Investigating a Die Quench Cracking Problem in 52100 Steel Bearing Rings With Computer Simulation

Quenching using a press with controlled die loads, commonly referred to as press quenching, is a specialized technique used to minimize distortion of critical components such as gears and high quality bearing races. Improper press load magnitudes or timing of the load application may restrict part movement during quenching to the point of imposing stresses that cause cracking, especially in a common bearing steel such as AISI 52100, high carbon, high strength steel. This paper applies a finite element based heat treat simulation tool, DANTE®, to investigate the sensitivity of cracking to press quenching process parameters. The typical method for designing a press quench process to control flatness, out-of-round, and taper is by experience coupled with trial-and-error. This is accomplished by adjusting oil flow rates, flow directions, die loads, and the timing of die loads. Metallurgical phase transformations occur during the quenching process as austenite transforms to martensite and possibly to diffusive phases. Thermal contraction due to cooling and volumetric expansion due to the phase changes therefore occur simultaneously during the heat treating process. A constantly changing stress state is present in the part, and improperly applied die loads, oil flow or oil flow rate can add additional stress to result in cracking. An inconsistent cracking problem in an AISI 52100 bearing ring was evaluated using production trials, but the process statistics were not conclusive in identifying the source of the problem. Heat treatment process modeling using DANTE was used to investigate the effects of quench rate, die load pulsing, and several other process variables to determine how these parameters impact the resulting stresses generated during the press quenching operation.