Removal of hydrogen in the vacuum treatment of steel

Abstract

The degassing of 09Г2C steel produced in an arc furnace and treated in a ladle–furnace unit at AO Uralskaya Stal is analyzed. The vacuum-treatment parameters that determine the effectiveness of hydrogen removal from the steel are identified: the depth and duration of vacuum treatment; the argon flow rate; the steel temperature; the thickness of the slag layer; and the free board in the vacuum chamber. The hydrogen content changes most significantly when the degassing time is increased to 20 min. Longer treatment is not recommended. The greatest effect of the residual pressure in degassing is observed with simultaneous decrease in the minimum pressure to 2 mbar. Vacuum treatment of the steel is considerably impaired with increase in the residual pressure. Hydrogen removal is improved with increase in the steel temperature to 1600–1620°C, but slows considerably at higher temperatures. The influence of the vacuum-treatment parameters is established quantitatively, and a regression equation is derived for predicting the results of hydrogen removal and selecting the parameter values corresponding to specified hydrogen content in the steel. Vacuum-treatment parameters that permit the economical production of steel with 2.1 ppm are determined: steel heating before vacuum treatment by 100–110°C; vacuum treatment for 20 min at a pressure no higher than 1.5 mbar in the vacuum chamber; argon flow rate 0.05 m³/t. The temperature losses of the metal are determined by the total treatment time, consisting of the active degassing time and the auxiliary time (the preliminary evacuation time), which depends on the capabilities of the equipment and the organization of the process. The minimum residual hydrogen content in the steel for the given equipment (1.6 ppm) is ensured by vacuum treatment for 40 min at a pressure no higher than 1 mbar in the vacuum chamber, with preliminary heating of the steel by 120–125 °C and with an argon flow rate up to 0.072 m³/t.