Sulfonitrocarburizing of High-Speed Steel Cutting Tools: Kinetics and Performances.

Mihai Ovidiu Cojocaru,Leontin Nicolae Druga,Mihai Branzei,Cosmin Mihai Cotrut,Ioana Arina Gherghescu,Mariana Ion,Sorin Ciuca

doi:10.3390/ma14247779

Mihai Ovidiu Cojocaru, Leontin Nicolae Druga + Show 5 more

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https://doi.org/10.3390/ma14247779

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Abstract

The scholarly literature records information related to the performance increase of the cutting tools covered by the superficial layers formed “in situ” when applying thermochemical processing. In this context, information is frequently reported on the carbamide role in processes aiming carbon and nitrogen surface saturation. Sulfur, together with these elements adsorbed and diffused in the cutting tools superficial layers, undoubtedly ensures an increase of their operating sustainability. The present paper discusses the process of sulfonitrocarburizing in pulverulent solid media of high-speed tools steel (AISI T1, HS18-0-1) and its consequences. The peculiarity of the considered process is that the source of nitrogen and carbon is mainly carbamide (CON2H4), which is found in solid powdery mixtures together with components that do not lead to cyan complex formation (non-toxic media), and the sulfur source is native sulfur. The kinetics of the sulfonitrocarburizing process, depending on the carbamide proportion in the powdered solid mixture and the processing temperature, was studied. The consequences of the achieved sulfonitrocarburized layers on the cutting tools’ performance are expressed by the maximum permissible cutting speed and the maximum cut length. An interesting aspect is highlighted, namely the possibility of using chemically active mixtures. Their components, by initiation of the metallothermic reduction reaction, become able to provide both elements of interest and the amount of heat needed for the ultrafast saturation of the targeted metal surfaces.

Highlights

When operating the cutting tools in an extremely complex state of stress, defined as contact stresses of the order of gigapascals and more, at the cutting edge, the pressure required for the deformation and cutting of the processed material is at a high level.Gheller [1] states that the level of contact stress between the active part of the tool and the workpiece can exceed 4 GPa in the cutting process
Applying thermochemical treatments to the cutting tools obviously leads to an increase in their working performances, as expressed among other parameters by the maximum permissible cutting speed and by the maximum cut length
Perfectly adherent and dimensionally uniform and within dimensional limits and phase compositions, as is recommended for T1

Summary

Introduction

When operating the cutting tools in an extremely complex state of stress, defined as contact stresses of the order of gigapascals and more, at the cutting edge, the pressure required for the deformation and cutting of the processed material is at a high level.Gheller [1] states that the level of contact stress between the active part of the tool and the workpiece can exceed 4 GPa in the cutting process. Sergheicev and Pecicovski [2], referring to high-speed steels (HSSs), indicate that they have a special behavior during the processing of steels with ultimate strength over 1 GPa, or austenitic steels, which are difficult to process. Under these conditions, the cutting edge is subjected to multidirectional compression, unevenly distributed, generating tangential stresses, which engender much more plasticlike states for these parts of the tool material when compared to their initial state. At very high values of these stresses and especially in situations where their presence is accompanied by local heating, the deformation of thin surface areas can be recorded (even for materials with low plasticity, with a martensitic structure and high proportion of carbides, as in the case of HSSs) [1,2,3].

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