Effect of cooling after welding on microstructure and mechanical properties of 12 Pct Cr steel weld metals |
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Authors: | Guang-Jun Cai Hans-Olof Andrén Lars-Erik Svensson |
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Affiliation: | 1. Department of Materials Engineering, Southwest Jiaotong University, 61 00 31, Chengdu, People’s Republic of China 3. the Department of Physics, Chalmers University of Technology, S-412 96, G?teborg, Sweden 4. the Central Laboratories, The Esab Group, S-402 77, G?teborg, Sweden
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Abstract: | The microstructure of three 12 pct cr steel weld metals with different nickel and nitrogen contents was studied in as-welded
condition and after postweld heat treatment with and without intercooling. Tensile strength and impact toughness of the weld
metals were investigated in different postweld heat treatment conditions. In weld metals heat treated without intercooling,
austenite decomposed by a eutectoid reaction that resulted in M23C6 aggregates around retained δ-ferrite. Two morphologies of M2N and MN precipitates were found in a low-dislocation α-ferrite. It was concluded that these phases were also transformed from austenite. In weld metals heat treated with intercooling,
M23C6 precipitates were smaller and more homogeneously distributed. Different MN precipitates were found in the tempered martensite.
The fracture mode of the weld metals at room temperature was mainly transgranular cleavage with some fibrous fracture. Intercooling
treatment improved Charpy impact toughness of the 12 pct Cr steel weld metals substantially. It was found that the important
microstructural factors affecting the impact toughness of the weld metals which were heat treated without intercooling were
the sizes of the α-ferrite grains, nonmetallic inclusions, and M23C6 aggregates. For the weld metals heat treated with intercooling, the factors which affect the toughness of the weld metals
were the sizes of martensite packets and nonmetallic inclusions. |
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