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. S1, S2, S5, S6, and S7 are the types of shock-
resisting steels. The hardenability of group S steels can be controlled by
varying their 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 section will discuss in detail about S6 shock-resisting tool
steel, which has high silicon content and good hardenability.
Chemical Composition
The following table shows the chemical composition of S6 tool steels.
Element |
Content
(%) |
Iron, Fe |
Balance |
Carbon, C |
0.40-0.50 |
Manganese, Mn |
1.20-1.50 |
Silicon, Si |
2.00-2.50 |
Chromium, Cr |
1.20-1.50 |
Molybdenum, Mo |
0.30-0.50 |
Vanadium, V |
0.20-0.40 |
Copper, Cu |
0.25 |
Phosphorus, P |
0.03 |
Sulfur, S |
0.03 |
Physical Properties
The physical properties of S6 tool steels are given in the following
table.
| Properties |
Metric |
Imperial |
| Density |
7.75 g/cc |
0.280 lb/in3 |
| Melting point |
1432°C |
2610°F |
Mechanical Properties
The mechanical properties of S6 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 S6 tool steels.
| Properties |
Conditions |
| T
(°C) |
Treatment |
| Thermal expansion |
12.6 x 10-6/ºC |
20-425 |
- |
Other Designations
Other designations that are equivalent to S6 tool steels include:
- ASTM A681
- FED QQ-T-570
- UNS T41906
Fabrication and Heat Treatment
Machinability
The machinability rate of S6 tool steels is 85% of that of the W group
steels.
Forming
S6 tool steels have good forming characteristics under annealed
conditions.
Welding
S6 tool steels can be readily welded. However, steels with high silicon
content have to be handled carefully.
Heat Treatment
S6 tool steels are slowly preheated at 760ºC (1400ºF). Temperature is then
increased to 927ºC (1700ºF) followed by holding the steel sections at that
temperature for 10 to 30 mins. They are finally quenched in oil.
Forging
Forging is carried out in S6 tool steels at temperatures ranging from 899 to
1093ºC (1650 to 2000ºF). Forging below 871ºC (1600ºF) is not recommended.
Cold Working
S6 tool steels are cold worked under annealed conditions using conventional
methods.
Annealing
Annealing of S6 tool steels is performed at 816ºC (1500ºF) followed by
cooling in the furnace at a temperature of - 4ºC (25ºF) per hour.
Tempering
S6 tool steels are tempered at 204 to 315ºC (400 to 600ºF) to obtain Rockwell
C hardness of 56 - 54.
Applications
The following are the applications of S6 tool steels:
- Hammers
- Chisels
- Rivet sets