Effect of vacuum smelting method on the quality of pipe steel of northern application

Abstract

Pipe metal of Northern application must meet increased requirements of strength properties, low-temperature ductility, cold resistance and weldability. Cracks, skins, flaws, roll-ins and other defect are not allowed on the surface of pipes. The fulfillment of the requirements substantially can be provided by the process of steel smelting by a vacuum remelting method. Study of the effect of 03ХГ grade pipe steel smelting in vacuum and without vacuum on its contamination by nonmetallic inclusions and resistance against hydrogen cracking was accomplished. The smelting of ingots of adjusted chemical composition was carried out in a vacuum induction furnace ZG-0.06L. To imitate the process of hot roughing rolling, hydraulic press П6334 of 250 t force was used. Finishing rolling was carried out at reversible hot rolling mill 500 duo, combined with a controlled cooling facility. It was determined, that the samples, smelted in vacuum, had insignificant number of nonmetallic inclusions and withstand the test of resistance against hydrogen cracking; cracks were not detected on them. After testing on resistance against hydrogen cracking of the samples smelted without vacuum, cracks were discovered, located on both the surface and central layers amounting to 600 mm and 1700 mm length correspondently. It was shown, that steel smelting in vacuum allows to reach a high degree of the steel purity, results in increased crack growth resistance and in decreased number of nonmetallic inclusions in the pipe steel of Northern application.