Swirl motions of a bubbling jet in a cylindrical bath with bottom gas injection through a centric single-hole nozzle were investigated. The swirl motions were classified into two kinds. One was observed when the bath depth HL, was less than about the bath diameter D, while the other occurred for HL/D_??_2. These two kinds of swirl motions were named the first and the second kind, respectively. For the first kind swirl motion, conditions giving the onset and cessation of it were clarified. An empirical correlation for the cessation of the swirl motion was proposed. The swirl cycle was found to be closely related to the cycle of sloshing. On the other hand, the second kind swirl motion was considered to be caused by an instability of a large scale ring vortex enclosing the bubbling jet. Empirical correlations for the onset of swirl motion and the swirl cycle were derived.
As a fundamental study on the melting process of injected ore and coal powders in an inbath smelting reduction furnace, a cold model experiment was done to reveal the effects of gas flow rate and nozzle diameter on the mass transfer coefficient from a solid body immersed in a cylindrical bath with bottom gas blowing. The mass transfer coefficient was measured by means of an electro-chemical method. Spheres of three different diameters and a flat plate made of platinum were chosen as representative bodies. Since the turbulence intensity of liquid flow in the bath became very high due to gas blowing, a correlation for the mass transfer coefficient was proposed for each body as a function of turbulence intensity Tu in addition to usually used Reynolds and Schmidt numbers. The correlation can predict the heat transfer coefficient from solid bodies immersed in bubbling jet as well. Therefore, it can be said that an analogy between heat and mass transfer exists in bubbling jet, too. On the basis of the present experimental results, a correlation for the mass transfer from a circular cylinder was newly proposed. The present correlation was found to be useful for the prediction of the mass transfer from a circular cylinder.
In order to improve or eliminate centerline segregation of continuously cast strand, various methods have been introduced but have to date produced satisfactory results. With a view to substantially solving the problem, the authors proposed a continuous forging technique based on a completely new solidification mechanism. In this method, the thickness of the strand is drastically reduced at the stage of final solidification by anvils so that the solute-enriched liquid in the mushy zone is discharged upstream and dendrite is crushed, and squeezed out into the liquid pool. The method was applied to No. 1 and No. 3 bloom casters at Mizushima Works to investigate the effect with various steel grades covering high carbon and low alloy steels. The segregation ratio of carbon C/C0 can be controlled to an aimed value between 0.61.0 by choosing an appropriate ratio of reduction to the unsolidified thickness. The qualities of final products such as wire and rod are remarkably improved. This paper presents the concept of this new technique, the effect of forging conditions on internal quality, and the results in final products.
In order to put a new type of continuous billet mill with an arrangement of H-V stands where the vertical roll stands are drive-free to practical use, it is necessary to establish the method to estimate various rolling loads for mill design. In this paper, the variations in rolling force at driven horizontal roll stands and non-driven vertical roll stands, rolling torque at driven roll stands and inter-stand tension or compression during hot rolling experiments through 5 stands continuous billet mill were measured. Furthermore, the rolling load at each roll stand, the rolling torque at the driven roll stand and the inter-stand compression on the process where materials are pushed into the non-driven vertical roll stand from the adjacent driven horizontal roll stand were measured, analyzed theoretically and compared with experimental results. Calculated results of the rolling load at each roll stand, the rolling torque at the driven roll stand and the inter-stand compression generated between the driven horizontal roll stand and the non-driven vertical roll stand almost agreed with the experimental results. And the rolling loads can be estimated with practical accuracy.
The newly developed organic composite coated sheet steel is as follows. Zn-Ni alloy plated sheet steel with a coating weight of 30 g/m2 and average Ni concentration of 11.5 12.0% is chromated through electrolysis. The coating weight of chromate film is 5090 mg/m2 in Cr. Furthermore, emulsified olefin-acrylic acid copolymer resin mixed with colloidal silica of particle size 78nm is applied to a thickness of 1.01.8μm. Orefin-acrylic acid copolymer resin and colloidal silica are mixed at the rate of 100 and 30 (parts by weight). The result of mixing the colloidal silica with the resin is that abration resistance of the organic film is remarkably improved and it therefore maintains excellent corrosion resistance and paint adhesion. The new sheet steel maintains excellent corrosion resistance, including flat plate, even after bead forming and 20% stretch forming and furthermore excellent paint adhesion and cathodic electro deposited paint corrosion resistance. As a result of the combination of the above-mentioned properties, it has excellent perforation resistance. However, it should be used such that the organic film of two peaces of the coated sheet steel make contact with. The product has excellent weldability, too.
The hydrogen cracking susceptibility of mild steel was studied to determine the overprotection potential in soil and acetic acid solution by slow strain rate test (SSRT), constant load test and hydrogen permeation test. The following results were obtained: (1) The elongation was tend to decrease and the tensile strength was tend to increase in the overprotection environment compared with air environment. (2) The reduction of area did not decreased in 20% water content soil under overprotection conditions. (3) The reduction of area decreased in 30% water content soil with shifting less noble potential, and also SEM photograph indicated quasi-cleavage fracture surface. (4) Mild steel exhibited hydrogen cracking susceptibility when hydrogen content was more than 10 ppb. The cathodic potentials, which cause hydrogen cracking susceptibility, were -1.4V (vs. Cu/CuSO4) in 30% water content marine clay and -1.2V in 14% water content sand, respectively.
On a boron containing 18%Ni maraging steel of high strength grade, a small amount of austenite was retained at room temperature by the unrecrystallization solution treatment (URST). Toughening due to short time URST can be realized when the microstructure after the solution treatment consists of fine martensite and a small amount of retained austenite. In the present alloy whose chemical composition is 18% Ni, 12%Co, 5%Mo, 1.5%Ti and 0.003%B, strength and toughness level achieved by the short time URST is up to 2.4GPa and 50MPa√m, respectively. The values are 1.4 times larger than those after the usual heat treatment.
Intergranular stress corrosion cracking (IGSCC) of sensitized SUS304 has been investigated at 288°C water under γ-ray irradiation with a high dose rate of 2.6 × 103 C/kgh using a developed slow strain rate tensile test equipment. The IGSCC susceptibility was increased by γ-ray irradiation in water with 8 ppm dissolved oxygen (DO), and the corrosion potential was also increased by γ-ray irradiation. The IGSCC susceptibility was decreased with decreasing DO in water from 32 ppm to 0.2 ppm. No IGSCC susceptibility was observed in the hydrogen injected water under γ-ray irradiation. Radical concentrations decomposed by γ-ray irradiation into water were calculated using a computer code. The result suggested that, the radiolytic products were mainly H2O2. An increase in IGSCC susceptibility by γ-ray irradiation seems to be related to an increase in corrosion potential due to the formation of H2O2 by γ-ray irradiation. H2O2 concentration is remarkably decreased due to hydrogen injection into water under γ-ray irradiation.
A process of producing a grain size-gradient structure was proposed for low alloy steels containing nitride formers such as Ti, V, Al and Zr. Using a 1Cr-1Mo-3/4V steel, the grain size-gradient structure which combines a fine grain surface region and a coarse grain interior was obtained by the process, and an effect of the structure on the fatigue bebavior was examined. The producing process is as follows:(a) precipitation of VN in the surface region through heating at 1000°Cin N2, (b) grain refining by recrystallization at 1000°C, (c) grain coarsening in the interior through solution treatment at 1150°C.In the surface region, the fine grain swere maintained by the grain growth inhibitor of VN after the solution treatment.The obtained grain size-gradient structure is composed of a fine grain (<10μm)surface region(01mm depth), a traRsient grain size(1080μm)region(12mm depth), and a comparatively coarse grain(80μm)interior. The specimens with the grain size-gradient structure were tested at 550°C in arotating-bending fatigue machine and found to display better fatigue behavior than non-gradient homogeneous grain specimens. It was thought that the fine grain surface region suppresses the fatigue crack initiation and increases the fatigue life.
Transition behaviour of impact absorbed energy is well known for 18%Mn-18%Cr-N steel. The cleavage-like transgranular facets are detected on fracture surface of impact specimens tested at low temperature. Impact absorbed energy decrease when these cleavage-like facets are found on fracture surface of test specimen. The ductile-brittle transition temperature of the materials shifted to lower temperature by increased of nickel content, decrease of nitrogen content or pre-straining at high temperature. The relationship between cleavage-like fracture and plastic deformation stracture at the crack tip of impact test specimen has been investigated.
The nucleation and growth behavior of γ' and η precipitates in A286 was investigated by micro-Vickers hardness test and transmission electron microscopy. The morphology and the crystallography of them were also discussed. The obtained results are as follows: (1) The hardness of A286 aged at 893-1073 K for durations up to 720 ks closely related to the mean size of γ' precipitates. (2)The growth kinetics of the γ' precipitate in η-phase free region was explained by Lifshitz Slyozov-Wagner's theory for diffusion controlled growth at 993-1073K. The activation energy for the growth of the γ' precipitates was estimated to be 283 kJ/mol. (3) The interlamellar spacing of η-phase in each precipitates was inversely proportional to the degree of undercooling from the equilibrium temperature of γ/(γ+η)-phase boundary. (4) On the basis of the theory of diffusion controlled eutectoidal growth, the equilibrium temperatures of the cellular and the Widmanstatten precipitation were estimated to be 1218 and 1210K, respectively. These values were consistent with the experimental results.
β type titanium alloy, Ti-15V-3Cr-3Sn-3Al alloy, was conducted with conventional heat treatment, conventional thermomechanical processings and newly proposed thermomechanical processings. Mechanical properties, toughness and microstructures of them were examined by microstructural observations, tensile tests and instrumented Charpy impact tests. Tensile strength, σB, and yield stress, that is, 0.2% proof stress, σy, increased with increasing the rolling reduction ratio in the alloys conducted with conventional thermomechanical processing where one or two step aging was carried out after cold rolling while elongation, El, and reduction of area, RA, decreased. Dynamic toughness and maximum load of the alloys conducted with the conventional thermomechanical processing where two step aging was carried out after cold rolling increased with increasing cold rolling reduction ratio while they were decreased in the alloys conducted with the conventional thermomechanical processing where one step aging was carried out after cold rolling. Grain refinement by RI-ITMT was effective for improving toughness and strength of the alloy. Newly proposed thermomechanical processing in the present study gave greater toughness at greater strength level.