US2484231A - Free cutting bessemer steel - Google Patents

Description

Patented Oct. 11, 1949 FREE CUTTING BESSEMER STEEL Frank T. Kent, Pittsburgh, Pa., assignor to Jones & Laughlin Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application October 19, 1946,

Serial No. 704,527

4 Claims. (Cl. 75123) This invention relates to non-rimmed free cutting Bessemer steel having unusually good machinability together with the property of being readily deformed by hot or cold working.

Conventional Bessemer screw steel (grade B-1113) is made to the following specification:

Per cent Carbon 0.08 to 0.13 Manganese 0.70 to 1.00 Phosphorus About 0.100 Sulphur 0.240 to 0.330

Other grades have lower sulphur contents but are otherwise the same.

In making Bessemer steel, whatever manganese is present in the iron is practically all oxidized during the blow and accordingly the relatively high manganese content specified for screw steels is provided by additions of ferromanganese to the blown steel in the ladle. It is conventional practice to employ what is sold as standard 80% ferromanganese for these additions, 1. e., a ferro-alloy containing in the neighborhood of 80% manganese and about 6% carbon, the balance being substantially iron. An addition of this ferro-alloy suflicient to bring the manganese content of the steel in the ladle up to about 1% raises the carbon content by about 0.07% so that if the carbon content of the blown metal is 0.03% or 0.04%, the carbon content of the steel after the addition of ferromanganese will be about 0.10% or 0.11%, which is in fact average for Bessemer screw steel.

It has been known for years that a free cutting steel must be relatively brittle so that the chips formed in machining will break off in short lengths and not pack around the point of the tool. It is well known that carbon is one of the elements which enhances brittleness and consequently a carbon content as high as is com- I patible with the hardness of the steel to be produced has always been considered desirable in free cutting steels. Thus, as above stated, in conventional Bessemer free cutting steels, the carbon averages about 0.10% or 0.11% and this carbon content has long been considered the optimum for such steels. It is also well known that open-hearth steels of relatively higher carbon contents-say 0.20% to 0.30%machine much better than those of lower carbon contents. In fact, open-hearth steels containing less than about 0.15% carbon are of notoriously poor free cutting quality; the soft steel tears instead of cutting cleanly and the long curled chips pack tightly around the tool unless Constantly removed. Thus all previous knowledge and.experience confirm the conclusion that free-cutting characteristics are not associated with extremely low carbon contents in steel.

In spite of the fact that in general, raising the carbon content of ferrous alloys increases their machinability, I have found the contrary to be the case with respect to Bessemer screw steels. I have found that the machinability of nonrimmed Bessemer screw steel is greatly increased if the carbon content is lowered below that used in conventional practice. Nonrimmed free cutting Bessemer steel contains not more than 0.06% carbon. Such steel can be made by employing low carbon ferromanganese as a ladle addition to the blown metal. I have used manganese alloys containing from to 99.4% manganese and up to 1.5% carbon for this purpose and I have found that by lowering the carbon content as compared with conventional Bessemer screw steel, the machinabilty is greatly improved. v v

In my steel, as above stated, the carbon does not exceed 0.06% and preferably it does not exceed 0.05%. It generally is not practical with the ferromanganese now commercially available to produce Bessemer steel having the desired high manganese required in free cutting steels without the steel containing an appreciable amont of carbon. Accordingly the carbon in my steel is generally at least 0.02%. Usually the carbon is from about 0.03% to 0.05%.

The manganese in my steel is between 0.70% and 1.60%, usually between 0.70% and 1.20% and is preferably between 0.80% and 1.10%. The sulphur is between 0.075% and 0.400%, preferably between 0.160% and 0.330%. The phosphorus is between 0.07% and 0.15 usually about 0.10%. The balance of the steel is substantially all iron except for incidental impurities.

Where the use of the steel is such as to require not only good machinability but also a high degree of deformability by either hot or cold working, it is preferred that the sulphur content be within the lower part of the range above specifled. Where machinability is the more important factor and deformability is of less importance, it is preferred to use sulphur in an amount within the upper part of the range above specified. In general, it is preferred that the content of manganese be increased as the content of sulphur increases, the ratio of manganese to sulphur preferably being between about 4:1 and 10:1.

Machining tests have been performed to determine the reiative machinability of conventional Bessemer screw steel and steel made according to my invention containing carbon not over 0.06%. Table 1 gives the analyses of six heats of steel. In this table, heats A, B and C represent conventional steels having about 0.10% carbon, iwhereas'heatsfll E andF represent steels having low carbon in accordance with my invention. The two types of steel are essentially the same except for the difference in carbon contents.

TABLE 1 Heat Analysis A B 1D ;E F

.10 .10 .11 .05 .06 .05 .83 .85 .35 -199 ..'89 .83 .090 .096 .100 .094 .099 .105 .310 .285 .315 .289 .301 .304 Bal. Bal. Bal. Ba]. Ba]. I Bal.

The machining results. are shown in Table 2. The steel was in cold-finished bar form and was machined on conventional automatic screw machines under standardized conditions .for continuous production. .All factors such as spindle speed, feed, and cutting fluid were'held constant. Machining operations included drilling, forming the :outer surface, and cutting off thepart, with approximately 65% of the metal being removed.

Machiningperformance "A 13 0 D E 1* Tool Life, Hours 3-4" 2-3 .2-3 .10 15 with the conventional grades of free cutting Bessemer steels, I have materially improved the machinability of the steels. Furthermore, from the prior knowledge of the art it would have been thought that improved machinability would have been obtained by increasing the carbon content rather. than by decreasing it.

The invention is not limited to the preferred embodiments but may be otherwise embodied or practiced within the scope of the following claims.

I claim: 1. A'n'omrimmed free cutting Bessemer steel containing up to 0.06% carbon, 0.70% to 1.60%

.man'ganese,0.075% to 0.400% sulphur and 0.07%

to-0.'l5'% phosphorus, the balance being substantially all .iron and: incidental impurities. 2. :A non-rimmed free cutting Bessemer steel containing 0.02% to 0.05% carbon, 0.70% to 1.00% manganese, 0.075% to 0.400% sulphur and 0.07% to 0.15% phosphorus, the balance being substantially all iron and incidental impurities.

'3. A non-rimmed free cutting Bessemer 'steel containing 0.02% .to 0.06% carbon, 0.80% to 1.10% manganese, 0.16% to 0.33% sulphur and 0.07% to 0.15% phosphorus, the balance being substantially all iron and incidental impurities.

4. A free cutting Bessemer steel containing up to 0.06% carbon, 0.70% to 1.50% manganese, 0.1% to 0.4% sulphur, the balance being substantially all iron and'inc'idental impurities.

FRANK T. KENT.

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

UNITED STATES PATENTS Number Name Date 2,013,137 Crafts Sept. 3, 1935 2,079,058 'Winkler May 4, '1937 2,157,673 Ridgly May'9, 1939 OTHER REFERENCES U. S. S. Carilloy Steels, page 193; copyright 1938; published by Carnegie-Illinois Steel Corporation, Pittsburgh, Pa.

.Stahl and Eisen, July .9, 1936, p es 790 to 794.