Stainless steel is also known as corrosion-resistant steels. Due to its versatility, durability, and affordability, its use is steadily growing worldwide.
Welding of Austenitic stainless steels
Stainless steel welding techniques differ from carbon steel or alloy steels.
Austenitic stainless steels show the following differences compared to common carbon steels:
In austenitic stainless steels the electrical resistance is about six times higher than that of carbon steel and its melting point is about 93 degrees centigrade. And its thermal conductivity is about 50% lower and thermal expansion is about 50% higher.
Given these factors, it is clear that austenitic stainless steels require less current of welding and greater expansion increases the tendency of warpage and deformation like cracking under resistance condition, especially in the higher alloys types of stainless steels.Weld under restraint conditions, especially in higher alloy types. May produce a high incidence of cracking.
When Austenitic stainless steels are heated within a temperature range of 427 to 870 ° C. Or it is slowly cooled through the boundary (as weld cool) carbon is released from the solid solution, mainly at the grain boundaries, which intermittently unites with chromium to form “rich chromium carbides”. The formation of these carbons effectively eliminates much of the chromium(from adjacent regions) that would otherwise be available to form protective chromium oxide.
Welding Techniques of stainless steel
Many welding processes are involved in stainless steel welding, some of the major welding processes are as follows:
- Oxy-acetylene welding
- Arc Welding
- Resistance welding
Heat treatment of austenitic stainless steel
The annealing heat treatment is a must where maximum corrosion resistance is required.
Heat the weldment between 1040ºC to1120ºC
|→Hold for at least one hour/25mm, the thickness of the workpiece|
|→ Cool rapidly through the range from 925ºC to 427º C|
For bellow of the thickness of 3mm the weldment can be coold in air.