Tool Steels - Shock-Resisting Tool Steels

Topics Covered

Introduction
Properties
Composition
Applications

Introduction

Shock-resisting tool steels are among the strongest tool steels. They are designated as group S steels according to the AISI classification system. These steels include the S1, S2, S5, S6, and S7 type steels. The hardenability of group S steels vary from shallow hardening to deep hardening.

In these steels, hardenability can be controlled by adjusting the composition rather than the grain size and melting methods. However, higher austenitizing temperatures are needed to obtain optimum hardness. Type S1, S5, and S6 steels are oil quenched and type S2 steels are water quenched. Type S7 steels are usually air-cooled, but the larger sections are oil quenched.

The primary alloying elements in shock-resisting tool steels are the following:

  • Molybdenum
  • Tungsten
  • Chromium
  • Silicon
  • Manganese
  • Small amounts of carbon (0.4% to 0.6%)

Usually molybdenum, chromium and manganese are added to tool steels to give them hardenability and tempering resistance. In S type steels, silicon is also added to not only enhance tempering resistance of tool steels, but also forms a microstructure, which resists deformation, under some tempered conditions.

Properties

The key properties of shock-resisting tool steels are the following:

  • High strength
  • High toughness
  • Wear resistance
  • High hardness
  • Resistance to shock loading

Composition

The following table shows the designation and composition limits of shock-resisting tool steels.

Designation Compositiona, %
AISI UNS C Mn Si Cr Ni Mo W V Co
S1 T41901 0.40-0.55 0.10-0.40 0.15-1.20 1.00-1.80 0.30 max 0.50 max 1.50-3.00 0.15-0.30 -
S2 T41902 0.40-0.55 0.30-0.50 0.90-1.20 - 0.30 max 0.30-0.60 - 0.50 max -
S5 T41905 0.50-0.65 0.60-1.00 1.75-2.25 0.50 max - 0.20-1.35 - 0.35 max -
S6 T41906 0.40-0.50 1.20-1.50 2.00-2.50 1.20-1.50 - 0.30-0.50 - 0.20-0.40 -
S7 T41907 0.45-0.55 0.20-0.90 0.20-1.00 3.00-3.50 - 1.30-1.80 - 0.20-0.30b -

aExcept group W, all steels contain 0.03 max S, 0.03 max P and 0.25 max Cu. Group W contain 0.025 max S, 0.025 max P, and 0.20 max Cu. As mentioned, the amount of sulfur may be increased from 0.06% to 0.15% to enhance the machinability of group A, M, T, H and D steels.
bOptional.

Applications

The major applications of the shock-resisting tool steels are the following:

  • Chisels
  • Rivet sets
  • Screw driver
  • Shear blades
  • Punches
  • Knockout pins
  • Driver bits.

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