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Yonemura S.,Kimitsu R and D Laboratory | Uenishi A.,Steel Research Laboratories | Kosugi S.,Mathematical Science and Technology Research Laboratory | Yoshida T.,A-D Technologies | And 2 more authors.
Nippon Steel Technical Report | Year: 2013

Bake-hardenable steel sheets are often used in exterior automotive body panels, such as doors, hoods, and fenders, because these applications require high strength for dent resistance as well as low yield strength for surface deflection. The dent resistance depends on the yield strength of materials after work hardening by forming and strain ageing by paint baking. In this study, the anisotropy of yield strength has been investigated in a uniaxially prestrained and baked bakehardenable steel. On the other hand, surface deflection is investigated by press forming experiments and their numerical simulations of the exterior door panel model. Emphasis is placed on the effects of mechanical properties and press forming condition on surface deflection are discussed. Furthermore, a new system for evaluation and visualization of surface deflection using Gaussian curvature is presented.


Yamada W.,Mathematical Science and Technology Research Laboratory | Honda K.,Kimitsu Works | Tanaka K.,Materials Characterization Research Laboratory | Ushioda K.,Nippon Steel & Sumitomo Metal Corporation
Nippon Steel Technical Report | Year: 2013

The solidification structure of the coating layer in hot-dip Zn-11%Al-3%Mg-0.2%Si coated steel sheet was studied by metallographic examinations together with the calculation of a phase diagram based on Thermo-Calc. The observation exhibited that the solidification structure is a combination of the Zn/Al/MgZn2 ternary eutectic structure, the primary fcc-Al phase and the MgZn2 phase, which is different from the predicted one under an equilibrium state in the sense that meta-stable MgZn2 instead of stable Mg2Zn11 was observed under the present condition. Excluding the Mg2Zn11 phase from the equilibrium phase diagram, the metastable phase diagram was calculated and excellent agreement was obtained between the calculation and the experiment in terms of the solidification structure of the coating layer. The small amount of Ti addition to the coating bath was confirmed to lead to the formation of fine dendrite structure. Detailed EBSD observation revealed that TiAl3 acts as heterogeneous nucleation sites of the primary fcc-Al.


Yamamoto K.-I.,Process Technology Center | Toh T.,Mathematical Science and Technology Research Laboratory | Hamatani H.,Nagoya R and D Laboratory | Tsunenari K.,Plant Engineering and Facility Management Center | And 4 more authors.
Nippon Steel Technical Report | Year: 2013

Tramp elements such as Cu cause a severe hot shortness. However, Cu is the useful alloying element for increasing hardness and improvement of the steel properties and Cu is often added to the steels. Therefore, by means of a steel surface melting technology, hot shortness should be suppressed by the addition of Ni only in the surface layer. After hotrolled, the sheets are sandblasted and checked for surface defects due to hot shortness. There are no defects and steel samples alloyed in the surface layer are very clean. Consequently, steel containing Cu alloyed Ni in the surface layer does not indicate hot shortness at the surface.


Kawakami K.,Mathematical Science and Technology Research Laboratory
Nippon Steel Technical Report | Year: 2013

The analysis ab-initio calculations about the trap state of hydrogen atoms by the carbides in bcc-Fe were performed and showed following results. The main trap site of small TiC precipitate is coherent interface, that of the small VC precipitate is carbon vacancy and the strain fields around the precipitates have only small trap energy. The cementite has week trap sites on the inside. The diffusion paths between them are through some semi-stable sites and the minimum potential barrier from the stable trap to the semi-stable site correspond to the activation energy of de-trap from cementite.


Tani M.,Yawata Steel Works | Zeze M.,Yawata Steel Works | Toh T.,Mathematical Science and Technology Research Laboratory | Tsunenari K.,Plant Engineering and Facility Management Center | And 4 more authors.
Nippon Steel Technical Report | Year: 2013

In the electromagnetic casting (EMC) technique, an electromagnetic field is imposed by a solenoidal coil and a Lorentz force is generated at a meniscus. Consequently, a smooth cast surface without defects can be expected. So far concerning with EMC, the billet casting plant test, the slab casting bench scale test on pilot caster and the numerical simulation have been conducted. Finally the slab casting plant tests with the EMC technique were conducted. The castings were very stable and produced without any major difficulties. The qualities of slab cast were greatly improved by the EMC technique.


Nakashima J.,Process Technology Center | Toh T.,Mathematical Science and Technology Research Laboratory
Nippon Steel Technical Report | Year: 2013

In order to achieve high quality slab production, to assess the cleanliness of the slab and the cleanliness of the molten steel in the tundish in continuous casting process, made it clear aggravating factor of cleanliness. To ensure the cleanliness of the continuously cast slabs, it is important to prevent the ladle slag outflow, tundish slag entrapment at the teeming point of tundish, and air oxidation. By the application of molten steel flow in mold control technology using electromagnetic force was developed by Nippon Steel Corporation (In-mold electromagnetic stirring and Level Magnetic Field), the slab can be manufactured with excellent internal cleanliness and surface cleanliness of slabs.


Yamamura K.,Process Technology Center | Matsuzaki S.,Process Technology Center | Toh T.,Mathematical Science and Technology Research Laboratory | Yamada W.,Mathematical Science and Technology Research Laboratory | Nakagawa J.,Mathematical Science and Technology Research Laboratory
Nippon Steel Technical Report | Year: 2012

The finite element method (FEM) has become the most popular and most widely used technique to analyze discrete structures. FEM made its debut in the 1950s and soon developed into an approximate analysis method based on the variational principle in solid mechanics. In the late 1960s, the application of FEM was extended first to nonlinear structural problems and then to nonstructural problems. In the meantime, many types of general-purpose code were announced. Most conventional analyses of solidifying shell behavior employ the non-steady method in which the system of coordinates is fixed to the unit intercept of the slab. This method permits calculating the temperature and stress while changing the surrounding boundary conditions on a time-serial basis. However, it neglects the temperature gradient and stress gradient in the casting direction. In view of the above problem, a method which takes viscoplastic behavior into consideration and which analyzes the solidifying shell behavior in the velocity field under the space-fixed system of coordinates as in the rigid-plastic analysis of rolling was proposed.

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