Aug 20 2012
Topics Covered
IntroductionChemical
CompositionPhysical PropertiesMechanical PropertiesThermal PropertiesOther Designations
Introduction
Shock-resisting tool steels are designated as group S steels according to the
AISI classification system. S1, S2, S5, S6, and S7 are the types of
shock-resisting tool steels. The hardenability of group S steels can be controlled by
varying thier composition instead of adjusting the melting procedures and grain
size. These steels can obtain optimum hardness at higher austenitizing
temperatures. The tempering resistance of group S steels can be enhanced by
addition of silicon, which also forms a microstructure to resist distortion in
tempered conditions.
The following sections will provide details about S7 shock-resisting tool steels.
Chemical Composition
The following table shows the chemical composition of S7 tool steels.
Element |
Content
(%) |
Iron, Fe |
93.85 |
Carbon, C |
0.45-0.55 |
Manganese, Mn |
0.20-0.80 |
Silicon, Si |
0.20-1.00 |
Chromium, Cr |
3.00-3.50 |
Molybdenum, Mo |
1.30-1.80 |
Vanadium, V |
0.20-0.30 |
Copper, Cu |
0.25 |
Phosphorus, P |
0.03 |
Sulfur, S |
0.03 |
Physical Properties
The physical properties of S5 tool steels are given in the following
table.
| Properties |
Metric |
Imperial |
| Density |
7.83 g/cc |
0.283 lb/in3 |
Mechanical Properties
The mechanical properties of S7 tool steels are tabulated below.
| Properties |
Metric |
Imperial |
| Hardness, Rockwell C (air cooled from 941°C, 649°C temper
temperature) |
41 |
41 |
| Hardness, Rockwell C (air cooled from 941°C, 449°C temper
temperature) |
53 |
53 |
| Hardness, Rockwell C (air cooled from 941°C, 149°C temper
temperature) |
57 |
57 |
| Modulus of elasticity |
207 GPa |
30000 ksi |
| Charpy impact (V-notch; air cooled from 941°C; 425°C temper
temperature) |
13.6 J |
10.0 ft-lb |
| Charpy impact (V-notch; air cooled from 941°C; 649°C temper
temperature) |
16.3 J |
12.0 ft-lb |
| Charpy impact (V-notch; air cooled from 941°C; 200°C temper
temperature) |
16.9 J |
12.5 ft-lb |
| Machinability (1% carbon steel) |
70.0 - 75.0% |
70.0 - 75.0% |
| Poisson's ratio |
0.27-0.30 |
0.27-0.30 |
Thermal Properties
The following table shows the thermal properties of S7 tool steels.
| Properties |
Conditions |
| T
(°C) |
Treatment |
| Thermal expansion |
12.6 x 10-6/ºC |
20-200 |
- |
Other Designations
Other designations that are equivalent to S7 tool steels include:
- ASTM A597
- ASTM A681
- UNS T41907