Hydrogen Measurement Technology 

Influence of Degassing Parameters on the Final Hydrogen Content

• Degassing time: the hydrogen level will decrease with increasing degassing times. However, the reduction in hydrogen will start to slow down as soon as hydrogen levels are being reached of 2 ppm. As soon as this level is reached, other degassing parameters will become more important.

• Vacuum pressure: agood maintenance of the degassing unit is crucial to ascertain very low hydrogen levels. Final hydrogen contents below 1 ppm can only be achieved with vacuum pressures of below 1mbar. The hydrogen level will not decrease if a working pressure of 100mbar is used.

• Initial hydrogen level:if only short degassing treatments are applied, it is essential to avoid too high hydrogen levels. Valuable time will be lost to eliminate the superfluous hydrogen. The initial hydrogen level is, however, less critical if longer degassing times are applied.

• Use of additions: additions at the end of the degassing cycle can spoil the degassing efforts as they can rise the hydrogen pick-up after additions of some alloys shortly before the end of the degassing treatment in an RH.

• Volume of inert gas blowing: the hydrogen reduction can be maximized by increased argon flow

• Type of steel grades:Some steel grades require longer degassing times to ascertain very low hydrogen levels.

Summary:

• Process Control: accurate hydrogen measurements before and after degassing enable the process to be understood and optimized. The potential exists both to reduce treatment cost and also final hydrogen concentration

• Labeling the product:immediate hydrogen measurement at the end of the degassing cycle provides the steel maker with an improved quality monitor prior sending the ladle to the caster or ingot station. This procedure imposes responsibility to the degassing unit and influences the final quality.