700MPa grade twisted steel and production method thereof

Abstract

The invention provides a 700MPa grade twisted steel and a production method thereof. The twisted steel comprises the following basic components: 0.28-0.32% of C, 0.40-0.80% of Si, 1.20-1.60% of Mn, 0.18-0.24% of V, 0.02-0.06% of Nb, 0.02-0.10% of Ni, 200-300ppm of N, and the balance of Fe and inevitable impurities, and optionally comprises any one or more than two of 0.001-0.020% of Ti, 0.01-0.05% of Mo and 0.02%-0.10% of Cu. The twisted steel is produced by a process comprising smelting in a converter or an electric furnace, refining in an LF (Ladle Furnace), continuous casting and continuous rolling of billets and cooling by using a cooling bed. The twisted steel produced from the components by the method has the lower yield strength of greater than 700MPa and the percentage elongation after fracture of greater than 14%; the microscopic structure of the twisted steel comprises ferrites and pearlites.

Description

technical field [0001] The invention relates to a 700MPa grade threaded steel bar and a production method thereof, belonging to the fields of iron and steel metallurgy and steel rolling. Background technique [0002] Construction steel bars account for a large proportion of the total steel output, while low-strength grade steel bars are used in a relatively high proportion, which will adversely affect the safety level of buildings and energy conservation and consumption reduction in the steel industry. With the development of economy, steel bars will develop in the direction of higher strength grade, multi-functionality and high quality. At present, the newly revised national standard has added 600MPa steel bar, making the existing national standard reach the international advanced level. But at the same time, it should be noted that 400MPa and above steel bars have been mainly used in foreign countries. At the same time, 500MPa steel bars are being promoted. The promotion ...

AI Technical Summary

Problems solved by technology

At present, there are a small number of 700MPa-grade steel bars researched by laboratories in China, but there are problems such as high alloy cost and difficult welding that greatly limit the promotion of high-strength steel bars. The chemical composition of steel bar is: C:0.20~0.25, Si:0.40~0.80, Mn:1.20~1.60, P≤0.035, S≤0.035, V:0.06~0.20, N:0.010~0.030, Ni:0.20~2.0, Cr: 0.20 ~ 2.0, Ti: 0.01 ~ 0.03, combined with its embodiment Cr, Ni content is the middle limit of the composition range, it can be seen that alloy elements such as Cr and Ni are relatively high, and the cost and carbon equivalent are difficult to control at an appropriate level. At the same time, Its maximum total elongation is only 5.5%-9.5%, and its plasticity is poor

However, waste heat treated steel bars and finished rolled threaded steel bars also have the limitations of welding difficulties, high cost, and poor plasticity. Therefore, it is of great significance to develop low-cost, easy-to-weld high-strength plastic hot-rolled threaded steel bars

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