Mn Stainless Steel Research Articles

Achieving ultra-high flow stress and hardness in a medium Mn stainless steel by the formation of strain-induced martensite and G-phase precipitates

This work demonstrates how the deformation of a medium Mn austenitic stainless steel and its subsequent thermal treatment results in the steel having an ultra-high flow stress, and with a microstructure containing strain-induced martensite (α′) and G-phase precipitates. A 14 wt.%Cr-8 wt.%Mn-1 wt.%Ni austenitic stainless steel was uniaxially compressed at room temperature and quasi-static strain rates to determine the evolution of strain-induced martensite with strain. Uniaxial compression resulted in a sigmoidal stress-strain curve (enhanced work-hardening) with the flow stress reaching ∼2.2 GPa, and the α′ fraction saturating at 0.8 true strain. Atom-probe tomography showed that aging at 400 °C for 72 h formed 2–3 nm sized G-phase precipitates containing Cu-rich clusters and having a nominal composition of Ni8Si2Mn20Cu17Cr8Fe44. Such a microstructure resulted in a steel with an ultra-high tensile strength and a compressive flow stress of around 2 GPa. Though the tensile ductility was low, there was sufficient flowability in compression.

Manganese Constituent in Stainless Steels Oxidized in Oxygen Containing Water Vapor at 800 °C: High Temperature Oxidation and Volatilization

Many industrial operations, such as solid oxide fuel cells (SOFCs) or combustion processes, have water vapor environments. Stainless steel was applied as part of these applications at high temperatures. The present work investigates high and low manganese content stainless steel that oxidized in an oxygen-containing 5% water vapor at 800 °C. SEM and EDX were performed to analyze oxide formation and ICP-OES was used to detect the volatile species that evaporated from steel surfaces. The results show that manganese in steel increases spallation and reduces Cr volatilization rates in high Mn stainless steel. The average Cr volatilization of high Mn samples is 0.09 × 10-11 g cm-2 s-1, which is about 14 times lower than the ones (1.25 × 10-11 g cm-2 s-1), while Fe and Mn volatilization rates increase by 10 and 62 times, respectively.

In-situ strain induced martensitic transformation measurement and consequences for the modeling of medium Mn stainless steels mechanical behavior

This work aims at studying the control of medium manganese austenitic stainless steels’ mechanical behavior and austenite to martensite transformation via chemical composition. Six grades of austenitic stainless steel were cast with chemical compositions variations small enough able to keep relatively constant the stacking fault energy (SFE) value, but high enough to change the martensitic start temperature Ms. These experiments allow the effect of the martensite transformation on the mechanical behavior in tension to be compared while the austenitic mechanical behavior is almost unchanged. Tensile tests were performed at room temperature and at a low strain rate (10−4 s−1). In-situ magnetic measurement is implemented to quantify the martensite volume fraction evolution with strain. Strain heterogeneities are detected by digital image correlation (DIC) analysis. For all grades, stress–strain curves exhibit Portevin–le-Châtelier (PLC) phenomenon related to localized martensite transformation within the deformation bands. For the two most unstable alloys, a Lüders plateau is detected at the yield stress. The martensite evolution is modeled using the Olson–Cohen approach, which confirms slower kinetics for the most stable grades. Moreover, it is shown that the martensite fraction evolves linearly with stress after a stress threshold function of the austenite stability represented by Ms. The martensite volume fraction vs stress slope is constant whatever the composition. This result leads to the development of a coupled metallurgical/mechanical model which depends on a single parameter Ms related to the chemical composition.

Effect of titanium addition on sub-structural characteristics of low carbon copper bearing steel in hot rolling

<abstract> <p>The low carbon copper-bearing steel exhibits high toughness and better weldability. In the present investigation, 0.05C–1.52Cu–1.45Mn stainless steel and its titanium added counterpart which is 0.05C–0.05Ti–1.52Cu–1.45Mn stainless steel were subjected to hot rolling. The hot rolling test followed by quenching to retain the microstructure was done using a hot-rolling mill. The rolling was done at two different temperatures of 800 ℃ and 850 ℃. The characterization of microstructure was done using electron back scattered diffraction and transmission electron microscopy analysis. The 0.05C–1.52Cu–1.45Mn stainless steel when subjected to hot rolling at a lower temperature envisaged a deformed microstructure rather transformed one. However, the same steel at a higher temperature envisages a transformed microstructure. There was no variation in hardness was observed. However, the addition of 0.05 wt% of titanium in 0.05C–1.52Cu–1.45Mn stainless steel influenced the softening and the microstructure showed some recrystallization; the hardness was decreased with the increasing rolling temperature because the solubility of titanium in the austenite phase increased with temperature which leads to suppression austenitic grain/sub-grain growth and hardness. The mean sub-grain size for 0.05C–1.52Cu–1.45Mn stainless steel was 2.75 µm. However, the addition of titanium leads to a decrease in the mean sub-grain size. A marginally larger mean sub-grain size was observed when 0.05C–0.05Ti–1.52Cu–1.45Mn stainless steel was rolled at a higher temperature. A comparatively finer precipitate of copper, titanium and oxy-silicates of Ferrous/Manganese in order of nanometer was formed during rolling at a higher temperature.</p> </abstract>

Effect of Grain Structure on the Mechanical and Corrosion Behavior of Advanced Medium Mn Stainless TWIP Steel

The influence of recrystallization annealing on the microstructure, mechanical properties and corrosion behaviour of an austenitic TWIP steel bearing medium Mn and V alloying was investigated. The steel undergone a heavy cold deformation of 65 % reduction. Subsequently, recrystallization annealing at 1000 °C and 1100 °C for 15 min was conducted to achieve different grain structures. The microstructural evolution was studied using optical microscopy and electron backscatter diffraction technique. Mechanical properties were determined using tensile tests at room temperature. Corrosion behaviour was measured by cyclic potentiodynamic polarization at 3.5 pct NaCl. For comparison, austenitic stainless-steel Type 201 was used in this study. It was observed that at 1000 °C, a non-uniform austenitic grain structure with vanadium carbides distributed throughout the matrix was obtained. However, a coarse grain structure without carbides was induced at 1100 °C. The fine-grained structure enhanced at 1000 °C exhibited higher strength and good ductility. Contrary to this, the corrosion results showed that a significant deterioration in the corrosion resistance could be observed in sodium chloride solution for the achieved structure at 1000 °C compared to 201 stainless steel.

Catalytic ozonation treatment of biochemically treated leachate from municipal waste solid using Ti–Mn oxide‐coated stainless steel mesh catalyst

AbstractBACKGROUNDLandfill leachate is a kind of complex organic wastewater, the discharge standard of which is difficult to meet after traditional biochemical treatment. In this work, a Ti–Mn stainless steel corrugated wire mesh (SSCWM) catalyst was prepared by the sol–gel method, which was used for the catalytic ozonation of biochemically treated leachate.RESULTSThe catalyst was characterized using scanning electron microscopy, energy dispersive X‐ray spectroscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy techniques. The data showed that the chemical oxygen demand (COD) removal efficiency of the leachate by ozone alone, SSCWM/O3, Ti–SSCWM/O3 and Ti–Mn/SSCWM/O3 system reached 55.06%, 64.44%, 68.97% and 78.43%, respectively. The catalytic effect of different layers of Ti–Mn oxide‐coated SSCWM catalyst showed that two catalytic layers had the best activity of COD removal efficiency, reaching 87.17%, and the final COD reached the national emission standard (<100 mg L−1). At the same time, the results of fluorescence spectrum and gas chromatography–mass spectrometry (GC‐MS) analysis confirmed this point. The stability of the catalyst decreased with the increase in usage times, and the final COD removal efficiency was 73.91% after six cycles of use. To understand the reason for catalyst deactivation, the adsorbed organic matter on the catalyst surface was determined by GC‐MS analysis. In addition, COD removal of the catalyst can be increased to 80.55% after in situ regeneration of the mesh catalyst by a sequential cleaning process consisting of alkali–acid–hydrogen peroxide–ethanol–water.CONCLUSIONIn short, application of the mesh catalyst in catalytic ozonation can be considered as a promising method for wastewater treatment, because of avoidance of solid–liquid separation and easy regeneration of catalytic activity. © 2020 Society of Chemical Industry

Insight to the Influence of Ti Addition on the Strain-Induced Martensitic Transformation in a High (about 7 wt.%) Mn Stainless Steel

The kinetics of strain-induced martensite (SIM) formation in a Ti-bearing 201L stainless steel were evaluated and compared to the existing results of two conventional stainless steel grades; i.e., 201L and 304L AISI. The effects of strain rate and rolling pass reduction on the kinetics of SIM formation during cold rolling were investigated. The Ti-microalloying was found to be intensifying the transformation due to lowering the stacking fault energy. It was seen that decreasing the rolling pass reduction strongly affected the variation of SIM volume fraction. Furthermore, a close correlation between the hardness and strain-induced transformation was found arising from microstructural evolution during the cold rolling process. Three stages in the hardening behavior were detected associated with lath-type martensite formation, transition stage of martensite laths break up and formation of dislocation-cell-type martensite.

Strong and ductile steel via high dislocation density and heterogeneous nano/ultrafine grains

High strength and high ductility are critical to metallic materials and have always been pursued. A novel strategy to produce a medium Mn stainless steel with high dislocation density and heterogeneous nano/ultrafine-grains was designed and outstanding mechanical properties were achieved. The special heterogeneous microstructure was fabricated by cold rolling followed by rapid reverse annealing at intercritical temperature and a final step of low-temperature tempering. The results of this study demonstrated that the heterogeneous microstructure consisted of 74% reversed austenite, 16% deformed austenite and 10% tempered martensite. The dislocation density in austenite of the final microstructure had a high value of 1.12 × 1015 m−2 and the average grain size was 0.63 μm. The high yield strength (1324 MPa) and tensile strength (1401 MPa) of the steel were achieved and combined with high uniform elongation of 34.7%. The combination of high dislocation density (dislocation strengthening) and heterogeneous nano/ultrafine grains (fine-grain strengthening) resulted in such high yield strength. Simultaneously, twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effect occurred within the heterogeneous nano/ultrafine grains leading to high strain hardening rate and good uniform elongation in the steel.

The Formation Mechanism of Mn–Al–O Inclusions in Fe–Cr–Mn Stainless Steel during Continuous Casting

The formation mechanism of Mn–Al–O inclusions in Fe–Cr–Mn stainless steel during continuous casting is investigated by industrial trials and thermodynamic calculation. The morphology, composition, and size distribution of inclusions in steel specimens are analyzed by scanning electron microscopy and energy dispersive spectroscopy. The main inclusions change from spherical Ca–Si–O and Ca–Si–Mn–O inclusions during LF refining to Mn–Al–O inclusions in continuous casting slab and hot‐rolled sheet. The size of most Mn–Al–O inclusions containing high MnO content is smaller than 4 µm. The formation of these inclusions is consistent with thermodynamic calculation, which indicates that MnO and Al2O3 inclusions are formed during continuous casting process. The calculation results of MnO and Al2O3 inclusions growth shown that the size of MnO inclusion (4 µm) is much larger than that of Al2O3 inclusion (0.4 µm) at the end of solidification, which also accords with the characteristics of inclusions in continuous casting slab and hot‐rolled sheet.

Welding Behaviour of Low Nickel Chrome-Manganese Stainless Steel

Chrome-Manganese steel is relatively new steel as compared to its counterpart 304 series stainless steels. There are relatively few studies on the welding behaviour of low nickel Cr–Mn stainless steel (in particular, on the effect of heat input on the microstructural developments). In the present investigation, a low nickel chrome-manganese stainless steel was welded (shielded metal arc welding process) to see the effect of heat input on the microstructural evolution and mechanical properties. At higher heat inputs (404.2 J/mm and 528.1 J/mm), tensile strength and hardness are lower compared to low heat input (316.6 J/mm). Fractographic investigation of the tensile tested specimen revealed dimple-like ductile fracture. An attempt was also made to evaluate the phases incorporated in the investigated steel using Schaeffler diagram.

Visualization of Solution Chemistry inside Crevice by pH and pCl Sensing Plates

Both pH and pCl sensing plates were fabricated using ethyl violet (pH indicator) and quinine sulfate (fluorescent dye for pCl indicator). The sensing plates were also used for crevice formers. The crevice corrosion for 18Cr-10Ni-5.5Mn stainless steel was studied at 0.3 V (vs. Ag/AgCl, 3.33 M KCl) in 0.01 M NaCl solution (pH 3.0, 298 K). The pH inside the crevice gradually decreased with time, whereas chloride ion concentration did not change. An etch pit was initiated inside the crevice at the pH of 1.7 and the chloride ion concentration of 0.007 M. Just after the etch pit initiation, the pH of the surrounding area of the pit suddenly decreased to 0.4, the chloride ion concentration sharply increased to above 4 M. The dissolved metal ions from the etch pit led to increased acidification, and then the depassivation of the steel matrix occurred.

Visualization of pH and pCl Distributions: Initiation and Propagation Criteria for Crevice Corrosion of Stainless Steel

Both pH and pCl sensing plates were fabricated, and the H+ and Cl− distributions in the crevice solution for 18Cr-10Ni-5.5Mn stainless steel were visualized at 0.3 V (vs. Ag/AgCl, 3.33 M KCl) in 0.01 M NaCl (pH 3.0, adjusted with H2SO4) at 298 K. While the pH inside the crevice gradually decreased with time, no accumulation of Cl− ions occurred. The SO42− ions that were added to adjust the pH probably accumulated to maintain electroneutrality. When the pH reached 1.7, a metastable pit was generated inside the crevice, providing a sharp decrease in pH to 0.4 and an increase in Cl− concentration to above 4 M. After that, the corroded area grew steadily with time, and the pH and the Cl− concentration remained constant at pH 0.4 and above 4 M Cl−. Acidification from pH 1.7 to 0.4 was induced by the hydrolysis of the dissolving metal ions from the pit and resulted in the depassivation of the surrounding steel matrix. The metastable pitting also caused the Cl− accumulation inside the crevice by electromigration. The crevice corrosion was found to be initiated when the pH and Cl− concentration inside the crevice reached the conditions for metastable pit formation.

Degradation of MgO–C refractories by MnO-rich stainless steel slags

In order to identify the influence of MnO on the wear rate of MgO–C bricks for the production of high Mn stainless steel, MgO–C refractory samples were exposed to slags containing different MnO levels (up to 26 wt.%). Although the investigations of the worn brick microstructures revealed the presence of numerous Mn-rich metal particles and the formation of a (Mg,Mn)O solid solution at the slag/refractory interface, no clear evidence of wear rate enhancement was observed due to high MnO concentration in the slags. With respect to refractory wear, the MgO content in the slag is the dominant factor. The degradation processes are discussed by combining experimental results and thermodynamic calculations.

Low-Loss NbTi Rutherford Cable for Application to the SIS-300 Dipole Magnet Prototype

INFN (Istituto Nazionale di Fisica Nucleare, Italy) has started in 2006 the DISCORAP project, which foresees the design, manufacture and test of a dipole prototype for the SIS-300 synchrotron of the FAIR facility at GSI. In order to minimize the losses produced by the fast ramp rate (1 T/s) at which the magnet is operated, we are developing with European industries, a Rutherford cable which incorporates several technologies to reduce the losses, and namely a NbTi filament diameter on the order of 2.5-3.5 mum, Cu 0.5 wt%Mn interfilamentary matrix and stainless steel core. In this paper we present the design principles and the first experimental results; we also analyze the impact of the CuMn paramagnetism on the field distortion at the different operating magnetic fields.

Alloying effects on the microstructure and phase stability of Fe–Cr–Mn steels

Austenitic Fe–Cr–Mn stainless steels interstitially alloyed with nitrogen have received considerable interest lately, due to their many property improvements over conventional Fe–Cr–Ni alloys. The addition of nitrogen to Fe–Cr–Mn stabilizes the fcc structure and increases the carbon solubility. The benefits of increased interstitial nitrogen and carbon content include: enhanced strength, hardness, and wear resistance. This study examines the effect of carbon, silicon, molybdenum, and nickel additions on the phase stability and tensile behavior of nitrogen-containing Fe–Cr–Mn alloys. Nitrogen and carbon concentrations exceeding 2.0 wt.% were added to the base Fe–18Cr–18Mn composition without the formation of nitride or carbide precipitates. Minor additions of molybdenum, silicon, and nickel did not affect nitrogen interstitial solubility, but did reduce carbon solubility resulting in the formation of M23C6 (M=Cr, Fe, Mo) carbides. Increasing the interstitial content increases the lattice distortion strain, which is directly correlated with an increase in yield stress.

Manganese and Chromium Distribution between CaO–SiO2–MgOsat.–CrO1.5–MnO Slags and Fe–Cr–Mn Stainless Steel

The Mn and Cr equilibria between a Mn rich stainless steelmaking slag (CaO–SiO2–MgOsat.–MnO–CrO1.5) and Fe–Cr–Mn stainless steel were investigated in a temperature range from 1823 to 1873 K under Ar atmosphere. The partition ratios LMn and LCr between liquid slag and steel were determined as a function of slag composition and temperature. By combining the experimental results with thermodynamic calculations, it was found that, as basicity increases, LMn decreases, while LCr increases. The elevated basicity leads to a high MnO activity coefficient. On the other hand, the CrO1.5 activity coefficient decreases with higher slag basicities. The influence of MnO and CrO1.5 contents on the activity coefficients was also considered. It is concluded that in order to maximize Mn recovery during high Mn stainless steel production, a basic slag with a high MnO activity coefficient must be employed whereas high temperatures should be avoided.

Effect of reactive elements on oxidation behaviour of Fe–22Cr–0.5Mn ferritic stainless steel for a solid oxide fuel cell interconnect

Ferritic stainless steel has become a promising material for metallic interconnects for solid oxide fuel cells (SOFCs) operating in an intermediate temperature range (650–800 °C). Ferritic stainless steels containing reactive elements (REs) such as Crofer22APU and ZMG232 have been developed for SOFC interconnects. Nevertheless, the effectiveness of REs on the growth kinetics of the chromia-rich scale that forms on the ferritic stainless steels is not yet well understood. The current study focuses on the investigation of the effect of REs such as Y, Ce and La on the oxidation behaviour and scale properties of Fe–22Cr–0.5Mn stainless steel. The results show that Y is the most effective reactive element for reducing the scale growth kinetics and area-specific resistance of the chromia scale which forms on this stainless steel. The growth kinetics of the chromia-rich scale can be effectively reduced by the dominant segregation of Y at the interface between the oxide scale and alloy substrate, and by the formation of a thin SiO 2 and MnO layer underneath the Cr 2O 3-rich oxide.

Proposals for the Final Design of the ITER Central Solenoid

The ITER central solenoid (CS) is 12 m high and 4 m in diameter. The CS consists of a stack of 6 electrically independent modules to allow control of plasma shape. The modules are compressed vertically by a pre-compression structure to maintain contact between modules. The CS conductor is CIC conductor with Nb/sub 3/Sn strands and a steel conduit. The CS model coil and insert coil test results have shown that the conductor design must be modified to achieve an operation margin. This required either to increase the cable diameter or to use strand with a higher current capability. A bronze-process (NbTi)/sub 3/Sn strand is proposed to achieve a higher critical magnetic field. A square conduit with a high Mn stainless steel is proposed as it can satisfy fatigue requirements. The inlets are in the high stress region and any stress intensification there must be minimized. The preload structure is composed of a set of tie-plates, flanges, buffer plates, and wedges. These design proposals satisfy all ITER operational requirements.

Correlation of martensitic transformation and surface mechanical behavior with cavitation erosion resistance for some iron-based alloys

Cavitation erosion resistance of four Fe–Mn–Si-based alloys and four Fe–Cr–Ni–Mn stainless steels has been investigated at a speed of 45 m/s using a rotating disc rig. Based on the research of surface mechanical effects and energy absorption of phase transformation, the role of martensitic transformation in cavitation erosion resistance of the tested alloys has been discussed. The results show that the effect of martensitic transformation on the resistance of the tested austenitic alloys is greatly influenced by cavitation-induced martensite structure. The resistance of the Fe–Mn–Si-based alloys is much better than that of the Fe–Cr–Ni–Mn stainless steels. The resistance of the tested alloys correlates with their localized surface elasticity H e and work-hardening capacity. The role of phase transformation in the resistance of the tested austenitic alloys is associated with the localized surface elasticity H e, work-hardening capacity and energy absorption of phase transformation, and it mainly depends on the elasticity H e and work-hardening capacity. As the values of H e of the tested martensitic and austenitic alloys are close, the resistance of the austenitic alloys can be obviously improved due to energy absorption of phase transformation. The excellent resistance of the Fe–Mn–Si-based alloys are mainly attributed to their excellent H e and excellent work-hardening capacity.

Effect of phase transformation on cavitation erosion resistance of some ferrous alloys

Cavitation erosion resistance of two Fe–Mn–Si–Cr shape memory alloys and five Cr–Ni–Mn stainless steels has been investigated at speed 45 m s −1 using a rotating disc rig. Based on the localized surface elasticity H e, the effect of phase transformation on cavitation erosion resistance has been discussed. The results show that the effect of phase transformation on the resistance of the tested alloys is significantly influenced by transformation characteristics. The resistance of two stress-induced hexagonal closed-packed martensite Fe–Mn–Si–Cr shape memory alloys is much better than that of three strain-induced body-centered cubic martensite Cr–Ni–Mn stainless steels. The role of phase transformation in the cavitation erosion resistance of the tested alloys is associated with the localized surface elasticity and energy absorption of phase transformation. The predominant factor characterizing the role of phase transformation in the cavitation erosion resistance of the tested alloys is the localized surface elasticity. As the value of H e is close, the resistance can be obviously improved owing to energy absorption of phase transformation.