Effect of arc power on microstructure and mechanical properties of austenitic stainless steel 316L fabricated by high efficient arc additive manufacturing
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摘要: 采用大功率MIG电弧热源熔化沉积316L奥氏体不锈钢金属焊丝制备试样，研究电弧功率对成形试样组织、力学性能以及断裂行为的影响并分析其机理，为高效、低成本电弧增材制造大型金属构件提供技术基础和理论依据. 结果表明，大功率MIG电弧增材制造316L奥氏体不锈钢内部形成柱状晶并生成δ相和σ相呈蠕虫状分布在γ基体中. δ相分布在晶内和晶界起强化作用. 随着电弧功率从3 763 W增加8 400 W，316L试样晶粒尺寸变大，δ相含量减少而σ相含量增加，使得材料抗拉强度从578 MPa降低到533 MPa，屈服强度从310 MPa降低到235 MPa，断后伸长率从53%降低到44%，断面收缩率从67%下降到60%. 当电弧功率增加到8 400 W时，在晶界上形成较多的σ相，试样断裂模式由较低功率时的穿晶韧窝断裂转变为沿晶韧窝断裂.
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关键词:
- 增材制造 /
- 316L奥氏体不锈钢 /
- 显微组织 /
- 力学性能
Abstract: The austenitic stainless steel 316L was fabricated by high power MIG arc additive manufacturing and its microstructure evolution, mechanical properties and fracture behavior were investigated. Results show that there are columnar grains forming in the MIG arc additive manufacturing 316L. The microstructure consists of vermicular δ and σ phases within γ matrix. The δ distributed both at grain boundaries and in the grains can strengthen the steel. With the arc power increasing from 3 763 W to 8 400 W, δ phases decrease and σ phases increase, as well as grain size increases. That leads to the ultimate tensile strength decrease from 578 MPa to 533 MPa, yield strength decrease from 310 MPa to 235 MPa, elongation decrease from 53% to 44%, reduction of area decrease from 67% to 60%. A pronounced feature is that the fracture type transfers from trans-granular dimple fracture to inter-granular dimpled fracture at the arc power of 8 400 W. -
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图 2 MIG电弧增材制造316L奥氏体不锈钢晶粒形貌
Figure 2. Grain morphologies of MIG additive manufacturing 316L.(a) P = 3 763 W; (b) P = 5 781 W; (c) P = 8 400 W
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图 3 MIG电弧增材制造316L奥氏体不锈钢显微组织
Figure 3. Microstructures of MIG additive manufacturing 316L. (a) P = 3 763 (low); (b) P = 3 783 (high); (c) P = 5 781 (low); (d) P = 5 781 (high); (e) P = 8 400 (low); (f) P = 8 400 (high)
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图 4 MIG电弧增材制造316L奥氏体不锈钢热影响区显微组织(P = 8 400 W)
Figure 4. Microstructures of HAZ in MIG additive manufacturing 316L. (a) low magnification photograph; (b) high magnification photograph
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图 5 MIG电弧增材制造316L奥氏体不锈钢显微硬度
Figure 5. Microhardness of MIG additive manufacturing 316L
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图 6 MIG电弧增材制造316L断口形貌
Figure 6. Fracture of MIG additive manufacturing 316L. (a) L-direction fracture photograph of P = 3 763 W; (b) T-direction fracture photograph of P = 3 763 W; (c) L-direction fracture photograph of P = 5 781 W; (d) T-direction fracture photograph of P = 5 781 W; (e) L-direction fracture photograph of P = 8 400 W; (f) T-direction fracture photograph of P = 8 400 W
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图 7 MIG电弧增材制造316L韧窝形貌
Figure 7. Dimpled morphology of fracture of MIG additive manufacturing 316L. (a) L-direction fracture photograph of P = 3 763 W; (b) T-direction fracture photograph of P = 3 763 W; (c) L-direction fracture photograph of P = 5 781 W;(d) T-direction fracture photograph of P = 5 781 W; (e) L-direction fracture photograph of P = 8 400 W; (f) T-direction fracture photograph of P = 8 400 W
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图 8 MIG电弧增材制造316L(P = 8 400 W)断口形貌与显微组织
Figure 8. Fracture and microstructure of MIG additive manufacturing 316L. (a) low magnification photograph of fracture; (b) low magnification photograph of microstructure; (c) high magnification photograph of fracture; (d) high magnification photograph of microstructure
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图 9 MIG电弧增材制造316L(P = 8 400 W)断口截面
Figure 9. Fracture section of MIG additive manufacturing 316L
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图 10 MIG电弧增材制造316L(P = 8 400 W)沿晶韧窝型断裂示意图
Figure 10. Schematic illustration of intergranular dimpled fractureracture in MIG additive manufacturing 316L.(a) original marphology; (b) crack initiation; (c) crack growth; (d) fracture
表 1 MIG电弧增材制造参数
Table 1 Process parameters of MIG additive manufacturing
试样 电流I/A 电压U /V 电弧功率P /W 扫描速度v /(mm·min−1) 沉积率r/(kg·h−1) 1 175 22 3 763 480 3.2 2 235 24.6 5 781 480 4.3 3 300 28 8 400 600 5.3 
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表 2 MIG电弧增材制造316L奥氏体不锈钢化学成分(质量分数，%)
Table 2 Chemical compositions of MIG additive manufacturing 316L
C Cr Ni Mo Si Mn P Cu Fe 0.014 18.74 11.82 2.67 0.56 1.55 0.03 0.17 余量
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表 3 MIG电弧增材制造316L奥氏体不锈钢试样晶粒大小和相含量
Table 3 Grain widths and volume fractions of δ and σ phase of MIG additive manufacturing 316L
试样 平均晶粒宽度 d /µm δ相含量 （%） σ相含量 （%） P = 3 763 W 241 12.2 1.0 P = 5 781 W 451 10.6 1.4 P = 8 400 W 722 7.8 4.5
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表 4 MIG电弧增材制造316L奥氏体不锈钢沉积层和热影响区平均显微硬度
Table 4 Average microhardness of HAZ and deposited layer of MIG additive manufacturing 316L
试样 沉积层硬度值H（HV） 热影响区硬度值H（HV） P = 3 763 W 244 217 P = 5 781 W 215 202 P = 8 400 W 202 191
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表 5 MIG电弧增材制造316L奥氏体不锈钢室温拉伸性能
Table 5 Room temperature tensile properties of MIG additive manufacturing 316L
试样 方向 抗拉强度Rm/MPa 屈服强度ReL/MPa 断后伸长率A（%） 断面收缩率Z（%） P = 3 763 W L 567 ± 10 288 ± 3 53 ± 2 67 ± 4 T 579 ± 3 310 ± 6 50 ± 2 63 ± 9 L-T/L −2% −8% 6% 6% P = 5 781 W L 555 ± 5 261 ± 0 50 ± 3 66 ± 5 T 561 ± 6 280 ± 8 48 ± 6 63 ± 6 L-T/L −6% −7% 4% 5% P = 8 400 W L 533 ± 23 235 ± 6 48 ± 2 64 ± 5 T 540 ± 8 258 ± 2 44 ± 10 60 ± 7 L-T/L −1% −10% 8% 6% 锻造[15] 505 ~ 578 222 ~ 265 56 ~ 63 76 ~ 81 标准[15] ≥450 170 40 50
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