High temperature crack prevention measures are: stainless steel shower pipe 9312; optimize the chemical composition of the base metal and welding materials; ② optimize the welding conditions (to optimize the depth of penetration).Low temperature crack detection methods are RT (ray detection), UT (ultrasonic), MT (magnetic particle detection) and other methods. High temperature crack detection methods are PT (penetration detection), RT, UT, MT. In addition, the use of welding materials with excellent resistance to low temperature cracking is also effective for preventing low temperature cracks.What is the welding crack in the steel plate?Posted by seedsteelplate on May 22nd, 2017Welding cracks are the most dangerous welding defects, resulting in the results may be destructive, should be given special attention to be prevented. Reducing the contents of C, P and S in carbon steel and reducing the contents of C, P, S and Ni in low alloy steels are effective ways to prevent high temperature cracks.
Therefore, the hardening degree index carbon equivalent and the welding crack sensitivity index should be used. In addition, when the height (H) width (W) ratio (H / W) of the weld cross section is too large, the weld bead is pear-shaped, and high temperature cracks are liable to occur.High temperature crack is the weld metal at high temperature in the ductile state, can not bear the shrinkage stress, the occurrence of dendritic grain boundary, columnar crystal grain boundary separation openings. Welding cracks can be divided into low temperature cracks and high temperature cracks.After welding to the room temperature before the heat treatment after welding to remove the diffusion area of the welding area, but also to prevent low temperature cracks in the effective method. The # degree of hardening of the heat affected zone of the welding is greatly influenced by the chemical composition of the parent metal. Whichever method is used, since the low temperature crack is delayed crack, the detection time must be carefully determined so that the low temperature crack can be reliably detected.Cracks are generated when the following three conditions are superimposed, or when they are placed in these conditions for a long time: (1) the weld heat affected zone is high in hardness; (2) the weld metal contains a certain amount of hydrogen;
Low temperature crack prevention measures are to control the above three factors. For example,low-alloy heat-resistant steel, martensitic stainless steel welding, if the manual arc welding electrode re-drying is not sufficient, when the welding preheating temperature is too low, a few hours after welding to 2-3 days, often produce low temperature cracks The Among them, the low temperature cracks produced after welding for a long time are also called delayed cracks. In addition, Mn and S combine to form Mn sulfide, can reduce the adverse effects of S. If the base metal can not be selected, it is recommended to take the following measures when welding: ① preheat, the temperature of the inter-layer control, adjust the cooling rate, inhibit the hardening of the welding area; ② use low hydrogen electrode and flux.1) low temperature cracksLow-temperature cracks generally occur inhigh-strength materials, high-strength materials sometimes welded immediately after the occurrence of low-temperature cracks, but under normal circumstances, after welding for some time to produce low-temperature cracks, or called cold brittle performance.2) high temperature cracksA typical high temperature crack is a crack that occurs during the welding solidification process. For example, RT inspection of the spherical tank welds should be carried out at least 2 days after welding. C, P, S and other segregation coefficient is large, expand the brittle temperature range of elemental content is too large, prone to high temperature cracks
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