Cold Rolled Automotive High-strength Steel Major Problem in the Production and Use



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16 March 18
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1, High-strength steel production technology and solutions

Steel-making problem: High-strength steel has a high content of alloys, the ingot chemical composition easy segregation, and in the cooling process is easy to crack. The billet is also susceptible to cracking due to the presence of certain defects and the need for flame cleaning or cutting.

Solution: Strict control of high-strength steel on the slab hot heat transfer, billet stacking and insulation conditions.

Hot rolling problem: High strength steel in the hot rolling process easier to crack or deformation, hot rolling temperature fluctuations will lead to high-strength steel grade performance fluctuations.

Solution: Hot rolling process, to strictly control the temperature, heating rate and heating uniformity.

Pickling problem: The Hot rolled ultra-high-strength plate has a bad shape, sometimes even more serious crack, pickling of easy-to-hard degree is also different. And the addition of various alloying elements to the high strength steel may also affect the purity and magnetic properties of the acid regenerated by-product iron oxide powder.

Solution: Real-time optimization of pickling production speed, acid concentration and acid spray and other parameters.

Cold rolling problem: High-strength steel has a high content of alloys, welding difficulties, easy to crack at the weld, and even broken and need big rolling force, and easy to happen roll bending problems.

Solution: Reduce the amount of rolling deformation, reduce the rolling speed.

2, Main problems of high-strength steel in the use

① high-strength steel forming problems
High-strength steel plasticity is poor, easy to crack when deformation, deformation resistance, after forming the rebound is also large, poor precision parts. Through the high-strength steel plate welding plate, so that the deformation of the larger parts from the mild steel or good shape of the high-strength steel to bear, and the small amount of deformation or need to withstand the larger load parts to use the high-strength grade steel. In addition, new forming techniques such as hydro-forming, therm-forming and hot stamping have been developed.

② high-strength steel welding problems
As the production process technology is different, the addition of alloying elements would be different. When the cooling rate is low, you must add more alloying elements, but also cause deterioration of welding performance. For high-strength steel coating products, coating composition and its structure and thickness of the coating all affect its welding performance.

③ high-strength steel coating problems
The surface enrichment and oxidation of high-strength steel alloy elements affect their coating properties. Coating chemical composition and coating surface morphology also affect the coating performance of the material. Through the heat treatment process furnace atmosphere control, to control the high-strength steel alloy surface enrichment and oxidation, thereby improving the high-strength steel coating performance. The pickling method is used to clean the alloy elements that diffuse onto the surface of the coating and then electroplating a very thin layer of nickel to improve its coating properties.

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Fiona.yu@sinowellmetal.com

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