Structure and properties of Fe−Cr−Mn steels after quenching with preheating in the intercritical temperature interval

Conclusions The quenching of high-alloy chromium-manganese steels, which includes preheating in the intercritical (+) temperature interval and subsequent short-term austenitizing, the latter eliminating homogenization of the -solid solution, increases the dispersity of the martensite and stabilizes the austenite.In this case, the strength and plastic properties of the steels are improved as compared with normal quenching.Mariupol' Metallurgical Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 45–47, June, 1990.     

Effect of NiAl phase on the mechanical properties of Cr−Mn−Ni steels

Metal Science and Heat Treatment -     

Effect of thermal treatment and ball milling on microstructure and phase transformation of Ni−Mn−Ga−Nb alloys

To clarify phase transformation evolution of Nb-doped Ni−Mn−Ga bulk alloys after aging and ball milling, the microstructure and phase transformation of the aged and ball-milled dual-phase Nb-doped Ni−Mn−Ga alloys were investigated by SEM, EDS, XRD, DSC and susceptibility measurements. The as-cast alloys were mainly composed of the second phase with layer-shape and presented a reduced martensitic transformation with increasing the second phase content. The second phase transformed from layer-shape to dense bar-shape and the martensitic transformation was enhanced after being quenched at 1173 K. After aging at 673 and 873 K, the 3% Nb alloy with less second phase exhibited a single-step phase transformation, whereas the 6% Nb and 9% Nb alloys with more second phase exhibited a two-step martensitic transformation and Curie transition. The martensitic transformation and Curie transition of the as-milled dual-phase particles disappeared and were retrieved after annealing at 1073 K due to the recovery of high ordered structure of the matrix.     

Effect of cooling rate and Fe/Mn weight ratio on volume fractions of α-AlFeSi and β-AlFeSi phases in Al−7.3Si−3.5Cu alloy

The crystallization behavior of iron intermetallic compounds in Al?7.3Si?3.5Cu alloy was investigated using thermal analysis, metallography, and a thermodynamic simulation performed with the Scheil module of ThermoCalc^®. We observed that β-AlFeSi disappeared when both high (>3.5°C/s) and low cooling rates (<0.1°C/s) were used. The elimination of β-AlFeSi at low cooling rates may be attributable to a decrease in the magnitude of microsegregation associated with low cooling rates. The disappearance of β-AlFeSi at high cooling rates may be related to growth difficulties when this phase precipitates during solidification of eutectic Al?Si: β-AlFeSi precipitation approaches the solidification onset of eutectic Al?Si when the cooling rate is increased. Moreover, the cooling rate at which the β-AlFeSi phase is suppressed should depend on the chemical composition of the alloy. According to thermodynamic simulations, the alloy composition determines the precipitation onset temperature of both β-AlFeSi (T _β) and eutectic Al?Si (T _eut). The cooling rate at which the β-AlFeSi phase disappears may be even higher as the difference betweenT _β andT _eut increases.     

Growth of austenite from as-quenched martensite during intercritical annealing in an Fe–0.1C–3Mn–1.5Si alloy

The growth of austenite from as-quenched martensite during intercritical annealing was studied in a quaternary Fe–0.1C–3Mn–1.5Si alloy. Fine austenite grains either grew from interlath-retained austenite films or were newly nucleated at lath and martensite packet boundaries. Both types grew to a size comparable to the width of the martensite lath. It was found both metallographically and by dilatometry that the austenite grew to an amount in excess of the volume fraction at final equilibrium. Simulation by DICTRA, which assumed local equilibrium at the α/γ boundary, confirmed that the development of austenite is composed of three stages: initial negligible-partitioning growth controlled by rapid carbon diffusion in ferrite, which is gradually replaced by carbon diffusion in austenite; intermediate slow growth, controlled by diffusion of Mn and/or Si in ferrite; and a final stage controlled by diffusion of substitutional elements in austenite for final equilibration, which may result in the shrinkage of austenite. The formation of austenite in excess of the equilibrium amount is considered to occur due to very slow substitutional diffusion in the growing austenite compared to the boundary migration.     

Effect of elevated-temperature annealing on microstructureand properties of Cu−0.15Zr alloy

Cu−0.15Zr (wt.%) alloy with uniform and fine microstructure was fabricated by rapid solidification followed by hot forging. Evolution of microstructure, mechanical properties and electrical conductivity of the alloy during elevated-temperature annealing were investigated. The alloy exhibits good thermal stability, and its strength decreases slightly even after annealing at 700 °C for 2 h. The nano-sized Cu₅Zr precipitates show significant pinning effect on dislocation moving, which is the main reason for the high strength of the alloy. Additionally, the large-size Cu₅Zr precipitates play a major role in retarding grain growth by pinning the grain boundaries during annealing. After annealing at 700 °C for 2 h, the electrical conductivity of samples reaches the peak value of 88% (IACS), which is attributed to the decrease of vacancy defects, dislocations, grain boundaries and Zr solutes.     

Effect of microalloying on the structure and properties of alloys in the Al−Si−Cu system

Conclusions  

Effect of the magnetic state of ferrite on transformations in Fe−C alloys

Conclusions Retardation of the austenite transformation in the interval end of the pearlite—austenite transformation to start of the ferrite—austenite transformation in low-carbon steels, which coincides with the magnetic transformation in ferrite, is connected with the fact that the latter inhibits diffusional transport of the interstitial atoms.Alma-Ata Institute of Railroad Transportation Engineers. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 11–12, February, 1990.     

Effect of aging and ball milling on the phase transformation of Ni50Mn25Ga17Cu8−xZrx alloys

This study investigated phase transformation of Ni₅₀Mn₂₅Ga₁₇Cu_8-xZr_x (x = 0, 4, 8) alloys after aging and ball milling. For the Cu₄Zr₄ and Zr₈ dual phase alloys, aging has enhanced magnetic susceptibility and magnetic exchange of the matrix, resulting in an increase of the Curie temperature of austenitic matrix. The decrease of martensitic transformation temperatures for the Cu₄Zr₄ alloy and the increase of martensitic transformation temperatures for the Zr₈ alloy after aging should be related to the dissolution and precipitation of the second phase in the matrix, respectively. Ball milling is effective to smash the Cu₄Zr₄ and Zr₈ alloys to fine particles, but cannot fracture the Cu₈ alloy to particles, indicating an inherent high ductility and strength of the Cu₈ alloy. Therefore, the macroscopic brittleness of the polycrystalline Cu₈ alloy was mainly caused by the weak grain boundaries. For the Cu₄Zr₄ and Zr₈ particles, the martensitic transformation and Curie transition of austenitic matrix disappeared and the Curie transition of second phase remained after ball milling. After post-annealing at 800 °C, the Curie transition of austenite was recovered due to the restoration of atomic order, but the martensitic transformation cannot be retrieved which might be caused by the grain refinement of the austenitic matrix after ball milling.     

Effects of carbon addition and aging on the shape memory effect of Fe–Mn–Si–Cr–Ni alloys

The effects of carbon content and aging treatment on the microstructures and shape recovery ratio of Fe–Mn–Si–Cr–Ni alloys were studied. It was found that the carbon content possessed significant effects on the shape recovery ratio of Fe–Mn–Si–Cr–Ni alloys. The shape memory effect of alloys containing different carbon amount could be improved through aging.     

Effect of Mn and MnS on corrosion properties of domestic pipeline steels and welds

Base metals of domestic pipeline steels were used to study the effect of Mn on corrosion properties of SSCC( Sulfide Stress Corrosion Cracking), and welds were carried out to study the effect of MnS on corrosion properties of HIC ( Hydrogen Induced Cracking) both in solutions with wet hydrogen sulfide ( H2 S ). They were respectively conducted by referring to the standards of SSCC and HIC. Testing results revealed that with the increase of content Mn, the resistance of SSCC will be decreased, from the point of metallurgic view, and it is Mn element not C element to lead to the testing results of SSCC. Meanwhile, even under the condition without inclusions MnS, HIC in welds still occurred. That is to say, MnS is not necessary for HIC, the presence of local banded structures in which Mn and P are inclined to aggregate cause to the phenomena of HIC.     

Effects of Mg content on microstructure and mechanical properties of low Zn-containing Al−xMg−3Zn−1Cu cast alloys

Effects of Mg content on the microstructure and mechanical properties of low Zn-containing Al?xMg? 3Zn?1Cu cast alloys (x=3?5, wt.%) were investigated. As Mg content increased in the as-cast alloys, the grains were refined due to enhanced growth restriction, and the formation of η-Mg(AlZnCu)₂ and S-Al₂CuMg phases was inhibited while the formation of T-Mg₃₂(AlZnCu)₄₉ phase was promoted when Mg content exceeded 4 wt.%. The increase of Mg content encumbered the solution kinetics by increasing the size of eutectic phase but accelerated and enhanced the age-hardening through expediting precipitation kinetics and elevating the number density of the precipitates. As Mg content increased, the yield strength and tensile strength of the as-cast, solution-treated and peak-aged alloys were severally improved, while the elongation of the alloys decreased. The tensile strength and elongation of the peak-aged Al?5Mg?3Zn?1Cu alloy exceed 500 MPa and 5%, respectively. Precipitation strengthening implemented by T′ precipitates is the predominant strengthening mechanism in the peak-aged alloys and is enhanced by increasing Mg content.     

Relation between phase transformations and mechanical properties of alloys in the Ti−Al−W−Zr system

Conclusions  

Study on the serialization and applications of low carbon ductile iron

1 Introduction Ductile cast iron can be got after the molten iron in either eutectic or hypereutectic compositions modified by RE-Mg alloy or treated by enough inoculation and heat treatment, since the birth of ductile cast iron. During the development of ordinary ductile cast iron, the content of carbon is never lower than 2.0%, the low carbon ductile iron that is not treated by heat treatment and mod- ified by the inoculation alloy mainly composed of anti- spherical surface active elements …     

Effect of thermal exposure on microstructure and mechanical properties of Al−Si−Cu−Ni−Mg alloy produced by different casting technologies

The effect of thermal exposure at 350 °C for 200 h on microstructure and mechanical properties was investigated for Al−Si−Cu−Ni−Mg alloy, which was produced by permanent mold casting (PMC) and high pressure die casting (HPDC). The SEM and IPP software were used to characterize the morphology of Si phase in the studied alloys. The results show that the thermal exposure provokes spheroidization and coarsening of eutectic Si particles. The ultimate tensile strength of the HPDC alloy after thermal exposure is higher than that of the PMC alloy at room temperature. However, the TEPMC and TEHPDC alloys have similar tensile strength around 67 MPa at 350 °C. Due to the coarsening of eutectic Si, the TEPMC alloy exhibits better creep resistance than the TEHPDC alloy under studied creep conditions. Therefore, the alloys with small size of eutectic Si are not suitably used at 350 °C.     

Influence of carbon content on the microstructure,martensitic transformation and mechanical properties in austenite/ε-martensite dual-phase Fe–Mn–C steels

We report on the effects of carbon content on the martensitic transformation and its contribution to the work-hardening behavior of Fe–Mn–C steels during tensile deformation based on analysis by X-ray diffraction, electron backscatter diffraction and transmission electron microscopy. Austenite/ε-martensite dual-phase Fe–17Mn–C (wt.%) steels containing different carbon contents (0.01, 0.10, 0.20 wt.%) were investigated before, during and after tensile deformation. Before deformation, the transformation of austenite to thermally induced ε-martensite on cooling was suppressed as the carbon content increases. To precisely monitor microstructural changes during deformation, stepwise loading experiments were carried out in combination with electron backscatter diffraction analysis. This approach revealed that with increasing carbon content, the kinetics of transformation of γ phase to deformation stimulated ε-martensite became faster, while that of ε-martensite to α’-martensite was sluggish. We attribute this controversial effect to an increased γ grain size by the microstructural refinement of thermally induced ε-martensite and the reduction of solid solution strengthening effects by the redistribution of solute carbon. In addition, the dependence of deformation-induced ε-martensite on the loading direction differed from that of α’-martensite, and the evolution of α’ morphology was controlled by achieving appropriate levels of strain during stepwise loading. Based on the observations at the surface and inside the bulk after deformation, insights into various deformation-driven displacive phenomena, such as the formation of α’-martensite at the nonintersecting parts of two ε_initial bands, the presence of nanotwinned bundles inside austenite, cementite precipitation inside α’-martensite, and the origin of the serrated flow in strain–stress curves, were obtained. Therefore, the present study is able assist in identifying whether the deformation-induced martensitic transformation varied as a function of carbon content and the resulting fracture behavior, thereby enabling us to understand the work-hardening behavior of these steels.     

Effects of Fe content on microstructure and properties of Cu–Fe alloy

Cu–Fe alloys with different Fe contents were prepared by vacuum hot pressing. After hot rolling and aging treatment, the effects of Fe content on microstructure, mechanical properties and electrical conductivity of Cu–Fe alloys were studied. The results show that, when w(Fe)<60%, the dynamic recrystallization extent of both Cu phase and Fe phase increases. When w(Fe)≥60%, Cu phase is uniformly distributed into the Fe phase and the deformation of alloy is more uniform. With the increase of the Fe content, the tensile strength of Cu–5wt.%Fe alloy increases from 305 MPa to 736 MPa of Cu–70wt.%Fe alloy, the elongation decreases from 23% to 17% and the electrical conductivity decreases from 31%IACS to 19%IACS. These results provide a guidance for the composition and processing design of Cu–Fe alloys.     

Effects of titanium addition on structural,mechanical, tribological,and corrosion properties of Al−25Zn−3Cu and Al−25Zn−3Cu−3Si alloys

To investigate the effect of grain refinement on the material properties of recently developed Al−25Zn−3Cu based alloys, Al−25Zn−3Cu, Al−25Zn−3Cu−0.01Ti, Al−25Zn−3Cu−3Si and Al−25Zn−3Cu−3Si−0.01Ti alloys were produced by permanent mold casting method. Microstructures of the alloys were examined by SEM. Hardness and mechanical properties of the alloys were determined by Brinell method and tensile tests, respectively. Tribological characteristics of the alloys were investigated by a ball-on-disc type test machine. Corrosion properties of the alloys were examined by an electrochemical corrosion experimental setup. It was observed that microstructure of the ternary A1−25Zn−3Cu alloy consisted of α, α+η and θ (Al₂Cu) phases. It was also observed that the addition of 3 wt.% Si to A1−25Zn−3Cu alloy resulted in the formation of silicon particles in its microstructure. The addition of 0.01 wt.% Ti to the Al−25Zn−3Cu and Al−25Zn−3Cu−3Si alloys caused a decrement in grain size by approximately 20% and 39% and an increment in hardness from HRB 130 to 137 and from HRB 141 to 156, respectively. Yield strengths of these alloys increased from 278 to 297 MPa and from 320 to 336 MPa while their tensile strengths increased from 317 to 340 MPa and from 334 to 352 MPa. Wear resistance of the alloys increased, but corrosion resistance decreased with titanium addition.