Engine crankshaft fillets intensify distortion defects, and super audio induction annealing equipment can easily deal with them.

The crankshaft is an important part of the diesel engine and is commonly made of QT600-3 ductile iron or 35CrNi3Mo steel or 35CrMo steel. When the crankshaft is working, it is subjected to alternating bending, torsional loads and certain impact loads. The failure form of the workpiece is mostly fatigue fracture failure, and the cracks mostly appear at the transition fillet between the journal and the crank arm. Therefore, in addition to improving the overall toughness of the workpiece and the fatigue strength of the workpiece surface, the heat treatment of the crankshaft must also focus on strengthening the crankshaft fillet and forming compressive stress on the surface of the fillet to improve its fatigue resistance. During production, it was found that due to the thermal stress and organizational stress generated during the heat treatment of the crankshaft, there are often machining residual stresses at the rounded corners of the crankshaft. The superposition of the above stresses at the rounded corners causes stress concentration in this part, which often becomes a source of fatigue cracks and occurs at the intersection. Under the action of variable bending, torsional stress and impact load, cracks expand rapidly, causing the crankshaft to break. When this stress is low and cracks have not yet occurred, the main manifestations are large distortion at the fillet and out-of-tolerance runout of the main journal. Since the rounded corners have been strengthened, cold straightening is very dangerous and may cause cracks or even cracking at the rounded corners. Therefore, on the one hand, an improved heat treatment process is used to reduce the deformation of the workpiece, and on the other hand, special methods are used to straighten the workpiece to eliminate distortion defects. The heat treatment process improvement measures to reduce and eliminate engine crankshaft fillet distortion are as follows:

(1) Stress relief annealing: Use ultrasonic annealing equipment to perform stress relief annealing heat treatment at 600-700°C.

(2) The crankshaft fillet should be straightened while rolling to ensure that the workpiece can expand and contract freely during rolling. For rolling correction, the rolling procedure and the rolling wheel angle should be reasonably designed to optimize the rolling and straightening effect. In addition, the rolling force and rolling times are reasonably designed to reduce deformation and achieve good straightening effects.

(3) Fillet quenching should ensure that the crankshaft can expand freely during heating, and should allow the crankshaft to contract freely during quenching and cooling. Appropriate parts should be selected for surface quenching. For example, the connecting rod journal surface and fillet surface are quenched at the same time, and the main journal surface is quenched. After that, the deformation of the workpiece can be eliminated by cold straightening method. In addition, the surface quenching sequence of each main journal should be designed according to the deformation law of the crankshaft, so that the deformations can restrain or offset each other, thereby minimizing the deformation of the crankshaft.