Low Carbon High Manganese Steels Research Articles

Understanding casting behaviour of low carbon high manganese steel through detailed characterization of mould powder and mould top slag

ABSTRACT This study focused on multistage characterization techniques in developing an understanding of the abnormal casting behaviour of low carbon high manganese (LCHMn) steel. In addition to raw mould powder used for casting LCHMn steel, mould top slag samples were also collected for normal and abnormal casting conditions. Raw mould powder and top slag samples were characterized using XRF, XRD, and SEM-EDS to determine chemical composition, crystallinity and morphology. The chemical composition results revealed deviation of normal and abnormal behaviours from the mould powder due to the pickup of oxides of Al, Mn, and Ti. The SEM analyses of raw mould powder showed different granular particle sizes while pores and glassy/crystalline structure were seen for normal and abnormal behaviour at casting. CaF2, CaSiO3, and Na2CaSi3O9 were revealed as the mineralogical phases. There was a modified crystalline phase present in the abnormal behaviours at casting due to pickup of other oxides.

Evolution of Al2O3 inclusions by cerium treatment in low carbon high manganese steel

The influence of cerium (Ce) treatment on the morphologies, size and distributions of Al2O3 inclusions in low carbon high manganese steel was investigated by OM, SEM-EDS and theoretical calculation. The results showed that Ce can modify the morphologies and types of Al2O3 inclusions. After Ce treatment, the irregular Al2O3 inclusions were replaced by smaller and dispersive spherical cerium oxysulfides. The effects of treatment time and Ce content on the evolution of Al2O3 inclusions were examined. It indicated that Al2O3 inclusions were wrapped by rare earth inclusions to form a ring like shape Ce-enriched band around the inclusions. Model was established to elucidate the evolution mechanism of Al2O3 inclusions. Evolution kinetics of inclusions was discussed qualitatively to analyze the velocity controlled step. It was found that diffusion of Ce3+ and Al3+ in solid inclusion core and the formed intermediate layer would be the limited step during the evolution process.

Effect of Rare Earth Cerium Addition on Microstructures and Mechanical Properties of Low Carbon High Manganese Steels

AbstractLow carbon high manganese steels with different Ce contents were melted in medium frequency vacuum induction furnace. The microstructures and mechanical properties of steels were studied by OM, SEM, EDS and mechanical property testing. The results showed that the microstructures of experimental steels were refined remarkably, inclusions distributed more finely and uniformly, the tensile strength and impact toughness of tested steels both improved greatly after the addition of Ce. Thermodynamic calculation results demonstrated that Ce contained inclusions were Ce2O3and Ce3S4, which agreed well with the results observed by SEM and EDS. By analysis of two-dimensional lattice disregistry, it was shown that the lattice misfit parameter between δ-Fe and Ce2O3, Ce3S4are less than 6 %, which indicated that Ce2O3and Ce3S4could effectively act as the heterogeneous nuclei of initial δ-Fe. Therefore, the microstructures were refined significantly and the mechanical properties were improved correspondingly in Ce-added low carbon high manganese steels.

Determination of low levels of retained austenite in low-carbon high-manganese steel using X-ray diffraction

A method involving the decomposition of the X-ray diffraction (XRD) peaks for the single wavelengths Kα1 and Kα2 was used to quantify the amount of retained austenite at levels lower than 5% in low-carbon high-manganese steels. By applying this method, it was possible to use the two main peaks of austenite (γ) and the two main peaks of ferrite (α) in the calculations, despite the partial overlapping of the (111)γ and (110)α peaks. The diffraction peaks were modeled with the Pearson VII equation using a nonlinear least-squares optimization technique. This allowed the integrated intensities of the XRD peaks to be calculated using only the Kα1 side. The method was used to measure the levels of retained austenite in samples of a metal-inert gas steel welding rod cooled at the rates of 10°C/s and 1.6°C/s. The accuracy of the method was determined by performing six measurements in different directions in both the longitudinal and the transverse section of the 1.6°C/s sample.

Microstructure Refinement in Low Carbon High Manganese Steel through Ti-Mg Deoxidation

The low carbon high manganese steel (C: 0.07, Mn: 2.0, mass percentage) was deoxidized by Ti and Mg alloys, and its features of inclusion and microstructure were systemically studied. Through the scanning electron microscope (SEM) and Energy Dispersive X-ray Detector (EDX), it can be seen that in inclusions, the element of magnesium always coexists with titanium, and no single-phase oxides of magnesium are observed. After etching in 3Vol% natal solution, it’s found that the Mg-contained and Ti-contained inclusions can act as nucleation sits for the intragranular acicular ferrite. These results imply that besides the pinning effect, the oxide of magnesium can also participate in the nucleation for intragranular acicular ferrite. Thus, it may be used in the oxide metallurgy to refine the ferrite microstructure.

Micro-structure Refinement in Low Carbon High Manganese Steels through Ti-Deoxidation, Characterization and Effect of Secondary Deoxidation Particles

This paper investigates the effect of de-oxidation inclusions on micro-structure in low carbon (0.07 mass%), high Mn (0.9 mass%) steel. De-oxidation tests were carried out by adding either aluminum (0.05 mass%) or titanium (0.05, 0.03 or 0.015 mass%) to an iron melt in a 400 g-scale vacuum furnace. A Confocal Scanning Laser Microscope (CSLM) was used to evaluate the effect of cooling rate by re-melting and quenching during solidification. Fine secondary de-oxidation particles were obtained in the Ti-killed samples, and the particle density increased with increasing oxygen content, and their size decreased with increasing the cooling rate during solidification.The secondary Ti de-oxidation particles were found to have an effect on microstructure evolution, such as solidifying microstructure, austenite grain growth and austenite decomposition. The de-oxidation particles were examined through FE-TEM and were identified to be TiO, MnTiO3 and Mn2TiO4, in low oxygen ([O]=7 ppm) and high oxygen ([O]=56, 81 ppm) Ti-killed steels respectively, which were qualitatively same as those predicted by thermodynamic calculations. Stabilities of TiO, MnTiO3 and Mn2TiO4 are influenced by Mn presence. Composition change and decomposition of oxide were estimated through thermodynamic calculations. The effect of the particles on ferrite formation was evaluated through thermo-mechanical treatments. TiO was the most effective for promoting ferrite formation through heterogeneous nucleation. The particles contributed to ferrite formation in the following order, TiO>TiN>MnS> MnTiO3>Ti2O3.It was found that the secondary Ti de-oxidation particles work are engulfed by the advancing solid phase during solidification based on analysis with PET (Pushing Engulfment Transition) velocity, particle sizes and solidification rates. The particles at dendrite tips and inter-dendritic regions are likely restraining the molten steel flow resulting in a finer solidification microstructure.

Deformation Behavior and Microstructure of Low Carbon High Manganese Steels in Tensile Strain

The mechanical properties of two high manganese steels with manganese contents (15% and 25%) were investigated during tensile tests at room temperature. The results indicated that the strengths of steels were a little low and the elongations were improved greatly with increasing the manganese content. Stress fluctuations were found during tensile tests of the Fe-15Mn steels, and as the strain increased the range of stress fluctuations became wider. The strain hardening exponent n of samples changed with strain in a parabola model. The microstructures before and after deformation were investigated and the results showed that phase transformation of γ (fcc) →ε (hcp) and γ (fcc) →ε (hcp) →α (bcc) induced plasticity occurred in the Fe-15Mn steels. However, in the Fe-25Mn steels, at the beginning stage of the deformation, phase transformation induced plasticity played an important role, and with the increase of deformation, the main mechanism was twinning induced plasticity.

Micro-structure Refinement in Low Carbon High Manganese Steels through Ti-deoxidation: Austenite Grain Growth and Decomposition

This paper investigates the effect of de-oxidation inclusions on micro-structure evolution in low-carbon steels. Low carbon (0.07 wt%), high Mn (0.9 wt%) steel in a Al2O3 or MgO crucible was deoxidized by adding either aluminum (0.05 wt%) or titanium (0.05, 0.03 or 0.015 wt%) in a 400 g-scale vacuum furnace, and cast in a Cu mold at cooling rates between 2.0–6.0 K/s. These cast samples were re-melted and cooled at various cooling rate, 1 through 100 K/s in the hot-stage of a conforcal laser scanning microscope (CSLM) in order to investigate the effect of cooling rate.Oxide inclusion sizes in all the Ti-killed steels were smaller and inclusion densities higher than those in the Al-killed steel. In Ti-killed steel, inclusion size and densities increased with increasing the oxygen content, inclusion size decreased and their densities increased with increasing the cooling rate.A Confocal Scanning Laser Microscope (CSLM) was used to study the differences in solid state micro-structural evolution between the Ti-killed and theAl-killed samples. The growth of austenite grains were studied under isothermal conditions and it was found that both grain-boundary mobility and final grain size were lower in the Ti-killed sample than for the others. With regards to austenite decomposition, during continuous cooling from a comparable austenite grain structure, the resulting austenite decomposition structure was finer for the Ti-killed sample due to a higher Widmanstatten lath density due to precipitation at. The inclusion size was found to have a significant effect on both austenite grain size and austenite decomposition structure. Different orientations of ferrite precipitates originating at inclusions were observed in the Ti-killed samples. The highest lath concentration was obtained for the sample that had the smallest average inclusion size rather than the sample with highest density of sub micro-meter inclusions.

Micro-structure Refinement in Low Carbon High Manganese Steels through Ti-deoxidation—Inclusion Precipitation and Solidification Structure

The substitution of Al by Ti as a de-oxidizing agent in a carbon (0.07 wt%) and Mn (0.9 wt%) containing steel was studied for two purposes. The first one was to establish whether inclusion precipitation during solidification (secondary de-oxidation) can be promoted. The second purpose was to investigate the influence of secondary inclusions on the subsequent evolution of the steel solidification-structure, varying initial oxygen and titanium contents along with cooling rate during solidification.In the Ti-killed steel samples, the oxide inclusions were identified as MnO–TiO2 (0.5–5 μm) and MnS (1–3 μm) in the samples with the higher initial oxygen contents (Total Oxygen (T.O)=50–80 ppm) while Ti–Al–(Mg)–O (0.3–1 μm) in the samples with the lower oxygen contents (T.O=7–10 ppm). Comparing with thermodynamic calculations, the latter inclusions are considered to be the result of solely secondary de-oxidation precipitated in the inter-dendrite regions. For the high initial oxygen content, the inclusions were found as a result of both primary and secondary de-oxidation. The influence of cooling rate during solidification was investigated by controlling the cooling rate between 3–10 K/s by using different molds in a vacuum induction furnace. In addition, cooling rates were controlled at 1.1, 14 and 84 K/s by re-melting the samples in a gold-image furnace attached to a Confocal Scanning Laser Microscope (CSLM). An increase in the cooling rate resulted in an increase in the inclusion density in the Ti-killed samples while such an effect was not observed in the Al-killed sample. The secondary particle sizes for the Ti-killed sample predicted by a solute segregation model during solidification agreed well with the observed average particle sizes.In the Ti-killed samples, the solidification structure was finer with increasing density of inclusions below 1 μm, whereas such an effect was not observed in the Al-killed samples.

Interface Migration Behavior of the δ→γ Interface in Low Carbon High Manganese Steel Samples De-oxidized with Ti or Al

The effect of inclusions, generated during de-oxidation and solidification, of low carbon (0.07wt%) and high manganese (0.9wt%) steels, on the rates of migrations of the boundaries between delta-ferrite/gamma-austenite interfaces, during austenite formation was investigated. The presence of two types of de-oxidation products were investigated, namely Al 2 O 3 (1-3μm) in Al-killed steel samples, and Ti-AI-(Mg)-O (0.3-1 μm) in Ti-killed steel samples. The samples were prepared in a vacuum-induction furnace and a Confocal Scanning Laser Microscope was used to image in real time the interface movement on the surface of the samples. Austenite was found to precipitate at the triple-points of the delta-ferrite grain boundaries during cooling from 1 500 to 1 460 and 1 450°C and the growth appeared to be diffusion controlled. The migration rates of delta/gamma interfacial boundaries were higher in the Al-killed steel samples than in the Ti-killed steel samples and this is attributed to the finer oxide particle population in the latter. When the samples were cooled to 1 440°C and below sword-like precipitation was observed in all samples that grew at a higher rate than what was observed at higher temperatures and the growth appeared to have linear time dependence, and thus the process appears to not be governed by long range diffusion.

Effect of Ti De-oxidation on Solidification and Post-solidification Microstructure in Low Carbon High Manganese Steel

This paper investigates the effect of de-oxidation inclusions on micro-structure in low-carbon steels. Low carbon (0.07 wt%), high Mn (0.9 wt%) steel in a Al2O3 or MgO crucible was deoxidized by ad ...

Microstructures and Mechanical Properties of Fe-Mn-(Al, Si) TRIP/TWIP Steels

Abstract The mechanical properties and microstructure of two low carbon high manganese steels with 23.8% (No. 1) and 33% (No. 2) (mass percent) of manganese were investigated. The results showed that No. 1 steel possesses high strength and high plasticity, and No. 2 steel has a relatively high strength and extraordinary plasticity. The No. 1 steel exhibits both TRIP (transformation induced plasticity) and TWIP (twin induced plasticity) effects during the deformation; while only TWIP effect appeared under the same deformation condition for No. 2 steel. The comparison between the microstructures and mechanical properties of two steels was made, and the strengthening mechanisms were also analyzed.