Use high-frequency induction quenching machine heat treatment to save bearing ring outer diameter grinding waste

The grinding of the outer diameter of the rolling bearing sleeve causes the workpiece to fail and be scrapped. The usual rescue measure is to electroplating hard chromium and then grinding the outer diameter. However, the electroplating method is complex, costly and polluting. In addition to the grinding process, the production cycle is long and the economic benefits are low. Difference. After analysis and research, it is found that using a high-frequency induction quenching machine to transform the retained austenite that still exists after quenching GCr15 steel causes the size of the workpiece to expand to repair the outer diameter of the over-worn bearing outer ring. This is an energy-saving, time-saving, and low-cost way to save over-grinding. The workpiece method has achieved good results through test analysis and process improvement, and has saved a large number of failed products in many years of production. Bearing steel contains 10-20% (volume fraction) of retained austenite after quenching. Due to the high free energy of austenite, the retained austenite spontaneously transforms into martensite at room temperature, and the bearing size expands. However, this transformation is very slow at room temperature. Aging treatment or cold treatment of GCr15 steel at 140-2700C will accelerate the transformation of retained austenite. For the outer diameter of the bearing outer ring that is overground by 0.001-0.010mm, aging treatment can save the failed and scrapped workpiece and restore it to the size required by the process. Tests and analyzes indicate that 10%-20% (volume fraction) of retained austenite in the structure of GCr15 steel bearings after quenching and tempering will obviously decompose when heated at 140-1500°C, and basically achieve decomposition at 250°C-2700°C. The entire decomposition process. However, tests have found that although aging of GCr15 steel above 1700°C accelerates the decomposition of retained austenite, the increase in temperature will reduce the hardness, strength, impact toughness, contact fatigue strength and wear resistance of the bearing, so high-temperature aging is not advisable. After comparison, the artificial aging process of (160 - 170) ℃ x 10h was selected. Afterwards, the factors that increase the size of the bearing are not only related to the outer diameter and wall thickness of the workpiece, but also mainly depend on the amount of retained austenite in the workpiece. The greater the amount of retained austenite, the greater the increase in outer diameter after artificial aging. . The main influencing factors on the amount of retained austenite after quenching of bearing parts are as follows:

(1) The higher the C, Mn, and Cr content in the steel, the greater the amount of retained austenite in the workpiece structure after quenching.

(2) Before the workpiece is quenched and heated, the structure is in the form of coarse flakes or point-like pearlite, which can increase the residual austenite after the workpiece is quenched.

(3) The quenching heating temperature is high, which increases the amount of retained austenite.

(4) High oil temperature during quenching or high oil temperature during tempering will also increase the amount of retained austenite.

Tests and production practices have shown that the excessive wear on the outer diameter of the bearing sleeve cannot be too large. If the outer diameter of the bearing outer ring exceeds 20 μm, the possibility of saving the bearing outer ring by this method is very small, and other measures and methods can only be used. In addition, it should be noted that the hardness of most workpieces treated with the above process is reduced by 1HRC. This point should be considered when implementing the production process and workpiece performance inspection requirements.