J. Mater. Sci. Technol. ›› 2019, Vol. 35 ›› Issue (11): 2665-2681.DOI: 10.1016/j.jmst.2019.05.047
• Orginal Article • Previous Articles Next Articles
Liu Guoliangab, Yang Shanwua*(), Ding Jianwena, Han Wentuob, Zhou Lujuna, Zhang Mengqiab, Zhou Shanshanc, Misra R.D.K.d, Wan Farongb, Shang Chengjiaa
Received:
2018-12-10
Revised:
2019-04-17
Accepted:
2019-05-11
Online:
2019-11-05
Published:
2019-10-21
Contact:
Yang Shanwu
About author:
1The authors equally contributed to this work.
Liu Guoliang, Yang Shanwu, Ding Jianwen, Han Wentuo, Zhou Lujun, Zhang Mengqi, Zhou Shanshan, Misra R.D.K., Wan Farong, Shang Chengjia. Formation and evolution of layered structure in dissimilar welded joints between ferritic-martensitic steel and 316L stainless steel with fillers[J]. J. Mater. Sci. Technol., 2019, 35(11): 2665-2681.
Sample | C | N | Si | Mn | S | P | Ni | Cr | W | V | Ta | Mo | Fe |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
CLAM | 0.098 | 0.0085 | 0.29 | 0.52 | 0.0084 | 0.0072 | / | 8.83 | 1.60 | 0.21 | 0.13 | / | Bal. |
316 L | 0.025 | 0.023 | 0.69 | 0.99 | 0.024 | 0.0025 | 10.2 | 17 | / | / | / | 2.18 | Bal. |
310S | 0.05 | 0.0466 | 0.51 | 0.94 | 0.027 | 0.0010 | 19.29 | 25.42 | / | / | / | 1.1 | Bal. |
Nickel | 0.06 | / | 0.08 | 0.04 | 0.004 | 0.002 | >99.5 | / | / | / | / | / | 0.04 |
Table 1 Composition of base metals and filler metals (wt%).
Sample | C | N | Si | Mn | S | P | Ni | Cr | W | V | Ta | Mo | Fe |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
CLAM | 0.098 | 0.0085 | 0.29 | 0.52 | 0.0084 | 0.0072 | / | 8.83 | 1.60 | 0.21 | 0.13 | / | Bal. |
316 L | 0.025 | 0.023 | 0.69 | 0.99 | 0.024 | 0.0025 | 10.2 | 17 | / | / | / | 2.18 | Bal. |
310S | 0.05 | 0.0466 | 0.51 | 0.94 | 0.027 | 0.0010 | 19.29 | 25.42 | / | / | / | 1.1 | Bal. |
Nickel | 0.06 | / | 0.08 | 0.04 | 0.004 | 0.002 | >99.5 | / | / | / | / | / | 0.04 |
Welding speed | 10 mm/s | Scanner function | Circular oscillation |
---|---|---|---|
Working distance | 400 mm | Amplitude | 1 mm |
Acceleration voltage | 90 KV | Frequency | 100 HZ |
Focus current | 1750 mA | Heat input | 1.89 kJ/cm |
Welding current | 21 mA | Width of top surface | 4 mm |
Table 2 Electron beam welding parameters.
Welding speed | 10 mm/s | Scanner function | Circular oscillation |
---|---|---|---|
Working distance | 400 mm | Amplitude | 1 mm |
Acceleration voltage | 90 KV | Frequency | 100 HZ |
Focus current | 1750 mA | Heat input | 1.89 kJ/cm |
Welding current | 21 mA | Width of top surface | 4 mm |
Fig. 3. Composition distribution in (a) 310S-WM, (b) Ni-WM, and (c) Schaeffler diagram predicting the microstructure of dissimilar welded joints. The position in Fig. 3(a) and (b) corresponded to the boxes 1-16 in Fig. 2(a) and (b), respectively.
Sample | C | N | Si | Mn | Ni | Cr | W | V | Ta | Mo |
---|---|---|---|---|---|---|---|---|---|---|
Ni-WM | 0.059 | 0.014 | 0.45 | 0.68 | 16.80 | 11.63 | 0.65 | 0.085 | 0.053 | 1.03 |
310S-WM | 0.053 | 0.023 | 0.53 | 0.83 | 8.57 | 15.91 | 0.52 | 0.068 | 0.042 | 1.27 |
Table 3 Calculated composition of resultant WMs (wt%).
Sample | C | N | Si | Mn | Ni | Cr | W | V | Ta | Mo |
---|---|---|---|---|---|---|---|---|---|---|
Ni-WM | 0.059 | 0.014 | 0.45 | 0.68 | 16.80 | 11.63 | 0.65 | 0.085 | 0.053 | 1.03 |
310S-WM | 0.053 | 0.023 | 0.53 | 0.83 | 8.57 | 15.91 | 0.52 | 0.068 | 0.042 | 1.27 |
Fig. 4. Microstructure of resultant WMs in as-welded state: (a) optical micrograph of 310S-WM etched by Beraha’s II reagent (austenite is white, and ferrite is black), characteristic areas marked with boxes are analyzed by EBSD; (b, c) magnified Euler maps corresponding to boxes b and c, respectively, in Fig. 4(a), showing dendritic austenite of 310S-WM near base metals. Euler map represents for FCC phase, band contrast (BC) map represents for BCC phase; (d) enlarged SEM micrograph of the solidified dendritic structure of 310S-WM etched by aqua-regia; (e) optical micrograph of Ni-WM etched by Beraha’s II reagent; (f, g) Euler maps corresponding to boxes f and g in Fig. 4(e), respectively, exhibiting the coarse austenitic columnar grain of Ni-WM; (h) enlarged SEM micrograph of cellular structure in Ni-WM electron-etched by oxalic acid solution. The insets in Fig. 4(d) and (h) were the result of EDS-line corresponding to yellow line in Fig. 4(d) and (h), respectively.
Fig. 5. (a) SEM micrograph of layered structure in 310S-WM in as-welded state etched by aqua-regia, the inset was the BC map of layered structure, blue color represents BCC phase, (b) results of EDS point test corresponding to the points in Fig. 5(a) and (c) SEM micrograph of CLAM-HAZ in as-welded state etched by Villella’s reagent, revealing coarse lath martensite with some δCLAM-ferrite near fusion line.
Fig. 6. Mechanical properties of dissimilar joints in as-welded state, cross-sectional hardness distribution of (a) 310S-filler welded joint, (b) Ni-filler welded joint, (c) the engineering stress-strain behaviors of longitudinal tensile for WMs and (d) optical macroscopic of cross-section of transverse tensile specimens after tests as well as the test results. The points in Fig. 6(a) and (b) corresponding to the indentations in Fig. 2(a) and (b), respectively.
Fig. 7. Mechanical properties of dissimilar joints after PWDT, cross-sectional hardness distribution of (a) 310S-filler welded joint, (b) Ni-filler welded joint, (c) the engineering stress-strain behaviors of longitudinal tensile for WMs and (d) optical macroscopic of cross-section of transverse tensile specimens after tests as well as the test results.
Fig. 8. SEM micrographs of (a) CLAM-HAZ after PWDT etched by Villella’s reagent, showing tempered martensite, the δCLAM-ferrite still existing near fusion boundary and (b) Ni-WM after 740 °C/2 h electron-etched by oxalic acid solution. The insets in Fig. 8(a) was the enlarged SEM micrographs.
Fig. 9. Micrographs of layered structure in 310S-WM after PWDT: (a) optical micrograph (OM) etched by Beraha II’s reagent; (b) SEM micrograph of layered structure zone etched by Kalling’s reagent; (c) enlarged SEM micrograph of the layered structure, exhibiting a large amount of σ-phase existed in this zone. The inset was EDS-line corresponding to yellow line in Fig. 9(c); (d) SEM image showing the δpe-ferrite in 310S-WM matrix, the inset was the corresponding EDS of the σ-phase of Fig. 9(d).
Fig. 11. Micrographs of layered structure in 310S-WM after PWNT: (a) optical micrograph (OM) etched by Beraha’s II reagent; (b) SEM image of layered structure zone etched by Kalling’s reagent; (c) results of average composition of areas in Fig. 11(b); (d) enlarged SEM micrograph of the 310S-WM matrix with δpe-ferrite after PWNT.
Fig. 12. Cross-sectional hardness distribution of (a) 310S-filler welded joint after PWNT, (b) the average hardness in four zones of 310S-filler welded joints in various conditions, (c) Ni-filler welded joint after PWNT, (d) the average hardness in four zones of Ni-filler welded joints in various conditions and the mechanical properties of dissimilar joints after PWNT, (e) the engineering stress-strain behaviors of longitudinal tensile for WMs and (f) optical macroscopic of cross-section of transverse tensile specimens after tests as well as the test results.
Fig. 13. SEM micrographs of (a) CLAM-HAZ after PWNT etched by Villella’s reagent, exhibiting fully tempered martensite, fine PAGs and no evidence of δCLAM-ferrite and (b) Ni-WM after PWNT with electron-etched by oxalic acid. The inset in Fig. 13(a) was the enlarged SEM micrograph.
Fig. 14. Formation mechanism of layered structure in dissimilar high-energy beam welding: (a) sketch of stirred weld pool; (b) formation of peninsula, layered structure as well as unmixed zone (UMZ); (c) liquidus surface projection of ternary Fe-Cr-Ni phase diagram [41]. Raw materials and resultant weld metals were marked in diagram based on the Schaeffler contents to obtain the corresponding liquidus points; (d) vertical section at 70%-Fe for the Fe-Ni-Cr phase diagram [42], and solidus lines relevant for solidification sequence of Ni-WM and 310S-WM. The vertical orders (I-IV) were the solidification sequence of these two dissimilar weld metals, corresponding to the data in Table 4.
Fig. 15. SEM micrograph of the peninsula and its surrounding microstructure etched by Villella’s reagent in as-welded state in cross-section of (a) 310S-filler welded joint, (b) Ni-filler welded joint. The insets are the EDS distribution in Fig. 15(a) and (b), respectively. The SEM micrographs showing the peninsula and layered structure in horizontal-section in as-welded state for (c) 310S-filler welded joint and (d) Ni-filler welded joint.
Materials | Position | Solidification mode | Phase transformation path | Final solidified microstructure |
---|---|---|---|---|
Ni-WM | (Ⅰ) Ni-WM matrix | A | L→L + A→A | Coarse columnar (width 100-200 μm) consisting of cellular grains with same orientation |
(Ⅱ) alloy-depleted zone in Ni-WM, less ? 4% Ni | A | L→L + A→A | Coarse columnar (width 100-200 μm) consisting of cellular grains with same orientation | |
310S-WM | (Ⅲ) 310S-WM matrix | FA | L→L+δ→L+δ+A→δ+A | Austenite dendritic structure with δpe-ferrite distributed along the solidified dendritic boundary |
(Ⅳ) Layered structure zone in 310S-WM, less ? 2% Ni | F | L→L+δ→δ→δ+A | δL-ferrite dispersed in γ-phase, existed a large amount of phase-interface (δL/γ) |
Table 4 Transformation sequence of the microstructure in the dissimilar WMs.
Materials | Position | Solidification mode | Phase transformation path | Final solidified microstructure |
---|---|---|---|---|
Ni-WM | (Ⅰ) Ni-WM matrix | A | L→L + A→A | Coarse columnar (width 100-200 μm) consisting of cellular grains with same orientation |
(Ⅱ) alloy-depleted zone in Ni-WM, less ? 4% Ni | A | L→L + A→A | Coarse columnar (width 100-200 μm) consisting of cellular grains with same orientation | |
310S-WM | (Ⅲ) 310S-WM matrix | FA | L→L+δ→L+δ+A→δ+A | Austenite dendritic structure with δpe-ferrite distributed along the solidified dendritic boundary |
(Ⅳ) Layered structure zone in 310S-WM, less ? 2% Ni | F | L→L+δ→δ→δ+A | δL-ferrite dispersed in γ-phase, existed a large amount of phase-interface (δL/γ) |
Item | δCLAM-ferrite | δL-ferrite | δpe-ferrite |
---|---|---|---|
Composition | 9Cr | 14Cr-7Ni | Chromium ? 16Cr, Nickel ? 9Ni |
As-welded | Incompletely transformation of δCLAM → γ at fast cooling, δCLAM formed in the CLAM-CGHAZ near fusion boundary | Incompletely transformation of δL → γ due to a relatively lower transformation temperature, formed a mass of lath δL-ferrite | Formed through peritectic-eutectic reaction, δpe-ferrite was distributed along the solidified dendritic boundary |
PWDT | δCLAM-ferrite still existed, some carbide formed in the HAZ | a large amount of σ-phase formed through eutectoid decomposition of δL-ferrite (δL→σ+γ2) | σ-phase formed through eutectoid decomposition of δpe-ferrite (δpe→σ+γ2) |
PWNT | δCLAM-ferrite completely transformed into γ-phase at 980 °C, sheared into martensite after cooling, finally formed uniform tempered martensite after tempering (δCLAM→γ→M→tempered M) | Most of δL-ferrite transformed to γ-phase at 980 °C, and remained stable at room temperature (δL → γ) | Due to the higher Cr content, δpe-ferrite was not eliminated at 980 °C, formed σ-phase through δpe→σ+γ2 during subsequent tempering |
Table 5 Evolution of three types of δ-ferrite in the dissimilar joints during the PWHTs.
Item | δCLAM-ferrite | δL-ferrite | δpe-ferrite |
---|---|---|---|
Composition | 9Cr | 14Cr-7Ni | Chromium ? 16Cr, Nickel ? 9Ni |
As-welded | Incompletely transformation of δCLAM → γ at fast cooling, δCLAM formed in the CLAM-CGHAZ near fusion boundary | Incompletely transformation of δL → γ due to a relatively lower transformation temperature, formed a mass of lath δL-ferrite | Formed through peritectic-eutectic reaction, δpe-ferrite was distributed along the solidified dendritic boundary |
PWDT | δCLAM-ferrite still existed, some carbide formed in the HAZ | a large amount of σ-phase formed through eutectoid decomposition of δL-ferrite (δL→σ+γ2) | σ-phase formed through eutectoid decomposition of δpe-ferrite (δpe→σ+γ2) |
PWNT | δCLAM-ferrite completely transformed into γ-phase at 980 °C, sheared into martensite after cooling, finally formed uniform tempered martensite after tempering (δCLAM→γ→M→tempered M) | Most of δL-ferrite transformed to γ-phase at 980 °C, and remained stable at room temperature (δL → γ) | Due to the higher Cr content, δpe-ferrite was not eliminated at 980 °C, formed σ-phase through δpe→σ+γ2 during subsequent tempering |
Fig. 16. SEM fractographs of the longitudinal tensile samples after test (a) L-310S-as-welded, (b) L-310S-PWDT, (c) L-310S-PWNT, (d) L-Ni-as-welded, (e) L-Ni-PWDT and (f) L-Ni-PWNT.
Samples | 310S-WM | Ni-WM | 316 L-BM |
---|---|---|---|
Md30 (°C) | 14.3 °C | -157.9 °C | -54.6 °C |
Deformation at 20 °C | TRIP | No TRIP | No TRIP |
Table 6 The Md30 value of γ-phase in the resultant WMs.
Samples | 310S-WM | Ni-WM | 316 L-BM |
---|---|---|---|
Md30 (°C) | 14.3 °C | -157.9 °C | -54.6 °C |
Deformation at 20 °C | TRIP | No TRIP | No TRIP |
Fig. 17. Transverse creep test of dissimilar welded joints in PWNT condition: (a) creep strain versus time curves; (b) hardness profiles after creep test; (c) cross-section macrographs of transverse creep fracture specimens. The points in Fig. 17(b) corresponding to the indentations in Fig. 17(c).
Raw materials | Dilution rates | |
---|---|---|
310S-WM | Ni-WM | |
CLAM | 32.85% | 40.68% |
316 L | 48.22% | 47.28% |
310 s filler | 18.93% | / |
Ni filler | / | 12.04% |
Table 7 Dilution rates of WMs.
Raw materials | Dilution rates | |
---|---|---|
310S-WM | Ni-WM | |
CLAM | 32.85% | 40.68% |
316 L | 48.22% | 47.28% |
310 s filler | 18.93% | / |
Ni filler | / | 12.04% |
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