Isothermal precipitation behavior of copper sulfide in ultra low carbon steel

Copper and sulfur are typical residual elements or impurity elements in steel.Sufficient removal of them during steelmaking process is difficult for copper and costly for sulfur.Utilization of copper and sulfur in steel, especially in steel scrap,has been an important issue for a long period for metallurgists.Copper and sulfur may combine to form copper sulfide,which may provide a prospect to avoid the detrimental effects of copper and sulfur in steel.Unfortunately the formation mechanism of copper sulfide in steel has not been completely clarified so far. In the present paper,solution treatment of samples containing copper and sulfur are firstly performed at 1623 K for 2.7×10~3 s followed by quenching into water.The samples are then isothermally heat-treated at 673 K,873 K, 1073 K,1273 K and 1373K for different time followed by quenching into water again.The size,morphology, constituent and crystallography of sulfide precipitates in these samples are investigated by scanning electron microscope(SEM) and TEM equipped with EDS.Fine copper sulfides(less than 100 nm) are observed to coexist with silicon oxide in samples even isothermally heat-treated at 1 373 K for 1.44×10~4 s;Film-like copper sulfides are generally observed to co-exist with iron sulfide in all samples;Plate-like copper sulfides are observed especially in sample isothermally heat-treated at 1 073 K for 1.44×10~4 s.The formation mechanisms of these copper sulfides have been discussed.     

Interstitial precipitation in Fe-Cr-Al alloys

Two separate stages of precipitation have been identified during the aging of ternary Fel8Cr3Al and Fel8Cr5Al alloys at temperatures in the vicinity of 475 °C. The first stage involves the formation of interstitial precipitates resulting from C and N impurities; the second and slower stage is the formation of the Cr-rich α′ phase. Transmission electron microscopy (TEM) results show that carbonitride precipitation occurs preferentially at dislocations, stacking faults, and grain boundaries, and also uniformly through the matrix. Aging for times in excess of 400 hours at 475 °C promotes coarsening of the heterogeneous precipitates and dissolution of the uniformly distributed matrix particles. A resistometric analysis shows that the kinetics of the initial stages of precipitation can be described by a (time)^2/3 relation. This kinetic behavior is explained in terms of stress-assisted diffusion in the highly stressed matrix resulting from coherency strains accompanying carbonitride precipitation. Experimental values of the activation energy for the first stage reaction correlate closely with those reported for the interstitial diffusion of C and N in alpha iron.     

Discontinuous precipitation in aluminum-base zinc alloys

The kinetics of discontinuous precipitation in Al-21.6 at. pct. Zn and Al-22 at. pct. Zn-0.01 at. pct Sn alloys was determined by quantitative metallographic measurements on solution-treated and aged specimens. The growth rate of the discontinuous precipitate appears to be controlled by interfacial diffusion. It was found that the addition of a small amount of tin reduced the overall reaction rate. Nucleation of the discontinuous precipitate was confined to grain edges or boundaries, filling the available sites (site saturation) at a very early stage in the reaction. It was observed that a variation in quench rate markedly affected the growth rate of the precipitate and the site-saturating-dimensionality during a room-temperature aging treatment.     

Laves phase precipitation in Fe-Ta alloys

Development of an iron-base alloy hardened by particles of an intermetallic compound rather than a carbide is a desirable goal because of the greater thermal stability of such a dispersion. As a first step in the development of iron-base alloys hardened with the Laves phase, structural studies of binary Fe-Ta alloys have been undertaken. The structures of two phase Fe-Ta alloys have been studied by means of optical and transmission electron microscopy, X-ray diffraction, electron beam microprobe analysis, and scanning electron microscopy. The hardness change as a function of time at 600°, 700°, and 800°C has been determined for binary alloys with 1 at. pct Ta and 2 at. pct Ta in iron. Also, the uniaxial tensile strengths of solution treated, quenched, and aged samples have been determined. These studies suggest that the compound, Fe₂Ta, is isomorphous with the structure type, MgZn₂, (C14) and has a range of compositional homogeneity. The latter results correspond with the predictions of the Engel-Brewer correlation. Also, it has been found that precipitation occurs at grain boundaries, dislocations, and randomly throughout the matrix. Particles which form at dislocations have a (100)α habit plane; whereas a (110)α habit plane has been reported by others^1,3 for the hexagonal Laves phase in α iron. Hypereutectoid composition alloys quenched from the ö phase field have a completely retained § structure. Isothermal decomposition at 600°, 700°, and 800°C of alloys with the retained § structure results in a sizable hardness increase in 2 at. pct Ta alloys but only a modest increase in 1 at. pct Ta alloys. Brittle fracture of aged tensile specimens tested at room temperature reveals that the ductile-brittle transition temperature in tension is above room temperature.     

铁基自润滑合金硫化钼形成规律

利用中频感应炉炼制四种不同钼、硫含量的钢,通过SEM观察组织并结合XRD分析物相,研究合金中的硫化钼形成规律.结果表明:Mo的质量分数为1.5%时,只能形成FeS,极少量的Mo以Fe₃Mo₂形式存在;Mo为6.5%时,Mo仍以Fe₃Mo₂的形式存在;Mo达到11%时,虽有少量的MoS₂形成,但多数Mo与Fe形成化合物Fe₃Mo₂;Mo达到19.5%时生成较多的MoS_x;Mo低于10%时很难形成钼的硫化物;退火有利于MoS_x的形成,但未发现纯的MoS₂生成.由此初步认为:MoS_x是FeMoS化合物分解析出的,是亚稳的;在合金中起细化晶粒作用的V,Nb和Ti有过强的硫亲和力,不利于钼的硫化物形成;脱氧的铝也应少加.     

Radiation-induced solute segregation and precipitation in alloys

Solute segregation and precipitation in dilute alloys during irradiation have been studied by means of the Johnson-Lam kinetic model. The model is based on a combination of chemical reaction rates and diffusion equations for free defects, solutes, and bound defect-solute complexes. The enrichment of solute at sink surfaces and solute depletion in the matrix have been calculated as functions of temperature, damage rate, defect-solute bind-ing energy, and initial solute concentration. Using parameters appropriate for Be in Ni, significant solute segregation is found in the temperature range from 0.2 to 0.7 Υ_m. The temperature for maximum segregation is higher for the high displacement rates typically used in charged-particle bombardment experiments than for the low displacement rates used in fast-reactor irradiations. The solute concentration at the sink surface builds up at high temperatures, without surpassing the solubility limit, until a steady state is at-tained. However, at lower temperatures solute enrichment at sinks becomes larger and the solubility, in general, becomes lower. Precipitation will occur when the local solute concentration reaches that of the phase boundary. The solute concentration at the precipi-tate-matrix interface is determined by the solubility limit, and precipitation continues until the matrix is sufficiently solute-depleted to achieve a steep concentration gradient that will balance the defect-induced solute flow by back-diffusion. Hence, the steady-state matrix composition is determined by radiation conditions and is independent of the initial alloy composition when precipitation occurs. The solute depletion at steady state is more severe at low displacement rates than at high rates. The calculations are quali-tatively compared with recent experimental observations of the temperature and com-positional dependence of solute precipitation in the Ni-Be system. This paper is based on a presentation made at a symposium on “Radiation In-duced Atomic Rearrangements in Ordering and Clustering Alloys” held at the annual meeting of the AIME, Atlanta, Georgia, March 7 to 8, 1977, under the sponsorship of the Physical Metallurgy and Nuclear Metallurgy Committees of The Metallurgical Society of AIME.     

Discontinuous precipitation and coarsening in Al-Zn alloys

The morphology and kinetics of discontinuous precipitation (DP) and discontinuous coarsening (DC) in solution treated and isothermally aged Al-Zn alloys containing 39.3 and 59.3 at.% Zn have been investigated at temperatures ranging from 323 to 523 K by light microscopy, electron microscopy and X-ray diffraction. At all aging temperatures the supersaturated α solid solution was observed to decompose rapidly by DP into a lamellar mixture of solute depleted α phase and β phase precipitate. DP occurred so rapidly in the 59.5 at.% Zn alloy that the heat of transformation raised the temperature of the alloy significantly. With further aging a slower DC reaction transformed the lamellar DP into a coarser lamellar structure of the same two phases; however, the composition of the α phase of the DC was closer to the equilibrium solvus composition than that of the DP. With still further aging a second, much slower DC reaction was observed to decompose the lamellar product of the first DC reaction in the 59.5 at.% Zn alloy into a still coarser lamellar structure. Analysis of the kinetics of both the DP and DC reactions showed them to be controlled by boundary diffusion in the advancing reaction interface. Reaction front migration rates for both DP and DC increased markedly with increasing Zn content. This increase seems to be associated partially with an increase in boundary diffusivity with increasing Zn content.     

硫化锌沉淀分离-EDTA滴定法测定废水中硫化物

水样经盐酸酸化,将其中的HS-和S2-全部转化为H2S,加入过量的金属锌,反应产生的大量氢气作为载气与一并逸出的硫化氢通入热的氨性溶液及过量的锌标准吸收液中,以铬黑T为指示剂,用EDTA标准滴定溶液滴定形成ZnS沉淀后的剩余Zn2+,实现了采用吹气吸收-沉淀分离-EDTA滴定法测定实验室废水中硫化物含量的方法。讨论了水样的酸化效果,吸收液选择,气体分离等实验条件对测定的影响,避免了碘量法所产生的干扰。测定结果与标准方法相符合,相对标准偏差为3.02%~3.08%,加标回收率在96.0%~99.5%之间。     

Electrochemical oxidation of nickel sulfide metallic alloys

The sequence of the electrochemical oxidation of phase components of the converter matte is confirmed and variations in the composition of its surface during the anode oxidation are revealed. It is shown that regularities of this process that are characteristic of its phase components, namely, nickel and its sulfides, are inherent to the converter matte. The oxidation of nickel sulfides in sulfide-metallic alloys starts at lower potentials (1.1–1.2 V) than that of synthesized nickel sulfide (1.2–1.3 V). During the oxidation of the converter matte, metal nickel initially oxidizes and, only as this stage finishes, the oxidation of sulfides accompanied by the isolation of elemental sulfur is developed. Copper impurities weakly affect the oxidation of the converter matte, although the shift of potentials takes place as the Cu/Ni ratio increases.     

Effect of homogenization on sulfide inclusions in ferrous alloys

The effect of high temperature homogenization on sulfide inclusions was studied in directionally solidified AISI 4340 low alloy steel of various sulfur contents and in directionally solidified iron-carbon-manganese-sulfur alloys. The morphological modifications of the various types of inclusions caused by coarsening were investigated versus homogenization time. The decrease of the number of inclusions per unit volume of matrix, and that of the sulfide-matrix interface area per unit volume of sulfide, and the increase of the mean over-all inclusion size with homogenization time were quantitatively established. These variations were compared in a specific case with analytical predictions based on a coarsening model.     

The Bauschinger effect in precipitation strengthened aluminum alloys

The Bauschinger effect in precipitation strengthened Al-Cu-Mg, Al-Zn-Mg and Al-Cu polycrystals was measured as a function of applied strain. Alloys heat treated to contain easily shearable precipitates,i.e., GPB, GP and θ″ exhibited a small Bauschinger effect, on the order of that in pure aluminum. In contrast, alloys with nonshearable precipitates, S′, η and θ′ showed an anomolously large effect. A unique hysteresis loop shape, with a region of convex curvature between sharp inflection points, was observed in the nonshear-able precipitate alloys. The large Bauschinger effect and unusual hysteresis loop shape are due to internal elastic or back stresses exerted by the strong precipitates on the matrix. A nonlinear elastic hardening model is proposed in which the overall work harden-ing is partitioned into an elastic back stress component and a frictional dislocation forest hardening term. Plastic relaxation around the precipitates and inhomogeneous deformation in the polycrystal reduces the level of the internal stresses below that predicted theoretically by the Brown and Stobbs hardening theory.     

The discontinuous precipitation reaction in dilute Al-Li alloys

The first observation of a discontinuous reaction in dilute Al-Li alloys is reported. It is of the relatively uncommon type in which a pre-existing dispersion of fine precipitates is converted to lamellae at the reaction front so that it is essentially a coarsening process. Transmission electron microscopy has been used to investigate the mechanisms of initiation, propagation and termination of the reaction. The composition and temperature limits over which it occurs have been defined, and it has been shown by direct high resolution microanalysis that the mechanism of Li redistribution is primarily diffusion in the advancing colony interface. The grain/grain orientation relationship has been shown to influence the occurrence of the reaction.     

耐蚀合金中TiN析出机制

摘要：TiN颗粒尺寸及其分布对耐蚀合金性能有明显的影响,因此有必要对TiN在铸坯中的分布及其析出行为进行研究。采用扫描电镜(SEM)、金相显微镜（OM）观察了TiN夹杂物在铸坯中的分布、尺寸及其形貌;基于热力学和动力学理论分析了耐蚀合金铸坯中TiN夹杂物的析出时机及其尺寸,结合试验结果和理论计算明确了TiN夹杂物在凝固后铸坯中的位置和尺寸与析出时机的关系,为控制TiN夹杂物提供理论指导。结果表明,冶炼过程中析出的TiN夹杂物尺寸较大,在凝固过程中被枝晶吞没,位于铸坯枝晶内和等轴晶内;微观偏析计算结果表明,在凝固分数为0.55时,TiN开始析出,最开始析出TiN夹杂物的逐渐长大,长大后的TiN易于被二次枝晶吞没,最终位于铸坯中的枝晶间和等轴晶内,后期析出的TiN则在枝晶间和等轴晶间。固相中析出的TiN夹杂物长大较慢,尺寸细小,最终位于奥氏体晶界。     

Strengthening of cobalt-tungsten alloys upon discontinuous precipitation

Precipitation and hardening were investigated in cobalt-tungsten alloys containing 5–13 at.% W. A significant hardening up to 860 HV in alloys aged at 600°C is caused by discontinuous precipitation. Transmission electron microscopy shows that as-quenched alloys consist of f.c.c. α-Co grains with frequent twins and martensitic plates. During ageing L1₂-type order develops within α-Co and simultaneously discontinuous precipitation starts at a grain boundaries. The microstructure consists of hexagonal ε-Co and Co₃W lamellae as found during in situ high temperature studies in the electron microscope. High resolution electron microscopy reveals coherency strains within a few atomic layers at the ε-Co/Co₃W interface and nonhomogeneous D19 ordering within the Co₃W lamellae, resembling in some places nonstoichiometric B19 ordering.     

Internal oxidation of dilute Co-Ti alloys

The kinetics of internal oxidation of Co-Ti alloys and the crystal structures and morphologies of the internal oxide particles have been investigated in the temperature range 900 to 1080°C. Three oxides were observed:δ-TiO, TiO₂ (rutile) and CoTiO₃. The permeabilities of oxygen in Co were calculated from the observed internal oxidation kinetics using an analysis due to Meijering as well as an analysis based on a more rigorous solution of the diffusion equations. The factors affecting the size and morphology of internal oxide particles are discussed. Formerly graduate student assistant, Department of Metallurgical and Materials Engineering, University of Pittsburgh, Pittsburgh, PA 15261 This paper is based, in part, on a thesis submitted by J. Megusar in partial fulfillment of the requirements for the Ph.D. Degree, University of Pittsburgh, April, 1974.     

Internal oxidation of dilute Co-Ti alloys

The kinetics of internal oxidation of Co-Ti alloys and the crystal structures and morphologies of the internal oxide particles have been investigated in the temperature range 900 to 1080°C. Three oxides were observed:δ-TiO, TiO₂ (rutile) and CoTiO₃. The permeabilities of oxygen in Co were calculated from the observed internal oxidation kinetics using an analysis due to Meijering as well as an analysis based on a more rigorous solution of the diffusion equations. The factors affecting the size and morphology of internal oxide particles are discussed.     

Internal oxidation of dilute Cu-Ti alloys

Metallurgical and Materials Transactions A - The kinetics of internal oxidation of dilute Cu-Ti solid solutions, containing up to 1 wt pct Ti have been investigated over the temperature range 700...