Gas Nitriding Treatment Research Articles

Study on surface nitriding treatment of the sintered SUS430 ferritic stainless steel

Ferritic stainless steels with the advantages of high thermal conductivity, low expansion coefficient, excellent oxidation resistance, resistance to stress corrosion capacity, and low cost are widely applied. The parts are prepared by powder metallurgy with SUS430 ferritic stainless steel. Under an H2 protective atmosphere, the compactions are sintered at 1300 °C, and the density of the as-sintered sample achieves 7.4 g/cm3. Then, high-temperature solid solution nitriding treatment is carried out at 1110 °C under an N2/H2 mixed atmosphere. The nitride layers are formed on the surface of the samples. The thickness of nitride layers is about 130–150 μm, and its microhardness is 490 HV. Moreover, it suggests that gas nitriding treatment can effectively improve surface hardness and wear resistance. Still, the core matrix with ferritic microstructure maintains good plasticities and ductilities, and its hardness is about 126 HV.

Processing and surface modification of titanium open cell porous structures for PEM fuel cell bipolar plates

Bipolar plate (BP) and porous transport layer (PTL) materials and designs are critical for the performance of a proton exchange membrane fuel cell (PEMFC) and electrolyser (PEMEC) due to their role as fluid distributor and electron transporter between cells. Designs based on open cell porous structures require a good control on the porosity features. The aim of this work is to use powder metallurgy to manufacture titanium porous structures and the use of suitable surface modification techniques that can improve the performance of the PEM systems, focusing on fuel cells. Using the space holder method, porous structures of up to 63% porosity and controlled pore size can be processed to tailor the characteristics for an optimal design and, through a simple gas nitriding treatment, the performance of the material in terms of interfacial contact resistance (below 10 mΩcm2 after corrosion) and corrosion resistance (below 1 μAcm−2) are improved for both dense and porous structures.

Effect of Nitriding Process on Wear Behavior of Dual Phase (Ferrite+Martensite) Ductile Cast Iron

In this study, it was aimed to improve the surface hardness by applying gas nitriding treatment to dual-phase ductile cast iron and to produce ductile cast irons with a good strength-ductility combination. Thus, it has been tried to develop a ductile cast iron with high wear resistance, strength, and ductility. Ductile cast iron specimens with a dual-phase microstructure consisting of ferrite + martensite were produced by oil quenching at 70 °C after intercritical austenitizing at 800 ⁰C in the ferrite + austenite zone. Instead of the tempering process, nitriding treatment was applied to the dual-phase ductile cast iron specimens at 560 °C for 540 minutes. The tempering process required to be applied to the martensitic structure was also performed by the nitriding process and a hard 10 µm thick nitride layer was obtained on the surface. Optical microscope and XRD analysis were performed for microstructural characterization of nitrided dual-phase ductile cast iron specimens. The wear properties were tested with a tribometer. For comparison reasons, microstructural characterization and wear tests were also performed on non-nitrided dual-phase ductile cast iron. In ductile cast iron, microstructures consist of a hard nitride layer (10 µm white layer) on the surface and a ferrite + tempered martensite (43% martensite volume fraction) structure in the center can be produced by oil quenching from intercritical austenitizing and nitriding treatment. Surface hardness of 510 HV in nitrided dual-phase ductile cast iron, 193 HV in dual-phase ductile cast iron, and 353 HV in austempered KGDD were obtained. The lowest weight loss and coefficient of friction were obtained in nitrided dual-phase ductile cast iron. The highest weight loss and friction coefficient values with wear were obtained in dual-phase ductile cast iron. The wear resistance of nitrided dual-phase ductile cast iron is 2 times higher than that of dual-phase ductile cast iron and austempered ductile cast iron.

Research on improving durability of high-strength spheroidal graphite cast iron gears by nitriding heat treatment

The vibration damping property of high-strength spheroidal graphite cast iron is higher than that of steel materials, and it is possible to reduce gear meshing vibration, which is effective in reducing noise in gear devices. This material is significantly stronger than conventional spheroidal graphite cast iron. However, the problem is that the fatigue strength is inferior at the as-cast material level compared to conventional railway gear materials. Gas nitriding can significantly improve the fatigue strength of cast iron. In this study, we report the results of material fatigue test and improvement of nitriding heat treatment property by adding alloying elements in order to determine the optimum gas nitriding treatment conditions for cast iron gears. Furthermore, we manufactured the nitriding gear for railway vehicles and this noise performance was evaluated by rotation test. The thermal strain of the gear due to the nitriding heat treatment is less than that of carburizing, and the noise is reduced by about 2 dB on average compared to the conventional material tooth grinding gear.

Influence of Crystal Structure of Nitride Compound Layer on Torsion Fatigue Strength of Alloy Steel

The demand for high-strength components for commercial vehicles has recently increased. Conventional gas nitrocarburizing has been used to increase strength and productivity of the crankshaft. A potential-controlled nitriding process was recently developed to control the crystal structure of the nitride compound layer. It has been found that this treatment improves the bending fatigue strength compared with conventional treatment, and has the potential to cope with the increase in crankshaft strength. However, the effect of torsional fatigue strength has not been studied. Therefore, in this study, the influence of the crystal structure of the nitride compound layer on torsional fatigue strength was investigated. Two kinds of test specimens with different crystal structures of the compound layer were prepared using gas nitriding treatment with controlled nitriding potential for an alloy steel bar (JIS-SCM435). Torsional fatigue tests were carried out using these test specimens. Although the compound layer of these test specimens had different crystal structures, the hardness distribution and residual stress distribution on the diffusion layer were almost the same. The relationship between stress amplitude and number of cycles to failure (S-N curve) showed that the torsional fatigue limits of the specimens were almost the same. This indicates that the crystal structure of the nitride compound layer did not affect the torsional fatigue limits, because the origin of the torsional fatigue failure is inside the specimen.

Two‐Step Nitriding Behavior of Pure Iron with a Nanostructured Surface Layer

A two‐step gas nitriding treatment (280 °C for 2 h plus 550 °C for 6 h) is designed for pure iron with a nanostructured surface layer induced by surface mechanical attrition treatment (SMAT). The microstructure and surface properties of the SMAT sample after two‐step nitriding treatment are investigated in comparison with those of the SMAT sample after single‐step nitriding treatment (550 °C for 6 h). Experimental results show that a much thicker compound layer (up to 25 μm in thickness) is generated on the surface of the SMAT sample after two‐step nitriding treatment, in which the mean grain size of the Fe2‐3N phase is below 25 nm. The enhanced nitriding kinetic may be attributed to the formation of a large number of Fe(N) solid solutions and a small amount of dispersed Fe2‐3N particles on the SMAT sample after first low‐temperature nitriding, which enhances the thermal stability of nanostructured iron grains. Due to the enhanced nitriding kinetic and refined nitride structure, the SMAT sample after two‐step nitriding treatment displays higher surface hardness and improved wear resistance relative to its single‐step nitrided counterpart.

Assessment of Cavitation Erosion of Gas-Nitrided Cr-Ni-Mo Steels

The effect of the gas-nitriding thermochemical treatment on the cavitation erosion resistance of a Cr-Ni-Mo alloy is analyzed using a piezoceramic vibrating equipment and following the ASTM G32-2010 standard. The evaluation of the cavitation erosion behavior was made based on the analysis of the mean depth of erosion (MDE) and mean depth of erosion rate (MDER), for samples subjected to the cavitation erosion for different times. The surface topography and the structural changes in the marginal layer were analyzed through optical and scanning electron microscopy. Following nitriding the cavitation erosion resistance was about 9.6 times higher compared to the annealed state and about 8.2 times higher compared to the hardened and tempered state.

Mechanical characterization of a new low carbon bainitic steel for high performance crankshaft

In the actual automotive environment, the need to increase the performances of materials is requiring extra engineering efforts. The possibility to develop new materials is very important. Indeed alternative solutions in terms of material choice allow designers to optimize their projects and keep low costs of production. Dealing with potential alternatives to traditional quenched and tempered steels for high stressed components, as just seen in previous work, bainitic grades could be a valid solution. This is particularly true if the mechanical performances are kept without compromise the economic savings of bainitic grades. So a detailed evaluation of the mechanical properties of these steels needs a further deepen also for applications requiring case hardening treatment. The scope of this article is to introduce and show the characterization phase of a new bainitic low carbon content for a high-performance crankshaft application. In details, a long-life fatigue resistance staircase test is performed after a gas nitriding treatment and the results are compared to the untreated material. The increment of the fatigue resistance is quantified and can be utilized by structural engineers to develop and optimized their projects. Moreover, the case hardened depth and microhardness profiles are collected and evaluated in terms of nitriding effectiveness (nitrogen diffusion).

Magnetic Properties of Austenitic Stainless Steel 316l and 316lvm after High Temperature Gas Nitriding Treatment

Biometallic materials for implant devices not only have to good corrosion resistance but also stable nonmagnetic properties. Various method have been developed for enhanced the corrosion resistance i.e low temperature gas nitriding treatments. Unfortunatelly, low temperature gas nitriding produce weakly ferromagnetic due the presence of expanded austenitic phases. Another treatments methods which is capable for improvement the mechanical properties is high temperature gas nitriding. However, the evaluation of magnetic properties of austenitic stainless steel 316L and 316LVM not yet investigation. The evaluation of magnetic properties of austenitis stainless steel 316L and 316LVM after high temperature gas nitriding treatments have been succesfully done. The magnetic properties are evaluated by vibrating sample magnetometre (VSM) test. The magnetic properties such as magnetic remenance, magnetic saturation and magnetic permeability are improved. As treated 316L and 316LVM have more stable non-magnetic properties and they more safe and compatible for MRI test

Nanomechanical properties of iron nitrides produced on 42CrMo4 steel by controlled gas nitriding and laser heat treatment

Abstract Nitriding, as one of the most widely used surface treatment, was often applied in order to improve the hardness, fatigue strength as well as wear and corrosion resistance of steels. The controlled gas nitriding resulted in a formation of a compound zone e+(e+γ′) of limited thickness close to the surface and the diffusion zone below it. It was easy to identify the two separate zones in the microstructure: more porous zone with only e-Fe 3 N iron nitrides and zone with e+γ′ iron nitrides' mixture (Fe 3 N + Fe 4 N). In this study, the laser modification without re-melting was carried out after the controlled gas nitriding in order to change microstructure. The nanomechanical properties of the zones with iron nitrides, observed in the compound zone, were examined using the nanoindenter with a Berkovich diamond tip. Young's modulus and hardness were measured and compared to the literature data. The load-displacement curves and the indentation images were shown for the selected measurements. The advantageous influence of laser heat treatment on the Young's modulus and hardness was confirmed for the outer e zone as well as for the laser quenched diffusion zone. The higher average values of indentation modulus and hardness characterized e iron nitrides ( E IT = 165.72 ± 18.67 GPa and H IT = 9.90 ± 0.47 GPa) and laser quenched diffusion zone ( E IT = 199.06 ± 28.80 GPa and H IT = 7.11 ± 0.61 GPa) after laser heat treatment. The diminished porosity of e zone and the presence of martensite in the diffusion zone were the reason for such a situation. The laser heat treatment almost didn't influence the indentation modulus of zone with e+γ′ iron nitrides' mixture ( E IT = 175.27 ± 4.81 GPa), whereas its hardness was slightly increased ( H IT = 11.87 ± 0.43 GPa). The conclusion regarding the percentage of the separate phases (e and γ′) in this zone was ambiguous.

HIGH TEMPERATURE GAS NITRIDING TREATMENT OF AISI 430 USING LOW AND HIGH PURITY NITROGEN GAS

The properties of stainless steels can be improved by high temperature gas nitriding (HTGN) treatment. The improving of their properties are obtained from nitrogen atom which diffuse into stainless steel. Nitrogen gas is the main source of nitrogen atom on the HTGN treatment. Generally, these treatment use high purity of nitrogen gas. The aim of this research is to investigate the effect of nitrogen gas purity on the HTGN treatment for AISI 430. Stainless steel AISI 430 plate 2 mm thick was processed by HTGN treatment. The specimens was exposed at nitrogen gas atmosphere at temperature 1200oC and held for 2 hours prior quenching in water. The treatment used industrial/welding grade (99.5%) as low nitrogen gas purity and ultra high purity (UHP) grade (99.999%) as high nitrogen gas purity. The vickers micro-hardness test was conducted to evaluate the hardness distribution from surface into middle section of the specimens before and after treatment. Light optical microscope was applied to examine the microstructure of specimens after treatment. Metallographic examination shows both treatments using low and high purity gas have the same grain size. However HTGN treatment using low purity of nitrogen gas produces hardness slightly lower than the high purity. This is due the high content of impurity of the low purity gas that reduces the partial pressure of nitrogen gas. Another effect of impurity is the reaction between nitrogen gas and its impurity especially oxygen gas. These reactions reduce the amount of free nitrogen atom which diffuses on the stainless steel.

Nitride coating enhances endothelialization on biomedical NiTi shape memory alloy

Surface nitriding was demonstrated to be an effective process for improving the biocompatibility of implantable devices. In this study, we investigated the benefits of nitriding the NiTi shape memory alloy for vascular stent applications. Results from cell experiments indicated that, compared to untreated NiTi, a superficial gas nitriding treatment enhanced the adhesion of human umbilical vein endothelial cells (HUVECs), cell spreading and proliferation. This investigation provides data to demonstrate the possibility of improving the rate of endothelialization on NiTi by means of nitride coating.

Improved tribological, electrochemical and biocompatibility properties of Ti6Al4V alloy by gas-nitriding and Ti–C:H coating

Ti–C:H coatings are deposited on untreated Ti6Al4V alloy samples and high-temperature gas-nitrided Ti6Al4V alloy samples by means of CFUBMS. Therefore, four types of specimen, i.e., Ti6Al4V, nitrided Ti6Al4V (N-Ti6Al4V), T–C:H-coated Ti6Al4V (Ti–C:H/Ti6Al4V) and T–C:H-coated nitrided Ti6Al4V (Ti–C:H/N-Ti6Al4V) are considered. The microstructure, adhesion and hardness of the Ti–C:H coatings are examined using a Raman spectrometer, scratch tester and nanoindenter, respectively. The tribological properties of the coated and uncoated samples are investigated using a reciprocating sliding wear tester in NaCl solution. The corrosion performance of the four specimens is evaluated by means of potentiodynamic polarization tests. Finally, the biocompatibility of the various samples is investigated using purified mouse leukaemic monocyte macrophage cells (Raw 264.7). Overall, the results show that the gas-nitriding treatment increases both the hardness and the surface roughness of the samples. Moreover, of the various samples, the Ti–C:H/Ti6Al4V sample exhibits excellent tribological properties and the best corrosion resistance and biocompatibility performance.

Excellent enhancement of corrosion properties of Fe–9Al–30Mn–1.8C alloy in 3.5% NaCl and 10% HCl aqueous solutions using gas nitriding treatment

The as-quenched Fe–9.0Al–30Mn–1.8C (in wt.%) alloy gas nitrided at 550°C for 4h show excellent corrosion resistance investigated in 3.5% NaCl and 10% HCl solutions. Owing to the high corrosion resistance components, the gas-nitrided layer consists mainly of AlN with a slight amount of Fe3N and Fe4N identified by grazing incidence X-ray diffraction technique. Therefore, the pitting potential and corrosion potential of the nitrided sample are +1860mV and +30mV, respectively. Surprisingly, it is worthy to be pointed out that the nitrided and then tensile-tested alloy reveals very shallow in fracture depth and the excellent lattice coherence is shown between the nitrided layer and the substrate. Moreover, due to the extremely high nitrogen concentration (about 17–18wt.%) at stretched surface, the corrosion resistance of present gas-nitrided and then tensile-tested alloy is superior to those optimally gas-nitrided or plasma-nitrided high-strength alloy steels, as well as martensitic stainless steels. The nitrided and then stretched alloy still retains a satisfactory corrosion resistance (Epit=+890mV; Ecorr=+10mV). Furthermore, only nanoscale-size pits were observed on the corroded surface after being immersed in 10% HCl for 24h.

Research on the effect of gas nitriding treatment on the wear resistance of ball seat used in multistage fracturing

• A new application of surface modification for ball seat was proposed and performed. • The wear mechanisms of specimens were indentified based on tribological tests. • The on-site experiment indicated that wear resistance was improved obviously. With the further development of unconventional oil and gas reservoirs, multistage fracturing technique has played an important role in completion process. Wear problem has severely restricted the development of this technique. However, surface modification of fracturing tools has not been studied widely. In this study, ball seats which act as key component in multistage fracturing were nitrided in ammonia (NH 3 ) and the nitride layer characterizations were investigated. Tribological tests were carried out to study the wear resistance of specimens. The test results show that microhardness and wear resistance are improved significantly by gas nitriding treatment. Based on the comprehensive analyses of the wear morphologies and debris, wear mechanisms are identified. The on-site fracturing experiment results indicate that the ball seat shows better wear resistance after gas nitriding treatment.

Effect of gas nitriding treatment on cavitation erosion behavior of commercially pure Ti and Ti−6Al−4V alloy

In this study, the microstructure, hardness depth profile and cavitation erosion behavior of commercially pure Ti (CP Ti) and Ti−6Al−4V alloys nitrided at 973, 1123 and 1273K for 16h were examined. The results revealed that the cavitation erosion behavior of both CP Ti and Ti−6Al−4V alloy was considerably improved by gas nitriding process. The CP Ti nitrided at 973K has a 2.65-fold increase in cavitation erosion resistance (Re) as compared with untreated specimens, whereas the CP Ti nitrided at 1273K has the lowest Re. In contrast, the Ti−6Al−4V alloy nitrided at 1273K exhibited the highest Re while the specimen nitrided at 973K has the lowest resistance. These results were mainly due to the different properties of the nitrogen diffused zone (NDZ) for CP Ti and alloy. For CP Ti, the NDZ prevented the propagation of microcracks to interior and retarded the erosion due to its homogeneous structure with high hardness, crack-free and good metallurgical bonding. However, the well-organized microstructure was damaged by high temperature (1273K) treatment and induced the decrease of Re. For Ti−6Al−4V alloy, the NDZ consisted of hard α-Ti grains and soft β-Ti grains resulted in a selective attack for cavitation damage and accelerated the erosion process. But high temperature (1273K) treatment induced the transformation of β-Ti to α-Ti due to solid solution of nitrogen, which promoted the formation of nitrogen-enriched α-grains (α-Ti(N)) layer on the top of NDZ and sequentially increased the Re up to 6.72 folds. In summary, the significant improvement of cavitation erosion behavior after gas nitriding treatment was mainly attributed to the formation of a unique and homogenous α-Ti(N) layer on the top of the NDZ.

Influence of surface nitriding treatment on rolling contact behavior of Fe-based plasma sprayed coating

Fe–Cr coating was prepared by plasma spraying process. Gas nitriding treatment was conducted on the coating. Rolling contact fatigue (RCF) experiments were conducted using a ball-on-disc setup. RCF lifetime of the coating was calculated by two-parameter Weibull distribution. The worn morphologies of the coating were observed. Correlative failure mechanism was investigated based on fracture analysis and theoretical calculation. Results showed that the dense nitriding layer with high microhardness was formed on Fe-based coating surface. Unfortunately, the deposition of nitriding layer decreases RCF lifetime of the coating. The coating with nitriding layer always failed owing to cohesive delamination. The “born” microdefect and high brittleness of nitriding layer are the main reasons for the failures under rolling contact.

Investigation of Gas Nitriding on Wear and Corrosion Behavior of 40Cr Steel

The influence of gas nitriding on the wear and corrosion resistance of 40Cr steel was investigated. Gas nitriding experiments were carried out at 550°C for 2h and 10h. The microstructure and hardness gradient were observed and analyzed through metallurgical microscope and micro hardness tester. The polarization curves were scanned by the M398 Corrosion Integrated Test System. Using MG-200 high speed friction and wear testing machine did end mill test and calculated the wear rate. By scanning electron microscopy (SEM) observationing the worn surface morphologies. The results show that after different nitriding time, the specimen surface forms with nitrided layer of different thickness, and changes with the hardness decreased with the penetration depth. Furthermore, the gas nitriding treatment may change the corrosion potential positively and reduce the density of the electric current of 40Cr steel. In addition, wear mechanism of the matrix is mainly adhesive wear, but after nitriding is mainly abrasive wear. The wear rate reduces significantly.

The characteristics of high temperature Gas Nitriding heat treatment and tempering in 0.8Mo added 17Cr-1Ni-0.5C

The effect of the High Temperature Gas Nitriding (HTGN) and tempering treatment of 17Cr-1Ni-0.5C-0.8Mo (CNMo) steel was experimentally investigated. The HTGN was carried out at 1050 °C for 1 h in a gaseous atmosphere containing 98.07 kPa of nitrogen. Chromium nitrides in the austenite and martensite phase appeared at the nitrogen-permeated surface layer after the HTGN treatment. The hardness of the outmost surface of the HTGN treated specimen measured 708 Hv. When it was tempered at 500 °C for 1 h, the hardness of the outmost surface was 763 Hv as a result of the precipitation of mostly micro Cr2N, which was densely packed with a small amount of Cr23C6 and the secondary hardening effect. In addition, an improvement in the corrosion resistance was observed in the tempered specimen.

A study on high temperature gas nitriding and tempering heat treatment in 17Cr–1Ni–0.5C

Abstract The effect of the high tempering gas nitriding (HTGN) and tempering treatment in 17Cr–1Ni–0.5C (CN) steel was experimentally investigated. The HTGN was carried out at 1050 °C for 1 h in a gaseous atmosphere containing 98.07 kPa of nitrogen. Chromium nitrides and the austenite phase appeared in the nitrogen-permeated surface layer, whereas, the interior region, into which nitrogen did not permeate, exhibited martensite and austenite phases along with the chromium carbides. The nitrogen content was approximately 0.3% at a depth of 5 μm below the surface layer in the CN specimen after the HTGN. The hardness of the outmost surface of the HTGN treated specimen measured 538 Hv. When it was tempered at 550 °C for 1 h, the hardness of the outmost surface was 860 Hv as a result of the precipitation of mostly Cr 2 N along with a small amount of Cr 23 C 6 and the secondary hardening effect.