Cutting-edge hardness testing

Inspection of manufactured goods has increasingly become standard practice to ensure products meet more and more demanding specifications. In some cases, this can mean that long established methods of quality control need to be pushed to their limits. One example is the heat treatment of steel. Hardness test-ing has been used to check heat treatments for more than 100 years. As applications have become more specific, and technical developments more refined, the test methods have developed further alongside of technology. In the highly competitive cutting blades industry, it is vital for the blade to have sufficient hardness to retain an edge, while too hard can cause brittle failure. When hardened materials are ground, residual heat may alter the microstructure and soften the blade edge. By design, the blades have little mass, so control of residual heat during the final finishing process is also critical. Accurate testing for hardness is therefore vital to ensure a high quality product. Testing the hardness of the cutting blades becomes challenging as indents must be made and measured accurately, using low loads and correspondingly small indents. This requires proper specimen preparation and careful use of hardness testing equipment. This article will review a guide to metallographic preparation and micro-hardness test processes for this application, although the principles are relevant to the use of Vickers testing for any hard material applications.