Low-alloy high-strength steel and its manufacturing method

Abstract

The high strength low alloy steel comprises: C 0.06-0.09 wt%, Mn 1.30-1.40 wt%, Si 0.195-0.305 wt%, P not more than 0.015 wt%, S not more than 0.006 wt%, V 0.025-0.035 wt%, Nb 0.015-0.025 wt%, Ti 0.010-0.020 wt%, Al 0.020-0.035 wt%, and Ca 0.0015-0.0045 wt%, except Fe and inevitable impurity. The making process includes: a. smelting in converter with C content in blowoff not less than 0.04 wt% and free oxygen controlled in 550-650 ppm; b. RH vacuum deairing for over 6 min; c. calcifying treatment at the overheat temperature controlled in 10-20 deg.c higher than liquid phase line temperature; and d. casting at temperature of 10-20 deg.c higher than liquid phase line and casting speed of 1.1-1.3 m / min. The present invention has lowered Nb content for avoiding edge crack, reasonable V content for required strength, and calcification for pure steel content and stable quality.

Description

technical field [0001] The invention relates to a low-alloy high-strength steel and a manufacturing method thereof. Background technique [0002] With the take-off of the national economy and the continuous expansion of the scale of basic construction, especially the rapid development of urban construction, road construction, and port construction, the demand for low-alloy high-strength structural steel continues to increase. The requirements for internal quality and surface quality are higher than national standards and enterprise standards. [0003] The chemical composition of the current national standard Q345 low-alloy high-strength steel is as follows: % by mass [0004] C≤0.20, Mn 1.00-1.60, Si≤0.55, P≤0.035, S≤0.035, V 0.02-0.15, Nb0.015-0.060, Ti0.02-0.20, Al≥0.015. [0005] Its mechanical properties: [0006] 1. Yield strength: 325Mpa; [0007] 2. Tensile strength: 470-630Mpa; [0008] 3. The elongation rate is 22%; [0009] 4. Impact energy 0°C (longitudinal)...

AI Technical Summary

Problems solved by technology

[0011] The above-mentioned low-alloy high-strength steels are prone to serious edge cracks during production, which leads to the failure of hot rolling production. By adopting manual block-by-block inspection and flame cleaning, the edge corner cracks are removed and sent to hot rolling production, but the cracks cannot be eliminated in the end. Defects, defects such as edge warping still occur on hot-rolled steel coils

Through analysis, it was found that the high Nb content in the chemical composition of the low-alloy high-strength steel resulted in the generation of edge cracks