Influence of Manganese and Nickel on the α´ Martensite Transformation Temperatures of High Alloyed Cr‐Mn‐Ni Steels

The martensite start temperature (M_s), the martensite austenite re‐transformation start temperature (A_s) and the re‐transformation finish temperature (A_f) of six high alloyed Cr‐Mn‐Ni steels with varying Ni and Mn contents in the wrought and as‐cast state were studied. The aim of this investigation is the development of the relationships between the M_s, A_s, A_f, T₀ temperatures and the chemical composition of a new type of Cr‐Mn‐Ni steels. The investigations show that the M_s, A_s and A_f temperatures decrease with increasing nickel and manganese contents. The A_f temperature depends on the amount of martensite. Regression equations for the transformation temperatures are given. The experimental results are based on dilatometer tests and microstructure investigations.     

Thermodynamics of the Mn-P system

The free energy of mixing in the Mn-P melts in the composition range ofX _p = 0.0 to 0.333 was estimated by coupling the phase boundary information with reliable ΔG° formation for the Mn2P phase. This information was used to obtain the dilute solution properties of P in Mn. P_(l,pure) = P_{(l,Henrian, Mn)} ΔG ^°(Joules) = -203,611.39 + 41.003T The free energy is shown to be more negative than in the Fe system, reflecting a stronger interaction between Mn and P atoms than between Fe and P atoms. Presenting the activity coefficient of P with the expression used by Lupis and Elliott, the first and second interaction coefficients are obtained as follows: ε _P ^P (Mn) = 10.538 + 9728.14/T ρ _P ^P (Mn) = 28.148 + 9101.83/T The Gibbs free energy of formation for Mn₃P was estimated in the temperature range of {dy1233} to {dy1378} K to be 3Mn _l + P_(l = Mn₃P_(s ΔG ^°(Joules) = -241,461.65 + 65.031T     

The evaluation of in-service materials degradation of low-alloy steels by the electrochemical method

The nondestructive evaluation procedure for detecting in-service materials degradation of low-alloy 2.25Cr-1Mo and CrMoV steels by the electrochemical method has been investigated. The results can be summarized as follows. (1) For 2.25Cr-1Mo steels, the peak current mainly caused by the selective dissolution of coarse carbides M₆C appears at ∼+100 mV during potentiodynamic polarization measurements in dilute sodium molybdate solution. This peak value of current density, ΔI_p, can be chosen as a reflective parameter of an amount of coarse carbides M₆C and shows excellent correlations both with shifts in fracture appearance transition temperature (FATT) caused by carbide coarsening and with hardness change. Actual operational temperature can be estimated from operational period, since the Larson-Miller time-temperature parameter (LMP) value of materials has a unique relationship with ΔI_p values. (2) For CrMoV steels, the evaluation of temper embrittlement of CrMoV cast steel by a novel electrochemical technique is described. Intergranular corrosion (IGC) occurs only on temper-embrittled samples during anodic polarization process in calcium nitrate solution. The characteristic changes in polarization curves attributed to IGC have an excellent correlation with shifts in FATT caused by temper embrittlement.     

Effects of alloying elements upon austenite decomposition in Low-C steels

The kinetics of austenite decomposition were studied in high-purity Fe-0.1C-0.4Mn-0.3Si-X (concentrations in weight percent;X represents 3Ni, 1Cr, or 0.5Mo) steels at temperatures between 500 °C and 675 °C. The transformation stasis phenomenon was found in the Fe-C-Mn-Si-Mo and Fe-C-Mn-Si-Ni alloys isothermally transformed at 650 °C and 675 °C but not in the Fe-C-Mn-Si and Fe-C-Mn-Si-Cr alloys at any of the temperatures investigated. The occurrence of transformation stasis was explained by synergistic interactions among alloying elements. The paraequilibrium model was applied to calculate the metastable fraction of ferrite in each alloy. This fraction was shown to coincide with cessation of transformation in the Mo alloy transformed at 600 °C. Transformation stasis was found in both the Ni and the Mo alloys isothermally reacted at 650 °C and 675 °C. The interactions among Mn, Si, and Mo, as well as interactions among Mn, Si, and Ni, appear to decrease the threshold concentrations for transformation stasis in Fe-C-Mn-Si systems. Segregation of Mn and Mo to the α/yγ boundary, assisted by the presence of Si, was suggested to enhance the solute draglike effect (SDLE) and lead to transformation stasis. In the Ni alloy, a lower driving force for ferrite formation resulting from the Ni addition could be responsible for the occurrence of transformation stasis.     

Strain aging kinetics of vanadium or titanium strengthened high-strength low-alloy steels

The strain aging kinetics of two commercially available high-strength low-alloy (HSLA) steels were investigated. Strain aging was found to be caused by interstitial solutes and is thought to occur in two stages: Snoek rearrangement and “Cottrell atmosphere” formation. The latter phenomenon can be satisfactorily described by an Arrhenius relationship with an average activation energy of 34.5 kcal/mole. This high activation energy is believed to be the result of interactions between interstitial solutes and strain fields of the coherent precipitates which strengthen HSLA steels. Consequently, strain aging in HSLA steels is considerably slower than in plain carbon steel. A simple relationship was developed for predicting equivalent strain aging times in these steels. It was shown that the relationship: logt ₁/t ₂= 7500[1/T ₁ - 1/T ₂], whereT ₁ <T ₂ < 478 K can be used to predict the timet ₁ necessary at temperatureT ₁ for producing strain aging identical to that observed in a shorter time at a higher temperature.     

Thermodynamic equilibrium in the low-solute regions of Pu-group MIA metal binary systems

The low-temperature fcc(δ) → monoclinic(α) transformation in Pu-Al and Pu-Ga alloys has been shown to proceedvia a diffusionless, martensitic mechanism. Typically, δ/δ+ α “equilibrium” phase boundaries reported in the literature are based on measurements of the M_s or A_s (forward and reverse) martensite transformation temperatures, which are functions of grain size, strengthening mechanisms, or nucleating defect structures and, hence, do not represent a state of thermodynamic equilibrium.Via a thermodynamic model, in which a regular solution parameter was fit to experimental equilibrium temperatures (T₀) and pressures (P₀) and available solution calorimetry data on two PuAl alloys to define the Gibbs free energy for the δ and α phases, equilibrium phase boundaries were determined using free-energy minimization techniques over the compositional and temperature ranges 0 ≤ X≤ 0.30 and 300 K≤T ≤ 700 K, respectively, for both Pu-Al and Pu-Ga systems. A eutectoid decomposition of δ→ α + Pu₃M is predicted at 335 ± 50 K for the Pu-Al system, while for Pu-Ga the eutectoid occurs at 354 ± 50 K. These findings are consistent with other group III A Pu-M systems (In and TI) which also exhibit the invariant reaction.     

Effect of Ternary Alloying Elements Addition on the Order-Disorder Transformation Temperatures of B2-Type Ordered Fe-Al-X Intermetallics

The effect of alloying element additions on B2↔A2 order-disorder phase transformation temperatures of B2-type ordered Fe_0.5(Al_1−n X _n )_0.5 intermetallics (X = Cr, Ni, Mo, Ta, Mn, Ti, and W) that readily form single-phase solid solution for X = 1 at. pct were investigated experimentally. It was shown that the type of the ternary substitutional alloying elements have a profound effect on the variation of order-disorder transition temperature of Fe_0.5(Al_1−n X _n )_0.5 alloys. Based on the magnitude of partial ordering energies of the Al-X and Fe-X atomic pairs, predicted normalized transition temperatures, ∆T/T _o , were verified experimentally. Besides the normalized transition temperature, the relative partial ordering energy (RPOE) parameter, β, was also defined to estimate the extent of variation in B2↔A2 order-disorder phase transformation temperatures upon ternary alloying additions. The RPOE parameter, β, takes into account both the effects of magnitude of partial ordering energies of Al-X and Fe-X atomic pairs and also the lattice site occupation preferences of X element atoms over B2-type ordered Fe-Al sublattices. The alloying elements, which are preferentially distributed Fe sublattice sites, β > 0, and owing to β >> 1, are more effective in increasing order-disorder transformation temperature in Fe-Al (B2) intermetallics. On the contrary, alloying elements having β < 1 tend to decrease the transition temperature slightly relative to the binary FeAl intermetallic. The experimentally determined B2↔A2 order-disorder transition temperatures are in good qualitative or semiquantitative agreement with theoretical predictions for all X ternary alloying elements. Accordingly, the present experimental results confirm the validity of the theoretical model and calculations proposed in our previous study on the B2↔A2 order-disorder transition temperatures of single-phase Fe_0.5(Al_1−n X _n )_0.5 intermetallics.     

Continuous cooling transformation temperatures determined by compression tests in low carbon bainitic grades

The transformation behaviors of six steels containing microalloying additions of B, Nb, and Mo were investigated under continuous cooling conditions. Continuous cooling compression (CCC) tests were employed to study the effects of chemical composition (mainly, Nb, Mo, and B) and deformation parameters (reheat temperature, prestrain, and holding time) on the transformation temperatures (A _r3 and B _s). It was found that for the Mo-Nb-B, Mo-B, and B steels, the transformation temperatures are relatively stable, and vary in a range of about 20 °C when the reheat temperature is changed from 900 °C to 1200 °C. Both the stress-temperature curves and the associated microstructures show that transformation in the Mo-Nb-B steel is basically of the γ-to-B type; i.e., the resulting microstructure is low carbon bainite. By contrast, for the Nb-B steels, the transformation temperatures vary significantly when the reheat temperature is changed. The concentration of boron in solution strongly affects the transformation behavior of this type of steel. In the Nb-48B steel, the latter is of the γ-to-B type, while in grades with either higher (Nb-64B) or lower (Nb-15B) boron concentrations, it is mainly of the γ-to-α type. Large Fe₂₃(C,B)₆ particles, which were found at low reheat temperatures and long holding times, are considered to be responsible for raising the transformation temperatures.     

Continuous cooling transformation temperatures determined by compression tests in low carbon bainitic grades

The transformation behaviors of six steels containing microalloying additions of B, Nb, and Mo were investigated under continuous cooling conditions. Continuous cooling compression (CCC) tests were employed to study the effects of chemical composition (mainly, Nb, Mo, and B) and deformation parameters (reheat temperature, prestrain, and holding time) on the transformation temperatures (A _r3 and B _s). It was found that for the Mo−Nb−B, Mo−B, and B steels, the transformation temperatures are relatively stable, and vary in a range of about 20°C when the reheat temperature is changed from 900°C to 1200°C. Both the stress-temperature curves and the associated microstructures show that transformation in the Mo−Nb−B steel is basically of the γ-to-B type; i.e., the resulting microstructure is low carbon bainite. By contrast, for the Nb−B steels, the transformation temperatures vary significantly when the reheat temperature is changed. The concentration of boron in solution strongly affects the transformation behavior of this type of steel. In the Nb−48B steel, the latter is of the γ-to-B type, while in grades with either higher (Nb−64B) or lower (Nb−15B) boron concentrations, it is mainly of the γ-to-α type. Large Fe₂₃(C,B)₆ particles, which were found at low reheat temperatures and long holding times, are considered to be responsible for raising the transformation temperatures. T.M. MACCAGNO, formerly with the Department of Metallurgical Engineering, McGill University     

Evaluation of hydrogen-trap binding enthalpy l

In order to evaluate hydrogen-trap binding enthalpy H_s from the elevated temperature hydrogen evolution peaksT _P, theH _B-T _P relation was analytically deduced in low hydrogen concentration approximation. The plot of H _B againstT _P revealed that in aT _P regionT _P ≧T _O + ΔT whereT _O is the initial temperature in heating and ΔT ≈ 80 K, H _B + 0.11 eV is substantially proportional tok _B T _P ,i.e., H _B + 0.11 eV = γ(N, ώ _O )k_B T _P for fixed geometrical and heating conditions, and the proportionality factor γ(N, ώ _O ) is influenced by hydrogen trap densityN and parameter of release ώ _O defined in the text. Thus for exact and precise determination of H _B parameter of release ώ _O as well as hydrogen trap densityN generally play an important part. In the present theory it is assumed that a specimen contais two kinds of deep traps (irreversible in the diffusion process at ambient temperature) and does not contain shallow traps (reversible at ambient temperature). The theory was applied to steels which vary in sulfur contents. The steels produced hydrogen release peaks at slightly different temperatures ranging from 588 K to 613 K, but the hydrogen-trap binding enthalpies H _B for these steels are shown to be substantially the same:H _P = 0.86 ± 0.005 eV.     

Effect of TiN particles and microstructure on fracture toughness in simulated heat-affected zones of a structural steel

Thermally stable TiN particles can effectively pin austenite grain boundaries in weld heat-affected zones (HAZs), thereby improving toughness, but can also act as cleavage initiators. The HAZs simulated in a GLEEBLE 1500 TCS using two peak temperatures (T _p ) and three cooling times (Δ∼ _8/5) have determined the effects of matrix microstructure and TiN particle distribution on the fracture toughness (crack tip opening displacement (CTOD)) of three steels microalloyed with 0.006, 0.045, and 0.1 wt pct Ti. Coarse TiN (0.5 to 6 μm) particles are identified in steels with the two higher levels of Ti, and fine Ti(C, N) (35 to 500 nm) particles were present in all three steels. Large prior austenite grain size caused by higher T _p decreased fracture toughness considerably in steels containing coarse TiN particles but had little effect in their absence. Fracture toughness was largely independent of matrix microstructure in the presence of coarse particles. Cleavage fracture initiation was observed to occur at coarse TiN particles in the samples with a large prior austenite grain size. Alloy thermodynamics have been used to rationalize the influence of Ti content on TiN formation and its size.     

Influence of alloying elements on the strain rate and temperature dependence of the flow stress of steels

After a short introduction to the theoretical background of thermally activated glide of dislocations, a constitutive model is presented, which describes the temperature and strain-rate dependence of the flow stress. The properties of this constitutive equation were estimated for several plain carbon steels in normalized conditions, for quenched and tempered low-alloy steels, as well as for some high-strength low-alloy (HSLA) steels based on the temperature dependence and strain-rate sensitivity of the flow stress at temperatures 81 K≤T≤398 K and strain rates 5 · 10⁻⁵ s⁻¹≤ε≤1 · 10⁻² s⁻¹. The constitutive equation enables the extrapolation of flow-stress data to higher strain rates (ε≲10⁺⁴ s⁻¹), which are in good agreement with the results obtained from high strain-rate deformation tests. The influence of solute-alloying elements on the thermal stress, the activation enthalpy, and the constitutive parameters will be discussed. This article is based on a presentation given in the symposium entitled “Dynamic Behavior of Materials-Part II,” held during the 1998 Fall TMS/ASM Meeting and Materials Week, October 11–15, 1998, in Rosemont, Illinois, under the auspices of the TMS Mechanical Metallurgy and the ASM Flow and Fracture Committees.     

Phase chemistry and precipitation reactions in maraging steels: Part IV. Discussion and conclusions

This article summarizes our studies of phase chemistry and precipitation reactions in a variety of maraging steels. The roles of different phases and alloying elements are investigated by comparing the behavior of different steels. The phases considered are Ni₃Ti, Fe₇Mo₆ μ phase, Fe₂Mo Laves phase, ω phase, Ti₆Si₇Ni₁₆ G phase, “Z phase,” austenite, and α matrix. The alloying elements discussed are Ti, AI, Mo, Si, Mn, Ni, Cr, and Co. By comparing the aging behavior of both commercial steels and model alloys, a major role of Co is confirmed to be the lowering of the matrix solubility of Mo. Of the two main hardening elements in maraging steels (namely, Ti and Mo), Ti is much more active than Mo in the very early stage of precipitation. The main Mo-rich precipitate found in this work was Fe₇Mo₆μ phase instead of Laves phase. The precipitation of Mo is modified by the presence of Ti. ω phase appears only in Ti-free alloys, especially when aged at a low temperature. The quantity of Ni-containing precipitates and the presence of Cr in the steels change the austenite reversion behavior. Other phases, such as G phase and “Z phase,” contribute to age hardening in different types of maraging alloys. Formerly Graduate Student with the Department of Materials, Oxford University.     

Influence of strain-induced martensitic transformations on fatigue crack growth rates in stainless steels

The fatigue crack growth rates (FCGR) of two unstable austenitic stainless steels (Fe-16 Cr-13Ni) and (Fe-18Cr-6.5Ni-0.19C) were determined in theM_s-M_d temperature range where a strain induced μ → α′ martensitic transformation occurs near the crack tip. These FCGR were compared to the rates measured in the stable austenitic phase of a Fe-31.5Ni and a Fe-34 Ni alloy and in the martensitic phase obtained by quenching the Fe-31.5 Ni alloy below M_s. In the Fe-31.5 Ni, the FCGR are an order of magnitude higher in the martensitic than in the austenitic structures for ΔK ≤ 40 ksi in. The FCGR of the stainless steels decrease markedly when the test temperature approachesM _s in theM _s - M_d range. The FCGR for the alloy Fe-18Cr-6.5 Ni-0.19 C in a warm-worked condition are consistently higher than for the same alloy in the annealed condition for ΔK ≤ 40 ksi √in.. The results are discussed in terms of the influence of phase structures, stacking fault energy and work hardening exponent on the FCGR.     

Effect of deformation parameters on the

The recrystallization behavior of three Nb-bearing high-strength low-alloy (HSLA) steels was investigated during multipass deformation under continuous cooling conditions. The niobium concentrations of these steels varied from 0.05 to 0.09 wt pct. The specimens were tested on a computerized torsion machine using a simulation schedule of 17 passes. Deformation tem-peratures of 1180 °C to 700 °C were employed, together with pass strains of 0.1 to 0.7, strain rates of 0.2 to 10 s^-1, and interpass times of 5 to 200 seconds. By means of mean flow stressvs 1000/T diagrams, the effect of the deformation conditions on the no-recrystallization tem-perature (T _nr ), the temperature at which recrystallization is no longer complete, was determined. It decreases with increasing strain and also decreases slightly with increasing strain rate. There is aT _r minimum at times of about 12∼15 seconds, and both increases and decreases from this value raise this characteristic temperature. When the interpass times are short, solute atoms control the rate of recrystallization, the extent of which decreases as the time is decreased. When the interpass times are long, precipitation takes place and retards recrystallization, so that the extent of softening decreases. Formerly Research Associate, McGill University, Department of Metallurgical Engineering.     

Influence of alloying elements on the strain rate and temperature dependence of the flow stress of steels

After a short introduction to the theoretical background of thermally activated glide of dislocations, a constitutive model is presented, which describes the temperature and strain-rate dependence of the flow stress. The properties of this constitutive equation were estimated for several plain carbon steels in normalized conditions, for quenched and tempered low-alloy steels, as well as for some high-strength low-alloy (HSLA) steels based on the temperature dependence and strain-rate sensitivity of the flow stress at temperatures 81 K≤T≤398 K and strain rates 5·10⁻⁵ s⁻¹≤ε≤1·10⁻²s⁻¹. The constitutive equation enables the extrapolation of flow-stress data to higher strain rates (ε<~10 ⁺⁴s⁻¹), which are in good agreement with the results obtained from high strain-rate deformation tests. The influence of solute-alloying elements on the thermal stress, the activation enthalpy, and the constitutive parameters will be discussed. This article is based on a presentation given in the symposium entitled ‘Dynamic Behavior of Materials-Part II,” held during the 1998 Fall TMS/ASM ASM Meeting and Materials Week, October 11–15, 1998, in Rosemont, Illinois, under the auspices of the TMS Mechanical Metallurgy and the ASM Flow and Fracture Committees.     

Bragg–Williams Model of CsCl-Type Ordering of the FeCo System in Strong Magnetic Fields

A modified Bragg–Williams (B–W) model of α and α′ FeCo is extended to estimate the effect of strong magnetic fields on the critical ordering temperature (T _ORDER) taking into account long-range chemical and magnetic ordering. The model discussed here is generalized from our previous work in which only the larger average exchange per atom in the chemically ordered state was taken into account. A positive shift of critical temperatures for the higher order α→α′ order-disorder phase transformation has been predicted in the presence of a strong field. In this work, the experimentally observed dependence of the average magnetic moment of Fe atoms on the degree of chemical order has been accounted for explicitly. The estimated shift in the critical ordering temperature (ΔT _ORDER) is larger when the dependence of the Fe moment on the degree of chemical order is taken into account, particularly in the case of Fe-rich compositions (e.g., ΔT _ORDER ∼ 13 K vs ΔT _ORDER ∼ 10 K for H ∼ 50 T at equiatomic composition). For most compositions, however, the contribution to ΔT _ORDER associated with the larger average exchange per atom in the chemically ordered state accounts for the majority of the shift. The estimated effect remains quite small and is only expected to be experimentally observable in static fields larger than currently available in most laboratories (ΔT _ORDER is only predicted to be larger than ∼2 to 3 K for H > ∼10 T). This article is based on a presentation made in the symposium entitled “Phase Transformations in Magnetic Materials”, which occured during the TMS Annual Meeting, March 12–16, 2006, in San Antonio, Texas, under the auspices of the Joint TMS–MPMD and ASMI–MSCTS Phase Transformations Committee.     

Fatigue crack propagation in carburized high alloy bearing steels

Fatigue cracks were propagated through carburized cases in M-50NiL (0.1 C,4 Mo, 4 Cr, 1.3 V, 3.5 Ni) and CBS-1000M (0.1 C, 4.5 Mo, 1 Cr, 0.5 V, 3 Ni) steels at constant stress intensity ranges, ΔK, and at a constant cyclic peak load. Residual compressive stresses of the order of 140 MPa (20 Ksi) were developed in the M-50NiL cases, and in tests carried out at constant ΔK values it was observed that the fatigue crack propagation rates,da/dN, slowed significantly. In some tests, at constant peak loads, cracks were stopped in regions with high compressive stresses. The residual stresses in the cases in CBS-1000M steel were predominantly tensile, probably because of the presence of high retained austenite contents, andda/dN was accelerated in these cases. The effects of residual stress on the fatigue crack propagation rates are interpreted in terms of a pinched clothespin model in which the residual stresses introduce an internal stress intensity, K_i where K_i, = σ_id _i ^1/2 (σ_i = internal stress, d_i = characteristic distance associated with the internal stress distribution). The effective stress intensity becomes K_e = K_a + K_i where K_a is the applied stress intensity. Values of K_i were calculated as a function of distance from the surface using experimental measurements of σ_i and a value of d_i = 11 mm (0.43 inch). The resultant values of K_e were taken to be equivalent to effective ΔK values, andda/dN was determined at each point from experimental measurements of fatigue crack propagation obtained separately for the case and core materials. A reasonably good fit was obtained with data for crack growth at a constant ΔK and at a constant cyclic peak load. The carburized case depths were approximately 4 mm, and the possible effects associated with the propagation of short cracks were considered. The major effects were observed at crack lengths of about 2 mm, but the contributions of short crack phenomena were considered to be small in these experiments, since the two steels were at high strength levels, and short cracks would be expected to be of the order of 10 μm. Also, the two other steels behaved differently and in a way which followed the residual stress patterns. Both M-50NiL and CBS-1000M have a high fracture toughness, with K_lc = 50 MPa · m^1/2 (45 Ksi · in^1/2), and the carburized cases exhibit excellent resistance to rolling contact fatigue. Thus, M-50NiL, carburized, may be useful for bearings where high tensile hoop stresses are developed, since fatigue cracks are slowed in the case by the residual compressive stresses, and fracture is resisted by the relatively tough core.     

Thermodynamic properties of Ni-S melts between 700° and 1100°c

The vapor pressure of sulfur over Ni-S melts of various compositions was calculated from the equilibrium weight of the melt in gas streams of known H₂S-H₂ composition. The Gibbs-Duhem equation was used to calculate the activity of nickel and other thermodynamic properties. For the reaction: 3Ni(S) + S₂(g) ⇌ Ni₃S₂(l) the suggested free energy rslationship is: ΔG° = -57,910 + 15.89T (800° to 1100°C). The Calculations were extrapolated to predict that for the reaction: Ni(s) + 1/2S₂(g) ⇌ NiS(l), ΔG° = -26.730 + 10.5T (1000° to 1100°C)     

A Eutectoid Reaction for the Decomposition of Austenite into Pearlitic Lamellae of Ferrite and M<Subscript>23</Subscript>C<Subscript>6</Subscript> Carbide in a Mn-Al Steel

We discovered a eutectoid reaction in an Fe-13.4Mn-3.0Al-0.63C (wt pct) steel after solution heat treatment at 1373 K (1100 °C) and holding at temperatures below 923 K (650 °C). The steel is single austenite at temperatures from 1373 K to 923 K (1100 °C to 650 °C). A eutectoid reaction involves the replacement of the metastable austenite by a more stable mixture of ferrite and M₂₃C₆ phases at temperatures below 923 K (650 °C). The mixture of ferrite and M₂₃C₆ is in the form of pearlitic lamellae. The morphology of the lamellae of the product phases is similar to that of pearlite in steels. Thus, we found a new pearlite from the eutectoid reaction of the Mn-Al steel featuring γ  → α + M₂₃C₆. A Kurdjumov–Sachs (K-S) orientation relationship exists between the pearlitic ferrite (α) and M₂₃C₆ (C6) grains, i.e., (110)_α // (111)_C6 and [[`1] \overline{1} 11]<sub>α</sub> // [0[`1] \overline{1} 1]_C6. The upper temperature limit for the eutectoid reaction is between 923 K and 898 K (650 °C and 625 °C).