Microstructure evolution and mechanical properties changes of automotive structural steel DP780 after simulated post-fire
By using heat treatment simulation methods,setting heating temperature,holding time and cooling method,the microstructure evolution and mechanical properties changes of automotive structural steel DP780 after being heated in a fire were studied.The results show that the microstructure of the DP780 steel is ferrite and martensite after being heated at 200-700 ℃,but the ferrite grain grows and martensite recrystallizes after the temperature increases;whether air-cooled or water-cooled,with the increase of heating temperature,the yield strength and tensile strength of the DP780 steel first slightly increase and then rapidly decrease,and the elongation is slightly lower than the original base material.Under heating conditions of 800-1000 ℃,air cooling and water cooling have a significant influence on the microstructure and properties of the DP780 steel.When heated at 800 ℃,the air cooling and water cooling microstructure of the steel is composed of original ferrite,regenerated ferrite and martensite,but the volume fraction of martensite in the latter is significantly increased,and the strength is much higher than the former.When heated at 900-1000 ℃,the austenite grain grows to form coarse bainite and martensite structure with high strength but low plasticity.The mechanical properties of the DP780 steel at high temperatures(200-700 ℃)were compared to those at room temperature.When the tensile temperature is below 400 ℃,the strength increases and the elongation decreases,and when the tensile temperature is above 400 ℃,the strength sharply decreases and the elongation increases.The results confirm that as long as the DP780 steel is heated at 200-1000 ℃,its comprehensive mechanical properties will decrease,which will pose a certain safety hazard for the continued service of accident vehicles using DP780 steel structural components.
DP780 dual-phase steelmechanical propertymicrostructurevehicle fire
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万方数据
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