Effect of the Heat Input and Ageing Treatment on Microstructure and Mechanical Properties of AISI 317L Stainless Steel Dissimilar Welded Joints

Abstract

The present work investigated the influence of heat input and aging time on the microstructural characteristics and the mechanical properties of dissimilar AISI 317L austenitic stainless steel welded joints. The AWS ER2209 wire-electrode was used as filler metal, and two different heat input levels were applied (4 and 8 kJ/cm), aiming to verify the influence of this parameter on the deleterious phases precipitation. An aging heat treatment (AHT) was carried out at 700 °C for two different exposure times: 50 and 100 hours. It was observed that aging promoted a refinement of the base metal region, and all delta ferrite was transformed into the sigma phase. The microstructure of the fusion zone (without AHT) presented a significant amount of austenite that precipitated in three different morphologies: allotriomorphific of grain boundary, Widmanstätten, and intragranular. For all the thermally treated samples, it was possible to identify the presence of the σ and χ phases. Additionally, the highest concentration of the χ phase was identified in the samples submitted to 50 hours of AHT. The welding condition and AHT that presented joints with higher mechanical resistance and remarkable toughness were those welded with 4 kJ/cm heat input and with 100 hours of AHT. All welded joints showed an increase in the hardness profile after AHT. The microhardness values showed a good correlation with the microstructure and the mechanical tests so that the highest values of microhardness were observed in welded joints with heat input of 4 kJ/cm and 100 hours of AHT

Kinetics of Intermetallic Phase Precipitation in Manual Metal Arc Welded Duplex Stainless Steels

“…Various morphologies of austenite are observed: allotriomorphic austenite (γ A ), Widmanstätten austenite (γ W ), and idiomorphic austenite (γ I ). Their occurrence is consistent with literature reports for welds in grades 2209 [38,[45][46][47][48][49][50][51][52], 2101 [53,54], 2205 [55][56][57], 2507, and 2304 [55]. Observations regarding the occurrence of non-metallic inclusions are also consistent with literature reports [58][59][60] and result from the specificity of the manual metal arc welding process.…”

“…Therefore, a level was achieved that was very similar to that obtained in the research (Figure 10). Also, Antunes et al [47] showed that after annealing of grade 2209 welds at a temperature of 700 • C for 50 and 100 h (3000 and 6000 min), γ austenite and χ and σ phases appear in the microstructure. No δ ferrite was found.…”