An important problem when
welding z-direction steel is that during the welding process, due to the low cooling rate of the weld heat-affected zone, it is easy to form a coarse-grained martensite structure during the crystallization process, which makes the steel brittle during welding. The tendency to produce cold cracks increases. Therefore, in the z-direction steel welding process, t8/5 must be strictly controlled, that is, the heat-affected zone of the weld, especially the weld fusion line, must be cooled from 800 degrees Celsius to 500 degrees Celsius.
If the cooling time is too short, the hardness of the
weld fusion line is too high, and hardening cracks are easy to appear; if the cooling time is too long, the critical transformation temperature at the fusion line will increase, reducing the impact toughness value. , The organization of the material changes. The occurrence of these two situations directly affects the quality of the welded joint. In order to prevent cracks, z-direction steel should be heated and preheated. An important issue that should be paid attention to during the welding process is the temperature control measures between the weld layers. If the temperature between layers is not controlled, multiple thermal strains will appear in the weld area, resulting in residual stress that is detrimental to the quality of the weld. Therefore, in the z-direction steel welding process, the interlayer temperature must be strictly controlled.
How to control the interlayer temperature?
The temperature between layers is generally controlled between 200-250℃. In order to maintain this temperature, z-direction steel is required to complete one continuous welding operation during welding. The temperature measurement method is the same as preheating temperature measurement. When the component is longer, the cooling rate of the z-direction steel is faster during the welding of the z-direction steel, so the pre-heating temperature is always maintained during the welding process to prevent the drop of the interlayer temperature caused by the rapid cooling after welding. It is also possible to cover the insulation board immediately after welding to prevent the temperature of the welding area from cooling too quickly.
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