Copper plates ,brass plates and copper/brass plates were friction stir welded with various parameters. Experimental results show that the microstructure of the weld is characterized by its much finer grains as contras...Copper plates ,brass plates and copper/brass plates were friction stir welded with various parameters. Experimental results show that the microstructure of the weld is characterized by its much finer grains as contrasted with the coarse grains of parent materials and the heat-affected zones are very narrow. The microhardness of the copper weld is a little higher than that of parent plate. The microhardness of brass weld is about 25% higher than that of parent material. The tensile strength of copper joints increases with increasing welding speed in the test range. The range of parameters to obtain good welds for copper is much wider than that for brass. When different materials were welded, the position of copper plate before welding affected the quality of FSW joints. If the copperplate was put on the advancing side of weld, the good quality of weld could be got under proper parameters.展开更多
Quenching and partitioning(Q&P)treatment is a novel method to produce advanced high strength steel with excellent mechanical properties.In this study,combination of multiple-cyclic annealing and Q&P process wa...Quenching and partitioning(Q&P)treatment is a novel method to produce advanced high strength steel with excellent mechanical properties.In this study,combination of multiple-cyclic annealing and Q&P process was compared with traditional cold-rolled Q&P steel to investigate the microstructural characteristics and austenite retention.The results showed that retained austenite in traditional Q&P sample was principally located in the exterior of austenite transformation products,while those in multiple-cyclic annealing samples were mainly distributed inside the transformation products.With the increase in cyclic annealing number,both of austenite fraction and austenite carbon content increased,attributing to higher initial austenite carbon content and larger number of austenite/neighbored phase interface to act as carbon partitioning channel.In traditional Q&P sample,the deformed ferrite was recrystallized by sub-grain coalescence,while the austenite was newly nucleated and grew up during annealing process.As a comparison,the ferrite in multiple-cycle annealing samples was formed by means of three routes:tempered martensite that completely recovered with retention of interior martensite variant,epitaxial ferrite that formed on basis of tempered martensite,ferrite that newly nucleated and grew up during the final annealing process.Both of lath martensite and twin martensite were formed as initial martensite and then tempered during partitioning process to precipitateεcarbide with C enrichment,Mn enrichment and homogeneous Si distribution.Compared with the traditional cold-rolled Q&P steel,the Q&P specimens after multiple-cyclic annealing show smaller strength and much larger elongation,ascribing to the coarser microstructure and more efficient transformation induced plasticity(TRIP)effect deriving from retained austenite with high carbon content and larger volume fraction.The application of double annealing treatment can optimize the mechanical properties of Q&P steel to show a striking product of strength and elongation as about 29 GPa%,which efficiently exploit the potential of mechanical performance in low carbon steel.展开更多
In this paper,the best final EMS frequency for bloom continuous casting is proposed.For 280×380 bloom,the best frequency is in the range of 4;Hz.Simulation results also show that,with this frequency,the electroma...In this paper,the best final EMS frequency for bloom continuous casting is proposed.For 280×380 bloom,the best frequency is in the range of 4;Hz.Simulation results also show that,with this frequency,the electromagnetic force in the molten steel in the bloom reaches stronger and the electromechanical transformation rate of the stirring equipment is higher.The flow fields in the bloom with the various stirring parameters are simulated also.The final EMS parameters for bloom are optimized base on the simulation results.The experimental results show that,for high carbon steel,the best stirring frequency is 7 Hz and the current is 500A.In order to alleviate negative segregation of the low and medium carbon steel,the stirring frequency and the current should be 4Hz and 430A,respectively.展开更多
文摘Copper plates ,brass plates and copper/brass plates were friction stir welded with various parameters. Experimental results show that the microstructure of the weld is characterized by its much finer grains as contrasted with the coarse grains of parent materials and the heat-affected zones are very narrow. The microhardness of the copper weld is a little higher than that of parent plate. The microhardness of brass weld is about 25% higher than that of parent material. The tensile strength of copper joints increases with increasing welding speed in the test range. The range of parameters to obtain good welds for copper is much wider than that for brass. When different materials were welded, the position of copper plate before welding affected the quality of FSW joints. If the copperplate was put on the advancing side of weld, the good quality of weld could be got under proper parameters.
基金financially supported by the National Natural Science Foundation of China(Nos.51974085 and 51674080)the National Key R&D Program of China(Nos.2017YFB0304105,2017YFB0304400)the Fundamental Research Funds for the Central Universities(No.531118010562)。
文摘Quenching and partitioning(Q&P)treatment is a novel method to produce advanced high strength steel with excellent mechanical properties.In this study,combination of multiple-cyclic annealing and Q&P process was compared with traditional cold-rolled Q&P steel to investigate the microstructural characteristics and austenite retention.The results showed that retained austenite in traditional Q&P sample was principally located in the exterior of austenite transformation products,while those in multiple-cyclic annealing samples were mainly distributed inside the transformation products.With the increase in cyclic annealing number,both of austenite fraction and austenite carbon content increased,attributing to higher initial austenite carbon content and larger number of austenite/neighbored phase interface to act as carbon partitioning channel.In traditional Q&P sample,the deformed ferrite was recrystallized by sub-grain coalescence,while the austenite was newly nucleated and grew up during annealing process.As a comparison,the ferrite in multiple-cycle annealing samples was formed by means of three routes:tempered martensite that completely recovered with retention of interior martensite variant,epitaxial ferrite that formed on basis of tempered martensite,ferrite that newly nucleated and grew up during the final annealing process.Both of lath martensite and twin martensite were formed as initial martensite and then tempered during partitioning process to precipitateεcarbide with C enrichment,Mn enrichment and homogeneous Si distribution.Compared with the traditional cold-rolled Q&P steel,the Q&P specimens after multiple-cyclic annealing show smaller strength and much larger elongation,ascribing to the coarser microstructure and more efficient transformation induced plasticity(TRIP)effect deriving from retained austenite with high carbon content and larger volume fraction.The application of double annealing treatment can optimize the mechanical properties of Q&P steel to show a striking product of strength and elongation as about 29 GPa%,which efficiently exploit the potential of mechanical performance in low carbon steel.
基金Item Sponsored by the Postdoctoral gathering project in Liaoning Province(No.2011921003)
文摘In this paper,the best final EMS frequency for bloom continuous casting is proposed.For 280×380 bloom,the best frequency is in the range of 4;Hz.Simulation results also show that,with this frequency,the electromagnetic force in the molten steel in the bloom reaches stronger and the electromechanical transformation rate of the stirring equipment is higher.The flow fields in the bloom with the various stirring parameters are simulated also.The final EMS parameters for bloom are optimized base on the simulation results.The experimental results show that,for high carbon steel,the best stirring frequency is 7 Hz and the current is 500A.In order to alleviate negative segregation of the low and medium carbon steel,the stirring frequency and the current should be 4Hz and 430A,respectively.
