Selection and calculation of quenching heating temperature

The quenching temperature is related to the chemical composition of steel

Subeutectoid steel t = Ac3+(30 ~ 70)°C

Eutectoid steel, supereutectoid steel t = Ac1+(30 ~ 70)°C

Why should subeutectoid carbon steel be quenched after being heated to Ac3 or above?

If the heating temperature between Ac1 ~ Ac3, part of the ferrite were found to exist in the organization, in subsequent quenching, preserved due to ferrite don't change, and it is the existence of steel quenching organization exists in the soft point, reduces the hardness of hardened steel, at the same time it also affects the uniformity of steel, influence the mechanical properties, heat above Ac3 too high also not line, steel oxidation decarbonization serious, on the other hand A fine grain of bulky, M thick, after quenching steel performance deteriorate.

Why is the quenching temperature of supereutectoid steel between Ac1 and Ac3?

Before the first hypereutectoid steel quenching heating, go through spheroidizing, when heated to Ac1 ~ between Acm group as part A and unfused Fe3C, and after quenching, A - > M, Fe3C be preserved, Fe3C hardness is very high, it's there, can improve the hardness and wear resistance of steel, if the hypereutectoid steel quenching heating to Acm above, has the following disadvantages:

1. Due to the incorporation of Fe3C into A, the carbon content of steel increases, the Ms point decreases, and the amount of residual A increases after quenching, which in turn reduces the hardness and wear resistance of steel.

2.A fine grain is coarsed, M is thicker after quenching, the crystal microcracks increase, and the brittleness of steel increases greatly.

3. The oxidation and decarbonization of steel is serious, which reduces the surface quality of steel.

4. The increase of quenching stress increases the tendency of workpiece deformation and cracking.

In addition to the above steel quenching heating temperature selection principle, for the same chemical composition of the steel, due to the shape and size of the workpiece, quenching cooling medium or quenching method is different, so the quenching heating temperature to consider the influence of various factors, combined with the specific situation.