Low-cost, high-toughness and excellent-weldability 800 MPa-grade quenched and tempered steel plate and manufacturing method thereof

Abstract

The invention discloses a low-cost, high-toughness and excellent-weldability 800 MPa-grade quenched and tempered steel plate and a manufacturing method thereof. An ultra-low C- ultra-low Si-high Mn (Cu + Ni + Mo + high Cr) alloying-(Ti + V + B) micro-alloyed component system is taken as a foundation, the content of acid-soluble Als in steel is properly improved, and (% Als) is larger than or equalto 10 * [(% Nt)-0.292 (% Ti)], metallurgy technology control measures are adopted, specifically, a large-angle bainite lath / a martensite lath grain boundary forming index chi is controlled to be larger than or equal to 2.1, (% C) * [(% Si) +0.83 (% Mo) +1.12 (% Nb) +0.89 (% Als) +0.45 (% V)] is controlled to be less than or equal to 0. 031, a Di index * zeta * T cooling acceleration start temperature * [(T cooling acceleration start temperature-T cooling acceleration stop temperature) / (T cooling acceleration start temperature +T cooling acceleration stop temperature)] / t is controlled to be larger than or equal to 1535, Ca is treated and the Ca / S ratio is within 1.00-3.00, and CR + DQ + an off-line tempering process T is optimized, so that the microscopic structure of a finished steel plate is composed of uniform and fine lower bainite and lath martensite, the average size of eutectic cells is 20 micrometers or below, and excellent strong plasticity and high toughness are obtained.

Description

technical field [0001] The present invention relates to a high-strength steel plate, in particular to a low-cost, high-toughness and excellent weldability 800MPa quenched and tempered steel plate and a manufacturing method thereof. Single value) ≥ 47J, elongation at break δ 5 ≥15%, with excellent weldability. Background technique [0002] As we all know, low-carbon (high-strength) low-alloy steel is one of the most important engineering structural materials, widely used in oil and gas pipelines, offshore platforms, shipbuilding, bridge structures, boiler containers, building structures, automobile industry, railway transportation and machinery manufacturing. The performance of low-carbon (high-strength) low-alloy steel depends on its chemical composition and manufacturing process, among which strength, toughness, plasticity and weldability are the most important properties of low-carbon (high-strength) low-alloy steel, which are ultimately determined by the finished product...

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Problems solved by technology

[0007] In addition, the chemical composition of the steel plate does not contain Cu and Ni elements, but the impact toughness can only meet the temperature requirements of -20°C and above (such as Chinese Patent No. CN200910048287 low-cost 80 kg extra-thick quenched and tempered steel plate and its manufacturing method)

In addition, the controlled rolling + off-line quenching + tempering process is adopted; this not only has many manufacturing processes, long manufacturing cycle and high manufacturing cost, but also relatively high energy consumption in the manufacturing process (steel plate rolling is completed and naturally air-cooled to room temperature, followed by After shot blasting, reheat to quenching temperature), which is not conducive to energy saving and environmental protection; and the off-line quenching + tempering process cannot give full play to the hardenability and hardenability potential of alloy elements, and the hardenability and hardenability of elements cannot be maximized Therefore, in order to obtain the same level of strength and toughness, more alloying elements (especially Ni, Mo, Cr, etc.) must be added, which not only further increases the manufacturing cost, but also damages the weldability of the steel plate, especially for ultra-high-strength steel plates, The sensitivity of welding cold cracking is greatly increased, and welding preheating and postheating (ie PWHT) are required at higher temperatures. The range of suitable welding heat input is narrower, and the processing and manufacturing costs are correspondingly greatly increased.

Chinese Patent No. CN201210209649.5 discloses "nickel-free high-toughness 80kg grade high-strength steel and its manufacturing method", which uses no added Cu, Ni and other precious alloy elements, and successfully developed 800MPa grade quenching and tempering with excellent performance by using DQ process Steel plate, but the low temperature toughness cannot meet the low temperature requirement of -50°C and the steel plate cannot be welded without preheating, and the welding heat input cannot be higher than 50kJ / cm

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