The Effect of Ca Content on the Formation Behavior of Inclusions in the Heat Affected Zone of Thick High-Strength Low-Alloy Steel Plates after Large Heat Input Weldings
Abstract
:1. Introduction
2. Materials and Methods
3. Results
3.1. Thermodynamic Calculations
3.2. Number Densities, Sizes, and Compositions of Inclusions
3.3. Morphologies of Typical Inclusions
3.4. Microstructure and Impact Toughness at −20 °C
4. Discussion
4.1. Effect of Ca on Formation of Inclusions
4.2. Effective Inclusions in Enhancing the HAZ Toughness
5. Conclusions
- The Ca addition decreases the number density of the pure MnS sulfide, and increases that of the complex oxysulfide. It also increases the size of the complex oxysulfide, thereby increasing the average size of the total inclusions. The average compositions of Mn and S in these non-metallic inclusions decrease and then increase as the Ca content increases, but the Ti composition decreases continuously.
- The pure MnS sulfide forms the spherical morphology through the metastable monotectic reaction below the solidus temperature, due to its small solubility in γ-austenite and δ/α-ferrite. The Ca addition increased the formation temperature of the CaS sulfide and CaO oxide, leading to the formation of the complex oxysulfide with the core (oxide) and shell (sulfide) structure in the molten liquid.
- The HAZ toughness of these thick HSLA steel plates is increased as the Ca concentrations increase, primarily owing to the positive effect of the inclusions on the refinement of the HAZ microstructure. The complex oxysulfide with the core–shell structure can form the MDZ and thus prevent the formation of the brittle FSP by the strong IAF. These fine complex oxysulfide can also retard the grain boundary migration and ultimately decrease the size of the prior austenite grains.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Steels | C | Si | Mn | P | S | Al | N | Ti | O | Ca |
---|---|---|---|---|---|---|---|---|---|---|
2Ca | 0.08 | 0.2 | 1.5 | 0.006 | 0.004 | 0.001 | 0.0034 | 0.0093 | 0.0018 | 0.0002 |
7Ca | 0.08 | 0.2 | 1.5 | 0.007 | 0.006 | 0.003 | 0.0032 | 0.012 | 0.0022 | 0.0007 |
11Ca | 0.08 | 0.2 | 1.5 | 0.009 | 0.007 | 0.004 | 0.0048 | 0.013 | 0.0019 | 0.0011 |
18Ca | 0.08 | 0.2 | 1.5 | 0.007 | 0.004 | 0.006 | 0.0044 | 0.0096 | 0.0012 | 0.0018 |
25Ca | 0.08 | 0.2 | 1.5 | 0.007 | 0.005 | 0.007 | 0.0037 | 0.011 | 0.0019 | 0.0025 |
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Zhang, Y.; Yang, J.; Xu, L.; Qiu, Y.; Cheng, G.; Yao, M.; Dong, J. The Effect of Ca Content on the Formation Behavior of Inclusions in the Heat Affected Zone of Thick High-Strength Low-Alloy Steel Plates after Large Heat Input Weldings. Metals 2019, 9, 1328. https://doi.org/10.3390/met9121328
Zhang Y, Yang J, Xu L, Qiu Y, Cheng G, Yao M, Dong J. The Effect of Ca Content on the Formation Behavior of Inclusions in the Heat Affected Zone of Thick High-Strength Low-Alloy Steel Plates after Large Heat Input Weldings. Metals. 2019; 9(12):1328. https://doi.org/10.3390/met9121328
Chicago/Turabian StyleZhang, Yinhui, Jian Yang, Longyun Xu, Yunlong Qiu, Guoguang Cheng, Meiyi Yao, and Jianxin Dong. 2019. "The Effect of Ca Content on the Formation Behavior of Inclusions in the Heat Affected Zone of Thick High-Strength Low-Alloy Steel Plates after Large Heat Input Weldings" Metals 9, no. 12: 1328. https://doi.org/10.3390/met9121328