Welding of Crane Rail Flat Steel and Q235 Steel
The fixing of the crane rail flat steel is not fixed by the common pressing plate, but the crane rail steel flat is welded to the bottom plate, and then the bottom plate is bolted to the upper steel structure of the slow cooling pit, so that the crane rail flat steel can be fixed to the upper steel structure of the slow cooling pit. The higher carbon equivalent causes strong harden tendency of the workpiece during the rapid cooling process after welding, and a hard and brittle martensite structure appears in the heat affected zone of the base metal, especially near the weld line. Under the action of welding stress, the tensile strength of the hard and brittle martensite structure is exceeded, causing it to crack and generate cold cracks. Welding of crane rail flat steel and Q235 low carbon steel belongs to dissimilar steel welding. Q235 steel is a kind common carbon structural steel with good weldability. The crane rail flat steel is usually high carbon steel, and the hot shadow area after welding is prone to cold cracks. Therefore, the welding of the crane rail flat steel and the Q235 low carbon steel is mainly to solve the problem of cracks generated after the welding of the rail heat affected zone. According to the general welding specifications, for the welding of carbon steel of different strength grades, the welding material should be selected to ensure that the tensile strength of the weld metal, which should be higher than or equal to the lower limit of the parent metal standard on the lower strength side.
Before welding, the rust, oil, moisture and other impurities within 50mm on both sides of the weld should be removed. For electrode arc welding, the electrode needs to be baked at 350°C for 1 hour, and it can be used as needed. For CO2 gas shielded welding, it is necessary to put the CO2 gas cylinder upside down and drain the water in the bottle to check that the dryer is in good condition. Before welding, the crane rail flat steel side was heated to 350°C with an oxyacetylene flame within 100 mm, and the temperature was measured by the temperature measurement ratio. Then welding should be according to certain parameters, continuous welding is to ensure that the interlayer temperature is not less than the preheating temperature. After welding, the weld bead and the side of the crane rail flat steel base material should be slowly cooled with aluminum silicate fiber felt immediately. After cooling to room temperature, the weld should be inspected, and after the coloration flaw detection, no cracks were observed in the arc welding of the electrode. However, there was crack in the middle of the arc-welding section of the first weld side with the CO2 gas shielded welding. On the second day of the arc welding of the electrode, crack was found in the heat-affected zone on the side of the rail appeared crack along the fusion line. After the arc welding of the electrode, there is a delayed crack in the heat affected zone of the rail. It may be because of the uncomplete slow cooling after welding. After the welding, the aluminum silicate fiber felt does not completely wrap the crane rail flat steel, and the martensite structure is hardened in the heat-affected zone, and steel rail cracks under the welding stress. The CO2 gas shielded welding heat is concentrated, the heat affected zone is narrow, and the hardening tendency is small, so there is no crack in the heat affected zone of the rail. However, for the welding lines s on both sides of the crane rail flat steel, cracks appear in the middle of the weld side of the former welding, which is caused by the simultaneous weld lines welding of the welds on both sides. When the first weld side weld is not completely crystallized, the other side begins to weld. Under the welding stress of the back weld side, the weld on the weld side is not completely crystallized and cracked, so that cracks will not appear in the middle of the welding line.
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