Microstructure and Mechanical Properties of Heat-Affected Zone of Repeated Welding AISI 304N Austenitic Stainless Steel by Gleeble Simulator

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.

Simulated Heat Affected Zone in Welded Stainless Steel 304l

“…Excessive heat input could result in a wide HAZ with low impact strength [8]. As reported DOI by Gu et al [9], the degradation in strength and toughness of welded joint, is always happens in HAZ. For this reason, weld thermal cycle simulation can be used for optimizing the welding technology since it enables some mechanical testing for properties that cannot be made on real welded joints because of small width of HAZ.…”

Heat Affected Zone in Welded Metallic Materials

“…Welding simulation is the appropriate technique to determine the different sub-zones in HAZ. This allows the prediction of the microstructure and the properties of these sub-zones [9]. Consequently, thermal cycle simulation in which the HAZ can be geometrically extended is the appropriate method in order to determine the different microstructures, which can be developed in real welded joints [12,13].…”

“…High heat input increases the size of the HAZ which induces a low impact strength [8]. As reported by Gu et al [9], the degradation in strength and toughness of welded joint, is generally happens in HAZ.…”