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Kitamoto, Japan

Matsui T.,MMC Superalloy Corporation
Materials Transactions | Year: 2013

Ni base superalloy is one of the representative heat resistant materials for high temperature environment in various industrial applications. As for cast and wrought material, thermo-mechanical processing during hot forging has a significant role to control and optimize crystal grain structure in order to attain required critical properties. The essential deformation and dynamic recystallization behavior of Ni base superalloy, Alloy718 during hot forging were revealed through hot compression tests and quantitative relations among various parameters that were available for numerical calculation were derived. Dynamically recrystallized grain diameter depended on temperature, strain rate and was independent of initial grain diameter and strain. And the grain diameter was expressed as a function of the temperature compensated strain rate, i.e., ZenerHollomon parameter quantitatively. Avrami-type equation was available for comprehensive and quantitative expression of dynamic recrystallization transition tendency. And the fraction of dynamic recrystallization was a function of the given strain and the strain for 50% recrystallization which depended on the initial grain diameter and ZenerHollomon parameter. © 2013 The Japan Institute of Metals. Source


Matsui T.,MMC Superalloy Corporation
Materials Transactions | Year: 2014

Ni base superalloy is one of the most important key materials for hot section parts in various applications. As for cast and wrought material, it is well known that grain size distribution and recrystallization ratio as well as precipitation condition have considerable effect on mechanical properties. The deformation and dynamic recrystallization behavior of representative Ni base superalloy, Waspaloy were revealed through various kinds of hot compression tests and quantitative relationship available for numerical calculation technology was derived. Dynamically recrystallized grain diameter depended on temperature, strain rate and was independent of the initial grain diameter and strain. The grain diameter could be expressed as a function of the temperature compensated strain rate, i.e., ZenerHollomon parameter quantitatively. Avramitype equation was available for comprehensive and quantitative expression of dynamic recrystallization transition. The approximation was a function of the given strain and strain for the 50% recrystallization which depends on the initial grain diameter and ZenerHollomon parameter. © 2014 The Japan Institute of Metals and Materials. Source


Sugahara K.,MMC Superalloy Corporation | Sugahara K.,Tohoku University | Sakai H.,MMC Superalloy Corporation | Saito H.,MMC Superalloy Corporation
Zairyo to Kankyo/ Corrosion Engineering | Year: 2011

Corrosion resistance to crevice corrosion attack of welds made with various Ni-Cr-Mo(-Ta) alloy fillers connected to Ni-based alloy plates in a hot concentrated NaCl solution was investigated using the technique of measuring repassivation potentials for crevice corrosion (ER, CREV). The ER,CREV of the test electrode with a weld could be regard as it of the weld. Under this condition it was made clear that the dendrite core where was the alloy element depleted region determined the corrosion resistance to crevice corrosion attack of the weld to be degraded it. ER, CREV of weld has linear relationship to Pitting Resistance Equivalent with tantalum (PRE(Ta)=[%Cr]+3. 3([%Mo]+[%0.5]0.5[%W])+7.7[%Ta]) which is calculated from dendrite core composition. The line consistents with the relationship between ER, CREV of base metal and PRE(Ta) which is calculated from its chemical compotion. Under more severe conditions for crevice corrosion such as higher temperature, the ER, CREV of alloy 22 showed the same value with it of the weld made with the filler having the same composition of the base metal. It was suggested that the depnendance of the corrosion resistance to crevice corrosion attack of the weld changed into its average chemical composition from the dendrite core composition. Source

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