US2336001A - Metallic blasting and abrasive material - Google Patents

Description

Patented Dec. 7, 1943 METALLIC BLASTING AND ABRASIVE MATERIAL John T. Eash, Westfield, and Kenneth A. De

Longe, Cranford, N. 1., assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application December 29, 1942, Serial No; 470,518

7 Claims. (o1. 51-309) The present invention relates to metallic blasting and abrasive material used in processes where the blasting material is thrown at high velocities against an object by. air or other gas pressure or by mechanical force to clean or cut the object or to obtain an abrading effect, and more particularly to cast iron material which is to be crushed and used as grit in such processes.

It has been proposed to make grit and the like, i. e., cast iron shot or other particles which are crushed or fractured and are angular or have sharp corners or edges, of hard white cast iron or of soft malleablized cast iron, but such blasting and abrasive material was not completely satisfactory. Unalloyed white iron grit possessed high hardness, but lacked the desired toughness and shattered on impact. Some modified compositions exhibited moderate improvement in toughness, but grit having such composition still suffered from the disadvantage of shatterin upon impact with the material being blasted and of having relatively short service life- Malleablized cast iron grit, having a microstructure containing principally ferrite and temper carbon, possessed higher toughness than white iron grit, but its hardness and wear resistance was at a much lower level. Although many attempts were made to remedy these and other shortcomings none, as far as we are aware, was entirely successful when carried into practice commercially.

We have discovered that an improved combination of properties, including high hardness, can be obtained by using a special composition for metallic blasting and abrasive material intended primarily to be used as grit, and the like, i. e., in

a form having angular or sharp corners or edges.

It is an object of the present invention to provide grit having an improved combination of properties.

It is another object of the invention to provide a metallic blasting and abrasive material having improved toughness at high hardness levels.

It is a further object of the invention to provide ametallic blasting and abrasive material having increased service life.

It is still another object of the invention to provide an improved martensitic-austenitic-carbidic alloy cast iron grit which has an improved combination of toughness, decreased tendency to shatter and high hardness.

It is also an object of the invention to provide an improved cast iron grit having a simple composition and improved impact resistance at'.high hardness levels.

Generally speaking, the present invention provides an alloyed cast iron grit and the like to be used in a form having angular or sharp corners or edges and made of cast iron containing about 2% to 4% carbon, up to about 0.8% manganese, about 2% to 3% silicon, about 0.25% to 3.5% nickel, and about 0.07% to 1.1% chromium, the nickel and chromium being present in a ratio of about 2:1 to 4: 1, e. g., a nickel to chromium ratio of about 3:1 or more. While manganese is not essential, when sulfur is present about 0.2% to 0.8% manganese should also be present. The grit provided by the present invention may also contain small amounts of incidental or minor constituents and impurities added for known purposes or present as the result of commercial practice, e. g., sulfur, phosphorus, titanium, molybdenum, etc. Thus, the cast iron grit may contain about 0.02% to 0.2% of sulfur, about 0.03% to 1% of phosphorus, about 0.01% to 0.05% of titanium, etc. It'is to be understood that when the term balance substantially iron is used herein, it is desired to exclude incidental or minor constituents or impurities which may be present in such amounts as occur in commercial products or in amounts not adversely affecting the desired properties of the cast iron grit.

In carrying the invention into practice, it is preferred to maintain the composition within the ranges of about 2.7% to 3.5% carbon, about 0.3% to 0.6% manganese, about 2% to 2.5% silicon, about 0.75% to 1.5% nickel, about 0.25% to 0.5% chromium, andthe balance substantially iron. A

satisfactory composition contains about 2.9% to 3.1% carbon, about 2.4% to 2.5% silicon, about 0.4% to 0.6% manganese, about 0.75% to 1.25% nickel and about 0.25% to 0.4% chromium.

It is a critical feature of the improved grit that a. balanced composition be maintained within the ranges set forth hereinbefore. If the silicon content falls below the amounts set forth, the high hardness of the grit provided by the invention is no longer obtained. It has been found that the effect of silicon in cast iron grit is not the same as in ordinary cast iron castings. High silicon contents in grit apparently promote high hardness and brittleness and favor the formation of martensite, whereas, in ordinary castings, high silicon contents promote low hardness and low toughness and favor the formation of graphite and pearlite. Nickel and chromium in the amounts set forth hereinbefore are essential to obtain the desired improved toughness, combined with high hardness, to give good service life.

The improved cast iron grit provided by the invention contains a large proportion of martens-- ite and has a microstructure constituted substantially entirely or carbide, i. e., cementite, in a matrix of martensite and austenite. It is essential that the grit contain a small amount of austenite, but the amount should not exceed about 15% of the total matrix of martensite and austenite, e. g., about5% to 10% of the matrix should be austenite and the balance martensite. When the term "martensite is used, it is intended to include not only the micro-constituent commonly referred to as martensite, but is also intended to include smaller amounts of other austenitic decomposition products, such as bainite, and troostite. In the grit provided by the invention, the carbide is markedly refined and the matrix is partially austenitic as compared to the more massive carbides and the entirely martensitic matrix of similar plain malloyed cast iron grit.

In order that those skilled in the art may have a better understanding of the present invention, the properties of grit compositions made in accordance with the invention are compared with unalloyed cast iron in the table set forth hereinafter. Compositions No. 1 to No. 4 in the table also contained about 3.5% carbon, about 0.5% manganese, about 0.08% sulfur, and about 0.6% phosphorus. Compositions No. 5 to No. 8 contained about 3.17% carbon, while No. 9 to No. 12 contained about 2.93% carbon and No. 13 to No. 16 contained about 2.85% carbon. All contained about the same amounts of manganese, sulfur and phosphorus as No. 1 to No. 4.

No. 1 to No. 4 were cast by pouring into cold water held at 55 to 60 F., whereas No. 5 to No. 12 were cast. in hot water held at 105 to 110 F. and No. 13 to No. 16 were cast in quenching oil held at 70 to 75 F. It will benoted that for the alloyed grit compositions provided by the invention, and illustrated by No. 2 to No. 4, No. 6 to No. 8, No. to No. 12, and No. 14 to No. 16, the maximum hardness as indicated by the Vickers hardness number (V. H. N.)-is obtained at the lower alloy contents and the maximum toughness, as indicated by the impact values, is obtained at the higher alloy contents. The impact values set forth in the table indicate the minimum blow in inch-pounds which was required to cause fracture of the shot and were obtained in the following manner.- A drop test procedure was used consisting of dropping a weight of about of the weight of the hammer in pounds and the minimum height of the fall in inches required to fracture the shot was taken as the impact strength.

The grit compositions provided by the invention have the desired high hardness with improved toughness. For example, No. 10 and No. 11 which are suitable for grit have a high-hardnessof over 900 V. H. N. combined with improved toughness compared to unalloyed specimen No. 9 which was not made in accordance with the invention. In some cases the hardness as well as the toughness are improved. Thus, No. 10, No.

0.6 pound upon a single shot, starting from a height of about two inches and increasing the height of fall successively by one inch increments until fracture of the shot occurred. The product ness than similar unalloyed compositions. It will be noted that the silicon content of these compositions is at a higher level than in No. 2 to No. 4, and No. 6 to No. 8 and that the quenching medium was such as would produce a slower cooling rate than that used for No. 2 to No. 4. Changes in the cooling rate or the sacrifice of some hardness for the sake of increased toughness may. require some'adjustment in the alloy content to obtain the desired combination of properties. In

general, too rapid cooling rates tend to reduce the hardness and should be avoided. Thus, casting a composition containing about 1.56% nickel, 0.52% chromium, 2.96% carbon, 2.46% silicon, 0.50% manganese, 0.08% sulfur and 0.01% phosphorus, which is very similar to No. 12, in cold water at 42 F. produced too rapid cooling and resulted in a soft product having a high impact value of 7.3 but a hardness of only 567 V. H. N. which is unsatisfactory for grit. In general, the cooling rate should be such as to produce a hardness of at least about 750 V. H. N.

The present invention is applicable to the production of metallic blasting and abrasive material, particularly to the production of material which is to be crushed or fractured and used in that form, e. g., as grit. A brief description of some blast cleaning processes, apparatus and illustrations of the diflerences in surfaces cleaned by grit and by shot may be foimd in Metals Handbook, 1939 ed., pages 1142 and 1143. The use of grit blasting for purposes other than cleaning are also well known to those skilled in the art, e. g., for cutting, abrading surfaces to be enameled, etc.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and of the appended claims.

We claim:

1. Cast iron grit containing about 2% to 2.5% silicon, about 0.75% to 1.5% nickel, about 0.25% to 0.5% chromium, the nickel and chromium being present in the ratio of about 3:1 to 4:1.

2. Cast iron grit containing about 2% to 2.5% silicon, about 0.75% to 1.5% nickel, about 0.25% to 0.5% chromium, the nickel and chromium being present in the ratio or about 3:1, said material being characterized by a microstructure comprised of carbide, martensite and a small amount of austenite.

3. As an article of manufacture, a cast iron particle having angular or sharp edges and of size suitable for grit blasting and the like made of cast iron comprising about 2% to 4% carbon, about 0.2% to 0.8% manganese, about 2% to 3% silicon. about 0.25% to 3.5% nickel, and about 0.07% to 1.1% chromium, the nickel and chromium being present in the ratio of about 2:1 to 4:1, said particle being characterized by a microstructure comprised substantially entirely of carbide, martensite and a small amount of austenite.

4. As an article of manufacture, a cast iron particle of size and shape suitable for grit blasting made or cast iron comprising about 2% to 4% carbon, about 0.2% to 0.8% manganese, about 2% to 3% silicon, about 0.25% to 3.5% nickel, about 0.07% to 1.1% chromium, the nickel and chromium being present in the ratio 0! about 3: 1, and the balance substantially all iron.

5. Cast iron grit made of cast iron particles containing about 2.7% to 3.5% carbon, about 0.3% to 0.6% manganese, about 2% to 2.5% silicon, about 0.75% to 1.5% nickel, about 0.25% to 0.5% chromium, the nickel and chromium being present in the ratio of about 3:1 to 4:1, said grit 2o being characterized by a microstructure comprised of carbide, martensite and a small amount of austenite.

6. Cast iron grit made of cast iron particles containing about 2% to 3% silicon, about 0.25%

to 3.5% nickel, about 0.07% to 1.1% chromium,

the nickel and chromium being present in the ratio of about 2:1 to 4:1, said grit being charactenzed by a microstructure comprised of carbide, martensite and a small amount of austenite.

7. Cast iron grit made of particles of cast iron containing about 2% to 3% silicon, about 0.25% to 3.5% nickel, about 0.07% to 1.1% chromium, the nickel and chromium being present in the ratio of at least about 3:1 and up to about 4:1, said grit being characterized by a Vickers hardness number of at least about 750.

JOHN T. EASH. KENNETH A. DE IDNGE.