Aug 20 2012
Topics Covered
IntroductionChemical
CompositionPhysical PropertiesMechanical PropertiesThermal PropertiesOther DesignationsFabrication and Heat
Treatment Machinability Forming Welding Heat
Treatment Forging Cold
Working Annealing TemperingApplications
Introduction
Shock-resisting tool steels are designated as group S steels according to the
AISI classification system. These steels include S1, S2, S5, S6, and S7 types.
The hardenability of group S steels can be controlled by varying thier
composition rather than adjusting the melting methods and grain size. They can
obtain optimum hardness at higher austenitizing temperatures. The tempering
resistance of group S steels can be enhanced by the addition of silicon, which
also forms a microstructure to resist distortion in tempered conditions.
The following section will give an overview of S2 shock-resisting tool
steels.
Chemical Composition
The following table shows the chemical composition of S2 tool steels.
Element |
Content
(%) |
Iron, Fe |
97.0 |
Silicon |
1.05 |
Carbon, C |
0.4-0.55 |
Molybdenum, Mo |
0.4 |
Manganese, Mn |
0.4 |
Vanadium, V |
≤0.5 |
Phosphorus, P |
≤0.03 |
Sulfur, S |
≤0.03 |
Physical Properties
The physical properties of S2 tool steels are given in the following
table.
| Properties |
Metric |
Imperial |
| Density |
7.79 g/cc |
0.281 lb/in3 |
| Melting point |
1421°C |
2590°F |
Mechanical Properties
The mechanical properties of S2 tool steels are tabulated below.
| Properties |
Conditions |
| T
(°C) |
Treatment |
| Poisson's ratio |
0.27-0.30 |
25 |
- |
| Elastic modulus |
190-210 GPa |
25 |
- |
Thermal Properties
The following table shows the thermal properties of S2 tool steels.
| Properties |
Conditions |
| T
(°C) |
Treatment |
| Thermal expansion |
10.9 x 10-6/ºC |
20-100 |
- |
Other Designations
Other designations that are equivalent to S2 tool steels include:
- ASTM A681
- FED QQ-T-570
- SAE J437
- SAE J438
- UNS T41902
Fabrication and Heat Treatment
Machinability
The machinability rating of S2 tool steels is 85% of that of the W group
steels.
Forming
S2 tool steels are formed using conventional procedures under annealed
conditions.
Welding
S2 tool steels are readily weldable using standard methods.
Heat Treatment
S2 tool steels are slowly preheated to 649ºC (1200ºF) and then directly
heated by increasing the temperature to 871ºC (1600ºF). This is followed by
holding the steels for 10 to 20 mins and quenching in brine or water.
Forging
Forging is carried out in S2 tool steels at temperatures ranging from 899 to
1093ºC (1650 to 2000ºF). Forging below 871ºC (1600ºF) is not preferred.
Cold Working
S2 tool steels can be cold worked under annealed conditions.
Annealing
Annealing is performed on S2 tool steels at 788ºC (1450ºF) followed by
cooling in the furnace at a rate of not more than 4ºC per hour.
Tempering
S2 tool steels are tempered at 177 to 427ºC (350 to 800ºF) to obtain Rockwell
C hardness of 60 to 50.
Applications
The following are the major applications of S2 tool steels: