INFLUENCE OF THE STATE OF THE SUR-FACE ON THE DEFORMATION BEHAVIOR OF PRODUCTS AND IMPROVEMENT OF AUTO SHEET PRODUCTS FORMABILITY
Journal Title: Вестник Харьковского национального автомобильно-дорожного университета - Year 2018, Vol 82, Issue
Abstract
It is known that most of the destruction processes (wear, fatigue crack initiation, corrosion) start in the surface layer. This allows us to consider the surface of the loaded product as an independent sub-system, whose behavior in the deformation process differs from the inner layers and has a significant impact on the properties of the product as a whole. Basically, surface treatment serves as a way to im-prove special performance characteristics (wear resistance, fatigue strength, heat resistance, corrosion resistance, etc.). However, information on the effect of modifying thin surface layers on the behavior of the deformation and mechanical properties of products made of common structural steels is of undoubted interest. This work is devoted to studying the possibilities of solving the actual problem of increasing the strength of products while maintaining plasticity (structural strength), as well as im-proving the technological characteristics of their material by changing the surface state. To address this issue, the effect of cementation, nitrating and ion bombardment of the surface of steel samples (steel 20, 40X, 08кп) on their deformation behavior and change in tensile properties was investigated. In addition, the issue of the influence of the state of the surface layer on the technological plasticity of cold-rolled auto sheet steel 08кп, intended for the manufacture of products by the method of cold forging, was also studied. It has been established that cemen-tation always embrittles the product while maintain-ing a viscous and plastic core. In nitrated specimens, the nature and magnitude of the effect of a change in tensile properties depend on the layer thickness. With a shallow depth of the layer (0.08 mm), the strength increases while maintaining high ductility. A layer thickness of 0.25 mm or more leads to a de-crease in strength, loss of ductility and brittle frac-ture. Ion bombardment is a very effective way to in-crease the structural strength and reliability of products - with increasing strength, an increase in plasticity of 2 or more times is provided. A signifi-cant improvement in the formability of 08кп cold-rolled steel was also found (the ГВ category, provided for it by GOST 9045-93, is increased to the requirements of the higher category of ВОСВ, recommended for more ductile and cleaner steel by 08U). The advantage is that an improvement in the ability to stretch is achieved not due to the softening of the sheet, but on the contrary, with increasing strength and resistance to destruction. Such effects cannot be obtained by any method of volume processing. It is important to conclude that changes in the defor-mation behavior and mechanical properties are not obtained by changing the material properties of products, but under the influence of the state of the surface layer.
Authors and Affiliations
І. V. Doschechkina, І. S. Tatarkina, V. V. Ozarkiv
Keywords
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- EP ID EP474114
- DOI 10.30977/BUL.2219-5548.2018.82.0.20
- Views 86
- Downloads 0
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