Quenched and Tempered
Quench hardening – Hardening a ferrous alloy by austenitizing and then cooling rapidly enough so that some or all of the austenite transforms to martensite. Tempering – Reheating a quenched-hardened or normalized ferrous alloy to a temperature below the transformation range and then cooling at any rate desired.
Source: API RP 7G, Recommended Practice for Drill Stem Design and Operating Limits, Upstream Segment, Sixteenth Edition, August 1998 (Addendum 2: September 2009). Global Standards