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QU80 Crane Rail Welding Material and Welding Process


QU80 Crane Rail Welding Material and Welding Process
Since the shape of the end face of the QU80 crane rail is complicated, the welding of the QU80 crane rail waist and the QU80 crane rail top needs to be continuously performed. Such welding method is completely different from the slag removal of each section of the welding. It requires the viscosity of the slag of the electrode to be small at a high temperature and the specific gravity should be small. The slag is not easily wrapped in the weld metal during welding, and the slag floats in the separation of the liquid metal. According to the characteristics of this process, the previous slag system was adjusted to improve the alkalinity of the slag, appropriately increase the content of Mn in the alloy composition, and improve the process performance of the electrode.
Before welding, the electrode is dried at 350 ° C – 400 ° C. Place the electrode in the insulated tub before use. The material of the QU80 crane rail is U71Mn, and the QU80 crane rail has a certain difference from the shape of the rail. The width of the rail top is relatively thick, and the slag is not easily removed during welding. At the beginning of the test, the middle of the rail waist or the lower corner of the rail head often showed no penetration. Sometimes, slag inclusions will appear in these areas. In order to solve this problem, the electrode strip formulation was further improved, and the mold was modified to increase the thickness of the inner wall of the mold. During welding process, the welding current of the rail waist is increased from 180A to 200A. When the welding enters the top of the rail, the welding current should be correspondingly small to prevent the base material at the top of the rail from overheating, and at the same time, the weld bead is fine and the surface is well formed. The time to solder the entire joint is approximately 30 minutes. The QU80 lifting rail is high carbon steel with a carbon content of 0.65%-0.77%. The welding performance is poor. In order to prevent quenching structure or martensite in the near seam area of the rail, the welding of the lifting rail must be heat treated. Preheating above 350 °C is necessary before welding to reduce the cooling rate of the weld zone and ensure the welding quality of the rail. The metallographic structure photograph was analyzed. The metallographic structure of the base metal was not pearlite, and the heat affected zone was not quenched. The main one was fine pearlite.
The static bending test of the actual butt joint was carried out on a 200-ton press. The test span was 1 meter and the top of the rail was facing upwards. A total of 5 tests were carried out, and the average result was 1112 KN. The fracture of the static bending specimen was examined, and as a result, no welding defects such as slag inclusions were found.

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