Pct Mn Research Articles

Influence of Ni and Process Parameters in Medium Mn Steels Heat Treated by High Partitioning Temperature Q&P Cycles

In this work, two medium Mn steels (5.8 and 5.7 wt pct Mn) were subjected to a quenching and partitioning (Q&P) treatment employing a partitioning temperature which corresponded to the start of austenite reverse transformation (ART). The influence of a 1.6 wt pct Ni addition in one of the steels and cycle parameters on austenite stability and mechanical properties was also studied. High contents of retained austenite were obtained in the lower quenching temperature (QT) condition, which at the same time resulted in a finer microstructure. The addition of Ni was effective in stabilizing higher contents of austenite. The partitioning of Mn and Ni from martensite into austenite was observed by TEM–EDS. The partitioning behaviour of Mn depended on the QT condition. The lower QT condition facilitated Mn enrichment of austenite laths during partitioning and stabilization of a higher content of austenite. The medium Mn steel containing Ni showed outstanding values of the product of tensile strength (TS) and total elongation (TEL) in the lower QT condition and a higher mechanical stability of the austenite.

Inclusion Engineering in Medium Mn Steels: Effect of Hot-Rolling Process on the Deformation Behaviors of Oxide and Sulfide Inclusions

Medium Mn steel (MMS) is a new category of the third-generation advanced high strength steel (3rd AHSS) which is developed in the recent 1-2 decades due to a unique trade-off of strength and ductility. Thus, this steel grade has a wide application potential in different fields of industry. The current work provides a fundamental study of the effect of hot-rolling on the inclusion deformation in MMS including a varied 7 to 9 mass pct Mn. Specifically, the deformation behavior of different types of inclusions (i.e., Mn(S,Se), liquid oxide (MnSiO3), MnAl2O4, and complex oxy-sulfide) was investigated. The results show that both MnSiO3 and Mn(S,Se) are soft inclusions which are able to be deformed during the hot-rolling process but MnAl2O4 does not. The aspect ratio of soft inclusions increases significantly from as-cast to hot-rolling conditions. When the maximum size of different inclusions is similar, Mn(S,Se) deforms more than MnSiO3 does. This is due to a joint influence of physical parameters including Young’s modulus, coefficient of thermal expansion (α), etc. However, when the maximum size of one type of inclusion (e.g., MnSiO3) is much larger than another one (e.g., Mn(S,Se)), this maximum size of soft inclusions plays a dominant role than other factors. In addition, the deformation behavior of dual-phase inclusion depends on the major phase, i.e., either oxide or sulfide. Last but not least, empirical correlations between the reduction ratio of the thickness of plate, grain size, and aspect ratio of oxide and sulfide inclusions after hot-rolling are provided quantitatively. This work aims to contribute to the ‘inclusion engineering’ concept in the manufacturing of new generation AHSS.

Development of Low-Yield Stress Co\u2013Cr\u2013W\u2013Ni Alloy by Adding 6 Mass Pct Mn for Balloon-Expandable Stents

This is the first report presenting the development of a Co–Cr–W–Ni–Mn alloy by adding 6 mass pct Mn to ASTM F90 Co–20Cr–15W–10Ni (CCWN, mass pct) alloy for use as balloon-expandable stents with an excellent balance of mechanical properties and corrosion resistance. The effects of Mn addition on the microstructures as well as the mechanical and corrosion properties were investigated after hot forging, solution treatment, swaging, and static recrystallization. The Mn-added alloy with a grain size of ~ 20 µm (recrystallization condition: 1523 K, 150 seconds) exhibited an ultimate tensile strength of 1131 MPa, 0.2 pct proof stress of 535 MPa, and plastic elongation of 66 pct. Additionally, it exhibited higher ductility and lower yield stress while maintaining high strength compared to the ASTM F90 CCWN alloy. The formation of intersecting stacking faults was suppressed by increasing the stacking fault energy (SFE) with Mn addition, resulting in a lower yield stress. The low-yield stress is effective in suppressing stent recoil. In addition, strain-induced martensitic transformation during plastic deformation was suppressed by increasing the SFE, thereby improving the ductility. The Mn-added alloys also exhibited good corrosion resistance, similar to the ASTM F90 CCWN alloy. Mn-added Co–Cr–W–Ni alloys are suitable for use as balloon-expandable stents.

Roasting and Leaching Behavior of Nickel Laterite Ore

Nickel is mostly extracted from sulfide ores, however, laterite ores account for over 60 pct of all nickel resources in the world, and despite its predominance, there is no well-established process to extract nickel from such ores. Nickel in laterites is hosted in many different compounds such as oxides, hydroxides, and silicates minerals. The sulfation-roasting-leaching process has the potential to change this scenario once it can be applied to all kinds of nickel laterite ores and does not consume much acid, as in the atmospheric leaching process. The main characteristic of the process is the iron sulfates decomposition during roasting steps, which produces sulfur trioxide (SO3). The sulfur trioxide is reactive with metals such as nickel and cobalt, converting them to soluble sulfates, and reducing acid consumption. Experiments were conducted to establish the optimal conditions to extract nickel from laterite ores using the sulfation-roasting-leaching process. Various parameters were investigated: water addition, sulfuric acid concentration, the number of heat-treatments steps, roasting temperature and time, leaching time, and solid/liquid ratio. Furthermore, the phase changes during thermal treatments were investigated to identify the mechanisms involved in the transformation of the minerals. Experimental results indicated that nickel forms sulfates through three different ways: reacting with H2SO4 during sulfation, with Fe2(SO4)3 (ferric sulfate) or Fe(OH)SO4 (basic iron sulfates) during the heat-treatments, and also throughout the leaching step due to iron-rich phase dissolution. More than 83.0 pct Ni, 90.0 pct Co, 61.3 pct Al, 17.3 pct Ca, 85.7 pct Mg, 87.5 pct Mn, 1.1 pct Ti, and 16.6 pct Fe were extracted under optimums conditions.

Mechanical Properties of Ausformed Carbide-Free Bainite

In this study, the effect of ausforming temperature and strain on the bainite transformation in a model alloy containing 0.39 pct C, 2.0 pct Mn, 1.9 pct Si, and 0.5 pct Cr (mass percent) was investigated. Samples were deformed at 300 °C, followed by isothermal holding to monitor the phase transformation kinetics. Dilatometry results confirm the acceleration of transformation kinetics when the material is deformed to small strains (0.05 to 0.20). Tensile testing results show that, for long isothermal holding times, no improvement in strength or ductility is achieved as a result of ausforming in comparison with the non-deformed state. However, the benefit of ausforming lies in its ability to accelerate the bainite transformation kinetics and to reduce the isothermal holding time needed to avoid premature fracture due to the presence of a high volume-fracture of fresh martensite. Fracture analysis reveals ductile fracture, with cracks along martensitic regions within the microstructure. The distribution of martensite in the final microstructure was associated with bands of Mn segregation. This banding effect was less visible within the ausformed microstructure because bainite was able to nucleate within both the high- and low-Mn regions. A second advantage of ausforming is, therefore, to reduce the microstructure heterogeneity associated with compositional banding within the steel sheets and, by so doing, eliminate crack propagation within the bands. In spite of the fact that ausforming accelerates the bainite transformation kinetics, the required transformation times for the present steel are still too long for use within industrial continuous annealing lines.

Thermodynamic Stacking Fault Energy, Chemical Composition, and Microstructure Relationship in High-Manganese Steels

Stacking fault energy (SFE) is related to activating complex high strength and ductility mechanisms such as transformation-induced plasticity and twinning-induced plasticity effects. This type of energy can be estimated by many different methods and its importance is in its ability to predict microstructure and phase transformation behavior when the material is submitted to stress/strain. In order to study the SFE, chemical composition, and microstructure relationships, eleven different welding parameters were chosen to obtain a large range of dilution levels. A new tubular wire electrode of high-manganese steel (21 wt pct Mn) was used as the consumable and an SAE 1012 steel plate (0.6 wt pct Mn) as the base metal in a flux-cored arc welding process. These welding parameters were related to the phases formed and phase transformation behavior in the fusion zone. The SFE of the austenite phase was calculated using a thermodynamic model. The welding parameters produced SFE values in the range of − 5 to 7 mJ/m2. $$\epsilon $$ -martensite and austenite were observed in all samples, but $$\alpha $$ ′-martensite was only found in those that presented negative SFE values, i.e., those with lower Mn content. Chemical Gibbs Free energy was the component with the most influence on the SFE. Nanoindentation detected the phase transformations during hardness testing for the medium and low dilution levels used, while the high dilution levels presented the highest hardness and modulus of elasticity values, and the lowest elastic and plastic deformation values. The results provide an improved method to develop high-manganese steels with microstructure control through welding parameters.

Compressive and Corrosion Properties of Lotus-Type Porous Mg-Mn Alloys Fabricated by Unidirectional Solidification

Lotus-type porous Mg-Mn alloys were fabricated by solid-gas eutectic unidirectional solidification (the Gasar process) by controlling and optimizing the process parameters. The microstructures, compressive properties and corrosion properties in a simulated body fluid solution were investigated. Porous pure Mg was prepared with a preferentially oriented (11$$ \bar{2} $$2) plane, whereas the Mg-2 wt pct Mn alloy showed a preferentially oriented (10$$ \bar{1} $$3) plane. Mn addition refined the grains, improved the Mn precipitates, activated the {10$$ \bar{1} $$2} twin at the end of the pores and increased the compressive strength from 64 MPa for pure Mg to 74 MPa for 1 wt pctMn and 80 MPa for 2 wt pct Mn. Electrochemical tests showed that 2 wt pct Mn addition could decrease the corrosion current from 1.84 × 10−3 to 4.22 × 10−4 A cm−2. Immersion tests suggest that 2 wt pct Mn addition reduced the sample mass loss, which indicated a better corrosion performance, and exhibited a smaller decrease in compressive strength compared with that of the porous pure Mg. This work shows that the Gasar technique can be a promising fabrication method to prepare lotus-type porous Mg-Mn alloys which are more attractive for application in degradable biomaterials engineering.

The Influence of Microstructural Characteristics on Austenite Formation Kinetics in a Plain Carbon Steel

Since the condition of austenite phase formed during intercritical annealing treatment has a crucial impact on the final microstructure and mechanical properties of dual-phase (DP) steels, detailed investigations with regard to austenite formation in this heat treatment process need to be done. In this study, the effects of different microstructural features, such as ferrite grain size, cementite particle size, and pearlite morphology, on austenite formation in a plain carbon steel (0.165 wt pct C, 1.15 wt pct Mn) during isothermal intercritical annealing treatment have been evaluated. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) model was used for modeling the kinetics of austenite formation in this steel during isothermal annealing treatment. The volume fraction of austenite (martensite at room temperature) at different intercritical annealing holding times was calculated by this model using the corresponding results obtained from the experiments. It was found that the starting steel microstructure from which austenite phase is formed has a significant effect on both austenite nucleation and growth. The effect of microstructural parameters on the kinetics of austenite formation in ferrite-cementite steel microstructures was more significant than that in ferrite-pearlite (F-P) steels. An increase in the average cementite particle size or ferrite grain size in ferrite-cementite steels caused a significant decrease in the rate of austenite formation. In F-P steels, on the other hand, pearlite morphology exhibited a small effect on the kinetics of austenite formation while ferrite grain size had a pronounced effect on the rate of austenite formation at the later stage of intercritical annealing, i.e., ferrite to austenite transformation stage.

Optimization of Aluminum Alloy AA5083 for Superplastic and Quick Plastic Forming

The high temperature formability of Al-4.6 wt pct Mg alloys with 0.5-1.5 wt pct Mn and 0.05-0.27 wt pct Fe has been evaluated by uni-axial tensile testing at 698.15 K to 798.15 K (425 °C to 525 °C) with strain rates from 2 × 10−5 to 8.75 × 10−2 s−1. The effects of Mn and Fe on the intermetallic phase, grain structure and cavitation were investigated and correlated to the superplastic behaviors. The superplasticity was found to be very dependent on the density, size and volume fraction of the Al6(Mn, Fe) particles. The increasing Mn and decreasing Fe not only refine and stabilize the grain structure, but also reduce the nucleation rate of cavities. Consequently, the grain boundary sliding is enhanced and the premature failure due to cavitation is retarded, resulting in a significant improvement of superplasticity. With optimized chemistry containing very high Mn, e.g., 1.7-1.9 wt pct, and very low Fe, e.g., below 0.1-0.15 wt pct, the maximum superplasticity could be achieved at 698.15 K to 773.15 K (425 °C to 500 °C) with strain rates from 10−4 to 10−2 s−1.

Characterization of Inclusions in 3rd Generation Advanced High-Strength Steels

Samples taken from laboratory-produced 3rd generation advanced high-strength steels, solidified at a low cooling rate, have been investigated to study the characteristics of non-metallic inclusions. Two steels, containing 2 and 5 pct Mn content, were produced for this purpose. A higher number of total inclusions were observed in 5 pct Mn steel. The four main types of inclusions observed were Al2O3, AlN, MnS, and AlSiMn-oxide. These classes were divided into subclasses according to variations in their chemistry. The major subclasses of AlN inclusions are either plate-like or regular in shape and have different size distributions. Thermodynamic calculations suggest that plate-like AlN inclusions are formed at the initial stage of solidification, while faceted/regular-shaped inclusions are precipitated toward the end of solidification. Moreover, it was found that the size of nitride inclusions is related to their N content. This phenomenon is discussed from the viewpoint of nucleation theory.

Effect of Solute Nb on Grain Growth in Fe-30 Pct Mn Steel

Niobium is known to segregate strongly to grain boundaries in steel. The strong interaction of Nb with grain boundaries results in an important reduction of the grain boundary mobility and strong retardation of recrystallization and grain growth. In this study, the effect of Nb on the mobility of grain boundaries in a second-generation Fe-30 pct Mn TWIP steel is investigated. Grain growth kinetics was measured in a series of Nb-containing Fe-30 pct Mn model alloys. An estimate of the grain boundary mobility was obtained for various temperatures and niobium contents. It was found that Nb slows down the mobility of random high-angle grain boundary segments that are not twin related. The effect of solute Nb on grain growth, in the presence of annealing twins, was modeled using Cahn’s theory of solute drag coupled with a recently formulated twin-inhibited grain growth model. The results are shown to be in very good agreement with the experimentally determined growth kinetics.

Analysis of Hot- and Cold-Rolled Loads in Medium-Mn TRIP Steels

The purpose of this work is to investigate the hot- and cold-rolling requirements to produce third-generation advanced high-strength steels (AHSS). Therefore, five medium-Mn (10 to 14 wt pct Mn) alloys that exhibit transformation-induced plasticity (TRIP) were compared to a commercially produced grade of AISI 1018 using hot- and cold-rolling experiments. Experimental data collected from a STANAT instrumented rolling mill was utilized to measure force and torque during hot- and cold-rolling. Experimental data were processed by a 1D analytical model, based on Orowan model, to determine rolling pressure. It was determined that pressures required to hot-roll TRIP alloys are 1.4 to 1.8 times greater than pressures for rolling AISI 1018 steel. Cold rolling of the medium-Mn TRIP steels was found to be 1.5 to 2.8 times greater than the AISI 1018 steel. Mechanical and microstructural characterization was also performed and the variation in rolling pressure was related to the starting microstructural constituents, and alloys containing greater starting quantities of e-martensite in the microstructure had higher flow stresses at equivalent rolling strains during cold rolling.

J-integral Fracture Toughness of High-Mn Steels at Room and Cryogenic Temperatures

The J-integral fracture toughness values of high-Mn steel (Fe-25 wt pct Mn) and 304L stainless steel were evaluated at 25 °C, 0 °C, − 50 °C, − 100 °C, − 163 °C, and − 196 °C using precracked compact tension (CT) specimens and compared to those determined using Charpy impact tests. The high-Mn steel exhibited excellent J-integral fracture toughness at both room and cryogenic temperatures, with values comparable to those of 304L stainless steel. However, the trend of the J-integral fracture toughness of high-Mn steel with the decreasing temperature differed from that of the Charpy impact test results. Electron backscattered diffraction and micrographic analyses suggest that the varying stacking fault energies of high-Mn steels at different temperatures affected the deformation behavior in the stretch zone at the crack tip of the CT specimen. The effect of this temperature-dependent deformation behavior of high-Mn steels on the fracture process in the J-integral test could differ from that in the Charpy impact test, resulting in the different trends in the fracture resistance with the decreasing temperature.

Effect of Mn and C on Grain Growth in Mn Steels

Grain growth in Fe-Mn austenites was examined at 1373 K and 1473 K as a function of Mn (0 to 30 wt pct) and carbon (0 to 0.5 wt pct) content. The addition of Mn had the effect of reducing the rate of grain growth. The observed inhibiting effect of Mn is believed to be mainly due to an increase in the occurrence of annealing twins with increasing Mn content. It is hypothesized that, upon intersecting with High-Angle Grain Boundaries (HAGBs), the twins result in low-energy, low-mobility boundary segments which ultimately slow the overall growth kinetics. Solute drag does not appear to significantly contribute to the slowing of the grain growth kinetics for Mn contents greater than 6 wt pct. Atom probe tomography studies confirmed weak or negligible segregation of Mn to HAGBs. The carbon content had a small but measurable effect on the grain growth kinetics. Reduction of the carbon content in an Fe-30 wt pct Mn alloy resulted in a decrease in effective grain boundary mobility.

Effect of Partial Substitution of Mn for Ni on Mechanical Properties of Friction Stir Processed Hypoeutectic Al-Ni Alloys

In this study, the mechanical properties of as-cast and FSPed Al-2Ni-xMn alloys (x = 1, 2, and 4 wt pct) were investigated and compared with those of the as-cast and FSPed Al-4Ni alloy. According to the results, the substitution of 2 wt pct Mn for 2 wt pct Ni leads to the formation of fine Mn-rich intermetallics in the microstructure increasing the tensile strength, microhardness, fracture toughness, and specific strength of alloy by 22, 56, 45, and 35 pct, respectively. At higher Mn concentrations, the formation of large Mn-rich platelets in the microstructure reduces the tensile properties. Friction stir processing at 12 mm/min and 1600 rpm significantly enhances both the strength and ductility of the alloy. The tensile strength, yield strength, fracture strain, fracture toughness, microhardness, and specific strength of FSPed Al-2Ni-4Mn alloy improved by 97, 83, 30, 380, 152, and 110 pct, respectively, as compared to those of the as-cast Al-4Ni alloy. This can be attributed to dispersion strengthening of Ni- and Mn-rich dispersoids, formation of ultrafine grains, and elimination of casting defects. The fractography results also show that the brittle fracture mode of the as-cast Mn-rich alloys turns to a more ductile mode, comprising fine and equiaxed dimples in FSPed samples.

Effect of Aluminum on Borocarbides and Temper Softening Resistance of High-Boron High-Speed Steel

The effects of aluminum content on the morphology of eutectic borocarbide and temper softening resistance of high-boron high-speed steel with 2.0 wt pct B-0.4 wt pct C-6.0 wt pct Cr-4.0 wt pct Mo-x wt pct Al-1.0 wt pct Si-1.0 wt pct V-0.5 wt pct Mn (x = 0.0, 1.0, 1.5, 2.0) have been investigated in the present work. The experimental results indicate that aluminum not only promotes the refining and nodulizing of borocarbide, but also improves the red-hardness of the alloy. The as-cast microstructure of high-boron high-speed steel (with different aluminum contents) consists of matrix α-Fe, eutectic borocarbide M2(B,C), and boron-cementite M3(B,C) (M = Fe, Cr, Mo, V, Mn). Borocarbide presents a continuous network structure in the microstructure of alloy without aluminum addition. With increasing aluminum content, borocarbide is spheroidized, and its size decreases. Furthermore, the variation in aluminum content barely affects the phase type. The hardness testing results of heat-treated samples at 1050 °C, 1100 °C, and 1150 °C reveal that the quenching temperature for obtaining the martensite matrix rises with an increase of aluminum content. However, the alloy matrix with 2.0 wt pct aluminum cannot transform to a martensite matrix through quenching, even at 1150 °C. The red-hardness is defined as the alloy hardness after four rounds of tempering at 600 °C for 1 hour. The hardness of alloy without aluminum addition reduces significantly after tempering, while the hardness of alloy with 1.0 wt pct aluminum exhibited the highest value. Moreover, no apparent change in borocarbide morphology occurred after tempering, indicating that the alloy microstructure renders good tempering stability.

Chemistry and Properties of Medium-Mn Two-Stage TRIP Steels

Eight medium manganese steels ranging from 10 to 15 wt pct Mn have been produced with varying levels of aluminum, silicon, and carbon to create steels with varying TRIP (transformation-induced plasticity) character. Alloy chemistries were formulated to produce a range of intrinsic stacking fault energies (ISFE) from − 2.2 to 13.3 mJ/m2 when calculated at room temperature for an austenitic microstructure having the nominal alloy composition. Two-stage TRIP behavior was documented when the ISFE of the γ-austenite phase was 10.5 mJ/m2 or less, whereas an ISFE of 11.9 mJ/m2 or greater exhibited TWIP (twin-induced plasticity) with single-stage TRIP to form α-martensite. Properties were measured in both hot band (hot rolled) and batch annealed (hot rolled, cold rolled, and annealed) conditions. Hot band properties were influenced by the Si/Al ratio and this dependence was related to incomplete recovery during hot working for alloys with Si/Al ratios greater than one. Batch annealing was conducted at 873 K (600 °C) for 20 hours to produce ultrafine-grained microstructures with mean free slip distances less than 1 μm. Batch-annealed materials were found to exhibit a Hall–Petch dependence of the yield strength upon the mean free slip distance measured in the polyphase microstructure. Ultimate tensile strengths ranged from 1450 to 1060 MPa with total elongations of 27 to 43 pct. Tensile ductility was shown to be proportional to the sum of the products of volume fraction transformed times the volume change associated for each martensitic transformation. An empirical relationship based upon the nominal chemistry was derived for the ultimate tensile strength and elongation to failure for these batch-annealed steels. Two additional alloys were produced based upon the developed understanding of these two-stage TRIP steels and tensile strengths of 1150 MPa with 58 pct total elongation and 1400 MPa and 32 pct ductility were achieved.

Correlation of the Solidification Path with As-Cast Microstructure and Precipitation of Ti,Nb(C,N) on a High-Temperature Processed Steel

The solidification path of a high-temperature processed (HTP) X65 sour service steel with 0.039 wt pct C, 0.09 wt pct Nb, and 0.54 wt pct Mn and its effect on the segregation, microstructure, and precipitation distribution of Ti,Nb(C,N) was studied using optical and confocal microscopy, scanning electron microscopy (SEM), and computational simulation (Thermo-Calc and DICTRA). The results were compared with those obtained for another commercial microalloyed steel, containing 0.09 wt pct C, 0.04 wt pct Nb, and 0.97 wt pct Mn. The results indicate that the main parameter that influences microsegregation is the C content, which has a large influence on the solidification path. The difference in segregation between different positions in industrial continuous cast slabs of the steels was also observed, as expected. The larger solidification interval (TL-TS) of the commercial microalloyed steel indicates the formation of a solidification front that has higher solute concentration than the X65 HTP sour service steel, which concurs with the higher macro- and microsegregation observed.

Orientation of Magnetized MnBi in a Strong Static Magnetic Field

Solidification of Bi-4.5 wt pct Mn alloy was investigated in the presence and absence of a strong static magnetic field (SSMF). A cooling rate (R) of 60 K/min caused MnBi to orient with the SSMF, owing to the force moment and attractive force. The attractive force and magnetic gradient force induced formation of multilayered MnBi when R was 5 K/min. The magnetic gradient force was damped when R was 60 K/min. Low cooling rates favored the aggregation process.

Effects of Fine Particle Peening Conditions on the Rotational Bending Fatigue Strength of a Vacuum-Carburized Transformation-Induced Plasticity-Aided Martensitic Steel

The effects of fine particle peening conditions on the rotational bending fatigue strength of a vacuum-carburized transformation-induced plasticity-aided martensitic steel with a chemical composition of 0.20 pct C, 1.49 pct Si, 1.50 pct Mn, 0.99 pct Cr, 0.02 pct Mo, and 0.05 pct Nb were investigated for the fabrication of automotive drivetrain parts. The maximum fatigue limit, resulting from high hardness and compressive residual stress in the surface-hardened layer caused by the severe plastic deformation and the strain-induced martensite transformation of the retained austenite during fine particle peening, was obtained by fine particle peening at an arc height of 0.21 mm (N). The high fatigue limit was also a result of the increased martensite fraction and the active plastic relaxation via the strain-induced martensite transformation during fatigue deformation, as well as preferential crack initiation on the surface or at the subsurface.