Hydrogen control during steel making for medium carbon wheels

Abstract

The control of hydrogen is essential to avoid flakes, internal microcracks and other types of steel defects. Vacuum degassing, introduced in late 1950s for bringing down the hydrogen of liquid steel, continues to be an important refining operation today to meet stringent requirement of hydrogen, which is sometimes as low as 1 ppm or lower. The net hydrogen level in steel depends on the extent of its pick up and removal during various stages of steel making. The measures to control pick up mainly include the use of inputs with low moisture or hydrogen content and those for removal are efficient degassing in VAD, control of ladle slag basicity etc. The hydrogen level in medium carbon wheel steel at Durgapur Steel Plant is controlled by utilising a number of measures in BOF and ladle treatment practices. These include avoidance of late addition of lime in converter, minimisation of carry over slag, delayed and just adequate deoxidation in ladle, recarburisation with low hydrogen pet coke, efficient degassing in VAD at deep vacuum and intense purging, restricting ladle slag basicity to less than 1.2 etc. The measures developed and implemented during the investigation resulted in hydrogen level of 1.2–1.8 ppm consistently.