Phase transformation kinetics of 13Cr15Ni4Mo3N semi-austenitic precipitation hardening stainless steel during continuous cooling
Phase transformation kinetics of 13Cr15Ni4Mo3N semi-austenitic precipitation hardening stainless steel during continuous cooling was studied using a quenching phase transformation dilatometer.The relationship between volume fraction of martensite and temperature is accurately described by the modified K-M equation.The results show that the critical temperatures Ac1 and Ac3 of the experimental steel are 600 ℃ and 720 aC,respectively.After austenitizing at 1040 ℃ and cooling at any cooling rate,only martensitic transformation occurs during continuous cooling.The starting temperature Ms and finishing temperature Mf of martensite transformation are respectively determined as 99 ℃ and-75 ℃ during cooling with cooling rate of 100 ℃/s.The volume fraction of martensite calculated by lattice expansion method and lever method is similar when the cooling rate is≥1 ℃/s,while,the result calculated by lattice expansion method is larger than that calculated by lever method when cooling rate is＜1 ℃/s.When the parameter α of phase transformation kinetics is 0.03258,the K-M equation can simply and conveniently describe the martensitic transformation kinetics process of the experimental steel,but the prediction accuracy of the transformation amount in the initial stage of phase transformation is relatively low.The modified K-M equation can accurately predict the amount of martensitic transformation when considering the variation of α with temperature.
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