On the heterogeneous microstructure development in the welded joint of 12MnNiVR pressure vessel steel subjected to high heat input electrogas welding

doi:10.1016/j.jmst.2019.03.035

Abstract

Abstract:

Microstructure features of 12MnNiVR pressure vessel steel welded joint deposited by the high heat input electrogas welding have been systematically investigated. It is revealed that the welded joint is featured by a heterogeneous juxtaposition. The coarse grained heat-affected zone (CGHAZ) primarily consists of lath bainites and minor granular bainites. The fine grained heat-affected zone (FGHAZ) is dominated by polygonal ferrites, pearlites, and fine cementite particles. Moreover, electron backscatter diffraction results further demonstrate that the CGHAZ is populated by coarse prior austenite grains (PAGs) with high frequency (61.3%) of low angle grain boundaries (LAGBs). On the other hand, the FGHAZ is filled with fine PAGs with a lower frequency (19.6%) of LAGBs. Such microstructural differences may likely contribute to differed mechanical properties for samples tested at designed positions.

Key words: 12MnNiVR pressure vessel steel, Electrogas welding, High heat input, Electron backscatter diffraction

Yang Shen, Ju Leng, Cong Wang. On the heterogeneous microstructure development in the welded joint of 12MnNiVR pressure vessel steel subjected to high heat input electrogas welding[J]. J. Mater. Sci. Technol., 2019, 35(8): 1747-1752.

Figures/Tables 6

Table 1 Chemical composition of 12MnNiVR base metal and EGW filler metal DW-S60 G (wt%).

Materials	C	Si	Mn	P	S	Ni	Cr	Mo
Base metal	0.1	0.19	1.5	0.006	0.0012	0.27	0.05	0.13
DW-S60G	0.08	0.32	1.67	0.010	0.008	0.71	0.03	0.25

Fig. 1. Schematic diagram of as-welded 12MnNiVR weldment showing positions where specimens for desired tests are taken.

Fig. 2. Typical microstructures of the 12MnNiVR steel welded joint: (a) WM; (b) CGHAZ; (c) FGHAZ; (d) BM.

Fig. 3. Crystallographic characteristics of 12MnNiVR steel welded joints analyzed by EBSD: (a) WM, (b) CGHAZ, (c) FGHAZ, (d) BM grain boundary maps and (e) WM, (f) CGHAZ, (g) FGHAZ, (h) BM Z axis invers pole figure in the transverse direction (TD). (Red lines indicate grain boundaries with a misorientation angle higher than 10° and blue lines indicate grain boundaries with a misorientation angle less than 10°).

Fig. 4. Mechanical properties of the welded joints: (a) Macrograph of a one-pass 12MnNiVR steel weldment (The region marked by white rectangle is used for hardness test); (b) Vickers hardness profile across the weldment; (c) Charpy impact test results from specimens in the as-welded condition for different V-notch positions at 258 K; (d) Tensile test results of full thickness tensile specimen tested at room temperature.

Fig. 5. Schematic diagram of heterogeneous microstructural features of the HAZ.

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