US2270762A

US2270762A - Cold rolled silicon steel strip

Info

Publication number: US2270762A
Application number: US253804A
Authority: US
Inventors: Morrill Weston
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1939-01-31
Filing date: 1939-01-31
Publication date: 1942-01-20
Anticipated expiration: 1959-01-20
Also published as: DE765294C; GB536119A

Description

Patented Jan. 20, 1942 2,270,762 COLD ROLLED SILICON STEEL STRIP Weston Morrill, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York No Drawing. Application January 31, 1939, Serial No. 253,804

" stabilizing anneal at about 850 C. in hydrogen,

9 Claims.

The present invention relates to cold rolled silicon steel strip and more particularly to cold rolling silicon steel strip at temperatures far below those heretofore employed in the production of such material. Processes heretofore employed in cold rolling silicon steel strip are set forth in the patent to Smith No. 1,915,766, June 27, 1933, and in the patent to Goss No. 1,965,559, July 3, 1934. While the Smith process usually employs only one cold reduction the process generally employed in the production of cold rolled strip for use in transformer cores is that disclosed in the Goss patent and comprises two cold rolling steps with intermediate normalizing at about 925 C. for a few minutes and, after the final cold reduction, a normalizing treatment at about 1100 C. in hydrogen for about four minutes.

It is one of the objects of the present invention to increase the permeability and reduce the total Watt losses in cold rolled silicon steel strip.

In a process such as disclosed in the Goss patent, the first cold rolling reduces the silicon steel from about .080 inch to .030 inch and the second or final cold rolling effects a reduction from .030 inch to .011 inch. Although the rolling operation is generally designated cold rolling the temperature of the material during rolling is generally about 80 C. and in many cases well above 100 C.

.I have found that if the cold rolling of silicon steel strip is carried out at lower temperatures, for example by maintaining the temperature of ,the steel within the range of 20 C. to 30 C.

during the rolling operation, a considerable improvement is obtained both in the permeability and total watt losses of the steel. The following table shows the results of permeability tests on silicon steel strip containing 2.96% silicon which was given two cold reductions at temperatures of --30 (2., 0., 100 C. and 200 C., with intermediate and final normalizing treatments as set forth above:

when the steel strip was thereafter given a the following results were obtained:

- Maximum Rolling temperature permeability 18, 640 0 C 18, 640 100 C 16, 620 200 C 12, 980

' terial rolled at 100 C.

Still further improvement in the magnetic properties of the cold rolled steel may be obtained if the steel after being normalized as usual in hydrogen at about 1100 C. is normalized for a few minutes at about 800 C. in a strongly oxidizing atmosphere or is annealed for a few hours at about 850 C. in a mildly oxidizing atmosphere. The effectof these heat treatments is to stabilize the steel by reducing some of the carbonin the steel thereby eliminatin the possibilityof ageing. While the improvement in magnetic properties obtained by the re-normalizing treatment or subsequent anneal at 850 C. is particularly efiective in silicon steel which has been rolled at temperatures between 20 C. and

30 C., this heat treatment is also effective in reducing the watt losses in any cold rolled silicon steel irrespective of the particular temperature employed in the cold rolling.

When more than one cold rolling step is employed the final cold rolling temperature appears to be more important than the temperature employed in the first cold rolling operation. The following table shows the effect on watt losses at cycles and 10,000 B, and 15,000 B. obtained with 3% silicon steel strip cold rolled in two steps at temperatures of C. Likewise the table shows the effect of two cold reductions at 0 C. and the effect of a first reduction at 80 C. and a second reduction at 0 C. In each case the first cold reduction was from .080 to .030 inch and the second cold reduction from .030 to .012 inch. In each case the strip was normalized at 925 C. for live minutes in a hydrogen atmos- Rolling silicon phere after the first cold reduction and was normalized at 1100 C. for three minutes in a hydrogen atmosphere after the second cold reduction.

Watt losses First Second rolling tolling Where a cold reduction of the silicon steel strip is efiected in one operation, as in Smith patent, theternperature for the cold reduction should be in the range of 20 C. to 30 C. for best resuits. Likewise, ,it two or more cold reductions are employed, as in Goss patent, it is essential that a temperature in the range of 20 C. to 30 C. be employed in the second or final cold rolling operation in order to obtain the best magnetic characteristics in the steel strip.

I In addition to the improvement in permeability and watt losses which may be obtained by rolling silicon steel strip at very low temperatures, I have also found that silicon steel strip containing about 3% silicon rolls easier at 0 C. than the same material rolled at temperatures of 30 0., 100 C., 200C. or 460 C. This latter result is of course contrary to what would be expected.

. What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In cold rolling silicon steel strip, the step which comprises maintaining the temperature 4. In cold rolling silicon which comprise effecting successive reductions of approximately 60 to 70% in the steel, the temperature of the steel being maintained within the range of C. to C. during the final reduction.

5. In cold rolling silicon steel strip, the steps which comprise effecting successive reductions of approximately to in the steel, the temrolling operation.

of the steel within the range of 20 C. to 30 C.

during the rolling operation.

2. In cold rolling silicon steel strip, the step which comprises maintaining the temperature of the steel strip about 0 C. during the rolling operation.

3. In cold rolling silicon steel strip containing about 3% silicon, the steps which comprise effecting successive reductions of approximately 60 to 70% in the steel, the temperature of the steel being maintained within the range of 20 C. to 30 C. during each of said reductions.

7. In cold rolling silicon steel strip, the steps which comprise rolling the steel at a temperature within the range of 20 C. to 30 C., normalizing the steel at about 1100 C. in a reducing atmosphere and thereafter heat treating the steel to reduce some of the carbon in the steel, the temperature of the steel being maintained within the said rangewluring the rolling operation.

8. In cold rolling silicon steel strip, the steps which comprise rolling the steel at a temperature within the range of 20 C. to 30 C., normalizing the steel at about 1100 C. in a reducing atmosphere and renormalizing the steel for a few minutes at about 800 C. in a strongly oxidizing atmosphere, the temperature of the steel being maintained within the said range during the rollmaintained within the said range during the rolling operation.

WESTON MORRILL.

steel strip, the steps