Causes and Improvement of Point Defects in 15-5PH Stainless Steel Producted by EAF+VAR

Abstract

The new process of EAF→VOD→LF+VD→ pouring 6 t electrode rod → vacuum consumable remelting （VAR） with lower smelting cost was adopted to produce 15-5PH stainless steel instead of the traditional VIM+VAR process， the causes of point defects were analyzed by scanning electron microscopy and ASPEX detection methods. The results show that calcium aluminate and aluminum spinite exist in the self-consuming electrode， the instability of vacuum consumable remelting process will draw the ingot crown and non-metallic float into the melting pool and remain in the consumable ingot， resulting in point defects after forging.Through process optimization and improvement， the VOD reduction slag is adjusted from 9 kg/t aluminum to 8 kg/t ferrosilicon and 5 kg/t aluminum， the composition of refining slag is adjusted from （mass fraction）CaO 50%-55%， SiO2 10%-15%， Al2O3 20%-25% to CaO 45%-50%， SiO2 5%-10%， Al2O3 33%-38%， vacuum consumable remelting speed is increased from 4.2 kg/min to 6 kg/min， and the melting drop time is increased from 0.23 s to 0.27 s， the cleanliness of consumable electrode has been greatly improved， the melting speed has been controlled steadily， the non-metal floating matter on the liquid surface of the molten pool has been removed， low and high magnification inspection of the finished material have met the standard requirements， and the inspection pass rate has been increased to more than 98%.

Keywords

• 15-5ph stainless steel； point defects； refining slag system； var； droplet time