US2142347A - Silicon steel strip and manufacture thereof - Google Patents

Description

Patented Jan. -3, 1939 PATENT OFFICE .SILICON STEEL .STRIP AND MANUFACTURE THEREOF Vere B. Browne, Brackenridge, and William E.

Caugherty, Natrona, Pa., assignors to Allegheny Ludlum Steel Corporation, a. corporation of Pennsylvania No Drawing. Application August 3, 1933.

- Serial No. 683,474

1 Claim.

Our present invention relates to cold rolled silicon steel strip of improved magnetic characteristics'and to the manufacture of the same..

It is known to produce silicon steel'strip by cold rolling and such has been heretofore produced in the industry with a silicon content of from about .5 to 4%. The method commonly employed consists in rolling the strip until it has been so hardened by cold-working that further reduction by cold rolling is either difiicult or impossible. At this stage the silicon steel strip is annealed to its softest state so that further cold reduction is made. possible. The amount of reduction between anneals depends upon the silicon content of the strip and also upon the diameterof the rolls employed for reducing purposes. For example, when rolls of largev diameter are used more frequent anneals are-necessary than when rolls of small diameter are. used, but with rolls of very small diameter it is sometimes possible to reduce the hot rolled strip to the final gauge without any intermediate anneals.

Silicon steel strip is extensively emplc ed in the manufacture of electrical apparatus and its magnetic characteristics determine its value for use in the construction of such apparatus. In

general, the characteristics desired are high per- I meability and low watt loss for the particular.

gauge and silicon content in question.

Silicon steel strip that has been rolled in the commonly employed manner described above is,

' however, characterized by low permeability and high watt loss and is of little value for the construction o f-electrical apparatus where low magnetic loss and low exciting current or high permeability is required.

One of the objects of our present invention resides in silicon steel strip not subject to the above noted defects and disadvantages and to a method of making such strip which has the indicated advantages.

. strip having desirable permeability and watt loss values can be produced if the colii rolling and annealing operations are carried out in specified manner. The common practice is to hot roll the strip to as thin a gauge as possible as hot rolling can be carried out with greater facility than cold rolling. Usually hot rolled strip of from .060" to .100" is easily obtainable although in some cases, it is possible to obtain strip of lighter gauges. In our present invention, we start with hot rolled strip about .075" thick although we may, of course, start with a somewhat lighter or heavier gauge. As hot rolled strip of the higher silicon content is not in its best condition for the cold rolling operation, we find that such strip should preferably be annealed before starting the cold rolling. With strip of low silicon content annealing is usually unnecessary. It is usually desirable also to remove the hot mill scale from the strip by either a pickling or sand blasting cold rolling operation need only be carried out in that manner which produces the best mechanical results. We-have discovered, however, that the amounts of reduction by coldrolling between the last two anneals are extremely important and determine the electrical characteristics of the strip. After the gauge of the strip is reduced to final thickness by the last cold rolling, the strip is then annealed at 1400 to 2000 F. to develop optimum magnetic characteristics.

The silicon steel to which the present invention pertains preferably contains from about .5 to 4% silicon and is, more broadly stated, less than 5%, since silicon steels containing over 5% of silicon are recognized as undesirable and uncommercial due to excessive hardness, brittleness, and unworkability.

For example, we find that by starting with hotat 10,000 E and 60 cycles of 1.704; When, however, we reduce such strip to .0235", anneal at 1200 to 1300 F., cold roll to .22", a reduction of about 6% and then anneal at 1550 E, the watt loss per pound at 10,000 B and 60 cycles is 1.456.

In the following table 'we have set forth additional examples which were obtained on .014

gauge strip having a silicon content of about 3.5% silicon. For obtaining these results we started with hot rolled strip having a thickness of .075", which was then pickled, annealed at 1500 F., cold rolled to the gauge shown below, annealed at 1500 F., cold rolled to final gauge (.014") and again annealed at 1500 F. The losses are given in watts per pound at 10,000 1? and 60 cycles.

. when; however, following the same-procedure reduction is made from .075" to .014", a reduc- I 'tions between'about 4 and 15%.

amass? tion of about 80%, the watt loss per pound is .715 and the maximum permeability is only 9,200.

A consideration oi the various examples indicates that the watt loss per pound decreases and at the same time the maximum permeability value increases, as the percentage of cold reduction between the last two anneals is decreased the lowest watt loss values and the highest permeability values being obtained for cold reduc- It is not intended that the above shall be strictly limitative but the same is rather intended in an illustrative manner.

What we claim as new and desire to secure by Letters Patent is:

The process or making cold rolled silicon steel strip having a silicon content 01' about 3.5%, a

maximum permeability 01' 13,000 and a watt loss value per pound of-about .51 at 10,000 B and 60 cycles which comprises producing a hot rolled silicon steel strip 01 suitable thickness, removing.

scale therefrom,- annealing it at about 1500 F., cold roll reducing it to approximately .016", reannealing it at about 1500' E, cold r011 reducing it to approximately .014" and annealing at about VERE B. WILLIAM E. CAUGHERTY.