Microstructural evolution of 405 stainless steel under high temperature

The ferrite-to-austenite phase transformation temperature of SA240 405 stainless steel was measured using the thermodilatometry method and calculated using Thermo-Calc.In addition,the effect of temperature and the soaking time on the microstructural evolution was investigated for various quenching and tempering treatments.The results indicated that the ferrite-to-austenite transformation of this steel started between 795 ℃and 832 ℃ and finished between 910 ℃ and 925 ℃.When the specimens were annealed above 1050 ℃,the austenite gradually transformed into ferrite;consequently,the content of as-quenched martensite decreased with increasing temperature.Moreover,when the specimens were quenched between 950 ℃ and 980 ℃,a microstructure of duplex phases comprising ferrite and martensite was obtained.Relatively high B-scale of Rockwell hardness(HRB)values were observed for quenching times of 30 60 minutes;then,the hardness gradually decreased with increasing quenching time.Tempering at 730 ℃ resulted in ferrite and tempered martensite,and no obvious residual austenite was observed.In addition,the hardness gradually decreased with increasing tempering time.