Guangzhou Steel News: slab steel welding crack control measures
A large slab of steel components, steel thick weld deposit large, complex nodes, residual stress, prone to crack, affecting the quality of welding, which is important and difficult project quality control. Production of general measures are:
1, measures to prevent hot cracking
1) Control of the chemical composition of the weld. I.e. to reduce the low-melting eutectic composition readily segregation elements, such as sulfur and phosphorus content in the welding material and the base material is formed. Reduce the carbon content in the steel, can reduce the thermal cracking tendencies; improve Mn content can improve weld thermal cracking performance.
2) control of welding parameters and conditions. Control of welding current and welding speed, so that the aspect ratio of each cross section of the upper part of bead reach 1.1 to 1.2, can improve thermal cracking performance, while controlling the weld pool shape, do not form easily understood in sharp elongated bath a longitudinal weld surface thermal cracks. Preheat reduces tendency to form cracks; reasonable welding sequence can make the most of the weld at the smaller restraint of welding, reducing the tensile stress suffered weld shrinkage, thermal cracking tendency can be reduced.
2, cold cracking prevention measures
1) Before welding procedure qualification test performed to determine the process parameters.
2) preheat prevents cracking, as well as improve the performance of a certain action.
3) manual welding using low hydrogen electrodes alkaline E5Q / E55 type; CO: gas shielded arc welding flux cored wire can be used; a H08MnA submerged arc welding can be used F5021, and in strict accordance with the provisions drying. Drying temperature is 350-450 ℃, after dried at 100-150cC temperature for 1 ~ 2h, put insulation cylinder used with the check.
4) Choose a reasonable weld profile, in strict accordance with the drawings machining parts groove.
5) each side of the weld within the range of 30 ~ 50mm rust and water clean, reducing the source of hydrogen.
6) cracks often occur on the head welds and weld root, so tacking length, welding foot height and spacing should also make corresponding provisions. If you have to locate the weld in the groove proceeds, weld height should be less than 2/3 of the groove depth, the length should be greater than 40mm. If necessary, prior to tack welding is preheated. Before welding, positioning the weld inspection, it must be removed when re-welding cracks. Tack welding length and spacing, should be considered the base material thickness, structure length.
7) To reduce stress and prevent cracking during welding, the assembly should avoid forced assembly.
8) appropriate to increase the current, lower cooling rate, helps prevent the formation of hardened tissue.
9) Control interlayer temperature should be slightly higher preheat temperature.
10) Q345C soldering should be carried out after a slow cooling to slow cooling rate of the weld and heat affected zone and prevent cold cracking, respond promptly weldment insulation, that is immediately after welding weldment is heated to 250 to 350. And use of asbestos and other insulation 2.6h after air cooling can reduce the hydrogen content in the weld and prevent cold cracking, heating methods, with preheat before width.
While slab steel construction difficult, but as long as proper control measures, the proportion of component cracking will be greatly reduced, the project will significantly improve the quality of weld cracks will be avoided, it can effectively control the quality of construction industry. Guangzhou Steel
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