There are two 35CrMo steel forged high-speed gear. One part is machined smaller during the processing, and the outer circle has been rough-machined. It is necessary to build-up welds with a width of 15mm and a height of 10mm. During surfacing welding, first preheat with oxyacetylene flame for about 1.5 hours, and preheat temperature is about 300 degrees. It is necessary to heat frequently during surfacing welding to prevent the temperature of the workpiece from dropping too much. Due to other reasons after surfacing, the workpiece was placed in the electric furnace three days later to eliminate the stress. After finishing, it was found that there were four transverse cracks on the processed surface, about 16mm in length, and the shape of the four cracks was similar, basically distributed symmetrically along the circumference. Use a milling machine to mill the crack (approximately 3mm at the weld penetration depth to remove all cracks). After analysis, the crack may be caused by welding stress not being eliminated in time, or it may be caused by uneven temperature during preheating.
The other gear forging blank was found to have surface cracks after rough machining. The cracks were about 80mm long. The cracks were also milled with a milling machine. When surfacing again, the box furnace is used to preheat the workpiece to 350C, heat preservation is 2.5h, and then the surfacing welding is performed. After welding, the workpiece is placed in the electric furnace to eliminate the welding stress. After finishing inspection and visual inspection and ultrasonic flaw detection, no defects were found in the gear, and its quality fully meets the requirements.
It can be seen that when surfacing 35CrMo steel gear forging blanks with larger dimensions, it is necessary to pay attention to the uniform preheating temperature and to eliminate welding stress in time after welding.