The Impact of Conflicting Heat Treat Processing Instructions on Microstructure

ASTM 193 B16 is a chrome, molybdenum, vanadium steel that is used for high temperature or high-pressure service and other special purpose applications. It is essentially a 4140 steel with a slightly higher molybdenum content and additions of vanadium. The heat treat processing callout for this chemistry is to austenitize and quench in a liquid medium and temper at a minimum of 1200F (649C). The customer’s heat treat processing instructions were to use the B16 material and air cool it instead of quenching it. An inspection audit of the M8 X 115mm studs resulted in a rejection because the parts were liquid quenched but met mechanical testing requirements of 32-40 HRC, 150,000psi. The studs were then processed per the customer’s instructions and were still-air-cooled and failed the mechanical testing requirements. This presentation walks us through the heat-treated microstructures and the corrective actions that were taken to satisfy customer requirements.