Exploring the Efficient Welding of the Metal World: Stainless Steel

Stainless steel, due to its excellent corrosion resistance, heat resistance, and low-temperature tolerance, is widely used in cutlery, household appliances, machinery manufacturing, architectural decoration, coal, petrochemicals, and other fields. From the early days of the People's Republic of China to the pre-reform and opening-up period, China's stainless steel demand was mainly for industrial and defense applications. Nowadays, China's stainless steel production accounts for more than 50% of the world's stainless steel output, establishing its significant position in the global stainless steel market. However, the welding process of stainless steel is not an easy task, requiring a mastery of a series of technical points and overcoming various technical difficulties.

I. Characteristics of Stainless Steel

Stainless steel, in short, refers to steel with a primary element of chromium (Cr) content higher than 12%. This composition places the steel in a passivated state, thus giving it the characteristics of stainless steel. Based on its structure and chemical composition, stainless steel can be broadly classified into four categories: austenitic stainless steel, martensitic stainless steel, ferritic stainless steel, and duplex stainless steel.

Austenitic stainless steel, with its superior corrosion resistance, heat resistance, and non-magnetic properties, is widely used in household appliances, automotive parts, and medical instruments.

Martensitic stainless steel, known for its good machinability, high hardness, and magnetic properties, is often used to make cutlery, blades, mechanical parts, etc.

Ferritic stainless steel, rich in titanium, is resistant to high temperatures and corrosion, commonly used in the production of automotive exhaust pipes, heat exchangers, and other components.

Duplex stainless steel combines the advantages of austenitic and ferritic stainless steels, offering high strength and excellent corrosion resistance.

In addition, stainless steel also has the following notable characteristics:

Excellent corrosion resistance: The chromium element in stainless steel can form a dense oxide film on its surface, effectively resisting the erosion of oxygen, water, and other corrosive media.

High strength and toughness: Stainless steel has high strength and toughness, capable of bearing significant mechanical stress.

Resistance to high and low temperatures: Stainless steel maintains good mechanical properties at high and low temperatures.

Aesthetic appeal and ease of processing: Stainless steel has a bright metallic luster, is easy to process and shape, suitable for manufacturing products of various complex shapes and structures.

However, stainless steel has relatively poor thermal conductivity and a large coefficient of thermal expansion, leading to issues such as hot cracks and intergranular corrosion during welding. To ensure the quality and performance of the welded joints, it is necessary to select appropriate welding methods, control welding parameters, and take proper protective measures.

II. Main Methods of Stainless Steel Welding

Resistance Welding

Characteristics: Resistance welding uses the resistance heat generated by the current passing through the contact surface to melt and connect the contact surfaces. Resistance welding has the advantages of fast welding speed, high production efficiency, and stable weld quality.

Application scope: Resistance welding is suitable for welding stainless steel sheets and pipes with relatively thin thicknesses and regular shapes.

Operating points: Before welding, ensure the workpiece surface is clean and flat; select appropriate welding current and welding time; control the welding pressure to ensure weld quality.

Manual Arc Welding

Characteristics: Manual arc welding is a method of welding by manually operating an arc welding gun, offering strong flexibility and applicability to various shapes and sizes of workpieces.

Application scope: Manual arc welding is suitable for welding stainless steel workpieces with relatively thin thicknesses and complex shapes.

Operating points: During welding, control the arc length and maintain a stable welding speed; select suitable welding electrodes and welding currents; pay attention to parameters such as protective gas flow rate and tungsten electrode extension length.

Gas-Shielded Welding (MIG/MAG Welding and TIG Welding)

MIG/MAG Welding: This uses inert gas or mixed gas as a protective layer, feeding welding wire into the molten pool through automatic or semi-automatic wire feeding devices for welding. It has the advantages of fast welding speed, stable quality, and low cost. Suitable for welding areas with high density distribution.

TIG Welding: This uses argon gas as the protective gas, heating the stainless steel welding electrode to the molten state, then contacting it with the workpiece to form a weld. It offers advantages such as good weld formation, high surface finish, and suitability for welding thin plates and medium to heavy plates of pipes. However, the process is complex, welding speed is slow, and costs are higher.

Laser Welding

Characteristics: Laser welding utilizes the high energy density of a laser beam to achieve welding, featuring high precision, high speed, and good weld quality.

Application scope: Laser welding is suitable for welding stainless steel workpieces with extremely high weld quality requirements and complex shapes.

Operating points: During welding, control the power and focal point position of the laser beam; maintain a stable welding speed; pay attention to the protective gas flow rate and stability of the laser beam.

Other Welding Methods

Submerged Arc Welding: Suitable for welding stainless steel plates of medium thickness and above, offering advantages such as high productivity and good weld quality. However, it can easily cause segregation of alloy elements and impurities.

Electroslag Welding: This uses the resistance heat generated by current passing through liquid slag for welding, suitable for mass production occasions. However, it has certain restrictions on the material and size of the workpiece.

III. Technical Difficulties and Solutions in Stainless Steel Welding

Hot Cracking Phenomenon

Technical difficulty: Austenitic stainless steel, especially steel grades containing more nickel, sulfur, and other elements, is prone to hot cracking during welding, affecting welding quality.

Solution: Adopt preheating and post-heat treatment to reduce welding stress; simultaneously, selecting appropriate filler materials and optimizing welding parameters (such as current, voltage, speed) are also crucial.

Intergranular Corrosion

Technical difficulty: The combination of carbon and chromium in austenitic stainless steel forms chromium carbide that precipitates at the grain boundaries, resulting in chromium depletion at the grain boundaries, thereby triggering intergranular corrosion.

Solution: Use stainless steel materials with low carbon emissions or eliminate or reduce the precipitation of chromium carbide through post-weld heat treatment.

Welding Deformation

Technical difficulty: Stainless steel has a large coefficient of thermal expansion, making it prone to deformation during heating and cooling processes.

Solution: Reasonably design the joint form, adopt a symmetrical welding sequence, and appropriately use fixtures for fixation to reduce welding deformation.

Welding Porosity

Technical difficulty: Poor protection during welding or contaminants on the base metal surface may lead to the formation of hydrogen pores or other gas pores.

Solution: Ensure thorough cleaning of the surface to be welded before welding and maintain a good gas protection environment during welding.

Stainless steel welding is a technically challenging process, requiring comprehensive consideration of material properties, welding methods, operational specifications, and other factors. By selecting appropriate welding methods and technical parameters and adopting effective solutions, the quality and performance of stainless steel welds can be ensured. In the future, we anticipate the emergence of more advanced welding technologies and equipment, opening up broader spaces for the application of stainless steel. Heron will also continue to deeply explore innovations in stainless steel welding technology, contributing its professional expertise to improving welding quality and performance.