The Effect of the Heat Treatment Condition of the Base Material on the Microstructure and Mechanical Properties of 17-4PH Stainless Steel Electron Beam Welded Joints

The study was intended to determine the effect of the input condition of the 17-4PH steel on the microstructure, mechanical properties and stress state of welded joints. The steel adopted for testing was in the solution condition at 1040°C, the aged condition at 550°C/4h and the overaged condition at 760°C/2 h + 620°C/4 h. Samples of 17-4PH steel, after heat treatment processed with different parameters, were electron beam welded (EBW). The microscopic observation (LM, SEM/EDS) showed that the microstructure of the weld consisted of martensite with a δ-ferrite lattice. In the heat-affected zone (HAZ), transformed martensite was found with evidence of niobium carbides. The results of hardness testing revealed the different nature of the hardness profile with the condition the material before the EB welding process. The hardness profile of the HAZ of the welded samples in the as-solution (ES2) and overaged (ES12) condition was varied (from about 340 HV to 450 HV). However, in the aged condition specimen of 17-4PH steel (ES22) showed a similar hardness level, at around 370 HV. The solution condition (ES2) had the highest strength properties Rm 1180.6 MPa with the lowest elongation A 7.6% of all samples tested. The aged welded specimen (ES22) retained high strength Rm 1103.4 MPa with a better relative elongation A 10.1%, whereas the overaged welded specimen (ES12) saw a reduction of strength Rm 950.4 MPa with an improvement in plastic properties A 18.8%. Obtained results showed a significant effect of the input steel condition on the obtained EB welded joints.