Heterogeneous Microstructure-Induced Mechanical Responses in Various Sub-Zones of EH420 Shipbuilding Steel Welded Joint Under High Heat Input Electro-Gas Welding

doi:10.1007/s40195-021-01245-x

Abstract

Abstract:

Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy, electron backscatter diffraction and mechanical testing. Comparing with the coarse-grained heat-affected zone (CGHAZ), the weld metal presents higher toughness (129.3 J vs. 37.3 J) as it contains a large number of acicular ferrites with high-angle grain boundaries (frequency 79.2%) and special grain boundary ∑3 (frequency 55.3%). Moreover, coarse austenite grains in CGHAZ and slender martensite-austenite constituents between bainite laths may likely facilitate crack propagation. Polygonal ferrites and tempered pearlites formed at the junction of the fine-grained heat-affected zone and the intercritical heat-affected zone induced a softened zone with an average hardness of 185 HV0.5, which is the main reason for the occurrence of tensile fracture.

Key words: Heterogeneous microstructure, Mechanical properties, Electro-gas welding, High heat input, Shipbuilding steel

Xu Xie, Tan Zhao, Heming Zhao, Song Li, Cong Wang. Heterogeneous Microstructure-Induced Mechanical Responses in Various Sub-Zones of EH420 Shipbuilding Steel Welded Joint Under High Heat Input Electro-Gas Welding[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(10): 1427-1433.

Figures/Tables 7

Table 1 Chemical compositions of the EH420 steel plates and WM (wt%)

Materials	C	Si	Mn	Ni	P	Mg	Ti	Al	S	O
EH420	0.052	0.13	1.66	0.32	0.011	< 0.001	0.010	0.003	0.006	0.002
WM	0.042	0.16	1.73	1.48	0.011	0.001	0.020	0.005	0.007	0.028

Fig. 1 Schematic illustrations of the different test specimen locations from the weldment

Fig. 2 Vickers hardness distributions of the welded joint. (Inset is a macrograph of EH420 shipbuilding steel welded joint)

Fig. 3 SEM micrographs showing typical microstructures of EH420 shipbuilding steel welded joint: a WM; b CGHAZ; c FGHAZ; d ICHAZ; e BM

Fig. 4 Crystallographic characteristics of EH420 shipbuilding steel at different sub-zones of the welded joint: a-d orientation image maps; e-h grain boundaries distribution maps; i-l special grain boundary ∑3 distribution maps (red lines represent HAGBs above 10°; blue lines represent LAGBs of 2°-10°; yellow lines represent special grain boundary ∑3)

Fig. 5 Mechanical properties of the welded joint: a full-thickness tensile test results; b Charpy impact toughness results at different sub-zones

Fig. 6 Schematic illustrations of heterogeneous microstructural variation: a entire welded joint; b acicular ferrites in WM; c lath bainites in CGHAZ; d FGHAZ; e ICHAZ

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