High-strength heat-treated steel bar and manufacturing method thereof

Abstract

The invention discloses a high-strength heat-treated steel bar and a manufacturing method thereof. The steel bar is processed through an induction heating process. During cooling, the steel bar is first annealed to a two-phase region, and then rapid cooling treatment is carried out. The steel bar satisfies mechanical performances of: a tensile strength of 1200-1800MPa, an elongation rate higher than 10%, and a yield strength ratio no higher than 0.9. The relaxation performance of the steel bar satisfies that: when initial stress is 70% of a nominal tensile strength, a stress relaxation rate of 1000h is no higher than 2%.

Description

technical field [0001] The invention relates to a high-strength heat-treated steel bar and a manufacturing method thereof, more specifically, the invention relates to a high-strength heat-treated steel bar with high tensile strength and resistance to delayed fracture and a manufacturing method thereof. Background technique [0002] When steel bars for concrete are used as prestressed tendons, they are generally required to have high tensile strength and low relaxation performance. For ordinary relaxed steel bars and low-relaxed steel bars of the same strength level, the initial load is 1425MPa and other conditions are the same. In this case, after 50 years, the final stress of the low-relaxation steel bar is 1131.5MPa, while that of the ordinary relaxation steel bar is 991MPa, and the final stress value of the low-relaxation steel bar is 14.2% higher than that of the ordinary relaxation steel bar. Compared with ordinary relaxation-grade steel bars, low-relaxation prestressed...

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Problems solved by technology

However, the yield strength ratio of the steel bars obtained by the traditional quenching and tempering heat treatment process is too high, which can reach 97%, resulting in a small difference between the tensile strength and the yield strength, and insufficient safety reserves, which are dangerous factors for building materials. The yield ratio of steel has become an important issue to meet the safety reserve of prestressed concrete structures

[0004] However, when steel bars are used as prestressed steel bars, the existing steel bars cannot achieve both high strength and high plasticity, low relaxation and low yield ratio

[0005] With the development of the automobile, machinery, construction and other industries, the requirements for high-strength steel are continuously put forward in the fields of engineering machinery, civil engineering, automobiles, and construction machinery. However, with the increase in strength, especially when the tensile strength exceeds 1200MPa When , the delayed fracture resistance is significantly reduced, which is one of the most important problems encountered in the high strengthening of low alloy martensitic steel

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