Nitrided Steel Research Articles

Cathodoluminescence analysis of nonmetallic inclusions of nitrides in steel

Identification of nitride inclusions such as boron nitride (BN) and aluminum nitride (AlN) is important in the steelmaking industry because BN inclusions deteriorate the creep strength of ferritic heat‐resistant steel, and AlN inclusions cause transverse cracking in twin‐induced‐plasticity steel. The conventional method employed for the analysis of such inclusions in steel comprises both optical microscopy and electron probe microanalysis (EPMA), which is the time‐consuming. The aim of this study is to investigate the application of cathodoluminescence (CL) analysis (both images and spectra) to the rapid identification of BN and AlN inclusions. Measurement samples were prepared by heating mixtures of 99 mass% Fe and 1 mass% B or Al powders at 1550°C in a nitrogen atmosphere. BN inclusions larger than 5 μm and AlN inclusions 20 μm in size were identified within 1 second on the basis of their luminescence color (blue‐violet for BN and blue for AlN) in the CL images. We demonstrated that BN, AlN, and alumina inclusions could be identified from their CL spectra without the conventional method of EPMA. Capturing a CL image can provide a means of rapidly identifying BN and AlN inclusions in steel. We also carried out CL analysis on a sample containing TiN inclusions which can trigger cleavage fracture in low‐carbon steels. No luminescence was detected in the CL image, and there were no CL spectral peaks, indicating that it is difficult to apply CL analysis to the identification of TiN inclusions.

Microstructure and Nanosize Precipitate of Nitrided 316L Stainless Steel

The microstructure and nanosize precipitates of nitrided 316L stainless steel were investigated mainly by transmission electron microscopy (TEM) and X-ray diffraction analysis. Nitriding treatment performed in a molten salt bath followed by cooling down to ambient temperature and further diffusion treated. Produced layer consist of surface layer at the top, compound layer in the middle and final diffusion layer. Supersaturated phase is γ′N not γ-Fe4N. The lattice parameter of γ′N is expanded about 16% by nitrogen supersaturation. Precipitates size of few nm were observed in the compound layers. These nanosize precipitates were coarsening up to ~ 40 nm by further heat treatment at 450 °C for 1 h. It was identified as Si3N4 by energy dispersive X-ray spectrometer, selected area electron diffraction patterns at two different zone axes [110], [114] and high resolution TEM analysis.

The effects of the flow rate and speed of lubricoolant jets on heat transfer in the contact zone when grinding a nitrided steel

In this paper, the influence of lubrication parameters, such as flowrate and jet velocity, on the cutting fluid efficiency are studied. A foil/workpiece thermocouple and an inverse matching method are used to observe changes in the heat partition ratio, the heat flux absorbed into the fluid, the convection heat transfer coefficient (CHCT) and the maximum temperature in the contact area. Low jet velocity and flowrate tend to decrease the cutting fluid efficiency however excessive flowrate or jet speed in grinding are useless and do not lead to an extra decrease in the temperature of the grinding zone.The “burn out” phenomenon is also studied and the temperature at which it occurs is compared to the auto-ignition point of the cutting fluid. When burn occurs, the fluid no longer lubricates or cools the contact area. It allows an increase in the temperature in the grinding zone which may damage the microstructure of the workpiece, and produce distortions and cracks.

Effect of microstructure on mitigating tool wear in diamond turning of nitrided steels

Tools used in diamond turning of steels undergo severe tool wear. In this study, several steels were heat-treated and nitrided to investigate the wear mitigating effect of the microstructure of nitrided steels. The results indicate that the tool wear is mitigated with increase in the chromium content of steel. The results also indicate that chromium carbides are transformed into chromium nitrides by nitriding. Thermodynamic analyses demonstrated that chromium nitrides are stable when in contact with diamond at the cutting temperature. Further, the ratio of iron nitrides to iron increased because the iron levels decreased as the chromium levels increased. Although diamond reacts with iron nitrides, the interaction is considerably weaker than that with iron.

Tribological Properties of Nitrided Steels Lubricated with Fully Formulated Oils in Boundary Lubrication Condition

Tribological Properties of Nitrided Steels Lubricated with Fully Formulated Oils in Boundary Lubrication Condition

Replacement of Nitrided 33CrMoV Steel with ESR Hot Work Tool Steels for Motorsport Applications: Microstructural and Fatigue Characterization

In this work tensile strength, fatigue resistance and fracture toughness of two electroslag remelted (ESR) tool steels and of 33CrMoV12 ESR steel (both in quenched and tempered condition, as well as nitrided condition) were evaluated. The role of hardness, residual stresses and inclusion sizes on the fatigue behavior was investigated. Tool steels have a tensile strength between about 1900 and 2300 MPa, fracture toughness between 35 and 33 MPa√m, while fatigue strength ranges between 725 and 992 MPa. The tensile strength and fracture toughness of the 33CrMoV12 ESR are, respectively, 1365 MPa and about 150 MPa√m. Nitriding induces a significant increase in fatigue strength from 560 to 980 MPa. These results highlight that appropriate ESR tool steels could replace nitrided steels.

The effect of argon admixing on nitriding of plain carbon steel in N2 and N2-H2 plasma

The aim of this study is to assess the effect of argon gas (0–30%) addition in pure nitrogen and nitrogen‑hydrogen admixture on the surface properties of plain carbon steel by cathodic cage plasma nitriding. The surface hardness is obtained using hardness tester, phase composition is evaluated by X-ray diffraction, surface features are observed using scanning electron microscope (SEM) along with energy-dispersive X-ray spectroscopy (EDS) and wear rate is assessed using the ball-on-disc tester. Insignificant change in hardness is found in nitrogen plasma (with or without argon admixing), whereas it is expressively improved in nitrogen-hydrogen mixture plasma. The samples treated in nitrogen atmosphere mainly contains oxides, whereas iron nitrides in the nitrogen-hydrogen atmosphere, both with and without argon. The thickness of the modified layer is drastically changed with gasses composition, and the thick layer is achieved in nitrogen‑hydrogen admixture. The wear rate is also significantly improved while using nitrogen‑hydrogen mixture, and best results are achieved by using 20% argon in this mixture. This study reveals that although argon addition can enhance the reactive species production, however the presence of hydrogen is compulsory to improve the surface properties.

Influence of hydrogen content in working gas on growth kinetics of hardened layer at ion nitriding of 16MnCr5 and A290C1M steels

The impact of hydrogen content from 10 to 30% in the mixture of operating gas environment on the growth kinetics and structure of a hardened layer during ion nitriding of martensite and pearlite steels has been studied. It is stated that hydrogen in the vacuum chamber in the range from 10 to 30% contributed to a 1.2-time increase of nitrogen diffusion rate in 16MnCr5 steel and 1.3-time increase in A290C1M steel. The dependence of the hardened layer thickness and microhardness distribution over the depth on the gas environment composition is stated. The structure of the nitrided layer of steels at different hydrogen contents during ion nitriding is studied.

Nanoindentation study of layers after chemical –heat treatment of 27MnCrV4 steel

Nanoindentation testing is a method that consists essentially of touching the material of interest whose local mechanical properties as are hardness and elastic modulus are unknown. Nanoindentation testing is simply an indentation test in which the length scale of the penetration is measured in nanometres (10-9 m) rather than microns (10-6 m) or millimetres (10-3 m), the latter being common in conventional hardness tests. Both load and depth of penetration are recorded at each load increment (ultimately providing a measure of modulus and hardness as a function of depth beneath the surface). The method is most suitable for evaluating of mechanical properties of thin surface layer or particular microstructural constituents and phases. In this sense, there were evaluated nanoindentation hardness and Young modulus of some structural constituent on saturated layer after nitriding of the 27MnCrV4 cast high strength steel during the realized experiments.

Non-self-sustained low-pressure glow discharge for nitriding steels and alloys

Structural steel 40Cr and die steels 8Cr4W2MoVSi2 and Cr12Mo were nitrided in the plasma of a non-self-sustained hollow-cathode glow discharge at a pressure of 1 Pa, negative bias of 300 V, and temperature of 520 °C and 400 °C. The method has been shown promising for low-temperature nitriding of steels to a depth of several tens of micrometers with minimum tempering.

Damage evolution and rupture prediction of 42CrMoA nitrided steel by acoustic emission and infrared thermography techniques

ABSTRACTThe real-time monitoring and qualitative assessment of damage evolution of surface hardening materials is desirable, but still intractable, especially for quantitative evaluation. In this paper, the acoustic emission (AE) and lock-in infrared (IR) thermography techniques are used to assess the damage evolution of 42CrMoA nitrided steel. The acoustic and IR signals were experimentally obtained by the AE sensors and IR detector, respectively, with the sensors and detector distributed rationally during the fatigue test of sine amplitude loading. Based on the theory of discrete-time Fourier transform, fracture behaviours of nitrided steel are discriminated and confirmed by the fractograph. The results show that the formation of micro-crack, micro-void and dimple during the failure process are the sources of AE signal, and their influence effects are evaluated based on the energy of AE events that correspond to a certain frequency range. Also, the thermal dissipation behaviours of crack propagation are studied. The crack length is quantified based on the theory of grey level. The rupture time can be predicted by the burst AE or IR signals.

Wear of different material pairings for the cylinder liner – piston ring contact

PurposeThis paper aims to investigate the wear behaviour of different materials for cylinder liners and piston rings in a linear reciprocating tribometer with special focus on the wear of the cylinder liner in the boundary lubrication regime.Design/methodology/approachConventional nitrided steel, as well as diamond-like carbon and chromium nitride-coated piston rings, were tested against cast iron, AlSi and Fe-coated AlSi cylinder liners. The experiments were carried out with samples produced from original engine parts to have the original surface topography available. Radioactive tracer isotopes were used to measure cylinder liner wear continuously, enabling separation of running-in and steady-state wear.FindingsA ranking of the material pairings with respect to wear behaviour of the cylinder liner was found. Post-test inspection of the cylinder samples by scanning electron microscopy (SEM) revealed differences in the wear mechanisms for the different material combinations. The results show that the running-in and steady-state wear of the liners can be reduced by choosing the appropriate material for the piston ring.Originality/valueThe use of original engine parts in a closely controlled tribometer environment under realistic loading conditions, in conjunction with continuous and highly sensitive wear measurement methods and a detailed SEM analysis of the wear mechanisms, forms an intermediate step between engine testing and laboratory environment testing.

Influence of Hydrogen on the Ion Nitriding of Steels

We present the results of experimental investigations of the contact durability of specimens of different steels after ion nitriding in hydrogen and hydrogen-free atmospheres tested in the І-20 lubricant. The detrimental influence of hydrogen on the contact durability of steels in rolling friction is demonstrated.

Microstructure and mechanical properties from an attractive combination of plasma nitriding and secondary hardening of M50 steel

Microstructure and mechanical properties of a quenched M50 steel plasma nitrided for 8 h at temperatures ranging from 480 to 540 °C in a gas mixture of 25% N2 + 75% H2 were investigated in this paper. Results show that, compared with the original specimen, microhardness and wear resistance of M50 steel after nitriding treatment are remarkably improved at various temperatures, wherein the N500 specimen achieved the optimum combination of surface hardness (1186 HV), substrate hardness (643HV) and wear resistance (wear rate reduced by 90% more than original specimen). Such significantly improvement could mainly be attributed to the formation of nanophase FeN0.076, occurrence of further secondary hardening of substrate and generation of a nitrided surface layer of M50 steel during nitriding process. Two types of carbides, identified as MC and M6C, were found to be the stable precipitates present in substrate of N500 specimen. These results provide us with an attractive method of combining nitriding with secondary hardening to achieve a comprehensive performance from surface to substrate of M50 steel.

Preparation and characterisation of diamond-like carbon films prepared by MW ECR/PACVD process deposited on 41Cr–Al–Mo7 nitrided steel

ABSTRACTIn the present work, Diamond-Like Carbon (DLC) films were deposited by the Microwave Electron Cyclotron Resonance/Plasma-Assisted Chemical Vapour Deposition process on 41Cr–Al–Mo7 nitrided steel using a benzene–argon gas mixture. The quality of DLC films grown on nitrided steel using different deposit conditions such as benzene flow rate, temperature and time was investigated. Microstructural analysis by Raman spectroscopy showed main G-band peaks are localised between 1564 and 1595 cm−1, while the D-band peaks are centred at 1297 cm−1. Fourier Transform Infrared Spectroscopy showed the peaks attributed to C–H bending and stretching vibration modes are in the range of 2600–3100 cm−1. The microstructure, surface morphology and mechanical properties of the films were examined by X-ray diffraction, atomic force microscopy and use of a Vickers indenter (Zwick). The deposition parameters of the coatings have been studied and optimised to improve mechanical properties. The observed increase in adhesion is related to the formation of (Fe,Cr)3C, Cr3C2 and Cr23C6 interlayer phases. DLC films showed a better wear resistance, higher hardness and low friction coefficient compared to nitrided layers tested for comparison.

Corrosion and Wear Resistance of Plasma Nitrided and Duplex Treated 42CrMo4 Steel

Plasma nitriding is generally used as a final operation to improve wear, corrosion resistance and fatigue limit of machine parts. The corrosion and wear resistance of nitrided steels can be further increased by converse coating. This paper reports the results of corrosion and wear tests of plasma nitrided and duplex treated (plasma nitriding and manganese phosphate coating) 42CrMo4 steel. Plasma nitriding was carried out at 500 °C in different nitriding atmosphere ratio of 3H2:1N2 and 1H2:3N2 [l/h] for 15 hours. Plasma nitrided samples were subsequently manganese phosphated (without lubrication). The experimental samples were exposed to neutral sodium chloride solution, visually and gravimetric evaluated during exposure tests and after removing corrosion products. The wear test "ball on disc" was carried out at temperatures of 21 ºC, 150 ºC, and 300 ºC, under a load of 20 N. The results confirmed the possibility of applying manganese phosphate coating to plasma nitrided steel to enhance its properties. X-ray diffraction phase analysis found the different volumes of ε-Fe2-3N and γ'-Fe4N nitrides in the compound layers and hureaulite Mn5 (PO3 (OH))2 (PO4)2 (H2O)4 in the manganese phosphate coatings. The results were supplemented by metallographical documentation, thickness and microhardness test.

Method for Emissivity Estimation of Metals

Abstract Knowledge of the surface emissivity of metals is becoming more and more important both from the material science, process modelling and control point of view. Previous research results have shown that the emissivity of most metals depends on the temperature of the surface. It has also been reported that the most important temperature region is between 300 – 1000 K degrees, where the change of the emissivity is the most intense, which is also the most significant from a process control point of view [1]. We also report temperature dependent emissivity observed during plasma nitriding of low alloy steels [2]. Related to one of our present research topics the study of the low alloy aluminum (AlMg1, AlMg3) emissivity has prooven relevant. In this article the developed emissivity estimation model is presented. In the first part a literature overview and the theoretical approach of the new method is discussed, followed by the experimental results for low alloy aluminium emissivity determination and a comparison with the results available in the literature.

Fretting wear resistance of DLC hard coatings deposited on nitrided martensitic stainless steel

In this work, the fretting wear behavior and adhesion of DLC coatings deposited by PACVD on nitrided and non-nitrided martensitic stainless steels were studied. Fretting wear tests were carried out with different duration and loads and pin-on-disk was also performed. The adhesion was evaluated by Rockwell C indentation and scratch test with constant and variable loads. The coating thickness was 2.5μm and the nitrided layer, 11μm. The coating hardness and Young's Modulus were about 16 and 110GPa, respectively. The duplex samples resulted with better adhesion than the only coated samples in all test conditions. In the scratch test, the critical load in the duplex sample was 58N and in the coated sample, 12N, showing a brittle failure mode. In the Rockwell C indentation test, the adhesion was better in the duplex sample because the nitriding treatment changed the failure mode of the system. The wear resistance was also related to adhesion, since in the experiments with high loads and long durations adhesive failures could be detected when stresses reached the interface and the substrate. In the duplex sample, the nitrided case, with higher load bearing capacity than the substrate, resulted in a better wear behavior of the system.

Study of plasma nitriding and nitrocarburising of AISI 430F stainless steel for high hardness and corrosion resistance

ABSTRACTIn order to improve both the hardness and corrosion resistance properties of AISI 430F stainless steel, plasma nitriding (PN) and nitrocarburising processes were carried out at different temperatures ranging from 350 to 500°C for 4 h. After PN, the nitrided layer was found to be thicker compared to that obtained by plasma nitrocarburising process. There was an increase in microhardness values by a factor of six to seven compared to the plasma nitrided and nitrocarburised specimens respectively, treated at 500°C. The electrochemical corrosion behaviour of the plasma nitrided and nitrocarburised AISI 430F specimens show that the plasma nitrided and nitrocarburised specimens treated at 400°C for 4 h showed better corrosion resistance and higher surface hardness than the untreated AISI 430F stainless steel specimens. This is mainly attributed to the presence of nitrogen in the modified layer existing as a solid solution in the ferrite phase.This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).

Effect of Nitriding on Antibacterial Performance of 8Cr17 and 4Cr13 Martensitic Stainless Steel

Abstract Martensitic stainless steel is widely used for medical apparatus, but it can carry a large number of bacteria and cause a potential risk of infection because it has no antimicrobial ability. In this paper, nitriding of 4Cr13 and 8Cr17 martensitic stainless steel was conducted to improve the antibacterial activity. The surface morphology and phase constituents of nitrided 4Cr13 and 8Cr17 specimens were characterized using scanning electron microscopy and X-ray diffraction. Nitrogen concentration profiles in the cross sections of the nitrided specimens were obtained by glow discharge spectroscopy. The antibacterial properties of this nitrided layer were evaluated by a plate-counting method. The antimicrobial ratios of nitrided 4Cr13 and 8Cr17 martensite stainless steel against Staphylococcus aureus were 98.13 % and 99.22 %, respectively, after 12 h. The results showed that the formations of chromium nitride (CrN) and two iron nitrides (Fe3N and Fe4N) are of vital importance to the antibacterial properties of martensitic stainless steel.