US2157673A - Free machining open hearth steel - Google Patents

Description

capable of mac Patented May 9, 1939 UNITED STATES,

2,157,673 FREEMACHINING OPEN HEARTH STEEL James A. Ridgely, W. J. Holliday &

' poration No Drawing. Original Serial No. 148,324.

Cincinnati, Ohio, assignor to I 0., Indianapolis, Ind., a corapplication June 15, 1937, Divided and this application January 8, 1938, S

erial No. 184,025

2 Claims. (cm-123) In the higher carbon range, SAE 1040 has a This invention relates to a new free machining open hearth steel having properties not heretofore developed in such steels. In the lower carbon .ranges, the new steel has the properties of a case hardening steel having high ductility and tensile strength. In the higher carbon ranges, the new steel is suitable for heat treatment. This application is a division of my copending applicatlon Serial No. 148,324, filed June 15, 1937 in which a process of manufacturing my new steel is described and claimed per se.

In the past, most open hearth and Bessemer free machining steels have been produced by increasing the sulphur and manganese content above that of the average commercial open hearth steel, the silicon and phosphorus content remaining about the same. For free machining case hardening steels the manganese content is often run as high as 1.20% and sometimes even to 1.50% with a sulphur content often of 0.20% and sometimes 0.30% as compared to manganese contents of 0.60% and 0.80% and sulphur content below 0.05% in ordinary steels. Such steels commonly carry a phosphorus content of about 0.04% and one commercial Bessemer steel of this type has a phosphorus range of from 0.09% to 0.13%. Their silicon content is usually in the range of ordinary steels and is not generally specified in the S. A. E. specifications since heretofore it has been considered of small importance. Such steels are free machining steels capable of case hardening but have, the disadvantage of being nonuniform and sometimes brittle. This lack of, uniformity and brittleness is caused by the formation of manganese sulphide in isolated masses known commercially as segregations and which weaken the bars at the points where they occur. Heretofore these segregations have been considered an inescapable high sulphur and manganese content which has been found advantageous in producing a steel 'ning at high speeds.

Heretofore the freest .machining steels have been known as SAE X1112, SAE 1112 and SALE X1314 in the low carbon range and SAE 1040 in the higher carbon ranges. SAE X1112 and- SAE 1112 have the best machining qualities but are rather brittle Bessemer steels having poor ductility and 'poor case'hardening properties. SAE X1314 is fairly good from the standpoint of free machining and case hardening but has a low yield point. Its ductility, while better than X1112 and 1112, is still rather poor. steels, the steel produced in accordance with this invention in the same carbon range has superior machinability, much better ductility; sup lior case hardening properties and a much higher yield point. In .case harder, deeper case in less time and with much less warpage.

evil accompanying the As compared with these hardening itproduces a good compensated-ductility but is relativelypoor from the standpoint of free machining. The new steelinthisrange has substantially the same ductility characteristics as SAE'1040 but has a machinability rating which compares favorably with that of the low carbon steels.

. Heretofore no free machining steel having a high compensated ductility rating has been manufactured. Steel produced in accordance with this invention up to 0.55% carbon has a machinability rating of at least 80, compared to SAE 1112 taken as 100. In addition, its compensated ductility rating is higher than any other free machining steel. The compensated ductility of steels produced hereunder is above 28 and generally of the order of 31--33. Compensated ductility (hereinafter referred toas D-C rating) is calculated according to the following formula:

D-c rating=E-F0.43C

and where E is the elongation percent in 2" for ,cold drawn material and C is the hundredths of percent of carbon.

The product likewise has a compensated machinability-strength rating considerably in excess of like steels. The compensated machineability-strength rating is calculated according to the following formula:

TX Y EXM 1011 where T is the ultimate tensile strength in pounds per square inch, Y the yield point inpounds per square inch, E M the. machinability based upon SAE 1112 as 100, and C is the carbon content of the steel MCS rating= +C expressing in hundredths of 1%.- T, Y, E and M are based on cold drawn material.

My new steel has an MCS rating of at least 140 and normally about 150. This compares with an MCS rating of 113 for X1112, 89 for 1112 and 102 for X1314. Rigidly 15% carbon steel produced hereunder had an MCS ratingof approximately My new' steel has a yield point ofat least 75,000 lbs. based on a 1" rod. 4

My invention contemplates a steel having sulphur and manganese contents sufficiently high to permit cutting speeds as high or higher than present steels but in which the excessive formation of manganese sulphide which produces segregation is reduced: to a minimum. According to my invention, the sulphur is believed to form soluble iron sulphides which are uniformly distributed throughout the heat and in turn throughout the ingot, billet and bar and which add materially to the free machining quality of thesteel. This result is accomplished by reducing the silicon and phosphorus content, which has heretofore the elongation percentage in 2",

ture ranges. Each of these four factors contributes to the reduction of manganese sulphide segregations.

The preferred specification of my new steel is as follows:

Per cent Sulphur 0.18 to 0.30 Manganese 1.00 to 1.40 Phosphorus 0.02 maximum Silicon 0.02 maximum The steel may be made with carbon contents from 0.08 to 0.75% or higher, the lower carbon steel having excellent case hardening characteristicsand the higher carbon steel having heat treating properties. Departure from these preferred specifications, within the usual commercial tolerances, may be made without extremely deleterious results.

It is important that the phosphorus and silicon content be kept as low as possible. More phosphorus or silicon than that specified above reduces the amount of sulphur and manganese which can be absorbed by the steel without producing segregations; Less silicon and phosphorus permits more manganese and sulphur to be used. The manganese and sulphur contents should be in the ratio of about 5 to 1.

In the manufacture of the steel, the furnace is preferably charged with pig iron and scrap steel or with scrap steel alone, as may be desired. A basic flux is used, lime in the proportion of about 8% of the charge being the preferred flux. This is foundsufiicient to reduce the phosphorus and silicon contents to the desired minimum. The carbon content is controlled by standard open hearth practice. Sufiicient ferro-manganese is added in the furnace to give about 70% of the final desired manganese and sulphur contents for a steel having a final manganese content of 1.20 to 1.30%, standard open hearth practice being followed in this respect. The amount of manganese added to this point should not be sufficient to cause appreciable segregations of manganese sulphide. Ordinarily the amount of manganese presentin the furnace is well below 1%--say'.84 to .91%.

The charge is preferably poured from the furnace at the usual pouring temperature of approximately 2850 F. and is allowed to stand in the ladle until it has cooled approximately F.

or more. In the case of a charge sufficient to pour 175 tons of ingots this cooling requires approximately 30 minutes. At the end of the desired cooling time, a further addition of ferromanganese is made sufiicient to bring the final manganese content to the desired amount. Free sulphur is also added at the same time if the sulphur contents of the original charge and the added ferro-manganese does not give the desired final sulphur contents.

The additions in the ladle still further-lower the temperature of the heat but not sufllclently to permit solidification before pouring of the ingots can be completed.

The addition of the last portion of manganese and sulphur at-a reduced temperature as inthe ladle appears to be an extremely important factor in'reducing the formation of manganese sulphide segregations. Apparently. at this reduced temperature, the reaction i rming manganese sulphide does not take plac to so great a degree as at the higher temperature, if at all. Furthermore, the time required to solidify from the lower temperature is so much less than from the higher temperature that such manganese sulphide as may possibly be formed does not have sumcient time to segregate before the charge has solidified in the ingot mold.

After the ingots have solidified, the molds are stripped and the ingots placed in the soaking pit and held at about 2460 F. until ready to roll. The rolling from ingot to billet is done with the least possible temperature drop. The billets, cut to proper length, are then reheated for the rolling from the billet to bar.

In the rolling of bars of the low carbon steel from the billets, the starting temperature is about 2400 F. and the finishing temperature is kept as high as possible. Preferably "at about -1860 F. to 1880 F. Below this finishing temperature it is found that cracks, seams and segregations occur which destroy in a large degree the desirable properties of the steel. For the high carbonsteel the criticalrolling temperatures are much lower, the preferable starting temperature being below 2100 F. Higher rolling temperatures for the high carbon steel produce a porous steel having incorrect density and excessive scale.

When used for case hardening, the new steel carburizes to the same depth in less time and gives a harder case and tougher core than other carburizing steels, and is uniform and free from brittleness. One of its most important charact'eristics is its freedom from excessive warpage. This characteristic is so marked that it maybe used for parts, such as relatively long pins with ground journals on each end, which cannot be made from other case hardening steels. This property is due in a large measure to the 'uniformity of the material.

The following table indicates the relative properties of the new steel and certain other steels, referring only to those steels in the cold drawn state:

A l B I C D E F G SAE X1112... 200 to 235 to 85,000 68, 000 14 SAE l1l2. 150 100 80,00064,000 l5 SAE x1314 94 79, 500 62,000 19 84E 1040 115 60 94,000 83,000 16 Ridgely 0.18 carbon 190 to 210 120 85, 000 80,000 26 6 00 Ridgely 0.39 carbon 150 100 105, 750 81, 000 16. 5 4 48-56 Ridgely 0.47 carbon to 90112,200 82,94013 2. 5 5665 Column A-Machining speeds in it. per min.

Column BMachinubility rating.

Column C-Tensile strength, pounds per sq. in.

Column D-Yield point, pounds per sq. in.

Column EPerceut elongation in 2".

Column F-Torslon tests, 300 turns in 12".

Column GImpact test, it.-lbs.

The figures given for Ridgely steels are conservative averages.

The new steel not only machines more readily than comparable steel, but machines in an entirely different manner. Instead of producing chips in the ordinary form, long spirals of material are produced which may be several feet in length. Machine surfaces in the new steel have a smoother appearance and texture than surfaces machined in the same manner with other steels.

Another important result of the new steel is increased tool life. It has been found in practice that tools used in machining the new steel may While the invention is particularly applicable to steels having no other metallic contents than heretofore mentioned, it may be used with steels containing small amounts of other metallic elements such as nickel, chromium, molybdenum, vanadium, etc. When so used, it produces a steel having superior machinabllity to steels of the same class. i

' Per cent Sulphur .18 to .30 Manganese 1.00 to 1.50 Phosphorus -i .02 maximum Silicon .02 maximum Carbon .08 to 0.75

and the balance being substantially all iron, said steel being sufliciently free from segregations of manganese sulphide to have a relatively high ductility, and a compensated machinabilltystrength rating of at least 140 based on cold drawn material.

2. An alloy steel having an approximate composition as follows:

Per cent Sulphur .18 to .30 Manganese 1.00 to 1.50 Carbon .08 to 0.75

Silicon in a percentage of commercial minimum Phosphorus in a percentage of commercial minimum the balance being substantially all iron, and such of the manganese and sulphur as may be present in the form of manganese sulphide being sumcient finely divided and in suiilciently small quantity to produce a. steel having a relatively high ductility. and a compensated machinabilitystrength rating of at least 140 based on cold drawn material.

JAMES A. RIDGELY.