CRUCIBLE S7
(AISI S7)
Crucible S7 is a shock-resistant air hardening tool steel, designed for high impact resistance at relatively high hardness. It offers toughness to withstand chipping and breaking, combined with high attainable hardness and good wear resistance. In small sections the grade can be quenched in air which assures minimal distortion. It is well suited for small to medium molds that require higher compression resistance while retaining a fair degree of toughness.
Typical Chemistry
Carbon 0.55%
Manganese 0.70%
Silicon 0.35%
Chromium 3.25%
Molybdenum 1.40%
Vanadium 0.25%
Typical Applications
Plastic Injection Molds
Rubber Molds
Slides
High Wear Molds
Hardening

Preheat: 1350/1400F, equalize.

High Heat: 1725/1750F, hold 30/45 minutes at temperature.

Quench: Air, positive pressure vacuum, interrupted oil to 150F. Sections over about 3" thick may require oil quenching to attain full hardness.

Temper: 350/1000F, hold one hour per inch of thickness (two hours minimum), air cool to room temperature. Double tempering is recommended.
Typical Properties
Tempering
Temperature
Hardness
HRC
Toughness,
Charpy C-Notch
°F
 ft-lbs
300 59 85
400 57 125
500 55 125
600 54 115
700 53 105
800 53 105
900 52 120
1000 51 150
1100 47 190
1200 41 –
Surface Treatments
Because of the low tempering temperatures normally used, S7 is not typically suitable for nitriding or similar treatments.

Annealing
A. Heat to 1550F, hold two hours, slow cool (50F/hour maximum) to 1000F, then air cool to room temperature.
Or
B. Heat to 1550F, hold two hours, cool to 1400F, hold 4 hours, then air cool to room temperature.

Typical annealed hardness: 187/220 BHN

Stress Relieving
Annealed Material: Heat to 1200/1250F, hold two hours, cool in still air.
Hardened Material: Heat to 25/50F below tempering temperature, hold two hours, cool in still air.

Welding
Use hot work tool steel filler material 4140 or 4150 type filler material may be satisfactory for small repairs or welds away from working surface of tool.
Annealed Material: Preheat to 400/600F. Maintain above 400F during welding. Reanneal or temper 1400F for four hours after welding.
Hardened Material: Preheat to original tempering temperature, (300F minimum). Maintain above 300F during welding. Cool to 150F. Temper at 25/50F below original tempering temperature (300F minimum).

Physical Properties
Modulus of Elasticity ...................................................................30 psi x 106
Density .............................................................................................0.283 lb/in3
Thermal Conductivity ....................(200F).......................... 16.5 BTU/hr/ft/°F
Thermal Expansion
Temperature
Range
Coefficient of Thermal
Expansion
°F
in/in/°Fx10-6
RT-400
7.0
RT-750
7.3
RT-1000
7.6
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