PSI - Issue 57

Yevgen Gorash et al. / Procedia Structural Integrity 57 (2024) 611–617

613

Y. Gorash et al. / Structural Integrity Procedia 00 (2023) 000–000

3

7 6

1 mm

top

1 2 3 5 4

middle

b

a

bottom

middle

top

bottom

e

c

d

Fig. 2. Measurements of Vickers hardness test HV 0.5 taken at di ff erent paths of S275JR + AR weldment: a) sequence of passes; b) macrostructure of full weld polished section; c) top path; d) middle path; e) bottom path.

3. Inspection of welds quality

All plates were welded manually at the welding facility of Doosan Babcock Ltd by an expert welder with corre sponding Welding Procedure Qualification Records (WPQR) and Radiographic (X-ray) & ultrasonic (US) inspection reports provided for each welded plate. According to WPQR, a produced weld consists of 7 passes in total, as shown in Fig. 2a. The preheating was not required as the plates are relatively thin. The first pass is applied to the root in the middle of the plate, and then the second pass completes the welding of one plate side, as can be confirmed by the microstructure image in Fig. 2b for the for the weld cross-section extracted from the plate ID no. ZL805. Before performing the welding of the opposite side, its groove is ground and wire brushed. Another 5 passes are deposited on the opposite plate side according to the schematics in Fig. 2a and confirmed by the micrograph shown in Fig. 2b. Cross-section of the welded plate ID no. ZL805 has been tested for Vickers low-force hardness with a hardness number of HV = 0 . 5. The hardness measurements were taken along three di ff erent paths of S275JR + AR weldment (top, middle and bottom), as shown in Fig. 2b. The obtained Vickers hardness results have the spikes visible on all three pathes over 190 HV 0.5 at the locations corresponding to Heat A ff ected Zone (HAZ):

• toppath: 155 with minimum of 129 and maximum of 192 (see Fig. 2c); • middle path: 140 with minimum of 122 and maximum of 166 (see Fig. 2d); • bottom path: 151 with minimum of 122 and maximum of 206 (see Fig. 2e).

These results show that the hardness of the HAZ is much higher than that of the base metal and slightly higher than that of the weld metal. Increased hardness of HAZ is usually associated with the “grain size hardening” mechanism, caused by the grain refinement due to the interaction between heat input and cooling rate. The smaller the grains, the more grain boundaries exist in the microstructure, so the harder the material would be. Fine-grained microstructure of HAZ can be easily seen in Fig. 2b.