This Guide provides recommendations and specifications for resistance spot, laser, and arc welding of Docol® advanced high-strength steels.
The Welding Guide covers best practices for the three major welding processes used by automakers on four key Docol AHSS/UHSS steel grades:
- Micro-Alloyed (LA)
- Dual Phase (DP)
- Complex Phase (CP)
- Martensitic (M)
In many cases, welding Docol AHSS/UHSS steels is like welding mild steels — but with some important considerations, especially for ultra-high-strength steels and zinc-coated steels.
The Guide presents basic specifications and mechanical properties for LA, DP, CP, and M grades, including substrate (hot or cold rolled), applicable industry standards, available coatings, yield and tensile strengths, and elongation percentages.
The resistance spot welding chapter focuses on maximizing the welding range — that is, the available range of welding currents — to attain the greatest possible safety margin for achieving high-quality welds. The chapter covers electrode force and welding times and their influence on the welding range. Additional information includes single-pulse vs. multi-pulse welding, AC vs. MFDC current modes, and recommended types of welding guns, electrodes, and domed tips. Graphs plot the shear and cross-tension strengths vs. base metal strengths for different grades of Docol AHSS/UHSS steels.
The laser welding chapter covers the recommended penetration levels for lap welding, the laser welding of zinc-coated AHSS/UHSS steels, and laser heat input ranges for very high strength UHSS steel. The chapter includes specifications for the hardness of the weld’s metal (fusion zone) vs. carbon content of base metal in laser welds, as well as tensile properties for butt welds at different welding speeds. For tailored welded blanks, there are reference tables for stretchability values for Docol DP grades. For both Docol DP and DP-GI (hot-dip galvanized) grades, charts plot the hardness and stretchability of laser butt welds.
The arc welding chapter covers gas metal arc welding (GMAW, MAG, MIG) parameters for Docol AHSS/UHSS steels. Topics include how to avoid distortion of thin metal sheets and special measures for zinc-coated grades. The chapter provides recommended filler metals and examples sequences for back-step welding. It also presents data on the Charpy V impact toughness of welding joints and MIG brazing of zinc-coated Docol AHSS/UHSS.
Each chapter also includes:
- Welding current ranges
- Hardness profiles across welds
- Charts on the strengths of welds for different thicknesses and steels grades