A kind of ultra-high strength and high toughness multi-step isothermal bainitic steel and its preparation method

Abstract

The invention relates to an ultra-high-strength, high-toughness multi-step isothermal bainite steel and a preparation method thereof. The technical solution is: first austenitize the hot-rolled billet at 850-1100°C for 0.2-5.0 hours, and then perform bainite multi-step isothermal transformation to obtain ultra-high strength and high toughness multi-step isothermal bainite steel . The multi-step isothermal transformation is as follows: the first step is to incubate in an isothermal medium for 0.2 to 3.0 hours at 250 to 450°C, the second step is to incubate in an isothermal medium for 2 to 50 hours at 220 to 350°C, and the third The first step is to keep warm in isothermal medium at 180-250°C for 24-240 hours, and the fourth step is to keep warm in isothermal medium at 150-220°C for 50-360 hours, and then cool to room temperature. The multiple steps are the first step to the second step, or the first step to the third step, or the first step to the fourth step. The bainite steel prepared by the invention has the characteristics of high hardness, high strength, high toughness, good volume stability and fine microstructure.

Description

technical field [0001] The invention belongs to the technical field of ultra-high strength steel. In particular, it relates to an ultra-high-strength, high-toughness multi-step isothermal bainite steel and a preparation method thereof. Background technique [0002] It is generally believed that the tensile strength exceeds 1500N / mm 2 The alloy structural steel is ultra-high strength steel. At present, the level of ultra-high-strength steel can be achieved through reasonable alloying and heat treatment process design, which can better meet the requirements of high efficiency and high safety. Ultra-high-strength steel is mainly used in construction machinery, high-rise buildings, rails, and armored vehicles , and other structural components subject to greater stress. Scholars at home and abroad have done a lot of beneficial exploration and development of ultra-high strength steel, in which martensite and bainite are the main matrix structures. [0003] Low-alloy ultra-high...

AI Technical Summary

Problems solved by technology

However, in these bainite steels, in order to ensure the bainite isothermal reaction at a lower temperature (200~300°C), it is usually necessary to add high carbon content to reduce the bainite finish and martensite start temperature, while high Carbon content often has a very negative effect on toughness, and the production cycle is relatively long

[0008] From the above analysis, it can be seen that the existing ultra-high-strength and high-toughness steels are either slightly insufficient in tensile strength, or insufficient in plasticity and toughness, or high in cost due to high alloying elements

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