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).