Nitriding of Long-Term Holes in the Cyclic-Commuted Discharge

Abstract

The effect of anhydrous nitriding in a glow discharge on microhardness, phase composition, and wear resistance of long holes in steels C45, 37Cr4, and 41CrAlMo7 with direct current supply and in cyclically switched discharge (CSD) was studied. Nitriding was carried out on a UATR-1 anhydrous nitriding unit with a discharge chamber diameter of 400 mm and a working height of 700 mm. Anhydrous nitriding in a glowing discharge was carried out at a temperature of 560 °С, a voltage of 730 V, a pressure in the chamber of 120 MPa, and the nitriding duration was 6 h. It was established that using holes with a relatively small diameter of glow discharge in a cyclically switched discharge for nitriding creates conditions for obtaining modified layers with higher physical, mechanical, and tribological characteristics. The results of microhardness measurement and their comparison with X-ray phase analysis data confirm the formation of ε, γ, and α phases during nitriding along the entire height of the samples placed in the experimental model. The tests carried out in the dry friction mode showed an increase in the wear resistance of samples made of steel C45, 37Cr4, and 41CrAlMo7 during nitriding in a cyclically switched discharge. To achieve 100 μm wear of 41CrAlMo7 steel during nitriding in CSD, 1400 m of friction path and 1000 m – during nitriding with direct current is required. It was established that using long holes of a glow discharge with different types of power for nitriding creates conditions for obtaining modified layers with variable characteristics. Nitriding of holes with a relatively small diameter of a glow discharge with a different power supply creates conditions for obtaining modified layers with different physicomechanical and tribological characteristics.

Diffusion Nitride Coatings for Heat-Resistant Steels

“…Oil is used as a quenching medium for the hardening of small parts with a section of up to 5 mm made of carbon steel and large diameter parts made of alloy steel. For AISI A290C1M steel, oil is used as a cooling medium, as oil reduces defects from cracks [27,28].…”

Physicochemical Conditions of Boron–Siliconizing of Molybdenum-Based Alloys in Chlorine and Fluorine Medium

“…Research on alloys based on refractory metals, such as molybdenum, is of active interest due to the possibility of manufacturing parts from them that operate at temperatures above 1300 • C. However, molybdenum undergoes severe destruction at temperatures above 730 • C [1]. The problem of increasing heat resistance is solved in several ways: by alloying alloys with elements that can form stable, protective films during oxidation [1][2][3][4], by applying protective coatings [5][6][7], or by a combined method. The most promising and realistic way to solve the heat resistance problem is using coatings.…”

“…The most promising and realistic way to solve the heat resistance problem is using coatings. The most common type of high-temperature protective coatings are coatings with the participation of silicon, the high heat resistance of which is explained by the ability to form a surface oxide film based on SiO 2 [1,[5][6][7].…”