Effect of Cr Content on Microstructure and Impact Toughness in the Simulated Coarse-Grained Heat-Affected Zone of High-Strength Low-Alloy Steels

The relationship of Cr content to microstructure and impact toughness in the simulated coarse-grained heat-affected zone of high-strength low-alloy steels subjected to varying heat input welding thermal cycles is investigated. Results show that the microstructures of the simulated coarse-grain heat-affected zone in steels with different Cr contents and welding heat inputs consist of predominantly bainite, a small proportion of acicular ferrite, and martensite–austenite constituents. With the Cr content increasing from 0.33 to 0.65% and 1.02%, the fraction of acicular ferrite is decreased and martensite–austenite constituents are increased. Meanwhile, when the heat input increased from 20 to 100 and 200 kJ cm−1, martensite–austenite constituents increase in amount and coarsen remarkably. The impact toughness of simulated coarse-grain heat-affected zone at −20 °C decreases obviously with increasing Cr content, especially subjected to high-heat input welding.