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Vacuum Quenching of GCr15 Steel Parts

Material: GCr15 steel

Technical requirements: Overall 63~64HRC, deformation 0.10mm.

Parts are: upper plate of textile machine

Figures 1 and 2 are representative of GCr15 steel parts widely used on knitting machines. The original structure is as-cast. The quenching temperature of GCr15 steel is about 840 °C, and the fatigue strength, hardness and impact toughness after quenching and tempering are the highest values. When quenched at around 840 °C, the mass fraction of dissolved carbides in austenite is 0.5% to 0.6%, the mass fraction of chromium is 0.8%, and there are still some undissolved carbides. Dissolved carbon and alloying elements ensure its hardenability and hardenability, while undissolved carbides prevent grain growth. If the quenching temperature is low, the amount of carbide dissolved in the austenite is small, and the carbon and chromium content in the austenite is low, which will inevitably affect the hardness after quenching. If the quenching temperature is too high, it will cause overheating, make the martensite needle after quenching thicker, increase the deformation, and affect the mechanical properties. Heating time is closely related to heating temperature, heat transfer medium, effective thickness of parts and furnace loading. Under the same temperature conditions, if the heating time is too short, the austenitization will be insufficient, the carbides will not be completely dissolved, and the alloying degree of the solid solution will be low, which will cause the quenching temperature to be low. If the heating time is too long, the grains will be coarse. and increased costs.

Fig 1 Knitting machine parts upper plate 0911A shape GCr15 steel,
Technical requirements 62~ 64HRC

Fig 2 The upper plate of knitting machine parts is 0019AGCr15 steel,
Technical requirements 62~ 64HRC

After a lot of tests, the vacuum quenching process curve shown in Figure 3 was determined. The quenching temperature is 855C, and the cooling time is properly controlled, so that it can be completely quenched, the hardness can reach 63~64HRC, and the deformation meets the process requirements.