US3295965A - Wear resistant cast iron - Google Patents

Description

1967 G. E. WILLEY ETAL 3,295,965

WEAR RESISTANT CAST IRON Filed Sept. 30, 1963 INVENTORS GORDON E WILLEY BY FRANKLIN w. KELLAM United States Patent 3,295,965 WEAR RESISTANT CAST IRON Gordon E. Willey and Franklin W. Kellam, Thornhill, Ontario, Canada, assignors to Union Carbide Canada Limited, Toronto, Ontario, Canada, a corporation Filed Sept. 30, 1963, Ser. No. 312,772 5 Claims. (Cl. 75-125) The present invention relates to cast irons. More particularly, the present invention relates to cast irons containing relatively large amounts of manganese as an alloying constituent.

A substantial quantity of cast grinding ball and other castings requiring a high order of wear resistance have previously been manufactured from a cast iron containing from about 2.5 to 5 percent nickel as the predominant alloying constituent. While castings of this alloy have been satisfactory, being strong and wear resistant, the increasing price of nickel has imposed a significant economic penalty on its use.

It is therefore an object of the present invention to provide a relatively inexpensive, strong, wear resistant cast iron containing little or no nickel.

It is a further object of the present invention to provid a wear resistant cast iron containing little or no nickel and which has a Brinell Hardness of 500 or more.

Other objects will be apparent from the following description and claims taken in conjunction with the single figure of the drawing which shows a photomicrograph of a cast iron of the present invention.

A cast iron in accordance with the present invention has a composition in the ranges shown in Table I.

It has been discovered, as part of the present invention, that by using relatively large alloying proportions of manganese in cast irons, and by controlling the proportions of silicon and carbon in specific ranges, a strong wear resistant cast iron material is obtained from which the usual nickel content can be eliminated in whole or in part without detrimental effect, while providing significant economic benefit.

The microstructure of the alloy of the present invention consists essentially of primary carbides in a matrix of martensite and anstenite and the alloy of the present invention derives its beneficial properties from its characteristic structure which is at least 70 percent martensite. The aforementioned structure imparts to the alloy a hardness, measured as Brinell Hardness Number, of 500 or more. The structure of the alloy of the present invention can be readily contrasted with the pearlite-cementite structure of unalloyed white cast iron.

The sturcture and resultant hardness of the alloy of the present invention is developed in a cast iron with a manganese content in the range of 3.5% to 12% when the silicon and carbon are in the range of 0.4%0.7%, and 2.9%3.6% respectively.

If lesser amounts of manganese are used, or if the carbon or silicon are outside the specified ranges, then a suitable hardness of 500 BHN or above is not obtained nor is the desired structure present in the material.

With reference to the drawing, the single figure shows a photomicrograph (original magnification: 900x) of a cast iron in accordance with the present invention. The composition of the material shown in the drawing is Patented Jan. 3, 1967 3.86% Mn, 1.52% Cr, 1.37% Ni, 0.64% Si, 3.35% C, bal. Fe. In the photomicrograph, the numeral 1 indicates a mixture of martensite which appears as a continuous area with needle like inclusions and anstenite in dendritic form. The white area 2 is anstenite and the gray islands 3, surrounded by anstenite, are primary carbides.

In the preparation of the cast iron of the present invention, consideration is given to the manufacturing technique employed when selecting the proportions of manganese and nickel (or copper) within the aforementioned ranges in order to obtain the desired structure and hardness.

For example, when using water cooled permanent metal molds, and when the casting mass is small relative to the mold, i.e., the cooling of the casting is relatively rapid, the manganese content can be selected from the lower part of the range. On the other hand, when the casting mass is large and the permanent mold walls are relatively thin, or the molded material has low heat conductivity as in sand casting, the manganese content should be selected from the upper part of the range.

By way of illustration, in the manufacture of a l-3 inch diameter grinding ball using a water-cooled cast iron mold, 1 to 2 inches thick, between 3.5% and 4% manganese can be used. When casting the same ball in a sand mold, 1 to 2 inches thick, between 8% and 9% manganese should be used in order to obtain substantially the same structure and hardness.

Also, if larger diameter balls were cast in the same type molds, about 4.0% to 5.0% manganese is recommended with the metal molds and 9.0% to 11.0% manganese with sand molds.

In the practice of the present invention, when the manganese content of the cast iron is 6% or more, nickel can be eliminated entirely from the alloy. At lower manganese levels, however, between 0.5% and 1.5% in the aggregate of nickel and copper is required. That is to say, at the lower manganese levels the alloy should contain between 0.5% and 1.5% nickel, or between 0.5% and 1.5% copper, or between 0.5% and 1.5% of copper+nickel. The selection of a particular aggregate value "in this range is made following the same considerations Table II Percent Manganese 3.5 to 8 Nickel-l-Copper 0.5 to 1.5 Chromium 1 to 2.5 Silicon 0.4 to 0.7 Carbon 2.9 to 3.6 Iron and incidental impurities Balance.

In preparing cast irons in accordance with the present invention ordinary practices can be followed and melting can be accomplished in most furnaces used for the melting of cast iron. Such furnaces include cupola, air furnace, gas fired furnace, direct and indirect are electric furnaces and induction types.

By way of illustration, the following Table III lists specific compositions in the form of grinding balls having a BHN of 500 or more and which are at least 70 percent 3 martensite. consists essentially of primary carbides in a matrix of martensite and austenite.

The microstructure of these compositions i 4 be eliminated in whole or in part with substantial savings without loss of hardness and wear resistance. The economic advantages of the present invention can be ap- T able III Composition Diameter of Balls Cast, Type Mould Percent Percent Percent Percent Percent Percent Inches Mn Or Ni Cu Si O 3.86 1.52 1.37 0.64 3.35 2.00 Cast; iron,water-cooled 3.98 1.38 0. 45 1. 03 0. 66 3.36 1. 50 Do. 4. 04 1. 45 0. 41 1.08 0. 60 3. 3s 1. 25 Do. 3. 57 1. 70 0. 39 1. 07 0. 62 a. 32 3. Do.

*Balance iron.

In all examples, the mold wall thickness varied between preciated in view of the fact that at the present time,-the one and two inches, with the thinner walls occurring in cost of nickel is to 8 times the cost of manganese. the molds used for larger balls. What is claimed is:

In order to maintain the best strength properties in the 1. A cast iron alloy consisting essentially of 3.5% to cast iron of this invention it is desirable that phosphorus 12% manganese; 1% to 2.5 chromium; (14% t0 be maintained at a level not exceeding 0.15%. Also silicon; 2.9% to 3.6% carbon; up to 1.5% in the aggresince sulphur forms deleterious compounds when present gate of copper and nickel; not more than 0.15 phosin excessive amounts and since sulphur is suspected to phorus; not more than 0.1% sulfur; the balance iron and promote porosity through gaseous reaction with manganese," it is desirable that this element be kept as low as possible, preferably below 0.05% and not exceeding about 0.10%.

The following example is provided to further illustrate the present invention.

EXAMPLE A heat of 2 inch diameter grinding balls was produced using a cupola furnace and cast iron wateracooled permanent molds having a wall thickness of 1 to 2 inches. The charge was 220 pounds of steel scrap, 50 pounds of manganese steel scrap containing 12% manganese, 140 pounds of grinding ball remelts containing 2.7% nickel and 1.40% chromium, 45 pounds of gray iron scrap, 1 pound of 75% ferrosilicon, 7 pounds of high-carbon ferrochrome containing 65% chromium, 36 pounds of standard ferromanganese containing 80% manganese, and 1 pound of nickel cathode. The coke addition between each metal charge was 90 pounds and a ladle addition of 1 /2 ounces of aluminum was made for 500 pounds of product.

A chemical analysis of sample balls made from this heat showed manganese 3.86%, nickel 1.37%, chromium 1.52%, silicon 0.64%, and carbon 3.35%. A sample ball was out, polished, etched, and examined under the microscope. The material contained about 75 percent martensite and the microstructure consisted essentially of primary carbides in a matrix of martensite and austenite. The same ball was subjected to Brinell Hardness measurement and exhibited a Brinell Hardness number of 500.

From the foregoing description it can be seen that the present invention provides a manganese containing cast iron in which the expensive nickel alloying ingredient can incidental impurities.

2. A cast iron alloy consisting essentially of 6% to 12% manganese; 1% to 2.5% chromium; 0.4% to 0.7% silicon; 2.9% to 36% carbon; not more than 0.15% of phosphorus; not more than 0.1% sulfur; the balance iron and incidental impurities.

3. A cast iron alloy consisting essentially of 3.5% to 8% manganese; 1% to 2.5% chromium; 0.4% to 0.7% silicon; 2.9% to 3.6% carbon; 0.5% to 1.5 in the aggregate of copper and nickel; not more than 0.15% phosphorus; not more than 0.05% sulfur; the balance iron and incidental impurities.

4. A cast iron alloy consisting essentially of 3.5% to 8% manganese; 1% to 2.5% chromium; 0.4% to 0.7% silicon; 2.9% to 3.6% carbon; 0.5% to 1.5% nickel; not more than 0.15% phosphorus; not more than 0.05 s'ulfur; the balance iron and incidental impurities.

5. A cast iron alloy consisting essentially of 3.5 to 8% manganese; 1% to 2.5% chromium; 0.4% to 0.7% silicon; 2.9% to 3.6% carbon; 0.5% to 1.5% copper; not more than 0.15 phosphorus; not more than 0.05 sulfur; the balance iron and incidental impurities.

References Cited by the Examiner UNITED STATES PATENTS 2,129,683 9/1938 Gontermann 7s 12s x FOREIGN PATENTS 450,089 7/1936 Great Britain. 464,901 4/1937 Great Britain. 467,159 .6/1937 Great Britain. 468,424 7/1937 Great Britain.

DAVID L. RECK, Primary Examiner.

' P. WEI-NSTEIN, Assistant Examiner.

Claims (1)

1. A CAST IRON ALLOY CONSISTING ESSENTIALLY OF 3.5% TO 12% MANGANESE; 1% TO 2.5% CHROMIUM; 0.4% TO 0.7% SILICON; 2.9% TO 3.6% CARBON; UP TO 1.5% IN THE AGGREGATE OF COPPER AND NICKEL; NOT MORE THAN 0.15% PHOSPHORUS; NOT MORE THAN 0.1% SULFUR; THE BALANCE IRON AND INCIDENTAL IMPURITIES.

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