Hardness of the Welded Joint

According to the results of hardness measurement with HV-5 load, it was determined that the hardness of welded joints both with a heat input of 15 ± 2 kJ/cm (Fig. 8) and 50 ± 2 kJ/cm is at approximately the same level and slightly exceeds the hardness of the base metal. The heat-affected zone is transitional where the hardness gradually increases from the base metal to the weld material. Hardness measurements were carried out in three planes of the welded joint: at the surface, at a distance of 1 mm from the immediate top face of the base metal; at the middle; and at the root of the weld, and also at a distance of 1 mm from the bottom surface of the welded joint.

Fig. 8 schematically shows the areas of hardness distribution and its average values in the welded joint with relative maximum and minimum limits obtained as a result of testing of all submitted specimens.

The level of weld hardness is characterized by the average values of 200 HV5 and 201 HV5 at the top surface and at the root of the weld, respectively, and 206 HV5 at the core of the weld. At the face of the welded joint, in the immediate vicinity of the fusion line (FL), the hardness level on both sides of the weld is ≈ 194 HV5. At the FL of the weld middle, it amounts to 182/201 HV5, and at the root – to 187/200 HV5. The increased values at the inclined bevel of the weld groove are the result of greater unevenness in certain sections of the fusion line.

At a distance of 2 mm from the fusion line (FL+2 mm), the values begin to level off over the entire thickness of the welded joint, and amount to: 188/195 HV5 at the surface, 191/187 HV5 at the core, and 194/198 HV5 at the root of the weld. The hardness level of the base metal measured at a distance of 60 mm from the fusion line (FL+60 mm) is fairly even and ranges from 173/175 HV5 at the face, to 187/191 HV5 at the middle and 184 HV5 at the root of the weld.