The Connection Between the Plasticity of Boronized Layers and the Mechanical and Exploitation Properties of Boronized Steels

Abstract

Boronized layers are a multi-phase system which can have different combinations of structural components (acicular, layered etc.) of different dispersability; their plasticity can broadly vary depending on the external conditions of processing and the type of material. The chapter analyzes the technological methods used to control mechanical and exploitation properties as well as the nature and formation patterns for most important characteristics of boronized layers: the hardness of homogeneous and heterogeneous layers; stress state after boriding and further thermal treatment; brittleness and its functional relation with microhardness; tribological properties with structural classification and usage recommendations in different conditions of wear; thermal fatigue and hear resistance which are necessary for improving the exploitation resistance of details and tools working in high-temperature conditions; corrosion and corrosion-mechanical properties providing the period of effective protection; mechanical and physical-mechanical properties. The chapter demonstrates the influence of different factors on the hardness values of boronized layers: the amount, size, form and mutual position of boride phases; texturedness and stress state of layer phases; the level of alloyness of the layer; the microstructure of sublayer and metal base. The methods used for calculating the microhardness of boronized layers with heterogeneous, eutectic and pseudo-eutectic structures are given. The authors suggest that the most favourable distribution of residual stresses in the boride layer is observed in one-phase structures. The level of residual stresses in boronized layers with composite structure is at minimum.