Tool Steels - Finish Grinding of Tool Steels

Tool steels generally are used at high hardness levels and consequently contain high levels of internal stress. This internal stress can be relieved and result in cracking if finish grinding is not carried out under prescribed conditions. Often grinding cracks are not visible to the naked eye and will lead to early tool failure caused by spalling or fatigue.

The heat generated by heavy grinding passes may cause overheating of the surface microstructure leading to the formation of martensite. Formation of untempered martensite can lead to cracking.

Another common problem caused by improper grinding is the localised tempering effect caused by the heat generated. The soft skin may not crack but poor tool life will result from a drop in hardness.

The necessity for care in grinding is of the utmost importance and the following guidelines should be observed:

•         Use soft, open grained alumina wheels. The harder the steel, the softer the grinding wheel and the grit

•         Ensure grinding wheels are properly dressed and in good condition

•         Minimise the peripheral speed of the wheels and ensure a copious and continuous supply of coolant

•         Ensure parts are fully tempered before grinding.

Source: Abstracted from “IMMA Handbook of Engineering Materials”, 5^th Edition.

For more information on this source please visit The Institute of Materials Engineering Australasia.