To improve the quenching medium to improve the quality of bearing ring GCrl5 steel quenching

My company in the early 90 s to the nitrogen base controlled atmosphere furnace cast chain automatic production line applied to bearing ring GCr15 steel quenching and tempering. Quenching medium mainly use N32 by mechanical blending machine oil. With the increase of ring size, sometimes appear quenching hardness problems such as imbalance and distortion, today yu Y15T rapid quenching oil additive on N32 by mechanical blending machine oil after modification, solved the ferrule uneven hardness, the effective control of the distortion. My company cast chain furnace production line from 1993 to early 1999 has quenching workpiece 7000 t, stable product quality control in JB/T1255 - 1991 standard range, quenching medium with N32 by mechanical blending machine oil is given priority to, winter also added some N15 machine oil, for quenching medium in addition to strictly control the moisture content did not take other detection means, has been for years to come up with a reason quenching quality problems. In early 1999, because of the old oil aging, the workpiece surface after quenching brightness down, lampblack is bigger when production, hence will cast chain furnace quenching tank in the groove with a new N32 by mechanical blending machine oil, followed soon found thick wall or big size ring ( Outside diameter> 100 mm, effective thickness> 10 mm) Part of the ring is seen after quenching ( Accounts for about 5% 20%) Thick end face to the uneven surface hardness and local hardness is unqualified, a level 6 ( JB / T1255 - 1991 the second level figure) The above hardening organization. As shown in figure 1 a, individual ring as shown in figure 1 b hardness distribution. Figure microstructure of hardness is qualified in the area for level 2, the residual amount of carbide, but coarser particles; Hardness is unqualified area mainly for 6, 8, occasional> 8, troostite shape for the block, block, block troostite central visible residual carbide particles. 1 quality problem analysis. 1 original organization with poor uniformity is one of the causes of unqualified quenching organization according to the check, the above problems appeared during the spheroidizing annealing temperature over 820 ℃, annealing organization rating of 4 ( JB / T1255 - 1991 the first level figure) , although the qualified, but as part of the carbide particles coarser and uneven distribution, cause the quenching process adjustment difficulties. Of annealing process immediately to correct, but after annealing billet production has been difficult to rework. 1. If 2 quenching temperature on the low side JB/T1255 - 1991 standard formulation explanations, six, eight quenching tempering organization show that quenching temperature on the low side. And improve the quenching heating temperature and prolonging holding time can improve carbon and chromium content in austenite, the austenitic composition homogenization, increase grain, improve the stability of supercooled austenite quenching, inhibition of pearlite type transformation, improve the GCr15 steel hardenability, lower critical quenching speed. On this basis, we would raise 8 - quenching heating temperature 10 ℃, the total heating time extend 10 - 15 min for batch production test, hardness unqualified problem can be solved. But many ring with - Parts hardness difference is bigger, 2 HRC, quenching tempering in the organization still occasionally find local there are a few small block troostite; Also began to have fine acicular martensite appeared at the same time, quenching deformation rising sharply. Diameter variations under super rate rise by an average of less than 10% to more than 25%, parts mechanical properties relative degradation. Thus, in the original organization under the condition of poor uniformity of pure improve quenching heating temperature and time to solve the problem of unqualified hardness is not the best way. 1. 3 quenching