Solidification microstructure evolution and inclusion analysis of Ce-containing 7Mo super-austenitic stainless steel
-
摘要: 采用稀土Ce处理是超级奥氏体不锈钢凝固组织调控研究的热点，系统分析了中试500 kg级Ce处理7Mo超级奥氏体不锈钢凝固相组织、夹杂物演变、元素偏析行为，为Ce处理7Mo超级奥氏体不锈钢提供理论依据。结果表明，7Mo超级奥氏体不锈钢非平衡凝固路径为L→L+γ→L+γ+δ→L+γ+δ+σ→L+γ+σ→L+γ+σ+Cr2N。降温凝固过程中存在中间相δ相，凝固末期δ相会分解成σ相和γ2相。钢中主要析出第二相为富Cr和Mo的σ相，铸态凝固组织由奥氏体相和σ相组成。7Mo超级奥氏体不锈钢Ce处理后，铸锭中的夹杂物主要为AlCeO3和Al11O18Ce组成的复合夹杂物，其具有低错配度AlCeO3结构，可以作为异质形核核心。降温凝固过程中Al脱氧能力增强，脱氧反应平衡被打破，导致Al11O18Ce包裹AlCeO3形貌的夹杂物生成。铸锭芯部微观晶粒粗大，枝晶间微观偏析严重，微观晶粒尺寸是影响枝晶间微观偏析的核心因素，微观凝固组织晶粒尺寸降低可以有效改善晶粒内部各元素的偏析程度，降低枝晶间σ相中Mo、Cr含量。
-
关键词:
- 7Mo超级奥氏体不锈钢 /
- 凝固偏析 /
- 热力学计算 /
- 夹杂物
Abstract: Rare earth Ce treatment is a hot topic in the modification of solidification microstructure for super austenitic stainless steel. In this study, the solidification phase structure, evolution of inclusions, and element segregation behavior of a 500 kg scale Ce-treated 7Mo super austenitic stainless steel were systematically analyzed, for the purpose of providing theoretical basis for Ce treatment of 7Mo super austenitic stainless steel. The results show that the non-equilibrium solidification path of 7Mo super austenitic stainless steel is L→L+γ→L+γ+δ→L+γ+δ+σ→L+γ+σ→L+γ+σ+Cr2N. During cooling and solidification process, an intermediate phase δ phase exists, and the δ phase decomposes into σ phase and γ2 phase at the end of solidification. The main second phase precipitated in the steel is the σ phase rich in Cr and Mo, resulting in a cast solidification structure composed of austenite and σ phase. After Ce treatment in super austenitic stainless steel, the inclusions in the ingot are mainly composite inclusions composed of AlCeO3 and Al11O18Ce, with a low mismatch AlCeO3 structure, which can serve as heterogeneous nucleation cores. During cooling and solidification process, the deoxidation ability of Al is enhanced, and the equilibrium of deoxidation reaction is broken, resulting in the generation of inclusions with Al11O18Ce encapsulating AlCeO3 morphology. The microstructure of the ingot core is coarse, with severe microsegregation between dendrites. The size of micro grains is the key factor affecting the microsegregation between dendrites, and reducing the size of micro solidification structure grains can effectively improve the degree of element segregation inside the grains and then reduce Mo and Cr content in the σ phase between dendrites. -
图 1 7Mo超奥钢铸锭观察取样示意
Figure 1. Schematic diagram for observation and sampling of 7Mo super austenitic stainless steel
图 2 7Mo超奥钢非平衡凝固相图
Figure 2. Non-equilibrium solidification phase diagram of 7Mo super austenitic stainless steel
图 4 7 Mo超奥钢铸锭组织SEM和EDS结果
Figure 4. SEM and EDS results on σ phase in 7Mo super austenitic stainless steel ingot
图 5 7Mo超奥钢XRD衍射结果
Figure 5. XRD diffraction results of 7Mo super austenitic stainless steel
图 7 钢中典型夹杂物成分组成三元图
Figure 7. Ternary diagram of composition of typical inclusions in steel
图 9 7Mo超奥钢基于Factsage的热力学计算结果
（a）Al脱氧能力与Cr含量关系； （b）Ce脱氧能力与Cr含量关系； （c）Al、Ce脱氧能力与温度的关系； （d）凝固过程中钢中夹杂物演变
Figure 9. Thermodynamic calculation results of 7Mo super austenitic stainless steel based on FactSage
图 10 铸锭低倍组织与主要合金元素偏析程度
（a）铸锭宏观低倍组织； （b）铸锭不同位置Mo、Cr元素宏观偏析
Figure 10. Macrostructure of ingots and degree of segregation of main alloy elements
图 11 铸锭不同位置组织形貌及晶粒数量密度和平均尺寸与σ相析出情况关系
（a）铸锭不同位置SEM结果； （b）铸锭不同位置OM结果； （c）铸锭不同位置晶粒密度和平均尺寸； （d）σ相平均宽度和体积分数与晶粒平均尺寸关系
Figure 11. The relationship between microstructure, grain number density and average size of ingot at different locations and σ precipitation
图 12 σ相中合金元素偏析程度和晶粒内部元素偏析程度与晶粒平均尺寸关系
（a）σ相中Mo元素偏析度； （b）σ相中Cr元素偏析度； （c）晶粒内部Cr元素偏析度； （d）晶粒内部Mo元素偏析度
Figure 12. The relationship among degree of segregation of alloying elements in σ phase, degree of segregation of elements in grain and the average grain size segregation degree
表 1 7Mo超奥钢化学成分
Table 1. Chemical composition of 7Mo super austenitic stainless steel
% Cr Ni Mo Cu Si Mn C N S P Al Ce TO Fe 24.07 18.97 7.22 0.47 0.05 2.97 0.0073 0.42 <0.01 <0.01 0.03 0.01 0.0055 Bal 
下载: 导出CSV
表 2 铸坯不同位置夹杂物特征
Table 2. Characteristics of inclusions at different positions of billets
铸坯位置 数量密度/（个·mm−2） 平均尺寸/μm 边缘 62.3 3.0 中心 28.2 3.8
下载: 导出CSV
-
[1] ZHANG S C. Manufacture, microstructure and properties of super austenitic stainless steel S32654[D]. Shenyang: Northeastern University, 2022. (张树才. 超级奥氏体不锈钢S32654的制备及组织与性能研究[D]. 沈阳: 东北大学, 2022.ZHANG S C. Manufacture, microstructure and properties of super austenitic stainless steel S32654[D]. Shenyang: Northeastern University, 2022. [2] LIAO L H. Research on microstructure and properties of S32654 super austenitic stainless steel[D]. Beijing: University of Science and Technology Beijing, 2023. (廖露海. 超级奥氏体不锈钢S32654组织与性能研究[D]. 北京: 北京科技大学, 2023.LIAO L H. Research on microstructure and properties of S32654 super austenitic stainless steel[D]. Beijing: University of Science and Technology Beijing, 2023. [3] KIM W Y, NAM G J, KIM S Y. Evolution of non-metallic inclusions in Al-killed stainless steelmaking[J]. Metall Mater Trans B, 2021,52:1508-1520. doi: 10.1007/s11663-021-02119-4 [4] LIU W Q, WANG L J, ZHANG F C, et al. Review on development and second phase regulation of super austenitic stainless steel[J]. Journal of Iron and Steel Research, 2023,35(8):907-927. (刘文强, 王丽君, 张福成, 等. 超级奥氏体不锈钢发展及第二相调控研究现状[J]. 钢铁研究学报, 2023,35(8):907-927.LIU W Q, WANG L J, ZHANG F C, et al. Review on development and second phase regulation of super austenitic stainless steel[J]. Journal of Iron and Steel Research, 2023, 35（8）: 907-927. [5] HAO Y S. Research on alloying element segregation behavior and microstructure evolution of super austenitic stainless steel[D]. Shenyang: Northeastern University, 2022. (郝燕森. 超级奥氏体不锈钢合金元素偏析行为与显微组织演变规律研究[D]. 沈阳: 东北大学, 2022.HAO Y S. Research on alloying element segregation behavior and microstructure evolution of super austenitic stainless steel[D]. Shenyang: Northeastern University, 2022. [6] XIAO J, ZHANG Y, ZHANG W, et al. Precipitation mechanism of σ phase in S32654 super austenitic stainless steel[J]. Materials Letters, 2023,349:7871-7881. [7] YU J T. Research on effect of cerium on hot deformation behavior of super austenitic stainless steel 654SMO[D]. Shenyang: Northeastern University, 2020. (禹江涛. 稀土铈对超级奥氏体不锈钢654SMO热变形行为的影响研究[D]. 沈阳: 东北大学, 2020.YU J T. Research on effect of cerium on hot deformation behavior of super austenitic stainless steel 654SMO[D]. Shenyang: Northeastern University, 2020. [8] XU S G, HE J S, ZHANG R Z, et al. Hot deformation behaviors and dynamic softening mechanisms of 7Mo super-austenitic stainless steel with high stacking fault energy[J]. Journal of Materials Research and Technology, 2023,23:1738-1752. doi: 10.1016/j.jmrt.2023.01.108 [9] ZHANG S C, YU J T, LI H B, et al. Refinement mechanism of cerium addition on solidification structure and sigma phase of super austenitic stainless steel S32654[J]. Journal of Materials Science & Technology, 2022,102:105-114. [10] LIU H H, FU P X, LIU H W, et al. Effects of rare earth elements on microstructure evolution and mechanical properties of 718H pre-hardened mold steel[J]. Journal of Materials Science & Technology, 2020, 50:245-256. [11] CHEN L, MA X C, WANG L M, et al. Effect of rare earth element yttrium addition on microstructures and properties of a 21Cr–11Ni austenitic heat-resistant stainless steel[J]. Materials and Design, 2011, 32(4): 2206-2212. doi: 10.1016/j.matdes.2010.11.022 [12] ZHANG S C, LI H B, JIANG Z H, et al. Unveiling the mechanism of yttrium significantly improving high-temperature oxidation resistance of super-austenitic stainless[J]. Journal of Materials Science & Technology. 2022.115. 103-114. [13] YANG S, MA J Y, CHEN C. et al. Effects of B and Ce grain boundary segregation on precipitates in super austenitic stainless steel[J]. Metals, 2023,13:326. doi: 10.3390/met13020326 [14] ZHANG R Z, HE J S, XU S G, et al. The roles of Ce and Mn on solidification behaviors and mechanical properties of 7Mo super austenitic stainless steel[J]. Journal of Materials Research and Technology, 2023, 22: 1238-1249. doi: 10.1016/j.jmrt.2022.11.148 [15] GUO Z S, LI Y P, MA J Y, et al. Effect of Ce content on precipitation behavior in S31254 Super Austenitic Stainless Steel[J]. Journal of Alloys and Compounds, 2023,966:171254. doi: 10.1016/j.jallcom.2023.171254 [16] WANG H L, DU S M, CAO M J, et al. Influence of rare earth on microstructure and carbide of 21-4N steel[J]. Iron Steel Vanadium Titanium, 2020,41(1):119-124. (王洪利, 杜思敏, 曹美姣, 等. 微量稀土元素对奥氏体不锈钢21-4N显微组织及碳化物的影响[J]. 钢铁钒钛, 2020,41(1):119-124. doi: 10.7513/j.issn.1004-7638.2020.01.021WANG H L, DU S M, CAO M J, et al. Influence of rare earth on microstructure and carbide of 21-4N steel[J]. Iron Steel Vanadium Titanium, 2020, 41（1）: 119-124. doi: 10.7513/j.issn.1004-7638.2020.01.021 [17] MENG X H, WANG W, BI S, et al. Research on IAF nucleation behavior induced by Ce/Ce-Zr inclusion in high strength steel plate for shipbuilding[J]. Iron Steel Vanadium Titanium, 2022,43(2):146-151. (孟祥海, 王伟, 毕胜, 等. Ce/Ce-Zr夹杂物诱导高强船板钢中针状铁素体形核行为的研究[J]. 钢铁钒钛, 2022,43(2):146-151. doi: 10.7513/j.issn.1004-7638.2022.02.022MENG X H, WANG W, BI S, et al. Research on IAF nucleation behavior induced by Ce/Ce-Zr inclusion in high strength steel plate for shipbuilding[J]. Iron Steel Vanadium Titanium, 2022, 43（2）: 146-151. doi: 10.7513/j.issn.1004-7638.2022.02.022 [18] ZHANG Y. Solidification microstructure evolution and segregation law of super austenitic stainless steel[D]. Beijing: University of Science and Technology Beijing, 2023. (张月. 超级奥氏体不锈钢凝固组织演变及偏析规律[D]. 北京: 北京科技大学, 2023.ZHANG Y. Solidification microstructure evolution and segregation law of super austenitic stainless steel[D]. Beijing: University of Science and Technology Beijing, 2023. [19] MARIN R, COMBEAU H, ZOLLINGER J, et al. σ-phase formation in super austenitic stainless steel during directional solidification and subsequent phase transformations[J]. Metall Mater Trans A 51, 3526-3534 (2020). [20] LAN J, HE J J, DING W J, et al. Study on heterogeneous nuclei in cast H13 steel modified by rare earths[J]. Journal of the Chinese Society of Rare Earths, 2001,19(2):142-145. (兰杰, 贺俊杰, 丁文江, 等. 变质CH13钢中Ce2O3异质核心作用的研究[J]. 中国稀土学报, 2001,19(2):142-145. doi: 10.3321/j.issn:1000-4343.2001.02.011LAN J, HE J J, DING W J, et al. Study on heterogeneous nuclei in cast H13 steel modified by rare earths[J]. Journal of the Chinese Society of Rare Earths, 2001, 19（2）: 142-145. doi: 10.3321/j.issn:1000-4343.2001.02.011 [21] WANG Q, WANG L J, ZHANG W, et al. Effect of cerium on the austenitic nucleation and growth of high-Mo austenitic stainless steel[J]. Metallurgical and Materials Transactions B, 2020. -
点击查看大图
计量
- 文章访问数: 115
- HTML全文浏览量: 25
- PDF下载量: 17
- 被引次数: 0
