Change of tensile behavior of a high-strength low-alloy steel with tempering temperature

The tensile behavior of a high-strength low-alloy (HSLA) steel after tempering at different temperatures from 200 to 700 degrees C was investigated. The steel showed similar tensile behavior with almost no change in strength for tempering below 400 degrees C. However, when the tempering temperature was increased from 500 to 650 degrees C, the steel displayed not only a decrease in strength, but also gradually the upper yield points and lower strain-hardening ability. When the tempering temperature was increased up to 700 degrees C, the steel exhibited a "round roof" shaped tensile curve and a high strain-hardening exponent. These interesting phenomena of tensile behavior are well explained in view of the interactions of mobile dislocations and dissolved C and N atoms and their effects on the strain-hardening exponent. (C) 2009 Elsevier B.V. All rights reserved.