Carburized Stainless Steel Research Articles

Accelerated Testing to Investigate Corrosion Mechanisms of Carburized and Carbonitrided Martensitic Stainless Steel for Aerospace Bearings in Harsh Environments

Carburizable martensitic stainless steels (MSSs) are attractive candidates for bearings due to their high corrosion resistance, high hardness, and high temperature performance. Wear performance in tribocorrosion applications is strongly influenced by the surrounding environment. Electrochemical testing was used to evaluate three different surface treatments on AMS 5930 steel developed for advanced gas turbine engine bearing applications: low temperature (LTT), high temperature (HTT), and carbonitrided (CN). HTT had a higher corrosion rate that increased with time, whereas LTT and CN had lower corrosion rates that were stable over time. Accelerated testing revealed that surface treatment significantly influenced how corrosion propagated: HTT was more uniform; conversely, LTT and CN showed localized attack. Degradation mechanisms developed from electrochemical methods provide rapid insight into long-term wear behavior.

Interfacial fracture behavior of a stainless/carbon steel bimetal plate in a uniaxial tension test

The interfacial fracture behavior of a stainless/carbon steel bimetal plate in a uniaxial tensile test was investigated in this paper. The ultrasonic C-scan results showed that the internal fracture had already appeared in the necking area before the tensile sample snapped, and the internal fracture occurred in the middle of the necking area and propagated with the tensile strain increase. The fractography showed that the internal fracture occurred at the interface between the diffusion layer and carburization stainless steel. The contribution of the internal stress to the interface fracture was analyzed by finite element method. The FEM results showed that, due to the different material mechanical properties, the large stress difference between the diffusion layer and the carburized stainless steel induced the interface shear stress. The shear stress value was related to the location and tensile strain, and when the stress difference was larger than 500 MPa, the interface would crack.

Microstructure and corrosion behavior of low temperature carburized AISI 304 stainless steel

In the present investigation, AISI 304 austenitic stainless steel was low temperature plasma carburized at 460 °C using gaseous acetone. Optical Microscopic observation (OM) and x-ray diffraction analysis (XRD) technology were used to characterize the microstructure and phase composition of the carburized layers. The hardness of the carburized layer was tested by microhardness tester. The corrosion behaviors of the carburized layers, especially the inner layers, were preliminary characterized based on the potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS). The experimental results show that after plasma carburizing, typical microstructure with ‘three layers’ characteristics was formed on stainless steel surface, i.e. the thin topmost layer, the top ‘grey layer’ and the inner ‘white layer’. The phases on the surface layer are mainly of the carbon ‘expanded’ austenite (γC), the carbon ‘expanded’ martensite (αC) and a trace of Fe3C phases. The surface hardness of the carburized stainless steel can be up to 933 HV0.1, which is about 5 times higher than that of the untreated one. For the stainless steel specimen plasma carburized for 8 h, the corrosion resistances of the topmost layer and the ‘white layer’ are better than that of the ‘grey layer’ under the present corrosion test conditions.

Effect of Interstitial Carbon on Anodic Polarization Behavior of Fe-33Mn-C Austenitic Steels

Interstitial carbon has been reported to successfully improve the corrosion resistance of austenitic stainless steels.1,2 Low-temperature carburizing treatments have been applied to introduce a substantial amount of interstitial carbon at the surface region of austenitic stainless steels. The carburizing treatments are known to dramatically improve the pitting corrosion resistance of austenitic stainless steels in chloride-containing environments. It has been proposed that the formation of a stable Cr2O3-rich passive film on the surface of the carburized stainless steel improves the corrosion resistance of these steels. 3 However, it has yet to be clarified whether interstitial carbon improves the corrosion resistance of non-chromium containing steels. With the aim of analyzing the effect of interstitial carbon on the corrosion behavior of steel, five Fe-33Mn-C steels, which were referred to as 0 C, 0.3 C, 0.6 C, 0.8 C, and 1.1 C steels according to their carbon content in mass%, were prepared in this study. The XRD patterns of the five steels indicated that the 0.3 C, 0.6 C, 0.8 C, and 1.1 C steels had a fully austenitic structure with no carbide precipitate, and the 0 C steel had a mechanical-grinding-induced ε-martensite in an austenite matrix. The increase in the lattice parameters of the 0.6 C, 0.8 C, and 1.1 C steels up to 0.78% over that of the 0.3 C steel calculated from the γ(111) peaks suggested that the added carbon was presented as interstitial carbon in the steels. Dot-like MnO and Mn-S-O inclusions with a diameter of less than 10 μm were evenly dispersed in the five steels. The 0.6 C, 0.8 C, and 1.1 C steels were passivated during the anodic polarization in 0.1 M Na2SO4 solution at pH 12.0, whereas the 0 C and 0.3 C steels actively dissolved. The anodic polarization measurements of the 0.3 C, 0.6 C, 0.8 C, and 1.1 C steels in 0.05 M Na2B4O7-NaOH buffer solution at pH 10.0 with 0.1 M Na2SO4 revealed that the dissolution current density of the steels decreased with higher amounts of interstitial carbon. The dissolution current density at 0.3 V vs. Ag/AgCl (3.33 M KCl) of the 1.1 C steel was reduced to about 1 × 10-2 A m-2, which was one hundredth that of the 0.3 C steel. A new finding demonstrated here is that a higher interstitial carbon content in the Fe-33Mn-C steels resulted in a stronger inhibition in the dissolution current density of the steels, resulting in an improvement in the corrosion resistance of the steels. The dissolution current density of the steels was not inhibited by CO3 2- ions, which is the expected dissolution product of the interstitial carbon, during the anodic polarization in Na2CO3-NaHCO3 buffer solution (0.1 M CO3 2-) at pH 10.0 with 0.1 M Na2SO4. It was confirmed that the decrease in the dissolution current density of the steels as a function of the interstitial carbon content measured in 0.05 M Na2B4O7-NaOH buffer solution at pH 10.0 with 0.1 M Na2SO4 was not the effect of the formation of CO3 2- ions in the solution. The XPS analysis of the 1.1 C steel detected the chemical shifts approximately 0.1 eV higher in the Fe 2p 3/2 electron binding energy and approximately 0.2 eV higher in the Mn 2p 3/2 electron binding energy compared with the peak positions of the Fe 2p 3/2 and Mn 2p 3/2 spectra measured for the 0 C steel. This can likely be attributed to the partial chemical bonding of interstitial carbon to iron and manganese, respectively. References. Y. Sun, Corros. Sci., 52, 2661 (2010).A. Chiba, S. Shibukawa, I. Muto, T. Doi, K. Kawano, Y. Sugawara, and N. Hara, J. Electrochem. Soc., 162, C270 (2015).A. H. Heuer, H. Kahn, F. Ernst, G. M. Michal, D. B. Hovis, R. J. rayne, F. J. Martin, and P. M. Natishan, Acta Mater., 60, 716 (2012).

Effect of Plasma Carburizing Treatment on Pitting Corrosion Resistance of Type 304 Stainless Steel

Pitting corrosion resistance of stainless steels was improved by plasma carburizing at low temperatures. From anodic polarization, carburized stainless steels showed higher pitting potential than that of untreated stainless steels, and no stable pit was generated. Inclusions acted as initiation sites for metastable pits, but no stable pit was observed on the carburized stainless steels. It is likely that active dissolution of steel matrix was suppressed by the interstitial carbon.

Enhancement of Stainless Steel's Mechanical Properties via Carburizing Process

Carburizing process is a method to disperse carbon into the steel surface in order to enhance its mechanical properties such as hardness and wear resistance. This paper study investigates the effect of carburizing temperature to the carbon dispersion layer in stainless steel. The standard AISI 304 stainless steel was carburized in two different temperatures which were 900°C and 950°C. The effect of carbon dispersion layers were observed and the results indicated that the increasing value of the average dispersion layer from 1.30 mm to 2.74 mm thickness was found to be related to increment of carburizing holding temperature . The increment of carbon thickness layer also resulted in improvement of hardness and tensile strength of carburized stainless steel.

Effect of Plasma Carburizing Treatment on Pitting Corrosion Resistance of Type 304 Stainless Steel

Stainless steels suffer from pitting in corrosive environment. Pitting corrosion resistance of stainless steels is known to be improved by carburizing at low temperatures.1,2)Plasma carburizing is suitable for stainless steel, since it is possible to keep low temperatures during the treatments to prevent sensitization. In this study, we analyzed the effect of plasma carburizing treatments on the pitting corrosion resistance of type 304 stainless steel. Specimen used was Type 304 stainless steel. Chemical composition in mass% was C: 0.036, Si:0.61, Mn:0.82, Cr:17.92 and Ni:7.93. The specimen was heat-treated at 1373 K and quenched in water. Before plasma carburizing, the surface of specimen was polished using SiC grinding paper and 1μm diamond paste. Plasma carburizing was carried out at 573 K or 743 K under the atmosphere of CH4:H2:Ar = 1.5:13.5:15 (sccm). The total pressure was kept at 550 Pa (at 573 K) or 650 Pa (at 743 K). The analysis of lattice parameters and phases was conducted using X-ray diffraction (XRD). The surface composition was analyzed by grow discharge optical emission spectroscopy (GD-OES). A scanning transmission electron microscope (STEM) equipped with an X-ray energy dispersive spectroscopy (EDS) system was used to identify the microstructure of the carburized specimen. In the electrochemical measurement, the surface of specimen was coated using epoxy resin and paraffin without the electrode area (ca. 0.05 mm2 or 100 mm2). The counter electrode was a Pt plate. The reference electrode was an Ag/AgCl electrode (3.33 M KCl). Anodic polarization measurements were conducted in 0.1 M NaCl (298 K).The potential scan rate was 23 mV min-1. After polarization, the specimen surface was observed using confocal laser scanning microscope and a field emission scanning electron microscope (FE-SEM). Figure 1a shows the XRD patterns of the carburized and untreated specimens. The lattice parameter of the austenitic phase was changed from 0.3599 nm to 0.3688 nm. And also, after the carburization, the austenitic phase was partly transformed into martensite. Figure 1b shows the GD-OES depth profile of the relative concentration of C, Ni, Cr and O in the specimen treated at 743 K. The thickness of the carburized layer was determined to be around 16 μm. The average of relative concentration of C was 2.5 mass%. Figure 1c shows the anodic polarization curves of specimens. In the case of untreated specimen, pit was initiated around 0.55 V, but the large current increases were observed at lower potentials for the carburized specimens. Figure 1d shows the surface appearance of the electrode area after the polarization. The intergranular corrosion occurred on the surface of the carburized stainless steel at 743 K. From STEM observation, Cr23C6 was precipitated after the plasma carburizing treatments. References 1) F.J.Martin, E.J.Lemieux, T.M.Newbauer, R.A.Bayles, P.M.Natishan, H.Kahn, G.M.Michal, F.Ernst, and A.H.Heuer, Electrochem.Solid-State Lett,10,C37(2007) 2) A.Chiba, S.Shibukawa, I.Muto, T.Doi, K.Kawano, Y.Sugawara, and N.Hara, J. Electrochem. Soc, 162,C270-C278(2015) Figure 1

Effect of Low-Temperature Carburizing Treatment on Improving Pitting Corrosion Resistance at Manganese Sulfide Inclusion in Type 304 Stainless Steel

Stainless steels suffer from pitting corrosion in chloride-containing environments. Sulfide inclusions, such as MnS, are known to act as the initiation sites of pitting on stainless steels. In our previous works, we studied the pit initiation behavior at the MnS inclusions in stainless steels. The pit initiation mechanism was found to be as follows: 1) the dissolution of the MnS inclusions in chloride-containing solutions leads to the deposition of elemental sulfur on and around the inclusions; 2) the synergistic effect of the elemental sulfur and chloride ions causes the dissolution of the steel matrix at the MnS/steel boundaries, resulting in the formation of trenches; 3) the hydrolysis reaction of Cr3+ released from the steel matrix dissolution decreases the pH in the trenches, and at the same time, the electrode potential at the bottom of the trenches decreases due to the IR-drop. Finally, the pit initiation is defined as the local transition from the passive to active state at the bottom of the trenches. It would appear that inhibiting the dissolution of the steel side at the MnS/steel boundaries improves the pitting corrosion resistance of stainless steels in chloride-containing environments. In recent years, it has been reported that low-temperature carburizing treatments which result in interstitial carbon content of more than 10 at% with no precipitation of carbides improve the corrosion resistance of stainless steels; however, the mechanism is not well understood. In addressing the improvement of the pitting corrosion resistance of stainless steels, it is necessary to understand the mechanism of the effect of low-temperature carburizing treatments on the pit initiation at the MnS inclusions in stainless steels. The anodic polarization curves of a micro-scale electrode area with a MnS inclusion of the untreated and the carburized re-sulfurized Type 304 stainless steels (Mn: 1.32, S: 0.029 mass%) were measured in 0.1 M NaCl. Figure 1 shows the microscopic anodic polarization curves and the surface appearances of the inclusions after the polarization. The surface dissolution of the MnS inclusions resulted in broad peaks around 0.4 V in the anodic currents both of the untreated and the carburized specimens (Fig. 1a). In the polarization curve of the untreated specimen, sharp increases in current density due to the pit initiation were measured in the potential range of the dissolution of the MnS inclusion. These pits were initiated at the MnS inclusion marked by the arrows in Fig. 1b. The current peaks in the polarization curve of the carburized specimen were much smaller than those indicating the pit initiation on the untreated specimen. Neither metastable nor stable pits were initiated at the MnS inclusions in the carburized specimen (Fig. 1c). Figures 1d-e display enlarged views of the areas enclosed by the broken lines in Figs. 1b-c, respectively. A wide and deep trench was formed at the MnS/steel boundary on the untreated specimen (Fig. 1d). In contrast, a narrow and shallow trench was formed at the boundary on the carburized specimen (Fig. 1e). These results suggest that the improved resistance to pitting corrosion at MnS inclusions after the carburizing treatment can be attributed to the reduced scale of the trenches formed at the MnS/steel boundaries in chloride-containing solutions. It is assumed that the dissolution of the steel matrix forming the trenches at the MnS/steel boundaries is caused by the synergistic effect of elemental sulfur and chloride ions. To compare the active dissolution rate of the untreated and the carburized stainless steel matrix in a sulfur suspension with chloride ions, macroscopic anodic polarization curves were measured. The low-sulfur Type 304 stainless steel (Mn: 0.82, S: 0.0002 mass%) was used. The sulfur suspension was produced by the acidification of a thiosulfate-containing solution. It has been reported that the dissolution of the MnS inclusions produces thiosulfate ions (S2O3 2-) and hydrogen ions which decrease the solution pH around the inclusions to approximately 3. The polarization curves were therefore measured in 3 M NaCl – 1 mM Na2S2O3 solution at pH 3.0 (Fig. 2). The active dissolution rate at -0.3 V of the untreated stainless steel was about 500 A/m2, whereas that of the carburized stainless steel was reduced to about 5 A/m2, approximately one hundredth that of the untreated stainless steel. From these results, we can conclude that the carburizing treatment inhibits the active dissolution rate of stainless steel matrix in solutions with elemental sulfur and chloride ions, resulting in a reduction in the dissolution depth of the trenches at the MnS/steel boundaries. Therefore, no pit initiation occurs at the MnS inclusions on the carburized stainless steel in chloride-containing solutions. Figure 1

Microelectrochemical Aspects of Interstitial Carbon in Type 304 Stainless Steel: Improving Pitting Resistance at MnS Inclusion

Type 304 stainless steel was subjected to low-temperature carburizing treatment to add excess interstitial carbon to its surface. The average carbon concentration in the carburized layer was ca. 2.6 mass%, and the lattice parameter was expanded by ca. 2.5% without any carbide precipitation. No pitting was initiated on the carburized stainless steel in 0.1 M NaCl. Microscopic polarization measurements of a small area with a MnS inclusion were performed in NaCl and Na2SO4 solutions to clarify the mechanism of the improved resistance against pitting corrosion. The anodic polarization in 0.1 M NaCl and 0.1 M Na2SO4 demonstrated that the carburizing treatment has little or no effect on the electrochemical dissolution behavior of the MnS inclusions. However, from the anodic polarization of the steel in the solution that simulates the vicinity of the dissolved MnS inclusions in chloride-containing environments, it was clarified that the carburizing treatment inhibits the active dissolution rate of the steel matrix to about one hundredth. It would appear that interstitial carbon inhibits the dissolution rate of the steel, resulting in a reduction in the dissolution depth of the trenches at the MnS/steel boundaries. It is likely that the carburization resulted in a suppression of both the acidification due to the hydrolysis reaction of Cr3+ and the potential decrease due to IR-drop in the trenches to the extent that the corrosivity inside the trenches is insufficient for the localized transition from the passive to active state. Therefore, pit initiation does not occur at the MnS inclusions on the carburized stainless steel in chloride-containing environments.

An XAS Study of the Surface of Low-Temperature Carburized Stainless Steel

X-ray absorption spectroscopy (XAS) is used to study the surface of low temperature carburized 316L stainless steel (SS) and untreated 316L SS to determine how the carburization process affects the surface structure of the treated samples. Low temperature carburization greatly improves the corrosion resistance and mechanical properties of stainless steel. The step heights in the XAS for the primary metal atoms remain the same for both carburized and untreated samples, indicating no significant change in the relative concentrations of each of the different metals in the surface. The location of the carbon has been determined to be in the octahedral interstices of the FCC lattice.

An XAS Study of the Surface of Low-Temperature Carburized Stainless Steel

not Available.

Tribocorrosion behavior of low temperature plasma carburized stainless steel

Low temperature plasma carburizing is a plasma surface engineering technique developed for austenitic stainless steels to achieve combined improvements in tribological and corrosion resistant properties. However, until recently very little work has been conducted to study the response of carburized stainless steel to combined actions by wear and electrochemical corrosion. In this paper, the tribocorrosion behavior of low temperature plasma carburized AISI 316L stainless steel under unidirectional sliding in 1M H2SO4 and 0.5M NaCl solutions is compared. It is found that in both test solutions, the carburized layer exhibits much better resistance to material removal than the untreated specimen at anodic potentials, but its effectiveness in improving wear resistance at open circuit and cathodic potentials is less significant. Particularly, in the pitting environment containing 0.5M NaCl, numerous corrosion pits are formed inside the wear track on the untreated specimen at potentials much lower than the pitting potential, while no corrosion pits are observed inside the wear track on the carburized specimen at anodic potentials as high as 1000mV(SCE). Further experiments conducted in 1M H2SO4 solution at various contact loads and frequencies reveal that the carburized layer has a much better ability to repassivate than the untreated specimen. The much improved tribocorrosion behavior of the carburized layer can thus be attributed to its high hardness, good corrosion resistance and excellent repassivation ability.

Surface Polishing of Plasma Carburized Austenitic Stainless Steel

After being plasma carburized, the surface of AISI 316 austenitic stainless steel was covered with a layer of compact black thin-film. The surface polishing treatment, electrochemical brightening was carried out to remove the black thin-film and renew the original color of the stainless steel. The surface appearance, microstructures, micro hardness, surface roughness and corrosion resistance of the samples treated by electrochemical brightening process were analyzed. Experimental results show that the electrochemical brightening treatment can remove the black thin-film from and restore the original color of the plasma carburized stainless steel. After electrochemical brightening treatment, the thickness and surface hardness of the carburized layer were all decreased little, but the corrosion resistance was improved significantly. And the surface roughness (Ra) was lower than before. Therefore, the electrochemical surface brightening treatment can be used to improve the surface quality of the austenitic stainless steel treated by plasma carburizing.

Low-Temperature Carburized Stainless Steels: An XAS Study

not Available.

Plasma Carburizing and Post-Treatment of Austenitic Stainless Steel

Plasma carburizing of AISI 316L austenitic stainless steel was carried out at low temperature to improve the surface hardness without degradation of its corrosion resistance. And the post-treatment, namely electrochemical surface brightening process was carried out to clear away a layer of thin black film on the plasma carburized samples and improve the surface quality of the hardened stainless steel. The surface appearance, roughness, microstructures, microhardness and corrosion resistance of the samples before and after brightening were analyzed and compared. Experimental results of plasma carburizing at low temperature showed that high-quality hardened layers can be produced at the appropriate process parameters.The electrochemical brightening process can be used as a post-treatment to restore the original color and further improve the corrosion resisitance of the plasma carburized stainless steel.

Effect of electrochemical potential on tribocorrosion behavior of low temperature plasma carburized 316L stainless steel in 1 M H 2SO 4 solution

Low temperature plasma carburizing is a surface engineering technique developed for austenitic stainless steels to achieve combined improvements in tribological and corrosion resistant properties. However, very little work has been conducted to study the response of carburized stainless steel to combined actions by wear and electrochemical corrosion. In the present work, experiments have been conducted to study the tribocorrosion behavior of low temperature plasma carburized AISI 316L stainless steel, under unidirectional sliding in 1 M H 2SO 4 solution, using a pin-on-disk tribometer integrated with a potentiostat for electrochemical control. Sliding wear tests were conducted under potentiodynamic and potentiostatic conditions at a wide range of applied potentials. It is found that the carburized layer exhibits much better tribocorrosion resistance than the untreated specimen at anodic potentials, but is not effective in improving wear resistance at cathodic potentials. The results are discussed in terms of the accumulation of the third body wear particles, material transfer and the contribution of mechanical wear and chemical wear to overall material removal by tribocorrosion.

Surface Roughness and Initial Pressure Effect on Superplastically Carburized Duplex Stainless Steel

Superplastic carburizing (SPC) is a carburizing process that combines carburizing with superplastic deformation. Since SPC involves direct interaction between the superplastically deformed surface and the solid carbon medium, the effect of surface roughness on the process cannot be disregarded. This paper presents the study of surface roughness and initial pressure effects on superplastic carburizing of duplex stainless steel (DSS). SPC was conducted under four different surface roughness (Ra) conditions of 0.9, 0.3, 0.1 and 0.03 μm. The microstructure, surface hardness, and carburized layer thickness were studied. Comparisons were also done on non-superplastic material which has a coarse microstructure. The results showed that the surface roughness strongly affected the properties of the superplastically carburized duplex stainless steel while its effects on the non-superplastic material were not that obvious.

Transformation of expanded austenite to an amorphous ferromagnetic surface layer during laser carburization of austenitic stainless steel

Abstract The presented experiments that were carried out in order to advance the understanding of the transformation of expanded austenite into an amorphous ferromagnetic surface layer during laser carburization of austenitic stainless steel. Therefore laser carburized austenitic stainless steel was investigated by means of X-ray diffraction, Mössbauer spectroscopy, Rutherford backscattering and magneto-optical Kerr-effect. Five to seven sub-spectra attributed to different iron sites were resolved in the Mössbauer spectra for this iron-carbon austenite. The isomer shifts, the quadrupole splittings and in particular the subspectra fractions depend on the carbon content. The formation of an amorphous and soft ferromagnetic phase was found in the laser treated surface.

Surface modification by ion chemical and physical erosion

Physical and chemical ion erosion surface interactions are observed for various elements and composite materials such as Si, B, C, TiB 2, WCCo cermet, and stainless steel which have been bombarded by low energy (50–1800 eV) hydrogen ions. Extrapolations of hydrogen erosion yields to zero hydrogen ion energy indicate that compounds or elements which are capable of forming volatile compounds with hydrogen undergo selective removal from surface and near surface regions. Auger depth profiling indicates that carbon can be selectively removed from near surface regions of cemented carbides and carburized stainless steel. Similarly, boron can be selectively removed from TiB 2. The results of this study may be extended to a variety of materials in which surface composition modifications are of interest.

Surface modification by ion chemical and physical erosion∗

Abstract Physical and chemical ion erosion surface interactions are observed for various elements and composite materials such as Si, B, C, TiB 2 , WCCo cermet, and stainless steel which have been bombarded by low energy (50–1800 eV) hydrogen ions. Extrapolations of hydrogen erosion yields to zero hydrogen ion energy indicate that compounds or elements which are capable of forming volatile compounds with hydrogen undergo selective removal from surface and near surface regions. Auger depth profiling indicates that carbon can be selectively removed from near surface regions of cemented carbides and carburized stainless steel. Similarly, boron can be selectively removed from TiB 2 . The results of this study may be extended to a variety of materials in which surface composition modifications are of interest.