A study of heat treatment of high‐boron high‐speed steel roll

High‐boron high‐speed steel (HSS) is a cheap roll material. In the paper, the authors research the effect of heat treatment on the microstructure and properties of high‐boron high‐speed steel HSS roll containing 0.54% C, 1.96% B, 3.82% W, 7.06% Mo, 5.23% Cr and 2.62% Al by means of the optical microscopy (OM), the scanning electron microscopy (SEM), X‐ray diffraction (XRD) and hardness test. The results showed that as‐cast structure of boron‐bearing high‐speed steel HSS consisted of martensite, pearlite, M₂(B, C), M₃(B, C) and M₂₃(B, C)₆ type borocarbides. After quenching, the matrix transformed into the lath martensite, and M₃(B, C) dissolved into the matrix. When quenching temperature is lower than 1050°C, the hardness is increased with the increase of quenching temperature under oil cooling, while quenching temperature excels 1100°C, the hardness will decrease with the increase of quenching temperature. Under the condition of salt bath and air cooling, the effect of quenching temperature on the hardness is similar to the above law, but the quenching temperature obtaining the highest hardness is higher than that of oil cooling. The highest hardness is obtained while tempering at 525°C. The hardness of high‐boron high‐speed steel HSS roll is 66.5 HRC, and its impact toughness excels 13.1 J/cm². Using in pre‐finishing stands of high‐speed hot wire‐rod rolling mill, the wear rate of high‐boron HSS rolls is 0.26 mm/one thousand tons steel. However the manufacturing cost of high‐boron HSS rolls is obviously lower than that of powder metallurgy hard alloy rolls, it is only 28% of that of powder metallurgy (PM) hard alloy rolls.     

Diffusion Coefficients Estimated by Dynamic Fluorescence Quenching at High Pressure: Pyrene, 9,10-Dimethylanthracene, and Oxygen in n-Hexane

The fluorescence quenching of pyrene (PY) by carbon tetrabromide (CBr₄) at pressures of up to 400 MPa in n-hexane was investigated. It was found that the fluorescence quenching is not fully, but nearly, diffusion-controlled. From the pressure-induced solvent viscosity dependence, the quenching rate constant, k _q , was separated into the contributions of the bimolecular rate constant in the solvent cage, k _bim, and that for diffusion, k _diff. Using the values of k _diff separated, together with those of the diffusion coefficient of CBr₄, the diffusion coefficients of PY were successfully estimated. This analysis was applied to the quenching systems of 9,10-dimethylanthracene (DMEA)/CBr₄ and of PY/O₂ and DMEA/O₂ that were studied previously. Using the values of k _diff for these systems, together with those of the corresponding diffusion coefficients of the fluorophore or quencher, the diffusion coefficients of DMEA and O₂ were also evaluated. Based on the results, the pressure-induced solvent viscosity, , dependence on the diffusion coefficients is discussed.     

Microstructure and tensile properties of modified 9Cr–1Mo steel (grade 91)

Abstract

The influence of different soaking temperatures in the range 973–1623 K (below Ac ₁ to above Ac ₄) before oil quenching and tempering, on the microstructure, hardness, grain size, and tensile properties of modified 9Cr–1Mo steel has been studied. This was done in an effort to assess the tensile behaviour of the different microstructures likely to be encountered in the heat affected zone of a fusion welded joint of the steel. The steel developed predominantly martensitic structure after quenching. Soaking of steel in the intercritical temperature range (between Ac ₁ and Ac ₃) reduced the prior austenitic grain size and hardness. Soaking temperatures above Ac ₃ increased the grain size and hardness of the steel until the formation of δ ferrite at temperatures above Ac ₄. The δ ferrite formation at soaking temperatures above Ac ₄ reduced the grain size and hardness of the steel. The tensile strength of the steel exhibited a minimum for soaking in the intercritical temperature range where the ductility was highest. Strength increased and ductility decreased with further increases in soaking temperatures above Ac ₃. The formation of δ ferrite at soaking temperatures above Ac ₄ improved the ductility. The tensile properties have been correlated with the microstructures.     

Effect of heat treatment on microstructure and property of Fe‐Cr‐B alloy

In this article, the effect of heat treatment in different quenching temperature on microstructure and hardness of Fe‐Cr‐B alloy was studied, by contrast with boron‐free Fe‐Cr alloy. The results indicated that microstructure of boron‐free Fe‐Cr alloy consisted of the martensite and a few (Cr, Fe)₇C₃ type carbide. The microstructures had no obvious change with the increase of quenching temperature, but its hardness increased from 51.5 HRC to 60.8 HRC. When boron element was added into the Fe‐Cr alloy, the netlike eutectic structure began to break and spheroidizing after quenching, in which the borocarbide turned into spherical groups and network Fe₂B phase was broken. Moreover, the portion of martensite increased, and the amount of secondary carbide decreased, and the size of secondary carbide began to largen after quenching. When the quenching temperature reached 1100°C, secondary carbide particles dissolved in the matrix wholly. The hardness of Fe‐Cr‐B alloy increased with the increase of quenching temperature below 1050°C. The hardness of sample containing 2.0% B and quenching at 1050°C reached 66.7 HRC. The hardness of Fe‐Cr‐B alloy had no obvious change when quenching temperature continued to increase. After tempered at 200°C, the microstructure of Fe‐Cr‐B alloy had no significant change and its hardness had slight decrease. The hardness of sample containing 2.0% B tempered at 200°C reached 63.9 HRC.     

Systematic hardness measurements on mixed and doped crystals of rubidium halides

Efforts are made to improve the hardness of rubidium halide crystals by (i) solid solution hardening and (ii) impurity hardening. Systematic microhardness measurements have been made on rubidium halide mixed crystals (RbBr-RbI and KI-RbI) and rubidium halide crystals doped with Sr²⁺ ions. The composition dependence of the hardness of mixed crystals follows the law ΔH _v =K x (1− x),where ΔH _v is the enhancement in hardness,K a constant andx and (1 −x) the concentrations of the first and second component of the mixed crystals, respectively. The hardness of doped crystals increases with the concentrationC of the dopant according to the law, ΔH _v+6 =k C ^m ,wherek andm are constants. The relative efficacy of the two methods of hardening is discussed.     

Influence of Temperature on the Lifetime of Electronically Excited Uranyl Ion: I. Liquid and Supercooled H2SO4 Solutions

The influence of temperature (varied in the range 77-300 K) on the lifetime () of electronically excited uranyl (UO₂ ^{2 +})* in 0.2-5.0 M aqueous solutions of H₂SO₄ was studied. The activation parameters of the temperature quenching of the uranyl photoluminescence (PL) were determined. The temperature dependences of the rate constant of (UO₂ ^{2 +})* PL decay (k = 1/) in 0.5 and 5 M H2SO4 obey the Arrhenius equation only at T > 265 K and T > 280 K, respectively. The deviations at low temperatures are probably due to both non-exponential temperature dependence of the viscosity of these solutions and a change in the chemical composition of the solvent (H₂SO₄ dissociation), which affect the uranyl speciation and hence the luminescence parameters.     

Effect of quenching on microstructure and wear‐resistance of Fe–10Cr–1.5B–2Al Alloy

Cast Fe–10Cr–1.5B–2Al alloy was quenched at different temperatures. The effects of quenching temperature on microstructure and hardness and wear‐resistance of Fe–10Cr–1.5B–2.0Al alloy were investigated by means of the optical microscopy, the scanning electron microscope, X‐ray diffraction, energy dispersive spectrometer, Vickers hardness and Rockwell hardness tester, and the MM‐200 block‐on‐ring wear testing machine under dry friction condition. The results indicate that the as‐cast microstructure of Fe–10Cr–1.5B–2.0Al alloy consists of ferrite, pearlite and netlike eutectics which are distributed in the grain boundary. The eutectics mainly include herringbone M₂B and chrysanthemum M₇(C, B)₃. The matrix gradually turns into single martensite with the increase of the quenching temperature. The type of borocarbides has no obvious change after quenching. The netlike boride almost totally fractures and transforms from the fish‐bone structure to the graininess. There is some retained austenite in the quenched structures when the quenching temperature is more than 1100 °C. When the quenching temperature is in a range of 1000 °C to 1100 °C, the hardness and wear resistance show a sharp increase with an increase of temperature, and show a slight decrease after surpassing 1100 °C.     

Study on quenching sensitivity of an Al–Zn–Mg–Cu alloy containing trace amounts of Sc and Zr

The quenching sensitivity of an Al–Zn–Mg–Cu alloy containing trace amounts of Sc and Zr is studied by interrupted quenching experiments. Electrical conductivity of the quenched samples and the hardness of the samples subjected to one-stage and two-stage aging, are measured to construct the time–temperature–transformation (TTT) curves and the time–temperature–property (TTP) curves. It is revealed that the quenching sensitivity of the alloy is mainly influenced by the precipitation of coarse η phases during slow quenching, which preferentially nucleate and grow at grain boundaries and at the Al₃(Sc, Zr) dispersoids that are incoherent with the matrix. The quenching sensitivity increases with the size and quantity of the coarse η phases. The nose temperature is 290 °C for both TTT and TTP curves, where the phase transformation rate is the fastest and the quenching sensitivity is the highest. Compared to one-stage aged samples, two-stage aged samples exhibit lower quench sensitivity due to the reduced transformation rate from η′ phases to η phases after slow quenching. The quenching sensitive temperatures range from 206 to 358 °C for the one-stage aged samples and from 213 to 352 °C for the two-stage aged samples. Moreover, based on the simulated TTT and continuous cooling transformation curves, an optimized quenching process is proposed in the present work.

     

A study of microstructure and performance of cast Fe–8Cr–2B alloy

The effects of quenching temperature on microstructure and hardness of cast Fe–8Cr–2B alloy containing 0.3 wt% C, 2.0 wt% B, 8.0 wt% Cr, 0.6 wt% Si, and 0.8 wt% Mn were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X‐ray diffraction (XRD), Rockwell hardness and Vickers microhardness testers. The experimental results indicate that the as‐cast microstructure of cast Fe–8Cr–2B alloy consists of M₂B (M = Fe, Cr), M₇(C, B)₃, α‐Fe, and γ‐Fe. The dendritic matrix composed of lath martensite mixed with a small amount of retained austenite, and the netlike boride M₂B distribute in the grain boundary. After quenching between 950 °C and 1100 °C, the netlike eutectic boride are broken up and a new phase‐M₂₃(C, B)₆ which is distributed in the shape of sphere or short rod‐like are precipitated from the matrix. Both the macrohardness and microhardness of specimens increase with the increasing quenching temperature. At about 1050 °C, the hardness reaches the maximum value. However, when the temperature exceeds 1050 °C, the hardness will decrease slightly. With the increase of tempering temperature, the hardness of cast Fe–8Cr–2B alloy quenching from 1050 °C decreases gradually and its impact toughness increases slightly. Crusher hammer made of cast Fe–8Cr–2B alloy quenching from 1050 °C and tempering from 300 °C has good application effect, and its service life improves by 150–180% than that of high manganese steel hammer.     

Synthesis and some properties of Ti3SiC2 by hot pressing of Ti,Si and C powders Part 2 – Mechanical and other properties of Ti3SiC2

Abstract

Some properties of the remarkable Ti₃SiC₂ based ceramic synthesised by hot pressing of elemental Ti, Si, and C powders have been investigated. Its flexural strength by using three point bending tests and fracture toughness by using single edge notched beam tests were measured at room temperature to be in the range 310–427 MPa and about 7·MPa m^1/2, respectively. This material is a relative 'soft' ceramic with a low hardness of 4 GPa. Ti₃SiC₂ is similar to the soft metals and is a damage tolerant material that is able to contain the extent of microdamage. An oxidation test has been performed in the temperature range 1000–1400°C in air for 20 h. The oxidation resistance below 1100°C was good. Two oxidized layers were formed, the outer layer consisting of pure rutile-type TiO₂, and the inner layer a mixture of SiO₂ and TiO₂. The average coefficient of thermal expansion (CTE) of Ti₃SiC₂ was measured to be 9·29 × 10^?6 K^?1 in the temperature range 25–1400°C. The thermal shock resistance of Ti₃SiC₂ was evaluated by quenching the samples from 800°C, 1200°C, and 1400°C, respectively. The retained flexural strength drops dramatically at quenching temperature, but shows a slight increase after quenching from 1400°C compared with quenching from 800°C and 1200°C.     

The effect of chloride ions on the optical properties of TeO2-CuO-CuCl2 glasses

The glasses with composition 65TeO₂-(35–x)CuO-xCuCl₂ (x=0, 1, 2, 3, 4, 5 mol%) were prepared by a melt quenching technique and thin films of different thicknesses were made by blowing. The optical energy gap was studied and its variation with composition is discussed in terms of the effective role played by chloride ions which reduce the non-bridging oxygen ions and modify the structure of the network. The infrared spectra of all these glass samples at room temperature, recorded between 200 and 2400 cm^–1, are discussed in terms of anti-symmetric vibrations of the heteronuclear atoms.     

Kinetics of Redox Reactions of U, Pu, and Np in TBP Solutions: VIII. Kinetics of Reduction of Pu(VI) and Np(VI) with N,N-Dibutylhydroxylamine in Undiluted TBP

The kinetics of Pu(VI) and Np(VI) reduction in TBP containing HNO₃ was studied spectrophotometrically. The rate of the reduction of Pu(VI) with N,N-dibutylhydroxylamine in undiluted TBP is independent of the Pu(VI) concentration and is described by the equation -d[Pu(VI)]/dt = k[(C₄H₉)₂NOH][H₂O]⁵, with k = (2.17±0.13) × 10^-5 l⁵ mol^-5 min^-1 at 12°C. The activation energy of the reaction, E = 85.2± 4.6 kJ mol^-1, was determined from the temperature dependence of k in the range 12.0-33.5°C. Reduction of Np(VI) in undiluted TBP is approximately described by the kinetic equation -d[Np(VI)]/dt = k[Np(VI)] × [(C₄H₉)₂NOH]/[HNO₃], with k 40 min^-1 at 25°C, and in a 30% solutio of TBP in n-dodecane, by the equation -d[Np(VI)]/dt = k[Np(VI)][(C₄H₉)₂NOH]/[HNO₃]0.7 with the rate constant k = 18.4±1.8 l0.3 mol-0.3 min^-1 at 25°C.     

Temperature-dependent luminescence of gallium-substituted YAG:Ce

The temperature-dependent lifetime of trivalent cerium was determined in (Y_1−x Ce _x )₃Al_2.5Ga_2.5O₁₂ (where x = 0.1 and 0.2) over a temperature range of 20−120 °C. In both samples, the quenching temperature is significantly lower compared to (Y_1−x Ce _x )₃Al₅O₁₂. The difference in quenching temperatures is explained by evaluating the changes in the lattice, which occur as a result of substituting the Al³⁺ for Ga³⁺. The information presented in this report is useful for future design of phosphors for use as non-contact temperature sensors.     

Photoelectrochemical reactions on semiconductor materials

The cathodic reduction of Fe³⁺ ions and I₂ on ann-GaAs electrode was studied. The variation in the current density with the concentration of the oxidant has been interpreted as being the result of a reduction mechanism involving interface or surface states, an interpretation that is amply substantiated by experimental data. The effect of the surface modification with SiW₁₂O₄₀ ^4– on the reduction process was studied. Prior to this electrode activation, the rate constant for electrons being transferred from the conduction-band to the interface or surface states,k _S, was observed to be independent of electrode potential, whereas in the case of the modifiedn-GaAs,k _S depends on band-bending. On the other hand, the rate constant for electrons being transferred from the interface or surface states to oxidant species,k _ox, does depend on electrode potential in the case of the unmodifiedn-GaAs, and is independent of band-bending in the case of the modifiedn-GaAs. This change may be attributed to the filling of the active surface or interface states or their redistribution after the electrode surface activation.     

Trends in the microhardness of monocomponent and multicomponent chalcogenide glasses

The results of Vickers microhardness (MH_v) measurements on several series of chalcogenide semiconductor glasses are presented. The glasses were prepared under vacuum by the melt quenching technique. Trends of the hardness are explained in terms of the natural and compositional changes of the glasses as well as their glass formation tendency. The compositional variation of MH_v at room temperature is characterized by being even for the binary system, Se-As; quasi-binary (ternary) systems, As₂Se₃-As₂Te₃ and AsSe-AsTe; and the ternary system, Ge-Se-Si; and by being uneven at certain specific concentrations for the binary isoelectronic system, Se-S (< 5 at%S); quasi-binary system, As₂Se₅-As₂Te₅ (40 mol% As₂Te₅); ternary system As-Se-TI (20 at%TI); and quaternary system, As-S-Se-Te (TeSe=1). In addition, it is found possible to prepare samples of glassy selenium having certain predicted mechanical properties by controlling the temperature before quenching (T _s).     

Linear response and instability of vortex lattice in type-II superconductors

The wave vector dependent linear response of the vortex lattice in type-II superconductors is studied by calculating the superfluid density and is shown to have a singular behavior with respect to the long wave length perturbation of vector potential. The calculations are carried out in terms of the nonlinear elastic theory of the vortex lattice, which is, in principle, a low temperature expansion, and the terms up to the first order in temperature are taken into account, which is beyond the usual Gaussian elastic theory. The superfluid density is found to behave as ~ k_BT ¦k¦² log ¦k¦,for the small wave vector,k,perpendicular to the external magnetic field, where Tand k_B are the temperature and the Boltzmann constant, respectively. This behavior causes the divergence of the magnetic susceptibility at a critical wave vector, k_c.We show that this behavior is associated with an instability of vortex lattice to the externally applied perturbation.     

On the elastic-plastic rotating shrink fit with linearly hardening hub exhibiting variable thickness in exponential form

Summary The plane state of stress in a rotating shrink fit is investigated. The analysis is based on Tresca's yield condition, its associated flow rule and linear strain hardening. The rotating shrink fit consists of an elastic solid inclusion and a partially plasticized hub with variable thickness in the exponential formh=h ₀e^{–n(r/ro) k}, whereh ₀, n andk are real constants. It is assumed that the hub is thin and the variation of thickness is radial and symmetric with respect to the midplane. The stresses are obtained in terms of confluent hypergeometric functions.Dedicated in memory of my mother Edibe Güven (1927–1993).     

Rolling wear of EPDM and SBR rubbers as a function of carbon black contents: correlation with microhardness

The rolling friction and wear of ethylene/propylene/diene (EPDM) and styrene/butadiene rubbers (SBR) with different carbon black (CB) contents were studied against steel in orbital rolling ball (steel)-on-plate (rubber) test rig (Orbital-RBOP) and oscillating rolling ball (steel)-on-plate (rubber) set-up (Oscillating-RBOP). The universal hardness (H), coefficient of friction (COF), and specific wear rate (W _s) of EPDM and SBR were determined. Incorporation of CB increases the universal hardness and the COF (the latter marginally) and decreases the specific wear rate for both EPDM and SBR. The wear mechanisms were concluded by inspecting the worn surfaces in scanning electron microscope and discussed as a function of CB modification. An inverse relationship between the specific wear rate and universal hardness was proposed in form of W _s = kH ⁻ⁿ , where k and n are constants for a given rubber and testing condition.     

Effects of cooling process on microstructure and hardness for 1·0C–1·5Cr bearing steel

Effects of cooling rate (V_cr) and final cooling temperature (T_ft), after hot deformation, on microstructure and hardness for 1·0C–1·5Cr bearing steel were investigated. The results show that if V_cr increases from 2 to 25°C s^?1 and T_ft remains at 650°C, pearlite colony size and grain size both decrease, hardness increases. When V_cr exceeds 8°C s^?1, carbide network can be restrained effectively. TEM micrographs indicate that there exist branches in the local region of lamellar cementite and ferrite, and a ferrite thin film is also found around the proeutectoid carbide. Under the cooling rate of 10°C s^?1, with the increase in T_ft, the microstructure changes from martensite into pearlite, carbide network becomes more serious and hardness decreases.     

The Prediction of the Dissolution Rate Constant by Mixing Rules: The Study of Acetaminophen Batches

The purpose of this article is to promote two simple and scalable methods to accelerate the formulation development of formulated granules using acetaminophen as a model system. In method I, formulated granules made from the batch of small particle–sized acetaminophen (1) by ball milling the batch of large particle–sized acetaminophen (2), and the mixture of the two batches at equal weights (mix) gave the dissolution rate constants (k) of k₁?=?0.43 ± 0.15 minutes^?1, k₂?=?0.18 ± 0.01 minutes^?1, and k_mix?=?0.30 ± 0.03 minutes^?1 for 75 wt percent formulation; k₁?=?0.75 ± 0.01 minutes^?1, k₂?=?0.18 ± 0.01 minutes^?1, and k_mix?=?0.34 ± 0.03 minutes^?1 for 62 wt percent formulation; and k₁?=?0.28 ± 0.01 minutes^?1, k₂?=?0.16 ± 0.01 minutes^?1, and k_mix?=?0.22 ± 0.02 minutes^?1 for 30 wt percent formulation. In method II, the mixture of the formulated granules produced by mixing the formulated granules from the two batches at equal weights gave dissolution rate constants of k_mix?=?0.30 ± 0.03 minutes^?1, 0.30 ± 0.02 minutes^?1, and 0.22 ± 0.01 minutes^?1 for 75 wt percent, 62 wt percent, and 30 wt percent formulations, respectively. After fitting the three data points of k₁, k₂, and k_mix to the 10 mixing rules in materials science—series mixing rule, Hashin and Shtrikman upper bound, logarithmic mixing, Looyenga mixing rule, effective media approximation (EMA), three-point lower bound, Torquato approximation, three-point upper bound, Maxwell mixing rule, and parallel mixing rule—we found that the selection of the best suited mixing rules based on k₁, k₂, and k_mix was solely dependent on the formulations under a given operating condition and regardless of whether the system was a powder mixture or a granular mixture. The values of k₁, k₂, and k_mix in both the 75 wt percent and 30 wt percent formulations were enveloped by the parallel mixing rule and Maxwell mixing rule, whereas the values of k₁, k₂, and k_mix for the 62 wt percent formulation were encompassed by the logarithmic mixing rule, Hashin and Shtrikman upper bound, and the series mixing rule. Apparently, the best suited mixing rules could be used to predict the right proportions of either the powder mixture (Method I) or the granular mixture (Method II) for obtaining any other desired dissolution rate constant, k_mix, whose value fell in between the values of k₁ and k₂.