On Mechanical Properties of Welded Joint in Novel High-Mn Cryogenic Steel in Terms of Microstructural Evolution and Solute Segregation

Abstract

There is a growing demand for high-manganese wide heavy steel plate with excellent welding performance for liquefied natural gas (LNG) tank building. However, studies on welding of high-Mn austenitic steel have mainly focused on the applications of automotive industry for a long time. In the present work, a high-Mn cryogenic steel was welded by multi-pass Shielded Metal Arc Welding (SMAW), and the microstructural evolution, solute segregation and its effect on the properties of welded joint (WJ) were studied. The yield strength, tensile strength and elongation of the WJ reached 804 MPa, 1027 MPa and 11.2% at −196 °C, respectively. The elongation of WJ was reduced with respect to the BM due to the poorer strain hardening capacity of weld metal (WM) at −196 °C. The WM and coarse-grained heat affected zone (CGHAZ) had the lowest cryogenic impact absorbed energy of ~55 J (at −196 °C). The inhibited twin formation caused by the higher critical resolved shear twinning stress ( τ T ) in the C-Mn-Si segregation band, the inhomogeneous microstructure caused by solute segregation, and the hardened austenite matrix deteriorated the plastic deformation capacity, finally resulting in the decreased cryogenic impact toughness of the CGHAZ. To summarize, the cryogenic toughness and tensile properties of the WJ meet the requirements for LNG tank building.

Study on the Novel High Manganese Austenitic Steel Welded Joints by Arc Welding for Cryogenic Applications of LNG Tanks

“…On the other hand, the similar welding consumables for the high-Mn steel in this research prevented some bad issues from dissimilar welding. It had been reported that welding high-Mn steel using nickel-based weld consumables (matched 9Ni steel) worsened cryogenic impact toughness at the coarse grain heat-affected zone (CGHAZ) [ 23 ]. This was confirmed to attribute mainly to the difference of chemical composition between the weld metal and the base metal, which led to the twinning difficulty and the lower plastic deformation capacity [ 24 ].…”

“…This was confirmed to attribute mainly to the difference of chemical composition between the weld metal and the base metal, which led to the twinning difficulty and the lower plastic deformation capacity [ 24 ]. Meanwhile, the hardened austenite developed a high defect density, hindered the dislocation migration, and finally worsened the cryogenic impact toughness in CGHAZ [ 23 ].…”

“…With respect to SMAW of high-Mn steel, J.K. Ren [ 23 ] and X.Y. Fan [ 24 ] provided the mechanical properties of dissimilar welded joints using the Ni-based welding electrode, due to the lack of high-Mn steel welding electrodes, which have met the requirement of IMO.…”

The Dominant Role of Recrystallization and Grain Growth Behaviors in the Simulated Welding Heat-Affected Zone of High-Mn Steel

“…Similarly, γ −→ δ phase transformation has been reported to lead to a deterioration in the mechanical properties of the HAZ in austenitic stainless steel [10] and high manganese low-density steel [11], however, it is difficult to find in high manganese austenitic steel. A common factor that deteriorates the HAZ of high manganese austenitic steel [16][17][18] and austenitic stainless steel [19] is the precipitation of a M 23 C 6 -type carbide caused by the macrosegregation and/or grain boundary segregation of C, Mn, and Cr elements. Meanwhile, in regions depleted in solutes for high manganese austenitic steel, the ε/α ′ phase may occur due to low stacking fault energy [20].…”

Microstructure, non-metallic inclusions and impact toughness of high-Mn cryogenic steel weld metal

“…It can be seen that the inhomogeneous microstructure formed during welding process of high-Mn steels and the inclusions generated by metallurgical reaction are extremely complex. In recent years, the research on high-Mn steel weld metal mainly focuses on the control of stacking fault energy (SFE) and deformation mechanism during impacting [18, 19]. However, to the best of the authors’ knowledge, there are still few reports up to date investigating the characteristics of microstructure and non-metallic inclusions of high-Mn austenitic weld metal for LNG tanks and need in-depth study.…”