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Takahashi M.,Steel Research Laboratorie | Suehiro M.,A-D Technologies | Ochi T.,Muroran R and D Laboratory | Miyazaki Y.,Welding and Joining Research Center
Nippon Steel Technical Report | Year: 2012

Steel production in Japan grew in tandem with the growth in domestic automobile production. Understandably, therefore, past development and expansion of the Japanese steel industry cannot be discussed without reference to the automotive industry of Japan. While the collision characteristics of a complete car body are ultimately evaluated through crash tests using real automobiles, to clarify the effects of individual improvement measures, it is necessary to examine the deformation behavior of the structure of the whole body prescribed parts and of the individual parts. While the crash energy absorbing property of frontal or rear collision by plastic deformation increases with increasing strength of the steel used, press formability improves with decreasing strength, and for this reason, steel sheets that are soft at the time of press forming and harden at the time of use, or those having strength highly dependent on strain rate, are desirable. However, the strain-rate dependence of steel strength decreases as the strength increases.

Tarui T.,Bar and Wire Rod Research Laboratory | Kubota M.,Muroran R and D Laboratory
Nippon Steel Technical Report | Year: 2012

Evaluating the delayed fracture characteristics of steel materials on the basis of the hydrogen amount has been made possible largely by establishment of the know-how of hydrogen charging and hydrogen analysis, as well as development of the gas chromatograph and quadrupole mass spectrometer that permit measuring extremely small amounts of hydrogen contained in steel with an accuracy of 0.01 ppm. In addition, hydrogen thermal desorption spectroscopy using those hydrogen analyzers has made it possible to separate non-diffusible hydrogen from diffusible hydrogen in steel and estimate the existence state of hydrogen in steel. On the other hand, alloy carbides having a fine and coherent stain field help trap hydrogen. Takahashi et al. charged deuterium into steel material containing fine TiC precipitates and analyzed the condition of the hydrogen in the steel using a three-dimensional atom probe (3DAP).

Monden A.,Muroran R and D Laboratory | Yamasaki S.,Muroran R and D Laboratory | Miyanishi K.,Muroran R and D Laboratory | Ochi T.,Muroran R and D Laboratory
Nippon Steel Technical Report | Year: 2013

Many mechanical parts for automotive power train and undercarriage are manufactured by forging, machining, and heat treatment using special steel bars and wire rods. Cold forging can give more precise dimensions than hot forging, therefore machining cost can be greatly reduced by converting hot forging to cold forging. Although Nippon Steel Corporation already developed softened low-carbon steels for cold forging by applying TMCP technology to bar and wire rod rolling processes, demands for middle-carbon steels for cold forging have arise recently. This paper outlines the development of middle-carbon steel bars and wire rods for cold forging "Super Forging steel (SF)".

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