The Effect of Low Temperature and Strain Rate on the Mechanical Behavior of Precipitation-Strengthened HSLA Steels Alloyed with Ti and Nb
摘要
The uniaxial tensile behavior of four precipitation-strengthened high-strength low-alloy (HSLA) steels was investigated. The microstructure was ferritic and precipitation simulations showed that increased alloying of Ti/Nb resulted in higher volume fractions of carbides, carbonitrides, and TiN precipitates. The average grain size of the steels varied from 1.5 µm to 2.6 µm, leading to high grain size strengthening. Tensile tests were conducted at strain rates ranging from 0.003 s−1 to 1 s−1, and temperatures ranging from 24°C to − 80°C. Grain size and precipitation-strengthening contributions were estimated for the steels and the elevated volume fraction of carbides results in the high 781 MPa yield strength of Gr100. Uniaxial testing and fitting of the flow stress data with a temperature and strain rate-dependent hardening model revealed that all the steels exhibited similar plastic flow behavior, strain rate, and temperature sensitivity, which was scaled by the yield strength of the steel and did not appear to correlate with precipitate content. However, uniaxial ductility was affected by temperature and strain rate for the highest strength and predicted precipitate content Gr100 steel. Charpy V-notch tests did not exhibit a strong correlation between energy absorption and the predicted carbide content, but did correlate with the yield strength.