How to Harden S7 Steel
American Iron and Steel Institute S7 tool steel is a very specialized steel formulated to be extremely shock and impact resistant. Where most tool steel break or shatter upon blunt force impacts, S7 is able to resist it. It has a medium carbon content at .50 percent, .70 percent manganese and 1.40 percent molybdenum. Because of this composition, the steel is often referred to as a moly-blend steel. Because of its unique properties, S7 can be a challenging steel to properly heat treat and harden. To properly harden, the steel must be cycled through heat treatments. Does this Spark an idea?
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Instructions
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Heating
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Place the steel in a heat treat furnace or forge and slowly raise the temperature to 1,200 to 1,300 degrees Fahrenheit at a rate of no more than 20 degrees per hour to anneal the steel to remove stresses within the steel.
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Raise the temperature of the steel to 1,700 to 1,750 degrees and hold the steel at temperature for 20 minutes plus an additional five minutes per inch of maximum thickness. Remove the steel and quench in the oil.
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3
Place the steel back in the furnace and raise the temperature to 400 degrees, holding the temperature for one and one-half hours to two hours for every inch of thickness measured at the widest point. For a part that is two inches thick at the widest point, it would need to remain in the furnace for three to four hours. Remove the steel after the correct amount of time has elapsed and allow to cool at room temperature.
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Tips & Warnings
If a controlled atmosphere furnace is unavailable, the part can be placed in an iron casing, such as a pipe, filled with steel or iron pellets.
Extreme temperatures are needed to properly harden any steel. Proper safety equipment and procedures must be followed to prevent serious injury.
References
Resources
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