Mn Stainless Steel Research Articles

Electron Spectroscopy for Chemical Analysis Study of Corrosion Films Formed on Manganese Stainless Steels

Abstract Films formed on two grades of Mn stainless steels in 1 M hydrochloric acid (HCl) freely exposed to air at different potentials were examined using electron spectroscopy for chemical analysis (ESCA). The Cr content of the film, which is related closely to corrosion resistance of the base alloys, was lower within the films formed on Mn stainless steels as compared to a normal type 304 (UNS S30400) stainless steels. The film also contained significant amounts of Mn, Ni, and Cu. It was proposed that the presence of higher amounts of Mn, an electrochemically active element, with Cu resulted in poor passivation behavior of the present high Mn stainless steels.

Nitrogen Bearing Austenitic Stainless Steels for Surgical Implants

Nitrogen addition promotes substantial improvements on general and localized corrosion performance of stainless steels. In recent times high Nitrogen (up to 0.6 wt%) and Mn bearing super austenitic stainless steel has been studied for medical applications due to its low Ni content, the so called body friendly alloys. 18%Cr, 0.4%N and 15%Mn stainless steels were cast either from electrolytic or commercial master alloys in induction furnace, forged, solubilized at 1423K for 3 hours and water quenched. Delta ferrite and carbide precipitate free structures were observed. Potentiodynamic corrosion tests of all alloys in 0.5M sulfuric acid solution presented passive current density as low as those observed for AISI 316L stainless steel. Intergranular corrosion susceptibility testing, according to ASTM A262 - Practice A, were performed and samples made of electrolytic raw material presented step structures with no ditches at grain boundaries, pointing out no sensitization. Mechanical testing presented high yield and tensile strengths with 60% elongation. These properties can be attributed to the Nitrogen action on stacking fault energy of austenitic structure of the alloy. These results fulfill orthopedic implant materials application requirements. In vivo biological compatibility tests for two months showed no adverse reactions, no necrosis and no evidence of corrosion products on implanted materials.

Effect of Cold Working and Aging on High Temperature Deformation of High Mn Stainless Steel

By the addition of N, the strength of high Mn stainless steel can be increased. Cold rolling and aging are effective to increase its strength further, and with those treatments this grade is often used for high temperature applications. In this study, creep deformation behavior and high temperature strength of the high Mn stainless steel in cold rolled and aged conditions are discussed as compared to Type 304 stainless steel. It has been revealed that as-rolled specimens show instant elongation at the beginning of creep tests and its amount is larger in the high Mn grade than in Type 304. Also, the creep rate of the high Mn stainless steel is smaller than that of Type 304. These facts may be related to the change in microstructure.

Effect of applied potential on the nature of surface film and SCC of a high Mn stainless steel in 1 M HCl

The Stress Corrosion Cracking (SCC) behavior of a high Mn austenitic stainless steel (SS) with 14.67 wt % Mn was studied in 1 M hydrochloric acid at room temperature as a function of potential. At open circuit potential (OCP) thick black surface film formation and a transgranular mode of cracking were observed. At all applied anodic potentials general dissolution and ductile cracking were observed. X-ray photoelectron spectroscopy (XPS) studies were conducted to characterise the surface films formed at different potentials. The nature of the surface film was found to be different with a change in potential. The nature of the film formed was found to govern the dissolution behavior and therefore the fracture morphology of the alloy.

Initial oxidation of type 430 stainless steels with 0.09–0.9 Mn in O 2-N 2 atmosphere at 1273 K

Initial oxidation of type 430 stainless steels with Mn (0.09, 0.38 and 0.9 mass%) was studied in 0.165 atm O 2-N 2 atmosphere at 1273 K. For 0.09 Mn steel, only corundum type oxide was formed. Initially the oxide film was rich in Fe and the Cr concentration in the oxide increased with oxidation time until 30 s when the film composition became constant. The oxidation behavior of the 0.38 and 0.9 Mn stainless steels was similar to that of 0.09 Mn steel until 30 s, after which it became different: Mn(II) was detected at the film surface and spinel type oxide, which was nucleated from pre-existing corundum type oxide, appeared simultaneously. Between 30 and 300 s, the oxide composition and growth mechanism changed and finally the oxidation behavior reached a steady state. Different models of the oxidation processes are proposed for type 430 stainless steels with different manganese contents.

Evaluation of the corrosion and mechanical properties of a range of experimental CrMn stainless steels

In this resumed investigation, the effectiveness of manganese as an austenite-forming element in 17% and 20% chromium stainless steels has been investigated. The effect of manganese on the corrosion and mechanical properties of a range of experimental, low-cost, manganese-containing, dual-phase stainless steels is evaluated and reported.Metallographic examination and image analysis of the alloys revealed that manganese contents of up to 9%, in both 17% and 20% chromium alloys, are effective in producing a dual-phase structure comprising ferrite and austenite/martensite. It was found that manganese acts as an austenite-forming element under the conditions of the investigation.Mechanical testing of the alloys included hardness, tensile and Charpy impact testing. The results of the hardness testing showed that a 1050 °C normalizing treatment, followed by a 600 °C heat treatment and water quenching, resulted in alloys in their softest condition. It was found that manganese additions increased the toughness of the stainless steels, while tensile testing revealed that manganese additions increased the ultimate tensile strength of the alloys, but had little effect on the yield strength.The addition of manganese was found to reduce both the general and pitting corrosion resistances. Under reducing conditions, manganese additions resulted in a dramatic deterioration of the corrosion properties of the alloys.

High silt wear of hydroturbine runners

Turbine runners show an unusually high rate of wear in river water with a high silt content. Cast ferritic stainless steel of CA6NM type is the normal turbine runner material. The slurry erosion characteristics of stellite 6, 15wt.% Cr-15wt.% Mn stainless steel, type 316L stainless steel and CA6NM were evaluated in a specially designed equipment. The different wear rates of the alloys are explained in terms of the microstructure, hardness and work-hardening rate.

Superplastic deformation and cavitation of a 14CrMn stainless steel

An experimental stainless steel containing 14Cr20Mn was found to exhibit moderate superplastic behaviour in the temperature range 800–1000 °C at strain rates of 10 −4–10 −3 −1. The strain rate sensitivity index was found to be insensitive to test temperatures between 825 and 875 °C but varied with strain rate, reaching a maximum of about 0.5 at 3 × 10 −4 s −1. A model is proposed to estimate the rate of grain growth that occurred during superplastic deformation in terms of static grain growth, which is a function of time and the activation energy of grain boundary self-diffusion, and strain-enhanced growth, which is a function of strain rate and volume self-diffusion. Cavitation accompanied superplastic deformation and increased with increasing local strain, increasing temperature and decreasing strain rate. The cavitation results were analysed using strain-based and time-based models. The latter gave a more consistent estimate of the cavities present in the prestrain condition.

The oxidation of Fe-19.6Cr-15.1Mn stainless steel

The oxidation behavior in air of Fe-19.6Cr-15.1Mn was studied from 700 to 1000°C. Pseudoparabolic kinetics were followed, giving an activation energy of 80 kcal/mole. The scale structure varied with temperature, although spinel formation occurred at all temperatures. At both 700 and 800°C, a thin outer layer of γ-Mn2O3 formed. The inner layer at 700°C was (Fe,Cr,Mn)3O4, but at 800°C there was an intermediate layer of Fe2O3 and an inner layer of Cr2O3 + (Fe, Cr,Mn)3O4. Oxidation at 900°C produced an outer layer of Fe3O4 and an inner layer of Cr2O3+(Fe,Cr,Mn)3O4. Oxidation at 1000°C caused some internal oxidation of chromium. In addition, a thin layer of Cr2O3 formed in some regions with an intermediate layer of Fe3O4 and an outer layer of (Fe,Mn)3O4. A comparison of rates for Fe3O4 formation during oxidation of FeO as well as for the oxidation of various stainless steels, which form spinels, gave good agreement and strongly suggests that spinel growth was rate controlling. The oxidation rate of this alloy (high-Cr) was compared with that of an alloy previously studied, Fe-9.5Cr-17.8Mn (low-Cr) and was less by about a factor of 12 at 1000°C and by about a factor of 100 at 800°C. The marked differences can be ascribed to the destabilization of wustite by the higher chromium alloy. No wustite formation occurred in the high-Cr alloy, whereas, extensive wustite formed in the low-Cr alloy. Scale structures are explained by the use of calculated stability diagrams. The mechanism of oxidation is discussed and compared with that of the low-Cr alloy.

The effect of nitrogen additions upon the pitting resistance of 18 pct Cr, 18 pct Mn Stainless Steel

The effect of nitrogen additions upon the pitting resistance of 18 pct Cr, 18 pct Mn stainless steel has been investigated by potentiokinetic techniques in a 1000 ppm NaCl solution. Nitrogen additions increased the pitting resistance of the steel irrespective of structure, however, the ferritic steel was less pit resistant than the (duplex) steels containing both austenite and ferrite which, in turn, were less pit resistant than the totally austenitic steels. For steels having a duplex structure, the effect of nitrogen on the pitting resistance was observed to follow a linear function of the relative amount of austenite in these steels due to the area effects of the austenite and ferrite which are galvanically coupled in these steels. The addition of nitrogen was found to increase the amount of austenite at a rate of approximately 200 times the percent nitrogen addition from 36 pct austenite for the 0.02 pct N steel to 100 pct for the 0.40 pct nitrogen steel. The addition of nitrogen to the totally austenitic steels increased the pitting resistance at the rate of approximately 0.31 volts per pct nitrogen added, but no mechanism was found for the increased resistance.