Welding is an important link in metal processing and has wide applications in many fields. To ensure product quality, product safety can be improved. This article will discuss the causes and solutions of welding cracks in stainless steel welded tubes .
Reasons for cracking of stainless steel welded tube
Cracks can be divided into hot cracks, cold cracks, stress corrosion cracks and lamellar tears according to the generation temperature and generation time. The locations where cracks form during the welding process are different. Cracks are visible on the welding surface and can be observed with the naked eye; some can be hidden inside the weld and can be discovered by flaw detection; some are on the weld and some are in the heat-affected zone. It should be noted that cracks in stainless steel welded pipes are sometimes generated during the welding process, and sometimes appear after being put in or running for a period of time after welding. The latter is called delayed cracking, which is more harmful.
1. Inferior raw material steel strip
The quality of stainless steel strips is the basis for determining the quality of stainless steel welded pipes. According to the level of copper content, it can be divided into low copper materials, medium copper materials and high copper materials. The ductility effect of the stainless steel pipes produced in this way is gradually enhanced, and at the same time the price will also increase accordingly. Because there are many brands of stainless steel pipes on the market and peers are lowering prices with each other, profits are getting thinner and thinner. Therefore, some unscrupulous manufacturers choose to use intermediate frequency furnace materials. In fact, they use recycled stainless steel scraps to reprocess and forge steel strips. This material contains many impurities. It has high carbon content and high hardness, so it is prone to crack after processing and using for a long time.
2. Hardening during processing
Effects of work hardening: Steel pipes produce a large amount of plastic deformation during cold drawing, causing obvious lattice distortion, which increases the lattice energy and the internal energy of the metal, resulting in uneven internal stress in the metal and generating residual internal stress. This increases the hardness of the metal and decreases its toughness. The higher the hardness of the metal, the greater the residual internal stress during cold drawing, and the more obvious the work hardening phenomenon. When the residual stress reaches a certain value, the metal will tear along a certain row of grain interfaces, causing cracks in the steel pipe.
3. Excessive polishing of stainless steel welds
If the weld seam of stainless steel welded pipe cracks, it may also be because the stainless steel weld seam has been excessively polished, resulting in the weld seam being too thin, so cracking occurs during processing and use. This is a quality problem of the product. Good stainless steel pipe manufacturers often strictly control the quality of their products and have corresponding product certificates.
4. Hydrogen embrittlement phenomenon
Influence of hydrogen embrittlement phenomenon: During the process of removing scale with acid solution, sulfuric acid reacts with iron to release hydrogen gas. Hydrogen penetrates into the steel in the form of atoms or ions, forming a solid solution. The influence of hydrogen on the mechanical properties of steel is typically manifested in the phenomenon of hydrogen embrittlement.
Solutions to cracking of stainless steel welded tubs
1. Use the appropriate amount of lubricant
It has an obvious improvement effect on the deep drawing and bending cracking of 304 stainless steel pipes. The lubricant can form a thin film with certain toughness and elongation between the convex and concave dies, which is beneficial to the stretching and bending of stainless steel welded pipes.
2. Use white cast iron as the blank holder grinding tool
White cast iron has good oil storage properties and is easy to form a lubricating oil film; for example, using a tapered edge ring and smoothing the edges of the workpiece to remove micro-cracks can also effectively prevent stainless steel welded tubes from cracking.
Reasons for cracking of stainless steel welded tube
Cracks can be divided into hot cracks, cold cracks, stress corrosion cracks and lamellar tears according to the generation temperature and generation time. The locations where cracks form during the welding process are different. Cracks are visible on the welding surface and can be observed with the naked eye; some can be hidden inside the weld and can be discovered by flaw detection; some are on the weld and some are in the heat-affected zone. It should be noted that cracks in stainless steel welded pipes are sometimes generated during the welding process, and sometimes appear after being put in or running for a period of time after welding. The latter is called delayed cracking, which is more harmful.
1. Inferior raw material steel strip
The quality of stainless steel strips is the basis for determining the quality of stainless steel welded pipes. According to the level of copper content, it can be divided into low copper materials, medium copper materials and high copper materials. The ductility effect of the stainless steel pipes produced in this way is gradually enhanced, and at the same time the price will also increase accordingly. Because there are many brands of stainless steel pipes on the market and peers are lowering prices with each other, profits are getting thinner and thinner. Therefore, some unscrupulous manufacturers choose to use intermediate frequency furnace materials. In fact, they use recycled stainless steel scraps to reprocess and forge steel strips. This material contains many impurities. It has high carbon content and high hardness, so it is prone to crack after processing and using for a long time.
2. Hardening during processing
Effects of work hardening: Steel pipes produce a large amount of plastic deformation during cold drawing, causing obvious lattice distortion, which increases the lattice energy and the internal energy of the metal, resulting in uneven internal stress in the metal and generating residual internal stress. This increases the hardness of the metal and decreases its toughness. The higher the hardness of the metal, the greater the residual internal stress during cold drawing, and the more obvious the work hardening phenomenon. When the residual stress reaches a certain value, the metal will tear along a certain row of grain interfaces, causing cracks in the steel pipe.
3. Excessive polishing of stainless steel welds
If the weld seam of stainless steel welded pipe cracks, it may also be because the stainless steel weld seam has been excessively polished, resulting in the weld seam being too thin, so cracking occurs during processing and use. This is a quality problem of the product. Good stainless steel pipe manufacturers often strictly control the quality of their products and have corresponding product certificates.
4. Hydrogen embrittlement phenomenon
Influence of hydrogen embrittlement phenomenon: During the process of removing scale with acid solution, sulfuric acid reacts with iron to release hydrogen gas. Hydrogen penetrates into the steel in the form of atoms or ions, forming a solid solution. The influence of hydrogen on the mechanical properties of steel is typically manifested in the phenomenon of hydrogen embrittlement.
Solutions to cracking of stainless steel welded tubs
1. Use the appropriate amount of lubricant
It has an obvious improvement effect on the deep drawing and bending cracking of 304 stainless steel pipes. The lubricant can form a thin film with certain toughness and elongation between the convex and concave dies, which is beneficial to the stretching and bending of stainless steel welded pipes.
2. Use white cast iron as the blank holder grinding tool
White cast iron has good oil storage properties and is easy to form a lubricating oil film; for example, using a tapered edge ring and smoothing the edges of the workpiece to remove micro-cracks can also effectively prevent stainless steel welded tubes from cracking.
