Welding of carbon steel and low alloy steel
(1) When the carbon equivalent exceeds 0.3%, the challenges in welding increase due to greater difficulty, increased sensitivity to cold cracking, and increased tendency to brittle fracture of the material under fatigue and low temperature conditions. To mitigate these challenges, the following measures can be taken:
- Preheating or postheating
- Adopting double beam welding, with one beam focused and the other defocused
- Ensure penetration using lower power and welding speed as far as possible.
(2) Welding of high-carbon materials and low-carbon materials can be facilitated by the use of offset welding, which limits the transformation of martensite and reduces the formation of cracks.
(3) The performance of laser welding of dead steel and semi-finished steel is superior because deoxidizers such as silicon and aluminum are added before casting, reducing the oxygen content in the steel to very low levels.
(4) Steel with sulfur and phosphorus content greater than 0.04% is prone to thermal cracking during laser welding.
(5) Laser welding is generally not recommended for galvanized steel with overlapping structures.
Stainless steel welding
(1) Stainless steel has excellent laser welding performance.
(2) Compared to carbon steel, austenitic stainless steel has lower thermal conductivity, being only 1/3 of that of carbon steel. However, it has a slightly higher absorption rate. This results in slightly deeper penetration during laser welding (about 5% to 10%) compared to regular carbon steel.
(3) During laser welding of Cr-Ni stainless steel, the material has high energy absorption and efficient melting.
(4) Ferritic stainless steel has improved weld plasticity and toughness when welded using laser welding compared to other welding methods.
(5) Laser welding of stainless steel is used in various industrial applications, such as welding of stainless steel pipes and nuclear fuel packages in nuclear power plants, as well as in the chemical industry.
Laser welding of non-ferrous metals
1. Laser welding of aluminum alloy
Deep penetration welding is a technique commonly used in laser welding of aluminum alloys. The main challenges in this process are the high reflectivity of the aluminum alloy to the laser beam and its high thermal conductivity.
One problem that arises during laser welding of aluminum and aluminum alloys is the sharp increase in hydrogen solubility in the material as the temperature increases, leading to the formation of pores in the weld.
In deep penetration welding there is also a risk of root cavities and poor weld bead formation.
When laser welding aluminum and aluminum alloys, there are three main challenges that must be addressed: porosity, thermal cracking, and significant weld irregularities.
The high reflectivity of aluminum alloys makes laser welding very challenging. To overcome this, a high power laser must be used.
2. Laser welding of titanium alloy
Titanium alloy is an excellent structural material with remarkable specific strength, good ductility and toughness, and exceptional corrosion resistance.
However, titanium has highly reactive chemical properties and is highly susceptible to oxidation.
Furthermore, titanium is also extremely sensitive to embrittlement caused by the presence of oxygen, hydrogen, nitrogen and carbon atoms.
Therefore, it is essential to pay close attention to joint cleanliness and provide adequate gas protection during the welding and manufacturing processes.
3. Laser welding of superalloys
Laser welding is capable of welding all types of superalloys, including those with high levels of Al and Ti that are difficult to weld by arc welding, resulting in high quality joints.
For welding of superalloys, laser generators typically used are pulsed lasers or continuous CO2 lasers with power from 1 to 50 kW.
It is recommended to use helium or a mixture of helium and a small amount of hydrogen as a shielding gas during laser welding of superalloys.
4. Laser welding of different materials
Laser welding can be used to join dissimilar metals such as copper-nickel, nickel-titanium, titanium-aluminum and low-carbon steel-copper under specific conditions.
In addition to metals, laser welding can also be used to weld ceramics, glass, composite materials, and more.
When welding ceramics, preheating is necessary to prevent cracking. The recommended preheating temperature is 1500°C and welding is carried out in air.
A long focal length focusing lens is typically used for laser welding of ceramics, and filling with welding wire can also be done to improve joint strength.
However, when welding metal matrix composites, brittle phases can easily form, leading to cracking and decreased joint strength.
