Multi-scale simulation of thermal processes and microstructure evolution in wire arc additive manufacturing of 921A steel

Lei Shi^¹(), Xiaohui Lyu^¹, Ji Chen^¹, Chuansong Wu^¹, Ashish Kumar^¹, Ming Zhai^², Wenjian Ren^³

1MOE Key Lab for Liquid–Solid Structure Evolution and Materials Processing, Institute of Materials Joining, Shandong University, Jinan 250061, China

2Metals and Chemistry Research Institute, China Academy of Railway Sciences Co., Ltd., Beijing 100081, China

3Shandong Aotai Electric Co., Ltd., Jinan 250101, China

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Abstract

Wire arc additive manufacturing (WAAM) offers distinct advantages, including low equipment cost, high deposition efficiency, and suitability for fabricating large-scale components. 921A steel (10CrNi3MoV) is widely used in the offshore industry and shipbuilding, making the development of WAAM technology for 921A steel crucial for manufacturing and repairing ship components. In this study, a two-dimensional melting‒solidification model was developed to investigate the melt pool dynamics and microstructure evolution during the WAAM process. This model integrates computational fluid dynamics (CFD) with the cellular automata (CA) method, utilizing the open-source ExaCA code for microstructural simulation. The model successfully predicted the temperature and flow fields, as well as the microstructural evolution within the deposition layer. Macroscopic metallography revealed columnar grains aligned with the heat flow direction, accompanied by acicular and granular ferrite, as well as bainitic morphologies. The simulated forming dimensions at various deposition speeds agreed reasonably well with the experimental results. An increased deposition speed reduced the fluid flow intensity within the molten pool. The ExaCA simulation demonstrated that columnar grains grew perpendicular to the fusion line, whereas nucleated equiaxed grains formed in the center of the molten pool under low-temperature gradients, obstructing the progression of the original columnar grains.

Keywords

wire arc additive manufacturing (WAAM)921A steel microstructure cellular automata (CA)deposition speed columnar grains

References

[1]

Yi H, Jia L, Ding JL, et al. Achieving material diversity in wire arc additive manufacturing: Leaping from alloys to composites via wire innovation. Int J Mach Tools Manuf 2024, 194: 104103.

Parameter	Value
Density	$7850 k g / m^{3}$
Liquidus temperature	$1790 K$
Solidus temperature	$1760 K$
Vapour temperature	$2900 K$ [32]
Latent heat of fusion	$2.5 e$ +5 $J / {k g}^{}$
Thermal conductivity	$25.4 W / (m^{} \cdot K^{})$
Coefficient of thermal expansion	$2.5 e - 5 K^{- 1}$
Specific heat	Temperature-dependent [33]
Viscosity	$0.006 k g / {(m}^{} \cdot s^{})$
Temperature coefficient of surface tension	$- 0.0003 N / (m^{} \cdot K^{})$ [34]
Surface tension	$1.2 N {/ m}^{}$ [34]
Convective heat transfer coefficient	25 $W / {(m}^{2} \cdot K^{})$ [35]
Radiation emissivity	0.8 [35]
Magnetic permeability	$1.26 e - 6 H / m^{}$
Stefan–Boltzmann constant	$5.67 e - 8 W / (m^{2} \cdot K^{4})$

Parameter	Value
$Δ t$	10 μs
$Δ x$	5 μm
A	$7.325 \times 10^{- 6} m / (s^{} \cdot K^{3})$
B	3.12 $m / (s^{} \cdot K^{2})$
C	0
$N_{0}$	${5 \times 10}^{12} m^{- 3}$
$Δ T_{N}$	5 K
$Δ T_{σ}$	0.5 K
$S_{0}$	25 μm

Case	Deposition speed (mm $/$ s)	Macroscopic morphology	Cross-sectional metallography
1	3
2	4
3	5
4	6