工程科學學報

The Deoxidation Process of GCr15 Steel

It is shown that the average [O] in the steel can be decreased to 12.86 ppm and there is an optimal [%Si] at the end of melting as 0.11%, at which [O] after vacuum carbon deoxidation （VCD） is minimum. A kinetical model has been deduced to simulate the VCD process. The results show that adding Si before Al is superior to the adding Al before Si with respect to the final [O] in the steel. It is suggested that the melting point of covering slag should be lower than 1550℃, and （FeO+MnO） should be less than 1%, so as to effectively refine GCr15 steel.

工程科學學報. 1989 11(6): 493-500.

The Behavior of Inclusions during the Special Melting Processes of Superalloys

The behavior of nitride inclusions during the VIM, VAR and ESR processes of superalloys has been investigated. The experimental results have proved that the inclusions in the original metals, even if the pure TiN power added rapidly decompose at the superalloy liquid processing temperature and the nitrides in the remelted metals are mainly precipitated from solution during the sulidification process.

工程科學學報. 1989 11(6): 501-509.

Investigation of Heat Transfer in the Spray Cooling of Continuous Casting

The heat transfer coefficient between spray water droplets and hot surface is measured in the laboratory. The effect of spray water flow rate, water pressure, spray distance of nozzle from the surface of strand, spray water temperature on the heat transfer is made a detail studied. And meanwhile, the effect of the strand surface FeO scale on the heat transfer is also investigated. According to the experimental results, the influence of above factors on the heat transfer coefficient has been discussed and a experience formula between the heat transfer coefficient and spray water flow rate is given out.

工程科學學報. 1989 11(6): 510-515.

The “Point” and “Volume” Fusion Behaviour of Prefused Type Powder Fluxes

The relationship among particle size, properties of heat transfer and melting rate of fluxes as well as the main factors which have effect on the prefused fluxes have been studied. Under the conditions of same components and particle size, the melting temperature of prefused fluxes is lower than that of mixed fluxes. With the decreasing of particle size, the difference of melting temperature between the two type of fluxes decreases also. The larger the particle size, the greater the melting rate of prefused type fluxes.

工程科學學報. 1989 11(6): 516-525.

Equilibrium between Slag and Molten Iron in the Direct Alloying of Steel with Nb<sub<2</sub<O<sub<5</sub<-Bearing Slag

Equilibrium between slag and molten iron at 1600℃ was investigated for the direct alloying of steel with Nb<sub<2</sub<O<sub<6</sub<-bearing slag. The activity of niobium oxide in the slag was measured. The α<sub<Nb<sub<2</sub<O<sub<5</sub<</sub< is in the range of 10<sup<-2</sup<-10<sup<-4</sup<. Theδ<sub<Nb<sub<2</sub<O<sub<5</sub<</sub< is ranged in 10<sup<0</sup<-10<sup<-2</sup<.Niobium partition decreases with the increase of[Si]% and CaO/SiO<sub<2</sub<. When α<sub<[0]</sub< and ΣFeO decrease, niobium partition decreases too. The δ<sub<Nb<sub<2</sub<o<sub<5</sub<</sub< and the ratio of γ<sub<siO<sub<2</sub<</sub< to γ<sub<Nb<sub<2</sub<O<sub<5</sub<</sub< decrease with the incre-ase of slag basicity. The suitable thermodynamic conditions in direct alloying of steel with Nb2O5-bearing slag have been found.

工程科學學報. 1989 11(6): 526-532.

On Niobium Reduction in Blast Furnace

The Baotou Iron Ore of China contains very high niobium. This paper reported the results through laboratory and practical experiments on niobium enrichment in blast furnace. The effect of temperature, constituents of slag and silicon content in hot metal on niobium recovery was studied and the results had been verified by blast furnace operation. According to the reaserch, a comprehensive extraction process that extraction combines with ore dressing and with pyro--hydro-metallurgy should be adopted for Baotou niobium resource which is difficult to concentrating. The methods of increase in niobium recovey were also suggested in this paper.

工程科學學報. 1989 11(6): 533-538.

Modification of Nonmetallic Inclusions in Steel with Yttrium

The modification affects of yttrium on formation of nonmetallicinclusions in steel has been studied by use of metallographic method. The effect of added quantity of modificater on type and size of inclusions was also studied in this work.

工程科學學報. 1989 11(6): 539-543.

Some Factors Affecting on the Structure-formation and Mechanical Properties of As-Cast High Toughness Nodular Cast Iron

Using sand moulds for step-shape casting tests and different silicon percentage of nodular cast iron it was possible to separate structural variations produced during freezing from those occurring at Ac1 transformation temperature. The results show that an increase in silicon content leading to different variation in the matrix structure> leads to a changing mechanical properties of nodular cast irons. Tensile strength and elongation of obtained as-cast nodular cast iron with the composition of 3.9%C, 3.2%Si, 0.5%Mn are maximum of about 524.5N/mm2 and 19.8% accordingly. In the same nodular cast iron, but only with 0.1% Mn the silicon addition first increases after decreases elongation, impact toughness and hardness. But tensile strength changes to the opposite side.

工程科學學報. 1989 11(6): 544-550.

Hot Corrosion of Plasma Sprayed Coatings for Waste Gas Turbine Blades

High temperature corrosion tests in 75%Na<sub<2</sub<SO<sub<4</sub<-25%. NaCl molten salt have been conducted on waspalloy specimens plasma sprayed with Co-Cr-B-Si, Ni-Cr-B-Si-hCr<sub<3</sub<C<sub<2</sub<, X-40, X-40 + TiC and Ni/Al + Al<sub<2</sub<O<sub<3</sub< coatings, test coupons were exposed isothermally at 750℃up to 200 h. After the corrosion tests, each sample was examined by OM, SEM and EMPA. It was found that X-40, X-40 + TiC and Ni/Al + Al<sub<2</sub<O<sub<3</sub< were violently corroded by the molten salt due to cracking and spalling of the coatings, whereas Co-Cr-B-Si and Ni-Cr-B-Si + Cr<sub<3</sub<C<sub<2</sub< exhibited superior corrosion resistance, which were thought to be related to the formation of chromium and silicon oxide film. A possible corrosion mechanism had been proposed and it is suggested that the excellent corrosion resistance and high hot-hardness of the two B-Si containing coatings may be of significance for applications in petroleum refining industry as protective coatings of power generating turbine blades which are used under severe corrosion/erosion conditions.

工程科學學報. 1989 11(6): 551-559.

Role of Mg on Structure and Mechanical Properties in Alloy 718

The role of Mg in alloy/718 has been systematically investigated. Mg raises not only high temperature tensile and stress-rupture ductilities but also increases considerably smooth and notch stress-rupture life. Mg containing alloy 718M is free of stress-rupture notch sensitivity. Mg improves creep and fatigue interaction properties （LCF or cyclic stress rupture） at any grain size. The basic role of Mg is equilibrium segregation at grain boundaries which helps to change continuous grain beundary (5-Ni3Nb morphology to discrete globular form which has a retardation effect on intergranular fracture. Mg promotes the change from intergranular to transgranular fracture mode.

工程科學學報. 1989 11(6): 560-567.

Interfacial Phase in Ti-5Al-2Mo-3Zr Alloy

Under appropriate cooling condition, intcrfacial phase appeared between α and β phases in Ti-5Al-2M0-3Zr alloy. Its thickness could reach 100 nm. The interfacial phase was either single layer structure or double layer structure. The monolithic layer adjacent to 3 phase was indentified as fee structure with relationship （110）<sub<β</sub<// （001）<sub<m</sub<, [11$\mathop 1\limits^{{\rm{ - - }}} $]<sub<β</sub< /[110]<sub<m</sub<. The striated layer adjacent to a phase was indentified as hep with twin relationship {10$\bar 1$1}<1$\bar 0$12> to α. Thus, the study provided a new experimental fact for the controversial topic on structure of striated layer. Chemical composition of interfacial phase varied slightly with heat treatments, but always between that of α and β phases.

工程科學學報. 1989 11(6): 568-574.

Heat Treatment of WC-Co Hardmetals and Transformation Temperature of Cobalt Phase

The Present work has found that the transverse rupture strength of WC-Co hardmetals can be improved by queuching heat treatment. The increment of transverse rupture strength （ΔTRS） was dependent on the cobalt content of hardmetal. The higher the cobalt content of hardmetal is, the more the increment of transverse rupture strength is. The main reason is that the transformation of face centered cubic cobalt stabilized at high temperature to hexagonal close packed cobalt can be depressed by quenching. The transformation temperature of hexagonal close packed cobalt binder phase was determined by differential thermal analysis. It was found that the transformation temperature increases with increase of cobalt content of hardmetal. The reason is that the cobalt binder phase of high cobalt hardmetal contains higher tungsten content than that of low cobalt hardmetal after quenching.

工程科學學報. 1989 11(6): 575-580.

The Microstructure of Graphite Spherulites in Cast Iron

The microstructure of graphite spherulites （G.S.） in Ce addition ductile cast iron was carried out using transmission electron microscopy （TEM） techniques. The structral characterization of the graphites is as following: there are platelets growing along the periphery as well as fan-like structure formed from platelet aggregates in the diameter section of spherulite, in which most of the platelets are with sizes ranging from several to tens nm in radial; the [001] direction of the platelets would have a tend to parallel to radial of the G. S. and meanwhile, they also a small misorientation deviated from the radial among the platelets each other. It shows that the anisotropy of graphites has been restrained by adding Ce element in cast iron and the structural characterization of the G. S. is consistent with the Double’ s model of the conical helixes formed in helical growing and branching.

工程科學學報. 1989 11(6): 581-584.

Microcracks in MDF Cement

The relationspip between the microcracks and the mechanical behaviors and the characteristics of fracture of MDF cement have been studied. The results show that most of the microcracks lie and propagate in the matrix or along the boundary of the clinkers. The microcracks improve the toughness of MDF cement. The Griffith’s equation is invalid to describe the fracture of MDF cement.

工程科學學報. 1989 11(6): 585-589.

Physico-Chemical Behaviour of Rare Earth Elements and Ability for Corrosion Resistant

The physico-chemical behavior of rare earth elements in low sulphur 16Mn steel and their ability to enhance the corrosion resistance of the steel in sea water studied in this paper. The results indicate that Ce and La in 16Mn steel all have the abilities such as deoxidation, desulphidation, refining grains and cleaning grain boundaries and matrix etc. The anodic and cathodic polarization curves show that the rare earth elements added in 16Mn steel enhance the corrosion resistance of the steel in sea water.

工程科學學報. 1989 11(6): 590-597.

Measurement and Calculation of ReCl<sub<3</sub<-LiCl (Re: La, Ce) Phase Diagrams

In this paper the phase diagrams of LaCl<sub<3</sub<-LiCl and CeCl<sub<3</sub<-LiCl systems have been experimentally determined and theoretically calculated. Bath are simple eutectic systems. The eutectic points are at 25mol% LaCl<sub<3</sub<, 508℃ and 27mol% CeCl<sub<3</sub<, 494℃, respectively. The optimized phase diagrams and thermodynamical data of LaCl<sub<3</sub<-LiCl and CeCl<sub<3</sub<-LiCl systems with self consistency are a better basis for constructing ternary phase diagrams.

工程科學學報. 1989 11(6): 598-603.

High Temperature Corrosion of Fe-25Cr and Fe-17Cr-1.5Si-0.5Al Alloys in Oxidizing and Sulfidizing Enviornments

The simultaneous oxidation and sulfidation of Fe 25Cr and Fe-17Cr-l.5Si-0.5Al alloys was studied at 1023K and 1223K in H<sub<2</sub<-H<sub<2</sub<O-H<sub<2</sub<S gas mixtures. The kinetic boundary which indicates the transition from oxide to sulfide has heen found in these two alloys. The critical oxygen partial pressures of Fel7Crl.5SiO.5Al alloys were systematically lower than those of Fe-25Cr alloy. The reaction kinetics were measured by the stainless steel spring balance, and the reaction products were characterized by X-ray diffraction and scanning electron microscopy. The reaction rate usually decreased with the increase of the oxygen partial pressure at the constant sulfur partial pressure. The exista-nce of silicon plays an important role to suppress the sulfidation of Fel7Cr alloy.

工程科學學報. 1989 11(6): 604-610.

Discussion of the Constitutive Relation on Cyclic Stress-Strain of Engineering Materials

Based on the experimental results and analysis of the cyclic deformation, there is an obvious yield stage on the cyclic stress-strain curve at the stage of small plastic deformation （in room or low temperatures）. This phenomenon is similar to that of monotonic tensile curve case. But for the former the deformation amount at which the yield begins is much smaller than that for the latter. The cyclic stress-strain constitutive relation needs to be further studied according to the actual cyclic stress-strain curve. The conventional constitutive equation <i<σ</i<=<i<Aε</i<<sup<n</sup< is based on the results only corresponding to the cyclic strengthening stage. It is not appropriate for the stage of the small plastic deformation and the stage of yield.

工程科學學報. 1989 11(6): 611-615.