Thursday, 30 August 2018

Effect of cryogenic treatment on case-hardening steels


Process alternatives to optimize their final properties

Induction hardening faridabad
In the field of Induction Hardening in Faridabad, it is usually considered that cryogenic temperatures are those below 120 K (-153°C). Consequently, conventional subzero treatments, often referred to as shallow cryogenic treatments and usually performed at temperatures around -80°C, cannot be regarded as real cryogenic processes.

Cryogenic temperatures couldn’t be achieved until the late 19th century and, therefore, the emergence of cryogenic treatments in industry is relatively recent. The development of this technology has been based mainly on empirical results. The basic research of the transformations produced in the materials when exposed to cryogenic temperatures is usually conducted with significant delay with regard to development of practical applications.

In general, cryogenic treatments have been considered as separate operations, added to the conventional heat treatments. This is something that has conditioned the development of knowledge in this field, and also the reliability of the results obtained with these processes. Maybe this happens because, very often, this technology is used in tools and finished components, without paying much attention to the previous operations. This approach doesn’t enable a good control over the process results since these depend on the material history before the cryogenic treatment. And, obviously, the previous heat treatments play a crucial role.

In this regard, the consideration of cryogenic treatments as independent operations is a mistake. The right way to contemplate them is not as a supplementary step, but as an integral part of the overall heat treatment process. Only in this way its full potential will be exploited, selecting the route that is most adequate in each Case Hardening in Faridabad depending on the material considered and the application in which it will be used.
Induction hardening faridabad

We will try to illustrate it with an example. Let’s consider a case hardening steel like 18NiCrMo5, which is commonly used in applications where high yield strength and good wear resistance are required (shafts, gears, cams, etc.). The heat treatment process of this steel starts with a cementation step in order to increase the carbon content in the surface of the component. The subsequent quenching, followed by a tempering cycle at not more than 200°C, provides a very hard surface while the core remains soft and tough.

When considering the cryogenic treatment of a component made of case hardened steel, two basic strategies could arise. One is to apply it to the already heat treated part, that is, after tempering. The other one is to perform the cryogenic process after quenching but before tempering.

Several investigations focused on studying the effects of cryogenic treatments in this steel grade have been carried out in recent years, but the results seem confusing and sometimes even contradictory. Actually, this happens because in most of these studies only one of the two approaches has been considered, not taking into account that the results that are obtained with each of the treatment strategies are significantly different.



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