| SHI Zhen-yan,ZHANG Yan,DONG Li-jin,ZHENG Huai-bei,WANG Qin-ying,LIU Ting-yao.NP Effect of Microstructure on Mechanical Properties and Sulfide Stress Corrosion Cracking of Incoloy 825[J],52(1):141-151 |
| NP Effect of Microstructure on Mechanical Properties and Sulfide Stress Corrosion Cracking of Incoloy 825 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.01.015 |
| KeyWord:Incoloy 825 inclusion microstructure three-point bending experiment sulfide stress corrosion cracking slow strain rate tensile test |
| Author | Institution |
| SHI Zhen-yan |
School of New Energy and Materials, Southwest Petroleum University, Chengdu , China |
| ZHANG Yan |
School of New Energy and Materials, Southwest Petroleum University, Chengdu , China |
| DONG Li-jin |
School of New Energy and Materials, Southwest Petroleum University, Chengdu , China |
| ZHENG Huai-bei |
Chengdu Advanced Metal Materials Industrial Technology Research Institute Co., Ltd., Chengdu , China |
| WANG Qin-ying |
School of New Energy and Materials, Southwest Petroleum University, Chengdu , China |
| LIU Ting-yao |
Chengdu Advanced Metal Materials Industrial Technology Research Institute Co., Ltd., Chengdu , China |
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| Abstract: |
| The object of this study is to clarify the effect of microstructure on the sulfide stress corrosion cracking of Incoloy 825. Optical microscope (OM), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) were used to analyze the metallographic structure, inclusions, grain boundary character, the distribution of residual strain and grain size. The microhardness and mechanical properties of two type of alloy 825 were evaluated by Vickers hardness tester and tensile tests respectively. The susceptibility of hydrogen embrittlement and sulfide stress corrosion cracking were evaluated by hydrogen microprint tests, slow strain rate tensile tests under hydrogen charging, and three-point bending experiments. The results show that the inclusions in these alloys are mainly TiN, which could be divided into type B and D. The distribution of type B inclusions in both alloys are quite similar. Most of inclusions are dispersed near grain boundaries. The distribution of type D inclusions in alloy 1# tends to be concentrated while the inclusions are more homogeneous in alloy 2#. The grades of type B and D inclusions in alloy 1# are 0.91 and 1.4, respectively. However, the quantity and size of inclusions in alloy 2# are smaller, in which the inclusion grades of type B and D are reduced to 0.54 and 1.33, respectively. In addition, MnS and TiN eutectic is formed at a part of grain boundaries of alloy 1#. Hydrogen microprint technique tests confirm that the hydrogen atoms are prone to concentrate at the inclusions and some of grain boundaries in alloy 1#. EBSD analyses show that both of alloys are consisted of equiaxed austenite grains. However, the average grain size of alloy 1# is slightly bigger than that of alloy 2#. In addition, the grain size distribution in alloy 2# is more uniform in comparison to the alloy 1#. The residual strain near the grain boundaries and grain size of alloy 1# is a little higher than that of alloy 2#, in which low Σ boundaries present a large fraction. The microhardness and yield stress of alloy 1# are 184.67HV and 285.30 MPa while the alloy 2# has a microhardness of 207.75HV and a yield stress of 300.03 MPa. The result of slow strain rate tensile tests under hydrogen charging revealed a tendency of hydrogen embrittlement for both alloys. The fracture elongation of alloy 1# decreased by 2.6% while that of alloy 2# only decreased by 1.6%. The difference of mechanical properties may be attribute to the distribution of inclusions and grain size. Three-point bending experiments indicate the surface of alloy 1# is severely corroded, and macroscopic cracks are found near the opening. High-magnification observation of the crack initiation region reveal that inclusions and cavities existed at the crack site in alloy 1#. After initiation, the cracks propagate mainly transgranularly. Nevertheless, the surface of alloy 2# still shows the metallic luster and only small cracks with a size of several microns exist at the stress concentration region. In conclusion, the inclusions as effective hydrogen traps, reduce the yield stress and lead to residual strain concentration at grain boundaries, thus result in the sulfide stress corrosion cracking of alloy 825. In addition, a galvanic cell could form between the inclusion and surrounding metal, promotes the anodic dissolution of the matrix, and therefore the cracking susceptibility of the alloy is increased. |
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