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Abstract
The longitudinal cracks on the surface of high-alloyed steel ingot are serious defects not only affecting the quality of steel, but also the quality of the products machined by the steel. The surface of the product has a significant effect on the performance of the product. Therefore, the quality of a steel ingot affects not only its own performance but also the performance of the products machined from it. The quality of high-alloyed steel ingot relies on the technological parameters of smelt and rapid cooling as well as various process factors. This article focuses on the study of the effect of longitudinal cracks on the surface of high-alloyed steel ingot.
High-alloyed steel is a kind of high grade steel which contains a certain amount of special alloy elements, such as chromium, molybdenum, and vanadium, etc. Compared with common carbon steel, it has higher hardness and strength, and better wear and corrosion resistance. Therefore, it has a wider range of applications, especially in the field of mechanical parts. In order to ensure its excellent performance, during the process of smelt and rapid cooling, we should also pay attention to the quality of steel ingot produced. When the Ingot surface has longitudinal cracks, it will affect the size and performance of the product.
The reason why high-alloyed steel appears longitudinal cracks is mainly because of the defects of cooling rate and unreasonable process parameters, thermal stress, and segregation in the smelt, as well as the effect of the friction on the surface of the steel. Generally speaking, the rapid cooling speed of steel ingot is too high, and the accumulated thermal stress will cause the cracking of long and shallow transverse cracks on the surface of the steel. In addition, the unreasonable process parameters and segregation in the smelt will also result in heavier long cracks.
Longitudinal cracks will seriously affect the size and performance of the products machined from high-alloyed steel ingot. The surface of the machining product will be uneven and rough, and the profile and tolerance of the product may not meet the requirements. Besides, the fatigue strength of the product may be also lower significantly, as the cracks are in favor of the propagation of the stress concentration cracks.
To prevent the longitudinal crack, the smelt process should be improved and rationalized. The smelt parameters take into account the segregation of alloy elements, and the cooling device should also be applied reasonably so that the cooling rate can be controlled, in order to reduce the concentrated thermal stress as much as possible. To reduce the friction between the surface of steel and the mold material, antirust oil should be used for the protection of cooling.
The study and improvement of smelt parameters should be the foundation for improving the quality of the steel ingot and the performance of the machined products. Besides, it is feasible to use ultrasonic crack detection to screen out the products with longitudinal cracks. In addition, it is necessary to do the thorough annealing to the steel with longitudinal cracks in order to reduce and eliminate this defect, which can ensure that the mechanical properties and size accuracy of the products can meet the requirements of the application.
In summary, the longitudinal cracks on the surface of high-alloyed steel ingot are serious defects, which will not only affect the quality of the products machined from the steel, but also the performance of them. Through comprehensive consideration of the smelt process and selection of materials for high-alloyed steel ingot, the reasonable process parameters can be set to prevent the occurrence of longitudinal cracks.
