Reverse Transformation Behavior And Characterization Of Martensite In00Cr13Ni4Mo Steel For Hydraulic Turbine

00Cr13Ni4Mo martensitic stainless steel is widely used in turbine runners and blade materials due to its excellent comprehensive properties.Reversed austenite generated by martensite during tempering of this steel has received much attention.Existing research on the reversed austenite in 00Cr13Ni4 Mo steel mostly focuses on the influence of heat treatment process on its quantity,distribution and material properties,and scanning electron microscope(SEM)and transmission electron microscope(TEM)are the most commonly used methods to characterize the reversed austenite,metallographic number point method and X-ray diffraction(XRD)analysis are also used to determine the content of inverted austenite,but these methods are only suitable for the characterization and calculation of residual austenite at room temperature.Therefore,how to track the reverse transformation behavior of martensite in real-time in situ is of great significance for the in-depth understanding of the characteristics of reversed austenite.This thesis aims at 00Cr13Ni4 Mo martensitic stainless steel(1# steel)and a kind of00Cr13Ni4 Mo martensitic stainless steel(2# steel)micro-alloyed with V and N,using thermodilatometry to characterize the reverse transformation behaviour of martensite in real time,which carrys out in reheating and holding processes in the two steels after quenching,and estimate the content of the reversed.Then it was verified by XRD quantitative analysis.The effect of N element on the reverse transformation behavior of martensite was discussed,the main conclusions obtained are as follows:The experiment proves that the reduction of the expansion amount of the two steels after quenching at 950℃ and then holding the temperature between 580℃ and 670℃ is caused by the reverse transformation of martensite into austenite,which is estimated by the dilatometry.The content of reversed austenite is basically consistent with the XRD quantitative analysis results,which provides a new method for real-time in-situ study of the reverse transformation behavior of martensite.The content of reversed austenite generated during the heating and holding process of1# steel after quenching increases with the increase of the holding temperature,reachingthe maximum value at 670℃(50.31vol%);the content of reversed austenite generated during the heating and holding process of 2# steel after quenching shows an increase first and then a decrease trend,reaching the maximum value at 650℃(32.26vol%).The content of residual austenite at room temperature of both steels increases first and then decreases with the increase of heating and holding temperature after quenching.The stability of reversed austenite gradually reduces with the increase of heating and holding temperature.Under the same heating and holding temperature,the amount of residual austenite in 2# steel is less than 1# steel at room temperature.The incubation period of reversed austenite generated in both steels shortens with the increase of reheating temperature after quenching,and the incubation period of reversed austenite generated in 2# steel is longer than 1# steel under the same reheating temperature.The addition of elements N can increase the incubation period of reversed austenite,that is,it can inhibit the generation of reversed austenite.