Is medium carbon steel difficult to weld? How should it be welded?

Is medium carbon steel difficult to weld? How should it be welded? Medium carbon steel refers to carbon steel with carbon content of 0.25% ~ 0.60%, including 30, 35, 45, 50, 55 and zg230-450, zg270-500, zg310-570, zg340-640 and other steel grades in cast carbon steel. Because the carbon content of medium carbon steel is higher than that of low carbon steel, its weldability is worse than that of low carbon steel. When the mass fraction of carbon is close to 0.30% and the content of manganese is not high, the weldability is good, but with the increase of carbon content, the weldability gradually becomes significantly worse. When the mass fraction of carbon reaches about 0.50%, the weldability obviously becomes worse. A, welding carbon steel easy problems and technological measures The problems that may occur when welding medium carbon steel are as follows: 1. Cold crack problem Due to the high carbon content of steel, it is easy to produce hard and brittle martensite structure in heat affected zone during welding, so cold cracks are easy to occur. If the welding material is not chosen properly or the welding process is not designed properly, the welding seam is also easy to produce cold crack. 2. Hot crack problem During welding, after the base metal with high carbon content is melted, carbon will also be brought into the welding seam to increase the carbon content in the welding. Carbon can aggravate the role of sulfur and phosphorus in metal to cause thermal crack. Especially when the content of sulfur and phosphorus in the base material or welding material is not strictly controlled, it is more likely to produce thermal cracks. In addition, high carbon content in steel also increases the tendency of CO porosity in welding joints. Process measures Due to the defects of cold crack, hot crack and so on, it is necessary to take some special technological measures to weld medium carbon steel. 1. Welding method Various arc welding methods can be used for welding medium carbon steel. As medium carbon steel is used for manufacturing machine parts, not large welding structure, so the most widely used welding rod arc welding method in production. 2. Welding materials In order to prevent cold and hot cracks in welded joints, low hydrogen electrode is usually used in arc welding. Low hydrogen welding rod not only makes the content of hydrogen in the weld lower, but also has a certain desulfurization, phosphorus, can improve the plasticity and toughness of the weld. When the carbon content in the steel is low and the joint constraint is not large, can also use ilmenite type or titanium calcium type electrode welding, but must take strict technical measures, such as reducing the fusion ratio, strict preheating of welding parts and control the temperature between layers. If the welding parts cannot be preheated, chromium-nickel austenitic stainless steel electrode may also be used for welding. For example, e308l-16 (A102), e308l-15 (A107), e309-16 (A302), e309-15 (A307), e310-16 (A402), e310-15 (A407), etc. 3. Preheating temperature and interlayer temperature Preheating before welding is the most effective method to prevent cracks in medium carbon steel. Preheating can not only reduce the cooling rate of joints, thus preventing the formation of martensite, but also reduce welding stress and accelerate the diffusion and escape of hydrogen. Most of the time you need to warm up and maintain the temperature between layers. The preheating temperature and interlamination temperature are determined by the carbon equivalent of the steel, the thickness of the base material, the rigidity of the structure, the type of electrode, etc. The preheating temperature can be determined by the weldability test, or by the empirical formula T0=550 (c-0.12) +0.4 delta, where T0 represents the preheating temperature (℃), C represents the mass fraction (%) of the welded base material, and delta represents the steel plate thickness (mm). 4. Groove type It is better to open u-shaped or v-shaped groove, which can reduce the proportion of base metal into the weld. If it is welding to repair the casting defect, the groove shape should be smooth, so as to reduce the amount of base material into the weld. 5. Welding parameters Welding should adopt dc reverse polarity power supply. In multi-layer welding, as the proportion (mass fraction) of base material dissolved into the first layer of weld can be up to about 30%, it is advisable to use small diameter electrode, small current, slow welding speed welding. 6. Post-welding heat treatment After welding, stress relief heat treatment should be carried out immediately. Especially for large thickness welding parts, large rigid structure parts and welding parts working under dynamic load or impact load. Stress relief tempering temperature is generally 600 ~ 650℃. If stress relief heat treatment cannot be carried out immediately after welding, post-heating, i.e. heating slightly higher than the preheating temperature, shall be carried out for approximately 1h per 10mm thickness. Typical medium carbon steel welding process compilation 35 steel and zg270-500 cast carbon steel The mass fraction of 35 carbon steel is 0.32% ~ 0.39%, and that of zg270-500 cast carbon steel is 0.31% ~ 0.40%. The carbon equivalent is about 0.45%, so the steel is weldable. However, it is possible to produce hard and brittle martensite structure in the heat affected zone during welding, which tends to crack. 1. Selection of welding materials When welding rod arc welding, E5016 (J506) or E5015 (J507) welding rod can be used for welding when the strength of welding seam and base material is required. When the strength of weld and base metal is not required, welding electrodes such as E4316 (J426), E4315 (J427), E4303 (J422) and E4310 (J423) can be used. For submerged arc welding, flux HJ430 and HJ431 can be used. Welding wire can choose H08MnA, H10Mn2, etc. When electroslag welding, flux can choose HJ430, HJ431, HJ360; Welding wire can choose H10Mn2, H08Mn2Si, H08Mn2SiA, etc. 2. Preheating temperature and interlayer temperature When welding 35 steel and zg270-500 cast steel, the preheating temperature and interlayer temperature of welding parts are usually about 150℃. When the rigidity of welding parts is relatively large, the preheating temperature and interlayer temperature should be increased to 200 ~ 250℃. The heating range of local preheating is 150 ~ 200mm on both sides of the groove. 3. Post-welding heat treatment For welding parts with large thickness, large rigid structure and welding parts with dynamic load or impact load, stress relief tempering should be carried out immediately after welding. Tempering temperature is generally 600 ~ 650℃. For welding parts of normal thickness, post heat can be used to allow hydrogen diffusion to escape. The post-heating temperature is generally 200 ~ 350℃, and the insulation time is 2 ~ 6h, depending on the thickness of the welding parts. 45 steel and zg310-570 cast carbon steel The mass fraction of 45 steel carbon is 0.42% ~ 0.5%, and that of zg310-570 cast steel carbon is 0.41% ~ 0.50%. The carbon equivalent is about 0.56%, the tendency of quenching is relatively large, easy to crack, poor weldability. 1. Selection of welding materials When welding electrode arc welding, try to choose low-hydrogen electrode, when the requirement of welding seam and base metal strength, can choose e5516-g (J556), e5515-g (J557) electrode; E4316 (J426), E4315 (J427), E5016 (J506), E5015 (J507), E4303 (J422), E4301 (J423) and other welding electrodes can be used when the strength of weld and base metal is not required. For submerged arc welding, the flux can be HJ350 or SJ101, and the welding wire can be H08MnMoA. 2. Selection of welding parameters Welding 45 steel and zg310-570 cast carbon steel, should choose a small welding current, to reduce the weld fusion ratio, reduce the amount of carbon in the base material to weld. 3. Preheating temperature and interlayer temperature Before welding this kind of steel, it is best to take the whole preheating, preheating temperature is above 200℃. For t-joint, because of more heat dissipation direction than the flat joint, it will lead to the welding joint cooling speed, increase the cold crack tendency, preheating temperature should be appropriately increased, preheating temperature is 250 ~ 400℃, depending on the thickness of the welding parts. The interlayer temperature should not be lower than the preheating temperature. 4. Post-welding heat treatment Stress relief tempering should be carried out immediately after welding, tempering temperature is 600 ~ 650℃.铜焊丝,Copper Welding Rods,铝焊丝,aluminium welding wire,镍焊条,Nickel electrode,药皮焊条,Flux Coated Brazing Welding Rods