Stainless Alloys Research Articles

Pressure variation of the magnetic state in Co–Fe–Cr stainless Invar alloy

Magnetic properties of a Co 52.5Fe 38Cr 9.5 Invar alloy have been investigated under high-pressure by ac susceptibility measurements. With increasing pressure, ferromagnetic ground state disappeared and new high-pressure magnetic states came to appear. Further increasing pressure up to 4.6 GPa, the high-pressure magnetic states vanished and no magnetic signal observed in the investigation range 5–300 K. These pressure variations of magnetic phases are similar to Fe based Invar alloy. So far considering from the series of our experimental results, it is concluded that the moment-volume instability in Invar alloys are associated with a several magnetically ordered phases that exist in low volume side of ground state. These facts support some theoretical model for the origin of Invar effect.

Residual stress characterization of welded specimens by non-destructive activation technique

Welded specimens consisting of Type 304L stainless steel and/or Alloy EP-823 were tested for evaluations of the extent and nature of resultant residual stress in terms of line-shape parameters based on the activation technique associated with positron annihilation spectroscopy. A maximum residual stress was estimated near the welded region of specimens of similar and dissimilar materials. It is suggested that the compressive residual stress in the vicinity of the fusion line of Alloy EP-823 side of the welded specimen may be attributed to the volume increase and plastic strain developed during its rapid cooling and solidification.

Creep behavior of a new cast austenitic alloy

A new cast austenitic alloy, CF8C-Plus, has been developed by Oak Ridge National Laboratory (ORNL) and Caterpillar for a wide range of high temperature applications including diesel exhaust components and turbine casings. The creep strength of the CF8C-Plus steel is much greater than that of the standard cast CF8C stainless steel and is comparable to the highest strength wrought commercial austenitic stainless steels and alloys, such as NF709. The creep properties of CF8C-Plus are discussed in terms of the alloy design methodology and the evaluation of some long-term creep tested specimens (over 20,000 h). Microcharacterization shows that the excellent creep strength is due mainly to the precipitation of very fine nano-scale and stable MC carbides, without the formation of deleterious intermetallic phases.

Corrosion of Austenitic Alloys in Supercritical Water

Abstract The purpose of this study was to determine the mechanism by which austenitic iron- and nickel-based alloys oxidize in pure supercritical water. Austenitic stainless steel alloys Type 304 (UNS S30400) and Type 316L (UNS S31603) and nickel-based Alloy 625 (UNS N06625) and Alloy 690 (UNS N06690) were exposed in deaerated supercritical water over the temperature range from 400°C to 550°C. Exposure experiments resulted in the formation of a two-layer oxide on Type 304 and Type 316L in which the outer layer is porous magnetite (Fe3O4) and the inner layer is a denser iron-chromium spinel. In Alloy 690 the outer layer is iron-rich and the inner layer is composed of chromia (Cr2O3), nickel oxide (NiO), and Ni(Cr,Fe)2O4. The oxide on Alloy 625 was too thin to measure. Inner and outer oxides have the same grain orientation as the matrix on the stainless alloys, and on Alloy 690, the inner oxide has a common orientation with the matrix but the outer layer consists of randomly oriented oxides. The inner/outer...

Corrosion properties of Fe–24Cr stainless alloy modified by plasma immersion ion implantation in 0.5 M sulfuric acid solution

Ruthenium (Ru) and mixed Ru–Ti ions were implanted respectively into ferritic Fe–24Cr alloy using the plasma immersion ion implantation (PI 3) technique. Potentiodynamic and potential-time response measurements were used to characterize the corrosion behavior of Fe–24Cr alloy exposed to a deaerated sulfuric acid solution. The results showed that the ferritic alloy does not passivate in dilute sulfuric acid. However, plasma-implanted Ru ions can induce spontaneous passivation of the alloy exposed to a sulfuric acid solution. X-ray photoelectron spectroscopy (XPS) analysis showed that Ru is incorporated as Ru 4+ species in the hydrated chromium oxyhydroxide passive film formed on the Ru-implanted Fe–24Cr alloy.

Creep Strength and Microstructure of AL20-25+Nb Alloy Sheets and Foils for Advanced Microturbine Recuperators

The Oak Ridge National Laboratory (ORNL) and ATI Allegheny Ludlum worked together on a collaborative program for about two years to produce a wide range of commercial sheets and foils of the new AL20-25+Nb™ (AL20–25+Nb) stainless alloy for advanced microturbine recuperator applications. There is a need for cost-effective sheets/foils with more performance and reliability at 650–750°C than 347 stainless steel, particularly for larger 200–250 kW microturbines. Phase 1 of this collaborative program produced the sheets and foils needed for manufacturing brazed plated-fin air cells, while Phase 2 provided foils for primary surface air cells, and did experiments on modified processing designed to change the microstructure of sheets and foils for improved creep-resistance. Phase 1 sheets and foils of AL20-25+Nb have much more creep-resistance than 347 steel at 700–750°C, and those foils are slightly stronger than HR120 and HR230. Results for Phase 2 showed nearly double the creep-rupture life of sheets at 750°C/100 MPa, and similar improvements in foils. Creep data show that Phase 2 foils of AL20-25+Nb alloy have creep resistance approaching that of alloy 625 foils. Testing at about 750°C in flowing turbine exhaust gas for 500 h in the ORNL Recuperator Test Facility shows that foils of AL20–25+Nb alloy have oxidation-resistance similar to HR120 alloy, and much better than 347 steel.

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Welding skelp in continuous metallurgical units

One of the most important problems in modern metallurgy is ensuring the continuous (infinite) operation of metal-processing lines and equipment. Continuous electric-welded pipe production lines (EWPL) built by the Elektrostal’ Heavy Machinery Plant for making cylindrical tubes and shapes of low-alloy, medium-carbon, and stainless steels, copper, brass, and alloys of aluminum and titanium are equipped with butt-welding machines and pit-type, floor-mounted, or spiral loopers. Butt-welding machines and loopers of the indicated types are also installed in the strip-preparation lines of units used to make cored wire, cable sheating, and bent sections.

Applications of High Damping Stainless Alloy (HIDAS)

Fe-12Cr-22Mn and Fe-12Cr-22Mn-2Co (High Damping Stainless Alloy HIDAS) were developed and applied for suppression of noise or vibration. Since these alloys have high strength (1400Mpa) as well as high damping capacity (1020) due to/ interface, their direct replacements for the parts of machines were possible. In this respect, the applications were tried mainly to machineries and nanotechnologies. Those were bolt and nut, gear, bite shank, cutting tool of numerically controlled (NC) machine, brake and arm of hard disk drive (HDD) and others. In those applications, all data obtained showed better results compared with other materials. Cost down and quality control would be the remaining problems.

Microstructure and Machinability with Alloying Elements in the 304 Stainless Steel

To enhance the machinability of the austenite stainless alloys, Mn and S were added to form MnS in the austenite matrix. Recently, Ca is also added to increase machinability. The alloying elements, such as C, Mn, S, Ca, and Al, are known to affect machinability, but those roles are not well understood. In this study, the ingots, controlled of alloying elements, C, Mn, S, Ca, Al, were prepared in the 304 stainless steel. The relationship between microstructure and machinability was compared to understand the role of alloying elements. It was proved that Mn and S enhanced machinability but C reduced it by analyzing cutting force on machining in the lathe. The alloying elements, Ca and Al, made a complex oxide compound of Mn-S-Ca-Al-Si-O, which results in increasing tool life. The ferrite volume fraction was changed with alloying elements and the effect of the ferrite fraction on machining was also discussed.

Fe-Cr-Mn-(Co) High Damping Stainless Alloy (HIDAS)

Based on the recent requirements, high strength, high damping stainless alloy HIDAS was developed. The chemical compositions are Fe-12%Cr-22%Mn and Fe-12%Cr-22%Mn-2%Co. After solution annealing, microstructure consisting of austenite fcc , martensite hcp and bcc ’. When cold work was given, and increased. Damping capacity increased with the increase of phase. The mechanism of high damping capacity would come from the hysteretic motion of Shockley partial dislocations which are lying at interphase interface of /. This alloy has also high strength. This is due to fine structure of /. Because of these properties, HIDAS can be applied to machinery industries.

Development of a hydrothermal deposition process for applying zirconia coatings on BWR materials for IGSCC mitigation

An in situ hydrothermal deposition process is being developed to apply a film of zirconia (ZrO 2) onto interior surface of 304 stainless steel and Alloy 600 as a potential method for mitigating intergranular stress corrosion cracking (IGSCC) in boiling water reactors (BWRs). The coating process is discussed. The obtained zirconia coatings are adherent. Monoclinic ZrO 2 is the dominant phase when ZrO(ClO 4) 2 was the oxidant; tetragonal ZrO 2 became the dominant phase when ZrO(NO 3) 2 was the oxidant. A preliminary experiment did not measure significantly lower values of the electrochemical potential (ECP), relative to the uncoated specimen over a wide range of dissolved oxygen in 265 °C water.

Corrosion Rate and Oxide Scale Characteristics of Austenitic Alloys in Supercritical Water

Corrosion properties were investigated on stainless steels and Ni base alloys in supercritical water containing 0.01mol/kg-H2SO4 at 400°C/30MPa as a function of oxygen concentration ranging from 3ppb to 800ppm. Alloys with high Fe content showed an interesting contrast in corrosion property in sulfuric acid-containing supercritical water between at the high oxygen condition (800ppm) and at the lower oxygen conditions (3ppb and 8ppm). At 8ppm of oxygen concentration or lower, corrosion rate was a unique function of Cr content of the alloys including both Ni base alloys and stainless steels. However, corrosion resistance of the iron-based alloys (316 stainless steels) was remarkably improved when oxygen concentration was increased up to 800ppm. Corrosion rate of alloy C-276, which contains 5.7% of iron, was also somewhat reduced under the high oxygen condition, while corrosion rate of the other “iron-less” Ni base alloys was accelerated as oxygen level was increased. Characteristics of oxide scales, in terms of chemical composition and compound structure, have been examined in connection with the corrosion properties of the alloys.

Prediction of pitting corrosion behavior for stainless SUS 630 based on grey system theory

There are a number of factors that affect the pitting corrosion rate of stainless alloy with time being the definitive factor. Other factors such as environmental conditions and material properties cannot be controlled accurately. The trend prediction of pitting corrosion is usually based on a long-term experimentation process that requires large amounts of resources i.e. manpower, time and material and is dominated by the data collection activity. Due to the human factor and the uncontrollable sea condition factors in environmental test, it is possible to make errors during the experimentation period. In such a system grey theory is suitably utilized to predict the tendency of pitting corrosion behavior of stainless alloy used onboard ships.

Room-temperature aging of manganese-alloyed high nitrogen duplex stainless steels

The room-temperature aging behavior of two duplex stainless alloys with different austenite stability was investigated. Both alloys readily aged at room temperature. Even for aging times as short as 30 seconds, the originally continuous yielding behavior becomes discontinuous upon reloading after prestraining. The magnitude of the stress increase due to aging was higher in the presence of strain-induced martensite, even though it was shown that aging also occurred in the austenite phase. The aging response was shown to be thermally activated, with increasing age hardening associated with increasing aging times. The results could be explained by the combination of aging phenomena in the bcc phases by interstitials and the aging by interstitial-vacancy complexes in the fcc phase, where the interstitials are thought to be immobile during the short aging times used and aging would occur due to short-range migration of vacancies instead.

New Application of Stainless Steel

Several rigid substrates such as stainless steel, titanium alloy, aluminum alloy, nickel foil, silicon, and sodium lime glass have been employed for manufacturing high quality TiO2 films by metal organic chemical vapor deposition (MOCVD). The as-deposited TiO2 films have been characterized with SEM/EDX and XRD. The photocatalytic properties were investigated by decomposition of aqueous orange II. UV-VIS photospectrometer was employed to check the absorption characteristics and photocatalytic degradation activity. The results show that films synthesized on metal substrates display higher photoactivities than that on absolute substrates such as silicon and glass. It is found that solar light is an alternative to UV-light used for illumination during photodegradation of orange II. TiO2 film on stainless steel substrate was regarded as the best one for photocatalysis.

Atmospheric Stress Corrosion Cracking (ASCC) Susceptibility of Stainless Alloys for Metallic Containers

ABSTRACTMetallic canisters placed in concrete casks and containing spent nuclear fuel elements, will be exposed to a moist oceanic atmosphere while the decay heat generated in the fuel elements cools for more than fifty years. Thus, the surface environment of the metallic canisters will be wet and covered with chloride compounds. The canisters may suffer atmospheric stress corrosion cracking. Therefore, corrosion tests for some potential alloys were conducted in an aqueous bittern solution, containing 22% enriched chloride compounds simulating the expected surface conditions of the canisters, to aid in selecting appropriate alloys based on corrosion resistance. The results suggest that the corrosion resistance of ordinary stainless steels, such as SUS304 and SUS316, is not high enough to avoid ASCC (atmospheric stress corrosion cracking) in the environment. Thus, a higher-grade stainless steel, namely, NSSC270 (20Cr-18Ni-6Mo-0.2N-Low C)or SUS836L (23.5Cr-25Ni-5.5Mo-0.2N-Low C, equivalent to AL-6XN) has been selected for this application.

Proper coating selection for improved galling performance of forming tool steel

The aim of the present work was to investigate and compare different hard coatings as to the tendency for work material adhesion and galling properties when applied on forming tool steel and sliding against different work materials. The surface coatings included were PVD deposited TiN, TiB 2, VN, TaC and DLC coatings. They were all applied to cold work tool steel. Tribological evaluation was carried out in a load-scanning test rig, with the normal load being gradually increased during each test from 100 to 1300 N (1–3.5 GPa). The coated steel was tested against austenitic stainless steel and alloys of aluminium and titanium. This investigation clearly indicates that work material adhesion and galling performance of coated forming tool steel greatly depends on the type of work material. In the case of stainless steel, carbon-based coatings provide the best protection against the work material transfer, while forming of aluminium and titanium alloys, requires nitride type coatings, such as TiN.

Effects of dissolved oxygen on passive behavior of stainless alloys

A potential-control circuit has been devised to measure passive-current (corrosion rate) on stainless alloys in conditions simulating the usual noble drift of the open-circuit corrosion potential in the presence of passivating dissolved oxidizers. Open-circuit corrosion potential and passive-current decay were measured with and without dissolved oxygen in dilute sulfuric acid solutions as a function of time on austenitic stainless steel and a Ni-base Cr–Mo–W alloy. The results confirm the long-standing assumption that constant-potential potentiostatic tests give a good approximation of passive-film growth kinetics in the presence of passivating dissolved oxidizers. Mott–Schottky measurements showed that passive films on each alloy have similar semiconducting properties whether formed potentiostatically or by dissolved oxygen. In both cases, the passive film on stainless steel seems to be composed of an inner n-type barrier layer covered with an outer p-type layer. The passive film on the nickel-base alloy is primarily n-type with only weak evidence of p-type behavior in an outer layer. Results are in general agreement with predictions of the point-defect passive-film model proposed by Macdonald and coworkers.

An in vitro comparison of implant materials, cell attachment, cytokine and osteocalcin production

Bone deposition, for any implant system, is the deciding factor for the success. The biochemical signals at the cellular level will help elucidate the direction of host response. In this report, intercellular messenger, cytokines, that are regulatory for osteoblast and osteoclast function, were measured. Production of osteocalcin, a marker for osteoblast maturation was also estimated. Human osteoblast-like cells from osteosarcoma cell line MG 63 were grown in wells in the presence of titanium (Ti), titanium alloy (Ti6A14V) and stainless steel implant materials incubated at 37 degrees C. Interleukin-1alpha (IL-1alpha), IL-6, IL-8, IL-11 and osteocalcin were quantitated using standard enzyme linked immunosorbant assay (ELISA) kits from the growth media extracted at specific intervals over the critical ten day period. In all dishes, cells were seen adhering to the base after 24 hours and to confluence at 96 hours. Both IL-1alpha and IL-11 were not produced in sufficient quantities to be measured in the assay (< pg/ml). Interleukin-6 production was significantly higher for stainless steel than for titanium and the alloy. There was a progressive rise in osteocalcin production for titanium contrasted to a basal rate for stainless steel and alloy. Interleukin-8 levels for all metals and controls increased markedly after two days implicating inherent cellular characteristics. A relatively high constant range for macrophage colony stimulating factor from the first day was seen for all metals, including the controls. In conclusion, it appears that titanium implants activate osteocalcin production while stainless steel activates IL-6.