Estimation of Maximum Inclusion Size in High Carbon Chromium Bearing Steels by Extreme Value Analysis Method

The maximum inclusion size in high carbon chromium bearing steels has an important effect on their fatigue life. With the improvement of steel cleanliness due to the progress of metallurgy process, the conventional inclusion rating method of rolled materials has not been able to meet the requirements for further improvement of bearing steel quality. A method for estimating the inclusion size in bearing steels-the extreme value analysis method, was studied and proposed. This method was adjusted in many aspects such as the size and quantity of metallographic samples, the observation and size calculation of inclusions and the parameter estimation of Gumbel distribution function, to make it practical. On this basis, the method was used to estimate the maximum inclusion size in the rolled material of bearing steel, and the compositions of the large-sized inclusions were analyzed by energy spectrometer. The results show that the extreme value analysis method based on Gumbel distribution function can be used to estimate the maximum inclusion size in bearing steels. Controlling B-type coarse and DS-type spherical inclusions and reducing the titanium content in steels are the efforts to further improve the quality of bearing steel products.