Showing papers by "Kaneaki Tsuzaki published in 2001"

Grain refinement in copper under large strain deformation

Abstract: Structure evolution taking place in pure polycrystalline copper was studied in multiple compressions at room temperature. Rectangular samples were compressed with consequent change in the loading direction from pass to pass. The deformation behaviour at high strains of above 2 shows an apparent steadystate flow following a rapid rise in the flow stress at an early stage of deformation. The structural changes are characterized by the evolution of many mutually crossing subboundaries at low to moderate strains, finally followed by the development of very fine grains with medium- to large-angle boundaries at large strains. These new grains are concluded to be evolved by a kind of continuous reaction, that is continuous dynamic recrystallization (DRX). The grains developed under continuous DRX are much finer than expected from the extrapolation of discontinuous DRX data for hot deformation. An average grain size of about 0.2μ evolved at room temperature is roughly similar to that for subgrains develo...

Method for setting shape and working stress, and working environment of steel member

Abstract: A delayed fracture is effectively prevented by appropriately setting a shape and working stress, and working environment of a high strength member having more than 1,000 MPa of tensile strength. For this end, the relationship between a maximum value of diffusible hydrogen contents of unfailed specimens (Hc) and Weibull stress are found and the content of diffusible hydrogen entered into steel from the environment due to corrosion during the use of the steel member (He) is also found. Then, Weibull stress in the Hc that is equal to the He is found, thus determining the shape and working stress of the steel member so as to provide stress below the Weibull stress.

Microstructure development by thermomechanical processing in duplex stainless steel

Abstract: In the case of two-phase alloys, a refinement of matrix phase and a uniform distribution of second phase are important to improve mechanical properties. In this paper, microstructure change of a (ferrite)+γ (austenite) two-phase structure, especially microduplex structure consisting of a and y in a fine-grained form (1-3 μm), in the duplex stainless steel by various thermomechanical processings and heat treatments is briefly reviewed. Main topics are as follows, 1) formation process of fine-grained α+γ structure (microduplex structure) by various thermomechanical processings, 2) nature of microduplex structure and its stability during prolonged aging, 3) microstructure change of microduplex structure by annealing after heavy cold rolling and 4) microstructure change of microduplex structure during superplastic deformation.

Effect of dispersed particles on microstructure evolved in iron under mechanical milling followed by consolidating rolling

Abstract: The microstructure and the strength of an iron mechanically milled with various amounts of oxygen (i.e., 0.2, 0.6, and 1.5 mass pct) were studied. The samples were subjected to a mechanical milling in an argon atmosphere for 100 hours followed by consolidating bar rolling to a total reduction of about 86 pct at 700 °C. The microstructure of the steels sensitively changed depending on the oxygen content, i.e., on the volume fraction of the oxide particles. The average grain size decreased from about 0.7 to 0.2 µm with an increase in the amount of oxygen. Moreover, the misorientation distributions of the grain boundaries were different in the samples with various amounts of oxygen. A relatively large fraction of low-angle boundaries arranged crosswise to the rolling axis was registered in the samples with 0.2 and 0.6 pct oxygen, while the near random distribution of the boundary misorientations was obtained in the specimens with 1.5 pct oxygen. The effect of dispersed particles on the structure evolution and the relationship between microstructures and some mechanical properties are discussed.

Effect of plastic strain on grain size of ferrite transformed from deformed austenite in Si-Mn steel

Abstract: The effect of plastic strain on the grain size of ferrite transformed from deformed and unrecrystallised austenite has been investigated for a low carbon Si-Mn steel. An explicit finite element technique was used to evaluate the plastic strain distribution introduced by deformation in a specimen. The specimen was compressed by a pair of anvils controlled to keep the strain rate constant. The contact condition between the anvil and the specimen was determined by the experimental result from an identically deformed screw set in the specimen. The interrelation between the equivalent plastic strain epsiloneq, numerically obtained in the range 0.1

Excellent weldability steel thick wall material and its mfg. method

Abstract: A tough high strength heavy wall steel material having superior weldability is provided, said steel material has a diameter or a side 5 mm or more in length, and comprises oxides 1 mu m or less in particle diameter homogeneously dispersed at a dispersion density in a range of from10,000 to 100,000 particles/mm and uniform ferrite grains 2 mu m or less in grain diameter formed over the entire plane making a right angle with respect to the rolling direction

Method of evaluating high fatigue strength material in high tensile strength steel and creation of high fatigue strength material

Abstract: The present invention provides a method of designing a high fatigue strength material in high tensile strength steel, comprising the steps of: obtaining the values of tensile strength σ B (unit thereof is MPa) and Vickers hardness Hv of the steel; measuring the flaw area of inclusion, when the fracture origin is located only at the surface of the steel; and estimating, in designing the high fatigue strength material, that the fatigue limit σ w (unit thereof is MPa) of the steel satisfies either σ w ≧0.5σ B or σ w ≧1.6 Hv, when a square root of the flaw area, (area) ½ (unit thereof is m), contained in the steel is no larger than 45.8 /σ B 2 or 4.47 /Hv 2 . According to the present invention, a method of evaluating high fatigue strength material in high tensile strength steel, in which method the relationship between the flaw dimension (area) of ODA and the fatigue strength is considered, as well as a high fatigue strength material, can be Provided.

Method for evaluating a delayed fracture of a steel member

Abstract: A delayed fracture in high strength steel is effectively prevented by appropriately setting a shape and working stress, and working environment of a high strength member having more than 1,000 Mpa of tensile strength. To this end, the relationship between a maximum value of diffusible hydrogen contents (H c ) of unfailed specimens and Weibull stress (σ w A) are found and the content (H e ) of diffusible hydrogen entering the steel from the environment due to corrosion during the use of the steel member is also found. Then, the value of Weibull stress for the hydrogen content H c that is equal to the environmental value H e is found, thus determining the shape and working stress of the steel member so as to provide stress (σ w B) below the Weibull stress (σ w A).