Hot cracks refer to the hot cracks generated when the weld and heat-affected zone metal cools to the high temperature range near the solidus during welding.

Cold cracks refer to the cold cracks generated when the weld joint cools to a lower temperature (i.e., below the temperature at which austenite begins to transform into martensite).

Reheat cracks refer to the cracks generated when the stainless steel plate is heated again within a certain temperature range after welding (stress relief heat treatment or other heating process) and then produced.

Stainless steel is a type of delayed crack steel. This type of steel has a lower thermal conductivity than ordinary carbon steel, a higher expansion coefficient, and slow heat conduction. It is easy to expand when heated and the expansion amplitude is large. Based on this property, many problems may occur in the welding process of stainless steel plates, such as undercut, pores, lack of fusion, cracks, etc.

Factors that cause cracking in stainless steel after welding include improper welding process, influence of material properties, improper preparation and handling, and stress changes during operation.

Stainless steel itself contains elements such as chromium and nickel, has excellent corrosion resistance and high temperature resistance, and is not easy to rust and deform during use. However, if the material quality is poor or impurities are mixed in, it will cause cracking during welding.

From the perspective of welding process, inappropriate welding parameters, uneven heating speed, and lack of proper cooling conditions may all lead to cracking. Stress caused by thermal expansion and contraction during stainless steel welding is also one of the main causes of cracking. The heat capacity and thermal conductivity of the material will also affect the stress of welding. If the temperature and stress distribution are not properly controlled during welding, welding cracking will occur.

The main components of steel are iron and carbon, but different types of steel also contain some other elements, such as manganese, silicon, etc. The content of these elements and the heat treatment method of steel will affect the properties of steel, and then affect its durability and tensile strength. A certain amount of one or more alloying elements must be added during the smelting of steel. After the material is formed, a simple heat treatment can be performed to obtain different microstructures, thereby changing the original properties of the steel; If the carbon content of steel is too high or the treatment method is improper, it will cause it to break easily.

The production process of steel will also affect its properties. If the temperature, cooling rate and other factors in the production process are not properly controlled, defects will occur inside the steel, making it easy to break. In addition, if there are defects or unevenness on the surface of the steel, it will also affect its service life and safety.


Because the defects generated during steelmaking and casting, especially concentrated defects (such as pores, inclusions, etc.) are extremely sensitive during rolling, and different changes occur between different furnaces of steel with the same chemical composition, and even in different parts of the same billet, thus affecting the quality of the steel.

1. The effect of too high zinc liquid temperature or too long zinc dipping time on the rough surface of the angle steel galvanized layer. The hot-dip galvanized angle steel will also appear rough due to slow cooling after being taken out of the zinc liquid, or the steel section is too thick, or the angle steel is stacked immediately without isolation after hot-dip galvanizing.

2. "Over-pickling" occurs during the pre-plating process, making the steel surface rough or producing bean marks, which is also one of the reasons for the rough surface of the workpiece after hot-dip galvanizing.

3. The surface of the steel used for hot-dip galvanized angle steel is originally rough and uneven, with rust pits or obvious rolling stripes. After hot-dip galvanizing, its surface is generally not as flat and smooth as before.

4. When the welder strikes the arc on the metal surface, the surface of the hot-dip galvanized angle steel will show rough defects, which will damage the protective film of the hot-dip galvanized angle steel.

The thickness of the zinc coating directly affects the roughness of the surface of the galvanized angle steel. When the zinc layer is thicker, due to the difference in thermal expansion and contraction between the zinc and the steel substrate, the zinc layer is prone to forming microcracks during the cooling process, resulting in a rough surface. This phenomenon is more obvious when the zinc layer is thicker.

During the hot-dip galvanizing process, the roughness of the surface of the angle steel will also be affected to a certain extent during the period from the time the angle steel is taken out of the zinc bath to the end of cooling. If the cooling process is too rapid, the atomic structure on the surface of the zinc layer cannot be completely smooth, resulting in a rough surface. In addition, if the angle steels are stacked together without being properly isolated after hot-dip galvanizing, the heat generated by friction will aggravate the roughening of the surface of the zinc layer.

In addition, the composition and surface conditions of the steel used also affect the roughness of the galvanized layer. Different steel compositions and surface treatment methods will result in different parameters such as the bonding strength and surface flatness of the zinc layer and the steel substrate, which will in turn affect the final appearance of the galvanized layer. Impurities such as scale and oil on the surface of the steel will increase the roughness of the zinc layer and affect its flatness.