Process Optimization and Practice on CC Soft Reduction in GCr15 Bearing Steel Billet

Abstract

 For improving the level of GCr15 bearing steel CC billet chemical homogenization and defects such as inner crack and shrinkage cavity， the soft reduction process was optimized by the physical calculation of shell thickness growth ratio， steel grade thermal property test， desin casting process under large pressure and combined soft reduction test， monitor the surface temperature of the casting process and the working condition of the tension leveler. The results show that the reasonable starting position R of continuous casting SR is 42%～45%， in order to obtain better macrostructure quality， the starting position of three CC billet sizes 200 mm×200 mm， 240 mm×240 mm， 300 mm×340 mm is 1～3 m behind the original process； Taking 200 mm×200 mm GCr15 billet as an example， increasing the amount of casting reduction from 1.25 mm/m to 2.5 mm / m， which can reduce the cracks of billet， significantly improve the Y-Z longitudinal of casting billet macrostructure composition and homogenization， and the central carbon segregation index of the rolling material generally reaches 0.97～1.03， realizing the goal of not producing obvious cracks under soft reduction， and modifying the central segregation and V-segregation defects.

Keywords

• gcr15 bearing steel； macrostructure of cc billet； soft reduction； chemical homogenization； solidification and heat transfer； strain