Wear Performance Under Dry and Lubricated Conditions of Post Boriding Heat Treatment in 4140 Steel

The tribological performance of borided, post borided heat-treated and uncoated 4140 steel, under dry and lubricated conditions, was studied. The boriding process was conducted by powder-pack method at 900 °C with 1 h of exposure time. After boriding, a heat treatment (quenching and tempering) was conducted to obtain a hardened core microstructure of the 4140 borided steel. The tribological tests were performed with an Al2O3 ball of 6.35 mm of diameter, setting sliding distances of 25, 50, and 100 m. The loads used were 20 and 40 N in dry and lubricated conditions, respectively. Overall samples, the coefficient of friction was reduced around five times when lubricant was used, in comparison to dry tests. After 100 m of sliding distance, it was observed that the wear resistance increased around ten times with boriding. The dry results showed that borided (B) exhibited better wear-rate kB = 7.06 × 10−7 mm3 N−1 m−1 than borided and heat-treated (BHT) kBHT = 9.93 × 10−7 mm3 N−1 m−1, attributed to its higher hardness. Nevertheless, the lubricated results showed that the surface characteristics of BHT improved its wear resistance kBHT = 5.25 × 10−8 mm3 N−1 m−1 over kB = 1.68 × 10−7 mm3 N−1 m−1 of borided only, because it permitted a better adsorption of the lubricant.

EFFECT OF INTERRUPTED BORIDING ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 16MnCr5 STEELS

The microstructure, microhardness and tensile properties of continuously borided and interrupted borided 16MnCr5 steel were compared. In the continuous process, boriding was carried out continuously at 1273[Formula: see text]K for 16[Formula: see text]h. In the interrupted process, after 5[Formula: see text]h of boriding at 1273[Formula: see text]K, the crucible containing the specimens and the boriding powders was removed from the furnace and cooled to 873[Formula: see text]K in still air for 30[Formula: see text]min and this procedure was repeated three times. Both boriding treatments were achieved in a solid medium using the powder pack method with commercial Ekabor-I powders as the boron source. X-ray diffraction studies indicated the presence of FeB and Fe2B phases in the boride layers for both boriding treatments. The transition zone was more pronounced in the continuously borided steel. The average hardness values of the boride layers were 1759 and 1648[Formula: see text]HV0.1 for the continuously borided and interrupted borided steels, respectively. The hardness of the boride layers were considerably higher than the 200[Formula: see text]HV0.1 hardness of the untreated steel. No significant difference in tensile properties could be observed between the two different boriding procedures.

Laser borided composite layer produced on austenitic 316L steel

Abstract Austenitic 316L steel is well-known for its good resistance to corrosion and oxidation. Therefore, this material is often used wherever corrosive media or high temperatures are to be expected. The main drawback of this material is very low hardness and low resistance to mechanical wear. In this study, the laser boriding was used in order to improve the wear behavior of this material. As a consequence, a composite surface layer was produced. The microstructure of laser-borided steel was characterized by only two zones: re-melted zone and base material. In the re-melted zone, a composite microstructure, consisting of hard ceramic phases (borides) and a soft austenitic matrix, was observed. A significant increase in hardness and wear resistance of such a layer was obtained.