Mn Si Cr Research Articles

Phase transformation behavior under uniaxial deformation of an Fe–Mn–Si–Cr–Ni–VC shape memory alloy

In the present study, the phase transformation behavior of an Fe–17Mn–5Si–10Cr–4Ni–1(V,C) (ma.-%) shape memory alloy is investigated by thermo-mechanical tests with various stress–temperature histories under uniaxial deformation conditions. The stress–strain response and the microstructural evolution of the alloy during deformation at different temperatures reveal that mainly stress induced martensite phases form until the stress level reaches the yielding point for the irrecoverable slip. The reverse transformation occurred mainly within the temperature range of 0‒175°C. Based on the microstructural and thermo-mechanical analysis, a complete stress–temperature phase diagram for the FCC/HCP transformation of this alloy is presented.

The effects of Cr on isothermal oxidation behavior of Fe–30Mn–6Si alloy

The oxidation behavior of Fe–Mn–Si and Fe–Mn–Si–Cr alloys was investigated under isothermal atmosphere. The oxidation rates of the alloys are significantly increased with isothermal temperature. The oxidation of FeMnSi alloy is decreased with incorporation of Cr into FeMnSi alloy. The oxidation activation energies of the Fe–Mn–Si and Fe–Mn–Si–Cr alloys were found to be 126.79kJ/mol and 105.74kJ/mol, respectively. The activation energy is decreased with incorporation of Cr. The obtained oxides were found to be SiO2, MnO and MnO2 for FeMnSi. With the incorporation of Cr, the CrO3, SiO2 and MnO oxides were observed.It is evaluated that the oxidation behavior of FeMnSi shape memory is decreased with incorporation of Cr into the same shape memory alloy.

Microscopic residual stress evolution during deformation process of an FeMnSiCr shape memory alloy investigated using white X-ray microbeam diffraction

Microscopic residual stress evolution in different austenite (γ) grains during shape memory process in an FeMnSiCr alloy was investigated using the white X-ray microbeam diffraction technique. The use of high-energy white X-ray microbeam with small beam size allowed us to measure the microscopic residual stress in coarse γ grains with specific orientation. After tensile deformation large compressive residual stress was evolved in γ grains due to the formation of stress-induced ε martensite, but upon recovery heating it almost disappeared as a result of reverse transformation of martensite. The magnitude of compressive residual stress was higher in grains with orientations close to 〈144〉 and 〈233〉 orientations than in a grain with near 〈001〉 orientation. Analysis of the microstructure of each grain using electron backscattering diffraction suggested that the difference in the magnitude of compressive residual stress could be attributed to different martensitic transformation characteristics in the grains.

Effect of copper addition on the microstructure and shape recovery of Fe–Mn–Si–Cr–Ni shape memory alloys

The effect of Cu addition on the microstructure and shape recovery behaviour of Fe–Mn–Si–Cr–Ni shape memory alloys has been studied. Microstructural characterization revealed that Cu is soluble in these alloys at least up to 3wt% in the austenite (γ) phase and acts as a strong γ stabilizer. The γ–ε martensite transformation start temperature (MS) and the reverse ε–γ transformation start temperature (AS) were observed to decrease with Cu addition, although at different rates. Copper addition promotes the formation of incoherent Fe5Ni3Si2 type intermetallic π-phase precipitate during ageing and its amount increases with the amount of Cu in the alloy. Most importantly, Cu results in the deterioration of shape recovery of Fe–Mn–Si–Cr–Ni shape memory alloys, by increasing stacking fault energy (SFE), by decreasing the resistance to plastic deformation and by lowering the MS temperature of the γ phase.

Investigation of the structure and impact-abrasive wear resistance of coatings of the Fe–C–Cr–Mn–Si system, additionally alloyed with nitrogen

Special features of the formation of the structure and properties of plasma-powder coatings of 250Kh15G20S are investigated. The effect of additional alloying of the coating with nitrogen by adding nitrided ferrochrome to the filler powder is considered. The effect of the deposition conditions and of the chemical composition of deposited metal on its hardness and impact-abrasive wear resistance is described.

Mechanical properties of Al–Mg–Si alloy sheets produced using asymmetric cryorolling and ageing treatment

An asymmetric cryorolling technique was used to reduce the thickness of an Al–Mg–Si alloy sheet from 1.5mm to 0.19mm. The samples were subsequently aged for 48h at 100°C. The hardness and tensile strength of both rolled and aged sheets increased with the number of passes up to the sixth pass, but the tensile stress decreased after the seventh pass. Investigation of the microstructure of the sheets showed that the grain size after seven passes was about 235nm and revealed the presence of Fe–Cr–Mn–Si particles in the samples. The deformation of Fe–Cr–Mn–Si particles and sheet thickness affects the ductility when the sheet thickness is less than 0.4mm, and the strength when the thickness is less than 0.2mm.

Development and Testing of Materials with Reduced Wear by Fixed Abrasive

Abrasive wear into embedded abrasive (Al2O3) of Fe–C–Si–Mn–Cr–B layers welded by an electric arc has been studied. The amounts of carbon (0.45–2.92%), chromium (1.1–18.7%) and hardness (73–82 HRA) of welded layers have no impact on wear. Due to great differences in hardness of welded layers and abrasive, the metal surfaces are intensively wearing due to microcutting. It is determined that the harder the layers, the greater their resistance to wear. Alloying of a medium content carbon layer (0.45% C) with boron of 0.51% reduces the wear up to 27%. Minimal amounts of carbon 0.45%, chromium 1.1%, boron 0.5% guarantee stable and high resistance of welded layers to wear.

The Development of a Processing Window for the Continuous Galvanizing of a Mn–Cr–Si Martensitic Steel

AbstractMartensitic or complex phase steels are leading candidates for automotive impact management applications. However, achieving high strengths while obtaining high quality coatings via continuous galvanizing is a challenge due to cooling rate limitations of the processing equipment and selective oxidation of alloying elements such as Cr, Mn, and Si adversely affecting reactive wetting. The galvanizability of a CrMnSi steel with a target tensile strength above 1250 MPa was investigated within the context of the continuous galvanizing line. The continuous cooling transformation behavior of the candidate alloy was determined, from which intercritical and austenitic annealing thermal cycles were developed. The evolution of substrate surface chemistry and oxide morphology during these treatments and their subsequent effect on reactive wetting during galvanizing were characterized. The target strength of 1250 MPa was achieved and high quality coatings produced using both intercritical (75% γ) and austenitic (100% γ) annealing using a conventional 95%N2–5%H2, −30°C dew point process atmosphere and 0.20 wt% dissolved (effective) Al bath, despite the presence of significant Mn and Cr oxides on the substrate surfaces. It is proposed that complete reactive wetting by the Zn(Al, Fe) bath was promoted by in situ aluminothermic reduction of the Mn and Cr‐oxides by the dissolved bath Al.

A carbide-free bainite/martensite/austenite triplex steel with enhanced mechanical properties treated by a novel quenching–partitioning–tempering process

A novel quenching–partitioning–tempering (Q–P–T) process was employed in a Mn–Si–Cr alloyed steel to obtain a triplex microstructure comprising carbide-free bainite, martensite and retained austenite. The carbide-free bainite formed during the quenching step (rather than partitioning step) of Q–P–T process can enhance the mechanical properties (e.g. the product of strength and elongation, ∼31.4GPa%) by extending the partitioning time up to 30min. A good combination of strength and elongation (Ultimate tensile strength: ∼1655MPa; Elongation: ∼19%) has been realized for the Mn–Si–Cr alloyed high strength steel without expensive alloying, e.g. Ni, Mo, Nb in previous Q&P/Q–P–T processes. The enhanced mechanical properties could be attributed to the various types of retained austenite in the Q–P–T treated carbide-free bainite/martensite/austenite triplex microstructure.

Influence of VC Precipitation on the Shape-Memory Effect and Corrosion Resistance on an Fe–Mn–Si–Cr–Ni Alloy

The shape-memory effect (SME) and corrosion resistance of an Fe-20Mn-5Si-10Cr-5Ni- 0.7V-0.2C alloy, before and after aging, were investigated. The results showed that VC precipitation and bending temperatures obviously affect the alloy’s SME. Nearly perfect SME (90.2% of initial 4% bend) was achieved when the 2h aged sample was deformed at 223K. At the meantime, the electrochemical impedance spectroscopy (EIS) showed that the alloy, aged for 2h to 4h, exhibited the worst corrosion resistance in the research system related with the fine VC precipitates. The morphology and distribution of VC were observed by SEM.

Influence of alloying elements on the corrosion properties of shape memory stainless steels

The corrosion properties of three Fe–Mn–Si–Cr–Ni–(Co) shape memory stainless steels were studied based on X-ray photoelectron spectroscopy (XPS) analyses, immersion and polarization tests. The test results were compared with those of a type 304 austenitic stainless steel. The XPS analyses indicated substantial Si content in the anodic passive films formed on shape memory stainless steels in sulfuric acid solution and that the high protectiveness of these films results from a protective film consisting of a (iron, chromium)–mixed silicate. The corrosion rate of the shape memory stainless steels in boiling nitric acid solution was lower than that of austenitic stainless steel. The high silicon content was found to play an important role in the corrosion behavior of these shape memory alloys in highly oxidizing environments. Due to their high manganese content, the shape memory stainless steels showed poor corrosion behavior in 3.5% sodium chloride solution when compared with austenitic stainless steel.

Pseudoelasticity of thermo-mechanically treated Fe–Mn–Si–Cr–Ta alloys

Abstract The effects of slight Tantalum (Ta) addition on the microstructures, martensitic transformation and pseudoelasticity of Fe–28Mn–6Si–5Cr alloy were investigated. Experimental results show that the slight addition of 0.1 wt% Ta can effectively inhibit the slip deformation, increase the M d temperature and hence improve the pseudoelasticity of Fe–28Mn–6Si–5Cr alloy. Meanwhile, the cold rolling can also significantly increase the alloy's pseudoelasticity, especially when the specimens are tested at near M d temperature. The pseudoelasticity can reach 62% at the sixth loading–unloading cycle for the 30% cold-rolled Fe–28Mn–6Si–5Cr–0.1Ta alloy.

Thermo‐Mechanical Properties of an Fe–Mn–Si–Cr–Ni–VC Shape Memory Alloy with Low Transformation Temperature

Thermo‐Mechanical Properties of an Fe–Mn–Si–Cr–Ni–VC Shape Memory Alloy with Low Transformation Temperature

Characterization of passive films on shape memory stainless steels

Passive films formed on three Fe–Mn–Si–Cr–Ni–(Co) shape memory stainless steels (SMSSs) were studied based on polarization tests, EIS, XPS and Mott–Schottky analyses. The test results were compared with those of a type 304 austenitic stainless steel. The results indicated that silicon plays an important role in the passive film properties of Fe–Mn–Si–Cr–Ni–(Co) SMSSs. Anodic passive films formed on Fe–Mn–Si–Cr–Ni–(Co) SMSSs are highly protective and consist of a chromium oxyhydroxide with incorporation of silicon in the chemical form of a silicate. Mott–Schottky analyses suggested that passive films on Fe–Mn–Si–Cr–Ni–(Co) SMSSs are less defective and thicker than those on austenitic stainless steel.

Thermo‐Mechanical Properties of an Fe–Mn–Si–Cr–Ni–VC Shape Memory Alloy with Low Transformation Temperature

AbstractFe‐based shape memory alloys are supposed to be an interesting and cost‐effective alternative to NiTi‐based alloys. In this work, the thermo‐mechanical behavior of a novel Fe–Mn–Si–Cr–Ni–VC shape memory alloy produced using standard air‐casting facilities is characterized as well as in the hot forged and cold rolled state. Besides a certain pseudoelasticity, the alloy shows good shape recovery properties and remarkably high shape memory stresses after heating to temperatures of only 160 °C, making the alloy interesting for commercial applications that make use of the shape memory effect.

Superplastic martensitic Mn–Si–Cr–C steel with 900% elongation

High-strength (1.2–1.5)C–(2–2.5)Mn–(1.5–2)Si–(0.8–1.5)Cr steels (mass%) consisting of martensite and carbides exhibit excellent superplastic properties (e.g. strain rate sensitivity m ≈ 0.5, elongation ≈900% at 1023 K). A homogeneous martensitic starting microstructure is obtained through thermomechanical processing (austenitization plus 1.2 true strain, followed by quenching). Superplastic forming leads to a duplex structure consisting of ferrite and spherical micro-carbides. Through 1.5–2% Si alloying, carbides precipitate at hetero-phase interfaces and martensite blocks at the beginning of superplastic forming. Via Ostwald ripening, these interface carbides grow at the expense of carbides precipitating at martensite laths, thereby promoting ferrite dynamic recrystallization. Simultaneously, carbides at ferrite grain boundaries retard the growth of recrystallized ferrite grains. Due to 2–2.5% Mn and 0.8–1.5% Cr alloying, carbide coarsening is suppressed owing to the slow diffusion of these elements. As a result, fine and homogeneous ferrite plus spherical carbide duplex microstructures with a ferrite grain size of ∼1.5 μm are obtained after superplastic forming.

Corrosion behavior of shape memory stainless steel in acid media

The corrosion behavior of three Fe–Mn–Si–Cr–Ni–(Co) shape memory stainless steels (SMSS) in 0.5 M H 2SO 4 solution was studied through electrochemical and immersion tests. The test results were compared with that of a type 304 (SS 304) austenitic stainless steel. The three SMSSs exhibited a passive behavior in 0.5 M H 2SO 4 solution; however, their anodic behavior in the active dissolution region was markedly different. The passive current densities of the SMSSs were similar to that of SS 304, although the critical anodic current required for passivation was higher. The corrosion rate of the SMSSs was much higher than that of SS 304. It was observed that the amount of Cr and Mn plays an important role in the corrosion behavior of SMSSs. The best corrosion behavior in acid media was shown by the SMSS that contained the highest amount of Cr and the lowest amount of Mn.

Influence of ageing on wear resistance of an Fe–Mn–Si–Cr–Ni–Ti–C shape memory alloy

To further improve the wear resistance of Fe–Mn–Si–Cr–Ni based shape memory alloys, the effects of ageing at 1123 K with and without pre-deformation at room temperature on the precipitation of second-phase particles and their effects on wear resistance were investigated in an Fe–Mn–Si–Cr–Ni–Ti–C alloy. Results showed that the solution treated Fe–Mn–Si–Cr–Ni–Ti–C alloy exhibited much better wear resistance than the solution treated AISI 321 stainless steel; ageing with pre-deformation improved the wear resistance of Fe–Mn–Si–Cr–Ni–Ti–C alloy more effectively than ageing without pre-deformation, especially under the heavy load condition.

A Novel Training‐Free Cast FeMnSiCrNi Shape Memory Alloy Based on Formation of Martensite in a Domain‐Specific Manner

AbstractThe proposed key to producing a good shape memory effect in FeMnSi alloys is to reduce or even prevent the collisions between martensite bands. A method for realizing this is to make stress‐induced martensite bands form in a domain‐specific manner. We developed a novel training‐free cast Fe18Mn5.5Si9.5Cr4Ni alloy with residual lathy delta ferrite based on this idea. The recovery strain reached 6.4% only after annealing the cast Fe18Mn5.5Si9.5Cr4Ni alloy. Microstructure observations indicated that the lathy delta ferrite made the stress‐induced martensite form in a domain‐specific manner by first subdividing grains into smaller domains. We hypothesize that through adjusting alloy compositions, solidification parameters, and heat treatment technique, the shape recovery of cast FeMnSi alloys can be further improved. Such a finding will provide a novel method for developing training‐free FeMnSi shape memory alloys.

Factors affecting recovery stress in Fe–Mn–Si–Cr–Ni–C shape memory alloys

The effects of the heating temperature, the carbon content, the amount of pre-strain, the annealing temperature, and the conventional training on the recovery stresses at room temperature of cold-drawn Fe–Mn–Si–Cr–Ni–C shape memory alloys were studied. The results showed that the addition of carbon or the refining of grains could more significantly enhance the recovery stress than the conventional training. The recovery stress of a cold-drawn Fe–Mn–Si–Cr–Ni alloy with 0.18%C could reach 565MPa only after annealed at 1023K. Its recovery stress was only improved to 452MPa after it was subjected to annealing at conventional temperature 1373K and then four cycles of the conventional training. The dominating factors affecting the recovery stress were the amount of the plastic deformation and that of the martensitic transformation induced by the recovery stress in cooling, not the recovery strain under no constraints.