A thermal straightening method for low-carbon bainite steel plate with a thickness of 25mm

Abstract

The invention relates to a hot straightening method for a low-carbon bainite steel plate with the thickness of 25 mm. The hot straightening method comprises a pre-straightening stage and a main straightening stage. In the pre-straightening stage, the steel plate is straightened twice or three times, the inlet roll gap is 21.5 mm-23.5 mm, the outlet roll gap is 24.0 mm-25.0 mm, and the straightening speed is 1.1 m / s-1.3 m / s; in the main straightening stage, the steel plate is straightened once or twice, the inlet roll gap is 20.0 mm-21.0 mm, the outlet roll gap is 23.5 mm-24.5 mm, and the straightening speed is 0.8 m / s-1.0 m / s. According to the hot straightening method, a 9-flat-roll type straightening machine is adopted, in this way, straightening force of all straightening rolls can be reduced effectively, and equipment safety is ensured; meanwhile, the thickness proportion of a plastic deformation area in the thickness direction of the steel plate to the steel plate can be controlled to be 80%-85%, and thus the qualification rate of the shape of the steel plate is effectively controlled to be above 95%.

Description

technical field [0001] The invention relates to a hot straightening method for a low-carbon bainite steel plate with a thickness of 25 mm, and belongs to the technical field of hot-rolled plate straightening technology. Background technique [0002] Low-carbon bainite steel is a new type of steel with high strength, high toughness and easy welding. Its yield strength at room temperature is usually 550-850MPa. All over the world, low-carbon bainitic steel plates with excellent weldability have the characteristics of large consumption and multiple uses, especially low-carbon bainitic steel plates with a thickness specification of 25mm, which can be cut, bent, stamped and welded. And other processes are made into various products and components with high mechanical properties, so the application range is very wide, and it occupies a very high share in the medium and thick plate product market. The steel type with this thickness specification belongs to micro-alloyed steel, and...

AI Technical Summary

Problems solved by technology

This straightening method is too dependent on the adjustment of the roll gap of the straightening machine. During the implementation of its related processes, the following problems are often prone to occur: (1) When the straightening roll gap is adjusted too large, the steel plate thickness direction If the area where plastic deformation occurs cannot reach more than 80% of the total section thickness, the residual stress inside the steel plate cannot be effectively released even after repeated straightening. Even if the steel plate is temporarily leveled, the steel plate is placed on the cooling bed During the process, affected by further cooling, the internal structure of the steel plate will continue to undergo phase transformation, and the residual stress inside the steel plate will continue to superimpose. When the superposition reaches a certain level, it will cause the steel plate to recur.

(2) When the straightening roll gap is adjusted too small, although it is easier to expand the plastic deformation area of ​​the steel plate along the thickness direction, the load of the straightening machine will also increase accordingly, which will easily lead to equipment damage

Although this method can reduce the deformation resistance of low-carbon bainitic steel, so that the steel plate can be straightened due to plastic deformation more easily, and the load of the straightening machine can also be greatly reduced, but at the same time, low-carbon bainitic steel The mechanical properties of non-tensitic steel will also be greatly reduced due to the ineffective precipitation of microalloying elements carbon and nitrogen compounds in the steel. Even if the original loss of mechanical properties of the steel can be compensated by increasing the content of chemical elements in the steel, its The production cost will also be greatly increased, so this method is not suitable for the current production mode that seeks a win-win situation for product performance and cost