CHALLENGE OF STEEL WELDING BY LASER
STEEL REMAINS THE MOST WIDESPREAD PARENT MATERIAL IN METAL CONSTRUCTION AHEAD OF ALUMINUM AND STAINLESS STEEL.
Its high strength and the low costs make it a popular construction material. Out of all materials, steel is the easiest to weld. The biggest challenge is keeping the material distortion as low as possible. Selecting the correct welding process plays an important part in this. Here comes our laser welding up to the front as best solution.
INTERESTING FACTS ABOUT STEEL
Steel is primarily composed of iron and a maximum of 2.06% carbon. Alloys with a higher proportion of carbon are known as cast iron. If the proportion of sulfur and phosphorus accompanying iron is less than 0.025%, it is called stainless steel.
Not every steel can also be welded: only pure steels, i.e. alloys with a carbon content of less than 0.22%, are suitable for this process. As a rule, the more impure the alloy, the harder it is to weld the steel.
Of particular importance are high-strength and super-high-strength steels. In addition to lightweight construction in the automotive industry, for example, they are also used for mobile cranes, concrete pumps, agricultural and forestry machinery. However, they are more difficult to weld than conventional steel alloys. The manufacturer's processing instructions should always be followed without fail.
Steel exists in a wide range of forms:
- Flat steel
- Round steel
- Profile pipes
- Square pipes
THIS IS HOW TO PREPARE STEEL FOR WELDING
- Clean
Before welding, remove coarse contamination from the steel in order to achieve good results. - Remove rust
Remove rusty areas in the parent material before welding so that no bonding flaws occur in the weld metal. - Remove oil or grease
Oily parent material makes the welding process more difficult and may, among other things, cause poor results. You should therefore remove the oil from the steel before welding. - Preheat
In case of higher material thicknesses, you should preheat the part before welding to slow down the cooling time. This prevents a high degree of hardness in the microstructure, in turn preventing cracking.
Carbon steel is the backbone of fabrication.
It’s strong, affordable, and welds beautifully if you treat it right. You’ll find it in everything from building frames to truck chassis to heavy equipment. But for all its versatility, carbon steel still comes with its quirks, especially when you’re chasing clean welds and tight tolerances.
Usually, MIG or stick welding is the go-to for thicker carbon steel. It’s fast and forgiving, but it brings a lot of heat. That’s fine on heavy plate, but once you get into thinner material like tubing, sheet, or formed parts, excess heat leads to distortion, burn-through, and time-consuming rework.
Laser welding solves that by dialing the heat input way down without sacrificing penetration. It’s like having a scalpel instead of a hammer. On 1 à 4 mm mild steel, laser welding gives you crisp, narrow welds that need little to no grinding. But what’s impressive is how well it performs on thicker material too. Fiber lasers like the PhotonWeld Master Pro-X can handle up to 12 mm with a clean keyhole weld in a single pass. And speaking of arc blow, that’s one headache you don’t deal with in laser. No magnetized part issues, no wandering arc, no fighting to keep the bead straight. The laser hits exactly where you aim, and it doesn’t flinch. And, … no preheat, no arc blow, no mess. That’s something even experienced arc welders have to respect.
Bottom line: carbon steel may be basic, but laser welding elevates it. You get repeatability, less post-processing, and tighter control, which adds up fast in production.
Laser Welding of Mild steels
Mild steel, or low-carbon steel, is a metal with a carbon content lower than 0.25%. Low carbon content provides excellent weldability, making mild steel one of the most weld-friendly metals, and that also applies to laser beam welding.
Mild steels don't have a reflective surface or high thermal conductivity. They quickly absorb laser light, allowing it to penetrate, melt, and fuse the pieces. You don't need a lot of power to do it, and they offer predictable melting and solidification, as well as reasonable weld pool control.
Due to their versatile properties and applications, mild steels are ubiquitous. You can find them in general fabrication, automotive structures, construction, and various other applications. The best part about them is that you won't have a hard time welding them. However, parameter control, laser focus, and direction are crucial in achieving high-quality, accurate, and immaculate laser welds.
There are considerably fewer problems with plasma formation in fiber laser welding than in CO2laser welding. This is related to a large extent to the difference in the wavelengths and intensity of their laser radiation. When using mild steel, fiber laser radiation is readily absorbed by the workpiece. There is no real need for welding gases with a helium content. Argon, an inert gas, is therefore a suitable welding gas for fiber laserwelding of mild steel. For certain applications, however, reactive welding gases such as carbon dioxide, argon/10% oxygen or argon/20% carbon dioxide may be considered as alternatives.
High-carbon Steel Laser Welding
Unlike mild steel, high-carbon steel contains a carbon content ranging between 0.60% and 1.5%. Increased carbon content improves steel's strength and resistance to wear and tear, making it ideal for cutting tools, springs, and high-strength wires.
However, as the carbon content increases, the metal becomes more challenging to weld. Rapid heating or cooling of the welded pieces will cause cracking, even if you do everything right. Cracking is an issue with any welding method, including laser welding. Although laser beams limit the heat input and provide low-hydrogen solutions, welding high-carbon steel can be highly unpredictable.
To laser weld high-carbon steel, you should heat treat the pieces before and after welding. Preheating the carbon steel to 150-280°C- before welding will minimize the initial heat stress. Also, welding carbon steel requires patient postheat treatment and slow cooling. Pieces can take up to 48 hours to slowly cool to ambient temperature.
Preheating and slow cooling will relieve heat stress in high-carbon steel. However, that still doesn't mean you'll avoid cracking. Sometimes, even if you do everything right and control the heat, high-carbon steel still can crack, so it is a hit-or-miss situation.
Alloyed Steel Welding
Lasers can readily weld alloyed steel, including low-alloy high-strength (HSLA) steels. However, the results may vary depending on the alloying elements (commonly carbon).
The high energy density of laser welding produces deep penetration and narrow welds in alloy steels. Deep-penetrating welds are particularly beneficial for attaining high tensile strength in HSLA steels. The welds can match or even exceed the properties of the base metal if needed.
Of course, like with other metal types, laser welding low-alloy steel requires careful attention to welding parameters and material characteristics (especially carbon content). Preparing will help you avoid potential cracking and reach optimal results.