A kind of 500mpa level large-scale straight bar rebar and its preparation method

Abstract

The invention discloses a 500Mpa large-scale straight threaded steel and a preparation method thereof. The chemical composition of the threaded steel contains: C: 0.22-0.25%, Si: 0.40-0.60%, Mn: 1.35-1.60% in mass percentage , P≤0.045%, S≤0.045%, V: 0.100~0.120%, N: 0.010%~0.020%, the rest is Fe and unavoidable impurities; the preparation methods include converter smelting, argon blowing and stirring, continuous casting, heating, Phosphorus removal and rolling; in the heating process, the furnace temperature in the preheating section is controlled to be 500~900°C, the furnace temperature in the heating section is 1100~1180°C, the furnace temperature in the soaking section is 1130~1180°C, and the heating time is 80~150min; In the rolling process, the rolling start temperature is 1000~1100°C, and the rolling speed decreases with the increase of the diameter of the straight rebar. The present invention eliminates or compresses the reticular ferrite in the finished straight rebar through proper heating temperature and rolling process to a very small range in the core, significantly improves the microstructure of 500MPa large-scale straight rebar, and ensures Its strength and bending properties meet the requirements.

Description

technical field [0001] The invention relates to straight threaded steel and a preparation method thereof, in particular to a straight threaded steel with a large size of 500Mpa to prevent abnormal tissue growth and a preparation method thereof. Background technique [0002] With the implementation of the new national standard GB / T1499.2, steel bars above 400Mpa have replaced HRB335 as the main building steel bars. With the development of projects such as high-rise buildings, large bridges, tunnels and nuclear power, to The use of large-scale 500Mpa grade steel bars and above is becoming more and more widely used, and the demand will also increase. Compared with the old national standard GB / T1499.2, the new national standard GB / T1499.2, the biggest change is that it stipulates the structure of the finished steel bar, which is required to be mainly composed of ferrite and pearlite, and tempered martensite must not appear on the base circle. Therefore, the original The commo...

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Problems solved by technology

Compared with the old national standard GB / T1499.2, the new national standard GB / T1499.2, the biggest change is that it stipulates the structure of the finished steel bar, which is required to be mainly composed of ferrite and pearlite, and tempered martensite must not appear on the base circle. Therefore, the original The commonly used process of cooling through water to strengthen the mechanical properties cannot continue to be used, and only micro-alloying strengthening methods such as adding V can be used to produce steel bars

For 500MPa class In order to ensure its strength, V and other micro-alloying elements generally need to be added to more than 0.10% for large-size straight rebar and above. In order to fully exert the effect of V, it is necessary to increase the heating temperature of the billet, but high heating temperature will easily cause rebar The temperature of the upper cooling bed of the finished product is relatively high, and the cooling time in the proeutectoid ferrite precipitation temperature range is long, and the abnormal structure of reticular ferrite and large pearlite clusters appears, thereby reducing the strength and bending properties of the finished product

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