Causes And Improvement Measures Of Fastener Surface Quenching Crack

Fasteners are a kind of mechanical parts which are widely used for fastening connections. Fasteners are widely used in all walks of life. All kinds of fasteners can be seen in all kinds of machinery, equipment, vehicles, railways, etc. It is one of the most widely used mechanical foundation parts. Fasteners are characterized by a wide variety of varieties and specifications, different performance and uses, and their standardization, serialization, and universality is also very high. Failure of fasteners can cause serious effects. Therefore, we should strengthen the analysis of the causes of fastener failure, and find the corresponding improvement measures. Based on the knowledge of fasteners, Xinchi Fastener Company shares the causes of surface hardening cracks and improvement measures of fasteners.

Causes of surface hardening cracks of fasteners

A surface quenching crack refers to the crack produced in the process of quenching or in the process of placing at room temperature after quenching, the latter is also called an aging crack. In the quenching process, when the quenching stress is greater than the strength of the material itself and exceeds the plastic deformation limit, it will lead to cracks. The quenching crack is often produced shortly after the martensitic transition begins. The crack distribution does not have a certain rule but is generally easy to form in the workpiece sharp Angle, section mutation.

The quenching cracks caused by high quenching heating temperature are distributed along the grain, the crack end is fine, and shows the characteristics of overheating. Coarse acicular martensite can be observed in structural steel and eutectic or angular carbides in tool steel. The high-carbon steel workpiece with the decarburized surface is more likely to form mesh cracks after quenching. This is because the volume expansion of the surface decarburized layer during quenching cooling is smaller than that of the undecarburized core, and the surface material will be pulled and formed into a network by the action of the core expansion. The quenching crack on the surface will cause the bolt to break suddenly, and the fracturing source of such fracture is located on the surface.

Measures to prevent surface hardening cracks

By reasonably adjusting the clearance between the induction quencher and the workpiece, and selecting the appropriate intermediate frequency power supply parameters and quenching process parameters in strict accordance with the process requirements, the uniform temperature rises around the circumference of the product is guaranteed, so as to prevent the local temperature from being too high and exceeding the normal quenching temperature.

The structure of the quenching inductor can be improved by changing the round section structure of the upper and tail end of the inductor into a rectangular section structure. In this way, the heating speed of the end and tail inductor can be reduced to prevent the end and tail from heating up too fast, exceeding the process control temperature, overburning phenomenon, and resulting in cracks.

Reduce the number of quenched inductors in the transition area at the end of quenching, and appropriately reduce the heat there.

Adopt preheating – heating – cooling quenching mode, so that the heating temperature of the product is uniform.

The delay cooling time after intermediate frequency heating can be properly extended.

Implement self-tempering. The quenching coolant pressure, flow rate, temperature, and cooling time should be controlled reasonably and in strict accordance with the technical parameters. After the liquid injection is stopped, the residual heat of the workpiece is used to make the temperature of the hardened layer rise, so as to carry out self-tempering, in order to maintain high surface hardness and good wear resistance, the quenched structure can be stabilized in time, and the peak tensile stress can be reduced.

Xinchi Fastener Company is a trustworthy fastener company, especially in furniture nuts. And we are the designated fastener supplier to“STAPLE”. As a trusted fastener supplier,  Xinchi Fastener Company can offer a wide range of high-quality fasteners, including tee nuts, screws, bolts, rivets, washers, etc. If you want to know more about fasteners or want to wholesale fasteners, please feel free to contact us. And then our experienced and expert service team will reply to you as soon as possible.