High-yield-strength and high-toughness-and-plasticity finish-rolled twisted steel and production method thereof

Abstract

The invention discloses high-yield-strength and high-toughness-and-plasticity finish-rolled twisted steel and a production method thereof. The high-yield-strength and high-toughness-and-plasticity finish-rolled twisted steel comprises the following chemical components of, in percentage by mass, 0.20%-0.35% of C, 0.25%-0.46% of Si, 1.7%-1.8% of Mn, less than or equal to 0.03% of P, less than or equal to 0.03% of S, 0.45%-0.5% of Cr, 0.4%-0.5% of W, 0.3%-0.45% of Cu, 0.02%-0.04% of Nb, and the balance Fe, wherein the sum of Cr, W and Cu is less than or equal to 1.5%, Cu is selectively added. The production method of the high-yield-strength and high-toughness-and-plasticity finish-rolled twisted steel comprises the steps of smelting, continuous casting, rolling and heat treatment, wherein after rolling, air cooling is carried out to obtain a bainite, martensite and retained austenite complex-phase refined structure; and high-temperature tempering is adopted, the martensite is decomposed and fully softened, pretreatment is not needed before tempering, and carbides in the tempered product do not grow obviously. The high-yield-strength and high-toughness-and-plasticity finish-rolled twisted steel has yield strength larger than or equal to 800 MPa, the tensile strength larger than or equal to 970 MPa, the ductility larger than or equal to 16%, and the impact energy KV2 larger than or equal to 50 J at 20 DEG C; and the finish-rolled twisted steel is excellent in comprehensive performance, has the characteristics of being high in yield strength, high in impact toughness and high in extension, is simple in production process, is particularly suitable for the field of anchor rod support, and can improve the safety level of deep mine support and save the support cost.

Description

technical field [0001] The invention relates to the field of low-alloy high-strength steel and the field of bolt support, in particular to a high-yield strength, high-toughness plastic finish-rolled threaded steel bar and a production method thereof. Background technique [0002] Bolt support is the most important support method for coal mine roadways in my country, accounting for more than 70% of the total coal mine roadway support, and has played an important role in safe and efficient mine construction and production. At present, according to GB / T 35056-2018 Coal Mine Roadway Bolting Technical Specifications, the bolt body materials in my country mainly use MG335, MG400, MG500 and MG600 series threaded steel bars, and their grades correspond to the yield strength grades, and their chemical components are mainly 20MnSi, 25MnSi, its metallographic structure is mainly ferrite and pearlite or tempered martensite structure, and its yield strength grade is still relatively low. ...

AI Technical Summary

Problems solved by technology

However, for high-strength air-cooled bainitic steel with a slightly higher carbon content, the plasticity effect induced by the phase transformation of the retained austenite with high carbon content is weakened, and the martensite plays a leading role in the ductility and plasticity of the material. The degree of softening of the phase martensite is still not enough. During the stretching process, it is easy to generate cracks along the martensite phase or martensite lath interface first, and lead to fracture failure of the material, which limits the further improvement of the plastic toughness of high-strength bainite steel. technical shortcomings

Moreover, in the existing high-temperature tempering process, more pretreatments are carried out before tempering, such as cryogenic treatment or bainite interval isothermal, to eliminate residual austenite, which reduces production efficiency and increases production costs

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