Effects of Heat Treatment and Severe Plastic Deformation on Microstructure, Mechanical Properties and Midsection Ultimate Strength of Shipbuilding Steel

Improving the strength values of low-medium-strength shipbuilding steels without changing the chemical properties will be very useful to meet the high-strength requirement in ships. Heat treatments and severe plastic deformation methods are the main methods used to increase the strength values of steel without changing the chemical structure. Considering the high improvement effect in strength values, quenching process and equal channel angular pressing (ECAP) method stand out among heat treatments and severe plastic deformation methods, respectively. In the current study, quenching and ECAP were applied to low-medium-strength shipbuilding steel and the changes in microstructure and mechanical properties of steel after these methods were comparatively investigated. While martensite was formed in the microstructure after quenching, the average grain size decreased compared to the base material without a phase change with ECAP. Hardness values increased by 100% after quenching and increased by 80% after ECAP. Yield and tensile strength values increased by 3.3 and 2.5 times, respectively, after quenching. On the other hand, yield and tensile strength values after ECAP raised less than after quenching and increased 1.5 and 1.7 times, respectively, compared to the base material. Impact toughness values decreased by 80% after quenching and 10% after ECAP compared to the base material. Also, corrosion resistance of the base material decreased by 13% after quenching and increased by 10% after ECAP. Changes in the mechanical properties of the material after these processes were reflected the middle section of a ship using finite element-based programs and approximately 3.3 times higher than that of the base material for all dimension load-ultimate strength values under uniaxial compression were reached in the model reflecting the mechanical properties of the quenched samples.