Welding Techniques for Sofa Leg Metal Hardware

In the realm of metal sofa leg hardware manufacturing, welding technology plays a crucial role in connecting key metal components. There are various welding processes commonly used in furniture sofa leg fabrication, including automated welding and manual welding. While the outcomes of these different processes may vary, they all involve the metal materials undergoing heat treatment, metallurgical reactions, stress, and deformation, which collectively affect the welding joint and result in performance differences compared to the base material. Therefore, the study and evaluation of weldability are of paramount importance for metal hardware products.
 

The Importance of Weldability Assessment

Weldability assessment is the first step in ensuring the quality of welding. It involves evaluating the chemical composition of materials, microstructure, dimensional and shape changes, as well as performance testing of the weld joint. These tests include, but are not limited to, low-temperature performance, high-temperature performance, corrosion resistance, and crack resistance. The quality of weldability directly affects the reliability of the weld joint and the service life of the product.
 

Weldability Estimation and Testing Methods
 

Indirect Assessment Methods for Welding Process:

Carbon Equivalent (CE): Since the influence of carbon is the most significant, the effects of other elements can be converted into the influence of carbon, thus using carbon equivalent to assess the quality of weldability. For carbon steel and low-alloy structural steel, the calculation formula for carbon equivalent is as follows: CE=C+Mn6+(Cr+Mo+V)5+Ni15CE=C+6Mn​+5(Cr+Mo+V)​+15Ni​ When CE is less than 0.4%, the steel has good plasticity, no significant hardening tendency, and good weldability. Under general welding conditions, the weld joint will not crack. When CE is between 0.4% and 0.6%, the plasticity of the steel decreases, and the hardening tendency gradually increases, resulting in poor weldability. Preheating of the workpiece before welding and slow cooling after welding are necessary to prevent cracks. When CE is greater than 0.6%, the steel's plasticity worsens, and the hardening and cold cracking tendencies are high, leading to even poorer weldability. The workpiece must be preheated to a higher temperature, and measures to reduce welding stress and prevent cracking must be taken. Appropriate heat treatment is also required after welding.
 

Direct Assessment Methods for Welding Process:

Welding Crack Test Methods: Cracks in the weld joint can be categorized into hot cracks, cold cracks, reheat cracks, stress corrosion, and lamellar tearing. Common test methods include the T-joint welding crack test, the plate docking welding crack test, and the rigid docking crack test method, which are used to assess the sensitivity to hot and cold cracks in different types of steel.
 

Welding Characteristics of Common Metallic Materials:
 

Welding of Carbon Steel:

Low Carbon Steel: Low carbon steel has low carbon content and little manganese and silicon, which does not cause severe hardening or quenched structures due to welding. This type of steel has excellent plasticity and impact toughness, and its weld joint also has excellent plasticity and toughness. Generally, no preheating or post-heating is required during welding, and no special process measures are needed to achieve a satisfactory weld joint.
 

Medium Carbon Steel: Medium carbon steel has a higher carbon content and is less weldable than low carbon steel. When the carbon equivalent is close to the lower limit (0.25%), weldability is good. As the carbon content increases, the hardening tendency also increases, and low plasticity martensite structures are prone to form in the heat-affected zone. Cold cracks are likely to occur when the weldment is rigid or when welding materials and process parameters are not properly selected.

High Carbon Steel: High carbon steel with a carbon equivalent greater than 0.6% has high hardenability and is prone to forming hard and brittle high carbon martensite. Cracks are likely to form in the weld and heat-affected zone, making it difficult to weld. Generally, this type of steel is not used for welded structures but for manufacturing high hardness or wear-resistant components or parts. Most of their welding is for repair and repair of damaged parts.
 

Welding of Low-Alloy High-Strength Steel: 

Low-alloy high-strength steel generally has a carbon content not exceeding 0.20%, and the total amount of alloy elements generally does not exceed 5%. It is the presence of a certain amount of alloy elements in low-alloy high-strength steel that makes its welding performance different from carbon steel, with welding characteristics manifested in weld joint cracking, embrittlement, and softening.
 

Welding of Stainless Steel:

Austenitic Stainless Steel: Austenitic stainless steel is easier to weld than other stainless steels. It does not undergo phase changes at any temperature and is not sensitive to hydrogen embrittlement. Austenitic stainless steel joints also have good plasticity and toughness in the as-welded condition. The main welding issues are hot cracking, embrittlement, intergranular corrosion, and stress corrosion. Additionally, due to poor thermal conductivity and a large linear expansion coefficient, welding stress and deformation are relatively large.
 

Austenitic-Ferritic Duplex Stainless Steel: Austenitic-ferritic duplex stainless steel is composed of austenite and ferrite phases. It combines the advantages of austenitic and ferritic steels, thus possessing high strength, good corrosion resistance, and ease of welding. The main characteristics of welding this type of steel are lower thermal tendency compared to austenitic stainless steel; lower embrittlement tendency after welding compared to pure ferritic stainless steel, and a lower degree of ferrite coarsening in the welding heat-affected zone, thus having better weldability.
 

In metal hardware welding processes, understanding these welding characteristics is crucial for selecting the appropriate welding methods and process parameters. By precisely controlling the welding process, the welding quality of metal hardware products can be ensured, meeting various application requirements.