HEAT TREATING S-7 STEEL

By Franklyn D. Garland Originally published in the UMBA Newsletter Vol. 17 Issue No. 3

S-7 is a general purpose, air hardening, tool steel with a high resistance to impact and shock. It is moderately "red-hard" which makes it one of those rare steels that does very well as either a hot work or a cold work steel. The breakdown is as follows:

TYPE ANALYSIS
Element Percentage
Carbon 0.50%
Manganese 0.70%
Silicon 0.30%
Chromium 3.25%
Molybdenum 1.40%

TYPE ANALYSIS
Element	Percentage
Carbon	0.50%
Manganese	0.70%
Silicon	0.30%
Chromium	3.25%
Molybdenum	1.40%

The critical temperature for S-7 is 1700 degrees to 1750 degrees F. A heat soak of 20 minutes plus 5 minutes per additional inch of thickness is recommended for a complete hardening (shorter times may be used for smaller pieces, for example chisels Ed.). Pieces up to 2" thick can be air cooled but at thicknesses greater than that an oil quench to 150 F is recommended. Tempering should be done as quickly as possible following the hardening process. The factory specification for cold work is an Rc hardness of 55-57, for hot work a Rc of 50-53 is suggested.

TEMPERING TABLE
Temperatures
in Degrees
Fahrenheit Rockwell
Hardness
(C scale)
As Hardened 59-61
300 57-59
400 55-57
500 53-55
600 52-54
700 51-53
800 51-53
900 51-53
1000 50-52
1100 43-48
1200 37-40

TEMPERING TABLE
Temperatures in Degrees Fahrenheit	Rockwell Hardness (C scale)
As Hardened	59-61
300	57-59
400	55-57
500	53-55
600	52-54
700	51-53
800	51-53
900	51-53
1000	50-52
1100	43-48
1200	37-40

S-7 is one of those hot work/cold work steels that many smiths "forge and forget" It can be difficult to find scrap sources of S-7, but it is readily available from steel suppliers and well worth the cost.

Author's Notice:
References for this article are from, but not limited to, the material specification sheets from Carpenter Technology Corporation, Steel Division and lecture material from Robb Gunter's 1994 ABANA conference demonstration on scrap tool steels.

Author: Franklyn Garland
HTML Editor: Roger Schmitt
ArtMetal Editor/Curator: Enrique Vega
Last Updated: Wed, Sep 27, 1995