Gas Nitrided Steel Research Articles

Nitriding Effect on the Tribological Performance of CrN-, AlTiN-, and CrN/AlTiN-Coated DIN 1.2367 Hot Work Tool Steel

In this study, heat-treated and multisurface engineered DIN 1.2367 tool steel was subjected to room and elevated temperature wear tests, and the effect of nitriding on its tribological behavior was investigated. CrN, AlTiN, and CrN/AlTiN coatings with a total thickness of 2 µm were obtained by arc cathodic physical vapor deposition on conventional heat-treated and gas-nitrided steels. The white layer formed during nitriding was removed, and a diffusion layer (100 µm) was achieved in the cross section of the steel having a tempered martensitic matrix. The highest surface hardness was attained with an integral coating (CrN/AlTiN), and surface hardness increased even more after nitriding due to the formation of a multicomponent ceramic layer on top of the diffusion layer. The room temperature wear tests performed against an alumina counterpart revealed that (i) CrN/AlTiN-coated steel had the highest friction coefficient of 0.26, which further increased to 0.33 by nitriding due to the increase in shear strength, and that (ii) with increasing surface hardness, the specific wear rates (W) of the heat-treated and coated steels could be ranked as follows: WCrN/AlTiN < WAlTiN < WCrN. The wear rates decreased when nitriding was carried out prior to coating. In order to simulate the aluminum extrusion conditions, hot wear behavior of the surfaces against AA6080 alloy at 450 °C was investigated. The hot wear tests revealed that (i) high friction coefficients were reached due to the adhesive characteristic of aluminum to the surfaces, (ii) the nitrided and CrN/AlTiN-coated sample exhibited the lowest wear rate among all studied surfaces, and (iii) the film damage on the worn surfaces mostly occurred in the form of droplet delamination.

Competition between surface and subsurface rolling contact fatigue failures of nitrided parts: A Dang Van approach

Abstract Mechanical contacts in rolling element bearings and gears are increasingly loaded nowadays. In high temperature applications, surface treatments such as gas-nitriding are used to increase their rolling contact fatigue life. This study focuses on the prediction of the location of crack initiation for gas-nitrided steels subjected to rolling contact fatigue taking into account the material property gradients induced by the nitriding process. Several approaches based on the Dang Van criterion are compared to experimental data to find the most reliable prediction model.

Investigation of dissolution resistance of blank and gas-nitrided carbon steels in stationary SAC305 solder alloy melt

The objective of the present study is to investigate the suitability of a series of gas-nitrided steels with varying C content as candidates for wettable selective soldering tool materials with enhanced lifetime. ? and ?? iron-nitrides were formed by gas nitriding on quenched and tempered DC04, C45, CK60 and S103 type steels. Contact angle measurements revealed that all four nitrided steels exhibit good wetting with SAC305 solder melt. In order to investigate the dissolution reactions between the nitrided steels and the solder alloy, an equipment was assembled in which the samples were submerged into stationary SAC305 solder melt for different time durations. Evidences of dissolution reactions and other degradation processes were searched for using scanning electron microscopy and energy dispersive X-ray spectroscopy. It was observed that no Fe dissolution occurred between the samples and stationary SAC305 solder melt during continuous tests with durations up to 20 days. Furthermore, no other visible degradation reactions occurred between the samples and melt during the experiments. It was concluded that gas-nitrided steels show good wetting with Sn-based solder melts which is combined with excellent resistance against Fe dissolution in a high Sn-containing molten solder. Thus, gas-nitrided steels/iron can be potential materials for wettable selective soldering tools with improved lifetime.

Microstructure and wear resistance of gas-nitrided steel after laser modification

Purpose: The aim of this work was to study the microstructure and wear resistance of hybrid surface layers, produced by a controlled gas nitriding and laser modification. Design/methodology/approach: Nitriding is well-known method of thermo-chemical treatment, applied in order to produce surface layers of improved hardness and wear resistance. The phase composition and growth kinetics of the diffusion layer can be controlled using a gas nitriding with changeable nitriding potential. In this study, gas nitriding was carried out on 42CrMo4 steel at 570°C (843 K) for 4 hours using changeable nitriding potential in order to limit the thickness of porous e zone. Next, the nitrided layer was laser-modified using TRUMPF TLF 2600 Turbo CO2 laser. Laser tracks were arranged as the multiple tracks with scanning rate vl=2.88 m/min and overlapping of about 86% using the two laser beam powers (P): 0.21 kW and 0.26 kW. Microstructure was observed by an optical microscope. Phase composition was studied using XRD. Hardness profiles in the produced hybrid layers was determined using a Vickers method. Wera resistance tests were performed using MBT-01 tester. Findings: Gas nitriding resulted in formation of compound zone, consisting of e nitrides close to the surface and a zone, composed of e + g' nitrides. Below the white compound zone, the diffusion zone occurred with nitric sorbite and precipitates of g' nitrides. In the microstructure after laser heat treatment (LHT) of nitrided layer, the zones were observed as follows: the re-melted zone (MZ) with e nitrides, nitric martensite and non-equilibrium FeN0.056 phase, the heat-affected zone (HAZ) with nitric martensite and precipitates of g' phase and the diffusion zone (DZ) without visible effect of laser treatment. Laser beam power influenced the depth of MZ and HAZ, so the thickness of hardened zone. The hardness of MZ was slightly decreased compared to the hardness of compound zone after gas nitriding. However, the significant increase in hardness was observed in HAZ. The formation of hybrid layers advantageously influenced the tribological properties. The laser-heat treated nitrided layers were characterized by improved wear resistance compared to the only gas-nitrided layer. Research limitations/implications: The effect of LHT on the microstructure and properties of gas-nitrided layer was limited to the two laser beam powers. In the future research, this range should be exceeded, especially, taking into account the lower values of laser beam power. It will result in laser modification without re-melting. Practical implications: The selection of suitable LHT parameters could provide the hybrid layers of modified microstructure and improved wear resistance. Originality/value: This work was related to the new concept of modification of nitrided layer by laser heat treatment.

The influence of laser re-melting on microstructure and hardness of gas-nitrided steel

Abstract In this paper, modification of nitrided layer by laser re-melting was presented. The nitriding process has many advantageous properties. Controlled gas nitriding was carried out on 42CrMo4 steel. As a consequence of this process, ε+γ’ compound zone and diffusion zone were produced at the surface. Next, the nitrided layer was laser remelted using TRUMPF TLF 2600 Turbo CO2 laser. Laser tracks were arranged as single tracks with the use of various laser beam powers (P), ranging from 0.39 to 1.04 kW. The effects of laser beam power on the microstructure, dimensions of laser tracks and hardness profiles were analyzed. Laser treatment caused the decomposition of continuous compound zone at the surface and an increase in hardness of previously nitrided layer because of the appearance of martensite in re-melted and heat-affected zones

Dry rolling-sliding wear of austempered cast iron

In the present investigation, the dry rolling-sliding wear of two austempered ductile irons (ADIs), characterized by different hardness values, was investigated. The tests were carried out using disks with 40 mm diameter and 10 mm height. The applied load was in the range between 50 and 500 N. Since the initial Hertzian pressures were quite large because of the line contact, a plasticity dominated wear with the formation of delamination was obtained. Therefore, the treatment cycle of some specimens was conducted with the aim of obtaining a mild wear during rolling-sliding through the formation of a surface oxide layer. As a comparison, the dry rolling-sliding wear of a gas nitrided steel was also investigated. The results show that the wear coefficients of the specimens with the oxide layer on their surface was actually mild. However, the specimens produced without such a layer displayed even lower wear coefficients. Although wear was by delamination, wear coefficients were still low because of the action of graphite, which was able to squeeze on the surface during sliding, thus reducing adhesional forces. In addition, a mechanically mixed layer formed on the sliding surfaces, and this provided an additional increase in the wear resistance. Because of this, the material with lower matrix hardness displayed a greater wear resistance. The wear resistance of the nitrided steel was found to be determined by the outer part of the compound layer, and it was found to be lower than that displayed by the two ADI.

Effects of Testing Temperature and Sliding Speed on the Wear Behavior of a Low Alloy Gas Nitrided Steel

Effects of wear testing temperature and sliding speed on the wear behavior of nitrided and untreated 31CrV3 steel were investigated. The specimens were tested at wear testing temperatures of 25°C and 500°C under a normal load of 15N at a sliding speed of 1m/s. The increase in the wear temperature from 25°C to 500°C led to a decrease in the wear rate and coefficient of friction of the nitrided steel samples. At 25°C, the wear resistance of the nitrided steel improved by 2.3 times compared to the untreated specimen. There was about 57 times improvement in wear resistance as the wear temperature increased to 500oC for the nitrided specimen. Scanning electron micrographs showed that the formation of compact and protective oxide layers on the worn surface of the nitrided steel was responsible for the improvement in the tribological behavior of nitrided steel at elevated temperatures. The effect of sliding speed on the wear of the samples was further tested at 500oC under a normal load of 15N at sliding speeds of 0.5 and 1.5m/s. The results showed that there was higher wear resistance at lower sliding speeds.

Influence of cold-work on the cavitation erosion resistance and on the damage mechanisms in high-nitrogen austenitic stainless steels

► Cold-rolling greatly improves the cavitation-erosion resistance of high temperature gas nitrided fully austenitic UNS 31803 stainless steel, when compared to the simply high temperature gas nitrided steel. ► Cold-rolled and recrystallized high temperature gas nitrided random textured fully austenitic UNS 31803 stainless steel specimens, showing a random texture are less cavitation-erosion resistant than the strongly (1 1 0) // surface textured as nitrided specimens. ► Cavitation-erosion damage in the cold-rolled specimens initiates mainly at coherent grain boundaries and slip lines initiation is rarely observed. ► Variations of the stacking fault-energy, grade of short range ordering and mechanical twinning are discussed as possible mechanisms of enhancing the cavitation erosion resistance of the cold-worked high temperature nitrided UNS 31803 stainless steel. UNS S31803 duplex stainless steel specimens, 1.5 mm in thick, were high temperature gas nitrided (HTGN) in order to obtain a 0.9 wt% N, through the thickness fully austenitic microstructure with increased cavitation-erosion (CE) resistance. The microstructure of the as received UNS S31803 duplex stainless steel consists of ferrite + austenite stringers (50% α + 50% γ). HTGN was performed at 1200 °C for 8 h, in a 0.1 MPa N 2 atmosphere, followed by direct quench in water. A fully austenitic microstructure, 330 HV 0.1 hard, containing 0.9 wt% N in solid solution, was obtained. Part of the specimens were 30% cold rolled and part of the specimens were annealed after cold-working, obtaining cold worked and recrystallized specimens. All the specimens, including the as received UNS 31803 duplex steel, were tested in a 20 kHz vibratory cavitation erosion testing equipment. The HTGN specimens showed lower CE wear rates and higher incubation times, when compared to the as received condition. The 30% cold worked HTGN specimens showed the greatest increase in incubation times and greatest decrease of cavitation wear rates. The recrystallized specimens showed lower CE resistance when compared to HTGN samples. The difference was attributed to development of a sharp {1 0 1}//surface texture during HTGN, which was weakened after recrystallization. The mechanisms responsible for the improvement of CE performance are discussed.

High temperature tribological behaviour of 31CrMoV9 gas nitrided steel

In the present study, high temperature tribological behaviour of gas nitrided 31CrMoV9 steel was investigated. Gas nitriding was carried out in ammonia gas atmosphere at 520°C for 24 h. The wear behaviour of the specimens was studied using a high temperature pin on disc wear tester at 25, 300 and 500°C. The results showed that the wear resistance of the nitrided steel improved by 1·8fold compared with the untreated specimen at room temperature. The wear tests at 300°C and notably at 500°C showed much better improvements in wear behaviour of nitrided steel by about 3·6- and 33fold respectively. Scanning electron microscopy study of worn surfaces indicated that the formation of solid compact layers was responsible for the higher wear resistance of the gas nitrided samples at higher temperatures.

The potential of plasma electrolytic oxidized eutectic aluminium-silicon alloy as a cylinder wall surface for lightweight engine blocks

A series of tests was conducted using a reciprocating tribometer to evaluate the tribological performance of a plasma electrolytic oxidation (PEO) treated eutectic aluminium-silicon alloy and was compared with a more conventional nickel-ceramic (Ni-SiC) coating as a reference. The counterpart was a gas-nitrided steel top piston ring and the lubricant was a group III base oil blended with standard detergent and dispersant additives, both with and without dispersions of very fine particles of molybdenum disulphide as a friction modifier. Scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, and stylus profilometry were employed to characterize the morphology, elemental composition, and surface force analysis of the tribofilm and the wear profile. The tribological performance of the PEO transformed surface was found to be similar to the Ni-SiC coating in the short-duration tribometer experiments undertaken with fully flooded lubrication and at low-speed conditions, with potentially greater durability in the longer term given the properties of the transformed surface layer.

Mechanical, tribological and electrical properties of gas nitrided steel: A.Salek et al. (Ustav Materialoveho Vyskumu SAV, Kosice, Czech Republic.) Pokroky Pras. Metal., vol 35, no 4, 1997, 47–56. (In Czech.)

Mechanical, tribological and electrical properties of gas nitrided steel: A.Salek et al. (Ustav Materialoveho Vyskumu SAV, Kosice, Czech Republic.) Pokroky Pras. Metal., vol 35, no 4, 1997, 47–56. (In Czech.)

Wear mechanism map of nitrided steel

Wear maps for untreated and gas nitrided BS970,905M39 (EN41B) steels have been constructed, which show the dominant wear mechanism regimes. The wear studies were carried out using a pin-on-disc machine under unlubricated conditions over a wide range of sliding speed and applied load, and the wear mechanisms were determined by examination of the worn specimens and wear debris. A sharp wear rate transition between mild (oxidative) and severe (metallic) regimes was identified for both untreated and gas nitrided steels. Gas nitriding expanded the mild wear region toward higher loads and sliding speeds.