Effects of Quenching and Tempering Heat Treatment Processing on the Microstructure and Properties of High-Strength Hull Steel

The construction of heavy polar icebreakers is usually done with special hull steels, which require comprehensive properties such as good low-temperature toughness, high strength, and superior fatigue resistance. Reasonable and satisfactory heat treatments should be investigated and applied to acquire the required high strength and superior low-temperature toughness, since this is deemed an effective approach to ameliorate the combined properties of high-strength hull steels. Regarding this, the present study specifically explores the effects of different laboratory-based quenching (850 to 930◦ C) and tempering (580 to 660◦ C) heat treatments on the final low-temperature toughness of the high-strength hull steels. The low-temperature toughness is eventually improved without significantly sacrificing the strength. The results show that a favourable combination of properties can be obtained in the specimens under 900◦ C quenching and 660◦ C tempering processes. Additionality, the specimens tempered at 620◦ C present the highest hardness, owing to the higher percentage of tempered martensite. Detailed mechanisms of the enhanced properties of the typical specimens subjected to the corresponding quenching and tempering processing are analysed and explicated.