US2789069A

US2789069A - Method for improving the machinability of steel

Info

Publication number: US2789069A
Application number: US459527A
Authority: US
Inventors: Elliot S Nachtman
Original assignee: Lasalle Steel Co
Current assignee: Lasalle Steel Co
Priority date: 1954-09-30
Filing date: 1954-09-30
Publication date: 1957-04-16
Anticipated expiration: 1974-04-16

Description

UnitedStates Patent Elliot S. Nachtman, Park Forest, 111;, assignor to La Salle Steel Co., Hammond, Ind., acorporation of Delaware No Drawing. A plication September 30, 1954, Serial No. 459,527

13 Claims. (Cl. 148-4) This invention relatesto-plain carbon and alloy steels and to a method of improving the machinability thereof.

It is concerned more particularly with a method of improving the machinability of plain carbon and alloy steels accompanied with improvements also in physical and mechanical properties of the steel.

It is an object of this invention to produce and to provide a method for producing plain carbon and alloy steels in which the machinability is improved by means easily and simply carried out during normal steel making and it is a related object to improve the machinability of steel with improvement also in other physical and mechanical properties of the steel, such as strength, resistance to wear, resistance to corrosion and toughness.

Numerous attempts have been made in the past to improve the machinability of such plain carbon and alloy steels. To the present, lead, selenium, sulphur and his muth have been found to provide noticeable improvements in the machinability of steel when added to provide certain concentration in the steels but certain undesirable conditions have been associated with their use. For example, improved rnachinability has been secured by the addition of lead in the manufacture of leaded steels but since lead is insoluble in the steel, it is diflicult to achieve the desirable uniform distribution of the lead inthe steel. In addition, lead releases toxic fumes under the processing conditions with the result that extensive precautions must be taken in the use thereof.

Similarly the distribution of sulphur in the desired concentration in the steel is also difficult to control and unless combined with manganese in substantial amounts, the sulphur will produce an undesirable condition in the steel during rolling, generally referred to as hot shortness. Bismuth and selenium have been used on a minor scale in stainless steel for the purpose of improving machinability. However, the additional cost occasioned by the use of such materials in desired amounts is a deterrent to their adoption. In addition, these various elements which have been added to steels to improve machinability in many cases cause an undesirable loss in some of the mechanical and physical properties of the steel.

It has been found in accordance with the invention described and claimed in my copending application 'Ser. No. 390,739, filed November 16, 1953, that the machinability of plain carbon and alloy steels can be improved materially by the addition of lead and copper in combination in amounts ranging from 0.03 to 0.35 percent by weight copper and 0.03 to 0.5 precent .by weight lead. The improvements resulting from the combination of copper and lead in such steels have been found to be enhanced further by the presence of sulphur, phosphorus and manganese.

It has now been found that copper alone can be used effectively in appropriate concentrations, without lead, to improve the machinability of plain carbon and alloy steels. It appears from analysis and observations of results that copper-alone functions in a manner substantially ice unlike that of lead; Whereas lead is substantially insoluble in steel, copper is soluble in steel, and whereaslead reduces some of the other properties ofsteel, copper provides additional improvements in the strength, corrosion resistance, and impact strength of plain carbon and alloy steel. Unlike lead, the copper in the desired concentration may be added to steel by normal procedure, requiring no special techniques, with practically percent recovery in the steel and. with uniform distribution.

To the best of my knowledge, no one before has introduced copper in plain carbonand alloy steelsv intentionally for the improvement of machinability and such formulation to modify the chemistry of the steelby'the presence of copper to improve machinability is believed to represent a completely new concept in the field of metallurgy. The discovery that'copper alone is effective in improving the machinability of steel is believed to constitute an important advance in the technology of such steels, particularly since along with achieving improve ment in machinability, desirable improvements in physical and mechanical properties are also secured. Such improvements have not been obtainable with elements previously addedto modify the chemistry of steel to improve machinability.

Little, if any, improvement in machinability is secured whencopp'er is present in the plain carbon or alloy steel in amounts less than0.06 percent by weight. Best results are secured and a marked improvement in machinability as well as other physical and mechanical properties, such as impact strength, corrosion resistance, and tensile strength are secured when copper is present in the steel in amounts within the range of 0.15 to 0.30 percent by weight. To the present, improvements in the machinability of the steel'have been secured by the use of copper in amounts up to 0.60 percent by weight, but it will be understood that the improvements in machinability can be securedby the use of. copper in greater amounts.

Improvements in machinability of steel by the use of copper are noticeable with low carbon steel (less than 0.25 percent carbon) as well as-with medium carbon steel (0.25 to 0.50 percent carbon) and high carbon steels (above 0.5 percent carbon). The general effect, for example, is illustrated in Table I in which a steel containing approximately 0.45 percent carbon was tested in a screw machine. For comparison, a steel of substantially the same composition was employed except for the presence of copper in one and the absence of copper in the other. A measure of the relative machinability was obtained by measuring'the wear on'the tools after 90 of the parts being machined had been cut under substantially identical con- In the test described in Table 1, parts were machined in a cycle time of 60 seconds, using a' surface speed of feet per minute and tool wear was measured after '90 pieces had been cut. The difference in ToolfWear is an indication of the difference in machinability of the two steels.

It will be apparent'from the datasecured that the steel containing copper showed approximately '1 7 percent better wear on the inch turning tool; 64 percent better tool wear on the /2 inch turning tool, and 38 percent better tool wear on the form tool.

The inventive concepts can be further illustrated by the effects of copper on the machinability of a low carbon steel (Table H).

1 This is a comparative machinability reading obtained by controlled mad'rtning on a constant pressure lathe in a standard test. (Transactions of the, ASME for July 1949 Constant-Pressure Lathe Test for Measuring the Machinability of Free-Cutting Steels, by F. W Boulger, H. L. Shaw, and H. E. Johnson.) j

In the past it has been recognized that residual metals such as nickel and chromium have caused marked depreciation in the machinability of steels even when present in small amounts. Contrary to the accepted limitations, it has been found that the deleterious efiects of the residual metals on machinability ofsteels is'reduced by the use of copper in accordance with the practice of this invention. While it is preferred to make use of a steel in which such residual metals are not present since copper is capable then of maximum use, it has been found that the presence of residual metals does not destroy the machinability characteristic of the steel in the presence of copper even though less improvement is secured by copper, nevertheless a steel containing copper in combination with the residual metals provides for better machinability than the same steel without copper or within the machinability available from the copper is thusly efiected.

It has been found that the improvement in machinability available from the use of copper in plain carbon steels and alloy steels can be extended by the addition of other elements with the copper, such for example as phosphorus, sulphur and nitrogen. To some extent these other elements have been used before because of their beneficial eifects on machinability but the improvement which is secured in a'system which makes use both of copper and sulphur together in plain carbon and alloy steels exceeds that which might be expected by way of aggregation to the extent that improvement in machinability is indicative more of a synergistic effect between these materials in steel. These unexpected results are secured when sulphur is present in amounts ranging from 0.01 to 1.0 percent by weight in the steel and when the copper is present in an amount within the range of 0.06 to 0.6 percent by weight of the steel.

When phosphorus is present, the best results are secured when the concentration of phosphorus is within the range of 0.01 to 0.2 percent by weight, and the copper is present within an amount ranging from 0.06 to 0.6 percent by weight, and sulphur, when present, is present in an amount less than 1.0 percent by weight. Nitrogen in amounts greater than 0.001 percent by weight also improves the. machinability of steed when present with copper alone or in a system which includes copper and one or more other elements, such as sulphur, phosphorus and nitrogen.

The following steels of the non-austenitic type are representative of the chemistries of steel or other iron base alloys embodying the features of this invention having out the residual metals and copper. improved machinability. In the examples the amounts Table III Change in Size Cycle Surface No. of

0 Mn S Nl Cr Cu Time, Speed Pieces Sec. PerMln. Cut %"Turn- Form ing T001 T001 .It will be apparent from the above table that the tool wear of medium carbon steels of similar composition are given are in percent by weight of the metal with the balance being substantially all iron.

C On Din P 81 N1 Mo 01 S N 15-. 23 00-. 00 1. 35-1. 05 04 17-. 22 05 05 1&0. 5

improved as much as 400 percent by the addition of cop- In the manufacture of steel and other iron base alloys, per and that the presence of nickel and chromium recopper may be introduced into the metal when in the duces the improvement secured by the presence of copper, furnace, ladle or mold, in the form of elemental copper, yet the copper present with such residual elements procopper oxygen sulphide, copper sulphide or as copper vides for animprovement in machinability over and above 70 sulphate or as a master metal containing copper, such the alloy without copper. In accordance with the inforas an iron-copper-sulphur alloy. It is an important conmation which has been developed to the present, the residcept of this invention that by the addition of copper in ual metals can be present in amounts totaling 0.25 perthe forms described, normal operating procedures may cent by weight of the steel with a maximum of 0.05 5 be employedinthe metallurgical processes for preparation percent by weight of any one element before improvement of the steel. Recoveries of copper are essentially .100

percent and-such additions to incorporate copper can be made- Without hazards and without requiring precautionary steps to be taken for the safety of personnel or equipment.

An important concept of this invention resides in the further discovery that the machinability of steel, for example as measured by the constant pressure lathe test reviously described, especially steels having copper present in the amounts described, show unexpectedly large improvements in machinability when cold worked. As used herein, the term cold working is meant to include deformation of the steel, as by cold drawing or rolling at room temperature or at elevated temperatures, such as described in copending applications Ser. No. 293,431, now abandoned, Ser. No. 293,432, now abandomed, and Ser. No. 293,433, now abandoned. The most striking effects by way of improved machinability by cold Working become apparent with steels containing 0.50 carbon or less. Particularly outstanding results are secured with steels having 0.15 to 0.35 percent carbon. To the present, such improvements in machinability are maximized by cold working the steel for reduction in excess of percent in cross sectional area and generally with reductions of between -50 percent depending upon the chemistry of the metal, the size of the raw material being cold worked, and in the case of drawing at elevated temperatures, the temperature of drawing.

The unexpected improvement in machinability of steel by cold working is illustrated by the following table which compares a steel having copper with the steel of the same composition except for copper. The two steels were reduced by cold drawing bars at room temperature, cold drawing bars which are at room temperature followed by strain relieving at high temperature, and cold drawing bars which are at an elevated temperature. Raw material for the test was hot rolled bar stock 1% inches in diameter.

Table IV Composition Composition B Carbon Manganese Phosphorus Sulphur Siliconr Copper Machinability index: 1

10% draft at room temperature followed by strain relieving 10% draft at elevated temperature 15% draft at room temperature 21% draft at room temperature 1 See footnote Table II.

it will be apparent from the data set forth in the above table that the machinability of steels containing copper within the amounts described is unexpectedly greatly improve-d by cold reductions, for example as by more than a 10 percent reduction in cross sectional area on a 1 inch bar, as compared to the machinability character istics of steel having less than the described amounts of copper. When steel is drawn at about room temperature to achieve the desired reduction, strain relieving by heat treatment at a temperature above 550 F. but below the lower critical temperature and preferably within the range of 550-950" F. may be desirable. W1th steels having from 0.2 to 0.4 percent carbon, maximum improvement in machinability is secured by taking heavy drafts which may be followed by strain relieving, especial- 1 when copper is present in such steels alone or in a system with sulphur and with less than 0.15 residual metals composed of nickel, chromium and molybdenum. When working is achieved by drawing at' elevated temperatures as described in the aforementioned copending applications, subsequent strain relieving. steps by heat treatment become unnecessary. V I

While cold working has been found tobe desirable to improve the machining. charcteristics of steel, the coinbination of cold working steels of thetype heretofore described cont'aining copper alone" or containing copper in a system with sulphur, and/or nitrogen, offers still further possibilities for providing high levels of ma chinability together with improved strength, resistance to corrosion, toughness, wear and other mechanical and physical properties without introducing limitations in the processing chracteristics of the steel. I

The unexpected improvements in machinability secured by metal working is not fully understood. It has been found that steels, particularly those containing carbon in the range of from 10-30 percent, can appreciably be benefited by heavy cold working. These beneficial efiects with respect to machinability are enhanced when the steel contains copper alone or in the presence of .phosphorus, sulphur, and/or nitrogen. Whatever the reason, the machin'ability of steels and iron base alloys, as determined by the energy required for metal separation and by reduction in Wear of the turning and forming tools has been found greatly to be improved by modific'ation in the chemistry of the steel to include copper as an essential component thereof, and further by working of the steel as by cold drawing to secure heavy drafts. Such improvements in machinability have been instru mental in accelerating output of steel products by euabling p'rccess'ing'with heavy feeds and higher speeds to increase the production rate while at the same time reducing the time required for replacement and repair of tools and parts. Iii addition to increased output at reduced costs, the presence of copper to improve inachinability has also provided im rovements in other physical and mechanical properties as previously pointed out.

Though not equivalent, it is suggested that improve nient in machinability of such iron base" alloys and steel can be obtainedby the addition'of cobalt, zin'c, cadmium, mercury, or tin. The chemical combination of these other elements in steel or other iron base alloys" appears to correspond more with that observe'd for copper as compared to that from lead. The amounts required of these other elements are somewhat similar to that for copper with variations depending upon the solubility of the element in the iron or steel base alloy and the particular chemistry of the steel.

It will be understood that changes may be made in the details of formulation, methods of incorporation and processing of the various steels prepared in a manner to provide the characteristics of this invention without departing from the spirit of the invention, especially as defined in the following claims.

I claim: I p

1. The metallurgical process'for improving the machim ability of steel comprising the steps of advancing the steel through a die to effect reduction in cross-sectional area wherein the steel is a free machining steel of the nonaustenitic type having copper present as an essential eler'nent in the range of 0.15 to 0.30 percent by weight, 0.04 to 0.50 percent by weight sulphur, and lesstharl' 0.25 percent by weight residual metals selected fr'o'ni' th'e'" group consisting of' nickel, chromium, vanadium and molyb= den'urn, with a maximum of 0.05 percent by weight of any one residual metal, and subsequently" machining the steel to produce parts. 7

2. The metallurgical process for improving the machinability of steel comprising the steps of advancin the steel through a die to effect reduction in cross' sectional area wherein the steel is a free machining steel of "the non austenitic type having copper present as an essential elementin the range of 0.15 'to'0.30 percent by weight, 0.04 to 0.50 percentby weightsulphunand less than 0:25

percent by weight residual metals selected from the group consisting of nickel, chromium, vanadium and molybdenum, with a maximumof 0.05 percent by weight of any one, strain relieving the steel, and subsequently machining the steel to produce parts.

3. The metallurgical process for improving the machinability of steel comprising the steps of drawing the steel through a die to effect reduction in cross-sectional area wherein the steel is a free machining steel of the nonaustenitic type having copper present as an essential element in the range of 0.15 to 0.30 percent by weight, 0.04 to 0.50 percent by weight sulphur, and less than 0.25 percent by weight residual metals selected from the group consisting of nickel, chromium, vanadium and molybdenum, with a maximum of about 0.05 percent by weight of any one residual metal, and subsequently machining the steel to produce parts.

4. The metallurgical process for improving the machinability of steel comprising the steps of drawing the steel through a die to eiiect reduction in cross-sectional area wherein the steel is a free machining steel of the non austenitic type having copper present as an essential element in the range of 0.15 to 0.30 percent by weight, 0.04 to 0.50 percent by weight sulphur, and less than 0.25 percent by weight residual metals selected from the group consisting of nickel, chromium, vanadium and molybdenum, with a maximum of about 0.05 percent by Weight of any one residual metal, strain relieving the steel, and subsequently machining the steel to produce parts.

5. The metallurgical process for improving the machinability of steel comprising the steps of extruding the steel through a die to effect reduction in cross-sectional area wherein the steel is a free machining steel of the nonaustenitic type having copper and sulphur present as essential elements in the range of 0.15 to 0.30 percent by weight copper and 0.04 to 0.50 percent by weight sulphur, and less than 0.25 percent by weight residual metals selected from the group consisting of nickel, chromium, vanadium and molybdenum, with a maximum of 0.05 percent by weight of any one residual metal, and subsequently machining the steel to form parts.

6. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a die to effect reduction in cross-sectional area wherein the steel is a free machining steel of the nonaustenitic type having copper present as an essential element in the range of 0.15 to 0.30 percent by weight, 0.04 to 0.50 percent by weight sulphur, 0.01 to 0.20 percent by weight phosphorus, and less than 0.25 percent by weight residual metals selected from the group consisting of nickel, chromium, vanadium and molybdenum, with a maximum of 0.05 percent by weight of any one, and subsequently machining the steel to form parts.

7. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a die to effect reduction in cross-sectional areawherein the steel is a free machining steel of the non-austenitic type having copper present as an essential element in the rangeof 0.15 to 0.30 percent by weight, 0.04 to 0.50 percent by weight sulphur, 0.01 to 0.20 percent by weight phosphorus, more than 0.001 percent by weight nitrogen, and less than 0.25 percent by weight residual metals-selected from the group consisting of nickel, chromium, vanadium and molybdenum, with a maximum of 0.05 percent by Weight of any one, and subsequently machining the steel to form parts.

8. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a'die to efiect reduction in cross-sectional area wherein-the steel is a free machining steel of the non-'austenitic type havingcopper present as an essential element in the range of 0.15 to 0.30 percent by weight,

0.04to 0.50 percent by weight sulphur, 0.01 to 0.20 percent by weight phosphorus, more than 0.001 percent by weight nitrogen, andless than 0.25 percent 'by weight residual metals selected from the group consisting of nickel, chromium, vanadium and molybdenum, with a maximum of 0.05 percent by weight of any one, strain relieving the steel, and subsequently machining the steel to form parts.

9. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a die to eifect reduction in cross-sectional area wherein the steel is a low carbon free machining steel of the non-austenitic type having up to 0.5 percent by weight carbon, copper present as an essential element in an amount within the range of 0.15 to 0.30 percent by weight, 0.04 to 0.50 percent by weight sulphur, and less than 0.25 percent by weight residual metals selected from the group consisting of nickel, chromium, vanadium and molybdenum with a maximum of 0.05 percent by weight of any one, and subsequently machining the steel to form parts.

10. The metallurgical process for improving the machinability of steel comprising the steps of heating the steel to a temperature within the range of 450 F. to the lower critical temperature for the steel composition, advancing the heated steel through a die to effect reduc tion in cross-sectional area while the steel is at a temperature within the range of 450 F. to the lower critical temperature for the steel composition and wherein the steel is a free machining steel of the non-austenitic type having copper present as an essential element in an amount within the range of 0.15 to 0.30 percent by weight, 0.04 to 0.50 percent by weight sulphur, and less than 0.25 percent by weight residual metals selected from the group consisting of nickel, chromium, vanadium and molybdenum with a maximum of about 0.05 percent by weight ofany one, and subsequently machining the steel to form parts.

11. The metallurgical process for improving the machinability of steel comprising the steps of heating the steel to a temperature within the range of 450 F. to the lower critical temperature for the steel composition, advancing the heated steel through a die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 450 F. to the lower critical tempera ture for the steel composition and wherein the steel is a free machining steel of the nonaustenitic type having copper present as an essential element in an amount within the range of 0.15 to 0.30 percent by Weight, 0.04 to 0.50 percent by weight sulphur, and less than 0.25 percent by weight residual metals selected from the group consisting of nickel, chromium, vanadium and molybdenum with a maximum of 0.05 percent by weight of any one, strain relieving the steel, and subsequently machining the steel to form parts.

12. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a draw die to efiect reduction in crosssectional area While the steel is at a temperature within the range of 450 F. to the lower critical temperature for the steel composition and wherein the steel is a free machining steel of the non-austenitic type having up to 0.50 percent by weight carbon, 0.15 to 0.30 percent by weight copper, 0.04 to 0.50 percent by weight sulphur, 0.1 to 0.20 percent by weight phosphoius, more than 0.001 percent by weight nitrogen, and less than 0.25 percent by weight residual metals selected from the group consisting of nickel, chromium, vanadium and molybdenum with a maximum of 0.05 percent by weight of any one, and subsequently machining the steel to form parts.

13. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a draw die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 450 F. to the lower critical temperature for the steel composition and wherein the steel is a free machining steel of the non-austenitic type having up to 0.50 percent by weight carbon, 0.15 to 0.30 percent by weight copper, 0.04 to 0.50 percent by weight sulphur, 0.01 to 0.20 percent by weight phosphorus, more than 0.001 percent by weight nitrogen, and less than 0.25 percent by 5 weight residual metals selected from the group consisting of nickel, chromium, vanadium and molybdenum with a maximum of 0.05 percent by weight of any one, heating to an elevated temperature to strain relieve the steel, and subsequently machining the steel to form parts.

References Cited in the file of this patent UNITED STATES PATENTS 1,957,427 Buckholtz May 8, 1934 OTHER REFERENCES 10 Metals Handbook, 1948 ed., pp. 309, 310, 369, 370,

Open Hearth Proceedings," pub. by AIMME, vol. 38,

Claims

1. THE METALLURGICAL PROCESS FOR IMPROVING THE MACHINABILITY OF STEEL COMPRISING THE STEPS OF ADVANCING THE STEEL THROUGH A DIE TO EFFECT REDUCTIN IN CROSS-SECTIONAL AREA WHEREIN THE STEEL IS A FREE MACHINING STEEL OF THE NONAUSTENITIC TYPE HAVING COPPER PRESENT AS AN ESSENTIAL ELEMENT IN THE RANGE OF 0.15 TO 0.30 PERCENT BY WEIGHT, 0.04 TO 0.05 PERCENT BY WEIGHT SULPHUR, AND LESS THAN 0.25 PERCENT BY WEIGHT RESIDUAL METALS SELECTED FROM THE GROUP CONSISTING OF NICKEL, CHROMIUM, VANADIUM AND MOLYBDENUM, WITH A MAXIMUM OF 0.05 PERCENT BY WEIGHT OF ANY ONE RESIDUAL METAL, AND SUBSEQUENTLY MACHINING THE STEEL TO PRODUCE PARTS.