Solidification synthesis of cast metal-ceramic particle composite materials by dispersing hard or soft ceramic particles (including microballoons) and short fibres in molten alloys before solidification is described. Microstructures synthesized using a variety of casting techniques such as gravity or pressure die casting, centrifugal casting, and squeeze casting are discussed. Techniques to obtain a selected distribution of dispersed particles in cast alloy matrices by controlling solidification parameters and inducing melt particle wettability are reviewed. These cast metal-ceramic particle composites represent low cost, high performance, tailor made substitute materials for a variety of automotive and electromechanical applications such as pistons, cylinder liners, bearings, and current collectors, resulting in savings of material and energy.

Solidification, structures, and properties of cast metal-ceramic particle composites

Effect of strain-induced martensite on hydrogen environment embrittlement of sensitized austenitic stainless steels at low temperatures

The influence of nanocrystalline structure and processing route on corrosion of stainless steel: A review

On the dominant mechanism of irradiation embrittlement of reactor pressure vessel steels

The effect of hydrogen and stress (strain) on the stability of the austenite phase in stainless steels was investigated. Hydrogen was introduced by severe cathodic charging and by elevated temperature equilibration with high pressure H2 gas. Using X-ray diffraction and magnetic techniques, the behavior of two “stable” type AISI310 steels and an “unstable” type AISI304 steel was studied during charging and during the outgassing period following charging. Transformation from the fcc γ phase to an expanded fcc phase, γ*, and to the hcp e phase occurred during cathodic charging. Reversion of the γ* and e phases to the original γ structure and formation of the bcc α structure were examined, and the kinetics of these processes was studied. The γ* phase was shown to be ferromagnetic with a subambient Curie temperature. The γ⇆e phase transition was studied after hydrogen charging in high pressure gas, as was the formation of a during outgassing. These results are interpreted as effects of hydrogen and stress (strain) on the stability of the various phases. A proposed psuedo-binary phase diagram for the metal-hydrogen system was proposed to account for the formation of the γ* phase. The relation of these phase changes to hydrogen embrittlement and stress corrosion cracking of stainless steel is discussed.

Hydrogen-related phase transformations in austenitic stainless steels

The effect of dissolved hydrogen in soft iron and ferritic low alloy steel on general corrosion was investigated in acid solutions. Hydrogen charging was carried out in 1 to 28 MPa hydrogen at 723 K for 57.6 ks. Weight loss of hydrogen charged ferritic steels was markedly greater than that of hydrogen-free ones, and increased with increasing hydrogen content. Plastic deformation of steels increased the dissolved hydrogen content, and the anomalous corrosion increased with cold working ratio. Anodic polarization curves of hydrogen charged soft iron and low alloy steel in 0.5 kmol/m3-H2SO4 solution exhibited an increase of current density in the passive region in agreement with the corrosion data. This anomalous corrosion was partly recovered by dehydrogenation heating at 573 to 1223 K. The anomalous corrosion was dependent on the residual hydrogen content and independent of the structure. It is suggested that the anomalous behavior is caused by activated internal microdefects in steel formed by hy...

Anomalous Corrosion of Hydrogen-Containing Ferritic Steels in Aqueous Acid Solution

A new technique, Spray-Dispersion Method, which produces a steel containing homogeneously dispersed fine oxide particles sprayed from outside into the molten steel stream has been developed. The conditions for the distribution of particles in solid steel, and the mechanical properties of A12O3- or ZrO2-dispersed steels were studied. The homogeneous distribution of fine oxide particles is obtained by the addition of a certain suitable controlling element which lowers the contact angle of molten steel on various oxides and the interfacial tension at the oxide—molten steel interface. Among others columbium (niobium) was found to be the most effective on decreasing the average particle size of sprayed oxides. Because of fine dispersion of particles of less than 120 nm, the strength of steels increased with their volume fractions; for example, 1.15 vol pct ZrO2 causes an increment of 79 MN/m2 in proof strength and 94 MN/m2 in tensile strength. For practical applications, the Spray Dispersion Method makes it possible to produce 18 chromium-8 nickel austenitic stainless steels dispersion-strengthened by A12O3 or ZrO2 particles, and ThO2-dispersed nickel with an average particle size of 61.4 nm and a volume fraction of 5.1 pct.

Strengthening of steel by the method of spraying oxide particles into molten steel stream

The effect of dissolved hydrogen on intergranular and general corrosion of austenitic stainless steels was investigated. Hydrogenation was carried out in 1 to 28 MPa hydrogen at 723 K for 16 hours. The corrosion rate of hydrogenated AISI 304 stainless steel, with precipitated carbides in grain boundaries or contained martensites, was markedly greater than that of hydrogen-free ones. This anomalous corrosion increased with the hydrogen content of steel. The current density of the anodic polarization curves of hydrogenated specimens was greater than that of hydrogen-free ones, which coincided with the corrosion data. This anomalous corrosion recovered with the short time heating at 923 K and above, but not with the heating at 873 K and below. These behaviors can be interpreted by the formation of internal microdefects, which are active sites, and impair the passivation characteristics, caused by hydrogen trapping.

Anomalous Corrosion of Austenitic Stainless Steel Exposed to Hydrogen at High Temperature and Pressure

Ultrafine grained AISI 304 steel was produced by low temperature recrystallization after subzero working, and the corrosion behavior of these steels was investigated in various corrosive e...

Masayoshi Hasegawa

Papers

Anomalous Corrosion of Hydrogen-Containing Ferritic Steels in Aqueous Acid Solution

Strengthening of steel by the method of spraying oxide particles into molten steel stream

Anomalous Corrosion of Austenitic Stainless Steel Exposed to Hydrogen at High Temperature and Pressure

Corrosion Behavior of Ultrafine Grained Austenitic Stainless Steel

Effects of Copper and Phosphorus on Temper Embrittlement of Mn–Mo–Ni Low Alloy Steel (ASTM A533–B)