S6 Tool Steel - Shock-Resisting Steel (UNS T41906)

Topics Covered

Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
     Machinability
     Forming
     Welding
     Heat Treatment
     Forging
     Cold Working
     Annealing
     Tempering
Applications

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

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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

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