Quenching structure of Crl3 stainless steel

2Crl3 stainless steel is a hypoeutectoid steel. The temperature is raised to the austenite transformation temperature and kept for a period of time to make its austenite nucleate more evenly. Then, it is cooled rapidly. This process is called foreign fire. The MS of Crl3 type stainless steel is 250-350 ° C according to the C content, and the 2Crl3 is 280 ° C according to the data. Fig. 1 is the general Austenite Isothermal Transformation Curve of Crl3 type stainless steel. After the Cr content of the material changes, the “C curve” shifts to the right, because Cr element reduces the sensitivity of cooling rate.

Generally speaking, the quenching temperature of 2Cr13 is about 1000 ° C, and the dissolution effect of carbides in the matrix is not good at low temperature, which makes Cr and other alloy elements unable to perform good solid solution strengthening, resulting in poor strong bremsstrahlung effect and corrosion resistance of 2Cr13. More seriously, a “carbide net” will appear to separate and split the matrix structure. However, when the temperature is about 1050 ° C, It may lead to coarse crystal nucleus and improve the temper brittleness sensitivity, which we need to study and discuss in depth. However, the quenching temperature of steels with high carbon content, such as 3013 and 4Crl3, can be appropriately increased without causing coarse structure, because the increase of carbides improves the stability of the matrix, and the high-temperature unfused carbides prevent the growth of crystal nuclei.

a.920°C + L H b.1050°C + L H (X200)

Crl3 type 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 structure of the matrix is not completely recrystallized and the degree of alloying is high. The sorbite formed after high-temperature tempering has the martensite morphology of the quenching structure, This is also a basis for looking at the morphology and size of the original austenite. If the size of martensite is large, the original austenite grain size is also large, and the overheating is large and easy to see. Fig. 2 shows the comparison of the microstructure between quenching at 920 ° C + LH and panning at 1050 ° C + LH. It is obvious that the size of the original austenite grain is different. At 1050 ° C, the austenite has been heated, resulting in coarseness of austenite. The size of martensite is also greater than 50 μ m。

2Crl3 may have another situation under high temperature quenching conditions, that is δ - The precipitation of ferrite forms the mixture of carbide and austenite after cooling. This common eutectoid phenomenon in stainless steel is δ Eutectoid, the process is 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. This phenomenon makes the carbide and austenite thin-film layered. The microstructure as shown in Fig. 3 is obtained by querying the data. All performance indexes of this kind of organization have declined.

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