22MnB5钢溶质分配系数及TiN析出对微观偏析的影响

为了提高凝固过程中溶质微观偏析模型计算的准确性,基于溶质分配系数及夹杂物析出对溶质偏析的重要影响,定量分析了溶质分配系数以及TiN析出对凝固过程溶质元素含量的影响,为微合金高强钢凝固过程研究提供理论参考.针对22MnB5钢建立了耦合TiN析出热力学模型的溶质微观偏析模型,并探究了温度及钢液凝固路径对溶质分配系数的影响规...     

Spherical particles of intermetallic compounds of a large radius with a core-shell structure in aluminum alloys with scandium

The structures of two-phase alloys that form upon slow solidification of a dilute Al-Sc melt containing a small amount of titanium additives (0.06 wt %) are studied. Near-spherical scandium trialuminide particles having a considerable linear size (up to 10–20 μm) are found to grow. The study of the inner structure of the particles (dispersoids) reveals titanium impurities in the intermetallic structure. In addition, the following specific features of the structure are elucidated: a core-shell structure with a variation in the scandium and titanium content over the spheroid volume.     

Solidification of Pb particles embedded in Al

Hypermonotectic alloys of Al-5 wt% Pb and Al-5 wt% Pb-0.5 wt% X where X = Mn, Cu, Zn, Fe and Si have been manufactured by chill-casting and melt-spinning. The resulting microstructures have been examined by a combination of optical microscopy, scanning and transmission electron microscopy, and electron probe microanalysis. The as-solidified hypermonotectic alloys exhibit a homogeneous bimodal distribution of faceted Pb particles embedded in a matrix of Al, with chill-cast Pb particle sizes of 1–2 μm and 5–50 μm, and melt-spun Pb particle sizes of 5–10 nm and 50–100 nm. The larger Pb particles are formed during cooling through the region of liquid immiscibility while the smaller Pb particles are formed during monotectic solidification of the Al matrix. The Pb particles exhibit a cube-cube orientation relationship with the Al matrix, and a truncated octahedral shape with {111} and {100} facets. The as-solidified Pb particle distributions are resistant to coarsening during post-solidification heat treatment. The equilibrium Pb particle shape and therefore the anisotropy of solid Al-solid Pb and solid Al-liquid Pb surface energies have been monitored by in situ heating in the transmission electron microscope over the temperature range between room temperature and 550°C. The anisotropy of solid Al-solid Pb surface energy is constant between room temperature and the Pb melting point, with the {100} surface energy 14% greater than the {111} surface energy, in good agreement with geometric near-neighbour bond energy calculations. The {100} facets disappear when the Pb particles melt, and the anisotropy of solid Al-liquid Pb surface energy decreases gradually with increasing temperature above the Pb melting point, until the Pb particles become spherical at about 550°C. The kinetics of Pb particle solidification have been examined by heating and cooling experiments in a differential scanning calorimeter. Pb particle solidification is nucleated catalytically by the Al matrix on the {111} facet surfaces, with an undercooling of 22K and a contact angle of 21°C. Ternary additions of Mn, Cu, Zn and Fe do not influence the Pb particle solidification behaviour, but Si is a potent catalyst and stimulates the Pb particles to solidify close to the equilibrium Pb melting point.     

Milling of Carbide-Steel Powder Components and Their Mixtures in an Attrition Mill

Milling of wear-resistant steel and titanium carbide powders is studied with an attrition mill rotation rate of 980 rpm. The physical and technological properties of powders and particle size are determined. Particle shape and the change in material chemical composition during milling are studied. It is established that steel powder cannot be milled to particle sizes less than 3.6 μm whereas a mixture of steel and titanium carbide can be milled to a fine state (0.3 μm). Powders with a size of about 1 μm neither flow nor are formable. Use of benzene as a milling medium makes it possible to prevent steel powder oxidation, but the carbon content in titanium carbide decreases. During milling of the main part of the charge to a fine state rather large steel particles (up to 50 μm) remain.     

In situ studies of precipitate formationin Al-Pb monotectic solidification by X-ray transmission microscopy

Al-1.5 wt pct Pb monotectic alloys were unidirectionally solidified. X-ray transmission microscope (XTM) observations, both during and after solidification, revealed various new morphological/compositional features in the melt and solid. In the melt, nonuniform lead-rich interfacial segregation layers and droplets were observed to form well ahead of the interface. In the solid, periodic striae formed at translation/solidification velocities as low as 6 × 10⁻⁶ m/s. The striae shape does not replicate that of the interface. The striae spacing decreases from 4 to 2 × 10⁻⁴ m with an increasing solidification rate between 6 and 16 × 10⁻⁶ m/s. High resolution postsolidification XTM examination reveals that these striae consist of Pb-rich particles of 2 to 3 × 10⁻⁶ m diameter. At translation/solidification velocities below 6 × 10⁻⁶ m/s, Pb incorporation into the solid occurs in the form of continuous fibers and strings of particles of about 5 × 10⁻⁶ m diameter. Bands, parallel to the interface, in which these fibers were aligned in the solidification direction, alternated with bands of poor fiber alignment. The width of these bands is comparable to the striae spacings obtained at the high solidification rates.     

Synergistic Effect of Nitrogen and Refractory Material on TiN Formation and Equiaxed Grain Structure of Ferritic Stainless Steel

The effect of nitrogen content on the formation of an equiaxed solidification structure of Fe-16Cr steel was investigated. Moreover, two different kinds of refractory materials, i.e., alumina and magnesia, were employed to control the type of oxide inclusion. The characteristics of TiN(-oxide) inclusions were quantitatively analyzed in both molten steel and solidified samples. When the melting was carried out in the alumina refractory, the grain size continuously decreased with increasing nitrogen content. However, a minimum grain size was observed at a specific nitrogen content (approx. 150 ppm) when the steel was melted in the magnesia refractory. Most of the single TiN particles had a cuboidal shape and fine irregularly shaped particles were located along the grain boundary due to the microsegregation of Ti at the grain boundary during solidification. The type of TiN-oxide hybrid inclusion was strongly affected by the refractory material where Al₂O₃-TiN and MgAl₂O₄-TiN hybrid-type inclusions were obtained in the alumina and magnesia refractory experiments, respectively. The formation of oxide inclusions was well predicted by thermochemical computations and it was commonly found that oxide particles were initially formed, followed by the nucleation and growth of TiN. When the nitrogen content increased, the number density of TiN linearly increased in the alumina refractory experiments. However, the number of TiN exhibits a maximum at about [N] = 150 ppm, at which a minimum grain size was obtained in the magnesia refractory experiments. Therefore, the larger the number density of TiN, the smaller the primary grain size after solidification. The number density of TiN in the steel melted in the magnesia refractory was greater than that in the steel melted in the alumina refractory at given Ti and N contents, which was due to the lower planar lattice disregistry of MgAl₂O₄-TiN interface rather than that of Al₂O₃-TiN interface. When ?T_TiN (= difference between the TiN precipitation temperature and the liquidus of the steel) was 20 K to 40 K, the number density of effective TiN was maximized and thus, the grain size was minimized after solidification. Finally, although most of the TiN particles were smaller than 1 μm in the molten steel samples irrespective of the nitrogen content, TiN particles larger than 10 μm were observed in the solidified samples when the nitrogen content was greater than 150 ppm. The growth of TiN particles during melting and solidification was well predicted by the combinatorial simulation of the ‘Ostwald ripening model’ based on the Lifshitz–Slyozov–Wagner theory in conjunction with the ‘Diffusion controlled model’ using Ohnaka’s microsegregation equation.     

Effect of Electron-Beam Treatment on Wear-Resistant Coatings Applied by Electroexplosive Sputtering

TiC–Mo, TiC–Ni, TiB₂–Mo, and TiB₂–Ni coatings applied to the surface of Hardox 450 steel by electroexplosive sputtering are subjected to electron-beam treatment, After electroexplosive application, the surface relief of the coatings includes features such as deformed solidifying microglobules, buildup, microcraters, microcracks, and peeling. After electron-beam treatment, the microglobules, buildup, microcraters, and microcracks disappear from the coating surface. A polycrystalline structure containing cellular elements is formed. After electron-beam treatment, the surface roughness is 1.1–1.2 μm. The thickness of the layers modified by the electron beam in the electroexplosive coatings depends linearly on the surface energy density. The greatest coating thickness is observed when using the TiB₂–Mo system; the coating thickness is least for the TiC–Ni system. That may be attributed to the thermophysical properties of the coatings. The following substructures are observed in the coatings: cellular, striated, fragmented, and subgranular. Grains with chaotically distributed dislocations and reticular dislocations are also observed. Electron-beam treatment leads to the formation of composite filled structure over the whole cross section of the remelted layer. The structure formed in this layer is more disperse and uniform than in coatings formed without electron-beam treatment. The inclusions of titanium carbide or titanium diboride in the molybdenum or nickel matrix are 2–4 times smaller than immediately after electroexplosive sputtering. Within the molybdenum or nickel grains and at their boundaries, rounded particles of secondary phase (titanium carbide or titanium diboride) are observed. They may be divided into two classes by size: particles of the initial powder (80–150 nm) that have not dissolved on irradiation; and particles formed on solidification of the melt (10–15 nm). In the electroexplosive powder coatings, the structure is mainly formed by dynamic rotation of the sprayed particles, which form a vertical structure both in the coating and in the upper layers of the substrate. The coatings have excellent operational properties: nano- and microhardness, elastic modulus of the first kind, and wear resistance in dry slipping friction.     

LF-VD精炼过程中GCr15钢中夹杂物的行为

对GCr15在精炼过程产生的夹杂物进行分析,为减少夹杂、提升钢材质量奠定理论基础。采用金相、电子探针、光谱等方法,取样分析了西宁特钢EAF-LF-VD-CC流程冶炼的CA2r15在LFVD精炼时非金属夹杂物数量和尺寸的变化,并确定了各工位的夹杂类型和形成原因。试验结果表明,精炼过程夹杂总量一直呈下降趋势。LF精炼后,各...     

含钛低碳钢凝固过程中氧化钛形成的热力学

通过研究含钛低碳钢的热力学,确定了在凝固过程中形成氧化钛的最佳钢液条件。计算结果表明：在含钛低碳钢中,为促进凝固初期析出Ti2O3从而细化凝固组织,关键的工艺要点是控制钢液中氧含量在0．0005％～0．0030％,铝含量小于0．001％,氮含量小于0．014％。     

Ti-IF钢凝固过程中TiN的析出机理和规律

结合冶金热力学和凝固偏析模型分析了Ti-IF钢凝固过程中TiN的析出特点.Ti-IF钢凝固前期钢液中TiN夹杂无法生成,固相中TiN源自低温固相析出;凝固固相分数达到0.64时,Ti、N组元在凝固前沿富集程度增加,凝固前沿固相中开始有TiN析出;凝固末期,Ti和N的富集程度进一步增大,固液相中均能有TiN析出.采用扫描电镜分析了TiN在铸坯中的分布,从铸坯表层到中心TiN数量和尺寸存在显著变化:从铸坯表层向中心方向TiN尺寸不断增大,平均尺寸从1-2μm增大到5μm,在距离表层70-80 mm处尺寸达到最大;在铸坯厚度中间位置,TiN尺寸较大,平均尺寸为5μm左右;在铸坯中心TiN尺寸又有所变小,平均尺寸为3μm左右;在铸坯表层TiN密集程度较高,在铸坯中间和中心TiN数量密集程度显著降低.IF钢铸坯中TiN析出时机及其尺寸和数量与Ti、N组元偏析和凝固冷却速度关系密切.      

Solidification Structure Refining of 430 Ferrite Stainless Steel With TiN Nucleation

The thermodynamics of TiN precipitation in liquid steel of 430 ferrite stainless steel has been calculated to find out the condition of TiN precipitation during the initial solidification stage. The difference in the solidification structure of 430 ferrite stainless steel has been discussed through comparative tests of vacuum induction furnace melting with different contents of Ti. It has been found that the equiaxed grain proportion can be increased from 20% to 69% as the content of Ti from 0.1% up to 0. 4%. The size of the TiN particles precipitated is 1-3 μm and the number of TiN particles is about （200- 300）/μm^2. It is found that the effect of using TiN to refine the solidification structure has been confirmed under the strict process condition used for 430 ferrite stainless steel.     

Solidification parameters,microstructures, and mechanical properties of rapidly solidified iron-based alloys

Cooling rate measurements were carried out using a computer controlled melt spinning unit for the production of rapidly solidified Fe 6.3 wt.% Si and Fe 3.2 wt.% C melt spun ribbons employing a wide range of process parameters. The cooling rates are mainly a function of the ribbon thickness, and are independent of the alloy composition and wheel material. The resulting microstructures have been characterized by light optical and electron microscopy (SEM and TEM) investigations and were found to be influenced by the cooling conditions during and after solidification. Grain sizes and secondary dendrite arm spacings are related to the cooling rates by means of exponential relationships. In addition to this, rapidly solidified eutectic Fe 4.2 wt. %C alloy powder was produced by argon melt-atomization. Powder particles of 20 μm to 80 μm size solidified microcrystalline and exhibit cementite, metastable γ-phase, and martensite. The cementite matrix is of dendritic structure. After consolidating the powder by hot pressing below A, the microstructure changes to the fine equiaxed grains containing about 66 Vol.% Fe₃C and a dispersoid of ferrite ≤1 μm within the cementite matrix. This material exhibits high tensile strength and wear resistance at room temperature. At elevated temperatures in the region between 650°C and 750°C, and at strain rates of ε ? 10^?4s^?1 the fine grained ceramic-like material reveals superplastic behaviour.     

Assessment of Segregation in Hot Tear Cracks

In solidified slabs different types of segregations such as crystal segregation (micro segregation), centre segregation (macro segregation) and hot tear segregation (HTS) may occur. The present paper examines the segregation behaviour of different elements in hot tear cracks depending on the carbon content. The aim of this work is to determine the segregation factors in the hot tear cracks filled with residual melt and compare with micro and macro segregation. Within the scope of this examination, a microanalytical assessment was made of eight slab samples with different steel grades each showing different types of hot tear cracks that had been healed up by an inflow of residual melt. The hot tear cracks are located outside the primary dendrites in the dendritic interstices, parallel or transversal to the direction of casting. Segregation in the cracks healed up by residual melt depends on the carbon content and will become more pronounced as the carbon content increases. The intensity of segregation for the various elements in the hot tear cracks (hot tear crack segregation) is between that of crystal segregation and centre segregation. The thickness of the segregated zone in the hot tear crack area is 30 ‐ 50 μm. Apart from an enrichment of the alloying elements manganese, silicon and chromium, the healed up hot tear cracks also contain secondary precipitates of sulphides and niobium‐titanium‐carbonitrides. Towards the slab centre, the latter can cause, among other things, the development of niobium‐titanium‐carbonitrides (Nb_1‐x, Ti_x)(C_1‐y, N_y) networks in the primary dendritic interstices.     

Microstructure of shot-blasting casting roll and effect on strip solidification during strip-casting process

In the strip-casting process,the surface topography of the casting roll has a significant influence on the solidification microstructure and surface quality of the as-cast strip. Shot-blasting treatment is an important way to achieve a suitable surface topography on the casting roll. In this study,a casting roll of beryllium copper alloy was shot blasted using steel pellets in the laboratory,resulting in a randomly distributed discontinuous peak and dent surface topography,in which cold deformation-slip bands and fine-deformation twins were formed. The thickness of the deformed copper alloy was about 100 μm during the shot-blasting process,and the copper hardness value increased significantly within 40 μm of the surface,with a maximum increase of more than 20% compared to the mean substrate hardness value. Within 60-100 μm of the surface,the hardness at the peak position was still higher than the copper substrate mean value,but the hardness at the dents was not,which was mainly due to the copper alloy slip and twinning deformation mechanisms. The surface hardness was similar to that of the substrate after the shot-blasted sample had been subjected to thermal shock. The molten steel first chilled and nucleated at the surface peaks of the casting roll;furthermore,fine dendrites grew and crossed over the middle of the dents. Therefore,the peak intervals of the shot-blasted surface are an important factor in solidification quality control.     

Precipitation and Solid Solution of Titanium Carbonitride Inclusions in Hypereutectoid Tire Cord Steel

The properties of titanium carbonitride Ti(C_xN_(1-x))inclusions precipitated during solidification of tire cord steels and the thermodynamic conditions for their decomposition and solid solution during billet heating were investigated using a thermodynamics method.The solid solution of Ti(C_xN_(1-x))inclusions during high-temperature heating was also studied experimentally.The results revealed that:(1)the higher the content of carbon in the tire cord steel is,the greater the value of xin the Ti(C_xN_(1-x))inclusions is;(2)the higher the content of carbon in the tire cord steel is,the earlier the Ti(C_xN_(1-x))inclusions precipitated during the solidification process and the lower the solidification front temperature is during precipitation;(3)when an 82 Asteel sample was heated to 1 087℃,the Ti(C_xN_(1-x))inclusions possess the thermodynamic conditions of decomposition and solid solution;and(4)when 82 Asamples were heated to 1 150 and 1 250 ℃,the total number of Ti(C_xN_(1-x))inclusions larger than 5 μm in diameter decreased by55.0% and 70.3%,respectively.In addition,although smaller inclusions with diameter less than 2 μm continued to decompose when the sample was heated at 1 250℃for 2 hand then cooled to 1 000℃in the furnace,the number of inclusions larger than 5 μm in diameter increased.     

基于氧化物冶金技术的管线钢凝固脱氧热力学

通过X100管线钢(%:0.03～0.05C、1.70～1.90Mn、0.15～0.25Si、≤0.001S、≤0.002P)凝固过程脱氧热力学研究,确定了在凝固过程中的固液两相区析出Ti₂O₃夹杂的最佳钢液组成。研究表明,为使X100管线钢在凝固前沿的固液两相区中析出细小的Ti₂O₃夹杂颗粒,关键在于控制钢液中钛含量≤0.01%,铝含量≤0.002%,氧含量≤0.001%,氮含量≤0.004%。     

Formation of Small Blocky Al3Ti Particles via Direct Reaction Between Solid Ti Powders and Liquid Al

The evolution of titanium powders in the pure aluminum melt at a lower temperature was studied in our research. The process involved some titanium powders being added into the pure aluminum melt at 1003?K (730?°C), and then the melt was cast into an ingot after 5 minutes. A reaction layer composed of some loose Al₃Ti particles was formed on the solid Ti surface due to the reactive diffusion between titanium and aluminum. In-situ blocky Al₃Ti particles smaller than 5???m were produced in the aluminum matrix. A reaction-peeling model was suggested to illustrate the formation mechanism of Al₃Ti particles, and a simple approach for fabricating in-situ Al₃Ti/Al-alloy composites was proposed as well.     

Laser melt injection of austenitic cast iron Ch16D7GKh with titanium

The results of studying the microstructure and microhardness of Ni-resist cast iron ChN16D7GKh after laser melt injection by means of introducing titanium particles into the melt are presented. The treatment was performed using a fiber laser with a beam focused into a spot 0.2 mm in diameter with a radiation power of 1 kW and the motion velocity of the laser beam of 10–40 mm/s. Titanium is dissolved in the cast-iron melt, and TiC particles are formed in the structure upon cooling. The coefficient of using the titanium powder increases as the fusion zone size increases and reaches 50% in the best case. A modified layer has a composite structure with a metallic matrix and a comparatively uniform distribution of titanium carbide particles. The microhardness of the modified zone is 600–700 HV. Its further growth is suppressed by the partial removal of carbon from the melt zone in the composition of red fume evolved in the process. Therefore, the Laves phase (TiFe₂) is formed instead of an increase in the TiC content upon increasing the titanium supply. The experimental data on the regularities of the weight loss caused by the substance removal from the melt zone depending on laser melting parameters are presented.