Showing papers in "Tetsu To Hagane-journal of The Iron and Steel Institute of Japan in 1986"

Electronic Structure and Phase Stability of Titanium Alloys

Abstract: Synopsis : The alloying effect has been investigated on the electronic structure of both bcc Ti and hcp Ti by the DV-Xx cluster method. The two alloying parameters which are the metal d-orbital level (Md) and the bond order between atoms (Bo), were determined theoretically. The Md is related to the electronegativity and metallic radius of elements. The Bo is a measure of the strength of the covalent bond between titanium and alloying elements. Both the Md and the Bo change remarkably with alloying elements. A new approach based on the electronic theory has been developed for understanding the phase stability of titanium alloys. With using Md and Bo parameters, titanium binary phase diagrams are interpreted consistently. and various commercial alloys are classified into the three groups of the ƒ¿, ƒ¿+ƒÀ and βalloys.The β transus and the Ms temperature for the martensitic toansformation are predicted from alloy compositions. Furthermore, the activation energy for the impurity diffusion in bcc Ti is estimated in terms of the Bo.

Flow Characteristics of Gas and Fine Particles in a Two-dimensional Space of Packed Bed

Abstract: Hideyuki Yamaoka Synopsis: In order to evaluate the effect of powder on the blast furnace operation, the 2-dimensional behavior of gas and powder in packed bed with a tuyere on it's wall side were studied by a mathematical simulation model as well as a cold model experiment. Results obtained are as follows; 1) When the gas velocity along the wall side is decreased, powder tends to accumulate near the wall above tuyere resulting in the increase in pressure drop of gas and the decrease in gas flow rate near the wall. 2) The deterioration of gas permeability accompanied by the decrease in wall temperature at the lower part during the reduced production operation of blast furnace can be attributed to the accumulation of fine coke near the wall.

Martensitic Transformation and Internal Structure of the TiPd and TiPd-Fe Alloys

Abstract: Kazuyuki ENAMI, Hiroshi SEKI and Soji NENNO Synopsis : The crystal structures, internal structure and shape memory effect of the TiPd and TiPd—Fe martensitic alloys were investigated by electron microscopy and tensile testing. The B19(2H) martensite which was found in the earlier X-ray investigation was found to exist in both the TiPd alloy and the TiPd—Fe alloys. The internal structure of this martensite was found to be (111)2H twin. By substituting palladium by iron (the content of titanium is fixed at 54 at%), the Ms temperature decreases with increasing iron content. In the iron added alloys with 4, 5 and 6 at%Fe, a new martensite phase with 9R structure was found to exist in addition to the twinned B19(2H) martensite. In the alloys with 7 and 8 at%Fe, an \"intermediate phase\" which is very similar to the \"incommensurate phase\" in TiNi alloys was found to exist. Additional \"superlattice\" diffraction spots of this phase lie on 0.3n {110} B2 (7at%Fe), and 0.28n {110} B2 (8 at%Fe), (n: integer). The shape memory effect and pseudoelastic behaviour of the polycrystalline specimens of the 54Ti-39Pd-7Fe and 54Ti-38Pd-8Fe alloys were investigated by tensile testing. Recoverable strain by shape memory effect was about 1% (percentage of recovery 100%) and pseudoelastic strain 3%, in both the alloys.

Effect of Combined Addition of Niobium and Boron on Thermomechanically Processed Steel

Abstract: Synopsis : In the thermomechanical control process (TMCP) with accelerated cooling, the effect of the combined addition of boron with a grain-refining element, niobium, vanadium or titanium, on the mechanical properties and microstructures of low-carbon steels was studied. It was found that although the single addition of boron has little effect on the steel properties, the combined niobium-boron addition conspicuously improves the strength and toughness balance. In the case of the single addition of boron, coarse Fe23(CB)6 precipitates at ƒÁ-grain boundaries after rolling, and the ƒÁ-ƒ¿ transformation suppressing effect by boron is remarkably weakened. Niobium addition to boron steel has the effect of suppressing the precipitation of Fe23(CB)6 and strongly retards the ƒÁ-ƒ¿ transformation, and hence produces a fine-grained bainitic structure. Titanium has the same effect as that of niobium, but vanadium does not. The strengthening and toughening mechanism of steels by the combined niobium-boron addition was also discussed by examining the effect of alloying elements on the recrystallization stop temperature of ƒÁ during rolling, ƒÁ-ƒ¿ transformation behavior and so on.

The Effect of Stress on Degradation of 1Cr-1Mo-1/4V Steel at Elevated Temperatures

Abstract: Synopsis : The creep tests for the specimens aged and stress-aged in the temperature range from 550 to 700•Ž have been carried out at 550•Ž-28 kgf/mm2 to determine quantitatively the degree of degradation of a 1 Cr1Mo-1/4V steel. The decrease in creep resistance due to aging has been discussed in terms of two microstructural changes: (i) a homogeneous change; the coarsening of intragranular carbides, and (ii) a heterogeneous change; the formation of subgrains or ferrite grains along prior austenite grain boundaries. When the stress-aged specimens were compared with the specimens aged without stress at the same hardness level, the creep resistance of the former was substantially lower than that of the latter and the amount of subgrains or ferrite grains for the former was significantly greater than that for the latter. The decrease in the creep resistance was proportional to the increase in the width of recovered area, which was defined as a parameter representing the amount of subgrains or ferrite grains along the prior austenite grain boundaries. The loss of the creep resistance during elevated temperature exposure is caused not by the homogeneous microstructural change of the carbide coarsening, but by the marked local recovery along the prior austenite grain boundaries.

Analysis of Combustion Zone in Raceway under Operation of Pulverized Coal Injection

Abstract: Ji-Cheng HE, Mamoru KUWABARA and Iwao MUCHI Synopsis: A theoretical reaction model of combustion zone in the raceway has been developed on the basis of the reaction engineering by taking account of movement , volatilization and combustion of pulverized coal in the blow pipe and the tuyere. Furthermore the effects of some PCI(Pulverized Coal Ingection) parameters on the distribution of process variables in the combustion zone are examined . Volatilization and combustion of pulverized coal in the blowpipe zone considerably affect combustion reactions in the raceway region. The PCI operation not only shifts the distribution patterns of temperature and composition of gas in the raceway toward the tuyere nose , but also decreases the maximum temperature in the raceway. Such effects become particularly remarkable with the increasein injection rate of pulverized coal. At the operation with constant theoretical flame temperature, however, only the distribution of process variables is varied toward the tuyere nose while the temperature level is maintained . The increases of blast temperature and pressure also shift the distribution of process variables toward tuyere nose, and these effects are gradually saturated at Tb>1473 and P>0 .26 MPa.

Crack Growth Mechanism and Fracture Toughness in Acicular α Structure of Ti-6Al-4V Alloy

Abstract: Synopsis : To understand the microfracture process, Acoustic Emission three dimensional location, Acoustic Emission source characterization and fractography method have been applied for fracture toughness testing of acicular ƒ¿ structure in Ti-6Al-4V alloy. In this fracture process, quasi-cleavage microcracks of about 200 ƒÊm diameter were nucleated at the pre-fatigue crack tip along crack front, of which distribution in the direction normal to fracture surface was about ‡TMz=1.2mm. Main crack growth is related to the condition where the coalescence of these microcracks occurs through specimen thickness. From these results, fracture toughness KIC and crack tip opening displacement CTODc were evaluated quantitatively, using ductile fracture criterion, and it could be concluded that these microcrackings enhance the fracture toughness of acicular ƒ¿-Ti alloy.

A Study on Cosmetic and Perforation Corrosion Test for Automotive Steel Sheets

Abstract: Synopsis : The use of a cyclic corrosion tests, consisted of the salt spraying, wet and dry conditions, is desirable in the evaluation of the corrosion of automotive body panels in an accelerated manner. Defining a wet % as a percentage of a wet period in a total test time, it is required to use the wet % of below 40 for the evaluation of the cosmetic corrosion resistance. This is a reasonable requirement when the corrosion of actual automotive bodies is considered. In this experiment it was found that zinc coated sheets showed less blisters than cold rolled steel sheets and exhibited good cosmetic corrosion resistance at 40 wet %. When the wet % was above 70, significant blister occurred on the Zn coated sheets with the anodic Zn dissolution. For the perforation corrosion the percentage of the wet period should be above 50 % since the corrosion proceeds in a wet condition. It was found that the highfrequencies of a wet—dry cycle was effective to accelerate the corrosion and that zinc coated steels showed good perforation corrosion resistance.

The Relation between the Powdering and the Microstructure of the Coating of Galvannealed Steel Sheets

Abstract: Synopsis : The structure of the galvannealed coating was studied by etching and measuring the potential time curve for the electro-chemical stripping. The formation of ƒ¡ phase was found to have the following extreme cases : (1) ƒ¡ layer is formed along the Zn/Fe boundary, which was typically shown in 1.6% Mn steel. (2) ƒ¡ grains are scattered in the ƒÂ1(c) layer near the Zn/Fe boundary ((ƒÂ1+ƒ¡) layer), which is typically shown in P-Nb bearing steel. The behavior of cracks in the coating was observed after bending. The cracks were generated from the Γ layer or(δ1十 Γ)layer.The cracks propagated most easily in the Γ layer, fallowed by the(δ1十 Γ) layer. The length of crack propagating along the Zn/Fe boundary was mainly dependent upon the thickness of the ƒ¡ layer. Therefore, the form of ƒ¡ phase was found to affect the powdering behavior.

Combustion Rate of Coke at Different Existing States Prepared by Fine Alumina

Abstract: Synopsis : The combustion rate of coke in the course of iron are sintering is one of the important factors which govern the temperature pattern in the sintering bed and resulting properties of the produced sinter in the blast furnace. It has been pointed out by Hida et al. that there are some kinds of existing states of coke in the sinter raw mixture, such as S, C and P types, and the existing states remarkably influenced the rate of coke combustion. In this study, some quasi-granules, which were modeled S and P types, were prepared by using coke and alumina particles. The effects of melt formation and reduction and reoxidation of iron oxide, which occurred at the shell layer of the granules, on the coke combustion can be neglected . The combustion rates of coke in the bed packed with dense alumina spheres were measured by a sintering simulator system. On the other hand, a mathematical model for these coke combustions was developed by the application of the unreacted-core model. The calculated results of the combustion rates were compared with measured ones, in order to derive the combustion equations of the coke. The computed results and measured data, such as combustion rates and bed—temperatures, agreed fairly well at various preheating temperatures.

Development of Secondary Refining Process. and Its Application to Production of Clean Steel

Abstract: Synopsis : Recently the needs of ultra low [S] and ultra low [O] steel for many kinds of products increase. Secondary refining process to achieve less than 5 ppm sulfur and less than 10 ppm oxygen in molten steel was investigated. In order to produce ultra low sulfur steel the optimum slag composition was determined as 60% Ca0-32% Al2O3-43% SiO2 and the deviation of final slag composition could be decreased by the method of 2 times flux addition. In the case of producing ultra low oxygen steel, it was important for increasing deoxidation rate that the total content of FeO +MnO in slag before RH process was less than 1 wt% and then deoxidizing products were removed through RH process. On the basis of these results, the refining process, BOF-VSCNKAP-GI-RH process, was established. By this process it became possible to achieve less than 5 ppm sulfur and less than 10 ppm oxygen in steel.