On the Erosion–Corrosion Behavior of Active Screen Plasma Nitrided St52 Steel

In this work, samples of St52 steel were plasma nitrided using an iron screen, in an N₂: H₂ gas mixture ratio of 4 : 1, at 500 and 550°C for 5, 10 and 15 h. The X-ray diffraction and optical microscopy methods were used for structural characterization of the coatings. Results indicated that the coatings were composed of Fe_2–3N and Fe₄N phases growing at longer deposition times. Moreover, the Fe_2–3N phase was decomposed to Fe₄N after 10 h of plasma nitriding. The erosion–corrosion behavior of nitrided coatings and a bare substrate were studied in various impact angles: 30, 45, 60 and 90 degrees. Polarization curves of the coated and uncoated samples were recorded between–900 to 600 mV, as a function of the slurry impact angle. Results showed that an active screen plasma nitriding method significantly enhanced the erosion–corrosion resistance of the St52 steel. Moreover, an impact angle of 30° on the sample surface yielded a lower weightloss whereas increasing the impact angle up to 90° caused more weight-loss due to the brittle characteristic of iron nitride coatings. According to SEM micrographs, by increasing the impact angle up to 90°, the depth of the removed mass increased substantially.     

Microstructure and Properties of SAE 2205 Stainless Steel After Salt Bath Nitrocarburizing at 450 °C

Nitrocarburizing of the type SAE 2205 duplex stainless steel was conducted at 450 °C, using a type of salt bath chemical surface treatment, and the microstructure and properties of the nitrided surface were systematically researched. Experimental results revealed that a modified layer transformed on the surface of samples with the thickness ranging from 3 to 28 μm changed with the treatment time. After 2205 duplex stainless steel was subjected to salt bath nitriding at 450 °C for time less than 8 h, the preexisting ferrite zone in the surface transformed into austenite by active nitrogen diffusion. The main phase of the nitrided layer was the expanded austenite. When the treatment time was extended to 16 h, the preexisting ferrite zone in the expanded austenite was decomposed and transformed partially into ε-nitride precipitate. When the treatment time extended to 40 h, the preexisting ferrite zone in the expanded austenite was transformed into ε-nitride and CrN precipitate. Further, a large amount of nitride precipitated from preexisting austenite zone. The nitrided layer depth thickness changed intensively with the increasing nitriding time. The growth of the nitride layer takes place mainly by nitrogen diffusion according to the expected parabolic rate law. The salt bath nitriding can effectively improve the surface hardness. The maximum values measured from the treated surface are observed to be approximately 1400 HV_0.1 after 8 h, which is about 3.5 times as hard as the untreated material (396 HV_0.1). Low-temperature nitriding can improve the erosion/corrosion resistance. After nitriding for 4 h, the sample has the best corrosion resistance.     

Influence of Plasma Nitriding on the Microstructure, Wear, and Corrosion Properties of Quenched 30CrMnSiA Steel

The oil-quenched 30CrMnSiA steel specimens have been pulse plasma-nitrided for 4 h using a constant 25% N₂-75% H₂ gaseous mixture. Different nitriding temperatures varying from 400 to 560 °C have been used to investigate the effects of treatment temperature on the microstructure, microhardness, wear, and corrosion resistances of the surface layers of the nitrided specimens. The results show that significant surface-hardened layer consisting of compound and diffusion layers can be obtained when the oil-quenched steel (α′-Fe) are plasma-nitrided at these experimental conditions, and the compound layer mainly consists of ε-Fe_2-3N and γ′-Fe₄N phases. Lower temperature (400-500 °C) nitriding favors the formation of ε-Fe_2-3N phase in surface layer, while a monophase γ′-Fe₄N layer can be obtained when the nitriding is carried out at a higher temperature (560 °C). With increasing nitriding temperature, the compound layer thickness increases firstly from 2-3 μm (400 °C) to 8 μm (500 °C) and then decreases to 4.5 μm (560 °C). The surface roughness increases remarkably, and both the surface and inner microhardness of the nitrided samples decrease as increasing the temperature. The compact compound layers with more ε-Fe_2-3N phase can be obtained at lower temperature and have much higher wear and corrosion resistances than those compound layers formed employing 500-560 °C plasma nitriding.     

Effect of Plasma Nitriding on the Performance of WC-Co Cutting Tools

This paper presents the effect of nitriding process parameters on the cutting performance of WC-Co tools. The cutting performance was measured by CNC machining of GG25 cast iron parts. The hardness and phase composition of nitrided layer were determined for different plasma nitriding temperatures and times. The hardness of the nitrided layer increased at all plasma nitrided conditions investigated. However, the machining performance of the cutting inserts varied in the range between a 60% increase and a 40% decrease after plasma nitriding. The maximum number of machined parts was seen when the insert was nitrided at 600 °C-4 h and at 500 °C-4 h.     

Low-Temperature Nitriding of Nanocrystalline Stainless Steel and Its Effect on Improving Wear and Corrosion Resistance

In this study, an ultrafine-grained surface layer with the average grain size of about 10 nm was fabricated on a stainless steel plate by surface mechanical attrition treatment (SMAT). Plasma nitriding of the samples was carried out by a low-frequency pulse-excited plasma unit. Optical microscopy, x-ray diffraction, scanning electron microscopy, transmission electron microscopy, micro-indentation, and pin-on-disk wear and corrosion experiments were performed for characterization before and after plasma nitriding. It is found that the pre-SMATed sample developed a nitrided layer twice as thick as that on the as-received sample under the same nitriding conditions (300 °C for 4 h), which can be mainly attributed to the fast diffusion of nitrogen along grain boundaries in the nanostructured layer induced by means of SMAT. Results showed that nitriding layers of the as-received and pre-SMATed samples up to 300 °C are dominated by S-phase (γ_N), but its peak intensity for the pre-SMATed sample is sharper than that of the as-received one. During 500 °C nitriding treatment, the nitrogen would react with Cr in the steel to form CrN precipitates, which would lead to the depletion of chromium in the solid solution phase of the nitrided layer. Furthermore, the nitrided layer of the pre-SMATed sample exhibited a high hardness, and an excellent wear and corrosion resistance.     

Effects of Temperature on Microstructure and Wear of Salt Bath Nitrided 17-4PH Stainless Steel

Salt bath nitriding of 17-4 PH martensitic precipitation hardening stainless steels was conducted at 610, 630, and 650?°C for 2?h using a complex salt bath heat-treatment, and the properties of the nitrided surface were systematically evaluated. Experimental results revealed that the microstructure and phase constituents of the nitrided surface alloy are highly process condition dependent. When 17-4PH stainless steel was subjected to complex salt bathing nitriding, the main phase of the nitrided layer was expanded martensite (????), expanded austenite (??_N), CrN, Fe₄N, and (Fe,Cr) _x O _y . In the sample nitrided above 610?°C, the expanded martensite transformed into expanded austenite. But in the sample nitrided at 650?°C, the expanded austenite decomposed into ??_N and CrN. The decomposed ??_N then disassembled into CrN and alpha again. The nitrided layer depth thickened intensively with the increasing nitriding temperature. The activation energy of nitriding in this salt bath was 125?±?5?kJ/mol.     

Modification of Low-Alloy Steel Surface by High-Temperature Gas Nitriding Plus Tempering

The low-alloy steel was nitrided in a pure NH₃ gas atmosphere at 640 ~ 660 °C for 2 h, i.e., high-temperature gas nitriding (HTGN), followed by tempering at 225 °C, which can produce a high property surface coating without brittle compound (white) layer. The steel was also plasma nitriding for comparison. The composition, microstructure and microhardness of the nitrided and tempered specimens were examined, and their tribological behavior investigated. The results showed that the as-gas-nitrided layer consisted of a white layer composed of FeN_0.095 phase (nitrided austenite) and a diffusional zone underneath the white layer. After tempering, the white layer was decomposed to a nano-sized (α-Fe + γ′-Fe₄N + retained austenite) bainitic microstructure with a high hardness of 1150HV/25 g. Wear test results showed that the wear resistance and wear coefficient yielded by the complex HTGN plus tempering were considerably higher and lower, respectively, than those produced by the conventional plasma nitriding.     

Advance Complex Liquid Nitriding of Stainless Steel AISI 321 Surface at 430 °C

Liquid nitriding of type 321 austenite stainless steel was conducted at low temperature at 430 °C, using a type of a complex chemical heat-treatment; and the properties of the nitrided surface were evaluated. Experimental results revealed that a modified layer was formed on the surface with the thickness ranging from 2 to 30 μm varying with changing treatment time. When the stainless steel subjected to the advanced liquid nitriding less than 8 h at 430 °C, the main phase of the nitrided coating layer was the S phase generally. When the treatment time prolonged up to 16 h, S phase formed and partially transformed to CrN subsequently; and then the fine secondary CrN phase precipitated. All treatments performed in the current study can effectively improve the surface hardness. The nitrided layer thickness changed intensively with the increasing nitrided time. The growth of the nitride layer took place mainly by nitrogen diffusion according to the expected parabolic rate law. The highest hardness value obtained in this experiment was about 1400 Hv_0.25. Low-temperature nitriding can improve the corrosion resistance of the 321 stainless steel against diluted vitriolic acid. The immerse test results revealed that the sample nitrided for 16 h had the best corrosion resistance than the others. SEM examinations indicated that after nitriding, the corrosion mechanisms of the steel had changed from serious general corrosion of untreated sample to selectivity corrosion of nitrided samples in the diluted vitriolic acid.     

40Cr钢循环离子渗氮工艺及渗层硬度研究

目的探索循环离子渗氮与常规恒温离子渗氮技术的工艺效果。方法先对试样进行调质处理,分组进行离子渗氮,固定氨气和乙醇的流量,改变渗氮时间和渗氮温度两种工艺参数及渗氮工艺,分别测定渗氮后各试样的表面硬度及渗层厚度,观察其金相组织,并分析每组试样渗氮层的性能。结果循环离子渗氮530 6 h℃试样的表面硬度最高,随着渗氮温度的升高和渗氮时间的延长,试样的表面硬度增加,但是当温度超过530℃、时间超过6 h后,试样的表面硬度反而降低。循环渗氮550 10 h℃试样的渗层厚度最厚,随着渗氮温度的升高和渗氮时间的增加,试样的渗层厚度变厚,但时间超过6 h后,渗层厚度的增加较缓慢,6、8、10 h试样的渗层厚度差别不大。相同的渗氮温度下,循环渗氮6 h的试样的渗层厚度基本与常规恒温渗氮10 h试样的渗层厚度一样,相同渗氮时间内,循环渗氮510℃的试样的表面硬度高于恒温渗氮550℃试样的表面硬度,且两者的渗层厚度相差不多。结论循环离子渗氮工艺优于常规的恒温离子渗氮,循环离子渗氮550 8 h℃试样的综合性能最好。     

复合化学热处理对G13Cr4Mo4Ni4V钢组织和硬度的影响

采用扫描电镜、洛氏硬度计和维氏显微硬度计研究了渗氮140 h对渗碳+淬火+回火G13Cr4Mo4Ni4V钢微观组织及硬度的影响。结果表明,渗碳+淬火+回火后G13Cr4Mo4Ni4V钢有效渗碳层深度为1.45 mm,渗碳层最高硬度为785 HV,心部硬度为420 HV,经渗氮处理后有效渗碳+渗氮层深度降为1.34 mm,渗氮层深度为0.22 mm,渗氮层最高硬度可达到948 HV,心部硬度为451 HV,较未渗氮试样硬度略有提高。渗碳+淬火+回火和添加渗氮处理后G13Cr4Mo4Ni4V钢的表面洛氏硬度相当,均在62~65 HRC 之间,但渗氮处理后试样的硬度波动性较大。添加140 h渗氮的渗碳+淬火+回火后G13Cr4Mo4Ni4V钢实现了“表面硬心部韧”的目标,渗氮层深度满足工程需要,但添加渗氮处理后G13Cr4Mo4Ni4V钢在渗碳层和渗氮层出现类网状碳化物,因此在渗氮过程中需要综合考虑渗氮层深度和微观组织,以获得良好的综合力学性能。     

Wear Properties of Plasma Nitrided H13 Steel at Room and Elevated Temperature

H13 steel was nitrided using a plasma surface alloying technique at the temperature of 570℃.The nitrided layers with different thicknesses and components were obtained by changing nitriding pressure.The microstructure and composition of the nitrided layers were evaluated by optical microscopy(OM)and X-ray diffraction(XRD).The wear properties of the nitrided layer against Al2O3 ball at room temperature using a ball-on-disc tribometer and against Si3N4 ball at elevated temperature using a HT-2001 abrasive wear test machine were investigated.The results show that the nitrided layers are composed of compound layer and diffusion layer at the pressure of 100 and 450 Pa.No obvious compound layer appears at pressure of 200 and 300 Pa.XRD analysis shows the nitrided layers are mainly composed ofε-Fe2-3N,γ’-Fe4N,α-Fe,Fe2O3 and Fe3O4 phases.The surface hardness of plasma nitrided H13 steel is about 1100HV0.050 doubled that of substrate.The room temperature friction coefficient of H13 steel is reduced and wear rate is decreased by nitriding at 200 and 300 Pa.Elevated temperature wear test indicates the nitrided H13 steel at the pressure of 100 Pa shows lower friction coefficient and wear rate which are reduced more than 6 times compared with that of H13 substrate.     

Effect of ion nitriding on the abrasive wear resistance of ultrahigh-strength steels with different silicon contents

This article studies the effect of silicon (Si) on ultrahigh-strength AISI 4340 steels in connection with the thermal treatment, as well as the influence of this element on nitriding and, consequently, abrasive wear. Four alloys with different Si contents were nitrided at 350 °C (4 and 8 h) and 500 and 550 °C (2 and 4 h) in a gas mixture of 80 vol.% H₂ and 20 vol.% N₂. The nitrided layers were characterized by microhardness and pin-on-disk tests, optical microscopy, scanning electron microscopy with energy-dispersive x-ray spectrometry, and x-ray diffraction (XRD). The increase in Si enhanced the tempering resistance of the steels and also improved considerably the hardness of the nitrided layers. The increase in Si produced thinner compound layers with better hardness quality and high abrasive wear resistance. XRD analysis detected a mixture of nitrides in the layers γ′-Fe₄N, ε-Fe_2–3N, CrN, MoN, and Si₃N₄ with their proportions varying with the nitriding conditions.     

The Influence of Plasma Nitriding Pre-Treatment on Tribological Properties of TiN Coatings Deposited by PACVD

The aim of this study is to investigate the effect of plasma nitriding pre-treatment (PN) on mechanical and tribological behavior of TiN coatings produced by plasma-assisted chemical vapor deposition (PACVD). The heat treatment of quench and temper was carried out on hot work AISI H11 (DIN 1.2343) steel samples. A group of samples were plasma nitrided at 500?°C for 4?h in an atmosphere containing 25?vol.% nitrogen and 75?vol.% hydrogen. Then TiN layer was deposited on all of samples at 520?°C temperature, 8?kHz frequency, and 33% duty cycle. The microstructural, mechanical, and tribological properties of the coatings were investigated using SEM, WDS, AFM, microhardness tester, and pin-on-disc wear test. The load of wear test was 10?N and the samples were worn against different pins, ball-bearing steel (DIN 1.3505), and cemented tungsten carbide (WC-Co). The results indicate that the difference of hardness between the samples with PN-TiNlayer and those samples with only TiN layer without PN was 450 HV and the former samples showed a significant amount of wear resistance in comparison to the latter ones.     

Steam oxidation and surface hardness of power plant valve materials under the ultra super critical steam condition

Current supereritical steam power plants operate at 3,600 psi and 1,000°F. If the steam temperature is raised from 1,000 °F (538 °C) to 1,150 °F (621°C), the efficiency increases by 2%. Therefore, study on the high temperature corrosion of power plant materials under ultra-superciritical conditions (USC) is necessary to protect the plant from corrosion. In this study, valve materials of 17% Cr martensitic steels (17Cr steel), Incoloy 901 (1901) and their surface nitrided specimens were exposed to USC of 621 °C and 3600 psi (255 kg/cm²) steam for 200 °C, 400 °C, and 800 h. The oxidation of both 17Cr steel and 1901 under the USC for 800 h is very small due to the formation of a protective thin oxide layer formation on the surface. The USC oxidation of both nitrided specimens were increased due to the decomposition and formation of active nitrogen from the non protective nitrides such as Fe₄N, Fe_2–3N, and CrN. The oxidation of nitrided 17Cr steel (n17Cr steel) is about two times higher compared to nitrided 1901 (n1901). The surface hardness is improved by more than two times near the surface by nitriding, and the degradation of hardness by USC oxidation is rapid for n17Cr steel, but slow for n1901.     

Thermal fatigue of hot working steel after hybrid surface treatment

Abstract

The application of surface treatment methods like ion nitriding, physical vapour deposition (PVD) coatings and their combination in duplex treatments effectively reduces the occurrence of oxidation, corrosion, erosion and wear processes. However, it is still uncertain whether nitriding and duplex treatment have any real effect on the decrease in the nucleation and growth of thermal fatigue cracks on the surface. This paper presents the results of thermal fatigue investigations of a nitrided layer and different composite layers ‘nitrided layer/PVD coating’ (TiN, CrN and TiAlN) obtained on the EN X40CrMoV5·1 hot working steel. The ion nitrided only and three different duplex treated substrates were compared, based on the intensity of the thermal fatigue cracks observed after testing. The nitrided layer and composite layers investigated were obtained with the use of the hybrid surface treatment technology consisting of ion nitriding followed by arc evaporation coating deposition. Apparatus based on high frequency induction heating and water spray cooling was used for thermal fatigue tests under the following conditions: maximum temperature 600°C, minimum temperature 80°C and two different rates of thermal cycling: 500 and 1000. The thermal fatigue intensities of the nitrided layer and the three different composite layers were measured according to the surface crack density and crack length (i.e. penetration into the testpiece) after different numbers of thermal cycles. Finally, based on the results obtained, the influence of different PVD coatings in the composite layer on the increase in thermal fatigue resistance of hot working steel was discussed.     

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

ABSTRACT

In 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).     

喷丸预处理对Ti6Al4V合金低温等离子体氮化的影响

为改善钛合金表面耐磨性能,同时达到防止薄壁零部件变形和节约能源的目的,以Ti6Al4V钛合金为对象,研究了喷丸强化预处理对钛合金低温渗氮层及耐磨性的改善作用。结果表明,喷丸强化预处理能够有效促进钛合金表面低温离子渗氮过程,在500 ℃低温渗氮试验条件下,随着喷丸预处理强度的增大,钛合金渗氮效率逐步提高,渗氮层的表面硬度、承载能力和表观韧性逐步增加,使得渗氮层的耐磨性能逐步提高。当喷丸预处理强度增加到0.25 mmA时,Ti6Al4V钛合金渗氮层的表面硬度比单纯渗氮处理试样提高32.7%,磨损率降低42.3%,使钛合金基体的磨损率降低70.5%,较好地实现了喷丸预处理促进钛合金低温离子渗氮的目标。     

STUDY ON REDUCING THE CORE LOSS OF GRAIN ORIENTED SILICON STEEL AND IMPROVING ITS AGING PROPERTY BY LASER NITRIDING TECHNIQUE IN ATMOSPHERIC AMBIENT

1. IntroductionSince the needsofelectric pow erindustry developm entand forlack ofenergy source, to m anufac-ture softm agnetic m aterialsofquality hasalw aysbeen a very im portanttask.The invention ofgrain ori-ented silicon steelbroughtgreatbenefitto sav…     

A case of nitridation,carburization and oxidation on a stainless steel

A case of corrosion was studied on stainless steel tubes, exposed to a nitriding, carburizing and oxidizing environment (mainly NH₃ and CO₂) at 390–450°C. Due to the high nitriding potential prior formation of internally nitrided layers occurs, at higher temperatures (> about 425°C) under precipitation of CrN in the layer and at lower temperatures under formation of the γ_N‐phase, i.e. austenite with high N‐content and expanded lattice. The latter process causes more severe corrosion, due to the high expansion, the stresses in the nitrided layers lead to bursting and repeated spalling of the scales. Carburization and oxidation are less important. The carburization is slower than nitridation, Fe₃C formation is observed and carbon deposition. Also the oxidation by CO₂ is slow and converts the nitrides and carbides formed before, to unprotective oxide flakes.     

Nitriding of an H13 die steel in a dual plasma reactor

The performance of a dual plasma reactor in nitriding a H13 steel was investigated and compared to other nitriding methods applied to this material. The aim was to explore the advantages of combining a weakly ionized plasma unit and a postdischarge plasma reactor to process this material. Samples of H13 were nitrided at 500, 550, and 600 °C for times ranging between 5 to 10 h. The hardness distributions obtained revealed a substantial advantage of the present method over conventional gas nitriding and some improvement over other plasma-assisted methods, especially in the development of smooth profiles. This was attributed mainly to enhanced diffusion provided by the postdischarge flow. The evolution of hardness as a function of time and temperature displayed an aging type of behavior that was related to the formation and growth of CrN as the hardening phase.