TYPICAL WORKING HARDNESS RANGES

If tools deform (indenting, mushrooming, flattening, or rolling over), they are not hard enough to resist the compressive stress. They deform from lack of sufficient compressive yield strength. The compressive yield strength is related to the heat-treated hardness (see Figure 1 above) Try a steel designed for higher hardness. Figure 2 shows typical working hardness ranges for many tool steels. In most cases, high speed steels (M2, M4, T15) offer the highest hardness. However, there may be trade-offs in other properties, particularly toughness, depending on what they are replacing. (See Wear & Toughness comparison page.) Cruwear, M2, and CPM M4 all offer higher attainable hardness than A2 or D2. Note that all offer improved wear properties as well. Of these high attainable hardness grades, M2 is comparable to slightly lower in toughness than D2, CruWear is a little tougher than D2, and CPM M4 offers the best toughness at elevated hardness. Tools steels are generally intended for a specific hardness range. Using them at their maximum hardness, or above their intended design hardness range, usually results in a compromise. Often, the toughness of a grade decreases significantly as hardness is "pushed" to its maximum. The required heat treatment becomes more aggressive, and may cause an increased risk of toughness problems.

Figure 1: Relationship between hardness and compressive yield strength (schematic).

Typical Working Hardness Ranges (HRC) S7 56-58 A2 58-62 D2 58-62 M2 58-64 CRU-WEAR 58-62 3V 58-62 CPM M4 58-64 9V 52-56 10V 58-62 15V 58-62 Figure 2: Typical recommended working hardness ranges for some tool steels.