Study On The Quenching Mass Effect Of Medium-high Carbon And Low Alloy Steel Grinding Ball

In this paper, the finite difference discrete was applied on the heat transfer equation of the grinding ball in ball coordinates and the discrete formulation of boundary condition of the grinding ball under quenching process was given by using the principle of conservation of energy and finite volume method. On this basis, the temperature field of the progre ss of the grinding ball quenched in the water was programmed and calculated by Matlab software. and experiments of the determining surface recurrent temperature of the 120 mm diameter grinding ball quenched from water was conducted, which confirmed the rationality of the calculating method of implicit difference and the choice method of thermophysical parameters. On this basis, the temperature field changes and the average cooling rate of the 60 Mn and B2 grinding ball quenched in the water has calculated to study their quenching mass effect. The test results of B2 grinding ball in different diameters quenched in the water were compared with the calculation results, and the quenching mass effect of the 60 Mn and B2 ball were studied, including its influence factors. Furtherly, the quenching mass effect of medium-high carbon and low alloy steel grinding ball was analyzed and an experiment was conducted about a typical medium-high carbon and low alloy steel(B6) grinding ball.The results showed that the cooling regularity of the medium-high carbon and low alloy steel grinding ball in different diameters was that the cooling rate was very high within 10 mm depth from the surface to center and cooling rate decreased rapidly with the depth increased, the descending speed of the cooling rate slowed when reached the depth of 10 mm. The cooling rate would reach a stable numerical with the depth increased more,the stable numerical decreased with the grinding ball diameter increased and the depth of the grinding ball correspond to it increased with the diameter of the ball increased. The regularity of the quenching mass effect to 60 Mn ball was similar to B2 ball, it was that there was a martensite critical diameter(DL) of the grinding ball, when the diameter was less than the DL, the quenching mass effect coefficient(qe) was equal to 0 and DLB2 was more than DL60 Mn.When the diameter was more than the DL, qe increased rapidly and its increasing rate would decrease with the diameter increased, when the diameter of the grinding ball was more than DB2, then qe60 Mn was more than qe B2. The test results of different diameters grinding ball quenched in the water were consistent well with the calculating results.For 60 Mn grinding ball, quenching temperature has some influence on the stable numerical of the cooling rate in the grinding ball, the stable numerical would increase with the diameter increased, so the martensite critical diameter would increase but little, when the diameter was in this range, quenching temperature had significant effect on the quenching mass effect coefficient. When the diameter D was more than DL, different quenching temperature had little effect on qe. When choosing the oil or the water as the quenching medium, the martensite critical diameter of the B2 grinding ball in the water(DLw) was more than that(DLo) in the oil, when the diameter is more than DLw, the quenching mass effect coefficient in the oil(qeo) was more than that in the water(qew).For the medium-high carbon and low alloy steel grinding ball with more than the diameter of 90 mm, there was a critical cooling rate(VL) and it would decrease with the diameter of the grinding ball increased. When the critical cooling rate of martensite determined by the materials was less than VL, the quenching mass effect coefficient qe was equal to 0, qe would increase rapidly when the martensite-critical cooling rate was more than VL. For the B6 grinding ball with the diameter of 140 mm, the test results of the quenching experiment were consistent well with the calculating results.