Heat treatment method for improving mechanical property of low-carbon hardened and tempered steel

Abstract

Disclosed is a heat treatment method for improving mechanical property of low-carbon hardened and tempered steel. The steel comprises, in percentage by weight, not more than 0.08% of C, 0.3%-0.5% of Si, 1.0%-1.7% of Mn, not more than 0.020% of P, not more than 0.010% of S, not more than 0.12% of Nb, V and Ti, 0.3%-1.2% of Ni, 0.3%-1.2% of Cu, 0.3%-0.8% of Cr, 0.3-0.8% of Mo, 0.001%-0.002% of B, 0.02%-0.05% of Al, and the balance of Fe. The method includes subjecting rolled steel plates to quenching in a quenching furnace at the furnace temperature of 800-860 DEG C at the heating speed of 1.5-2.0m/mm for 5-40 minutes, and subjecting the plates to tempering in a tempering furnace at the tempering temperature of 500-700 DEG C, at the heating speed of 2.3-3.0m/mm and for 5-60 minutes. By the heat treatment method compared with the traditional hardening and tempering treatment, comprehensive mechanical property of the low-carbon hardened and tempered steel can be improved greatly. Impact energy and strain ageing impact energy of the steel plates at -80 DEG C can reach more than 200J, yield ratio ReH/Rm of the steel plates is not more than 0.90, and uniformity of mechanical property of different through-thickness positions of the steel plates can be improved greatly.

Description

technical field [0001] The invention belongs to heat treatment technology and relates to a heat treatment method for improving the mechanical properties of low-carbon quenched and tempered steel. technical background [0002] In order to ensure the mechanical properties of traditional quenched and tempered steel, the chemical composition of high carbon and high alloy is mainly used to ensure its hardenability. However, this high-carbon and high-alloy composition will make the weldability of the steel worse, and the structure is mostly tempered martensite, tempered sorbite and other structures, with a high yield ratio (ReH / Rm can reach more than 0.93), The low-temperature ductile-brittle transition temperature is mostly above -60°C. [0003] With the continuous improvement of market requirements for the welding performance of medium and heavy plate steel plates, the chemical composition of quenched and tempered steel has also changed from high carbon content to low carbon co...

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Problems solved by technology

Although low-carbon quenched and tempered steel has a small welding crack sensitivity coefficient, it has poor hardenability in production, serious plate thickness effects, and large fluctuations in mechanical properties such as strength and impact toughness.

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