THE EFFECTS OF HEAT TREATMENT VARIABLES ON THE MICROSTRUCTURE AND PROPERTIES OF ULTRA-HIGH STRENGTH STEELS DIFFERING IN TITANIUM CONTENT

摘要

The influences of different austenitizing and tempering temperatures on the microstructure and properties of three experimental ultra-high strength steels (UHS) have been investigated. The steels had different Ti content and were subjected to austenitizing treatment at 900, 1000, 1100 and 1200 degrees C followed by oil quench and tempering at 200, 300, 450 and 600 degrees C. It has been found that the high temperature (1100 and 1200 degrees C) austenitizing treatments, alter both microstructure and properties, and depending on the subsequent tempering temperature, may have a beneficial or detrimental influence upon the mechanical properties. Addition of up to 0.011 wt% Ti to the steel composition improves hardness, toughness and tensile strength. This improvement in mechanical properties is obtainable with any subsequent heat treatment. For higher Ti content (0.089 wt%), although some further improvement in hardness and tensile strength was obtained, significant degradation in toughness was achieved, particularly when the steel was subjected to high temperature austenitizing and tempering treatment. [References: 35]