A method for obtaining ultra-fine pearlite of low-carbon and low-alloy black skin forged steel shaft

Abstract

The invention relates to a method for obtaining a low-carbon low-alloy black skin forged-steel shaft superfine pearlite. The method comprises the steps that a decarburized layer on the surface of a low-carbon low-alloy black skin forged-steel shaft is utilized as a protective layer, the high-temperature black skin forged-steel shaft and cooling liquid perform transient heat exchange, the cooling speed is reduced through the protective layer, and accordingly a superfine pearlite structure is obtained. The method comprises the following steps that (a) the black skin forged-steel shaft is put in a heat treatment furnace and is heated to reach 30-50 DEG C above critical temperature, and heat preservation is performed for set time; (b) the shaft is discharged out of the furnace and precooled, wherein precooling is performed for set time; (c) the high-temperature black skin forged-steel shaft is put in the cooling liquid for transient cooling, and accordingly the superfine pearlite structure is obtained. By adopting the obtained superfine pearlite structure, the low-carbon low-alloy black skin forged-steel shaft can have good mechanical property, and especially the yield strength can be improved by 25-35% while the process cost is not increased.

Description

technical field [0001] The invention relates to the technical field of metal heat treatment technology, in particular to a method for obtaining ultra-fine pearlite structure inside a low-carbon and low-alloy black-skinned forged steel shaft, especially suitable for low-alloy steel with a carbon equivalent of no more than 0.6% and a carbon content of less than 0.3%. Steel, special requirements for comprehensive mechanical properties in specific environments. Background technique [0002] Pearlite: English is (pearlite), which is a common structure in steel. It is a mechanical mixture composed of ferrite and cementite. It can be distinguished under a 500-fold optical microscope, and its lamellar spacing is 0.5-2.0µm. Usually, the pearlite structure inside the large low-carbon and low-alloy forged steel shaft is obtained through the normalizing process, that is, the forged steel shaft is heated to 30-50°C above the critical temperature line, and after a certain period of time, ...

AI Technical Summary

Problems solved by technology

Usually, the pearlite structure inside the large low-carbon and low-alloy forged steel shaft is obtained through the normalizing process, that is, the forged steel shaft is heated to 30-50°C above the critical temperature line, and after a certain period of time, it is air-cooled or Water spray (spray), but this traditional process can only meet the general requirements, but cannot meet the forged steel shafts with special requirements, such as 16MnD black skin forged steel shafts for low temperature, in general, the mechanical properties require yield strength ≥ 265MPa , and in special cases, the yield strength is required to be ≥320MPa, the performance has been improved by 20%, and the internal structure of the shaft at room temperature is required to be pearlite + ferrite

In this case, neither air cooling nor spraying can meet the above requirements; while using water spraying process, due to the difficulty in controlling the cooling rate and uniformity of water spraying, the heat treatment process is extremely unstable, and it is impossible to make all parts of the whole forged steel shaft All meet the requirements, and local quenching structures cannot be avoided

Therefore, the traditional heat treatment process cannot meet the performance requirements of low-carbon and low-alloy black skin forged steel shaft yield strength ≥ 320MPa, and cannot obtain ultra-fine pearlite + ferrite structure at room temperature