Mass cracking of precision piston rod occurred in processing. The cracking reason of precision piston rod was tested by watching the fracture morphology, metallographic testing, mechanical property testing and SEM analyzing. Its crack property is brittle cracking of induction layer in the process of straightening. The cause of the straightening cracking is that the speed of moving the product in the Induction heating and quenching is discordant. And it leads to the appearance of soft bands in the hardened layer, making the fluctuation range of surface hardness and hardened layer greatly exceed the standard requirements, and the soft band area is in the state of residual tensile stress, and cracks are initiated under the action of straightening stress.
As a kind of carbon steel, 45 steel has wide controllable range of hardness and good comprehensive performance after quenching and tempering. However, due to the general quenching performance, it is often necessary to carry out high frequency or flame surface quenching, so that high surface hardness and good core toughness can be matched. For example, the "high hardness" after phenomenon high-frequency quenching, the surface hardness is up to 62 ~ 66HRC, the wear resistance and fatigue resistance of the workpiece is greatly increased, the notch sensitivity is quite small. So that this kind of process is often used in crankshaft and precision piston rod type components.
