Defect Analysis of Spheroidizing Annealing of High Carbon Chromium Bearing Steel Bearing Parts

High carbon chromium bearing kingdom steel is the main steel grade for the manufacture of rolling bearing parts (ferrules and rolling elements), of which GCr15 steel is the largest. Most of the bearing rings are forged from bearing steel bars into bearing ring forging blanks. The forging initial forging temperature is about 1100 °C, and the final forging temperature is about 850 °C. The hardness after forging is relatively high, generally 255-340 HBW, and the structure is flaky pearlite structure (see Fig. 1), which is not easy to cut.

In order to prepare a good original structure for the final quenching and tempering treatment, and at the same time obtain superior processing properties, it is necessary to undergo spheroidizing annealing to obtain a uniformly distributed fine-grained pearlite structure. Controlling the hardness at 170~220HBW is most beneficial for cutting.

The microstructure of high carbon chromium bearing steel parts after spheroidizing annealing is a small, evenly distributed spheroidized structure (see Figure 2), which should meet the "JB/T1255-2014 rolling bearing high carbon chromium bearing steel parts heat treatment technical conditions" standard Levels 2 to 4 in a level diagram allow for the presence of a somewhat spheroidal organization, and organizations with levels 1 and 5 are not allowed.

Usually in the actual production process, due to the size of the workpiece, the method of furnace charging, the number of furnace heating, the temperature of the spheroidizing heating and the original tissue inhomogeneity before annealing, the microstructure will be overheated after spheroidizing annealing (thickness Unqualified structures such as inferior heat (fine pearlite), uneven coarse-grained pearlite, etc., seriously affect the processing quality of the post-process, and even produce waste products, resulting in batch scrapping of products. Therefore, it is necessary to analyze the cause of the annealed defect and take effective corrective measures.


The spheroidized structure shown is an annealed superheated metallographic microstructure characterized by the appearance of granular pearlite and a portion of coarse-grained pearlite in the metallographic microstructure.