US2455954A - Process for producing white cast iron castings - Google Patents

Description

Patented Dec. 14, 1948 PROCESS FOR PRODUCING, WHITE CAST moN CASTINGS Oliver Small ey, Larchmont, N. Y., assignor to vMeehanite Metal Corporation No Drawing. Application September 22, 1945,. Serial No. 618,059

3 Claims (01. 75-130) My invention relates to the process of the W manufacture of cast iron, with or without alloy ing agents, under such control asto produce white iron castings that combine both hardness and toughness. I

By white iron, I mean a cast iron-alloy or otherwise-in which the bulk or all of the carbon is present in the form of iron carbide and which presents a white fracture.

White iron castings being rarely machined and selling at low competitive prices, have not advanced technologically and industrially during the past decade as have graycast iron castings. Generally white iron castings are the most unpredictable products of the foundry industry and the ideahas existed that an iron giving a white fracture is suitable for any type of hard wear service, and may be defined as white iron. In other words, the idea has prevailed, and still prevails in certain quarters, that if an iron fractures white, then the metal'is a serviceable ma- .terial for abrasion resisting conditions and perhaps for heat resisting purposes because it is substantially free from flake graphite or that it can be malleablized by prolonged annealing above the critical point.

White iron is however, not a specific material but rather a generic term. An iron that breaks with a white fracture may be extremely brittle or it may be reasonably tough. It may present superior or inferior resistance to abrasion. Under heat influence, it may stand'up reasonably well or it mayfail prematurely. It "may mal1eablize in a standard annealing time and give good'combined strength and ductility, "or its response to a malleablizing treatment may be quite unsatisfactory and inferior propertiesfrequently result.

White iron is commonly made-by adjusting the carbon and silicon to suitable ratio, orit may be produced by the simple expedient of adding car'-- usually an indeterminate material of uncertain properties. If it is to be used for abrasion resisting purposes its B. H. N.value may vary from 350 to 578. Its strength properties may differ as much as 100% or more, and the casting diniculties encountered often result in rejection of the casting because of the problemsof overcomingshrinkage defects and weakness -dependenton uncontrolled developmentof grain structure.

. Whichever method is used, the end product isi The basis of this invention is a process which is so controlled asto produce acasting to a predetermined degree of whiteness of known physical characteristics that has uniform liquid shrinkage for casting purposes and is free from columnar grain weakness and in which the degree of hardness and strength properties bear a direct relation to the sectional dimension and shape of the finished casting.

An object of my invention is to produce a White iron to a predetermined and controlled de-- gree of whiteness and of known physical characteristics.

Another object of my invention is to produce a white iron that is free from crystal weakness and inherent brittleness.

Another object of my invention is to produce a white iron whose structure is mainly equiaxed as distinct from the uncertain unbalanced columnar growth common to'ordinary white iron.

A further object of my invention is to produce a white iron to a predetermined abrasion resisting characteristic which is-substantially constant regardless of the sectional dimensions of the finished casting,

Another object of my invention is to produce a white iron' casting free from shrink voids and mechanical Weakness. I

Another object of my invention is to produce ,a 'white'iron casting Whose heat resisting properwhich can be malleablized by annealing at a given temperature and time to assure'dependable reaction to malleablizing treatment.

A'notherobject of my invention is a two-step process for the manufacture of white iron castings, the first step comprising selecting a mixture of raw materials which when melted Will have a structural constitution bearing a direct relationship to thethickness of the sections to be cast, and the second step comprising altering or modifying the massive cementite to produce a final structure that possesses the desired improved degree of toughness.

Another object of my invention is to give positive control over the physical properties in a White iron casting, comprising the control and measurement of constitutional carbide values and processed carbide values, and regulating through'said control the relation of the constitutional and process carbide values to each other and to the thickness of the casting to be made.

having substantially one-inch sections will be il-- casting of substantially oneinch thick and of generally rectangular shape. Next, I process the molten metal which, when tested, produces a processed carbide value embraced in a range having a minimum value of substantially .and a maximum value of A wedge value of (3 2) is equivalent to l-times white in a casting of substantially one inch thick and of generally rectangular shape and a wedge value of is substantially equivalent to 2 /z-times white. The maximum value of the constitutional carbide Value may not be greater than three times the maximum process carbide value. The maximum value for the constitutional carbide would be not greater than A wedge value of /32) is substantially equivalent to 7 -times white in a casting of one inch thick and of generally rectangular shape.

Corresponding proportionate wedge values would obtain for sections of different thickness. Thus, for castings of substantially 2 inches thick, the wedge values given above would be doubled, in which case, for example, the minimum constitutional wedge value for a 2-inch section would be A wedge value of 7 is substantially equivalent to I l -times white in a casting of substantially 2 inches thick and of generally rectangular shape. Other wedge values with respect to the thickness of castings will bear the same ratio as those set forth above for a 1-inch section.

From the above wedge values, it is noted that the minimum constitutional wedge value is substantially 1% times the section of a finished casting. The minimum processed wedge value is substantially 1%; times the section of the finished casting and the maximum processed carbide wedge value is substantially 2% times the average section of the casting to be made. The maximum constitutional wedge value is less than 3 times the maximum value of the processed wedge value.

The wedge values as given above may be translated in terms of the degree of whiteness of a casting of generally rectangular section, in which case the constitutional carbide value is embraced within a range having a minimum value of 1%- times white and a maximum value as hereinafter specified. The processed carbide values would be embraced Within a range having a minimum value of l-times white to 2 /2-times white. The maximum value of the constitutional carbide value would be not greater than 3 times the maximum processed carbide value.

Any white iron casting that is made having a constitutional carbide value and a processed carbide value falling within the limits of the above defined ranges, will have good wear resisting qualities and yet be tough. White iron castings made by values which lie close to the minimum values of the range of values will have somewhat different properties than white iron castings made by values lying close to the maximum values of the ranges given above. A range which may represent mean. values for making white iron. castings may be as follows: Thickness of Section yinch linch flinch Minimum Constitutional Carbide Wedge I Value"; %3 %2 %2- Maximum Constitutional Carbide Wedge Value %2 %2 %2 Minimum Processed Carbide Wedge Value %2 %2 %2 Maximum Processed Carbide Wedge Valuc %2 %2 962 White iron castings controlled by values lying in the mean range given above will have a high,

heavy physical impacts.

In practicing my invention, the foundry operator first melts a charge or otherwise prepares a mixture of molten materials which, when tested, 7

gives a constitutional value lying within the range of the values hereinabove specified with relation to the thickness of the castings to be made. Next, the operator processes the molten material which. when tested, gives a processed carbide value lying Within the range of the values hereinabove specified with respect to the thickness of the castings to be made. Having satisfied that the molten metal meets the above requirements, the operator may now pour the processed metal in the mold for making the finished white iron castings.

The foundry operator, in the practice of my invention, is able to produce white iron castings having a controlled degree of whiteness whereby castings made under my process have high abrasion and heat resisting characteristics which will assure long service life value. The castings will also have the proper characteristics, whereby they can be malleablized by annealing at any given temperature and time and assure dependable reaction to malleablizing treatment.

Although I have described my invention in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of the process, modification in the steps undertaken, variations in the materials used, and different values of wedges establishing carbide balance, may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

I claim as my invention:

1. A process to give positive control of the physical properties in a white iron casting which comprises providing molten cast iron which when cast in a wedge shaped test piece and then broken in two, exhibits upon the broken faces both gray and white iron with a line of demarcation therebetween of such a length as to be embraced within a range having a minimum value of more than 1% times the average section to be made and a maximum value as hereinafter specified, processing the molten material which when cast in a wedge shaped test piece and then broken in two, exhibits upon the broken faces a larger amount of gray iron and a smaller amount of white iron with a new and shorter line of demarcation than that exhibited on the first men tioned test piece, said new line of demarcation being of such length as to be embraced within a range having a minimum value of more than 1%; times the average section of the casting to be made and a maximum value of less than 2% times the average section of the casting to be made, said a ias-p54;

maximum value of the constitutional carbide value-being not greater than three times the maximum process carbide value: .hereinabove specified;

.3. sALDI'OGBSS to: give positive control of the physicallpropertiesin a white iron casting which comprises: providing molten cast iron which produciesca' constitutional carbide Wedge value embraced inia'range having a minimum value ofat leasta substantially 2 for castings /2-,inch thick, "5 33;xi'oracastingsrsubstantially 1-inch thick and kgator castingssubstantially 2-inches thick and havingia maximumvalue of at least substantially 8 for castings. substantially /g-iD-Ch' thick, V-for castings substantially 1-inch thick,.and lfor castings substantially Z-inches thick, and processing the molten'materialto giveca processed carbide wedge "value embraced within a range having a minimum value of at least substantially 1'0r castings substantially'V -inch thick, for castings substantially 1-inch thick, and 732 for castings substantially 2-inches thick and having-a maximum'value of at leastsubstantially for castings substantially /2-inch thick, jior castings: substantially 1-inch thick, and for castings vsubstantially 2-inches thick.

GLIVER v SMALLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,371,654 Smalley et a1 Mar. 20, 1945 FOREIGN PATENTS Number Country Date 105,619 Australia Oct. 25, 1938