Method for reducing strip grade of CrMo series semi-axle steel in completely annealed state

Abstract

The invention relates to a method for reducing strip grade of CrMo series semi-axle steel in a completely annealed state. The method comprises the following steps of sequentially carrying out molten iron pretreatment, converter steelmaking, refining, continuous casting, casting blank heating and rolling to obtain steel with the strip grade of less than or equal to 2.5 level, wherein the mass percentage content of sulfur in the molten iron obtained after molten iron pretreatment is less than or equal to 0.01%, the end point of operation in converter steelmaking is that the mass percentage of carbon in molten steel is greater than or equal to 0.08%, the mass percentage of phosphorus is less than or equal to 0.01%, and the slag amount is 5-7 t; the mass percentage of sulfur in the molten steel in the refining process is less than or equal to 0.005%; the content of O in the refined molten steel is less than or equal to 12 ppm, and the mass percentage content of Al is 0.025%-0.035%; the final temperature of rolling ranges from 830 DEG C to 980 DEG C. According to the method provided by the invention, through component design and finish rolling temperature selection in the molten iron pretreatment, converter steelmaking and refining processes, the strip grade in the prepared steel is less than or equal to 2.5 grades, and the heat treatment cost after hot rolling is also remarkably reduced.

Description

technical field [0001] The invention relates to the field of iron and steel, in particular to a method for reducing the band level of CrMo-based semi-shaft steel in a fully annealed state. Background technique [0002] The banded structure is one of the internal defects of the steel. It is arranged in parallel along the rolling direction, distributed in layers, and shaped like strips of ferrite grains and pearlite grains. This is because ferrite is preferentially formed in the strips formed by dendrite segregation and non-metallic inclusions when the steel undergoes phase transformation during the cooling process after hot rolling, resulting in the formation of ferrite strips, ferrite strips There is pearlite between them, and the two are distributed in layers. [0003] CrMo series bar products for automobile axle shafts are mainly medium carbon steel CrMo series, and there are two reasons for the banded structure: ①The segregation of alloy elements and impurities other tha...

AI Technical Summary

Problems solved by technology

[0007] Although some studies in the prior art have found that the segregation of alloying elements and impurities other than C in steel is the reason for the formation of banded structures, it has not explained how to control the components and whether the change of components depends on the configuration of process conditions. Reduces band formation