Varying Mn Content Research Articles

Mn-controlled martensitic variant selection significantly affects the strength and toughness of 2.3 GPa ultra-high strength spring steel

In this study, the microstructure and mechanical properties of 55SiCrVNb ultra-high strength spring steel with 0.7 and 1.5 wt.% Mn were systematically investigated. The results show that 0.7Mn steel exhibited higher strength and toughness. The morphology and content of retained austenite, content of element in solid solution and the type and quantity of precipitates were basically the same in 0.7Mn and 1.5Mn steels. Hence, the variant reconstruction, as a unique perspective, was used to unravel the strengthening and toughening mechanisms governing the evolution of variants across varying Mn contents. Compared with the 1.5Mn steel, the decrease in Mn content deteriorated the variant selectivity (decreased variant frequency over 50 %), which led to a more uniform distribution of close-packed plane (CP) and Bain groups in 0.7Mn steel, thus refining the block size and improving the grain refinement strengthening (σp). The 0.7Mn steel with a higher density of high angle grain boundaries (HAGBs) effectively constrained dislocation slip, thereby enhancing dislocation strengthening (σd). As the Mn content decreased, the block size decreased from 0.24 to 0.14 μm, and the contribution of σp and σd increased by about 107 and 96 MPa, thus improving the yield strength. In addition, the increased HAGBs, which were dominated by the highly selective V1/V2, V1/V3(V5) and V1/V6 variant pairs, and the uniform CP and Bain group also contributed to inhibiting crack deflection and enhancing the impact toughness. Moreover, the higher Schmid factor with high geometrically necessary dislocation of 0.7Mn steel improved the deformation resistance of variants and strength. This work provided a new mechanism of strengthening and toughening dominated by variants.

Corrosion resistance of FeCrMnxAlCu high-entropy alloys in 0.5M H2SO4 solution

In this study, FeCrMnxAlCu high-entropy alloys with varying Mn contents (x = 2.0, 1.5, 1.0, 0.5, and 0) were prepared using a vacuum arc melting furnace. The phase structure and microstructure of the alloys before and after corrosion were characterized via X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The corrosion resistance of the alloys in a 0.5 M H2SO4 solution was comprehensively evaluated through potentiodynamic polarization, electrochemical impedance spectroscopy, immersion tests, white light interferometry, and X-ray photoelectron spectroscopy. Microstructural characterization results revealed that the FeCrMnxAlCu high-entropy alloys exhibited mixed FCC and BCC phase structures and featured typical dendritic and interdendritic regions. Corrosion tests indicated that as the Mn content decreased, the corrosion resistance of the high-entropy alloys improved, and the corrosion type transitioned from dendritic to interdendritic. Among these alloys, the FeCrAlCu high-entropy alloy exhibited the highest corrosion resistance, with the highest positive corrosion potential (Ecorr = −0.11 V), the lowest corrosion current density (Icorr = 1.02 × 10−5 A∙cm2), minimal corrosion depth, and the lowest corrosion rate (0.1592 mm/y). After corrosion, a composite oxide protective film was formed on the alloy surface, effectively hindering further penetration of the H2SO4 solution and exhibiting excellent corrosion resistance.

Interpretable ensemble machine learning framework to predict wear rate of modified ZA-27 alloy

This study investigates the impact of adding manganese (Mn) to ZA-27 alloy on microstructure and tribological properties. The Mn content varied from 0.2% to 1%. Volumetric wear rates were measured under different operating conditions. XRD and SEM were employed for phase identification and surface analysis. Ensemble Machine Learning (EML) regression models, including bagging, decision trees, random forest, ada boost, gradient boosting, and extreme gradient boost, were used to predict wear properties. Results indicate that the lowest wear rate occurred at 0.5% Mn content. Different wear mechanisms were observed for varying Mn contents. Among the EML models, extreme gradient boost showed superior performance with R2 values of 0.999 and 0.985 in training and testing, respectively.

Manganese controlled transformation and twinning of the nanoscale austenite in low-carbon-medium-Mn steel

A Fe-10.5Mn-0.06C steel consisting of austenite and ferrite dual phases with a volume fraction ratio of 7:3 was fabricated via the quenching and partitioning (Q&P) processing. Tensile tests at various temperatures and strain rates were performed to reveal the mechanical properties of the steel, and the deformation microstructures were characterized by using TEM, t-EBSD and APT techniques. At a constant strain rate of 0.1 s−1, yield strength, tensile strength increase as the temperature decreases from 100 °C to −50 °C, and reach the highest values of 560 MPa and 1390 MPa at −50 °C, respectively. The specimens deformed at low temperatures (below 200 °C) exhibit a characteristic of three-stage work-hardening behavior, while those deformed at higher temperatures (200 and 300 °C) only show two-stage work-hardening curves. The extra hardening stage found at low temperatures is associated with the concurrent twinning and transformation in austenite with varying Mn contents as well as the interaction between twins and dislocations. With increasing temperature, the diffusion of Mn from austenite to ferrite is depressed, inhibiting the martensitic transformation. Consequently, the TRIP effect is weakened and the steel shows the reduced work-hardening rates at higher temperatures. In addition, a few nanoscale austenite residues (<200 nm) are remained even after −25 °C tensile deformtion, due to the highly localized Mn concentration of ∼15 wt%. These findings provide a guidance for designing advanced materials with combinations of ultrahigh strength and good ductility.

Tuning magnetic, electronic, and optical properties of Mn-doped NiCr2O4 via microwave method

The main aim of the paper to the synthesis of Mn (x)-doped NiCr2O4 nanoparticles by varying Mn content (x = 0.00%, 0.01%, 0.02%, and 0.03%) by microwave method for correlating the effect of NiCr2O4 on structural, optical, and magnetic properties of the materials. Understanding the optical, magnetic, and structural properties of huge reservoir factors has essential applications in various aspects of materials science. Our study is to relate the reduction of grain size of Mn content in NiCr2O4 host material. The XRD results revealed that there was an apparent decrease in the characteristic peaks of Mn in the MnNiCr2O4 nanostructure. Particularly, the peak position of (220) and (311) planes was decreased. This decrease in peak position is attributed to the creation of defects or disorders due to the Mn ions in the chromite lattice structure. This inter-site Mn cation migration is responsible for the breaking of long-range cation order and the introduction of defects at both the T-site and O-sublattices site simultaneously.

Oxidation and carburization behaviour of two type 316H stainless steel casts in simulated AGR gas environment at 550 and 600 °C

• Duplex oxide and carburized layers form on steels exposed to AGR reactor coolant • Cracking in the oxide layer increases the oxidation and carburization rates • Carbon locates in the austenite lattice and predominately M 23 C 6 carbides • Diffusion of substitutional solutes is the rate-limiting mechanism of carburization • Small precipitates lead to a reduced carburization rate at 550ºC The time-dependent oxidation and carburization behaviour of two type 316H austenitic stainless steels with varying Mn content and differing average austenite grain size of 142 µm in ‘Low Mn’ (0.98 wt.% Mn) and 81 µm in ‘High Mn’ (1.52 wt.% Mn), were assessed at 550 °C and 600 °C in the presence of simulated reactor primary gas coolant containing 500 vppm H 2 O, 100 vppm H 2 , 300 vppm CH 4 and 1 vol.% CO, balanced with CO 2 . Rupture and spallation of the initial protective chromia layer occurs in the ‘High Mn’ steel after 2000 h at 550 °C, and leads to the formation of a magnetite/spinel oxide layer that reaches 75% surface coverage only after 8000 h. In contrast, ‘Low Mn’ steel reaches ~ 85% coverage after only 1000 h at the same temperature. The development of an inner carburized layer occurs gradually in both steels once the duplex oxide layer is forming. The differences in steel behaviour are reduced at 600 °C, where both oxidation and carburization are significantly accelerated. Only 0.02 wt.% carbon remains in solid solution in the austenite lattice in the carburized layer, the excess carbon atoms precipitating out in the form of Cr-rich M 23 C 6 particles, present both inter- and intragranularly. The experimental values of the activation energy for carburization suggest that diffusion of substitutional solutes as the rate-limiting mechanism of the process. Previously observed carburization depths of ≥ 200 µm in ex-service austenitic stainless steels, may be achieved by pre-conditioning 316H steel in simulated reactor gas coolant for ≥ 6000 h at 600 °C.

Microstructure evolution and mechanical properties of low-silicon cast aluminium alloys with varying Mn contents

ABSTRACT The influences of Mn level (0–0.8 wt%) on the microstructure and mechanical properties of as-cast and T6 heat-treated low-silicon cast aluminium alloys were investigated. The results indicated that the addition of 0.5% Mn completely transformed the needle-like β-Fe phase in as-cast condition into a small-sized π-Fe phase, and the π-Fe phase was fully dissolved after T6 heat treatment. The as-cast and T6 heat-treated alloys with 0.5% Mn achieved the best combination of strength and ductility. However, an excess addition of Mn reduced the mechanical properties due to the occurrence of coarse π-Fe phase (as-cast state), α-Al(Fe, Mn)Si phase (T6 heat-treated state) and eutectic Si. With the increase of Mn content from 0 to 0.8%, the fracture modes of the as-cast alloys changed from intergranular + cleavage fracture to intergranular + quasi-cleavage fracture; The fracture modes of the T6 heat-treated alloys underwent a transition from intergranular + cleavage fracture to quasi-cleavage fracture and then to intergranular + cleavage fracture.

Effects of Al(MnFe)Si dispersoids with different sizes and number densities on microstructure and ambient/elevated-temperature mechanical properties of extruded Al–Mg–Si AA6082 alloys with varying Mn content

The effects of Al(MnFe)Si dispersoids, with different sizes and number densities, on the evolution of microstructure and ambient/elevated-temperature mechanical properties of extruded AA6082 alloys, with varying Mn content, under T5 conditions, were investigated. Compared to the low density of coarse dispersoids formed during conventional homogenization, the high density of fine dispersoids formed during a new low-temperature homogenization was more effective in increasing the material’s resistance to plastic deformation during extrusion, resulting in the dissolution of more constituent Mg2Si particles into the α-Al matrix. A large amount of β", some β′ precipitates and fine dispersoids co-existed in the α-Al matrix of 0.5% Mn containing alloy, which afforded this alloy a substantial increase in ambient-temperature yield strength of 65–75 MPa under T5 conditions compared to the base alloy without dispersoids. A further increase in the Mn content decreased the number density of the β" precipitates, resulting in a decline in the mechanical properties. Upon thermal exposure at 300 °C for 100 h, β"/β′ fully transformed into an undesirable equilibrium β phase and lost their strengthening effect, while fine and dense dispersoids became the dominant strengthener, leading to a 55–70% increase in the elevated-temperature yield strength relative to the alloys either without dispersoids or with coarse dispersoids. Dispersoid strengthening was more pronounced at 0.7% Mn addition as further increasing the Mn content mainly contributed to the fraction of insoluble Mn-containing intermetallics.

Effect of Compositional Variation Induced by EBM Processing on Deformation Behavior and Phase Stability of Austenitic Cr-Mn-Ni TRIP Steel

Electron beam melting (EBM) is an established powder bed-based additive manufacturing process for the fabrication of complex-shaped metallic components. For metastable austenitic Cr-Mn-Ni TRIP steel, the formation of a homogeneous fine-grained microstructure and outstanding damage tolerance have been reported. However, depending on the process parameters, a certain fraction of Mn evaporates. This can have a significant impact on deformation mechanisms as well as kinetics, as was previously shown for as-cast material. Production of chemically graded and, thus, mechanically tailored parts can allow for further advances in terms of freedom of design. The current study presents results on the characterization of the deformation and strain-hardening behavior of chemically tailored Cr-Mn-Ni TRIP steel processed by EBM. Specimens were manufactured with distinct scan strategies, resulting in varying Mn contents, and subsequently tensile tested. Microstructure evolution has been thoroughly examined. Starting from one initial powder, an appropriate scan strategy can be applied to purposefully evaporate Mn and, therefore, adjust strain hardening as well as martensite formation kinetics and ultimate tensile strength.

Pink all-inorganic halide perovskite nanocrystals with adjustable characteristics: Fully reversible cation exchange, improving the stability of dopant emission and light-emitting diode application

In this work, we proposed a straightforward and effective strategy for preparing pink all-inorganic halide perovskite nanocrystal (NC) phosphors for light-emitting diode (LED) application. The pink perovskite NCs with varying Mn contents could be easily and steadily obtained via postsynthetic ion exchange at room temperature. The dependence of the size and optical properties of pink NCs on dopant content was systematically investigated. The reversible anion exchange processes of pink perovskite NCs were conducted with halide salts containing or excluding Pb. The contrasting results suggested that the irreversibility of Mn-emission was mainly affected by the fully reversible cation exchange between Pb2+ and Mn2+. The pink NCs with better stability of dopant emission and high monodispersity were successfully developed by compounding with silica. A pink LED was further made by using the pink NCs/silica composites as pink phosphors on a 395 nm InGaN LED chip. This work provides a feasible strategy for the fabrication of pink LEDs, which may have great application prospects in the field of special lighting, like neon lights and plant growth lights.

High Catalytic Performance of Mn-Doped Ce-Zr Catalysts for Chlorobenzene Elimination.

Mn-Ce-Zr-O catalysts doped with varying Mn content were prepared and assessed for the catalytic combustion of chlorobenzene (CB). Nanosized MCZ-0.67 catalyst with amorphous phase exhibited a high and stable catalytic activity among the studied catalysts, achieving 90% CB conversion at 226 °C and withstanding stability tests, including time-based stability and the successive influence of various operating conditions. Meanwhile, the MCZ-0.67 catalyst used showed good recyclability by calcination in air. Characterization results suggested that Mn doping played a dominant role in improving the catalytic performance, resulting in larger surface area, better redox properties and greater amounts of surface active oxygen. In addition, the introduction of Zr was also indispensable for maintaining the good catalytic performance of catalysts. Finally, trace amounts of polychlorinated by-products during CB oxidation were monitored and the oxidation process was discussed.

Effect of Mn doping on the low-temperature synthesis of tricalcium phosphate (TCP) polymorphs

Effect of Mn doping on the low-temperature synthesis of tricalcium phosphate (TCP) polymorphs was demonstrated in α- and β-TCP polymorphs prepared by wet precipitation method under identical conditions and annealed at 700 °C. Calcium phosphates with Mn doping level in the range from 1 to 5 mol% were studied and the formation of desired polymorph was controlled by varying Mn content in as-prepared precipitates. It was found that increasing Mn content resulted in the formation of β-TCP, while α-TCP was obtained with low Mn doping level, whereas a mixture of two polymorphs was obtained for intermediate Mn concentrations. Moreover, doping with Mn ions allowed the synthesis of β-TCP at relatively low temperature (700 °C). Synthesized compounds were characterized by X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), inductively coupled plasma optical emission spectrometry (ICP-OES) and colorimetric MTT assay.

Highly selective catalytic reduction of NOx by MnOx–CeO2–Al2O3 catalysts prepared by self-propagating high-temperature synthesis

We first present preparation of MnOx–CeO2–Al2O3 catalysts with varying Mn contents through a self-propagating high-temperature synthesis (SHS) method, and studied the application of these catalysts to the selective catalytic reduction of NOx with NH3 (NH3-SCR). Using the catalyst with 18 wt.% Mn (18MnCe1Al2), 100% NO conversion was achieved at 200°C and a gas hourly space velocity of 15384hr−1, and the high-efficiency SCR temperature window, where NO conversion is greater than 90%, was widened to a temperature range of 150–300°C. 18MnCe1Al2 showed great resistance to SO2 (100 ppm) and H2O (5%) at 200°C. The catalysts were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, and H2 temperature programmed reduction. The characterization results showed that the surface atomic concentration of Mn increased with increasing Mn content, which led to synergism between Mn and Ce and improved the activity in the SCR reaction. 18MnCe1Al2 has an extensive pore structure, with a BET surface area of approximately 135.4m2/g, a pore volume of approximately 0.16cm3/g, and an average pore diameter of approximately 4.6 nm. The SCR reaction on 18MnCe1Al2 mainly followed the Eley-Rideal mechanism. The performances of the MnOx–CeO2–Al2O3 catalysts were good, and because of the simplicity of the preparation process, the SHS method is applicable to their industrial-scale manufacture.

Effect of oxygen treatment on structure and electrical properties of Mn-doped Ca0.6Sr0.4TiO3 ceramics

Different oxygen treatment methods, including O2 and N2 annealing, were conducted on Ca0.6Sr0.4TiO3 (CST) ceramics with varying Mn content (0 mol%, 0.5 mol% and 2.0 mol%). Structure characterization, including XRD and SEM, indicated the minimal effect of annealing on the microstructure. Grain boundaries were found to be sensitive to oxygen treatments, and annealing in O2 resulted in increased grain boundary resistance, while in N2 led to the opposite result. The insulating properties of bulk ceramics were found to be dominated by grain boundaries. Both the concentration and mobility of oxygen vacancies were confirmed to affect the energy storage properties to some extent in this work.

The electronic and magnetic properties and topological Hall effect in hexagonal MnNiGa alloy films by varying Mn contents

We report on a systematic study of the electronic, magnetic properties and topological Hall effect (THE) in the hexagonal MnNiGa alloy films as a function of Mn contents. It was found that the MnNiGa alloy films with pure hexagonal structure and flat surface could be obtained on oxidized Si(001) substrates through magnetron sputtering. An analysis of magnetic and transport properties reveals that MnNiGa alloy films show a magnetic structure transformed from ferromagnetic to ferrimagnetic structure with increasing Mn contents, accompanied by a maximum of the saturation magnetization near the stoichiometric composition. We have further investigated the stability of the large THE emerging in MnNiGa alloy films with various Mn contents over a wide temperature-magnetic field region. In contrast to bulk MnNiGa alloy, a reversion of the sign of THE was clearly observed in Mn-rich MnNiGa alloy film, indicating the THE of MnNiGa alloy can be manually controlled by varying Mn contents.

SSZ-13-supported manganese oxide catalysts for low temperature selective catalytic reduction of $$\hbox {NO}_{\mathrm{x}}$$ NO x by $$\hbox {NH}_{3}$$ NH 3

A series of Mn/SSZ-13 catalysts of varying Mn content were synthesized by hydrothermal and co-precipitation methods. Their performances for the selective catalytic reduction (SCR) of $$\hbox {NO}_{\mathrm{x}}$$ with $$\hbox {NH}_{3}$$ were evaluated. The results indicate that over 95% $$\hbox {NO}_{\mathrm{x}}$$ conversion was achieved at a low temperature of $$150^{\circ }\hbox {C}$$ with an Mn loading of 4.74 wt%. Meanwhile, the $$\hbox {NO}_{\mathrm{x}}$$ conversion rate remained greater than 90% at $$450^{\circ }\hbox {C}$$ . The Mn/SSZ-13 catalysts were characterized by X-ray diffraction, ultraviolet–visible diffuse reflectance spectroscopy, Raman spectroscopy, transmission electron microscopy, $$\hbox {N}_{2}$$ -adsorption, temperature-programmed desorption, and X-ray photoelectron spectroscopy. The analysis indicates that $$\hbox {Mn}_{2}\hbox {O}_{3}$$ , $$\hbox {Mn}_{3}\hbox {O}_{4}$$ , and amorphous $$\hbox {MnO}_{2}$$ coexist on the surface of the Mn/SSZ-13 catalysts, with $$\hbox {MnO}_{2}$$ comprising the largest proportion, which may contribute to the high SCR activity. Additionally, the specific surface area and pore volume both decrease with increasing Mn loading. The Mn/SSZ-13 catalyst with 4.74 wt% of Mn has a high concentration of lattice oxygen, a high amorphous $$\hbox {MnO}_{2}$$ content, and greatest number of strong Lewis acid sites, which are beneficial to the adsorption of $$\hbox {NH}_{3}$$ , and may account for its superior catalytic activity. SYNOPSIS Synthesis and characterization of Mn/SSZ-13 catalysts with varying Mn content by a hydrothermal and co-precipitation method are reported. Among the synthesized catalysts, Mn-SSZ-13-3 shows the best $$\hbox {NH}_{3}$$ -SCR, particularly at low temperature. Besides, the catalytic mechanism of Mn/SSZ-13 catalyst is reported.

NaFe1-xMnxPO4 (0≤x≤1) as Positive Electrode Materials for Na-ion Batteries

Recent progress in the development of sodium insertion materials for Na-ion batteries show that they can be considered as interesting alternative to Li-ion batteries owing to more abundant and widespread sodium resources and lower cost as compared to lithium [1,2]. Olivine transition metal phosphates isostructural to the well-known LiFePO4are good positives electrode candidates for Na-ion batteries. Indeed, it has been shown that 1 Na per formula unit can be reversibly deintercalated from olivine NaFePO4 at a potential of 2.8 V vs. Na/Na+ delivering a theoretical capacity of 154 mAh/g [3,4]. However, materials working at higher voltage and with higher cycling potential are highly desirable to increase the energy density. Following this approach, mixed Na[Fe,Mn]PO4compositions with olivine structure are very promising[5]. In this work, we describe the synthesis and characterisation of the solid solution NaMnxFe1-xPO4 (0≤x≤1) prepared from their lithium counterparts (LiMnxFe1-xPO4). We have analysed the structural evolution of these materials with varying Mn content and the electrochemical properties of carbon coated NaMnxFe1-xPO4(0≤x≤1) phosphate materials have been characterized in Na half-cells by galvanostatic cycling under various conditions. The results obtained will be here presented and discussed in terms of energy density and efficiency. [1]B. L. Ellis, W. R. M. Makahnouk, Y. Makimura, K. Toghill and L. F. Nazar, Nat. Mater. (2007), 6, 749. [2]V. Palomares, P. Serras, I. Villaluenga, K. B. Hueso, J. Carretero-Gonzalez and T. Rojo, Energy Environ. Sci., (2012), 5, 5884. [3] P. Moreau, D. Guyomard, J. Gaubicher, F. Boucher. Chem Mater. (2010), 22, 4126-4128. [4] M. Casas-Cabanas, V. Roddatis, D. Saurel, P. Kubiak, J. Carretero-Gonzalez, V. Palomares, P. Serras and T. Rojo, J. Mater. Chem. (2012), 22, 17421. [5] K. T. Lee, T. N. Ramesh, F. Nan, G. Botton, L. F. Nazar. Chem. Mater. (2011), 23, 3593-3600.

Microstructure and Improved Coercivity of Mn&lt;sub&gt;1.33&lt;/sub&gt;Ga Nanoflakes by Surfactant-Assisted Ball Milling

In recent years, Mn x Ga alloys with tetragonal structure have attracted much attention because of the erratic fluctuation of rare earth supply and especially the tunable magnetic properties from fer-rimagnetic to ferromagnetic by varying Mn content. It is theoretically estimated that MnGa compound in L1 0 structure owes high anisotropy constant K u of 26 Mergs/cm3 and magnetization Ms of 845 emu/cm3, and thus can be regarded as a potential candidate for rare-earth-free permanent magnets [1-2]. At present, surfactant-assisted high-energy ball milling (HEBM) method has been regarded as one of the effective ways to realize high coercivity for magnetic materials with large anisotropy. It was reported [3-4] that high-aspect-ratio single-crystal or textured polynanocrystalline flakes of Sm-Co-based permanent magnetic materials with a submicron or nanosize thickness and high coercivity can be achieved. In this study, textured rare-earth-free Mn 1.33 Ga polycrystalline nanoflakes were prepared by surfactant-assisted HEBM in heptane with 15wt. % oleic acid (OA), and the effects of milling time on structure and magnetic properties were also investigated.

Effect of lanthanide transition metal coupling on the structural, electronic and magnetic properties of Mn co-doped HoZnO system

We report on the effect of Mn substitution in controlling the structural, optical and magnetic properties of the HoZnO system. A series of samples were prepared by solid state reaction with varying Mn content. It is observed from the structural characterization that varying dopant concentration in the host lattice results in varying bond length leading to the inhomogeneous change in the lattice parameters. The Ho ions prefer to reside along the c-axis, while the Mn ions reside along the basal plane of the ZnO wurtzite structure leading to the Ho–Mn coupled pairs. Raman spectroscopy analysis shows that the pairs are coupled together via phonon mode. Results obtained from the UV–Vis spectroscopy show a decrease in the refractive index with Mn addition of the HoZnO system. The Ho–Mn coupling greatly enhances the magnetization making the ZnO a diluted magnetic semiconductor (DMS) material at 5K.

Effect of Mn Addition on Microstructural Modification and Cracking Behavior of Ferritic Light-Weight Steels

In the present study, effects of Mn addition on cracking phenomenon occurring during cold rolling of ferritic light-weight steels were clarified in relation to microstructural modification involving κ-carbide, austenite, and martensite. Four steels were fabricated by varying Mn contents of 3 to 12 wt pct, and edge areas of steel sheets containing 6 to 9 wt pct Mn were cracked during the cold rolling. The steels were basically composed of ferrite and austenite in a band shape, but a considerable amount of κ-carbide or martensite existed in the steels containing 3 to 6 wt pct Mn. Microstructural observation of the deformed region of fractured tensile specimens revealed that cracks which were initiated at ferrite/martensite interfacial κ-carbides readily propagated along ferrite/martensite interfaces or into martensite areas in the steel containing 6 wt pct Mn, thereby leading to the center or edge cracking during the cold rolling. In the steel containing 9 wt pct Mn, edge cracks were found in the final stage of cold rolling because of the formation of martensite by the strain-induced austenite to martensite transformation, whereas they were hardly formed in the steel containing 12 wt pct Mn. To prevent or minimize the cracking, it was recommended that the formation of martensite during the cooling from the hot rolling temperature or during the cold rolling should be suppressed, which could be achieved by the enhancement of thermal or mechanical stability of austenite with decreasing austenite grain size or increasing contents of austenite stabilizers.