The incomplete quenching of 45 steel is a sub-temperature quenching process, that is, the quenching process is heated in ferrite+austenite two-phase zone. The Ac 1 of 45 steel is 727℃, and the Ac3 is about 770℃. I have done relevant papers at school. This picture shows the heating temperature lower line. From the perspective of raw materials, your raw materials have not been normalized, and the grain of raw materials is uneven. If normalized, ferrite and granular bainite in the figure should be evenly distributed. There may be controversy about granular bainite, some of which are called island martensite, which is mainly due to the unstable structure and inaccurate phase transformation during sub-temperature quenching. If it is academic research, you can go deep into it and skip industrial production directly. White is ferrite, and black is granular bainite or island martensite.

This material is meaningless in production.

If you want to improve the organization, you can normalize it first. The best pretreatment is conditioning. After tempering, sub-temperature treatment is carried out, and the temperature of sub-temperature treatment can be 8 10-820, which is better.

In addition, sub-temperature treatment is not commonly used in production. If you want to get good strength and toughness, just change the material. There's no need to toss. It is better to use 40Cr or 42RrMo directly.