US1793268A - Method of casting - Google Patents

Description

Patented Feb. 17, 1931 UNITED STATES PATENT OFFICE EDWARD B. WILLIAMS, OF LATROBE, PENNSYLVANIA, ASSIGNOR TO VULGAN MOLD AND IRON COMPANY, 01 LATROBE, PENNSYLVANIA, A CORPORATION OF PENN- SYLVANIA METHOD OF CASTING No Drawing.

One object of this invention is to produce a cast iron which will have a pearlitic structure when cast in relatively thin sections as well as in heavy or thick sections in molds 5 at normal room temperature, the castings being cooled at normal speed without the application of external heat.

Hertofore, pearlitic structure has been produced in cast iron by properly heating the molds prior to pouring the casting, and by slowly cooling the castings made in molds at normal temperature, the cooling being slowed up by the application of external heat. These methods are expensive due to the extra operations involved and the degree of accuracy which must be maintained to procure good results.

I have discovered that in the manufacture of pearlitic cast iron castings the sulphur content determines to a large extent the percentage of carbon which is precipitated as free graphite. One analysis having a high sulphur content and cast into molds at room temperature might produce castings having a white or mottled structure. In such castings the percentage of carbon is above the eutectoid point of approximately .90% carbon in the cementite. If however, the same castings are produced from an analysis having the same percentages of other metalloids but with the sulphur content low, the castings will have the desired pearlitic structure. The molds in which the castings with low sulphur are produced need not be heated above normal room temperature nor need the cooling time be reduced by the application of external heat.

In the preferable practice of my invention I employ a cupola in which I add to the metal charged pig iron,'for example, from 10% to steel scrap, giving, for example, a total carbon content of approximately 3.00%. I

1929. Serial No. 378,059.

over .O5%, and depending on the coke used, the melting temperature, and the analysis of the charge, the sulphur may be as high as 15%. A sufiicient'quantity of de-sulphurizing material such as soda ash is added to reduce the sulphur content below .05%. The molten iron-so treated is then poured into molds at normal room temperature in the usual way.

Other melting mediums may be used such as an electric furnace in which the low sulphur content maybe obtained without the addition of a de-sulphurizing agent, but I have found that the structure of pearlitic cast iron produced in accordance with the preferable practice outlined herein is satisfactory and that this practice is less expensive. Pearlitic cast iron of low sulphur content has improved physical properties over pearlitic cast iron of high sulphur content. Due to the lessened amount of sulphides in the iron, improvement in the physical properties of the low sulphur content pearlitic cast iron is noted over pearlitic cast iron having a high sulphur content. Resistance to shock or impact at both low and high temperatures is increased, and improved machinability is produced with my improved pearlitic cast .iron. I claim: The method of making cast iron having a pearlitic structure which consists in melting a charge having a low content of carbon and silicon, reducing the sulfur content below .05%, pouring the molten metal into a mold which is at normal room temperature and cooling'the casting normally without the application of external heat, whereby a pearlitic structure is produced in thecastin In testimony whereof, I hereunto a x my signature;

EDWARD R. WILLIAMS.

prefer the silicon range 0 be from .80% to The percentages of phosphorous and manganese are normal. During the melting op- 1.30%, depending upon the total carbon.

eration in which coke is used as fuel, the

charge picks up sulphur from the coke to the extent of from .02% to .05% which makes the sulphur content in the molten iron generally