Weldability of seamless carbon steel pipe raw materials

According to the design requirements, the welding method of the welding material under the specified structural conditions of the component, and has the ability to meet the predetermined service requirements. Influenced by four factors: welding material, welding, component type and application requirements.

Mild Steel Seamless Carbon Steel Pipe Welding
Due to the low carbon content, manganese and silicon content of low carbon steel, there is usually no serious quenching structure or structure during welding. Low carbon steel welded joints have good plasticity and impact toughness, generally do not need preheating for welding, control the temperature and heat between layers, the use of post-weld heat treatment does not improve the structure, the whole process does not need to take special welding process measures, weldability.

Medium carbon steel seamless pipe welding
The carbon mass fraction of medium carbon steel is 0.25% to 0.60%. When the mass fraction of carbon and manganese is close to 0.25%, the content is not high, and the weldability is good. As the carbon content increases, the weldability becomes progressively worse. If the carbon content is about 0.45%, and according to the welding process used to weld low carbon steel, brittle martensite may be generated in the heat affected zone, which is easy to crack, that is, cold cracking. During welding, a certain amount of base metal melts into the weld, which increases the carbon content in the weld and promotes hot cracks in the weld, especially when sulfur impurities are strictly controlled. This crack is more sensitively distributed at the crater, the heat distribution in the weld is cracked and scaly, so the wavy line is perpendicular to the weld.

High carbon steel welding
When the carbon content of high carbon steel is greater than 0.60%, the sensitivity of welding cracks after quenching is relatively large, so the weldability is poor and cannot be used to manufacture welded structures. Parts that are more commonly used in the manufacture of hardness or wear resistance are required, and the welding work is mainly welding repair. Since the high tensile strength of carbon steel is mostly above 675MPa, the electrode types E7015 and E6015 are commonly used. When the member's requirements are high, the electrode structure of E5016 and E5015 can be used. In addition, we can use chromium-nickel austenitic steel electrodes for welding. In order to obtain high hardness and wear resistance of high carbon steel parts, the material itself needs to be heat treated, and annealing treatment should be carried out before welding. Preheating should be carried out before welding. The preheating temperature is generally above 250 to 350 °C, and the temperature of the insulation layer during the welding process should not be lower than the preheating temperature. After welding, the weldment needs to be slowly cooled and heated, and immediately sent to a 650 ℃ furnace for stress relief heat treatment.

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