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Publication numberUS3620856 A
Publication typeGrant
Publication dateNov 16, 1971
Filing dateDec 17, 1968
Priority dateDec 17, 1968
Also published asDE1954006A1, DE1954006B2
Publication numberUS 3620856 A, US 3620856A, US-A-3620856, US3620856 A, US3620856A
InventorsHiraoka Hideto
Original AssigneeSanyo Electric Works
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Process to improve magnetic characteristics of carbon steel
US 3620856 A
Abstract  available in
Images(1)
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Claims  available in
Description  (OCR text may contain errors)

United States Patent Hideto I-Iiraoka Karnitsuchii, Gifu, Japan [21] AppLNo. 784,405

[72] Inventor [22] Filed Dec. 17, 1968 [45] Patented Nov. 16, 1971 [73] Assignee Sanyo Electric Works Ltd.

Kamitsuchii, Giiu, Japan [54] PROCESS TO IMPROVE MAGNETIC CHARACTERISTICS OF CARBON STEEL OTHER REFERENCES Metals Handbook, Vol. 2, 8th Edition, Published by the American Society for Metals, 1964, pages 69- 71.

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-G. K. White Attorney-Mason, Fenwick & Lawrence ABSTRACT: The process to improve magnetic characteristics of conventional low-carbon, rimmed steel having the chemical composition, carbon: 0.25 weight percent, silicon: 0.5 weight percent, manganese: 1.65 weight percent, phosphorus: 0.05 weight percent, sulfur: 0.05 weight percent, copper: 0.5 weight percent, and other elements: 0.l weight percent, comprising:

A first stage of raising the temperature of carbon steel above the A, transformation temperature of approximately 850-910 C. wherein the a-phasefi-rphase transformation takes place in a controlled atmosphere with a dew point of approximately 5 to 50 C., or a water vapor pressure of 69-925 Torr.

A second stage of lowering rapidly the temperature of the carbon steel below 723 C., but not lower than 600C maintaining the carbon steel at this temperature for 3 to 10 hours in a weakly oxidizing atmosphere.

A third stage of lowering and maintaining said carbon steel at a temperature of 300 to 400 C. for l to 2 hours for the purpose of obtaining large ferrite grains in which less than 0.01 weight percent of carbon is present dissolved in the matrix and the residual carbon is present at ferrite grain boundaries, and not in the matrix.

A low-carbon, rimmed steel having a ferrite matrix and chemical composition: less than each of the following: 0.25 weight percent carbon, 0.5 weight percent silicon, 1.65 weight percent manganese, 0.05 weight percent phosphorus, 0.05 weight percent sulfur, 0.5 weight percent copper, and 0.1 weight percent other elements, and wherein the ferrite matrix is in the form of grains sufficiently large in particle size to be less than 10 particles per mm), said grains having less than 0.01 weight percent of carbon dissolved in the ferrite matrix, and the residual carbon being present at ferrite grain boundaries and not in the ferrite matrix.

l 1 l r r r I NIAQNETIC FLUK DQ SITY TH RH LOSS OF CARBON STGL AF ER EAT TIBATMINT CARBON STIEL BEFORE INNIALING CONVENTIQNQL FLETRIAL THE coRE CARBON STEEL BEFORE ANNEAuNc CONVENTIONAL CARBON ,STEEL BEFozE HEAT TREATMENT (O-4mm THIC K) CONVE NT \ONAL.

E LUCTRICAL ST BEI- (o-s m m THICK) MAGNETK'. FLUX DENSITY LOSS OF CARBON STEEL AFTER HEAT TREATMENT, if CONVENHONAL ELECTRICAL.

INVENTOR HIOIIIO HHZAOKA ATTORNEYS \J (GA-m m TmcK) PROCESS TO IMPROVE MAGNETIC CHARACTERISTICS OF CARBON STEEL This invention relates to the use of conventional low-carbon, rimmed steel sheet for a core of transformers and other electric devices and to a process to improve the magnetic characteristics of conventional low-carbon, rimmed steels.

As is well known, the magnetic materials used for transformers must posess high saturated magnetic flux density, high penneability, high electrical resistance, and low core loss.

In general, the art used many types of electrical steels as magnetic materials but, for economy, carbon steels are generally less expensive than electrical steels and would be therefore preferred if it were not for the undesirable magnetic characteristics of conventional low-carbon, rimmed steel.

It is the primary object of the present invention to improve the magnetic characteristics of conventional low-carbon, rimmed steels in order that such lower cost conventional lowcarbon, rimmed steels may be used in magnetic systems.

This and other objects of the present invention will be apparent from a careful study of the following specification accompanied by the drawing wherein the FIGURE is a graphic representation of the comparison of the carbon steel treated according to the present invention and conventional low-carbon, rimmed steel and electrical steel.

Carbon steels to which the present invention relates have the following chemical composition: carbon: 0.25 weight percent, silicon: 0.5 weight percent, manganese: 1.65 weight percent, phosphorus: 0.05 weight percent, sulfur: 0.05 weight percent, copper: 0.5 weight percent, and other elements: 0. 1 weight percent.

The process of this invention consists of three stages.

First stage--the temperature of given carbon steels is raised above A, transformation temperature of 850-910 C. wherein a-phase y-phase transformation takes place for 0.1 to 2.0 hours in an oxidizing atmosphere with the chemical composition; C: 0-10 volume percent, C0,: 6-13 volume percent, 1-1,: 0-5 volume percent, N,: residual, while keeping the water vapor pressure between 6.9 Torr to 92.5 Torr, enough to promote decarburization, desulfurization, and dephosphorization. The dew point of the atmosphere must be kept between to 50 C. for this purpose. This is because carbon, sulfur, and phosphorus are injurious to magnetic properties of carbon steels. During the first stage, the carbon steels are purified, and the original rolled structure is destroyed until no crystal anisotropy remains.

Second stage-The temperature of the carbon steel is lowered as rapidly as possible below 723 C. but not lower than 600 C., and kept at this temperature for 3 to hours. Through this quick lowering of temperature, stress energy induced by transformation is stored in the carbon steels, and this energy promotes the growth of ferrite grains. While the process is in progress, the dew point of the atmosphere must be lower than 5 C. and the chemical composition of this atmosphere in this stage is as follows:

CO: 2-12 volume percent, C0,: 6-12 volume percent, 1-1,:

1-15 volume percent, N,: residual. The atmosphere is preferably weakly oxidizing.

During this treatment, the cementite in the matrix precipitates along grain boundaries, the grain size becomes coarse, and the magnetic characteristics of the carbon steels are improved.

Third stage-The temperature of carbon steels is lowered slowly in order to avoid the appearance of thermal stress, and is kept at 300 to 400 C. for 1 to 2 hours. The chemical composition of this atmosphere in this stage is the same as that in the second stage. After this treatment, the carbon steels are taken out of the furnace.

The FlGURE shows the magnetic characteristics of the carbon steel sheets treated by the process mentioned above, together with those of conventional low-carbon, rimmed steel before annealing, and a conventional electrical steel for comparison.

EXAMPLE 1.

A low-carbon, rimmed steel sheet with the following chemical compositions: carbon: 0.08 weight percent, manganese: 0.28 weight percent, phosphorus: 0.0l5 weight percent, sulfur: 0.020 weight percent, and other elements 0.10 weight percent, was heat-treated as follows:

The temperature of material was elevated to 920 C. and kept at this temperature for 1 hour. The percentages of controlled atmosphere were as follows:

CO,: 13 volume percent, N,: residual, dew point: 25 C.

After rapidly lowering the temperature of the carbon steel to 710 C. the steel was kept at this temperature for 6 hours to obtain large ferrite grains. During this second stage, the percentages of controlled atmosphere were as follows:

CO: 8.7 volume percent, C0,: 6.5 volume percent, H,: 9.5

volume percent, N,: residual, dew point: 4 C.

After the second stage, the temperature of carbon steel and lowered to 350C. and kept for 1 hour. The percentages of controlled atmosphere were the same as that in the second stage. After this treatment, the carbon steel was taken out of the furnace, the core loss of the steel thus treated was 5.5 watts/kg. at 14 kilogauss, and 60 Hz.

EXAMPLE 2 A low-carbon, rimmed steel sheet with the following chemi cal composition: carbon: 0.15 weight percent, manganese: 0.40 weight percent, phosphorus: 0.017 weight percent, sulfur: 0.030 weight percent, and other elements are less than 0.10 weight percent, were treated as follows:

The temperature of the material was raised to 920 C. at first and kept at this temperature for 1.5 hours. The percentages of controlled atmosphere were as follows:

C0,: 13 volume percent, N,: residual, dew point: 35 C.

After rapidly lowering the temperature of the carbon steel to 710 C. we kept at this temperature for 7 hours to promote the growth of ferrite grains. During this second stage, the percentages of controlled atmosphere were as follows:

CO: 8.0 volume percent, C0,: 7.0 volume percent, 1-1,: 8.0

volume percent, N,: residual, dew point: 4.0C.

After the end of the second stage, the temperature of carbon steel was lowered to 350 C. and kept for 1.5 hours at this temperature. The percentages of controlled atmosphere were the same at that in the second stage. The temperature of the steel was then lowered uniformly to 200 C. and kept for 1 hour at this temperature in the gas atmosphere with the same composition as before. After this treatment, the carbon steel was taken out of the furnace. The core loss of the steel thus obtained was 5.7 watts/kg. at 14 kilogauss and 60 Hz.

The low-carbon, rimmed steel produced in accordance with the present invention has superior magnetic properties and having its ferrite matrix in the form of grains sufficiently large in particle size to be less than 10 particles per square millimeter. These grains also have loss than 0.01 weight percent of carbon dissolved in the ferrite matrix with the residual carbon being present at the ferrite grain boundaries rather than in the ferrite matrix.

From the foregoing detailed description, it will be evident that there are a number of changes, adaptations and modifications of the present invention which come within the province of those skilled in the art. However, it is intended that all such variations not departing from the spirit of the invention be considered as within the scope thereof as limited solely by the appended claims.

I claim:

1. The process to improve magnetic characteristics of carbon steels comprising a first stage including raising the temperature of carbon steel above the A transformation temperature wherein the a-phase :2 'y-phase transformation takes place, and maintaining the dew point of the atmosphere between 5 to 50 C.

a second stage including lowering and maintaining the temperature of the carbon steel below 723 C. but not lower than 600 C., for 3 to hours in a controlled atmosphere;

a third stage including lowering and maintaining the temperature of the carbon steels at 300 to 400 C. for l to 2 hours.

2. The process of claim I wherein the carbon steels have a composition of carbon: 0.25 weight percent, silicon: 0.5 weight percent, manganese: 1 .65 weight percent, phosphorus: 0.05 weight percent, sulfur: 0.05 weight percent, copper: 0.5 weight percent, and other elements: 0.l

weight percent, for the purpose of obtaining large ferrite grains in which less than 0.01 weight percent of carbon is present dissolved in the matrix and the residual carbon is present at ferrite grain boundaries, and not in the matrix.

3. The process of claim 1 wherein the atmosphere in the first stage is approximately 0-l0 percent by vol. C0, 6-l3 percent by vol. C0,, 0-5 percent by vol. H,, and residual N,.

4. The process of claim 3 wherein the atmosphere of the second and third stages are 2-10 percent by vol. CO, 6-l2 percent by vol. C0,, 1-] 5 percent by vol. l-l,, and residual N,

l U l

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2672429 *Jun 3, 1952Mar 16, 1954Stanley WorksElectrical steel
US3098776 *Dec 9, 1960Jul 23, 1963Western Electric CoMethods of heat-treating low carbon steel
US3180767 *Oct 8, 1962Apr 27, 1965Armco Steel CorpProcess for making a decarburized low carbon, low alloy ferrous material for magnetic uses
US3188250 *Feb 26, 1963Jun 8, 1965United States Steel CorpUse of a particular coiling temperature in the production of electrical steel sheet
US3287184 *Oct 22, 1963Nov 22, 1966Bethlehem Steel CorpMethod of producing low carbon electrical sheet steel
US3333987 *Dec 2, 1964Aug 1, 1967Inland Steel CoCarbon-stabilized steel products and method of making the same
US3420718 *Aug 20, 1965Jan 7, 1969Yawata Seitetsu KkProcess for the production of very low carbon-containing cold-rolled steel strips
Non-Patent Citations
Reference
1 *Metals Handbook, Vol. 2, 8th Edition, Published by the American Society for Metals, 1964, pages 69 71.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3730317 *Jul 21, 1971May 1, 1973Eaton CorpElectromagnetic coupling with permanent magnets
US3819426 *Jul 31, 1972Jun 25, 1974Nat Steel CorpProcess for producing non-silicon bearing electrical steel
US3909316 *Apr 20, 1973Sep 30, 1975Ishikawajima Harima Heavy IndMethod for annealing of strip coils
US3914135 *Mar 14, 1973Oct 21, 1975Nippon Kokan KkMethod of improving steel properties by using controlled cooling rates
US3948691 *Jun 21, 1974Apr 6, 1976Nippon Steel CorporationMethod for manufacturing cold rolled, non-directional electrical steel sheets and strips having a high magnetic flux density
US5236518 *Feb 14, 1992Aug 17, 1993General Motors CorporationVariable reluctance sensor with offset magnets having improved magnetic flux member
US5609696 *Jul 14, 1995Mar 11, 1997Ltv Steel Company, Inc.Process of making electrical steels
US6016029 *Aug 6, 1996Jan 18, 2000Toyo Kohan Co., Ltd.Raw material for magnetic shield, production method thereof, and color television receiver
US6068708 *Mar 10, 1998May 30, 2000Ltv Steel Company, Inc.Process of making electrical steels having good cleanliness and magnetic properties
US6217673Sep 29, 1997Apr 17, 2001Ltv Steel Company, Inc.Process of making electrical steels
US8361245 *Feb 24, 2006Jan 29, 2013Nippon Steel CorporationSteel excellent in resistance to sulfuric acid dew point corrosion
USRE35967 *Jul 21, 1997Nov 24, 1998Ltv Steel Company, Inc.Process of making electrical steels
Classifications
U.S. Classification148/121, 148/122, 148/306
International ClassificationC21D1/76
Cooperative ClassificationC21D1/76
European ClassificationC21D1/76