Medium-manganese TRIP (Transformation-Induced Plasticity) steel and preparation method thereof

Abstract

The invention provides medium-manganese TRIP (Transformation-Induced Plasticity) steel and a preparation method thereof. According to the medium-manganese TRIP steel and the preparation method thereof, medium-manganese cold rolled steel is taken as a raw material; the cost is low; the performance of a final product is realized by adopting critical region heat preserving, quenching cooling and partitioning processes; the structure of the medium-manganese steel is controlled by utilizing an over-aging stage in a continuous annealing production line, and the residual austenite volume fraction of the structure is improved in a relatively short critical annealing time, so that mechanical properties of a product are ensured, and meanwhile, the cost is reduced as much as possible; the performance of the steel is stable, the process fluctuation has little influence on performance, and industrial production is facilitated; and the prepared medium-manganese TRIP steel is high in strength, high in elongation and good in forming property, can be widely applied to reinforcing structural parts, such as a B-pillar reinforcing plate, to improve the collision safety of an overall vehicle, and achieves the effects of reducing weight and reducing emission.

Description

technical field [0001] The invention relates to the technical field of metal materials, in particular to a medium manganese TRIP steel and a preparation method thereof. Background technique [0002] High-strength and high-plasticity are the performance goals pursued by automobile thin plates, especially the light weight of automobiles and the improvement of safety requirements, requiring steels for automotive structural parts to have high-strength plasticity. The strength-plastic product of the first generation of automotive steel is at the level of 10-20GPa·%, which can no longer meet the dual requirements of lightweight and high safety for the future development of the automotive industry; the tensile strength of the second-generation automotive steel can reach 800- 1000MPa, the strength-plastic product has reached 60GPa·%, but the second-generation automotive steel has added a large amount of alloying elements, making the cost higher. In the past few decades, after the f...

AI Technical Summary

Problems solved by technology

However, due to the very short holding time in the critical zone, generally no more than 10 minutes or even shorter, the martensite-to-austenite phase transformation process of medium manganese steel during austenitization in the critical zone is mainly controlled by manganese diffusion. Due to the relatively slow diffusion of manganese, it takes a long time to reach an equilibrium state, therefore, a short annealing time in the critical zone will affect the volume fraction of reversed austenite in the critical zone, resulting in less retained austenite in the final structure, thereby reducing elongation

[0006] Theoretically, increasing the critical annealing temperature can increase the martensite martensite→austenite transformation process speed, but there will be the following problems: First, from the perspective of thermodynamic equilibrium, although increasing the critical annealing temperature can increase the reverse austenite However, the content of carbon and manganese in the reversed austenite decreases, so that martensitic transformation occurs in the subsequent cooling process, resulting in the reduction of retained austenite in the structure and the decrease of elongation; in addition, the phase From the perspective of variable kinetics, although increasing the critical annealing temperature can obtain the required amount of reversed austenite at a shorter critical annealing time, due to the influence of manganese diffusion rate, the composition of reversed austenite is not uniform, and some austenite The content of manganese in the tenite is low, and it is easy to undergo martensitic transformation in the subsequent cooling process, resulting in the reduction of retained austenite in the final structure

Therefore, the performance deficiency of medium manganese TRIP steel caused by the short annealing time in the critical zone of the continuous annealing production line cannot be compensated by increasing the annealing temperature.

Images