The success of a metal forming tool depends on optimizing all the factors affecting its performance. Usually, operating conditions (applied loads, abrasive environments, impacts, and other factors) determine how well a tool holds up. Most tool failures are related to such mechanical causes. However, with a variety of tool steels available for manufacturing metal forming tools, it is often possible to choose a tool steel with a favorable combination of properties for particular applications. By comparing the levels of metallurgical properties offered by different steels, tool users can determine which tool steels are best suited for fixing or resisting performance problems, or for enhancing tool performance. Tool steels can be categorized and compared by those properties which have a direct influence on tool performance: hardness, toughness (impact resistance), and wear resistance.
Cold work tool steels
|• General purpose
|— O1, A2, D2
|• Improved toughness (impact resistance)
|— S7, A9
|• Improved wear resistance
|— CruWear, M2
|• High performance CPM
|— 3V, M4, 9V, 10V, T15, 15V
Historically, tool steels used for stamping and forming tools have included A2 and D2, with occasional use of the high speed steel M2. A2 and D2 are familiar to most tool builders and tool users as common, general purpose cold work tool steels. They combine good all-around performance properties for stamping and forming with low cost, wide availability, and relatively easy fabrication. However, they sometimes do not provide the level of performance needed for high volume production. Specifically, where long runs and infrequent regrinding are desired, other higher alloy tool steels or carbide might be used to upgrade from these tool steels. Traditionally, other properties, such as impact resistance, may be sacrificed in order to gain the higher wear properties. Conversely, steels chosen for their resistance to impact or breakage may not be capable of high wear resistance. An understanding of these tool steel properties and related issues permits selection of the optimum steel for most applications.
Before discussing specific grades, it will be useful to discuss generally the properties of tool materials. The primary properties important to cold work tools are hardness, toughness, and wear resistance. Each of these properties may be varied independently in tool steels to some extent, so it makes sense to consider each separately. In fact, the same properties would be important to consider in carbide materials as well as steels. An understanding of these properties, combined with an understanding of what factors limit tool life for a particular tool (breakage, wear, deformation, etc.), will allow tool users to specify the best performing grade for nearly any application. Tool users can examine failed tools to determine which property may have been lacking in a tool, or which properties should be improved, and what other properties must be considered in alternate materials with the required improved properties.
|Properties of tool steel
|— resistance to deforming & flattening
|— resistance to breakage & chipping
|• Wear resistance
|— resistance to abrasion & erosion