Characteristics of stainless steel

Stainless steel, as a type of steel with high chemical stability, can resist the erosion of various corrosive media such as air, water, acid, alkali, salt and its solution. It is known for its excellent corrosion resistance, mechanical properties, process performance and wide operating temperature range (-269℃ to 1050℃), so it is widely used in the manufacture of parts and equipment that require corrosion resistance, oxidation resistance, high temperature resistance and ultra-low temperature resistance, especially in the field of furniture, such as sofa legs, coffee table legs, door handles, cabinet slides, etc.

 

 

Stainless steel can be divided into several categories according to its organizational state, such as martensitic steel, ferritic steel, austenitic steel, ferritic stainless steel and precipitation hardening stainless steel. In addition, according to the composition, it can also be divided into chromium stainless steel, chromium-nickel stainless steel and chromium-manganese-nitrogen stainless steel. Among them, the most widely used (accounting for about 70%) is a series of steel grades obtained by adding Ni, Mn, N and other elements to 18% chromium ferritic stainless steel. According to the different chromium and nickel contents, it can be further divided into 18-8 steel, 18-12 steel, 25-20 steel and chromium manganese low nickel type.

 

Weldability of stainless steel

Stainless steel is known for its high tensile strength, good plasticity and toughness, and low yield point. Compared with carbon steel, stainless steel can still maintain high strength and good oxidation resistance at high temperatures, so it is often used as heat-resistant steel. At the same time, stainless steel also has excellent impact toughness, good welding performance, is not sensitive to hydrogen embrittlement, and will not undergo phase change at any temperature. The joints in the welded state also have excellent plasticity and toughness. In addition, stainless steel has a low tendency to hot cracking during welding, generally does not require preheating before welding and post-weld heat treatment, and can be welded with dissimilar steels such as carbon steel. However, stainless steel welding also needs to pay attention to problems such as thermal cracking, embrittlement, intergranular corrosion and stress corrosion. At the same time, due to its poor thermal conductivity and large linear expansion coefficient, large stress and deformation may be generated during welding.

Welding process

Groove type and preparation

When selecting the groove type of stainless steel, the number of welding layers and the amount of filler metal should be comprehensively considered to ensure that the mechanical properties of the weld are met while improving work efficiency. For full penetration butt joints, V-shaped grooves are usually used, and the groove angle is controlled at 35±5℃. Before the weld is assembled, the scale, grease, impurities, etc. within 15mm on both sides of the groove need to be cleaned by mechanical methods. The positioning material of the groove should be the same as the material used for formal welding. After the assembly is completed, it is necessary to check whether the assembly gap meets the requirements of the technical regulations.

 

Manual arc welding

Manual arc welding is a method of welding by manually operating an arc electrode. During the welding process, an arc is generated between the electrode and the workpiece, and both are locally heated to a molten state. The melted droplet at the end of the electrode fuses with the molten base material to form a molten pool. As the arc moves, the liquid metal in the molten pool gradually cools and crystallizes to form a weld.

 

Advantages:

 

1. The electrode loss is small, the arc length is easy to maintain, and no flux and coating layer are required during the welding process, so it is easier to achieve mechanization and automation.

 

2. It is not limited by the position of the weldment and can be welded in all positions.

 

3. Argon gas, as a protective gas, can effectively isolate the surrounding air and does not react with the metal. At the same time, the arc in the TIG welding process also has the function of automatically removing the oxide film on the surface of the workpiece. Therefore, it is suitable for welding non-ferrous metals, stainless steel and various alloys that are easy to oxidize, nitride, and chemically active.

 

4. The heat source and filler wire can be controlled separately, and the heat input is easy to adjust. It is suitable for welding in various positions and is also an ideal method for achieving single-sided welding and double-sided forming.

 

Disadvantages:

The shallow melting depth and low deposition speed lead to low production efficiency and high production costs.