Nobuyasu Kawai

Behavior of Nitrogen Absorption into High Speed Tool Steel Powders

Behavior of nitrogen absorption into gas atomized high speed tool steel powders has been studied by using thermo-balance in nitrogen atmosphere from 950°C to 1195°C.As the results, it has become clear that the absorbed nitrogen contents of high speed tool steel powders are in proportion to vanadium contents of the powders and the nitrogen absorbed exists as vanadium carbonitrides in the powders. Also, the nitrogen contents of the powder are not dependent on particle size, but on nitriding temperature. And the saturated nitrogen contents are higher at lower temperature.Nitrogen absorption rate into the powders is faster as the particle is finer and nitriding temperature higher.It was found that the rate-determining process of nitrogen absorption into the powders is the reaction of nitrogen molecule dissociation to atomic nitrogen on the particle surface.

Properties of Ni-base Superalloy Powders Produced by Ar Gas Atomization

The fatigue properties of P/M superalloys can be significantly damaged by defects, which act as sites for fatigue fracture initiation. These defects can be introduced as inclusions either during the melting operation, during powder atomization or during subsequent handling.Equipments for producing cleaner powders by Ar gas atomization have been designed and installed, and the properties of produced MERL76 superalloy powders were examined. As a result, this method was capable of producing fine and clean powders with an average grain size of 56 μm and an oxygen content of less than 100 ppm. Results also indicated that the amount of non-metallic inclusions of produced powders was less than those in the commercialized powders, which was detected by the new water elutriation method.

Mechanical Properties of High Carbon Adamite P/M Steels

Five compositions of high carbon adamite steel powders (1.8%C, 2.2%C, 2.6%C, 2.9%C, and 3.7%C+1. 2%Ni+1.2%Cr+0.3%Mo) were produced by gas-atomization, and their fully densified P/M steel billets were made by hot isostatic pressing. Microstructures and mechanical properties of the P/M steels were investigated in comparison with the conventional adamite steel (1.7%C+l.2%Ni+l.2%Cr+0.3%Mo).In the P/M steels, fine carbides are uniformly distributed, whereas in the conventional steel, large-sized carbides are distributed among fine carbides.Mechanical properties of the P/M steels are as follows: The wear property of the P/M steels is improved with the increase of carbon content. On the contrary, the bend strength and fire cracking properties are decreased with increasing carbon content. But, these properties of the 2.5%C adamite P/M steel are found to be superior or equivalent to those of the conventional steel.