Process Optimization on Improving Center Segregation of Spring Steel Billet and Properties of Wire Rod

Abstract

For a steel factory production of 55SiCr spring steel，the reduction of area of the oil quenched and tempered treatment wire rod after processing is less than 40%， which affects the subsequent spring coiling process and the service life of the spring. The casting billet and wire rod were evaluated by methods of low-magnification pickling test， tensile test， oil quenched and tempered treatment， drill cuttings test， etc， it was found that the center segregation of the casting billet was the main cause of poor drawing performance. Through the optimization test study of continuous casting process， the results showed that high superheat had a significant effect on the segregation of billet and the drawing performance of wire rod.When the superheat was 35 ℃ compared with 18 ℃， the reduction of area and elongation increased by 2% and 0. 8% respectively. The electromagnetic stirring current of the mold was increased from 150 A to 320 A， and the center equiaxed grain rate was increased from 8%-8. 5% to 10. 5%， but the average center carbon segregation index also increased. When using the same mould electromagnetic stirring technology， reducing the electromagnetic stirring intensity at the solidified end was beneficial to improve the center segregation. When the average center carbon segregation index of the slab decreased from 1. 10 to 1. 02， the reduction of area of the oil quenched and tempered treatment wire rod increased from 39% to 47%.

Keywords

• spring steel； superheat； electromagnetic stirring； center segregation； reduction of area