IMPROVING THE INTERGRANULAR CORROSION RESISTANCE OF THE WELD HEAT-AFFECTED ZONE BY GRAIN BOUNDARY ENGINEERING IN 304 AUSTENITIC STAINLESS STEEL
YANG Hui1, XIA Shuang1,2(), ZHANG Zilong1, ZHAO Qing1, LIU Tingguang1, ZHOU Bangxin1,2, BAI Qin1,2
1 Institute of Materials, Shanghai University, Shanghai 200072 2 Key Laboratory for Microstructure, Shanghai University, Shanghai 200444
Cite this article:
YANG Hui, XIA Shuang, ZHANG Zilong, ZHAO Qing, LIU Tingguang, ZHOU Bangxin, BAI Qin. IMPROVING THE INTERGRANULAR CORROSION RESISTANCE OF THE WELD HEAT-AFFECTED ZONE BY GRAIN BOUNDARY ENGINEERING IN 304 AUSTENITIC STAINLESS STEEL. Acta Metall Sin, 2015, 51(3): 333-340.
The heat-affected zone (HAZ) produced by welding in stainless steel has higher susceptibility to intergranular corrosion, which is attributed to the Cr depletion induced by grain-boundary carbide-precipitation. The grain boundary engineering can be used to control over the grain boundary structure, which has significant influence on the carbide precipitation and the associated Cr depletion and hence on the susceptibility to intergranular corrosion. The grain boundary network in a 304 austenite stainless steel can be controlled by grain boundary engineering (GBE) with 5% tensile deformation and subsequent annealing at 1100 ℃ for 30 min. The total length proportion of Σ3n coincidence site lattice (CSL) boundaries was increased to more than 75%, and the large-size highly-twinned grain-cluster microstructure was formed through the treatment of GBE. Specimens were welded by gas tungsten arc-welding. Then the microstructure and the corrosion resistance of HAZ were characterized. The result showed that the high proportion of low ΣCSL boundaries and the optimum grain boundary character distribution were stable in the HAZ of the grain boundary engineered stainless steel, and the grain size was nearly the same. The weld-decay region of GBE samples performed better intergranular corrosion resistance during the intergranular corrosion immersion experiment and electrochemical potentiokinetic reactivation (EPR) test. The reported results indicated that the grain boundary engineering can effectively improve the intergranular corrosion resistance of the heat-affected zone in 304 austenitic stainless steel.
Fund: Supported by National Basic Research Program of China (No.2011CB610502) and Shanghai Science and Technology Commission Key Support Project (No.13520500500)
Table 1 Thermal-mechanical treatment of specimens A and B
Fig.1 Schematic of gas tungsten arc-welding (GTA-W) of specimens
Fig.2 OIM maps of different types of grain boundaries in specimens A (a) and B (b) (Large grain-clusters C1 and C2 formed in specimen B, the grain-clusters C1 and C2 enclosed by random boundary (R) consist of grains with Σ3n-orientation relationships)
Specimen
Length fraction of grain boundary / %
Average grain
Average grain-cluster
Σ3
Σ9+Σ27
Overall low Σ
size / μm
size / μm
A
44.0
1.0
45.0
24.3
51.1
B
66.5
9.1
75.6
28.1
124.4
Table 2 Grain boundary character distribution and grain sizes of specimens A and B
Fig.3 Macro-views of the microstructure of welded specimens A and B after corrosion (1—weld, 2—grain-coarsened area, 3—weld-decay region, 4—base material)
Fig.4 Grain boundary character distributions presented by OIM images of different microstructures for welded specimens A (a) and B (b) (1—weld, 1-2—weld-grain-coarsened area, 3—weld-decay region, 4—base material)
Fig.5 Proportions of low ΣCSL boundaries (a) and grain size (b) of different microstructures for welded specimens A and B
Fig.6 Surface macro-views of welded specimens A (a) and B (b) after 48 h corrosion, and high magnified SEM images of weld-decay region corresponding to rectangular areas I (c) and II (d)
Fig.7 Curves of mass loss of specimens A-W and B-W in weld-decay region after corrosion
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