Stainless Steel Welding
High-quality joints for stainless CrNi steels
Challenge of stainless steel welding
Stainless steel is one of the most demanding materials in welding technology. The varying requirements for corrosion resistance, toughness, and high-temperature resistance have led to the development of a wide range of alloys. These properties should be retained as positive characteristics even after welding.
Interesting facts about stainless steel
What is stainless steel?
In everyday life, stainless steel is usually understood to mean chromium-nickel steel (CrNi steel) – a material characterized by high corrosion resistance, mechanical strength, and good workability. Technically speaking, the term refers to any iron-carbon alloy that contains only small amounts of harmful accompanying elements such as sulfur and phosphorus.
Alloys
The most common alloy elements in stainless steel are chromium, nickel, molybdenum, titanium, niobium, vanadium and cobalt. From a minimum content of 10.5% chromium, stainless steel becomes corrosion-resistant. To counteract chromium depletion, the alloys contain slightly higher chromium contents, for example 12% or more. On the surface, a thin layer of chromium oxide forms due to the influence of oxygen. This protects the steel beneath it from other chemical influences.
The addition of further alloy elements can further improve the mechanical and chemical properties of stainless steel.
- Nickel is needed to maintain the austenitic structure at room temperature.
- Even in small quantities, molybdenum significantly increases corrosion resistance.
- Titanium and niobium stabilize the alloy at higher temperatures.
- Manganese, copper, and nitrogen are added in small proportions and each offer specific advantages, depending on the application.
What types of steel are there?
Stainless steels can be divided into different groups. Austenitic stainless steels (CrNi steels) and ferritic stainless steels are particularly common, differing mainly in their corrosion resistance, thermal conductivity, and thermal expansion.
Austenitic CrNi steels
These steels are also known as chrome-nickel steels (CrNi steels) and have a nickel content of more than 8%. They offer good mechanical properties, are resistant to corrosion and acid and can be processed easily. They are mainly used in aggressive environmental conditions, such as in the chemical or food industry.
Ferritic steels
Ferritic steels account for the majority of all welded structures. They are divided into:
- Unalloyed stainless steels: These contain a minimum of 0.3% chromium, nickel, and tungsten, as well as up to 1.65% manganese and 0.6% silicon.
- Alloyed stainless steels: These are easy to weld, provided that the carbon content is below 0.2% or the CEV value (carbon equivalent) remains below 0.4%.
Ferritic stainless steels are characterized by a chromium content of 10.5%. Depending on their microstructure, they are divided into ferritic stainless steels and martensitic stainless steels.
Ferritic-austenitic stainless steels (duplex steel)
Due to having both ferrite and austenite structure components, these stainless steels are often also called duplex steels. They combine two particularly good properties: increased strength as rust-free chrome-nickel steel and increased ductility and formability as rust-free chromium steel. Due to its high resistance to surface corrosion, duplex steel is mainly used in the chemical and petrochemical industry, as well as in offshore projects.
Martensitic stainless steels
These stainless steels have a chromium content of 12–18% and a carbon content of over 0.1%. They can be hardened by heating and rapid cooling, thereby achieving high strength, which increases with rising carbon content. They are used, for example, in the manufacture of razor blades, knives, and scissors. However, they are less corrosion-resistant than austenitic CrNi steels.
What needs to be considered during stainless steel welding?
Welding processes for stainless steel
Professional welding systems for stainless steel welding
