S7 Steel Heat Treatment Process Essentials
Preheating Procedure
For S7 chromium-molybdenum alloy tool steel, complex large workpieces require two-stage preheating: first heat to 621-677℃ for soaking, then raise the temperature to 704-760℃ for heat preservation, to avoid residual stress caused by thermal shock and ensure uniform microstructure in the subsequent austenitization stage.
Quenching Procedure
Heat S7 steel slowly to 941℃ for austenitization. The holding time is calculated as 30 minutes per 25mm of thickness. Air cooling, pressurized gas quenching or warm oil quenching can be adopted. For workpieces with a section thickness over 63.5mm, interrupted oil quenching is required to increase the cooling rate, and the hardness after quenching can reach HRC58-60.
Tempering Procedure
S7 steel must be tempered immediately after quenching. The tempering temperature for cold working dies is controlled at 204-260℃, while hot working dies need to be tempered above 482℃ for secondary tempering. Workpieces with a section larger than 152.4mm need to extend the holding time to 4-6 hours, and finally obtain a stable application hardness of HRC52-58.
S7 Steel Routine Maintenance Operational Essentials
Regularly perform low-temperature stress-relief tempering on S7 steel
dies to eliminate the residual internal stress after wire cutting and
machining, inhibit the initiation of fatigue cracks, and give full play
to the core advantage of the material's high impact toughness.
When storing S7 steel workpieces, surface protection must be done to
avoid contact with humid and corrosive environments, preventing defects
such as oxide scale and decarburization, and ensuring the wear
resistance of the die cutting edge.
For high-purity S7 steel dies produced by remelting process, long-term
over-temperature conditions exceeding 538℃ should be avoided during use,
so as to maintain the material's mechanical fatigue resistance and
extend the overall service life of the die.