(2) the annealing process of the three elements

GCr15 steel bearing ring blanks heated to a temperature slightly higher than the critical point Acl (the phase transition temperature), and stay at this temperature for a period of time, and then cooled down at a certain speed to be uniformly distributed, small, globular pearlite, this process is called annealing. Heating temperature, holding time, cooling rate are the three elements of the annealing process.

(1) the choice of annealing temperature

GCr15 bearing steel annealing temperature range 780 ~ 810 ° C, commonly used (790 ± 10) ° C is more appropriate.

GCr15 steel heating temperature exceeds the Acl (730 ~ 765 ° C), pearlite to austenite specifically changed, the higher the temperature, the austenite more uniform and not melt the carbide, the less easy to form a film after cooling -like pearlite. Therefore, 840 ° C annealing temperature limit, exceeding the temperature of annealing the organization will appear coarse flake pearlite. In short, if the temperature is too high, the workpiece will overheat and become non-conforming product; if the temperature is low, part of the lamellar pearlite after forging will be retained no longer crystallization into small globular pearlite, high hardness caused by failure.

(2) the choice of the length of holding time

A. Select the basic principles of

GCr15 steel in 780 ° C, the pearlite to austenite transformation can be completed within 5 ~ 10min. Even if the organization forging a fine mesh carbide below 800 ℃, 1h, can basically eliminate. But taking into account the size of the part size, wall thickness, installed furnace, installed furnace capacity, furnace power factors, to ensure that the organizational changes in the basic completion of the minimum time required


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