Detection of Heat Treat Defects and Grinding Burns by Measurement of Barkhausen Noise

Abstract

Grinding and heat treating processes are integral steps in the industrial production of most finished metallic parts. Among the parts whose properties may be adversely affected by improper grinding and/or heat treatment are camshaft lobes, bearing races, bearings, machine bolts, automotive U-joint trunnions, piston pins, gears, shafts, pipes, and many others. The benefits associated with proper grinding and heat treatment are well-known^1,2. Included among these benefits are controlled hardness, improved fracture toughness, and reliable dimensional control. Improper grinding may result in numerous surface defects, e.g., retempered areas, rehardened areas, and cracks. Heat treatment errors often result in regions of decreased hardness, i.e., soft spots, as well as decarburizing, denitriding, or overtempering. If left undetected, each of these defects may lead to catastrophic failure of a part operating under load. As a result, it is necessary to detect grinding and heat treat defects as they occur so that steps may be taken to correct the process immediately and prevent the incorporation of faulty parts into their end-products.