2Crl3 is a hypoeutectoid steel. Raise the temperature to the austenite transformation temperature, hold it for a period of time to make its austenite nucleate more evenly, and then cool it rapidly. This process is called foreign fire. The MS of Crl3 stainless steel is 250-350 ° C according to the different C content, and 2Crl3 is 280 ° 0 according to the data. Figure 1.3 shows the general Austenite Isothermal Transformation Curve of Crl3 stainless steel. After the change of Cr content, the “C curve” shifts to the right, This is because CR reduces the sensitivity of cooling rate.
Generally speaking, the quenching temperature of 2Cr13 is about 100ctc, and the dissolution effect of carbides in the matrix at low temperature is not good, so that Cr and other alloy elements can not play a good solid solution strengthening, resulting in poor strong bremsstrahlung effect and corrosion resistance effect of 2Crl3, More seriously, the “carbide net” will separate and split the matrix structure, but when the temperature is about 105ctc, it may produce coarse crystal nucleus and improve the sensitivity to tempering brittleness, which we need to further study and discuss. However, the quenching temperature of high carbon content steels such as 3013 and 4Crl3 can be appropriately increased without coarse structure, because the increase of carbides improves the stability of the matrix, and high-temperature unmelted carbides prevent the growth of crystal nucleus.
Crl3 stainless steel also has good temper brittleness resistance on the premise of rich Cr content. The general high-temperature tempering temperature can also maintain good strong initial property, because the matrix structure is not completely recrystallized and the degree of alloying is high. The sorbite formed after high-temperature tempering has the martensite morphology of quenching structure, This is also a basis to look at the morphology and size of the original austenite. If the size of martensite is large, the grain size of the original austenite is also large, and the overheating is coarse and easy to see. Figure 1.4 shows the temperature at 920 ° C + LH
Compared with the microstructure diagram of 1050 ° C + LH pan fire, there is an obvious difference in the size of the original austenite grain. After heat at 1050 ° C, the austenite is coarse, and the martensite size is greater than 50 due to foreign fire μ m 。
Another situation may occur in 2Crl3 under high temperature quenching conditions, that is δ － The precipitation of ferrite and cooling form the mixture of carbide and austenite. This common eutectoid phenomenon in stainless steel is δ Eutectoid process δ － Ferrite precipitates carbides between austenite grain boundaries, δ－ Ferrite is unstable and transformed into austenite, adjacent to δ － Ferrite will also be unstable and transformed into austenite and carbide, which makes the film layer between carbide and austenite. The microstructure as shown in the figure is obtained by querying the data. All performance indexes of this kind of tissue decreased.