Abstract
Heat-affected zone (HAZ) of welding joints critical to the equipment safety service are commonly repeatedly welded in industries. Thus, the effects of repeated welding up to six times on the microstructure and mechanical properties of HAZ for AISI 304N austenitic stainless steel specimens were investigated by a Gleeble simulator. The temperature field of HAZ was measured by in situ thermocouples. The as-welded and one to five times repeated welding were assigned as-welded (AW) and repeated welding 1–5 times (RW1–RW5), respectively. The austenitic matrices with the δ-ferrite were observed in all specimens by the metallography. The δ-ferrite content was also determined using magnetic and metallography methods. The δ-ferrite had a lathy structure with a content of 0.69–3.13 vol.%. The austenitic grains were equiaxial with an average size of 41.4–47.3 μm. The ultimate tensile strength (UTS) and yield strength (YS) mainly depended on the δ-ferrite content; otherwise, the impact energy mainly depended on both the austenitic grain size and the δ-ferrite content. The UTS of the RW1–RW3 specimens was above 550 MPa following the American Society of Mechanical Engineers (ASME) standard. The impact energy of all specimens was higher than that in ASME standard at about 56 J. The repeated welding up to three times could still meet the requirements for strength and toughness of welding specifications.
Highlights
Repeated welding in the same location is a necessary process for construction, maintenance, and repair in industrial sectors
Uniform Heat-affected zone (HAZ) specimens were prepared under the measured temperature field by the Gleeble weld-simulator to evaluate the microstructure of the repeated welding joints
With the increasing number of repeated welding, the average grain size of austenite fluctuated from 41.4 μm to
Summary
Repeated welding in the same location is a necessary process for construction, maintenance, and repair in industrial sectors. The repeated welding regulations in different standards are not the same. According to the GB50236 3.0.6 clause for pipelines [1], welding seams should not be repaired more than twice in the same location. In the IPS-C-PI-270(2) [2], it is expressed that a weld with unacceptable defects may be repaired only once. In the RCC-M IV Welding S7610 for nuclear power plants [3], it requires that two welding repairs may be performed at the same location. While in ASME BPVC III NB [4], the number of repeated welding is not limited, but the technical requirements for defect removal have been described in details
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