US 2182758 A
Description (OCR text may contain errors)
Dec. 5, 1939. O. E. HARDER 2,182,758
STEEL, [Filed May 12, 1938 iree cutting steels.
Patented 5, 1 939 UNITED STATES PATENT orr cs land Steel Company, C
tlon of Delaware hicago, Ill., a corpora- Application May 14, 1938, Serial No. 208,089
' before being ultimately placed in use, although it is not necessarily limited thereto.
In the prior art, the practice most generally resorted to for the purpose of improving the machinability of steel is the addition of sulfur to ste steel. Sometimes, selenium is used, though the cost thereof is somewhat prohibitive. Normally, where sulfur or selenium are proving the machinability of the steel, they are introduced in such quantities as to insure a recovery in the steel of more than .05 per cent sulfur or selenium, or if both are used a total in excess of .05 per cent is usually required.
For example, certain "free cutting steels have attained a well established and recognized classification in the steel industry. The Society of Automotive Engineers recognizes this special class of steel and has provided standard specifications for their chemical composition.
Tlriese steels are all characterized by higher suifur contents (.075-0300 per cent) in steels which do not fall within the class of It can probably be said that thus increasing the sulfur content is the commonly accepted method of improving the machinability of steels and bringing them within the class of free cutting steels. However, the use of sulfur in high percentages for the machinability of such relatively the steels has certain im- It has a tendency to cause trouble in hot-working the steel, as in rolling the ingot. Therefore, it is common practice to hot-work these free cutting steels containing relatively high sulfur contents at higher temperatures than with steels of lower sulfur contents. Also, it is general metallurgical practice to use relatively high percentages of when the sulfur content is increased or minimize manganese in order to avoid the steel, that is, strength of the steel at red heat. In addition, the use of too much sulfur in steel has a tendency -to impart thereto objectionable physical properties, such as low ductility.
lit is also recognized that, under some condi tions, increased phosphorus content tends to im--' prove the machinability of steels. This is especially true with steels which are low in carbon content and which are relatively soft and tend to drag during the machining operation. It is recognized that increasing the phosphorus content may serve to overcome this drawback. However, there are limitations to the improvement 0! used for imthan is common the purpose oiimproving' hot shortness in to avoidbrittleness or lack of the machinability of steels by increasing the much phophorus may detract from the desired ductility. In certain classes of steels a certain amount of ductility is necessary and the use of increased phosphorus contents for the purpose of producing a free cutting steel is impracticable because of its tendency to decrease ductility.
Bessemer steels normally make better iree' cutting steels than open-hearth steels. However, Bessemersteels are now somewhat more costly to produce and more diflicult to control as to composition than open-hearth steels and some steel plants do not have Bessemer furnaces. these and other reasons, the demand for openhearth steels, during recent years, has been in= creasing at the expense of the demand Bessemer steels. Therefore, it desirable to produce open-hearth steels having as good machinability as Bessemer steels. Neverthel'ess, it has-not been possible to accomplish this by increasing the sulfur content without for ' harmiully sacrificing important physical properties. "While considerable progress has been made in Because of would be highly improving the machinability of steel, mainly by the sulfur content, and
nine steels which are E. specifications, so that selections can be made from these types in accordance with the required machinability and the desired mechanical properties in the finished product, there still remains a need to further improve the free cutting characteristics of steel. This is especially true if such improvement can be attained without loss of other desirable characteristics, such as good hot working properties and adequate ductility and other physical properties. I It is irnow'n that investigators have conducted extensive researches directed to the improvement of free cutting steels in which they have varied the chemical compositions and have studied new methods of adding such elements as sulfur, phosphorus, manganese and carbon, and have varied the amount of retained oxygen in the steel.
However, there has been no marked improvement over the prior art until the present invention. This invention rests primarily in the fact that it has been discovered that the machin ability of steels can be improved by the incorporation of lead in. the steel, provided the lead is introduced under such conditions and in such increasing while the ina wayas to insure that there will be retained in the steel, upon solidification, an adequate quantity oi the leadexisting in the steel in a state of 30 mann (Z.
tially all of the sulfur commonly used in the socalled "free cutting" steels or as a supplement for such sulfur, provided the lead is added in such quantities and under such conditions as to inl would be classified as a "free cutting steel. Likewise, it has been found that the lead so incorporated does not materially reduce the desirable mechanical properties of the steel. The novelty of this discovery is accentuated by the fact that many investigators have studied the alloys of iron as an addition agent to steel for the purpose of improving the machinability and, particularly, for the making of free cutting steel.
page 716, reviews the information on iron-lead Page 277) that the solidified mann and Oelsen (Ber. Itsch Chem. Ges., vol
35 (1902), page 910), that the solubility of iron in lead is 3X10- per cent and from the use of lead as an addition agent to steel for the purpose'of improving the machinability and, particularly, for the making of free cutting steels.
I am aware patentees have suggested the use of lead in fer- 5 purify or alter the nature of the steel in such a machinability thereof, nor has any prior investifree cutting" any other element.
This application is my application, S. N. 1937.
a continuation in part of 177,292, filed November 30,
In the pursuance of my development, lead has been added to the steel by a num er of methods For example, mytests cent by weight of the with sulfur or and preferably starting the introduction of lead early in the filling of the mold. It is,also important that the lead be introduced in quantities sufiicient to .insure that the amount desired is retained in the steel.
show that the introduction of lead in percentages approximating 1 per steel may result in a recovery of about .50 to .70 per cent lead under favorable conditions.
Lead-containing steels, made in accordance with my invention are characteristic of these lead-bearing steels of improved machinabflity.
Duplications of photomicrographs, at a magniilcation of 500 diameters, are shown in the accompanying drawing and a comparison of the microstructure shown therein will make this relation clear.
Figure 1 represents a photomicrograph of steel A which is so designated in Table I, immediately following, which table sets forth the constituents of this steel and shows that it contains no lead.
Figure 2 shows the microstructure of steel '3 which is also included in following, which table shows that the steel has practically the same chemical composition as steel A, except that it contains 0.12 per cent of lead in addition to its other constituents.
The Table I referred to is as follows;
Tana: I.Chemical composition of steels A, B and C Chemical composition-percent The lead is apparently dispersed throughout the steel partly in sub-microscopic form. The multiplicity of small black spots, which are stains made apparent by the etching process and which are so prevalent in the lead-containing steels of Figures 2 and 3 in comparison with the substantial absencethereoi' in the steel of Figure 1 which contains no lead, clearly indicates that the lead is fully dispersed throughout the steel. cal conductivity tests which I have made show that resistivity is not this suggests that the Table I, immediately arcane tion in the steel but is present in a dlspersed form.
I have added lead to molten steels oi essentially the same compositions as steel A in different amounts as the mineral galena (PbS with approximately 36.6 per cent Pb and13.4 per cent S) to produce steels B and C. Many other steels containing lead have been made and studied using experimental heats ranging from 15 to 300 pounds and commercial ingots weighing oi the order of 11,000 pounds. 1
While the lead in steels B and C was added as galena, it has been found that the lead can be added by other means and this invention is, not limited to any particular method of adding the lead. In the experimental work which has been done it has been found that lead can be added to molten steel by using metallic lead, galena, an alloy of equal parts of lead, tin and antimony, a solder containing 60 per cent lead and 40 per cent tin, a bearing alloy containing 66 per cent copper, 32 per cent lead and 2 per cent tin, litharge and lead orthophosphate. It has been demonstrated that lead can be added to steel by all of the above as well as other lead-containing addition agents, and recoveries in the range of 15 to 64 per cent have been obtained. The recovery depends upon a number of factors. Increasing the holding time between the lead addition and pouring the steel seems to increase recovery of lead in the steel under some conditions. The recovery was better when relatively small additions, such as 0.40 per cent were made than when larger additions were made, such as 1.5 per cent. The chemical composition of the steel may have some influence on the recovery of lead but this relation has not been determined in a definite way. As will be shown hereinafter, lead has been added to steels of quite a range in chemical composition.
The solubility of lead in molten and in solid steel is not definitely known but a steel containing 0.53 per cent lead has been obtained with the indication that most, if not all, of the lead was in a state of dispersion instead of being in solution. It has been found that up to this amount, at least, the lead content continues to improve machinability.
Tests also show that, in cold drawing or leadcontaining screw stock, the load required for reduction is diminished by 7.5 to 14.3 per cent for reductions in area of 1 to 21 per cent by a lead addition of .14 per cent and that the loadis diminished by 10.2 to 19.6 per cent for similar reductions in area by a lead addition of .25 per cent. These cold drawn steels respectively con-- tained, in addition to the lead content, .18 C, .81 Mn., .022 P, .134 S, .015 Si and .18 C, .75 Mn, .021 P, .127 S, .014 Si. Furthermore, commercial experience in machining steels ance with my invention show that these steels containing lead remain much cooler than the socalled free cutting steels which is probably the result of less friction between the chip and the tool.
when lead is added in such amounts as 0.80 to 1.5 per cent it has been noted that there is a tendency for some of the lead to settle to the bottom of the containing vessel because of its high specific gravity. It is very probable, however, that by long holding and agitation at steel making temperature the lead contained in the steel can be materially increased above the value or 0.53 per. cent which is the maximum that has been obtained so far in trial melts.
made in accordmachinability index is The addition of lead to relatively high Sulful steel or about 0.20 per cent sulfur and relatively low sulfur steel of about 0.03 per cent sulfur has also been studied and it appears that there is no essential difference in the amount of lead retained in the steel or in the relative amount recovered. It was found that the addition or lead to steels containing either a low percentage or a highpercentage of sulfur definitely improved the machinability. When the lead is added in the form of galena. there is an increase in the sulfur in the steel, due to the sulfur in the galena.
Lead has been added to steels of 0.80 and 1.35 per cent manganese contents and essentially the same recoveries and the same improvements in machinability obtained. Likewise, lead has been added to steels of. 0.05 and 0.25 per cent silicon contents with no apparent differences in the amount of lead recovered or in its effect on machinability.
My researches have shown that the lead may be added at different stages in the production of the steel.
Lead in 'the various forms, such as metallic lead, lead sulfide and other compounds, has been However, my preferred method of adding lead is:
To add it to the molten steel in the ingot mold' in subdivided form after a small amount of steel has entered the mold by delivering a stream of sub-divided lead particles against the stream of steel pouring downwardly from the ladle and over a substantial period of time.-
In studying the machinabilityof steels use has been made of saw and drill tests. A comparison has been made between the time requlredto saw a bar of cold rolled S. A. E. 1020 steel and experimental steel bars of the same size. From these data a sawability index has beencalculated which is the time required to saw off a bar of the experimental steels-divided by the time required for the standard bar of S. A. E. 1020. Similarly comparisons have been made in drilling tests in which the time required to drill to the same depth with all other conditions fixed in the standard S. A. E. 1020 steel, gives a drillability index. It is evident that the smaller in'dices indicate better machinability. While many steels have been studied the following data will serve to in Table II.
TABLE IL-Efiect of lead on machinability Machinability indiees Chemicalcomposition-percent Drilling It is obvious from the data in Table II that the addition of lead and that in the range covered, that is, from substantially more than traces to 0.478 per cent lead, the machinability improved as the lead content increased. It should be pointed out that steel No. is present in traces only, is a relatively high-suliur steel such as is now used in the trade as a free issues 2962, in which the lead,
greatly improved by the e TABLE lIA.-Machinabili't1l tests on commercial f ee cutting steels Machinability steel indiees No Description Sawing Drilling l Commercial Bessemer .70 .06 2 do 77 92 3 .69 .92 4 .70 .95 6-1. Commercial open-hearth 88 95 5-2 Commercial Bessemer... 71 94 6 o .84 .94 7 Commercial Bessemer X-grade .72 .86
By comparing the data in Table IIA with those n Table III it is evident that the steels of this invention containing 0.122 have lower machinability indices and therefore have superior machinability. The superiority is most marked in the steels of higher lead content.
It is known that there are limitations to the steels of this invention have been studied in many respects and it has been found that the addition of lead within the range of about .10 to .478 per cent has no significant harmful effect on the mechanical properties. This relation was determined by making tensile tests and Charpy impact tests on the steels listed in Table 11', and it was found that by adding lead within the range shown in Table II the mechanical properties of yield strength, tensile strength, elongation and reduction of area were not materially changed by and are therefore made on materials representative of commercial practice with free machining steels. It is evident that the addition of lead up to 0.478 per cent did not materially reduce any of these mechanical properties whereas the data in' Table II show that such additions'of lead greatly improved the machinability.
The eifects of nitrogen and phosphorus addi-' tlons have been studied. These elements are both hardening and strengthening in their function when added to steels. For that reason they may or may not improve machinability. It the steel is so soft that it has poor machinability then the adidtion of nitrogen or phosphorus or both of.
theseelements tends to improve machinability. 0n the other hand, it the steel is sumciently hard for good machinability then the addition of nitrogen or phosphorus or both of these elements may be detrimental to machinability because they increase the hardness to a value greater than the optimumfor best machinability.
Using as a basis for comparison a low carbon steel of approximately .04 per cent carbon, .90 per cent manganese, .09 per cent silicon, .176 per cent sulfur, .012 per cent phosphorus and .008
per cent nitrogen, I have varied the nitrogen con- 5 steel and then Y by sawing per cent or more leadtent up to .020 up to .207 per cent and have added lead to this determined the hardness and tensile strength and the machinability as determined by sawing and drilling tests. Increasing the nitrogen as indicated above increased the hardness from 150 to 183 on the Brinell scale and the tensile strength from 71,000 to 81,500 p. s. i. Increasing the phosphorus as indicated above increased the hardness from 150 to 187 on the Brinell scale and the tensile strength from 71,000 to 91,000 p. s. i. Increasing the nitrogen as indicated above did not improve the machinability as determined tests and decreased it as determined by drilling tests. Increasing the phosphorus as indicated above: only slightly improved the machinability as determined by sawing tests and materially decreased it as determined by drilling tests. On the other hand, when lead was added to the same base analysis in progressively increasing amounts, there was a proportionately definite improvement in machinability, as shown by both sawing and drilling tests. The addition of lead did not increase the hardness of hot rolled or cold drawn bars. Thus, it is evident that in practicing this invention it maybe desirable in certain cases to vary the composition of the base steel to get the desired hardness and strength by adjusting the carbon,-phosphorus, manganese, silicon and nitrogen. When the desired mechanical. properties have been obtained lead is then added to improve machinability and the addition of lead has relatively little effect on the mechanical properties.
In the production of free cutting steels in accordance with my invention, the steels are preferably cold drawn to further improve the ma-- chinability thereof. This not only improves the machinability but facilitates the attainment of dimensional characteristics responding to the relatively close tolerances normally demanded by the industry.
As indicated above, my invention is directed mainly to steel. I am interested particularly in those ferrous alloys containing carbon in percentages less than 1.7 per cent. As stated above, my invention is applicable to any steel including high alloy steel which is intended for subsequent machining. My invention contemplates the use of lead in such steels in percentages ranging from 0.3 to 1 per cent. My invention also has especial utility in connection with the so-called free cutting steels wherein sulfur is present in percentages ranging from .05 to .30 per cent, since it has been found that the presence of lead therein in percentages rangingfrom .03 to l per cent markedly improves the free cutting characteristics of such steels. i
With particular relation to free cutting steels of the character indicated, it will be seen that I have obtained highly important and novel results by the use of lead in proper quantities. As a matter of fact, I am able to produce a steel containing merely traces of sulfur or such quantities thereof as are unavoidable and, at the same time, to have such steel so freely machinable that it fallswell within the class of free cutting steels, as far as adaptability forsimilarusesis concerned. Furthermore, the use of lead to obtain this enhanced machinability avoids all of the drawbacks which might result from the use of sulfur in relatively large quantities. In other words, the use of lead as a substitute for sulfur obtains the free machinability without any detrimental effects upon the properties of the steel.
per cent, the phosphorus content chinability than It will also be understood that I may obtain the free machinabillty desired by the use of lead in a steel which also contains substantial quantities of sulfur. As the result of this, it is possible to obtain better results from the standpoint of mahitherto possible where sulfur was mainly or entirely relied upon and without any sacrifice of the required or desired physical properties of the steel. As a matter of fact, by the use of lead either with or without sulfur, I have been able to produce asteel which is not only a free cutting steel but which will have physical properties superior to a steel 01 equal machinability wherein improve machinabillty.
-Heat treatment and physical sulfur is mainly relied on to The analyses given in Table III are the results of laboratory analyses of samples from the bars produced from the various melts and from r the bars actually used in machinability tests. It will be observed that steel 3494 has no lead added while steel 3495 contained 0.07 per cent lead. The lead was added to these melts in the form of the oxide so that, the sulfur content would not be increased by using galena. Likewise, for the remaining steels in Table III, one of each pair had no lead added while the other contained the amount shown.
The results of the mechanical tests on the heat treated bars are shown in Table IV.
properties of expe imental heats TABLE IV.
I Refine Charpy Brinell Heat treatment 1 1600; F. 1 in. air cooledo 1500 F. 1 hr. air cooled 1000 F. 2 hrs. do Water .....6
1450 F. 1 hr. air cooled..- 'ittte cooled.
Oil Q. from 1500 F. D.
' Intimate strength Yield Elongastrength' 32 2* impact hardness Lba/sq. in. Pmmt cmt FLILbs.
Values shown are averages of duplicatatests.
Also, it. will be seen that, by the use of lead to improve the machinability of the steel, I am also able to produce a steel which is more readily adaptable to hot-working. It may be hot-worked at lower temperatures without producing hot.
shortness in the steel, that is, without producing undue brittleness or lack of strength of the steel at red heat. In addition, this avoids the necessity for the prior art practice of ganese in the steel to offset the tendency towards hot shortness otherwise resulting from relatively large sulfur content. It will appearfrom this that a larger variety of free cutting steels can be produced where lead is mainlyor entirely relied upon to obtain the desired free machinability.
Additional investigations that have been made show that lead can be used to improve the machinability of carbon steelsof low to high carbon contents and of'low to high alloy contents. Also, lead has been shown to improve the machinability of steels in the heat treated condition without loss in desired mechanical properties. Thus, steels of the analyses shown in the following Table III, were cas forged and rolled into one-inch bar stock which was then heat treated and tested for machinability by saw tests.
TABLE 1H.-Compositions of experimental heats of carbon and alloy steelsv Chemical composition-percent Steel No.
0 Mn 81 Y P 8 Cr Ni Mn Pb 3494..-. 0.15 0 54 0 09 None 34 0.17 0 85 0 l1 0 07 34 0.47 0.74 009 None 3407-." 0.46 080 0 l7 l mu" 0.88 74 0 16 34 0.88 82 0 01B 3502-.-. 0.48 74 0 14 increasing the manv It is evident from Table IV that the addition of lead in the range of about 0.10 to about 0.20 per cent has not had a harmful eflect on the mechanical properties of the steels.
Machinability tests have been made on these steels after heat treating the specimens with and without lead to give the comparison specimens approximately the same Brinell hardness. The
results of my tests are shown in Table VIII.
TABLE V.- -Efiect of lead on sauiability Improve- Brinell Saw- Steel Cer- Y merit in Lead hardability Remarks bon noss index Par Par cmt cent Per cent 3494.--. l5 114 .93 3495- 17 07 121 73 21 3496---- 47 179 68 3497- 46 197 179 51 25 34 88 269 72 3499 88 183 277 56 22 3502...- 48 210' 64 Low alloy heat. 3503---- 49 158 210 55 14 D0. 3502"" .48 341 .73 Do. 3503- 49 158 341 58 21 D0. 3569 14 158 1. 55 18+8 stainless. 3570-.-- 14 08 159 1. 38 11 Do.
It is evident from the data in Table V that the addition of lead in every case improved the machinability, the improveme t ranging from .11 per cent for the 18 per cent (Jr-8 per cent Ni steel as quenched from 2000" to 25 per cent for the S. A. E. 1050 steel as normalized. The low alloy steel showed an improvement .of 14 per cent after tempering to a hardness of 210 Brinell but when the hardness was higher (at 341 Brinell) the machinability was improved 21.per cent.
Tests have also been made on a. high-manganese steel such as is known in industry as "austenitic manganese steel or Hadfield manganese steel. This steel contained approximately 1.25 per cent carbon and 13-14 per cent man- Eanese with no lead added to one heat and 0.50 per cent lead added to another. The rolled stock of these approximate analyses was heated to 1900 and produced a surface which showed less of markings on the in producing billets and bars. The analyses were .20 per cent sulfur,
of the low-carbon grade and the steels with and without the lead were essentially of the same analysis except steels E and F contained 0.10 per cent of lead. Mechanical Machinabillty index Steel No. Load Saw Drill materially improved, the machinability.
It will be understood that, in addition to free cutting steels and steels used for similarclass of work, my invention is applicable to deep drawing steels, sheet steel, steels in general of either straight carbon or alloy compositions.
My various tests are such as to indicate that the addition of lead in proper quantities to ingot irons and low-carbon steels that are ummy" on machining, will also result in improved ma chinability of these irons which have hitherto been known to possess poor machinabilit machinability, may have the machinability thereof greatly improved, even tothe extent of giving them a machinability at least substantailly equivalent to the normal addition of .03 to 1.00 per cent of lead.
It will be apparent from the above that my rements as manganese, silicon, nickel, copper, chromium, molybdenum, vanadium, tungsten, zirconium. itanium. columbium, and tantalum may be improved by having incorporated therein variable percentages of lead.
tests showed that these y from effective amounts to 1.7 per Combined free cutting steels, by the stantially uniformly Numerous will be apparent from the Having th described claim is:
1. A steel consisting of carbon from ell'ective amounts to 1.7 per cent, from .20 to 2.00 percent manganese, from .01 to .20 per cent from .05 to .30 per cent sulfur, from appended claims. my invention, what I percentages per cent, from 1.0 per cent silicon, from .03 to 1.0 per cent lead, the balance'being substantially all iron.
4. A steel consisting of carbon in percentages traces to 2.0
stantially all iron.
5. A steel consisting of carbon in from etl'ective amounts to 1.7 per cent,
stantially all iron.
6. A ferrous alloy consisting of carbon in percentages from traces to 1.0 percent silicon, to 1.0 per cent lead, the balance being tially all iron.
I. A steel containing carbon in efllective amounts up to 1.7 per cent, sulfur in amounts from 0.05 to .50 per cent and lead in amounts from 0.1 to 0.478 per cent, the sulfur and lead cooperating to produce a free cutting steel, and the lead being substantially uniformly dispersed throughout the steel and having no significant harmful effect on its mechanical properties.
8. A steel containing carbon in efl'ective amounts up to 1.7 per cent, sulfur in an amount less than 0.05 per cent, and lead in 0.1 to 0.478 per cent substantially uniformly dissubstan- 9..A steel containing carbon in effective cent, said lead being subdispersed throughout the steel and having no significant harmful effect on its-mechanical properties, and said its machinability so improved by the addition of lead that a sawability test shows an index better than that of otherwise identical steels containing substantially no lead.
OSCAR E. HARDER.
other advantages of this invention cent and lead in amounts CERTIFICATE OF CORRECTION. Patent No. 2,182,758. o December,5, 1959". osczm HARDER. 5
It is he'heby cez tified that error appears xiii-the printe'ii specification of the above nu mbered patent reqqi'rizigcorr eotion as follows: 'Pa ge 2, first column, line 25, beginning withf'Drf. H. Hanseh strike out all to and including the wordend period "eteele." 'iri line h 8;. an d that the said Letters Patent shouldfie read.- with this correction therein that the seine may. conform to the record of the case iii the Patent Office."
Signed and sealed-this 15th day effFebruahLfA. D. .1910.
'Henry' Van Arsdele (Seal) Acting l Commie si oner of Patents