US2173312A - Silicon-iron alloy - Google Patents

Description

Patented Sept. 19, 1939 UNITED STATES PATENT OFFICE Germany,

assignors to Heraeus-Vacuumschmelze A. G., Hanan, Germany, a company of Germany No Drawing. Original application August 14,

1937, Serial No. 159,194. Divided and this application May 20, 1938, Serial No. 209,148. In Germany June 27, 1936 1 Claim.

This invention relates to metallurgy and more particularly to an improved silicon-iron alloy adapted for use in the manufacture of various electrical devices such as transformers, wattmeters, etc., and is a divisional application of application Serial No. 159,194, filed August 14, 1937, now Patent 2,144,200. In such devices, material of relatively low energy loss characteristics is desired, for example, in transformer cores. Heretofore in the art, silicon-iron alloys containing silicon 3 to 5% have been proposed for use in these devices and various methods of rolling and heat-treatment have been proposed whereby the energy loss characteristics of the alloys are improved We have found, however, that the degree of purity of the silicon-iron alloy has a marked influence onthe energy loss characteristics of this type of alloy, and that residual amounts of carbon, metal andmetalloid oxides, dissolved and occluded gases, etc., should be eliminated from such alloys for best results and to obtain the lowest energy loss characteristics. We have found that the presence of up to .80% of at least one of the metals Cu, Al, Zr, and Ti in the purified iron-silicon alloy materially improves the electrical characteristics of the alloy.

The present invention aims to provide an improved magnetic alloy having a relatively low energy loss characteristic for use in the manufacture of electrical devices. 7 Other objects and advantages will be apparent as the invention is more fully disclosed.

The process of the present invention consists in first forming a molten iron bath substantially free from associated metal and metalloid impurities and of carbon and of dissolved and occluded gases; secondly, in adding to the said bath the desired amount of silicon and said second desired alloy constituent (Cu, Al, Zr, Ti) each of which has similarly been freed from associated impurities; thirdly, in solidifying the resultant alloy in such manner and under such conditions as to avoid contamination of the same. The resultant.

the well known duplex processes, is melted in a substantially inert but slightly oxidizing atmosphere maintained at pressures less than atmospheric pressure. This melting is preferably accomplished in an electric induction furnace of the type described and claimed in either of the Patents Nos. 1,431,686, 1,983,242 and 2,085,450 and. by methods as described and claimed in either of the Patents Nos. 1,555,313 and 1,555,314. The molten metal bath is thoroughly decarburized by introducing an oxidizing agent into or over the surface of the bath which agent does preferably not introduce into the bath any undesirable metallic or non-metallic constituent. We prefer to employ a solid oxidizing agent, such as iron oxide for this decarburizing step, inwhich case the molten bath containing the iron oxide in an amount in excess of that empirically necessary for the complete removal of the carbon is heated under gradually reducing pressures until no further gases can be exhausted therefrom.

The thus decarburized metal bath is then to initially pass the gas into or over the surface of the molten metal bath in a relatively strong free flow, at atmospheric or slightly reduced pressures, and to subsequently heat the bath for a prolonged time interval at more elevated temperatures under gradually reducing pressures until the excess metal oxide has been completely-removed and until the very lowest pressures have been obtained. The residual oxygen and nitrogen may be eliminated instead of or after a treatment with hydrogen by incorporating a proportion of a metallic reducing agent preferably by a readily vaporizable one in the bath. The'metallic reducing agents suitable for this purpose are metals of the alkaline, alkaline earth and cerium groups, magnesium and beryllium. The most satisfactory one of these reducing agents appears to be calcium and perhaps cerium. The calcium may be used as pure metal or as calcium-silicon alloy and the cerium as misch metal, a mix-- ture of metals of the cerium group.

After the addition of this reducing agent the heating of the bath is continued again under gradually reducing pressures until the excess of the metallic reducing agent has been effectively removed from the molten metal bath.

The substantially pure molten iron bath is now ready for the addition thereto of the desired amount of the silicon and other desired alloying metal. It is preferable to employ substantially pure silicon prepared by any of the available methods. Alternatively a -ferro-silicon alloy which is substantially free from associated impurities may be employed. It is important that the silicon be substantially free from oxide and from adsorbed, dissolved or absorbed atmospheric gases, otherwise deleterious compounds of iron, silicon and oxygen, for example, will be formed in the alloy. 1

After the addition .of the silicon to the molten iron bath, the bath should again be heated under' gradually reducing pressures for a time interval adapted to thoroughly distribute the silicon throughout the. bath and then should be cast'and solidified under conditions calculated to prevent the absorbing therein of deleterious impurities. Preferably the alloy should be cast in vacuo.

The resulting solidified ingot of silicon-iron alloy should preferably be mechanically deformed to sheets of the thickness desired by the process disclosed and claimed in Hiemenz application Serial No. 88,683, filed 2nd July, 1936, assigned to the same assignee as the present invention, care being taken in. the heating and rolling of the same to avoid the introduction into the alloy of deleterious amounts of oxygen and carbon and other impurities f. i. sulphur. To this end the hydrogen utilized in the heating furnaces should be substantially free from water vapor and of nitrogen and prior to such heating the surface of the metal should be cleaned to remove surface scale and carbon lubricants.

In the manufacture of silicon-iron alloys in accordance with the present invention we have been able to make material which is characterized by an energy loss measurement as-low as lowest energy loss measurements for the same stituents such as copper, aluminum, zirconium v and titanium has a beneficial effect on the properties of the purified iron-silicon alloy. The added .copper or other alloying constituent may be' added Just prior to the addition of the silicon or simultaneously therewith and also must be sub-' stantially pure and free from associated metal and metalloid impurities and gases. It is undesirable to add the copper or other of said addiiional alloying constituents after the silicon has been added for the reason that from the time the silicon is added to the bath. until the alloy is solidified the greatest care must be exercised to prevent oxygen from having access to the molten bath, and during the addition of the silicon the silicon and the bath must be carefully protected from oxidation.

Having broadly and specifically disclosed the present invention, it is apparent that many modiflcations and adaptations may be made therein and all such are contemplated as may fall within the scope of the accompanying claim.

What we claim is:

An iron-silicon alloycharacierized by having a relatively low energy loss measurement of between .48 and .60 W/kg., said alloy consisting 24% silicon. from small but effective amounts up to .80% of at least one of the metals Cu, Al, Zr and T1, with the balance of the alloy consisting of iron substantially free from metallic compounds of the gases oxygen, nitrogen and hydrogen, said alloy having been degasiiled under reduced pressure.

WILHELM ROHN. WERNER HESBENBRUCH.