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Research Papers

Modeling of Temperature Distribution in Laser Welding of Lapped Martensitic Steel M1500 and Softening Estimation

[+] Author and Article Information
Hongze Wang, Kunkun Chen

State Key Laboratory of Mechanical
System and Vibration,
Shanghai Jiao Tong University,
Shanghai 200240, China

Yansong Zhang

Shanghai Key Laboratory of Digital Manufacture
for Thin-Walled Structures,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: zhangyansong@sjtu.edu.cn

1Corresponding author.

Manuscript received August 3, 2015; final manuscript received March 30, 2016; published online June 23, 2016. Assoc. Editor: Hongqiang Chen.

J. Manuf. Sci. Eng 138(11), 111006 (Jun 23, 2016) (9 pages) Paper No: MANU-15-1388; doi: 10.1115/1.4033391 History: Received August 03, 2015; Revised March 30, 2016

With the implementation of more stringent emissions standards, ultrahigh strength steel has been increasingly used in vehicle body to reduce the carbon emissions, but softening in the heat-affected zone is one of the most serious issues faced with in welding of this steel. In this paper, a finite element model (FEM) was developed to estimate temperature distribution in laser welding of lapped martensitic steels M1500 considering the effect of interface. Three methods to characterize the effect of interface have been adopted. The comparison result shows that the method using two groups of contact elements with birth and death options could accurately characterize the thermal contact conductance properties of the interface before and after welding, respectively. Based on the simulated temperature–time curve, a carbon diffusion model was then developed to estimate the martensite tempering transformation in the softening zone. Maximum softening degree and location of the softening zone were estimated and validated by hardness measurement experiments.

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Figures

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Fig. 1

Schematic of laser welding of lapped martensitic steel

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Fig. 2

Schematic of heat transfer: (a) at the cross section and (b) at the longitudinal section of the weld seam

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Fig. 3

(a) Geometry model with boundary condition defined and (b) mesh

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Fig. 4

Temperature varying material properties of M1500: (a) density, specific heat, and thermal conductivity and (b) elastic modulus and Poisson's ratio

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Fig. 5

Simulation procedure for laser welding of lapped martensitic steels

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Fig. 6

(a) Thermal contact conductance value used in the simulation model and (b) pseudocode for updating the statuses of the contact elements

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Fig. 7

Comparison of the temperature distributions from these three models

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Fig. 8

Comparison of the simulated and experimental weld bead (p = 1500 W and v = 20 mm/s)

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Fig. 9

Comparison of the simulated temperature–time curve obtained from different welding speeds with the highest temperature equal to Ac1

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Fig. 10

Schematic of the highest temperature and hardness distribution for the section of welded martensitic steel M1500 ((1): fusion zone, (2): complete austenitization zone, (3): left softening zone, (4): right softening zone, and (5): base metal zone)

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Fig. 12

Comparison of the estimated and experimental locations of the fusion zone and the softening zone

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Fig. 11

Comparison of the estimated and experimental minimum hardness in the softening zone

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