The bucket body material of wY25 excavator is Q345, which has good weldability. The bucket tooth material is ZGMn13 (high manganese steel), which is single-phase austenite at high temperature and has good toughness and high wear resistance under impact load due to work hardening of the surface layer. But this steel weldability is poor: one is in the welding heat-affected zone precipitation of carbide caused by material embrittlement; second is the weld thermal cracking, especially in the near seam zone liquefaction crack.
1. heat-affected zone precipitation carbide caused by embrittlementZGMn13 high manganese steel may precipitate carbide along the grain boundary when it is heated again more than 250 ℃, so that the toughness of the material is greatly reduced and the excellent performance of high manganese steel is seriously damaged. After analysis, when the high manganese steel is heated again and the cooling speed is faster, carbide will first precipitate at the grain boundary, and with the extension of the residence time, the carbide at the grain boundary will change from discontinuous particle state to mesh distribution, and its brittleness will increase significantly. Therefore, when the high manganese steel in welding or reheating after welding, will be in the welding heat-affected zone of a section of the precipitation of carbide to varying degrees, and may be martensitic transformation, not only make the material brittle, but also reduce its wear resistance and impact toughness. And, in the heat-affected zone easy to precipitate carbide temperature range (650 ℃ or so) the longer the residence time, the more carbide precipitation. In order to reduce the precipitation of carbide and prevent the material from losing toughness and becoming brittle, measures should be taken to accelerate the cooling rate, that is, to shorten the residence time at high temperatures. For this reason, the excavator bucket body and bucket teeth welding to use short section welding, intermittent welding, soaking water welding, etc.
2. Welding thermal crackingPrevent thermal cracking is to reduce the content of S and P in the base metal or weld material; can also take measures to minimize welding stress from the welding process, such as the use of short section welding, intermittent welding, dispersion welding and hammering after welding. In the bucket body overlay welding high manganese steel, you can first weld a layer of Cr-ni, Cr-ni-Mn or Cr-Mn austenitic steel for isolation welding channel, can prevent cracking.
Excavator bucket body and bucket teeth welding process
1. Preparation before weldingFirst of all, remove the worn bucket teeth from the bucket body, and then use the angle grinder to polish the installation of the bucket teeth clean, no mud, rust, and carefully check whether there are cracks and other defects; open the bevel with carbon arc gas planer at the bucket teeth to be welded, and clean up with the angle grinder.
2. Welding① first in the bucket body (and the bucket tooth joints) with GBE309-15 welding electrodes for overlay welding, welding electrodes need to be 350 ℃, 15h drying before welding, welding current should be large, welding speed is slightly slower to ensure that the fusion zone nickel content of 5% to 6%, to prevent the production of crack-sensitive martensite.② Conduct positioning welding. After the bucket teeth are assembled in place, D266 welding rod with a diameter of 32MM is used for symmetrical positioning welding on both sides, the length of the weld does not exceed 30MM. water cooling and hammering immediately after welding.③Bottom welding. Use 32MM diameter D266 welding rod for bottoming welding. Use low current, DC reverse polarity, intermittent welding.
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