Papers by Keyword: Nitriding

Abstract: The effect of surface roughness of virgin specimens (prior roughness) made of low-alloyed high strength steel on their fatigue life after the case-hardening treatment was studied by rotating bending tests of virgin and nitrided samples. In a whole range of S-N curves, the fatigue strength of virgin samples after lathe-turning machining (high roughness) was naturally much higher than that of samples after grinding (low roughness). As expected, the fatigue strength of nitrided specimens was higher than that of virgin samples when averaged through the whole fatigue life range. When distinguishing the rough and smooth nitrided samples, the low-cycle fatigue strength of rough samples revealed to be lower than that of the smooth ones and vice a versa in the high-cycle region. This could be explained by the fact that, in the low cycle region, the cracks in the rough samples nucleated from deep surface defects while, in the smooth specimens, they nucleated from shallow defects (or as fish eyes) which prolonged their initiation stage. Almost all cracks in the high cycle region initiated as fish-eyes but the extent of nitrided layers in the rough specimens was slightly higher than that in the smooth specimens. Therefore, the fish-eye centers were shifted further to the interior of the rough specimens which increased their fatigue life.

Abstract: TC4 titanium alloy was treated by ion nitriding. The structure of nitriding layer was analyzed by scanning electron microscopy. The depth and microhardness of nitriding layer were measured. The frictional properties of titanium alloy before and after nitriding were compared by friction test. The results show that the ion nitriding technology can form a stable nitriding layer with a depth of up to 20μm and a surface hardness of 560 HV0.2. At the same time, after nitriding, the wear resistance of the titanium alloy surface is improved. And the coefficient of friction between the friction pair is reduced.

Abstract: Die soldering is a sticking phenomenon between molten aluminum with the surface of steel die in the die casting process, which results in damage to the cast products and l the steel die. In this research, two die materials, H13 and Cr-Mo-V steels were used. Those dies were then treated by two process variables, shot pinning and nitriding-shot pinning. To simulate the die casting process, the samples were dipped into molten Aluminum-Si alloy, ADC12 at 680oC for 30, 300, and 1800 seconds. Characterizations were focused on the surface of the steel, which includes microstructure observation by a microscope, microhardness profile, compound identification, and weight loss measurements. It was found that H13 steel and Cr-Mo-V steel treated by nitriding–shot pinning have higher hardness up to 100% and thinner intermetallic layer. On H13 steel, the compact layer thickness decreased from 19 μm to 17 μm and from 96 μm to 80 μm for the broken layer. Similar trends occurred for Cr-Mo-V steel, where the thickness of the compact layer and broken layer decreased from 38 μm to 19 μm and 119 μm to 45 μm respectively. These results indicate that H13 and Cr-Mo-V steels that were treated by nitriding–shot pinning have a better resistance to die soldering.

Abstract: This work provides the results of research of the wear resistance of the surface of samples of low carbon structural of 18HN3MA-SH steel, subjected to electrolytic-plasma treatment by nitriding and carbonitriding. The effect of the structure on the surface wear resistance of steel is shown. Changes in abrasive wear and dry friction characteristics were studied depending on temperature and processing time. The results of studies of tribological tests show that after electrolytic-plasma nitriding, the wear resistance of steel 18HN3MA-SH increases by 1.5–2 times compared with the initial state. The observed effects can be explained by the flowing surface modification - the formation of a modified surface layer with the formation of hardening phases. The nature of changes in the surface roughness R_a of steel samples after cementation, carbonitriding and nitriding was studied.

Abstract: Nowadays there is a growing need to reduce or control wear, corrosion and fatigue in order to extend the lifetime of mechanical parts, to make engines and devices more efficient, to develop new advanced products, to conserve material resources, to save energy and to improve the safety. The surface properties of mechanical parts may be improved through Duplex treatments. A Duplex treatment is a sequence of two treatments, combining their advantages and leading to better surface properties. A Duplex treatment consisting in nitriding and work hardening through shot peening has been chosen as a solution for improving the properties of EN 34CrNiMo6 alloyed steel. This paper reports the results obtained for hardness and bulk modulus on treated and untreated samples. The samples were examined using a Dynamic Ultra Micro Hardness (DUH) tester under a set of maximum loads ranging from 100 to 1000 mN. Each sample was subjected to load-unload cycle under the same amount of maximum load and the loads vs. penetration depth curves were plotted. Results showed a better mechanical behavior of Duplex treated.

Abstract: N-Quench, which is a new surface heat treatment to infiltrate nitrogen into steel parts followed by quenching to achieve hardening, is gathering attention in the nitriding field as it affords low distortion while maintaining a higher effective case depth (ECD) compared with conventional nitriding. N-Quench is conducted mainly between 680°C and 800°C, where the two-phase region of ferrite and austenite exists in the Fe-N phase diagram. However, a few studies have reported on nitriding at temperatures higher than 800°C due to decomposition of NH₃, which is a key source of nitrogen infiltration. Our results revealed that in a conventional furnace such as resistance heating furnace, no nitrogen infiltrated the specimen at 930°C, which is the general carburizing temperature. On the other hand, in the infrared heating furnace, nitrogen infiltrated the specimen at 930°C successfully with lesser NH₃ introduction than that required by the conventional furnace. Therefore, in this study, the limit of NH₃ decomposition is assessed and possibility of extending the applicability of N-Quench, especially increasing the ECD while maintaining a low distortion, is examined.

Abstract: In this paper, we present the results of plasma nitriding treatments on austenitic stainless steel substrates previously coated with a patterned silicon oxide layer. For this purpose, masks were made by PECVD for the deposition of a silicon oxide layer on polished austenitic AISI 316L samples. For the final nitriding treatment, we used a multi-dipolar plasma providing independent substrate polarization. The interactions between expanded austenite and fixed silicon oxide mask in different shapes (circular and square dots) are observed by atomic force microscopy (AFM) on the same area before and after the nitriding treatment. After this thermochemical treatment, we obtain strong distortions of the dots, in particular at the edges of the larger size dots. The role of elastic deformation, due to the expanded austenitic phase formed by the diffusion of nitrogen under the mask is of primary importance.

Abstract: The influence of nitriding temperature (900 and 850°C) and partial pressure of nitrogen (10⁵ and 1 Pa) on morphology and phase structural state of modified surface layers of commercially pure titanium (cp-Ti) was determined. It was shown that nitrided titanium provided much better anti-corrosion protection than nitrided Ti-6Al-4V alloy, and its corrosion resistance increased with decreasing nitriding temperature and partial pressure of nitrogen.

Abstract: One of the most urgent problems of modern machine engineering is to increase the wear resistance of machine parts. The appearance of new technologies of parts strengthening treatment and improvement of the existing ones, especially the technologies based on thermochemical method, remain quite sought-after and are successfully used to improve the operational properties of the parts. Parts surface layer nitriding as the most common method of improving the service life and reliability of the modern machine parts got a new quality due to the use of ion-plasma processes. At the same time, the ever-increasing requirements for performance of machines and devices of different purposes, intensification and tightening of the conditions for their operation requires the creation of new nitriding technologies to provide a range of required properties of parts surface materials. This article is dedicated to the development and research of new nitriding technologies for alloyed steel parts. The aim of the proposed nitriding technology is to provide a composite layer combining high wear resistance and ductility of surface layer material. A feature of the nitriding technology is creating the conditions of processes of thermochemical treatment of parts, making it possible to form the islet nitrided layer.

Abstract: A sintered material based on pre-alloyed powders (Fe-Ni-Mo) is expansively applied in the automotive industry and Distaloy is today the most widely used raw material worldwide for the production of complex, precise, high strength PM machine parts. In this study a diffusion bonded powder type of Distaloy DC (Fe-2 wt. % Ni-1.5 wt. % Mo, Höganäs-Sweden) was used. It was alloyed by 0.5 and 1 wt. % silicon carbide with the addition of 0.6 wt. % lubricant in the form of introlube®. All the powder mixtures were compacted at 600 MPa, and then sintered for 30 min. in argon atmosphere at 1120° C. After the completed sintering process, the sintered alloy samples were gas-nitrided 1h at 490 °C and 6h at 540 °C, respectively, and cooled slowly to room temperature still under the ammonia atmosphere. The effects of varied amounts of SiC particles on the tribological behavior of nitrided-sintered Distaloy DC composites were investigated.