This paper presents the results of a study on a new coating method for alloy steel. The coatings were synthesized on the surface of H21 die steel through a combination of thermal-chemical treatment (TCT) and electron beam processing (EBP). A paste containing boron and aluminum was applied to the test samples which were then heated to accelerate the diffusion process. After 2 h at 950 °C, the diffusion layers were found to be 120 μm thick, and after 2 h at 1050 °C, they were 580 μm thick. The subsequent EBP led to a complete transformation of the primary diffusion layer and an increase in thickness to 1.6 mm. XRD analysis showed significant differences in composition before and after EBP and the presence of tungsten and iron borides. It was also found that the distribution of microhardness and composition over the layer thickness had a more favorable profile after EBP.

This work investigates the effect of boriding and thermo-reactive deposition on 15B30 steel. The results presented in the paper show that these thermochemical treatments produce boride and carbide rich layers that improve surface hardness and wear resistance, and they do so without the adverse effects of adding more boron to the alloy.

The AISI 440B (DIN 1.2210, X90CrMoV18) steel is one of the hardest among martensitic stainless steels. This type of steel is used in a variety of industrial applications where wear and corrosion are determinant, such as molds, parts and tools for the automotive and biomedical industries. Their superior mechanical properties are due to its high carbon (0.75-0.95 % C) and chromium (16-18% Cr) contents. Suitable coatings can increase wear resistance and expand these materials usability range. Boride coatings, with their high hardness and wear resistance are good candidates for this purpose. Boride layers were obtained by boriding treatment in a salt bath (a mixture of sodium borate and aluminum). The layer properties, such as hardness, thickness, layer/substrate interface morphology and phases formed are influenced by steel composition. In this work, the layers produced on AISI 440B steel were harder, thinner, with a smoother interface when compared to plain carbon steels due the larger amount of alloying elements. In order to evaluate mechanical properties of borided layers in samples of stainless steel AISI 440B, Optical Microscopy (OM) microstructural analysis, Vickers microhardness tests and micro-adhesive and micro-abrasive wear resistance tests were performed. The layers produced exhibited a hardness close to 2250 HV and excellent wear resistance far superior to that of substrate.

Ductile cast iron can be heat-treated to obtain a significant property improvement austempering, resulting in Austempered Ductile Iron (ADI). Performance can be further improved by using boronized surface layers which are capable of reaching high hardnesses (2100 HV). In this work, samples of nodular cast iron alloyed with copper, copper-nickel and copper-nickel molybdenum were borided in a salt bath (borax + aluminum) at temperatures 850, 900 and 950 °C for 2 and 4 hours. After these treatments, the samples were directly austempered from the boriding temperature in salt baths at temperatures of 240, 300 and 360°C (boroaustempering) which avoided the need for a subsequent reheating for such processing. The boriding treatment produced uniform layers with thicknesses in the range 35-130 micrometers and hardness in the range from 1300 to 1700 HV.

Boriding thermochemical treatment produces layers with high hardness which improves the tribological performance of ductile cast iron while the austempering treatment improves the mechanical performance of the substrate. In this work, samples of the ductile cast iron alloyed with copper, copper-nickel and copper-nickel-molybdenum were borided in a salt bath (borax + aluminum) at temperatures of 850, 900 and 950°C during 2 and 4 hours. The data for the layers obtained were used to determine the diffusion coefficients and activation energies of this process. The results of the calculated diffusion coefficients were similar to those obtained by the direct measurements of the layer thicknesses. For the sample alloyed with Cu or Cu-Ni the activation energy obtained was 141.27 kJ/mol, and for the sample alloyed with Cu-Ni-Mo the value was 212.98 kJ/mol. The statistical parameters and the correlation coefficients (R) showed satisfactory agreement.

The use of high hardness surface layers can extend the life of components such as molds and dies by increasing their wear resistance. However, corrosion and oxidation resistance are also important to improve the durability of the components, especially for those that work under more demanding environments. In this work, samples of AISI H13 tool steel for hot work were borided by the pack cementation process, producing uniform and high hardness layers (1400-1800 HV). Afterwards the samples were subjected to a quasi-isothermal oxidation testing at 550 °C, the same working temperature of H13 steel in aluminum extrusion dies. Throughout the test, the mass gain of the untreated substrate, used for comparison, was 100%, while the borided sample treated at 900 °C for 2 hours had mass gain of 83% and the sample treated at 1000 °C for 4 hours presented a mass gain of 43%. The oxidation coefficients of the borided samples were similar, indicating similar oxidation kinetics but different from the untreated substrate.