Double-sided arc welding with a single power source can effectively increase the weld penetration, diminish distortion, improve welding speed and save energy. Compared to conventional arc welding processes, double-sid...Double-sided arc welding with a single power source can effectively increase the weld penetration, diminish distortion, improve welding speed and save energy. Compared to conventional arc welding processes, double-sided arc welding can generate a penetrating electromaguetic field to help to form fine dendritic microstrueture in the weld due to the symmetry of heating. Type 1Cr1SNi9Ti aastenitic stainless steel was bead-on-plate welded with double-sided arc welding and conventional plasma arc welding processes, respectively, and microstructure in the weld, heat-affected zone and base metal were examined. After analyzing the black carbon-enriched band in the weld during plasma arc welding with electron probe microanalyzer ( EPMA ) and X-ray diffraction (XRD) technology, it was found that the black band was shaped from the aggregation of ferrite in the fasion boundary. Hardness measurement showed that this black band does not apparently affect the microhardncss distribution in the weld.展开更多
High strength steel thick plate is widely used in shipbuilding, pressure vessels, etc. , the balance between weld quality and welding efficiency is becoming a research focus. In this paper, double-sided double arc fia...High strength steel thick plate is widely used in shipbuilding, pressure vessels, etc. , the balance between weld quality and welding efficiency is becoming a research focus. In this paper, double-sided double arc fiat-overhead welding experiments for high strength steel thick plate were conducted. Microstructures of weld have been observed through optical microscope (OM) and scanning electron microscope (SEM). Transformation of microstructures under thermal cycles of multi peaks was analyzed. Macro and micro hardness were also tested. The results show that the heat-affected zone (HAZ) near the fusion line experiences thermal cycles up to three times. The microstructures there are the most complex, including coarse lath martensite in original coarse-grained zone, and net-like structure along grain boundaries in critical reheat coarse-grained zone. After several times of tempering for bucking welding, the features of acicula and lath are weakened. Its microstructure approaches to the microstructure of base metal which is tempering sorbite. The hardness test shows that the maximum hardness occurs at critical reheat coarse-grained zone, the hardness of reticulation structure at grain boundary can be up to 450 HV.展开更多
This paper presents the results of equal channel angular pressing (ECAP) and subsequent heat treatment (HT) as a method to improve the wear resistance of metallic materials in friction sliding. The effect of ECAP and ...This paper presents the results of equal channel angular pressing (ECAP) and subsequent heat treatment (HT) as a method to improve the wear resistance of metallic materials in friction sliding. The effect of ECAP and HT on the microstructure and mechanical properties of low carbon steel is investigated in this work. The mechanisms of wear resistance of steel with ultrafine and nanostructures produced by equal-channel angular pressing is analyzed. The results show that ECAP at room temperature and annealing at 350°C and 450°C can be used as a technology of reducing wear in friction sliding.展开更多
The objective of this research is to design an effective and relatively simple method for controlled cooling of hot rolled steel channels by water spraying on the final cooling bed after continuous cast steel billets ...The objective of this research is to design an effective and relatively simple method for controlled cooling of hot rolled steel channels by water spraying on the final cooling bed after continuous cast steel billets passing through reheating furnace and sequential rolls to form channels. The need for this research arose as the channels were being cooled by forced air draft and natural convection which brought the temperature of the channels to about 270°C (518°F) at the shear stand. Steel at this temperature is too hot for convenient handling by the operators. Additional cooling by water spraying would be an acceptable solution but such cooling should be designed to enable an acceptable microstructure to be developed in the channel, as the microstructure of steel is strongly affected by nonequilibrium cooling through the eutectoid range: the mechanical properties of steel are a consequence of the microstructure. The approach followed in this investigation was first to develop a finite element method (FEM) to determine the temperature profiles in the channel subjected to cooling by water spraying and natural convection and arrive at suitable water spray rates to bring the temperature of the channel at the shear stand to levels suitable for convenient handling. PATRAN was used for preprocessing and ABAQUS for processing and post processing. Next, laboratory experiments were conducted to determine the microstructure and hardness of channels at the spray rates found suitable through FEM, to suggest the water spray rate most suitable for providing a temperature convenient for handling and for developing a desirable microstructure.展开更多
Semicontinuous equal-channel angular extrusion( SC-ECAE) is a novel severe plastic deformation technique that has been developed to produce ultrafine-grain steels. Instead of external forces being exerted on specime...Semicontinuous equal-channel angular extrusion( SC-ECAE) is a novel severe plastic deformation technique that has been developed to produce ultrafine-grain steels. Instead of external forces being exerted on specimens in the conventional ECAE,driving forces are applied to dies in SC-EACE. The deformation of interstitial-free( IF) steel w as performed at room temperature,and individual specimens w ere repeatedly processed at various passes. An overall grain size of 0. 55 μm w as achieved after 10 passes. During SC-ECAE,the main textures of IF steel included { 111} ,{ 110} ,{ 112} ,{ 110} ,and { 110} At an early stage,increasing dislocations induce new textures and increase intensity. When the deformation continues,low-angle boundaries are formed betw een dislocation cell bands,w hich cause some dislocation cell bands to change their orientation,and therefore,the intensity of the textures begins to decrease. After more passes,the intensity of textures continues to decrease w ith high-angle boundaries,and the sub-grains in dislocation cell bands continuously increase. The present study reports the evolution of textures during deformation; these w ere examined and characterized using high-resolution electron backscattered diffraction( EBSD) in a field emission scanning electron microscope. The mechanisms of texture evolution are discussed.展开更多
文摘Double-sided arc welding with a single power source can effectively increase the weld penetration, diminish distortion, improve welding speed and save energy. Compared to conventional arc welding processes, double-sided arc welding can generate a penetrating electromaguetic field to help to form fine dendritic microstrueture in the weld due to the symmetry of heating. Type 1Cr1SNi9Ti aastenitic stainless steel was bead-on-plate welded with double-sided arc welding and conventional plasma arc welding processes, respectively, and microstructure in the weld, heat-affected zone and base metal were examined. After analyzing the black carbon-enriched band in the weld during plasma arc welding with electron probe microanalyzer ( EPMA ) and X-ray diffraction (XRD) technology, it was found that the black band was shaped from the aggregation of ferrite in the fasion boundary. Hardness measurement showed that this black band does not apparently affect the microhardncss distribution in the weld.
基金Acknowledgments The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China under grant No. 51175119.
文摘High strength steel thick plate is widely used in shipbuilding, pressure vessels, etc. , the balance between weld quality and welding efficiency is becoming a research focus. In this paper, double-sided double arc fiat-overhead welding experiments for high strength steel thick plate were conducted. Microstructures of weld have been observed through optical microscope (OM) and scanning electron microscope (SEM). Transformation of microstructures under thermal cycles of multi peaks was analyzed. Macro and micro hardness were also tested. The results show that the heat-affected zone (HAZ) near the fusion line experiences thermal cycles up to three times. The microstructures there are the most complex, including coarse lath martensite in original coarse-grained zone, and net-like structure along grain boundaries in critical reheat coarse-grained zone. After several times of tempering for bucking welding, the features of acicula and lath are weakened. Its microstructure approaches to the microstructure of base metal which is tempering sorbite. The hardness test shows that the maximum hardness occurs at critical reheat coarse-grained zone, the hardness of reticulation structure at grain boundary can be up to 450 HV.
文摘This paper presents the results of equal channel angular pressing (ECAP) and subsequent heat treatment (HT) as a method to improve the wear resistance of metallic materials in friction sliding. The effect of ECAP and HT on the microstructure and mechanical properties of low carbon steel is investigated in this work. The mechanisms of wear resistance of steel with ultrafine and nanostructures produced by equal-channel angular pressing is analyzed. The results show that ECAP at room temperature and annealing at 350°C and 450°C can be used as a technology of reducing wear in friction sliding.
文摘The objective of this research is to design an effective and relatively simple method for controlled cooling of hot rolled steel channels by water spraying on the final cooling bed after continuous cast steel billets passing through reheating furnace and sequential rolls to form channels. The need for this research arose as the channels were being cooled by forced air draft and natural convection which brought the temperature of the channels to about 270°C (518°F) at the shear stand. Steel at this temperature is too hot for convenient handling by the operators. Additional cooling by water spraying would be an acceptable solution but such cooling should be designed to enable an acceptable microstructure to be developed in the channel, as the microstructure of steel is strongly affected by nonequilibrium cooling through the eutectoid range: the mechanical properties of steel are a consequence of the microstructure. The approach followed in this investigation was first to develop a finite element method (FEM) to determine the temperature profiles in the channel subjected to cooling by water spraying and natural convection and arrive at suitable water spray rates to bring the temperature of the channel at the shear stand to levels suitable for convenient handling. PATRAN was used for preprocessing and ABAQUS for processing and post processing. Next, laboratory experiments were conducted to determine the microstructure and hardness of channels at the spray rates found suitable through FEM, to suggest the water spray rate most suitable for providing a temperature convenient for handling and for developing a desirable microstructure.
文摘Semicontinuous equal-channel angular extrusion( SC-ECAE) is a novel severe plastic deformation technique that has been developed to produce ultrafine-grain steels. Instead of external forces being exerted on specimens in the conventional ECAE,driving forces are applied to dies in SC-EACE. The deformation of interstitial-free( IF) steel w as performed at room temperature,and individual specimens w ere repeatedly processed at various passes. An overall grain size of 0. 55 μm w as achieved after 10 passes. During SC-ECAE,the main textures of IF steel included { 111} ,{ 110} ,{ 112} ,{ 110} ,and { 110} At an early stage,increasing dislocations induce new textures and increase intensity. When the deformation continues,low-angle boundaries are formed betw een dislocation cell bands,w hich cause some dislocation cell bands to change their orientation,and therefore,the intensity of the textures begins to decrease. After more passes,the intensity of textures continues to decrease w ith high-angle boundaries,and the sub-grains in dislocation cell bands continuously increase. The present study reports the evolution of textures during deformation; these w ere examined and characterized using high-resolution electron backscattered diffraction( EBSD) in a field emission scanning electron microscope. The mechanisms of texture evolution are discussed.