PROCESS FOR PRODUCING LS-CRNIMO30C STEEL FORGING USING CONTINUOUS CASTING BILLET FOR SUBSEA OIL PRODUCTION WELLHEAD DEVICE

摘要

The present invention relates to a process for manufacturing CrNiMo30C forged steel for a wellhead device of deep-sea oil extraction by continuous casting. The forged round steel of Φ300-400mm is manufactured by continuous casting billet of Φ600mm, the process including steps of molten steel smelting, continuous casting, forging, annealing, cooling and etc, the macrostructure of the continuous casting billet meets the requirements of appendix A of YB/T4149 standard: center porosity is equal to or less than grade 2.0, center crack is equal to or less than grade 1.0, shrinkage cavity is equal to or less than grade 1.0, defects of intermediate cracks, white flakes and upwarping defects are forbidden. The billet is heated and the heating speed is equal to or less than 200°C per hour, the heating temperature of forging is 1200-1250°C, ensuring that the billet is completely heated, the initial forging temperature is higher than 1150°C, and the final forging temperature is not lower than 850°C; after leaving the production line, the forged steel is at a high temperature of equal to or greater than 500°C and is then slowly cooled in sand; after the temperature drops to 200°C or lower, the forged steel is taken out of pit and slowly cooled. The inner quality of the finished forged steel meets requirements of grade D/d of SEP 1921 standard, and the mechanical property should meet the requirements of APISPEC 6A standard.