Galling results from friction from high pressure contact between the tool and the workpiece material. Galling is most often encountered in situations involving:
- contact between similar materials
- soft work material (such as aluminum & copper alloys)
- stainless steel work material, especially austenitic stainless (non-magnetic 300 series)
Galling is often most effectively addressed by separating the contacting surfaces, such as with a lubricant or coating. Because most tool steels have similar physical surface properties, changes in tool material may be beneficial, but less effective than coatings or lubricants. Never the less, high wear, high toughness tool steels, such as 3V, or very high wear resistance tool steels, such as 10V or 15V, can sometimes be beneficial.
Coatings or surface treatments are often recommended where practical, especially for very soft workpieces, where smearing of the workpiece against the tool is the main cause of failure. When using coatings or surface treatments, the choice of tool steel material must be compatible with the coating or treatment process. In particular, the tempering temperature of the tool during heat treatment should be below the processing temperature for the coating or surface treatment
D2, A2, and S7 are typically tempered at about 400/600 F (205/315 C) during heat treatment to their normal working hardness. Exposure to higher processing temperatures may soften these grades. D2 can sometimes be tempered as high as 925/975 F (495/525 C), but hardness may be limited to mid-50's to high-50's HRC. Steels with high tempering temperatures, such as high speed steels (M2, CPM M4), or any tool steel tempered higher than the processing temperature (CruWear, 3V, 10V), may be more suitable, especially if high hardness (>HRC 60) is required in the finished tool.
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