Kawasaki Steel Corporation

Hiroshi Ohtsubo

Yoshisato Kiyota

Junichi Ohta

Kuniaki Ogura

Shigeaki Takajo

Minoru Nitta

Tatsuo Kawasaki

Yoshiaki Maeda

Isao Takada

Hiroyuki Ishikawa

Takeo Omura

Masakazu Matsushita

Masaki Kawano

Yasuhiro Habu

Ichio Sakurada

Yutaka Yoshii

Toshio Watanabe

Keisuke Yoshimura

Yutyaka Yoshii

Yukio Makiishi

Martensitic stainless steels that enable the fabrication of high-strength seamless steel pipe suited for use in oil-well pipe and pipeline tubing by means of a Mannesmann plug mill or Mannesmann mandrel mill process, without the formation of defects during production. The heat workability of these steels, which contain no more than 0.30% by weight of carbon and from 11 to 14% by weight of chromium, and have a ferrite content of at least 40% at 1200.degree. C., has been vastly improved by holding the phosphorus and sulfur levels therein to no more than 0.020% and 0.003% by weight, respectively.

Martensitic stainless steels for seamless steel pipe

This invention is to control the diffusion of C (carbon) from added graphite to particles of iron powder in the sintering to thereby improve the accuracy of dimensional change in the sintered body by using iron powder for powder metallurgy and a mixed powder thereof as a starting material in the production of sintered mechanical parts by adding the iron powder with Cu powder and graphite powder and companying and sintering them, in which 0.008-0.5 wt % in total of at least one element having a value of standard free energy of formation of oxide at 1000.degree. C. of not more than -120 kcal/l mol of O.sub.2 is included in the iron powder and not less than 20% of the element is rendered into an oxide, or 0.01-0.20 wt % in total of an oxide powder of at least one element having a value of standard free energy of formation of oxide at 1000.degree. C. of not more than -120 kcal/l mol of O.sub.2 is added to the mixed powder.

Iron powder and mixed powder for powder metallurgy as well as method of

A debinding method for use in a process for producing a sintered object, by effecting a debinding pre-treatment by heating the injection-molded object in an atmosphere of reduced pressure at a temperature at which the vapor pressure of the component of the organic binder having the highest vapor pressure does not exceed the pressure of the atmosphere, thereby removing the organic binder in the amount of at least about 18 wt %; and effecting a further debinding heat treatment in which the injection-molded object is heated to and maintained at a temperature higher than the temperature in the debinding pre-treatment.

Method of debinding for injection molded objects

There is provided alloy steel powders for the injection molding use manufactured by the atomizing method which are characterized by their substantially spherical particle shape and average particle diameters of 20 microns or less, a compound for the injection molding use which contains the alloy steel powders and one or more organic binders, a process for manufacturing sintered materials in performing injection molding of compound and subsequently debinding the obtained injection molded part followed by sintering the debound part, at least the first stage of the sintering step is performed in reduced pressure atmosphere, and the sintered material having a relative density ratio of 92% or more.

Alloy steel powders for injection molding use, their compounds and a

Corrosion-resistant sintered alloy steels and method for making same

A process is provided for the production of a sintered body. The process includes the following consecutive steps: i) mixing and kneading one or more metal powders and/or one or more alloy powder with a binder into a compound, said metal and alloy powders having an average particle size not greater than 30 .mu.m, ii) injection-molding the compound into a green body; iii) debinding the green body to form a debound body; and iv) subjecting the debound body to a first-stage sintering at 1,050.degree.-1,250.degree. C. in a reduced-pressure atmosphere and then to second-stage sintering at a temperature in a range of 1,100.degree.-400.degree. C. which is higher than that of the first-stage sintering. This process can provide sintered Ti bodies and sintered magnetic bodies of the Fe-Si type, which have a density ratio of at least 95%.

Sintered bodies and production process thereof

It is disclosed a method for preparing a large-sized powder metallurgical sintered product having a superior characteristic by charging mixtures of three types of metallic powder composed of coarse particles, middle particles and fine particles into the molding die while vibrating it, heating the charged material together with the molding die, sintering them, and infiltrating metal of low melting point into the sintered body. According to this method, it is possible to get a large-sized sintered body having a superior strength and surface smoothness or a sintered body prohibiting any cracks or slits by arranging the proper particle size.

Method for preparing powder metallurgical sintered product

A process is provided for the production of a sintered body. The process includes the following consecutive steps: (i) mixing and kneading one or more metal powders and/or one or more alloy powder with a binder into a compound, said metal and alloy powders having an average particle size not greater than 30 .mu.m, (ii) injection-molding the compound into a green body; (iii) debinding the green body to form a debound body; and (iv) subjecting the debound body to first-stage sintering at 1,050.degree.-1,250.degree. C. in a reducing or reduced-pressure atmosphere and then to second-stage sintering at a temperature in a range of 1,100.degree.-1,400.degree. C. which is higher than that of the first-stage sintering. This process can provide sintered Ti bodies and sintered magnetic bodies of the Fe-Si type, which have a density ratio of at least 95%.

A duplex stainless steel seamless pipe can be inexpensively produced in high productivity and yield without causing cracks during the working steps in the plug mill process by a proper combination of the composition of the steel and the working conditions of a billet and a hollow piece for the production of the pipe.

Duplex stainless steel seamless pipe and a method for producing the same

A method of manufacturing bimetallic tubes is disclosed. In this method, after an inner tube is inserted into an outer tube, the resulting tube assembly is heated, while pressurizing the inside of the inner tube with a gas, in the presence or absence of a solder material. When using no solder material, the materials of the inner and outer tubes are so selected that a thermal expansion coefficient of the inner tube is smaller than that of the outer tube.

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Chiba, Japan

Hiroshi Ohtsubo