A Comparative Study of Formability of Diode Laser Welds in DP980 and HSLA Steels

[+] Author and Article Information
M. Xia

Centre for Advanced Materials Joining, University of Waterloo, Waterloo, Ontario, Canada; Central Iron & Steel Research Institute, Beijing, P. R. China

N. Sreenivasan, S. Lawson

Centre for Advanced Materials Joining, University of Waterloo, Waterloo, Ontario, Canada

Y. Zhou

Centre for Advanced Materials Joining, University of Waterloo, Waterloo, Ontario, Canadanzhou@uwaterloo.ca

Z. Tian

 Central Iron & Steel Research Institute, Beijing, P. R. China

J. Eng. Mater. Technol 129(3), 446-452 (Jan 04, 2007) (7 pages) doi:10.1115/1.2744417 History: Received June 19, 2006; Revised January 04, 2007

Understanding effects of welding on strength and formability is critical to support wider application of advanced high strength steels in automotive components. In this study, High Strength Low Alloy (HSLA) and DP980 (Dual Phase, 980MPa) sheet steels were welded with a 4kW diode laser. Mechanical properties of welds and parent metals were assessed by tensile and limiting dome height tests, and related to microhardness distribution across the welds. The formability of HSLA welds was insensitive to the welding process and comparable to that of parent metal. For the DP steel, weld formability was much lower than that of corresponding parent metal, which appeared to be due to the formation of soft zones in the outer region of the Heat affected zone (HAZ) of the welds. It was found that increase of welding speed resulted in a slight increase of formability of the DP steel, associated with a reduction in the microhardness difference between base metal and HAZ soft zones.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Microstructures of the base metals: (a) DP980 and (b) HSLA

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Figure 2

Schematic diagram of tensile test coupons

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Figure 3

Schematic graph showing tooling and specimens for the limiting dome height test. Specimen after increase of deformation shown as dotted lines.

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Figure 4

Hardness profiles of (a) DP980 and HSLA at welding speed of 1.0m∕min; (b) DP980 and HSLA welds with different welding speeds; locations and dimensions of the soft zone were listed in Table 3

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Figure 5

Fusion zone microstructure of (a) DP980 and (b) HSLA welds. (c) Soft zone microstructure DP980 weld, showing martensite tempering.

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Figure 6

Stress-strain data on both steels. (a) Typical stress-strain curves for DP980 and HSLA transverse and longitudinal tests with the welding speed of 1.3m∕min. (b) Ultimate strength versus ultimate strain of HSLA and DP980 weldment with three welding speeds.

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Figure 7

Typical tensile tested DP welded specimens: (a) Transverse and (b) longitudinal

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Figure 8

Dome tested specimens. (a) Parent metal of DP980. (b) Details of crack in (a). (c) Welded specimen of DP980 at welding speed of 1.3m∕min. (d) Details of crack in (c). (e) Parent metal of HSLA. (f) Welded specimen of HSLA.

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Figure 9

Side views of dome tested samples. The dome heights of the parent metal and welded specimen are 30.4 and 13.2mm for DP980 (a), and 32.5 and 31.8mm for HSLA (b). Welding speed is 1.6m∕min and welding direction is parallel to the rolling direction.

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Figure 10

The stretchability and hardness difference as a function of welding speed (welding direction parallel to the rolling direction)



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