Showing papers by "Nobuhiro Fujita published in 2002"

Steel plate exhibiting excellent workability and method for producing the same

Abstract: The present invention provides a steel sheet excellent in workability, which may be used for components of an automobile or the like, and a method for producing the same. More specifically, according to one exemplary embodiment of the present invention, a steel sheet excellent in workability, including in mass, 0.08 to 0.25% C, 0.001 to 1.5% Si, 0.01 to 2.0% Mn, 0.001 to 0.06% P, at most 0.05% S, 0.001 to 0.007% N, 0.008 to 0.2% Al, at least 0.01% Fe. The steel sheet having an average r-value of at least 1.2, an r-value in the rolling direction of at least 1.3, an r-value in the direction of 45 degrees to the rolling direction of at least 0.9, and an r-value in the direction of a right angle to the rolling direction of at least 1.2.

High-strength hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet having fatigue resistance, corrosion resistance, ductility and plating adhesion, after severe deformation, and a method of producing the same

Abstract: The present invention provides: a high-strength high-ductility hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet having high fatigue resistance and corrosion resistance; a high-strength hot-dip galvanized steel sheet excellent in ductility, which improves non-plating defects and plating adhesion after severe deformation, and a method of producing the same; a high-strength and high-ductility hot-dip galvanized steel sheet having high fatigue resistance and corrosion resistance; a high-strength hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet having superior appearance and workability, which suppresses the generation of non-plating defects, and a method of producing the same; and a high-strength hot-dip galvannealed steel sheet and a high-strength hot-dip galvanized steel sheet, which suppress non-plating defects and surface defects and have both corrosion resistance, in particular corrosion resistance in an environment containing chlorine ion, and high ductility, and a method of producing the same.

Modelling Simultaneous Alloy Carbide Sequence in Power Plant Steels

Abstract: A method has recently been developed to estimate the speed with which precipitation reactions occur in power plant steels. It is based on Avrami theory but with an adaptation that allows the treatment of simultaneous reactions. In the present work, a number of approximations and inconsistencies in the theory have been eliminated and this kinetic theory for simultaneous reactions has been modified with the treatments of both diffusion-controlled growth and capillarity effect in multicomponent systems. The modified model can predict not only volume fraction changes of each carbide but also particle sizes. New experimental results on alloy carbide in 3Cr1.5Mo and 21/4Cr1Mo steels are reported and shown to be comparable to the modified theory.

High-strength high-ductility hot dip galvanized steel sheet and its production method

Abstract: PROBLEM TO BE SOLVED: To provide a high-strength high-ductility hot-dip galvanized steel sheet having a strength of >980 MPa, and its production method. SOLUTION: The high-strength high-ductility hot-dip galvanized steel sheet has a tensile strength of >980 MPa and has a hot dip galvanized layer comprising, by mass, 0.001-0.5% Al and 5-20% Fe and the balance being Zn and unavoidable impurities on the surface of a steel sheet. The steel sheet comprises, by mass, 0.0001-0.3% C, 0.1-0.1% Si, 0.001-3% Mn, 0.1-4% Al, 0.0001-0.3% P, ≤0.01% S, 0.01-4% total of Ni and/or Cu, 0.001-1% total of Ti and/or Nb and the balance being iron and unavoidable impurities and has a microstructure containing 50 vol.% ferrite in total as a main phase and ≥3% and <50% austenite and the remaining structure comprising bainite or martensite and bainite. COPYRIGHT: (C)2004,JPO&NCIPI

Modeling M6C precipitation in niobium-alloyed ferritic stainless steel

Abstract: Niobium is used as an important alloying element in the design of heat-resistant stainless steels for automotive exhaust systems. When in solid solution, the niobium improves both the high-temperature strength and the resistance to thermal fatigue life. However, it also forms coarse Fe3Nb3C carbides during service at elevated temperatures, making it important to understand the kinetics of carbide precipitation and coarsening. In the present work, the kinetics of M6C precipitation in ferrite have been modeled, taking into account the multicomponent nature of the diffusion process while at the same time allowing for capillarity effects. The lack of appropriate thermodynamic data has been dealt with using a solubility product based on new experiments on a 19Cr-0.8Nb mass pct steel.

High-strength high-ductility hot dip galvanized steel plate having excellent burring machinability, and method for manufacturing the same

Abstract: PROBLEM TO BE SOLVED: To provide a high-strength, high-ductility hot dip galvanized steel sheet of excellent burring property, and a method manufacturing the same. SOLUTION: This steel sheet contains, by mass, 0.0001-0.3% C, 0.001-4% Si, 0.001-3% Mn, 0.001-4% Al, 0.001-4% Mo, 0.0001-0.3% P, ≤ 0.01% S, 0.001-1% in total one or two or more kinds out of an element group of Mg, Zr, Ca, Y, Hf and lanthanoids group, and the balance Fe with inevitable impurities. In addition, a microstructure of the steel sheet has a composition consisting of, by volume, 50-97% bainite as a main phase, 3-<50% austenite as a second phase, and the balance ferrite. This high-strength, high-ductility hot dip galvanized steel sheet of excellent burring machinability has a plating layer on a surface thereof, having the composition consisting of, by mass, 0.001-0.5% Al, < 20% Fe, and the balance Zn with inevitable impurities. COPYRIGHT: (C)2004,JPO

High strength, high ductility hot-dip galvanized steel sheet having excellent fatigue durability and corrosion resistance

Abstract: PROBLEM TO BE SOLVED: To provide a high strength, high ductility hot-dip galvanized steel sheet which has excellent fatigue durability, and corrosion resistance. SOLUTION: In the high strength, high ductility hot-dip galvanized steel sheet having excellent fatigue durability and corrosion resistance, the surface of a base phase consisting of a steel sheet is provided with a hot-dip galvanizing phase. The maximum depth of an intergranular oxidation phase occurring in the grain boundaries between the plating phase and the base phase is ≤0.5 μm, or the maximum depth of the intergranular oxidation phase is ≤1 μm, and also, the mean grain diameter of the main phase in the microstructure of the base phase is ≤20 μm. COPYRIGHT: (C)2003,JPO

Galvanized high strength steel sheet having excellent formability and production method therefor

Abstract: PROBLEM TO BE SOLVED: To realize a galvanized high strength steel sheet which has excellent formability, and to realize a production method therefor on industrial scales. SOLUTION: The galvanized high strength steel sheet having excellent formability has a composition containing, by mass, 0.01 to 0.30% C, 0.005 to 0.3% Si, 0.1 to 3.3% Mn, 0.001 to 0.06% P, 0.001 to 0.01% S, 0.0005 to 0.01% N and 0.25 to 1.8% Al, and the balance Fe with inevitable impurities, and in which the mass% of Si, Mn and Al also satisfies the following inequality (A), and has a metallic structure containing ferrite and martensite: (0.0012×[TS target value]-0.29-[Si])/1.45 COPYRIGHT: (C)2003,JPO

Steel tube having excellent workability and production method therefor

Abstract: PROBLEM TO BE SOLVED: To provide a method for producing a steel tube which has better formability since the request for a steel tube having high strength to hydroforming increases, and its workability is made into a more serious problem compared with the conventional case, and to provide a production method therefor without spending a high cost. SOLUTION: The steel tube having excellent workability has a composition containing, by mass, 0.08 to 0.25% C, 0.001 to 1.5% Si, 0.01 to 2.0% Mn, 0.001 to 0.06% P, 0.008 to 0.2% Al and 0.001 to 0.007% N, and in which the content of S is controlled to =5 μm, and has an r* value of >=1.2: r*=ln (C0 /C)÷ln (C×L/C0 ×L0 ); wherein, C0 and C are the other circumference (mm) of the steel tube before and after testing, and L0 and L are the distance (mm) between the gauges in the longitudinal direction at each circumferential position of the steel tube before and after testing.

Method for producing steel tube having excellent formability

Abstract: PROBLEM TO BE SOLVED: To provide a steel tube which has excellent formability in hydroforming or the like. SOLUTION: A steel tube having a fundamental composition containing, by weight, 0.0005 to 0.4% C, 0.001 to 2% Si, 0.01 to 3% Mn, =0.03% N, and the balance iron with inevitable impurities is heated to an austenitic region. Its temperature is thereafter reduced to a two phase region, and the steel sheet is subjected to reduction rolling. In this case, its temperature is increased from the two phase region, and the fraction of ferrite is increased, so that both of its n value and r value can be increased. The increase of the temperature can be performed by using an external heat source, or can be performed by utilizing working heat generation.

Steel tube superior in formability and the production method for the same

Abstract: PROBLEM TO BE SOLVED: To provide a steel tube with excellent formability in hydro-forming or the like, and a production method for the same SOLUTION: This steel tube has an excellent formability characterized by the r value of 15 or more in the axial direction of tube, the average value of X-ray random intensity ratio of 20 or more in the group of directions of 110} - 111} on the plane at one half of the thickness of the steel sheet face, the X-ray random intensity ration of 30 or more in the direction of 110} on the plane at one half of the thickness of the steel sheet face and the average value of X-ray random intensity ratio of 30 or less in the group of directions of 100} - 223} on the plane at one half of the thickness of the steel sheet face

Good workability high strength steel pipe and its production method

Abstract: PROBLEM TO BE SOLVED: To provide a high strength steel pipe excellent in formability in hydroforming, or the like. SOLUTION: This good workability high strength steel pipe has a composition containing, by mass, 0.0005 to 0.30% C, 0.001 to 2.0% Si, 0.01 to 3.0% Mn, 0.0001 to 0.0050% S, 0.0001 to 0.0040% O and 0.0001 to 0.030% N, and, if required, containing other elements, and the balance iron with inevitable impurities, in which the area ratio of nonmetallic inclusions with an aspect ratio (the length parallel to the rolling direction/the length vertical to the rolling direction (parallel to the sheet thickness direction)) of >=2 is <=0.05%, and also, the area ratio of nonmetallic inclusions with an aspect ratio of <2 is <=0.03%.

Welded steel pipe superior in molding property and its manufacturing method

Abstract: PROBLEM TO BE SOLVED: To provide a steel pipe resistant to severe molding such as hydroforming and superior in molding property. SOLUTION: The shape and quality of a weld of a welded steel pipe are controlled to set a n-value and a r-value showing plastic deformability at characteristic ranges. For this purpose, the average r-value and shape of a raw plate and a temperature for reheating treatment after pipe formation are specified in specific ranges.

Method for manufacturing welded steel tube having excellent workability, and welded steel tube

Abstract: PROBLEM TO BE SOLVED: To provide a welded steel tube having excellent workability and uniformity including a welded area. SOLUTION: In the method for manufacturing the welded steel tube having excellent workability, a welded steel tube prepared by means of welding in a tube-axis direction is subjected, after welding, to reheating treatment, such as normalizing or solid solution heat treatment, where the weld zone including heat affected zone is held at a temperature not lower than the Ac3 transformation point of the material for >=1 s and inversely transformed and successively cooled to form the structure of the weld zone into recrystallized structure with respect to as-welded structure and then the steel tube is subjected to reheat treatment such as solution heat treatment and then subjected, in a tension- applied state, to diameter-reduction deformation at a temperature as high as >=500 deg.C. A steel sheet having >=1.0 average r-value and >=0.2 n-value can be used as a stock. As diameter-reduction rolling conditions, rolling finishing temperature and reduction of area are made to a value not higher than the Ac3 transformation point and >=40%, respectively.

Steel sheet excellent in workability and method for producing the same

Abstract: The present invention provides a steel sheet excellent in workability, which may be used for components of an automobile or the like, and a method for producing the same. More specifically, according to one exemplary embodiment of the present invention, a steel sheet excellent in workability, including in mass, 0.08 to 0.25% C, 0.001 to 1.5% Si, 0.01 to 2.0% Mn, 0.001 to 0.06% P, at most 0.05% S, 0.001 to 0.007% N, 0.008 to 0.2% Al, at least 0.01% Fe. The steel sheet having an average r-value of at least 1.2, an r-value in the rolling direction of at least 1.3, an r-value in the direction of 45 degrees to the rolling direction of at least 0.9, and an r-value in the direction of a right angle to the rolling direction of at least 1.2.