US1984474A

US1984474A - Malleable iron casting

Info

Publication number: US1984474A
Application number: US679079A
Authority: US
Inventors: Robert C Good
Original assignee: ELECTRO METALLURG CO
Current assignee: ELECTRO METALLURG CO; ELECTRO METALLURGICAL Co
Priority date: 1933-07-05
Filing date: 1933-07-05
Publication date: 1934-12-18
Anticipated expiration: 1951-12-18

Description

Patented Dec. 18, 1934 UNITED STATES MALLEABLE IRON CASTING:

Robert 0. Good, Pittsburgh, Pa, assignor to Electro Metallurgical Company, a corporation oi West Virginia No Drawing. Application July 5, 1050, Serial No. 679,070

4 Claims.

The invention relates to malleable iron castings, referring more specifically to malleable iron castings containing chromium and characterized by improved strength and malleability.

Malleable cast iron ordinarily has a composition within the limits: 0.5% to 2% silicon, 0.18% to 0.7% manganese, 1.5% to 3.5% carbon in the unannealed condition and somewhat less after annealing, 0.05% to 0.3% phosphorus, up to about 0.2% sulfur, remainder iron. A typical composition is 0.9% silicon, 0.3% manganese, 2.4% total carbon, 0.16% phosphorus, remainder iron.

Such iron when cast in suitable molds has a white fracture, is hard and brittle, and in this condition is unsuited to many uses. All the carbon is combined in the form of iron carbide, and the material is ordinarily known as malleable hard iron.

A prolonged heat treatment or anneal changes completely the properties of malleable hard iron. The anneal consists ordinarily in heating the casting, sometimes in a packing material of iron oxide or an inert material, at a temperature between about 1290 F. and 2000 F. for 6 to 60 hours, according to the temperature used, and then slowly cooling the castings so that substantially-complete graphitization of the carbon takes place. A typical heat treatment consists in heating to 1650 F. in 36 hours, holding at 1650 F, for 42 hours, cooling from 1650 F. to 1100 F. at 10 per hour, and then slowly cooling from 1100 F. to room temperature. Some treatments eliminate the slow cooling from 1650 F. to 1100 F., and others eliminate the slow cooling from 1100 F. to room temperature.

The heat treatment transforms the brittle malleable hard iron into a soft and ductile material, having a black fracture, the carbon of which is in the form of graphite nodules or temper carbon.

While malleable cast iron so produced is useful for a great many purposes, its relatively low wear-resistance and elastic limit are definite and material limitations upon its life in service and its adaptability to certain uses.

It is an object of the invention to provide malleable iron castings having an increased ultimate tensile strength, a higher elastic limit or yield point, and increased hardness, particularly as measured in Brinell hardness numbers.

It is known that additions of small amounts of chromium to malleable cast iron tend to increase its strength and hardness. But it is also known that small amounts of chromium have a strong inhibiting effect on the annealing operation, and tend to produce large patches of stable carbides which completely resist graphitization during 'the annealing operation. For this reason it has not been practicable to malleabilize completely cast iron containing chromium in amounts as great as about 0.15%.

It is discovered that if to a malleable cast iron composition additions of both chromium and silicon are made, and if the ratio of added chromium to added silicon is kept within certain limits, there is obtained a malleable cast iron composition which upon being annealed results in a strong, hard, wear-resistant, malleable casting having a structure of fine pearlite, fine temper carbon, chrome-ferrite (a solid solution of chromium and iron), and occasionally small amounts of .carbide.

The invention includes the addition to 11. malleable cast iron composition containing silicon, -manganese, and carbon so proportioned in known manner that upon casting amalleable hard iron would be obtained, of about 0.15 %'to 2 chromium and 0.3% to 2% silicon in addition to the silicon contained in the base composition, the ratio of additional silicon to chromium being between about 0.1 and 1.25, and preferably between 0.2 and 0.7. If the ratio of additional silicon to chromium is too low, it will be dimcult or impossible to secure satisfactory graphitization by anneal ng; while if the ratio is too high, the hardness, strength, and ductility of the annealed casting are unfavorably afiected.

Tests which have been made demonstrate the advantages of the invention. The following table includes typical data obtained in these tests. In this table, each casting had approximately the base composition: total carbon 2.35%, manganese0.3'7%, phosphorus 0.16%, sulphur 0.10%, and silicon 1.02%, remainder iron. To the base composition were added the respective percentages of chromium and silicon indicated in the table, the additions being made in the ladle and in the form of ferrochromium and ferrosilicon. Fiveeighths' inch standard malleable test bars were cast and given a standard anneal.

Ratlool g 1 01-00111 Percent added r1 3 33; g} 5119120 added a i d e d strength i i mass ber p.11 percent number 1 0 0 54,500 31,500 1&5 131 2 022 000' 0.00 70,000 42,400 11.0 115 a 0.21 0.22 000 72,000 40,000 0.0 170 4 0.24 0.25 1.04 15,000 41,000 0.0 100 s 10 7 0150 01:11 0:01 00,500 52,500 010 201 3 3'3 8% 3% 303% 20% 1'3 5 Silicon added as an alloy consistln of 61.9 Si 10.5% Mn, 21.8% Zr, remainder Al. g

The chromium and the silicon may be added in the furnace or in the ladle, or either one in the furnace and the other in the ladle, and may be added in the form of elements or alloys.

Graphitizing agents other than silicon, such as nickel, aluminum, titanium, and zirconium, may be substituted for silicon, in part or entirely, without departing from the invention.

I claim:

1. A malleable cast iron consisting in its metallographic structure substantially of pearlite chrome-ferrite, and temper carbon, andcontaining about 1.5% to 3.5% carbon, at least about 0.53% and not over about 4% silicon, 0.15% to 2% chromium, 0.18% to 0.7% manganese, 0.05% to 0.3% phosphorus, and up to about 0.2% sulfur; the silicon, manganese, and carbon being proportioned as in ordinary chromium-free white iron except that the silicon content is 0.03% to 2% higher than in said white iron, and the ratio of additional silicon to chromium being between about 0.2 and about 1.25.

2. A malleable cast iron consisting in its metallographic structure substantially of pearlite, chrome-ferrite, and temper carbon, and containing about 1.5% to 3.5% carbon, at least about 0.53% and not over about 4% silicon, 0.15% to 2% chromium, 0.18% to 0.7% manganese, 0.05% to 0.3% phosphorus, and up to about 0.2% sulfur; the silicon, manganese, and carbon being proportioned as in ordinary chromium-free white iron except that the silicon content is 0.03% to 2% higher than in said white iron, and the ratio of additional silicon to chromium being between about 012 and about 0.7.

3. A malleable cast iron consisting in its metallographic structure substantially of pearlite, chrome-ferrite, and tempercarbon, and containing about 1.5% to 3.5% carbon, at least about, 0.53% and not over about 4% silicon, 0.15% to 2% chromium, 0.18% to 0.7% manganese, 0.05% to 0.3% phosphorus, and up to about 0.2% sulfur; the silicon, manganese, and carbon being proportioned as in ordinary chromium-free white iron except that the siliconcontent is 0.03% to 2% higher than in said white iron, and the ratio of additional silicon to chromium being between about 0.2 and about 1.25; which casting has been annealed at temperatures between about 1290 F. and about 2000 F.

4. A malleable cast iron consisting in its metallographic structure substantially of pearlite, chrome-ferrite, and temper carbon, and containing about. 1.5% to 3.5% carbon, at least about 0.53% and not over about 4% silicon, 0.15% to 2% chromium, 0.18% to 0.7% manganese, 0.0 to 0.3% phosphorus, and up to about 0.2% sulfur; the silicon, manganese, and carbon being proportioned as in ordinary chromium-free white iron except that the silicon content is 0.03% to 2% higher than in said white iron, and the ratio of additional silicon to chromium being between about 0.2 and about 0.7; which casting has been annealed at temperatures between about 1290 F. and about 2000 F.

ROBERT C. GOOD.