Changes in mechanical properties of high strength steel DP800 under high temperature exposure and fire service conditions
In order to reveal the mechanical properties of DP800 steel under extreme high temperature exposure and fire service conditions,the"heating-holding-air cooling"and"heating-holding-water cooling"methods were used to simulate two high temperature service conditions.The microstructure morphology characteristics and mechanical property changes of the DP800 steel after high temperature service were studied by microstructure observation and static load tensile test.The results show that under different high-temperature air cooling conditions(room temperature-200 ℃),the microstructure of the DP800 steel is ferrite and island-like martensite which is distributed at the ferrite grain boundaries.With the increase of service temperature and time,the mechanical properties of the DP800 steel are improved.High temperature water cooling has a significant impact on the microstructure and mechanical properties of the DP800 steel.With the continuous increase of service temperature,the microstructure of the DP800 steel undergoes a change law of"martensite ferritization(300-700 ℃)→ ferrite+martensite dual phase structure(700-900 ℃)"under both holding time,and the tensile strength and yield strength show a change law of"continuous decrease(300-700 ℃)→ continuous increase(700-850 ℃)→ decrease again(850-900 ℃)".Using nonlinear regression method,an empirical model for predicting the changes of the tensile strength and yield strength of the DP800 steel under high-temperature water cooling conditions with service time not exceeding 60 min with service temperature is constructed,and the maximum prediction error is only 7.88%,which can provide theoretical reference for the evaluation of the mechanical properties of the DP800 steel after high-temperature service.
dual phase steelDP800high temperature servicemechanical propertymicrostructure