Heat Treatment Issues in Machining Stainless Steel Parts

Heat Treatment of Parts

The heat treatment process for stainless steel parts not only ensures the required hardness but also controls internal stresses to maintain dimensional stability during machining. Different materials require different treatment methods. With the development of the mold industry in recent years, the variety of materials used has expanded. In addition to Cr12, 40Cr, Cr12MoV, and cemented carbide, new powder alloy steels such as V10 and ASP23 are now used for high-stress, heavily loaded punches and dies. These materials exhibit high thermal stability and excellent microstructure properties.

For parts made of Cr12MoV, quenching is performed after rough machining. However, the quenched workpiece retains significant residual stress, which can lead to cracking during precision machining or service. Therefore, tempering should be carried out immediately after quenching to reduce these stresses.

The quenching temperature is controlled between 900-1020°C, followed by cooling to 200-220°C before air cooling. The workpiece is then rapidly tempered at 220°C. This method, known as single hardening, provides high strength and wear resistance, making it suitable for molds where wear is the primary failure mode. For workpieces with complex shapes or multiple sharp corners, tempering alone may not sufficiently reduce quenching stresses. In such cases, stress-relief annealing or multiple aging treatments are required before precision machining to fully release residual stresses.

For powder alloy steel parts, which can withstand high-temperature tempering, a secondary hardening process is applied. Quenching is performed at 1050-1080°C, followed by multiple high-temperature tempering cycles at 490-520°C. This process enhances impact toughness and stability, making it ideal for molds prone to chipping as the primary failure mode. Although powder alloy steels are more expensive, their superior performance is driving wider adoption in the industry.