provide guidance in searching for new classes of thermoelectric systems with high crystal symmetry or further improving the cost performance of other existing congruent-melting thermoelectric materials.

A systematic study has been carried out on the electronic band structure and density of states, crystal structures, thermoelectric properties, and hardness of the Cu2-xSe system with and without Te2− or I− substitutions for Se2−. Density functional theory calculations indicate that stoichiometric Cu2Se is a zero-gap material, and copper-deficient Cu1.875Se is a p-type conductor. Te2- substitution increases the total density of states at the Fermi level, whereas, the I− substitution leads to the reduction of the total and partial density of states for both Se and Cu. Highly dense undoped, Te-doped, and I-doped Cu2-xSe bulks have been fabricated by a melt-quenching method which only takes a few minutes. Rietveld refinements of the X-ray diffraction patterns reveal that the unit cells are expanded after doping. All the fabricated bulks are p-type conductors in accordance with band structure calculations, and they all have figure of merit, zT, values over or close to 1.0 at T = 973 K, except for the Cu2-xTe0.16Se0.84. Furthermore, the hardness is distinctly improved by the doping approach, with a maximum value of ca. 0.66 GPa for the Cu2-xTe0.16Se0.84, which is higher than those of polycrystalline Bi2Te3 and PbTe bulks.

Practical applications of the high temperature thermoelectric materials developed so far are partially obstructed by the costly and complicated fabrication process. In this work, we put forward two additional important properties for thermoelectric materials, high crystal symmetry and congruent melting. We propose that the recently discovered thermoelectric material Cu2-xSe, with figure of merit, zT, over 1.5 at T of ~ 1000 K, should meet these requirements, based on our analysis of its crystal structure and the Cu-Se binary phase diagram. We found that its excellent thermoelectric performance is intrinsic, and less dependent on grain size, while highly dense samples can be easily fabricated by a melt-quenching approach. Our results reveal that the melt-quenched samples and single crystals exhibit almost the same superior thermoelectric performance, with zT as high as 1.7-1.8 at T of ~973 K. Our findings not only provide a cheap and fast fabrication method for highly dense Cu2-xSe bulks with superior thermoelectric performance, paving the way for possible commercialization of Cu2-xSe as an outstanding component in practical thermoelectric modules, but also provide guidance in searching for new classes of thermoelectric systems with high crystal symmetry or further improving the cost performance of other existing congruent-melting thermoelectric materials.

Practical applications of the high temperature thermoelectric materials developed so far are partially obstructed by the costly and complicated fabrication process. In this work, we put forward two additional important properties for thermoelectric materials, high crystal symmetry and congruent melting. We propose that the recently discovered thermoelectric material Cu2-xSe, with figure of merit, zT, over 1.5 at T of ~ 1000 K, should meet these requirements, based on our analysis of its crystal structure and the Cu-Se binary phase diagram. We found that its excellent thermoelectric performance is intrinsic, and less dependent on grain size, while highly dense samples can be easily fabricated by a melt-quenching approach. Our results reveal that the melt-quenched samples and single crystals exhibit almost the same superior thermoelectric performance, with zT as high as 1.7-1.8 at T of ~973 K. Our findings not only provide a cheap and fast fabrication method for highly dense Cu2-xSe bulks with superior thermoelectric performance, paving the way for possible commercialization of Cu2-xSe as an outstanding component in practical thermoelectric modules, but also provide guidance in searching for new classes of thermoelectric systems with high crystal symmetry or further improving the cost performance of other existing congruent-melting thermoelectric materials.

A systematic study has been carried out on the electronic band structure and density of states, crystal structures, thermoelectric properties, and hardness of the Cu2-xSe system with and without Te2− or I− substitutions for Se2−. Density functional theory calculations indicate that stoichiometric Cu2Se is a zero-gap material, and copper-deficient Cu1.875Se is a p-type conductor. Te2- substitution increases the total density of states at the Fermi level, whereas, the I− substitution leads to the reduction of the total and partial density of states for both Se and Cu. Highly dense undoped, Te-doped, and I-doped Cu2-xSe bulks have been fabricated by a melt-quenching method which only takes a few minutes. Rietveld refinements of the X-ray diffraction patterns reveal that the unit cells are expanded after doping. All the fabricated bulks are p-type conductors in accordance with band structure calculations, and they all have figure of merit, zT, values over or close to 1.0 at T = 973 K, except for the Cu2-xTe0.16Se0.84. Furthermore, the hardness is distinctly improved by the doping approach, with a maximum value of ca. 0.66 GPa for the Cu2-xTe0.16Se0.84, which is higher than those of polycrystalline Bi2Te3 and PbTe bulks.

In this study, the feasibility of hybrid laser-gas metal arc welding process for replacement of conventional flux-cored arc welding procedure for welding high strength quenched and tempered steel was investigated. Experimental work focused on optimisation of process parameters to produce joint with desired properties. Hardness of the weld heat affected zone produced by both processes has been measured. Productivity and cost effectiveness of both processes were compared. It was concluded that hybrid laser-gas metal arc welding process is suitable for welding high strength quenched and tempered steel.

In this study, the feasibility of hybrid laser-gas metal arc welding process for replacement of conventional flux-cored arc welding procedure for welding high strength quenched and tempered steel was investigated. Experimental work focused on optimisation of process parameters to produce joint with desired properties. Hardness of the weld heat affected zone produced by both processes has been measured. Productivity and cost effectiveness of both processes were compared. It was concluded that hybrid laser-gas metal arc welding process is suitable for welding high strength quenched and tempered steel.

This paper concentrates on the form of the hardness gradient in the heat affected zones (HAZs) produced by submerged arc welding of two low-carbon Q & T steels. The results show unequivocally that the gradient differs from that found in steels of lower carbon equivalent in that the peak HAZ hardness is displaced from the grain coarsened heat affected zone (GCHAZ) into the grain refined heat affected zone (GRHAZ). Weld thermal cycle simulation has been used to confirm the results obtained from actual welds and to clarify the cause of this unexpected phenomenon.

This paper concentrates on the form of the hardness gradient in the heat affected zones (HAZs) produced by submerged arc welding of two low-carbon Q & T steels. The results show unequivocally that the gradient differs from that found in steels of lower carbon equivalent in that the peak HAZ hardness is displaced from the grain coarsened heat affected zone (GCHAZ) into the grain refined heat affected zone (GRHAZ). Weld thermal cycle simulation has been used to confirm the results obtained from actual welds and to clarify the cause of this unexpected phenomenon.

This paper concentrates on the form of the hardness gradient in the heat affected zones (HAZs) produced by submerged arc welding of two low-carbon Q & T steels. The results show unequivocally that the gradient differs from that found in steels of lower carbon equivalent in that the peak HAZ hardness is displaced from the grain coarsened heat affected zone (GCHAZ) into the grain refined heat affected zone (GRHAZ). Weld thermal cycle simulation has been used to confirm the results obtained from actual welds and to clarify the cause of this unexpected phenomenon.

This paper concentrates on the form of the hardness gradient in the heat affected zones (HAZs) produced by submerged arc welding of two low-carbon Q & T steels. The results show unequivocally that the gradient differs from that found in steels of lower carbon equivalent in that the peak HAZ hardness is displaced from the grain coarsened heat affected zone (GCHAZ) into the grain refined heat affected zone (GRHAZ). Weld thermal cycle simulation has been used to confirm the results obtained from actual welds and to clarify the cause of this unexpected phenomenon.

In this study, the continuous cooling phase transformation behaviour of a quenched and tempered armour steel was investigated. A continuous cooling transformation diagram was constructed providing valuable information for predicting microstructural evolution and mechanical properties at different cooling rates during actual welding fabrication. Welding trials were carried out utilising flux-cored arc welding technique in combination with an austenitic stainless steel consumable. The effect of various preheat and interpass temperatures on cooling rate and consequently on the heat affected zone microstructure and mechanical properties of multipass welds were investigated.

In this study, the continuous cooling phase transformation behaviour of a quenched and tempered armour steel was investigated. A continuous cooling transformation diagram was constructed providing valuable information for predicting microstructural evolution and mechanical properties at different cooling rates during actual welding fabrication. Welding trials were carried out utilising flux-cored arc welding technique in combination with an austenitic stainless steel consumable. The effect of various preheat and interpass temperatures on cooling rate and consequently on the heat affected zone microstructure and mechanical properties of multipass welds were investigated.

In this study, the continuous cooling phase transformation behaviour of a quenched and tempered armour steel was investigated. A continuous cooling transformation diagram was constructed providing valuable information for predicting microstructural evolution and mechanical properties at different cooling rates during actual welding fabrication. Welding trials were carried out utilising flux-cored arc welding technique in combination with an austenitic stainless steel consumable. The effect of various preheat and interpass temperatures on cooling rate and consequently on the heat affected zone microstructure and mechanical properties of multipass welds were investigated.

In this study, the continuous cooling phase transformation behaviour of a quenched and tempered armour steel was investigated. A continuous cooling transformation diagram was constructed providing valuable information for predicting microstructural evolution and mechanical properties at different cooling rates during actual welding fabrication. Welding trials were carried out utilising flux-cored arc welding technique in combination with an austenitic stainless steel consumable. The effect of various preheat and interpass temperatures on cooling rate and consequently on the heat affected zone microstructure and mechanical properties of multipass welds were investigated.