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The problem of batch cracking occurs in the production of precision piston rods. Experiments were conducted to investigate the cause of cracking in precision piston rods through observation of fracture morphology, metallographic examination, mechanical performance testing, and scanning electron microscopy analysis. Its crack nature is the brittle cracking of the induction layer that occurs during the straightening process, and the reason for the straightening fracture is due to the inconsistent movement speed of the product during induction heating quenching, resulting in the formation of soft bands in the hardened layer, greatly exceeding the standard requirements for surface hardness and fluctuation range of the hardened layer. The soft band area is in a residual tensile stress state, and cracks are initiated under the action of the straightening stress.
45 steel, as a type of carbon steel, has a wide controllable range of hardness after quenching and tempering treatment and good overall performance. However, due to its average quenching performance, it is often necessary to perform medium to high frequency or flame surface quenching, in order to achieve a combination of high surface hardness and good core toughness. For example, the "high hardness" phenomenon of high-frequency quenching can reach a surface hardness of 62-66HRC, which not only greatly improves the wear resistance and fatigue resistance of the workpiece, but also has less sensitivity to notches. This type of process is commonly used for crankshaft and precision piston rod components.