Overview
Stainless steel is readily welded, but it is hard to weld it well. Weld metal solidification cracking and heat affected zone (HAZ) crack can occur, especially in fully austenitic structures. This week we will introduce stainless steel weldability with the most commonly used stainless steel grades 304 & 316L.
Why Is It Hard to Weld Stainless Steel?
Welding stainless steels can pose two challenges. Firstly, it is hard to control the temperature. Due to the low thermal conductivity of stainless steel, the heat produced at the weld is not readily transferred to its surrounding area but remains at the area being welded. This can lead to HAZ crack without professional welding techniques.
Secondly, stainless steel features high thermal expansion which means high degree of expansion when heated. Mentioning on this can remind us of the case study introduced last week of the Gateway Arch construction where the legs were expanded under high temperature over time. The high expansion under heat can cause warping and distortion.
Why Choose Stainless Steel After All?
Despite these challenges, stainless steels are frequently chosen among many industries as their premium material, for their excellent corrosion resistance, high temperature oxidation resistance, the high strength, the aesthetical appeals, the affordability and so on. This is especially true for stainless steel 304 and 316L, justified by their wide applications.
Grade 304 is the most used stainless steel material. It can be used for general applications, ranging from home appliances to chemical engineering. However, it can fail at the working environment exposed to chlorides where 316L will come to play. For this, 316/316L is regarded as the marine grade.
The Challenges are Surmountable!
The above mentioned challenges can still be coped with optimized solutions. For example, 304 grade also known as food grade is widely used for making cookers. Fissler the Germany cooker brand introduced in previous article uses 18-10 stainless steel as the material for their stainless-steel -series cooking utensils.
To solve the low thermal conductivity, these stainless steel cookers are sandwiched with aluminum at the base to solve the problem of stainless steel low thermal conductivity presented in cooking experience. The solution combines the advantages of both stainless steel and aluminum, providing optimized stainless steel products where customers would like to pay premium.
Weldability of Stainless Steels
Stainless Steel 304 Weldability
Austenitic stainless steel 304 features good toughness. Under general conditions, 304 can be welded applying any of the arc welding processes without necessitating pre-heating or post-weld heat treatment. However, to avoid excessive heat which can trigger carbide precipitation and intergranular corrosion, the interpass temperatures should be controlled within 170 ℃. Using the low carbon version 304L is another way to reduce the risk of intergranular corrosion.
Stainless Steel 316L Weldability
Stainless steel 316L embodies excellent weldability. Welding 316L generally doesn’t involve preheating. Due to the extra low carbon content, 316L is unlikely to incur intergranular corrosion during welding. The addition of molybdenum gives 316L enhanced corrosion resistance in chloride environments where pitting and crevice corrosion can easily occur, meanwhile increases its strength at elevated temperatures. This makes 316L especially excelled at resisting intergranular corrosion and welding hot crack.
After welding 304 and 316L, there can be solution treatment such as stress-relief-annealing which is not regarded as post-welding heating. It is to stabilize the shape and eliminate residual stress.
Stainless Steel 304 & 316L at CIVMATS
At CIVMATS, we have 304 stainless steels regularly in stock, especially in flat products like 304 stainless steel sheet plate strip and coil. We can customize 304 long products like 304 stainless steel bar, wire and 304 stainless steel pipes in a short period of time. 316L is customizable in any shape per your demand. Welcome for your enquiry and purchasing for stainless steel 304, 316L and more.
