Production process for grade II screw thread reinforced bar

Abstract

The invention discloses a process for preparing 20MnSi II grade thread reinforcement bar. It comprises: taking nitrogen source as strengthening element for said thread reinforcement bar; adding other microscale nitride; controlling manganese content in 20MnSi steel to be between 0.4 -1.2%, silicon content 0.20- 0.60%, and carbon 0.15- 0.25%; adding nitrogen- containing alloy during tapping process to make nitrogen content in steel be 0.5- 0.025%, adding nitrogen-containing compound of 0.1-3.0kg / t steel into ladle to form element alloy; sub argon areating or top argon areating to ladle after tapping, the argon areating strength is 0.01- 0.10 m3 / min. t steel, time is 3- 8 minutes, the rolling temperature is 1000- 1300 Deg. C, the coling speed after rolling is 1.0- 3.5 Deg. C / second. The yield strength is larger than 345 Mpa, strength for extension is larger than 500 Mpa, yield ratio is about 0.68, elongation is larger than 17%, and the comprehensive cost is reduced by 5- 10 yuan / t thread reinforcement bar.

Description

technical field [0001] The invention relates to a production process of low-alloy steel, in particular to a production process of 20MnSi II grade threaded steel bars for construction. Background technique [0002] At present, about 90% of the steel bars used in construction in my country are 20MnSi II grade threaded steel bars. Grade II threaded steel bars belong to the carbon-manganese steel series, and are generally smelted by electric furnace or converter. During the tapping process, ferromanganese alloy or silicon-manganese alloy is used to alloy molten steel so that the steel contains manganese [Mn] = 1.2-1.6%, Silicon [Si] = 0.40-0.80%, carbon [C] = 0.17-0.25%, yield strength ≥ 335MPa, tensile strength (б b )≥490MPa, elongation (δ 5 ) ≥ 16%. The performance of this steel type is mainly strengthened by carbon, manganese and silicon in the steel. It is an old-brand steel type with mature production technology and high market recognition. However, the main disadvantag...

AI Technical Summary

Problems solved by technology

But the main disadvantage of this method is that due to the high content of carbon (C), manganese (Mn) and silicon (Si) in the steel, the cost of the alloy used is high

In addition, during the smelting process, manganese element segregation is prone to occur, the welding performance is unstable, and the yield is not obvious.

Another method is to control the chemical composition to the lower limit, and use controlled cooling after rolling to ensure that its performance indicators meet the above requirements. This method has a slightly lower production cost, but has the following disadvantages: ①Add water-piercing equipment, so that Increase equipment maintenance

② The performance of water-piercing steel bars is unstable, especially the welding performance of steel is greatly affected, and the market acceptance is very low