The choice of steel grade depends on a number of practical application factors, such as toughness (resistance to crack initiation and propagation), hardness (resistance of the material to penetration), thermal fatigue resistance (resistance to the effects of successive heating and cooling which can generate cracks), which can be translated into the simple application questions detailed below.
The following formulations should be kept in mind for questions of use:
- Does the use require a sharp and durable cut?
- Does the tool have to withstand impact loads (hammers, picks, axes, etc.)?
- Is abrasion resistance an important criterion?
- Is a special heat treatment required?
The answer to these questions will lead to the selection of a steel grade from six categories (grades) of special composition and treatment:
Air hardened (Grade A)
It is a versatile tool steel characterised by a low distortion factor during heat treatment due to its high chromium content. This tool steel has good machinability and a balance between wear resistance and toughness.
Typical applications include cams, die bending, cutting, stamping, cold forming, rolling, cold crimping, deburring, gauges, grinding knives, cold cutting knives, woodworking and centre lathe blades.
Type D (High Carbon and Chrome content with air hardening)
Type D steel, with high carbon and chromium content (air hardening), is formulated to combine abrasion resistance and air hardening characteristics. Common applications for these tool steels include forging dies, die-casting blocks and drawing dies.
Typical applications include burnishing tools, file cutting, paper cutters, die bending, cutting, stamping, cold extrusion, cold forming, rolling, cold swaging, thread rolls, cold cutting, drawing, jigs, paper irons, circular knives, chisels for cold working, woodworking tools.
Water hardening (Grade W)
It is essentially a high-carbon steel. Generally inexpensive, this steel can reach a high hardness, but it is rather brittle compared to other tool steels and cannot be used with high temperatures.
All W grade tool steels must be water quenched, which can increase the effects of warping and cracking.
Typical applications for W grade tool steel include cold cutting, cutting tools and knives, embossing, reamers and cutlery.
Oil hardening (Grade O)
Grade O steels are oil-hardening steels. Intended for general use, they have good abrasion resistance and good toughness for a wide range of applications: shafts, bushes, combs (wire cutters), collets, die cutting, cold forming, cold deburring, drill rings, gauges, knurling tools.
Impact resistant types (Grade S)
Grade S steels, with a low carbon content, are designed to withstand impacts at low or high temperatures (e.g. jackhammer bits); they have high impact toughness but low abrasion resistance.
Typical applications include hammering tools, boiler shop tools, cold and hot chisel work, pliers and jaws, clutch parts, cold and hot crimping, hot stamping, grinding and cold shearing blades.
Hot work (Grade H)
This group of tool steels is used for cutting materials at high temperatures, adding strength and hardness for prolonged exposure to high temperatures. These steels have a low carbon content and a moderately high content of complementary alloys.
Typical applications include cold heading die casings, die casting dies and cores for zinc and aluminium, hot extrusion for aluminium and magnesium, hot forging, hot gripper, hot crimping, hot stamping, dummy blocks (hot extrusion), hot shear blades.