When welding medium-carbon steel, how should one choose the appropriate welding electrode?
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Manual arc welding is currently the most commonly used method for welding medium-carbon steel. To improve the crack resistance of welded joints, low-hydrogen electrodes should be used. In some cases, titanium-calcium and ilmenite-type acidic welding electrodes can also be used, but strict process measures must be taken in such cases, such as preheating before welding and reducing the fusion ratio (to lower the carbon content in the weld). The selection of electrodes for manual arc welding of medium-carbon steel is shown in Table 6. Table 6: Selection of electrodes for manual arc welding of medium-carbon steelSteel grade of electrode, Carbon content (%) in workpiece, Mechanical properties of weld (≥), Selected electrode type, σs (MPa), σb (MPa), δ (%), ф (%), αK (J)
No requirement, Equal strength required, Equal strength
35: ZG270–500, 0.32–0.40, 0.31–0.40, Ordinary, Ordinary
315: 270, 530, 500, 20, 184, 5, 255, 5, 22
E4303, E4301; E4316, E4315; E5016, E5015
45: ZG310–570, 0.42–0.50, 0.41–0.50, Poor, Poor
355: 310, 600, 570, 16, 154, 21, 39, 15
E4303, E4301; E4316, E4315; E5016, E5015; E5016, E5015
55: ZG340–340, 0.52–0.60, 0.51–0.60, Very poor, Very poor
380: 340, 645, 640, 13, 1035, 18, — 10
E4303, E4301; E4316, E4315; E5016, E5015; E5016, E5015
In special cases, chromium-nickel stainless steel electrodes can be used for welding medium-carbon steel, such as E0-19-10-16 (A102), E0-19-10-5 (A107), E1-23-13-16 (A302), E1-23-13-15 (A307), E2-26-21-16 (A402), E2-26-21-15 (A407), etc. Since the austenitic weld metal has good plasticity, it can reduce stress in the welded joint; even without preheating of the workpiece, cold cracks in the heat-affected zone can be avoided. This post was last edited by shi*qumi on 2008-3-3 22:05]
⑴Preheating helps to reduce the maximum hardness in the heat-affected zone of medium-carbon steel, thereby preventing the formation of cold cracks. It is a key process measure when welding medium-carbon steel; preheating also improves the ductility of the joint and reduces residual stresses after welding. Generally, the preheating temperature for 35 and 45 steel is 150–250°C. If the carbon content is higher, or if the thickness and stiffness are large resulting in a higher tendency to cracking, the preheating temperature can be increased to 250–400°C. If the welded piece is too large and overall preheating is difficult, local preheating can be employed; the heating area for local preheating should cover 150–200 mm on each side of the weld joint. ⑵Welding electrodes: Alkaline welding electrodes should be preferred when conditions permit. ⑶Groove shape: The welded parts should be prepared with a U-shaped groove as much as possible for welding. In the case of casting defects, the shape of the groove created by chiseling should be smooth; this is done to reduce the proportion of base metal that merges into the weld metal, thereby lowering the carbon content in the weld and preventing cracks from forming. ⑷Welding process parameters: Since the proportion of base metal that melts into the first layer of weld metal can be as high as around 30%, it is necessary to use a low current and a slow welding speed when welding the first layer, in order to reduce the depth of melting of the base metal. ⑸Post-weld heat treatment: It is advisable to carry out stress-relief heat treatment on the welded parts immediately after welding, especially for thick-walled parts, highly rigid structural components, and those that operate under severe conditions (such as dynamic or impact loads). The tempering temperature for stress relief is 600–650°C. If stress-relief heat treatment cannot be carried out after welding, post-weld heat treatment should be performed immediately.