Alloys or metallic compositions – Ferrous – Nine percent or more chromium containing
Patent
1989-04-28
1990-09-18
Yee, Deborah
Alloys or metallic compositions
Ferrous
Nine percent or more chromium containing
420103, 420 62, 420 84, 148306, 148309, C22C 3806, C22C 3818
Patent
active
049576992
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a soft magnetic steel suitable for magnetic core materials for electronic fuel injection systems, solenoid valves, electromagnetic sensors, etc., improved in electric properties, magnetic properties such as coercive force, magnetic flux density, and magnetic response, cold forgeability, machinability, and corrosion resistance.
BACKGROUND OF THE INVENTION
High electric resistance for improved magnetic response and improved pulse response to increase pulse frequency are demanded for the magnetic core materials for the recently developed electronic fuel injection systems, solenoid valves, electromagnetic sensors, etc. Further, corrosion resistance to improve environmental adaptability, an excellent cold forgeability and machinability for cost reduction, are also required.
Pure iron, 3Si-iron, 13Cr-2.5Si steel, and 13Cr-1Si-0.25Al steel are currently used for the core materials of the above-mentioned applications.
Pure iron has excellent cold forgeability, however, is poor in electric resistance, magnetic properties and response, and coercive force. 3%Si-iron has an electric resistance of 60.mu..OMEGA..cndot.cm, which is not sufficient, and as the same as in the case of pure iron, is poor in magnetic response and coercive force in addition to corrosion resistance and cold forgeability.
13Cr-2.5Si steel shows excellent electric resistance and corrosion resistance, however, is inferior in magnetic properties, cold forgeability, and machinability. 13Cr-1Si-0.25Al steel excels in corrosion resistance and machinability, but on the other hand, does not have satisfactory electric resistance, magnetic response, coercive force, magnetic flux density, and cold forgeability.
As above mentioned, no currently available steel suffices in all the electric properties (electric resistance), magnetic properties such as magnetic response, coercive force, and magnetic flux density, cold forgeability, machinability, and corrosion resistance.
DISCLOSURE OF THE INVENTION
The invention, as a solution to the aforesaid problems of the conventional steels used as the core materials for electronic fuel injection systems, solenoid valves, electromagnetic sensors, etc., possess characteristics essential to the aforesaid core materials, which are electric resistance of 90 .mu..OMEGA..cndot.cm or higher, excellent magnetic properties such as a coercive force of 0.7 Oe or lower, magnetic flux density of 13000 G or higher, and magnetic response with relaxation time of 0.7 msec or shorter, together with improved cold forgeability with a tensile strength of 44 KgF/ mm.sup.2 or lower, and with increased corrosion resistance and machinability.
The inventors, with a view to overcoming the above mentioned problems of the conventional steels, have carried out concentrated studies on the effects of the each alloy element on the electric properties, magnetic properties such as magnetic response, coercive force, and magnetic flux density, corrosion resistance, and cold forgeability, and finally achieved the completion of the invention.
First, electric resistance and tensile strength are conflicting properties. When an amount of Si was increased to raise the electric resistance, the tensile strength also increased, leading to poor cold forgeability. This is clearly read in FIG. 1, wherein the tensile strength is related to the electric resistance of the Fe-Si system steel. It is illustrated in the Fe-Cr-Al system that at the addition of 7 to 13% Cr together with 2 to 5% Al, electric resistance, force are improved without significant raise in tensile strength.
Secondly, the addition of 7 to 13% Cr together with 2 to 5% Al noticeably increased the corrosion resistance, which was unpredictable from individual additions.
Thirdly, it was also without affecting of CR and al on the cold forgeability, the contents of the solid-solution strengthening elements such as C, N, Si, and Mn and impurities such as Cu, Ni, and Mo should be as reduced as much as possible. It was then found that when the impurit
REFERENCES:
patent: 1710805 (1929-04-01), Smith et al.
Fujii Hideki
Honkura Yoshinobu
Murata Koji
Aichi Steel Works Ltd.
Yee Deborah
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