The problem of residual elements in steel is one of the important problems faced by metallurgical industry. In the process of steelmaking, the raw materials for steelmaking (including molten iron, scrap steel and ferroalloy) will bring a large number of impurity elements into the steelmaking furnace. Some impurity elements can be removed, but some impurity elements will remain in the steel. This part of impurities (unintentionally added alloy elements) are collectively referred to as residual elements.
These residual elements are one of the main factors causing instability of steel quality. Some residual elements are prone to segregation, even if their content is very low, it will have a strong negative effect on the properties of steel.
For example, the residual titanium in bearing steel is a typical case. Ti is easy to react with N to produce high hardness inclusions, which greatly affects the service life of bearing steel.