Gas Metal Arc Welding of Advanced High- Strength Steels

? Min Kuo, ArcelorMittal
? Tom Natale, AK Steel Corporation
? Stephen Tate, AK Steel Corporation
? Hassan Ghassemi, ArcelorMittal
? Elliot Biro, ArcelorMittal
? Amanda Scherzer, FiatChryslerAmerica US LLC
? Doug Howe, Ford Motor Company
? Mike Palko, Ford Motor Company
? Richard Carlson, General Motors
? Weiping Sun, Nucor Corporation
? Chonghua (Cindy) Jiang, AET Integration Inc.
? Justin Hunt, AET Integration Inc.
? Donald F. Maatz, Jr. R&E Engineering Services
? Daniel L. Galiher, Tower International
? Vaidyanath B. Rajan, Lincoln Electric
? Richard Paul, Auto/Steel Partnership
? The objective of this project is to evaluate the effects of gas metal arc welding (GMAW) and gas metal arc brazing (GMAB) on AHSS and UHSS and to identify the impact of welding on joint strength and microhardness.
? Tests include X-ray inspection, micro hardness, quasi-static shear tension, and metallurgical cross-sections. Selected thin gauge steels were joined using both GMAW and GMAB. referencing ISO 17636-2 and ISO 5817.
? Cross-sections were taken from the welded and brazed plates. The microhardness indent spacing was 0.2 mm.
? Quasi-static shear tension testing was conducted to obtain nominal stress-displacement curves. Nominal stress was calculated as the load divided by the coupon cross-sectional area. Actual weld or braze geometry was not considered in the nominal stress value. Tests were conducted at 5.0 mm/min.
? X-ray inspections were conducted on all zinc coated materials,

? Steel grades obtained from the A/SP Sample Bank include the following:
? 0.67 mm BH210 HDGI
? 0.65 mm BH240 HDGI
? 0.69 mm DP490 HDGA
? 2.00 mm DP780 HDGI
? 2.53 mm CP780 HDGI
? 2.70 mm 780SF Uncoated
? 1.95 mm DP980 HDGA
? 1.38 mm DP1180 Uncoated
? 1.40 mm DP1180 EG
? 1.40 mm MS1700 Uncoated

Steel sheets were
sheared to 6” x 12”
and welded in a lap
joint configuration
along the 12”
length. Test
specimens were
waterjet cut from
the center of the
welded plates, in
order to avoid the
weld start and stop
locations.
Specimen length
was parallel to the
sheet rolling
direction.

Welded and brazed joints were
produced using an OTC DP400
power supply with an OTC Almega
AX-V6 robot. Both DC constant
voltage (GMAW) and DC pulsed
(GMAW-P) processes were used,
depending on the material
thickness and coating. All welds
were made in the 1F position.

? Lincoln SuperArc L56 (ER70S-6), Lincoln SuperArc LA-90 (ER80S-D2), and
? Lincoln SuperArc AK-10 (ER100S-G) steel filler were used with 90% argon 10%CO2 shielding gas for GMAW joints.
? Luvata LuvaWeld S1 (CuSi-A) silicon bronze filler was used with 100% argon shielding gas for GMAB joints.

Zinc coated steels were welded with lower travel speed than uncoated steels in order to reduce porosity. For thin zinc coated steels, it was found that the L2 leg length needed to be greater than the targeted 2.5t. Low current and the fastest feasible travel speeds were attempted in order to minimize heat input for all materials.

High quality joints were achieved with all materials. 

With appropriate parameters and sheet gaps targeted at 0.1 mm, zinc coated materials were able to be joined with minimal porosity. 

Coated materials exhibited moderate degrees of spatter. This is likely caused by the low current and voltage levels required to produce small weld sizes.

Minor porosity was observed in the weld or braze metal of zinc coated materials. The highest area percent porosity was 1.98%, as determined from X-ray images.

? Quality welded and brazed joints were achieved with all test materials
? The current practice consisting of mechanical, metallographic, X-ray, and microhardness testing quantifies joint characteristics and could be used as a GMAW and GMAB qualification procedure
? Zinc coated steels were able to be welded with average area percent porosity less than 2% using appropriate welding schedules and the test conditions used in this study
? Sheet gaps targeted at 0.1 mm were shown to minimize porosity
? Fractures occurred in the base metal, HAZ, weld metal, or near the weld fusion line,depending on material grade and thickness
? Joint efficiency ranged from 41% (MS1700 Uncoated GMAW) to 105% (BH240 HDGIGMAB)
? Nominal joint strength ranged from 357 MPa (BH210 HDGI GMAW) to 788 MPa (DP1180 uncoated GMAW).

? Of the 780 MPa tensile strength materials tested, ER100S-G filler increased nominal joint strength for both CP780 HDGI and DP780 HDGI compared to ER70S-6 filler
? Fracture location did not necessarily correspond to the areas with the lowest microhardness
? Fracture location may be dependent on the stress concentration at the weld root, microhardness distribution and microstructure difference (metallurgical notch)
? For BH210 HDGI and BH240 HDGI, fracture occurred in the heat-affected zone close to the weld for steel filler and in the base metal away from the joint for silicon bronze filler
? DP490 HDGA joints welded with steel filler fractured outside of the weld metal and provided close to 100% joint efficiency
? For DP490 HDGA brazed with silicon bronze filler, fractures occurred in the softer braze metal, with average joint efficiency approximately 91%
? Joint efficiency generally decreased as steel strength increased