A reader writes, "I am under the impression I need to quench a part right after the hardening process. Would delaying the quench cause problems? If, for example, we austenitize at 1600°F (870°C) and then allow it to cool to say 1300-1400°F (700-760°C) prior to quench, will this allow us to get the required hardness without generating other metallurgical problems?”
Dan H:Each material has a critical transformation temperature (on cooling) below which you will drop out of the austenite field and indeed cause a variety of metallurgical problems as well as loss of hardness. Usually you want to stay at least 150°F to 200°F (65°C to 95°C) above this temperature to ensure that all areas of the component are above the upper critical temperature (on cooling). A good source (and its free!!) for looking up these values for steel is The Timken Company’s “Practical Data for Metallurgists.” (www.timken.com).
Can Quench be Delayed?

Dan Herring is president of THE HERRING GROUP Inc., which specializes in consulting services (heat treatment and metallurgy) and technical services (industrial education/training and process/equipment assistance). He is also a research associate professor at the Illinois Institute of Technology/Thermal Processing Technology Center. tel: 630-834-3017; e-mail: dherring@heat-treat-doctor.com; web: www.heat-treat-doctor.com
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