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
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.
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.
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.
The same considerations applying to mild steels, such as plasma formation and nozzle arrangement, also apply to welding gases for stainless steels. The metallurgical impact of welding gases on the weldmetal, however, differs from that on mild steels. This is due to the factthat stainless steels contain considerably larger amounts of alloying elements.
The selection of welding gases depends on the type of stainless steel – austenitic steel, ferritic steel, or austenitic-ferritic steel – and its speciﬁcalloying composition. Welding gases containing oxygen and carbondioxide should generally be avoided. Oxygen leads to oxide inclusions in the weld metal and on the surface, which may decrease corrosionresistance. Carbon dioxide oxidises the weld and may increase the risk of intercrystalline corrosion.
Austenitic steels are the most common types of stainless steel. They contain chromium and nickel as their main alloying elements. Small amounts of nitrogen are sometimes added to improve mechanical strength and pitting corrosion resistance. Superaustenitic steel is an example of an austenitic steel that has a higher alloy content, particularly with reference to molybdenum and nitrogen, than ordinary austenitic steels.
Helium, argon and argon/helium mixtures (argon/30% helium andargon/50% helium) are frequently used when working with austenitic steels. The higher the laser power, the higher the helium content that the welding gas must have in order to reduce plasma formation.
Welding gases containing hydrogen, such as argon/6–10% hydrogen,can be used at lower laser powers. Besides controlling plasma formation, hydrogen also reduces surface oxides and affects the viscosity of the melt.
Nitrogen is a suitable welding gas component for those austenitic and superaustenitic steels that are alloyed with nitrogen. Nitrogen as a welding gas compensates for loss of nitrogen in the weld metal, which would otherwise occur, thereby reducing the pitting corrosion resistance of the welds.
However, nitrogen should not be used as a welding gas for austenitic steels alloyed with titanium and niobium. Nitrogen forms nitrides with these elements, so that there is less free titanium and niobium availablefor prevention of chromium carbide formation and intercrystalline corrosion.