Adjustment of heat treatment process of bearing steel parts

The heat treatment of a complete set of solid bearings is complicated by the quenching of the ring, among which the quenching distortion of the outer ring is the most prominent. On the premise of improving product quality, many enterprises have tightened the heat treatment requirements of hardness, roundness and taper, which requires good heat treatment equipment and advanced and reasonable heat treatment process.

To conveyor oven, using the appropriate lower heating temperature and heating time of heat preservation, according to the products of different specifications for different heating temperature (820 ~ 850 ℃), and had enough warm-up time, pendulum material way outside diameter < 50 mm ring, can bulk stacking, a diameter of 50 mm or ring need manual or automatic pattern, outside diameter > 100 mm ring to artificial colors, ring is 45 °, and should have a certain gap between the ring, prevent heated outer thermal expansion and the extrusion deformation. The choice of quenching oil products should be long service life and high temperature resistant grading quenching oil, the oil curtain in the quenching oil groove should be used under the liquid pump, for taper and roundness requirements higher thin-wall ring, need to adjust the small conveyor belt on the stepless governor up and down the frequency (0 ~ 5) and feed speed.

At the same time, it is necessary to raise the quenching oil temperature (90 ~ 120℃), and the running speed of the belt can be slowed down. For the rings with effective thickness ≥10mm, when the multi-purpose furnace of sealed box type is adopted, an isothermal soaking time of 500 ~ 600℃ is required. When the roller furnace is used, the temperature of each heating zone can be reasonably arranged. Quenching medium is nitro martensite graded quenching or lower bainite isothermal quenching technology, its nitro salt should be configured with good quality salt, it is not recommended to prepare their own.

As for high accuracy requirement of the miniature bearing ring quenching in the vacuum furnace is a very good choice, vacuum quenching can remove harmful impurity in steel, so as to improve the abrasion resistance and contact fatigue property of bearing ring more than 2 times, but not too high vacuum, generally in 1 ~ 10-1 pa, otherwise you will take off the chromium, cause local sticky when vacuum quenching, bearing parts decreased resistance to wear.

The general quenching heating time is 3 ~ 5 times higher than the general box multi-purpose furnace, so in 550 ~ 600℃ should have a phase of equalization, and then rise to the heating quenching zone insulation (830 ~ 850℃), according to the furnace load and technical requirements to choose different cooling speed of the vacuum quenching oil. Heating and quenching of roller must be in a roller furnace with protective atmosphere, with mesh belt furnace heating is a bad choice, rapid quenching cooling medium bright quenching oil or water-soluble quenching medium, the requirements of the quenching temperature on the high side some (840 ~ 860 ℃), for their hardness 1 HRC higher than ring, but metallographic organization must meet the technical requirements.

For heat treatment process of high precision bearing suggest adding below Mf martensitic transformation point - the end of 78 ℃ cold treatment, it can improve the dimension stability of bearing, is in commonly - 80 ℃ cold treatment insulation 2 ~ 4 h, the residual austenite is controlled in 8% (GCr15SiMn), without the need to - 180 ℃ cryogenic treatment, or because the residual volume (2.6%) is too little, that would make the organization stress is too big, can cause crack in super fiber, can reduce the contact fatigue life and impact toughness, so - 180 ℃ cryogenic treatment process is not recommended. In particular, there are two slots for cold and hot cleaning on the conveyor belt production line. The cold cleaning groove equipped with a refrigerator (4 ~ 7℃) should be directly connected to the quenching oil groove, and then connected to the hot cleaning groove.

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