Effect of Niobium on Isothermal Transformation of Austenite to Ferrite in HSLA LowCarbon Steel

Using thermomechanical simulation experiment, the kinetics of the isothermal transformation of austenite to ferrite in two HSLA lowcarbon steels containing different amounts of niobium was investigated under the conditions of both deformation and undeformation. The results of optical microstructure observation and quantitative metallography analysis showed that the kinetics of the isothermal transformation of austenite to ferrite in lower niobium steel with and without deformation suggests a stage mechanism, wherein there exists a linear relationship between the logarithms of holding time and ferrite volume fraction according to Avrami equation, whereas the isothermal transformation of austenite to ferrite in high niobium steel proceeds via a two stage mechanism according to micrographs, wherein, the nucleation rate of ferrite in the initial stage of transformation is low, and in the second stage, the rate of transformation is high and the transformation of residual austenite to ferrite is rapidly complete. Using carbon extraction replica TEM, niobium carbide precipitation for different holding time was investigated and the results suggested that NbC precipitation and the presence of solute niobium would influence the transformation of austenite to ferrite. The mechanism of the effect of niobium on the isothermal transformation was discussed.     

Nucleation Behavior Analysis of Intragranular Acicu-lar Ferrite in a Ti-killed C-Mn Steel

By using a Gleeble 3500Dthermo-mechanical simulator,the nucleation behavior of intragranular acicular ferrites(IAF)was studied in a Ti-killed C-Mn steel.During continuous cooling transformation,the allotriomorphic ferrite(AF)and ferrite side plate(FSP)microstructures grew more rapidly with the temperature decreasing from800to 650℃,and the IAF microstructure was dominant within austenite grain with further cooling to 600℃.The diffusion bonding experiment and the effect of C,Mn and Si concentrations on the Ae3temperature by thermodynamic calculation confirm that Ti2O3itself absorbs neighboring Mn atoms to form Mn-depleted zone(MDZ),which promotes the nucleation of IAF microstructure effectively.High temperature holding tests indicate that the nucleation potential of IAF microstructure was lowered in the Ti-killed C-Mn steel when it was treated at high temperature(1 250℃)for a longer time,which is attributed to the saturated absorption degree of Mn atoms by titanium oxide.     

Model of Primary Austenite Dendrite Structure in Hypoeutectic Cast Iron

Ｉｔｗａｓｒｅｐｏｒｔｅｄ[1] ｔｈａｔｔｈｅｍｉｃｒｏ ｓｔｅｒｅｏｓｔｒｕｃｔｕｒｅｏｆｐｒｉｍａｒｙａｕｓｔｅｎｉｔｅｉｎｃａｓｔｉｒｏｎｃｏｎｓｉｓｔｓｏｆｐｒｉｍａｒｙｓｔｅｍｓａｎｄｓｅｃｏｎｄａｒｙａｒｍｓｔｈａｔ ｇｒｏｗａｃｃｏｒｄｉｎｇｔｏｄｅｎｄｒｉｔｅｃｒｙｓｔａｌｓｂｒａｎｃｈｒｕｌｅ ,ａｎｄｓｏｍｅｏｆｐｒｉｍａｒｙａｕｓｔｅｎｉｔｅｅｖｅｎｈａｖｅｔｈｉｒｄａｒｍｓ .ＭｉｙａｋｅＨｅｔａｌ[2 ]ｐｒｏｐｏｓｅｄａｃｏｎｃｅｐｔｏｆｒｅｇｉｏｎｍｏｄｅｌｂｙｓｔｕｄｙｉｎｇ…     

Effects of Austempering and Martempering Processes on Amount of Retained Austenite in Cr-Mo Steels （FMU-226） Used in Mill Liner

The presence of retained austenite gives rise to deterioration of the wear resistance and fracture strength of Cr-Mo steels in many cases. Thus, the effects of heat treatments including direct quenching, martempering, and austempering on the retained austenite existing in the microstructure of these steels were investigated. Specimens were austenized at 950 ℃ followed by direct quenching using compressed and still air. The specimens were also isothermally quenched in salt bath at 200 and 300 ℃ for 2, 8, 30, and 120 min. Microstructures of the specimens were studied using optical microscope (traditional black and white etching as well as color etching), scanning electron microscope (SEM), microhardness tester, and X-ray diffraction (XRD). The results showed that the lowest amount of retained austenite in the microstructure was obtained in the specimens quenched isothermally at 300 ℃ for 120 min.     

Effects of Cerium Addition on Inclusions and Solidification Structure of a Low-Nickel Si–Mn-Killed Stainless Steel

The effect of cerium on inclusions and solidification structure of a low-nickel Si–Mn-killed stainless steel is studied using laboratory experiments. When the cerium content in steel increased from 0 to 250 ppm, modification sequence of inclusions is Si–Mn(–Al)–O and MnS → Ce–Si–Mn–O–S → Ce(–Si)–O–S → CeS and CeC₂. The number density and area fraction of inclusion first decrease with the increase in the cerium content and then increase due to the formation of CeC₂ inclusions when the cerium content is bigger than 150 ppm, which is precipitated in solid steel during solidification. When the cerium content increases from 0 to 250 ppm, the fraction of equiaxed grain zones of steel ingot first increases and reaches a maximum value when the cerium content is 54 ppm; then the fraction of equiaxed grain zones decreases with the increase of the cerium content. 2D lattice misfit calculations are performed and it is found that there are no heterogeneous nucleation cores in the steel without cerium during solidification. For the steel with cerium, Ce_4.67Si₃O₁₃, Ce₂O₂S, and CeS inclusions act as heterogeneous nucleation cores, increasing the fraction of the equiaxed grain zone. Bigger effective heterogeneous nucleation cores number density leads to a larger fraction of the equiaxed grain zone.     

The Influence of Sintering Temperature and Content of High-Carbon Ferrochrome on the Structure and Properties of Iron–FKh800 Powder Composites

Powder Metallurgy and Metal Ceramics - The influence of sintering temperature and content of high-carbon ferrochrome on the phase composition, structure, and mechanical properties of chromium...     

Effects of Temperature and Alloying Elements on γ Phase Fraction of Grain-oriented Silicon Steel

The effects of temperature and alloying elements on γ phase fraction of grain-oriented silicon steel,which contained 2.97-3.42mass% Si and 0.028-0.058mass% C,were studied by microstructure observation and statistics.Furthermore,the quantitative relationships of temperature as well as C,Si,and Mn contents to γ phase fraction were obtained by numerical fitting.The experimental results show that γ phase fraction firstly increases with increasing temperature,reaches a maximum and then decreases in the temperature range of 900-1 250 ℃.The temperature corresponding to the maximum γ phase fraction is about 1 150-1 200℃.Meanwhile,the γ phase fractions in steels at the same temperature have some differences because of different contents of various alloying elements.The verification results show that the values of γ phase fractions to C,Si,and Mn contents at the specific temperatures,which were obtained by multiple linear regression method,agree well with the measured values.In addition,the values of γ phase fractions to C,Si,and Mn contents in the temperature range of 900-1 250℃,which were obtained by binomial regression method,agree with the measured values when the contents of Mn and soluble Al are not more than 0.320mass% and 0.034mass%,respectively.The obtained equations can carry out the approximate prediction of γ phase fractions of grain-oriented silicon steels during the hot rolling process.     

Effects of Rare Earth on Structure and Mechanical Properties of Clean BNbRE Steel

The effects of REinsteel include cleaning,mod-ifyinginclusions and alloying[1 ~4]. With the develop-ment of steel-making and continuous casting process-ing,the fluctuation range of the composition of steelwas mini mized ,the cleanliness of steel was i mpr…     

The Influence of Annealing Temperature on the Structure and Magnetic Properties of Nanocrystalline BiFeO3 Prepared by Sol–Gel Method

In this work, BiFeO₃ powders were synthesized by a sol–gel method. The influence of annealing temperature on the structure and magnetic properties of the samples has been discussed. X-ray diffraction studies showed that the purest phase was formed in the temperature range of 400 °C to 550 °C and the samples annealed at a temperature below 550 °C were of nanocrystalline character. Mössbauer spectroscopy and magnetization measurements were used as complementary methods to investigate the magnetic state of the samples. In particular, the appearance of weak ferromagnetic properties, significant growth of magnetization, and spin-glass-like behavior were observed along with the drop of average grain size. Mössbauer spectra were fitted by the model assuming cycloidal modulation of spins arrangement and properties of the spin cycloid were determined and analyzed. Most importantly, it was proved that the spin cycloid does not disappear even in the case of the samples with a particle size well below the cycloid modulation period λ = 62 nm. Furthermore, the cycloid becomes more anharmonic as the grain size decreases. The possible origination of weak ferromagnetism of the nanocrystalline samples has also been discussed.

     

Effects of γ-irradiation and Deformation Temperature on Tensile Properties of Pb-2 mass% Sb Alloy

Effects ofγ-irradiation and deformation temperature(T)on the tensile properties of Pb-2mass% Sb alloys were studied.The samples were annealed at 458 Kfor 2hin air,then water quenched after they wereγ-irradiated(the different doses were 0.5,1.0,1.5,and 2.0 MGy).The tensile properties were performed using stress-strain measurements at a constant strain rate(1.2×10~(-3) s~(-1))and at different T(303-393K).It was found that at constant dose,the fracture stress(σF)decreases while the fracture strain(εF)increases as Tincreases.At particular T,σFincreases whileεFdecreases with increasing dose.The strain-hardening exponent(n),which is the slope of the relation between ln(σ)and ln(ε)of the parabolic part of the stress-strain curve,was determined and its values increase as Tincreases and decrease as the dose increases.The value of the activation energy increases as the dose increases from 0.07 eV for un-irradiated sample to 0.1eV for the 2 MGy-irradiated sample.These values are in accordance with that needed for dislocation movement and ordering process.An interpretation of the results was given,based on the creation of point and line defects due toγ-irradiation,and that results in a distribution of beta phase(Sb-phase),leading to a difficulty in the movement of dislocations,so there is an increase in alloy hardness.     

Effects of Rare Earths and Al on Structure and Performance of High Chromium Cast Iron Containing Wolfram

High chromiumcast ironis ani mportant grade ofwear-resistant material.It exhibits high hardness,ex-cellent wear resistance,andlowdeflection onrupture.Moreover,combined properties of high chromiumcastiron are better than that of other white cast irons.Therefore,it has many applications[1~4]in concrete,electric power,mine,metallurgy,and especially ap-plicationin ball mill with large diameter subjected toheavy i mpact loading[5].However,the brittle natureof this material often causesfailure under…     

The Influence of Synthesis Temperature on the Phase Composition and Structure of Ternary Compounds Produced from TiH2–Si–C Powder Mixtures

Powder Metallurgy and Metal Ceramics - The paper examines the formation of phases and structure in ternary compounds produced by thermal synthesis from the TiH2–Si–C powder mixture. The...     

Effects of La-Rich Rare Earth Alloys on Structure and Mechanical Properties of ZL101A Alloy

ＥｆｅｃｔｓｏｆＬａＲｉｃｈＲａｒｅＥａｒｔｈＡｌｏｙｓｏｎＳｔｒｕｃｔｕｒｅａｎｄＭｅｃｈａｎｉｃａｌＰｒｏｐｅｒｔｉｅｓｏｆＺＬ１０１ＡＡｌｏｙＬｉＨｕａｊｉ（李华基），ＴａｎＨｕｉｘｉｎ（谭会辛），ＺｈｕＺｈｅｎｃｈａｏ（祝阵超）（Ｃｈｏｎｇ...