US1991352A - Process for heat treating silicon steel sheets - Google Patents

Description

v ticed in the treating of such sheets.

Patented iii 2, I

resists PEOCESS FOR HEAT TREATING SILICON STEEL SHEETS William E. Gaugherty, Natrona, Pa.,

m n to Allegheny Steel Company, .a corporation of Pennsylvania No Drawing.

Application September 16, 1933. Serial No. 689,792

1 Claims. -(c1. 148-215) tured into Patent No. 1,706,438, there is set forth not only a method new with us at that time of 15 treating silicon steel sheets to improve their quality, but also various methods theretofore prac- While results are possible of attainmentwhich are superior to those methods in vogue at 20 the time of filing said application-by the method of said Patent No. 1,706,438, it is nevertheless a fact that sheets treated or annealed in the manner therein set forth are not as flat as box annealed sheets and in addition they have the dis; $5 advantage of having a fairly heavy marginal scale. This lack of flatness prevents sheets annealed in accordance with the method of said patent frombeing used to the best advantage for electrical apparatus of large size such as power transformers, because with sheets lacking in proper flatness,

laminations produced therefrom will not stack properly. The presence of the marginal scale is a serious disadvantage to users who punch laminations from suchsheets .as the scale causes ex 5 cessive wear on the punching dies. The scale is also a disadvantage when the sheets are to be used in transformers operating at high inductionsince, due to the scale, less active steel can be placed in a given space, thereby rendering a higher magnetizing force necessary for a given flux. An object of this invention is to provide a new method of treating silicon steel sheets for improving their magnetic properties.

Another object of this invention is to provide a method of so treating silicon steel sheets that,

their magnetic values as well as their physical characteristics are improved.

vide a method for the treatment of silicon steel sheets whereby (without the use of elaborate and costly equipment, such as is necessary for obtaining a high temperature hydrogen anneal) the 5 maximum values for use in electrical apparatus 1927, which application maand appreciable A still further object of this invention is to pro- -,may be obtained from a given batch of sheets of silicon-steel.

Broadly, my invention consists in normalizing or open annealing silicon steel. sheets and then stack, or mass or box annealing. .3

More specifically, my invention which is applicable to the treating of silicon steel sheets which have been rolled by any standard or suitable method (generallyhot rolled in accordance with mill methods) consists first, in giving the sheets one or more passes through cold rolls merely .to flatten the same; second, in pickling the sheets in a. suitable acid pickle to remove the scale; third, in normalizing or open annealing the sheets at a temperature of from about 1500? F. to about 1850 F. either singly or in packs of four or more; allow ing suffl'cient time for the sheets to attain the temperature required; fourth, in stack, mass or 7 box annealing the sheets at a furnace temperature of about 1580 F.

In the step of stack annealing, or in box annealing, where a relatively large number of sheets constituting a stack are placed in an annealing box which, is moved into a suitable furnace, the temperature of the stacks of sheets is gradually built up until the desired temperature is attained; this temperature is then maintained for a considerable period of time and then the temperature. of the stack of sheets is allowed togradually drop.

I have found that by utilizing a furnace temperature. of about 1580? F., I can obtain a sheet temperature or a temperature of the stack of sheets which is sufiicient to prevent aging. A furnace temperature of about 1580 F. Will impart to the sheets a temperature of about 1400 F. 1500 F., it being generally desirable to utilize such a furnace temperature as will raise the sheets to a minimum of about 1400" F Therefore the precise furnace temperature depends upon the particular type of furnace employed variations in, furnace tempera- F. are understood to be within the scope'of the invention. At a furnace temperature of 1580 F. as above described I obtain an inside temperature of about 1400" F. at the bottom and about 1500 F. at the top. I have found that it preferable, as I have said, to gradually raise the temperature of the stack of I sheets until it reaches the annealing tempera-' ture, to hold the stack at that temperature for aconsiderable period of time and then to gradually lower the temperature from annealing temperature. I have further found that satisfactory results can be obtained by taking one and onehalf times as long to build up the temperature of Q ture from '1580 the stack to annealing temperature as is utilized for holding the stack at annealing temperature and then in taking from seven to eight times as long in cooling the stack down from annealing temperature as is utilized in .holding the stack at annealing temperature. This annealing cycle will depend somewhat upon the gauge of the sheets being treated andthe weight of the stack' or mass of sheets.

There are two main reasons for following the open anneal or normalizing step by a box, mass or stack anneal. 'I'he first, as already pointed out, is to flatten the sheets which have become slightly warped by rapid cooling after the normalizing or open anneal step. The second, and, probably most important, is to render the sheet non-aging. It has been discovered that silicon steel sheets which have been normalized .or open annealed only, will, when subjected to a tem perature of about 200 F., even for a short period of time, show an increase in hysteresis loss or will, as is commonly expressed, age.

In the normalizing or open annealing step according to my method, I do not limit myself to temperatures of from about 1800 F. to 1850 F., since I have found that good results may be .obtainedat somewhat lower temperatures. I pre- 7 fer these higher temperatures, however, for the reason that the results desired can be obtained in a shorter period of time, than with lower temperatures. I have determined that by annealing at from about 1800" F. to 1850 F., the desired results can be obtained in about one-ninth the time a comparable result can be obtained if annealing occurs at about 1500 F. v

I do not limit my normalizing or open anneal-( ing step to' any particular type of furnace, but I prefer a continuous ,type either table roller driven or endless wire rope driven.

While it has been shown that by soaking silicon steel sheets at a temperature of from about 1800 F. to 1850 R, an increase'in-grain size is produced with consequent increased eddy curheld at such temperatures for but a short time and are then cooled rapidly, no appreciable increase in grain size is produced.

Silicon steel sheets that are normalized at about from I800 F. to 1850" F. and merely held at this temperature long enough to become thor- What I claim as new and desire to secure, by

Letters Patent is:-

rent losses, I have found that if the sheets are 1; A process of improving the magnetic properties of silicon steel material in sheet-like form comprising cold rolling the material to flatten the same; pickling it to remove scale, heat treating the material at about 1500-l850 F., and box annealing at a furnace temperature of about 1580" F. to produce material which is fiat and non-aging.

2. A process of improving the-magnetic properties of silicon steel material in sheet-like form comprising flattening the material bycold rolling, open annealing it at about 1500-1850 F. and thereafter box annealing it to produce material which is flat and non-aging 3. A process of improving the magnetic properties'of silicon steel'material in sheet-like form which comprises cold flattening the material, subjecting it to a relatively rapid anneal and then to a relatively slow anneal to produce material which is flat andv non-aging, the relatively rapid anneal being an open annealv can'ied 'out at about 1500-1850 F. and the relatively slow anneal being a box anneal carried out at such atemperature as will impart to the material a temperature of at least about 1400 F.

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