Interrupted boriding of medium-carbon steels

Abstract

The results of an extensive study on the microstructure, microhardness, corrosion, and tensile properties of continuously borided and interrupted borided specimens of medium-carbon steel are compared. Carbon repartitioning away from the surface is one of the principal modes to accommodate the high strains introduced on boron diffusion into the case. However, this is a kinetically constrained process and is more predominant on interrupted boriding. The effect of such a carbon redistribution is to result in microstructural modifications including (1) blunting of boride needle tips, (2) precipitation of nearly spherical and fine borocarbides, and (3) enhanced carbon segregation at the boride needle/ steel matrix interface on interrupted boriding. The mechanisms aiding the change in the morphology of the boride needles are discussed. The improvements in the mechanical and corrosion properties of the interrupted borided specimens over continuously borided specimens are described.

Solidification and phase formation of alloys in the hypoeutectic region of the Fe–C–B system

“…The thermodynamic data of the relevant phases -liquid, c-Fe, Diffusion of carbon and boron in the Fe 3 (C,B) and Fe 2 B phases is neglected because it is several orders of magnitude lower compared to the diffusion of both metalloids in the iron lattice [15,23,24]. Values of surface energy and interfacial mobility were taken from the literature [25][26][27].…”

“…Borides and carboborides with increasing B content are preferable with respect to hardness and elastic modulus as compared to carbides and thus decrease the abrasive wear rate [2,8]. Applications can be found in white cast iron [9,10], deposition welding [2,11,12], thermally sprayed coatings [13,14], and surface boriding [15].…”

Abrasive wear resistance of boronized carbon and low-alloy steels

“…In gas nitriding, the outermost sublayer (FeB) can be transformed into the ductile Fe 4 N phase, whereas the innermost sublayer (Fe 2 B) can be transformed into the Fe 4 N and B 25 N phases. Recently, Gopalakrishnan et al [12] showed that if boronizing is performed by cyclically interrupting the process, a change in the morphology of the typical boride needles is produced and an improvement in some mechanical properties (toughness and ductility) is obtained.…”

Laser modification of detonation-gun sprayed ferro-boron coatings on AISI 304L SS

“…All these properties offer great potential for developing protective boride coating so as to delay failure of metallic surfaces under severe wear, erosion and corrosion. Thermo chemical boriding is a well established technique for surface modification of steels [3], resulting in the formation of hard surfaces due to the formation of FeB and Fe 2 B phases in the case. However a major limitation of thermo chemical boriding is that it is a high temperature process and the maximum coating thickness is limited due to diffusion kinetic constraints.…”