18Cr-8Ni Stainless Steel Research Articles

High Temperature Oxidation of a High N, High Si, Mn Free Austenitic Stainless Steel

The oxidation of a high silicon content nitrogen containing austenitic stainless steel has been studied at 1173°K for 100 hours under synthetic air. The results are compared with those of a traditional 18Cr-8Ni stainless steel and show that the increased silicon content has a marked and beneficial effect. The oxidation behaviour of the high silicon content steel was shown by thermogravimetric data to have a weight gain 7.53 times less than the classical steel after 100 hours. Scale adhesion characteristics are improved and associated with the formation of a continuous SiO 2 sub-scale beneath the main Cr 2 O 3 scale. This continuous silica layer conferred increased protection against high temperature oxidation.

Cyclic Oxidation Performance of a CVD-FBR Aluminised 18Cr-8Ni Stainless Steel

Stainless steel is still the material of choice because it finds numerous applications and its good performance in different environments and its relatively low price. However, its poor mechanical strength and the formation of volatile CrO 3 oxide under oxygen environments restrict their upper operation temperature to less than 950° C. Thus, the application of aluminide coatings may increase the upper limit of temperature of these steels in case they did not have to withstand important mechanical loads. Chemical Vapour Deposition in Fluidised Bed Reactors (CVD-FBR) has been used to coat the AISI 304 stainless steel at temperatures of 525° C for 1.5 hours followed by a heat treatment up to 900° C under inert Ar gas. Cyclic oxidation experiments of both coated and uncoated specimens have been performed at 950° C under atmospheric pressure of air. The results will show that the application of the CVD-FBR is very promising as a surface modification technology since the behaviour of the coated specimens is much better than that of the uncoated ones.

Micro-bending of Thin Spring by Laser Forming and Spark Forming

To attain accurate bending of thin plate springs, spark forming in which a plate is bent by thermal stress due to electric spark is proposed. Experiments are performed with plate springs of 50μm or 70μm thickness made of beryllium copper, pure titanium, pure copper and 18Cr-8Ni stainless steel, and the results are compared with those of laser forming. The bending angle can be controlled with an accuracy of 1×10 −4 degree by the proposed method. It is concluded that spark forming has advantages in the variety of applicable materials, efficiency of energy, cost and space of apparatus over laser forming.

XPS, AES and ToF‐SIMS investigation of surface films and the role of inclusions on pitting corrosion in austenitic stainless steels

Chemical inhomogeneities (inclusions) present in the alloy are known to affect the stability of the passive film on stainless steels in the presence of chloride ions. In this work, three surface analytical techniques— XPS, AES and time-of-flight SIMS (ToF-SIMS)— have been used to characterize the surface films formed on stainless steels following mechanical polishing and immersion in an aggressive 6% FeCl3 solution, which is utilized for testing the pitting corrosion resistance of stainless steels. Two 18Cr8Ni stainless steels were investigated: one with a low sulphur content, DIN 1.4301 (0.003% S), and one with a high sulphur content, DIN 1.4305 (0.29% S). The XPS results show that the surface films on both steels are composed of mixed iron–chromium oxyhydroxides with a higher chromium content compared to the bulk composition. The average passive film composition and the film thickness remained unchanged despite increasing sulphur content in the steel after mechanical polishing. Angle-resolved XPS results suggest the presence of hydroxides in the outer layer of the passive film, which is confirmed by ToF-SIMS its high surface sensitivity. Auger and ToF-SIMS imaging with high lateral resolution allow the inclusions to be characterized: sulphur and manganese maps show the power of imaging SIMS for studying the distribution of elements that are present in very low concentrations. It is shown that on the MnS part of the inclusions no (protective) oxide or hydroxide film is formed after mechanical polishing. This might be the reason for the well-documented role of these inclusions as pit initiation sites. Copyright © 2000 John Wiley & Sons, Ltd.

XPS, AES and ToF-SIMS investigation of surface films and the role of inclusions on pitting corrosion in austenitic stainless steels

Chemical inhomogeneities (inclusions) present in the alloy are known to affect the stability of the passive film on stainless steels in the presence of chloride ions. In this work, three surface analytical techniques— XPS, AES and time-of-flight SIMS (ToF-SIMS)— have been used to characterize the surface films formed on stainless steels following mechanical polishing and immersion in an aggressive 6% FeCl3 solution, which is utilized for testing the pitting corrosion resistance of stainless steels. Two 18Cr8Ni stainless steels were investigated: one with a low sulphur content, DIN 1.4301 (0.003% S), and one with a high sulphur content, DIN 1.4305 (0.29% S). The XPS results show that the surface films on both steels are composed of mixed iron–chromium oxyhydroxides with a higher chromium content compared to the bulk composition. The average passive film composition and the film thickness remained unchanged despite increasing sulphur content in the steel after mechanical polishing. Angle-resolved XPS results suggest the presence of hydroxides in the outer layer of the passive film, which is confirmed by ToF-SIMS its high surface sensitivity. Auger and ToF-SIMS imaging with high lateral resolution allow the inclusions to be characterized: sulphur and manganese maps show the power of imaging SIMS for studying the distribution of elements that are present in very low concentrations. It is shown that on the MnS part of the inclusions no (protective) oxide or hydroxide film is formed after mechanical polishing. This might be the reason for the well-documented role of these inclusions as pit initiation sites. Copyright © 2000 John Wiley & Sons, Ltd.

Solidification Morphology and Microstructure Properties at Increased Cooling Rates for 18-8 Cr–Ni Stainless Steel

Solidification Morphology and Microstructure Properties at Increased Cooling Rates for 18-8 Cr–Ni Stainless Steel

Solidification Morphology and Microstructure Properties at Increased Cooling Rates for 18-8 Cr-Ni Stainless Steel

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In situ atomic force microscope observation of initial stages of corrosion at 18Cr–8Ni stainless steel

Atomic force microscope (AFM) was applied to the investigation of the initial stages of corrosion at 18Cr–8Ni stainless steel. Surfaces of electrochemically or mechanically polished specimens were in situ observed by AFM in a 0.89 M NaCl solution or a 1 M buffered Na2SO4 solution while measuring potentiostatic polarization curves. The mechanical polishing resulted in a substantial increase in corrosion rates, and a dramatic change in surface morphology to a facet structure has been observed in a 0.89 M NaCl solution during an anodic potential sweep up to 0.5 V. The electrochemical polish or the anodic polarization in 1 M buffered Na2SO4 leads to a lower corrosion rate, and the transition from passive to transpassive corrosion states has been clearly detected by AFM as well as in potentiostatic polarization curves. The detailed in situ observation has revealed that the transpassive film is formed on the surface with an oriented rectangle morphology.

Preparation of High Nitrogen Cr-Ni and Cr-Mn Stainless Steel Powders by Mechanical Alloying and their Compositional Dependence of Austenitizing

Mechanical alloying(MA) of elemental powder mixtures, with Fe-9.85mass% N alloy powders, of high nitrogen Cr-Ni and Cr-Mn stainless steel(SS) type compositions was performed in an argon atmosphere using a planetary ball mill. Using the MA process, high nitrogen Cr-Ni and Cr-Mn SS powders with nanostructures are readily prepared after ca. 300ks of processing. In the MA processing of Fe 80-x-y Cr 20 Ni y N x (x=0-20, y=2-17) and Fe 79.3-x-y Cr 19 Mo 1.7 Mn y N x (x=0-7, y=5-24) (at.%) materials, nitrogen markedly promotes austenitizing of the MA powders in both systems, the effect particularly being striking up to near x=4( ca. 1 mass%). The noticeable effect of N is also supported from the Gladman's equation indicating that in austenitic SSs the addition of N or C is most effective in lowering the onset temperature of the strain-induced martensite formation. The austenitic compositional region of MA materials of Fe-Cr-Ni-N is considerably wide compared with that of Fe-Cr-Mn-Mo-N. The austenitizing of MA materials of the Fe 96-y-z Cr z Ni y N 4 (y=4-16, z=20-26) and Fe 86.7-z Cr z Mn 8 Mo 1.7 N 3.6 (z=13-19) (at.%) systems increases with increased Cr content.

共晶組織を伴うボロン含有18Cr-8Niステンレス鋼の凝固過程における高温変形挙動

Tensile strength and ductility behavior of borated 18Cr-8Ni stainless steel samples during solidification has been studied by the technique for high temperature tensile test. Density of samples has been measured by a sessile drop method during solidification.Borated 18Cr-8Ni stainless steel has formed eutectic morphologies in addition to dendritic structure during solidification. The ratio of eutectic structure increased with increasing boron concentration. Eutectic composition was 2.2 mass% boron from the result of differential thermal analysis. The behavior of tensile strength and ductility has depended on the morphologies of solidification microstructure. When the ratio of eutectic structure was more than 70%, tensile strength and ductility has not appeared until fraction of solid became unity. Density of samples was unaffected by eutectic structure.

Hot and Cold Rolling of High Nitrogen Cr-Ni and Cr-Mn Austenitic Stainless Steels

Behavior of austenitic Cr-Ni-(0.14-0.50)N and Cr-Mn-(0.78-1.00)N steels in hot and cold rolling was investigated by rolling experiments and mechanical testing. Structure of the steels in the as-cast condition and fracture surfaces after the rolling experiments were investigated using optical and scanning electron microscopy (SEM). Resistance to deformation was calculated using rolling forces in hot rolling. Increase in strength in the rolling experiments was related to the nitrogen content of the steels. Resistance to deformation during hot rolling increased with decreasing rolling temperature and with increasing nitrogen content. In some steels, hot rolling led to edge cracking, which was more a function of impurity than nitrogen content. Microscopy revealed that the edge cracking occurred along grain boundaries and second phase particles. For the cold-rolled steels, the highest achievable reductions were limited due to a “crocodiling” phenomenon, that is, opening of the strip end. Fracture type at the opened strip end was a brittle-like fracture.

High temperature corrosion protection of austenitic AISI 304 stainless steel by Si, Mo and Ce ion implantation

Abstract The influence of implanted silicon, molybdenum and cerium on the oxidation behaviour of a 18Cr8Ni stainless steel was studied at 1173 K up to 144 h in air under isothermal conditions in order to verify the enhanced selective oxidation of chromium by these elements. The implanted surface and the corrosion products formed were characterized by means of AES, SEM, EDS and XRD. Implanted depth profiles were calculated by TRIM96 computational code. The implanted silicon and cerium markedly improved protection against oxidation of the alloy by enhanced chromium transport while molybdenum gave rise to an accelerated oxidation due to the formation of volatile MoO 3 species. Further, ion implantation was found to play a beneficial effect against decarburization of the alloy.

Epitaxial growth and phase formation of austenitic stainless steel weld metals near fusion boundaries: Study of solidification and transformation of Cr-Ni stainless steel weld metals (3rd Report)

Summary This paper describes an investigation of the solidification behaviour of austenitic stainless steel weld metals at fusion boundaries, focusing particularly on epitaxial growth and primary phase selection. In the AF solidification mode, the planar austenite grows epitaxially from the austenite grains in the base metal. Ferrite subsequently forms at the dendrite boundaries of the primary austenite after the austenite changes from planar to dendritic. In the FA solidification mode, the planar austenite grows epitaxially from the austenite grains in the base metal as a result of competition between ferrite nucleation and austenite growth. Ferrite nucleation then ensues through enrichment of Cr in the liquid and ferrite subsequently continues to grow as the primary phase. The ferrite establishes the Kurdjumov-Sachs crystallographic orientation relationship (K-S relationship) with the planar austenite. At the stage of primary ferrite solidification, austenite solidifies as the second phase at the dendrite boundaries and has the same crystallographic orientation as the original planar austenite. During FA mode solidification of the sample with the lowest Cr-Ni ratio, it is also possible for the austenite to solidify as the primary phase because of solute fluctuations in the liquid and sub-cooling changes due to local changes in the temperature gradient in the liquid.

Solidification and transformation behaviour of Cr-Ni stainless steel weld metals with ferritic single-phase solidification mode: Study of solidification and transformation of Cr-Ni stainless steel weld metals (4th report)

Summary This paper describes an investigation of the microstructural changes taking place in Cr-Ni stainless steel weld metals exhibiting ferritic single-phase solidification behaviour from the solidification stage down to room temperature. These steels initially show precipitation of the austenite at the ferrite grain boundaries on cooling. Continuous intergranular austenite is then formed by the coalescence of globular austenite along the grain boundaries. The austenite has the Kurdjumov-Sachs crystallographic orientation relationship (K-S relationship) with the ferrite on both sides and selects different combinations of close-packed planes and directions for each ferrite. Widmanstätten austenite, which has the same crystallographic characteristics as the intergranular austenite, subsequently grows into ferrite grains. In duplex stainless steel weld metals containing nitrogen, intragranular austenite precipitates after the formation of intergranular austenite. Nitrogen diffusion primarily controls the precipitation of both intergranular and intragranular austenite. With increasing Cr and Ni contents, precipitation of intragranular austenite increases because of an increase in microsegregation during solidification.

Efectos gammágenos del cobre en los aceros inoxidables 18Cr8Ni

From a series of 22 typical 18Cr8Ni stainless steel 40 kg ingots, with copper variable concentrations from 0.6 to 3.0 weight %, δ-ferrite is measured with a ferrite-meter device, calculating a nickel equivalent of 0.27 for copper. Some differences between the 8-ferrite and that on calculated by DeLong -excluding the copper γ-gene action- have been found because of different solidification and cooling regimes in ingot and weld cases.

PROJECT 70/PROJECT 7000 STAINLESS TYPE 304

Abstract Project 70 and Project 7000 Type 304 stainless steel are versions of conventional AISI Type 304 (18Cr-8Ni) stainless steel having improved machinability and higher tensile and creep strengths. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fracture toughness and creep. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SS-418. Producer or source: Carpenter. Originally published January 1983, revised September 1997.

Deformation Induced Martensitic Transformation in Cr–Ni Stainless Steel Irradiated by Neutrons

physica status solidi (a)Volume 163, Issue 1 p. R7-R8 Research Letter Deformation Induced Martensitic Transformation in Cr–Ni Stainless Steel Irradiated by Neutrons O. P. Maksimkin, O. P. Maksimkin Institute of Physics and Technology, 480082 Almaty, Kazakhstan Phone (32–72) 690163, Fax (32–72) 690–571,Search for more papers by this author O. P. Maksimkin, O. P. Maksimkin Institute of Physics and Technology, 480082 Almaty, Kazakhstan Phone (32–72) 690163, Fax (32–72) 690–571,Search for more papers by this author First published: 16 November 2001 https://doi.org/10.1002/1521-396X(199709)163:1<R7::AID-PSSA99997>3.0.CO;2-TCitations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume163, Issue1September 1997Pages R7-R8 RelatedInformation

Characterization of the transport processes in FeCrNi stainless steel

Measurements of electrical resistivity, X-ray diffraction and DTA were used to characterize the transport processes developed in an Fe-12.1 Cr-7.37 Ni (wt.%) stainless steel during heating from 300 to 980 K and subsequently during cooling to room temperature. The results revealed that this steel exhibits two transport regions during heating and only one during cooling. In case of heating, the first transition region (observed in the temperature range 650–730 K) is not to a structural but may be a magnetic transition. The second transition region (observed in the temperature range 885–915 K) is ascribed to the austenitic structural transformation. During cooling, a unique transition region was observed in the range 560-434 K. This was attributed to the martensitic transformation which may also be associated with a magnetic transition. From the DTA data, the effective activation energy for the austenitic transformation was determined to be 459.3 kJ mol−1. In the temperature ranges other than the transition regions the electrical resistivity fits a linear equation rather than the Bloch-Grüneisen equation.

Compression fatigue crack growth behavior of metallic alloys: Effect of environment

Many structures are subjected to cyclic compressive loading and corrosive atmosphere. However, research on environmentally-assisted compression fatigue of metallic materials has not yet been undertaken. In the present paper, the behavior of fatigue cracks under compressive cycling in laboratory air, mineral oil and 3.5% NaCl was studied on circumferentially notched cylindrical specimens of an Al-alloy and CrNi stainless steel. Fatigue tests were supplemented by fractographic observations. In oil and air, the non-catastrophic character of the compression fatigue crack growth process was confirmed for both materials. The saturation depth of the crack was found to depend on the material as well as on the nominal stresses, but was insensitive to the load frequency in a range of 2–110 Hz. In the case of the aluminum alloy tested at low load frequency in 3.5% NaCl, continuous growth of fatigue crack was observed. The role of hydrogen embrittlement and anodic dissolution in promoting fatigue damage under compressive cycling is discussed and the mechanism rationalizing observed behavior is proposed. The detrimental influence of corrosive environment is attributed to the crack tip blunting via anodic dissolution and concomitant development of the tensile residual stresses ahead of the crack growing under compressive cycling. If operative in service, the above mechanism may cause a catastrophic failure even under fully compressive cyclic loading.

Relative roles of ion energy, ion flux, and sample temperature in low-energy nitrogen ion implantation of FeCrNi stainless steel

A matrix of nitrogen ion energies (0.4, 0.7 and 1.0 keV) and ion fluxes (1, 2, and 3 mA/cm 2) has been selected to investigate the systematics of ion-beam processing of an austenitic FeCrNi stainless steel (AISI 304) at 400°C for 60 min. In addition, the role of temperature was examined over the range from 280°C to 475°C at fixed processing conditions of 0.7 keV, 2 mA/cm 2, and 60 min. Characterization of the composition, structure, magnetic nature, thickness and strength of the nitrogen-containing layers was made by a combination of Auger electron spectroscopy, X-ray diffraction, backscatter Mössbauer spectroscopy, and microhardness measurements. A high N content layer, which is a magnetic, fcc phase, is predominant for all conditions and its thickness increases linearly with either ion energy at fixed ion flux or with ion flux at fixed ion energy. This behavior is consistent with layer growth that is controlled primarily by the N supply rate into the first few atomic layers rather than by thermal diffusion.