US1919983A

US1919983A - Method for producing low loss nonaging silicon steel sheets

Info

Publication number: US1919983A
Application number: US596158A
Authority: US
Inventors: Morrill Weston
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1932-03-01
Filing date: 1932-03-01
Publication date: 1933-07-25
Anticipated expiration: 1950-07-25

Description

Patented July 25, 1933 UNITED STATES PATENT OFFICE w-ns'rox 303mm or rrr'rsrrmn, uassacnusn'r'rs, assrenon '10 GENERAL nLr-c'rme company, A conroaa'rron' or mew Yoax METHOD FOR PRODUCING LOW- LOSS NONAGING SILICON STEEL SHEETS ll'o Drawing.

The present invention relates to magnetic material and more particularly to a method for producing low loss silicon steel which does not age.

If silicon steel sheets are subjected to a single sheet anneal, i. e. an anneal in which spaced sheets are passed through an annealing furnace, as disclosed for example in Ruder Patent No.1,156,496, the resulting product has a low total watt loss when employed as core material for alternating current transformers and the like. The annealed sheets however do not retain their high magnetic qualities indefinitely. They have a tendency to age causing thereby an increase in the total watt loss of the material which may vary from about 30 to 60%.

It is an object of the present invention to provide a method for heat treating silicon steel sheets whereby low watt losses may be obtained particularly at high magnetic densities. A further object of the invention is to produce magnetic sheets which do not age and thereby cause an increase in the watt losses in the material.

In accordance with the present invention silicon steel sheets which may contain up to about 7% silicon and which have been pickled are placed in'a furnace the atmosphere of which is hydrogen andheated to a temperature of 700 C to 850 0., preferably 800 C. The sheets are annealed at this temperature for about five minutes and then removed and cooled either by quenching or rapid air cooling, preferably the latter. If the sheets are quenched it is desirable to quench them in a pickling solution. When cold, the single sheets may. be punched, sheared or cut into desired shapes and a ain placed in a furnace the atmosphere of w ich is hydrogen and annealed at a temperature above 850 C., for example 900 C. to 1100 C. but preferably 925 C. The sheets are maintained at this temperature for about five minutes and then removed and without quenching, cooled rapidly in air to room tem erature. Although in initiating my process I prefer to employ sheet.material which has been pickled the process may be carried out with 1932. Serial in. 586,158.

unpickled material if desired. I have also found that some'advantage may be obtained by pickling the sheets after the first anneal. A further improved magnetic quality results therefrom as well as greater adaptability to a straight line process. I prefer to employ a pickling bath consisting of a 10% sulphuric acid solution held at a temperature of about 90 C. My invention however is not limited to this particular bath since othe' pickling baths may be employed if desire v I have found it advantageous to shear or punch the sheets after they have been given their first anneal. Under such circumstances the annealed sheets are usually air cooled, pickled, punched and then annealed at a temperature of about 925 C. The second anneal removes all traces of cutting strain and leaves the punchings ready for use. i

While I prefer to employ a hydrogen atmosphere in the annealing furnace, the invention is not limited to the use of any particular atmosphere. Any other ordinary furnace atmosphere such as air, nitrogen, hydrogen-nitrogen mixtures or a vacuum may be employedif desired. Furthermore, although the period of time that the sheet material is maintained in the furnace is usually about five minutes this period of time is not critical. It is chosen in the interest of economy and may be longer or shorter if desired without adversely affecting the sheet material. It is merely neeessary that the sheets'should reach the desired temperature and this can usually be accomplished in about five minutes.

The present process may be adapted easily to any straight line continuous process for treating magnetic sheet material. Moreover, when magnetic sheet material is.

treated in accordance with the present invention it is possible to effect an appreciable reduction in total watt losses at high magnetic densities. For example at 15000 B the reduction in total watt losses may amount to 15 or 25%. Furthermore, the heat treated material does not age.

What I claim as new and desire to secooling said sheets, heating the sheet ma terial to e temperature hetween 850 C. and 1100 C. and quickly cooling the sheet ma,- teriel,

2. The method of treatingsilicon steel sheet material which comprises heating sin le steel sheets for a, few minutes in a hydrogen atmosphere and at a, temperature beween 700 C. and 850 (1, quickly cooling the sheets, heating the sheet material to a temperature between 850 C. and 1100 (l, and quickly cooling the sheet material in air without quenching.

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single sheets at a, temperature between 700 C. and 850 (1., quickly cooling said sheets, pickling the sheets, punching or cutting said sheets into desired shapes, heating the single punchings to a temperature between 850 C. and 1100 C., and quickly cooling the punchings without quenching.

WESTUN MURR LL.