S7 Tool Steel - Shock-Resisting Steel (UNS T41907)

Topics Covered

Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other 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

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