Mechanical Properties and Microstructure Transformation Behavior for Welded Joints in Ship Plate Steel with High-Heat Input Welding

Mechanical properties and microstructure transformation for welded joints in EH40 ship plate steel were investigated after an electro-gas vertical welding and welding thermal simulation. Effect of the inclusions on the prior to austenite grain size and nucleation of intragranular ferrites (IGFs) was examined. Results indicated that the experimental steel has a good ability for high-heat input welding. Excellent impact toughness at testing temperature of − 20 °C was obtained. An increase in impact energies at − 20 °C for the position away from fusion line (FL) is observed. The average impact energy (177 J) for heat-affected zone by simulation with heat input of 120 kJ/cm is similar with that (165 J) for FL+1 mm by electro-gas vertical welding with heat input of 207 kJ/cm. The TiN particle lost the pinning effect when the peak temperature reached 1400 °C. However, the titanium oxide particles play an important role in inhibiting the austenite grain growth because of the high melting point. Three IAFs nucleated on the TiOx-Al2O3-MgO-MnS particle with the size of 7.6 μm were observed. The inclusion size is not the dominant requirement for the nucleation of IGFs and IAFs. The MnAl2O4 and TiO particle have good lattice matching with ferrite, they have a strong ability to promote the nucleation of IAF.