US1990647A - Copper-containing steel - Google Patents

Description

provide steels which have relatively high strength Patented Feb. 12, 1935 PATENT OFFICE COPPER-CONTAINING STEEL Q Herbert Harris, Milwaukee, Wis., assignor to A. 0. Smith Corporation, Milwaukee, Wis, a corporation of New York No Drawing. Application .June 27, 1932,

Serial No. 619,531

8 Claims. (01. its-s1) Theinvention relates to alloys which are composed mainly of iron and contain copper with small additions of other metals.

It is among the objects of the invention to and ahigh rate of carburization as compared to carbon steel, and which are capable of being age hardened.

The alloys may be considered generally as high copper, low carbon steels containing additions of manganese from about 0.5% to about 2.0%. Copper is present from about 2.0% to 3.0%. More than about 0.25% carbonproduces brittleness. Carbon is commonly present in ferrous alloys but the smallest possible amounts of carbon may be present in these alloys. Howover, 0.05% carbon is mentioned as approximating the lower limit attained in commercially manufacturing the alloys, but less carbon may be present. Care should be taken in the preparation of the steel to avoid oxidation since iron oxide is an undesirable constituent in steel and has a tendency to'produce hot shortness.

More than about 3.0% copper renders the steels practically useless for carburlzing purposes. With 3.0% copper, the steel gives excellent carburized cases but with materially larger amounts, such as 3.4% copper, the carburized layer is too shallow for present commercial uses. As contents of 3.0% copper are approached, the steels have the best age hardening properties. I

As compared to carbon steels, .the alloys carburize rapidly and produce a sufllcient hardness when at least 0.5% of manganese is present. More than 0.5% manganese to about 2.0% increased the rate of carburization and toughened the core of the carburized material. It was found that chromium in amounts up"to 0.5%

gave the optimum grain size of 2 to 4 as referred to the McQuaid and Ehn classification. It materially increased the speed of carburization and the depth of the case. The smaller amounts of manganese alone give at least as great a speed of carburization as that commonly found in carbon steels. Higher amounts of manganese increase the speed of reaction. The chromium appears to intensify the action-of the manganese but with more than about 0.5% chromium, there is a loss of toilshnes in the core. The strongest" cores are found when the larger amounts of manganese and chromium are pres-- eat, and greater toughness is imparted by less manganese and chromium. The hardness of the cases developed by carburizing and 'heat treatment was about 83 to 05 Rockwell C which change is produced when the alloys are caris'about the hardness developed by carburizing and heat treating the best carbon steels.

By quenching from about 850 C. core strengths of about 200,000 pounds per square inch and ,good ductility are given especiallywith high 5 manganese, carbon and chromium. The alloys are relatively. easy to machine and forge in the unquenched condition;

After quenching, for example, to harden the case or otherwise coolingirom a high temperal0 ture such as-850 C. so as to bring the copper into solid solution with the iron, the alloys may be age hardened by heating the machined,- forged or carburized articles throughout for a short time to temperatures of about 400 C. to 500 C. and cooling in air. Larger articles require about 2 hours heating while some small specimens show age hardening with a treatment of 10 minutes. The articles are not distorted but the strength is greatly increased by this heat treatment. For example, specimens of the alloy in thelower manganese rangewere carburized, quenched and age hardened. The age hardening increased .the core strength from about 95,000 pounds per square inch in the quenched condition to about 135,000 pounds per square inch. The most pronounced age hardening is found in the alloys which contain less than about 1.0% manganese. Inthe age hardened condition, the structure consists of a copper-iron solid solution throughout which a copper or a copper rich phase is finely dispersed.

The alloys may be carburized at about 925 C. They take a case more readily than the carbon steels in that a case of 1 to 1.2 millimeters thick is commonly produced in less time than with carbonsteels. There is a gradual change from the composition and hardness of the outeflayers of the case to the alloy of the core and no abrupt burized. The carburized cases have a normal hypereuteetoid structure, with grain sizes of about 2 to 4 as referred to the McQuaid and Ehn classification. V The term, McQuaid and Ehn classification as used in the specification and claims refers to a standardized test for grain size. When applied the test is conducted by carburizing the alloy test piece for eighthours at 1700 F. The carburized layer is polished and etched to make the granular structure visible under the microscope. The

image of the structure is magnified times and for convenience the image may be projected upon a screen. The image is compared with a pa tern which is ruled oil in hexagons of known areas. A grain size of 2 corresponds to the pattern which has 2 hexagons per square inch, a grain size of 4 corresponds to the pattern which .has 8 hexagons per square inch, and a grain size cross-sectional area of the grains in .the car-.

burized case is one-eighth to one-half tenthousands of a square inch, composed of 2.0% to 3.0% copper, 0.5% to 2.0% manganese, and a small amount of carbon but not more than 0.25%, the balance being substantiallyall iron.

2. A carburized alloy having a core composed of about'2% to 3% copper, 0.5% to 2.0% manganese, and-carbon, but not more than 0.25%, the balance being substantially all iron.-

3. A carburized alloy having a core-composed manganese, carbon and .chromium; but not more than 0.25% carbon and 0.5% chromium, the balance being substantiallyall iron.

4. A carburized alloyhaving a core and a case having a higher carbon'content than'the core,

. said core being composed of about;2'.0% to 3.0%

copper, 0.5% to 2.0% manganese, and carbon, but not more than 0.25%, the balance of the core being substantially all iron.

.5. A carburized alloy having a core and a case having a higher carbon content than the core,

said core being composed of about 2.0% to 3.0% copper, 0.5% to 2.0% manganese, carbon, but not more than 0.25% and chromium, but not more than 0.5%, the balance being substantially all non.

6. Acarburized alloy having a core containing copper between about 2.0% and 3.0%, manganese about 0.5% to 2.0%, and carbon between about 0.05% and a small material amount, such as about 0.1% in excess of 0.05%, the balance being substantially all iron. V I

'7. A carburized, age-hardened alloy having a core composed of about 2.0% to 3.0% copper, 0.5%'to 2.0% manganese, and carbon, but not I more than 0.25%,the balance being substantially all iron.

core composed of about 2.0% to 3.0% copper, about. 0.5% to 1.0% manganese, and a small amount of carbon, but not more than" 0.25%, the

-8. A-carburized, age-hardened alloy having a I