BE428628A - - Google Patents

Description

       

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  1,). /,. The ".. 1)" STEEL "PATENT OF INVENTION This invention relates to steels, It relates in particular to the types of steel which are called upon to be subjected to machining operations before being finally. put into service, although it is not limited to them.



   To date, the most widely adopted practice to improve the ease with which steel can be worked has been to add sulfur to it. Selenium is sometimes used, although the cost of this element is a little too high. Normally, when sulfur or selenium is used to improve the workability of steel, these metals are introduced in quantities

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 such that more than 0.05% sulfur or selenium is obtained in the steel or - if these two elements are used at the same time - it usually requires a tobal greater than 0.05%.



   For example, some machined steels are the subject of a well-established classification accepted in the steel industry. This is how the American association S.A.E.



  (Society of Automotive Engineers) has established standard specifications for the chemical composition of this steel. The following table lists the common specifications: TABLE 1 - S.A.E.
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  S.A.E. <SEP> Scale <SEP> of <SEP> Scale <SEP> of <SEP> Scale <SEP> of <SEP> Scale <SEP> of
<tb> N <SEP> Carbon <SEP> Manganese <SEP> Phosphorus <SEP> Sulfur
<tb> 1112 <SEP> 0.08-0.16 <SEP> 0.50-0.90 <SEP> 0.09-0.13 <SEP> 0.10-0.20
<tb> X1112 <SEP> 0.08-0.16 <SEP> 0.60-0.90 <SEP> 0.09-0.13 <SEP> 0.20-0.30
<tb> 1115 <SEP> 0.10-0.20 <SEP> 0.70-1.00 <SEP> 0.045 <SEP> max. <SEP> 0.075-0.15
<tb> 1120 <SEP> 0.15-0.25 <SEP> 0.60-0.90 <SEP> 0.045 <SEP> max. <SEP> 0.075-0.15
<tb> X1314 <SEP> 0.10-0.20 <SEP> 1.00-1.30 <SEP> 0.045 <SEP> max. <SEP> 0.075-0.15
<tb> X1315 <SEP> 0.10-0.20 <SEP> 1.30-1.60 <SEP> 0.045 <SEP> max. <SEP> 0.075-0.15
<tb> X1330 <SEP> 0.25-0.35 <SEP> 1.35-1.65 <SEP> 0.045 <SEP> max. <SEP> 0.075-0.15
<tb> X1335 <SEP> 0.30-0.40 <SEP> 1.35-1.65 <SEP> 0.045 <SEP> max. <SEP> 0.075-0.15
<tb> X1340 <SEP> 0.35-0.45 <SEP> 1.35-1.65 <SEP> 0.45 <SEP> max.

   <SEP> 0.075-0.15
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It will be noted that these steels are all characterized by higher sulfur contents (0.075-0.300%) than those usual in steels which do not come within the class of machining steels. It can be said that increasing the sulfur content in this way is the commonly adopted method of improving the ease with which steels bond.

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 let them brave ut to center them in the class of machining steels.



   However, the use of sulfur in relatively high contents of this kind in order to improve the workability of steels has certain significant drawbacks and limitations. It tends to cause trouble in the hot working of steel, for example during the rolling of the ingot. Therefore, it is common practice to hot work these free-cutting steels containing relatively high sulfur contents at higher temperatures than in the case of lower sulfur steels.

   Likewise, it is common practice in metallurgy to use relatively high manganese contents when increasing the sulfur content in order to avoid or minimize the rouverine character of the steel, that is, that is, to avoid the broken character or lack of mechanical strength of the steel to red. Additionally, using too much sulfur in the steel, even if it falls within the scales given above, tends to impart detrimental physical properties to the steel, such as low ductility. .



   It is also accepted that, under these conditions, an increase in the phosphorus content tends to improve the workability of steels. This applies particularly to steels having only a low carbon content, which steels are relatively soft and tender to stretch during the machining operation. It has been recognized that increasing the phosphorus content may have the effect of overcoming this disadvantage. However, the improvement likely to be thus brought to the ease of working of steels by

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 the increase in their phosphorus content is limited. Too much phosphorus can make the steel excessively hard and decrease the desired ductility.

   In some grades of steels, a certain degree of ductility is required, and it is practically not possible to increase the phosphorus content in order to obtain a machined steel due to the tendency to achieve this. results in decreased ductility.



   Bessemer steels normally give better machining steels than Martin steels. However, Bessemer steels are currently a little higher in cost and are more difficult to adjust, in terms of composition, than steels apart from the fact that some steel plants do not have Bosseler furnaces. For these and other reasons, the demand for Martin steels in recent years has increased at the expense of the demand for Bessemer steels. It would therefore be very advantageous to manufacture Martin steels which are as easy to work with as Bessemer steels. However, it was not possible to achieve this desideratum by increasing the sulfur content without harming important physical properties.



   Although considerable progress has been made in steels with regard to their ease of work, mainly by increasing the sulfur content and although at least nine steels are now available in the industry which are listed in SAE specifications, so that one can choose from these types according to the ease of work required and the mechanical properties that the finished product must have, much remains to be done in this regard.

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 which relates to the desirable improvement in the machining characteristics of steels. This is particularly applicable where such improvement can be obtained without sacrificing other desirable characteristics, such as good hot working characteristic, adequate ductility and other physical properties.

   It is known that extensive research has been done with a view to improving machining steels by modifying the chemical compositions and that new processes have been studied which consist in adding elements such as sulfur, phosphorus, manganese and carbon and varying the amount of oxygen retained in the steel.



   However, no marked improvement had been made in the prior art prior to the present invention. This is mainly due to the fact that it has been discovered that it is possible to improve the ease with which steels can be worked by incorporating lead into them, provided that this is introduced under proper conditions and manner. ensuring the presence in the steel, after solidification, of an adequate proportion of the lead contained in the steel in the state of dispersion.

   Thus, a machining steel can be made by incorporating lead into the steel, either as a substitute for some or almost all of the sulfur commonly used in free cutting steels, or in addition to this sulfur, provided that the lead is added in such amounts and under such conditions as to ensure a comparatively uniform dispersion of the lead in all parts of the steel. It has also been discovered that the lead thus incorporated into the steel improves its ease of work,

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 even if this does not result in the production of a steel which fell into the class of machining steels.

   Likewise, it has been observed that the lead thus incorporated does not appreciably reduce the advantageous mechanical properties of the steel. The novelty of this discovery is accentuated by the fact that many researchers have studied alloys of iron and lead and special lead steels and that their reports, in the technical literature, specify that lead is insoluble in iron.



   Mr. Hansen, in his work on binary alloys, published by Julius Springer, Berlin, in 1956, page 716, verifies the above information relating to alloys of iron and lead. Its diagrams show no solubility below the melting point of iron, and above this temperature there are two liquid layers which have very low solubility. This author quotes Isaac and Tammann (Z.



    Anorg. Allg. Chem. Flight. 55 (1907) page 58) which concludes that metals are practically insoluble in each other in the liquid state. Hansen also quotes Stevenhagen and Schucard (Z.



  Anorg. All. Chem. Flight. 186 (1930) page 277) which indicate that the solidified product forms in sharply defined layers and that the metals are practically insoluble in each other. He quotes Tammann and Celsen (Ber. Itsch. Chem. Ges. Vol.35 (1902), page 910), who indicate that the solubility of iron in lead is 3x10-4 @ and that lead has no influence on iron conversion temperatures. It is probable that the research thus reported in the literature, as indicated above by way of example, has prevented other researchers from using lead as an addition agent.

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 steel with a view to improving the ease of work and, in particular, with a view to the manufacture of machining steels.



   The Applicant is aware that certain holders of prior patents have proposed the use of lead in ferrous metals, but suggestions of this kind either envisaged the use of lead in smelting iron or a special steel, or else were more or less based on this general idea that lead would purify steel or modify its nature in such a way as to minimize the defects that ingots made of that steel have. In some cases, the quantities of lead offered were so large as to indicate a complete lack of understanding of the practical points of view of steel making and selling.

   In any case, none of the patents of which the applicant was aware has taught or even suggested that the introduction of lead into normal steels was capable of improving their ease of work, any more than any researcher or inventor had suggested that, introduced into steel in appropriate proportions, lead would be capable of converting the treated steel into machining steel, either alone or in combination with sulfur or any other element.



   In view of the present improvements, lead has been added to steel by various methods which will be explained in more detail below. For now, it will suffice to mention that it seems important that lead be added to the steel in a divided state and under conditions such that considerable agitation of the steel occurs. For example, lead has been dispersed satisfactorily in all parts of the steel by a process of introducing it into molten steel disposed in a crucible enclosed in

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 a high frequency induction furnace, which obviously caused stirring of the steel.

   It has also been successfully dispersed in all parts of the steel by introducing it into ingot molds during casting and, preferably, by starting the introduction of lead into / the first part of the filling of the ingot mold. It is also important that the lead is introduced in sufficient quantities so that we can be sure that the steel will retain the desired quantity. For example, the applicant's tests show that the emboduction of lead in contents close to 1% by weight of the steel can, under favorable conditions, lead to obtaining a steel having a lead content of 0.5 to 0.7%.



   The pl> mb steels produced according to the invention have certain characteristic microstructures which can be demonstrated by the metalloraphic technique and which characterize these lead steels, the ease of working of which has been improved.



   The attached drawing gives reproductions of photomicrographs and the comparison of the microstructures shown in this drawing will bring out the above observation.



   FIG. 1 represents a photomicrograph of the steel designated by A in Table II given below, which table indicates the constituents of this steel, which does not contain lead.



   Figure 2, showing the microstructure of a steel designated by B in Table II, shows that this steel has practically the same chemical composition as steel A, except that it contains 0.12% lead in addition to its other constituents.

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   Figure 3 shows the microstructure of the steel designated by C in Table II, which gives the constituents of this steel and which shows that its chemical composition is practically the same as that of steel A, except that it contains 0.478% lead.



   TABLE II- Chemical composition of steels A, B AND C.
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  "cier Chemical Composiuion -) 1 -? 0 Si Mn s F Pb z1 eye 0.012 0163 0.193 oeol7 zero
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<tb>
<tb> B <SEP> 0.10 <SEP> 0.012 <SEP> 0.55 <SEP> 0.204 <SEP> 0.019 <SEP> 0.12
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 eye 0.008 0.62 0.235 0.017 0.478
The lead appears to have been dispersed throughout the mass of the steel in part in a submicroscopic form.



  The multiplicity of small black dots, which are spots made apparent by gnawing, and which one notices in the lead steels of figures 2 and 3 by comparison with the almost complete absence of these dots in the steel of the Figure 1, which does not contain lead, clearly indicates that the lead is fully dispersed throughout the mass of the steel. The electrical conductivity tests carried out by the Applicant show that the lead does not increase the resistivity, and this would seem to indicate that the lead is not contained in the steel in solid solution, but present in the dispersed state.



   Lead was added to molten steels having essentially the same compositions as steel A and in different amounts, in the form of mineral galena (PbS with about 86.6% Pb and 13.4% S) to obtain steels B and C. Many other steels have been manufactured and studied.

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 holding lead using experimental batches or loads of between 7 and 136 kg and industrial ingots weighing around 5 tonnes.



   Although the lead of steels B and C has been added in the form of galena, it has been found that it can be added by other means, the invention not being limited to any particular method of addition of lead. In the experimental work that has been done, it has been found that lead can be added to molten steel using metallic lead, galena, an equal parts alloy of lead, tin and antimony, a solder containing 60% lead and 40% tin, a bearing alloy containing 66% copper, 32% lead and 2% tin, litharge and lead orthophosphate. It has been shown that lead can be incorporated into the steel by all of the above addition agents as well as other lead-containing agents, eg, levels ranging from 15 to 65% lead have been found. .

   The content depends on several factors.



  It seems that we are increasing the. the lead content of the steel, under certain conditions, by increasing the time between the addition of the lead and the casting of the steel. The content obtained was better when relatively small additions were made, such as 0.4% than when larger additions were made, such as 1.5. $ 1. The chemical composition of steel may have some influence on the lead content, but this relationship has not been clearly determined. As will be seen from what follows, lead has been added to steels of very diverse compositions.



   The solubility of plomo in molten steel and solid steel is not known exactly, but a steel was obtained

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 containing 0.53% lead with the indication that most - if not all - of the lead was in the dispersed state rather than in solution. It has been found that up to this value at least, the lead content continues to improve the ease of work.



   Tests have also shown that in the cold drawing of leaded steel intended for the manufacture of screws, the load required to produce a given reduction is reduced from 7.5 to 14.3%, respectively, for section reductions of 1 and 21%, by an addition of 0.14% of lead; and that the load is reduced from 10.2 to 19.6%, respectively, for section reductions of the same order, by an addition of 0.25% of lead. These cold drawn steels contained respectively, in addition to the lead content, 0.18 C, 0.81 Mn, 0.022 P, 0.134 S, 0.013 Si; and 0.18 C, 0.75 Mn, 0.021 P, 0.127 S, 0.014 Si.

   In addition, the experience acquired industrially in the machining of steels manufactured according to the invention indicates that these steels containing lead remain much cooler than machining steels, which is probably the result of the fact that the friction is lower. between the chip and the tool.



   When adding lead in amounts such as 0.8 to 1.5%, it is noted that some of the lead tends to settle to the bottom of the container due to its high density.



  It is probable, however, that by long residence and stirring at the steelmaking temperature, the lead content of the steel can be raised significantly above 0.53%, which is the maximum value. having been obtained so far in the molten charges for the tests.

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   The addition of lead to a steel with a relatively high sulfur content (about 0.2% SI), on the one hand, and to a steel with a relatively low sulfur content (about 0.03% 3), on the other On the other hand, was also studied, and it does not seem that there is an essential difference in the quantities of lead retained in the steels or in the relative contents of lead of the steels obtained. It has been found that the addition of lead both to steels containing a low percentage of sulfur and to steels containing a high percentage of sulfur markedly improves the workability of these steels. When lead is added in the form of galena, the sulfur content of the steel is increased due to the. presence of sulfur in galena.



   Lead has been added to steels having manganese contents of 0.8 and 1.35% and substantially the same lead contents have been obtained and the same improvements in workability have been made. Likewise, lead has been added to steels of 0.05 and 0.25% silicon without any difference being observed in the quantity of lead retained and in the effect of this lead on the ease with which the lead is retained. steel lets itself work.



   The applicant's research has shown that lead can be added at different stages in the manufacture of steel.



   Lead under various forces, such as metallic lead, lead sulfide and other compounds, was added in the smelting furnace to the molten charge. He has. was also added in the ladle, when removing the steel from the furnace or a larger ladle. Although the lead can be introduced with the load in the Martin furnace,

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 for example, it is preferable not to introduce it in this way to avoid the risk of premature melting of the lead and of attack of the refractories of the furnace by this metal.



   When the steel has been melted, the lead can be added with less risk of attacking the refractories of the furnace.



  Some preferred ways of adding lead are listed below.



   Add it in the divided state to the molten steel contained in the ingot mold after a small amount of steel has been introduced into the ingot, directing a stream of particles of lead in the divided state to and against the steel current descending from the ladle over a fairly long period of time.



   Add it to the charge of molten steel just before pouring this charge out of the furnace.



   Add it to the ladle as it receives the molten steel from the oven.



   To study the way in which steels can be worked, we have resorted to sawing and drilling tests. A comparison was made between the time it takes to saw an S.A.E. 1.020 cold rolled and experimental steel bars of the same section. The results of these tests made it possible to calculate a so-called "sawing" index, which is the ratio of the time required to saw a bar of the experimental steels to the time required to saw a normal bar of S.A.E. 1.020.

   Likewise, comparisons were made between drilling tests in which the ratio between the times required to drill steels to the same depth, under the same conditions as those set for S.A.E. 1.020 normal, gives a

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 index of "Drilling". It is obvious that the indices are smaller the better the ease of working of the steel. Many steels have been studied, but only some of the information obtained to demonstrate the advantages of lead in steels will be given. Table III indicates the compositions of steels and their indices.



   Table III - Effect of lead on the ease of working of steels
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<tb>
<tb> Steels <SEP> Composition <SEP> Chemical <SEP> - <SEP>% <SEP> - <SEP> Indices <SEP> of
<tb> N <SEP> ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
<tb> C <SEP> Si <SEP> Mn <SEP> P <SEP> S <SEP> Pb <SEP> Sawing <SEP> Drilling
<tb> 2962 <SEP> 0.11 <SEP> 0.012 <SEP> 0.63 <SEP> 0.017 <SEP> 0.193 <SEP> traces <SEP> 84 <SEP> 98
<tb> 2966 <SEP> 0.10 <SEP> 0.012 <SEP> 0.55 <SEP> CI, 019 <SEP> 0.04 <SEP> 0.122 <SEP> 69 <SEP> 80
<tb> 2967 <SEP> 0.11 <SEP> 0.010 <SEP> 0.59 <SEP> 0.017 <SEP> 0.207 <SEP> 0.257 <SEP> 58 <SEP> 73
<tb> 2968 <SEP> 0.11 <SEP> 0.010 <SEP> 0.58 <SEP> 0.019 <SEP> 0.214 <SEP> 0.342 <SEP> 53 <SEP> 70
<tb> 2969 <SEP> 0.11 <SEP> 0.008 <SEP> 0.32 <SEP> 0.017 <SEP> 0.255 <SEP> 0,

  478 <SEP> 47 <SEP> 69
<tb>
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It emerges from Table III that the ease of working index is greatly improved by the addition of lead and that, at all the points of the above scale, that is to say with a content As lead corresponding to a little more than simple traces at a content of 0.478%, the ease of work has been improved in the same sense that the lead content has increased.



  It should be noted that N 2962 steel, in which lead is only present in trace amounts, is a relatively sulfur-rich steel, such as is currently used; in the industry as machining steel, but that the ease with which the steel can be worked is greatly increased as its pl'mb content is increased.

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   The workability of the present steels has been compared with that of commercial machining steels, purchased on the open market. The results obtained are given in Table III-A.



   Table III A- Machining tests carried out on commercial machining steels.
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  Steels <SEP>? <SEP> Description <SEP> Indices <SEP> of
<tb> sawing <SEP> drilling
<tb> 1 <SEP> Bessemer <SEP> Commercial <SEP> 70 <SEP> 96
<tb> 2 <SEP> "<SEP>" <SEP> 77 <SEP> 92
<tb> 3 <SEP> "<SEP>" <SEP> 69 <SEP> 92
<tb> 4 <SEP> "<SEP>" <SEP> 70 <SEP> 95
<tb> 5-1 <SEP> Martin <SEP> Commercial <SEP> 88 <SEP> 95
<tb> 5-2 <SEP> Bessemer <SEP> "<SEP> 71 <SEP> 94
<tb> 6 <SEP> "<SEP>" <SEP> 84 <SEP> 94
<tb> 7 <SEP> "<SEP>" quality <SEP> X <SEP> 72 <SEP> 86
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If we compare the information in Table III-A with that in Table III, it is evident that the present steels, containing 0.122% lead or more, have lower machining indices and, therefore, are let work better. The superiority is more marked in steels with a higher lead content.



   It is known that the improvement in the workability of steels by the addition of increasing amounts of sulfur and by other means currently used in industry is limited, one of the limiting factors being the loss of desirable properties. of the finished product. The properties of the present steels have been studied from many points of view and it has been found that the addition of an amount of lead

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 between about 0.1 and 0.478% has no significant adverse effect on the mechanical properties. This stands out; of Table IV relating to the same steels as those listed in Table III.
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  Table <SEP> IV- <SEP> Relationship <SEP> between <SEP> the <SEP> content <SEP> in <SEP> lead <SEP> and
<tb> the <SEP> mechanical <SEP> properties <SEP> of <SEP> steels
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 Elo lead steels Limits Loads Elongation- St; ric- csilienN d ', 7.a s- of ruptures fions these bicil-bé bure% u µ1 Charpy I (gi / mN2 Kg / mm2 2962 Trace 5t, 50 52, 85 17.5 b5.2 z'2.5 5% - 'fC + 53sc6 16.5 53 23.5 2966 0.122 49.98 51.31 17.5 56.5 20 50.82 51.59 19 56.2 19f5
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<tb>
<tb> 2967 <SEP> 0.257 <SEP> 51.24 <SEP> 52.01 <SEP> 17.5 <SEP> 52.8 <SEP> 18
<tb> 51.10 <SEP> 51.45 <SEP> 18.5 <SEP> 57 <SEP> 20.5
<tb>
 
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 2968 0.342 49.98 50.89 19t5 5'0 ,, 19 49.56 50.54 z, 55o;

  2 20 2969 Oe478 51.45 52.15 l'7f5 5-, 2 bzz5
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<tb>
<tb> 51.03 <SEP> 51.24 <SEP> 18.5 <SEP> 52.5 <SEP> 19.5
<tb>
 The tests specified in table IV were carried out
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 killed on cold bars, and represent; This is the consequence of industrial practice since machining steel bars are generally cold drawn by the manufacturer.
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 It is evident that the Lr¯ it of adding up to U, 4j; o of lead did not significantly diminish any of these mechanical properties, whereas the information in Table III shows that such additions of lead had greatly improved. ease of work.



   Nitrogen and phosphorus addition tests were studied. These elements have one and the other role of hardening and making more resistant the steels to which they are added.



  For this reason, they may or may not improve the ease of work. If the steel is so soft that it has only one

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 poor workability, the addition of nitrogen and / or phosphorus tends to improve the workability. On the other hand, if the steel is sufficiently pure to have a good workability, the addition of nitrogen and / and phosphorus can adversely affect the workability, because they raise the hardness to a value greater than that which is most favorable for the best ease of work.



   The effect of increases in nitrogen and phosphorus content on the hardness and strength of steels with the same basic composition is shown in Table V.



   Table V- Effect of nitrogen and phosphorus on the hardness and strength of steels.
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<tb>
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  Chemical <SEP> composition <SEP> - <SEP>% <SEP> - <SEP>
<tb> Lots <SEP> Hardness <SEP> Loads <SEP> of
<tb> C <SEP> Mn <SEP> If <SEP> S <SEP> p <SEP> N <SEP> Brinell <SEP> break
<tb> kg / mm2
<tb> Base $ <SEP> 0.04 <SEP> 0.90 <SEP> 0.09 <SEP> 0.175 <SEP> 0.012 <SEP> 0.008 <SEP> 150 <SEP> 49.70
<tb> 2255 <SEP> 0.07 <SEP> 1.06 <SEP> 0.08 <SEP> 0.170 <SEP> 0.016 <SEP> 0.014 <SEP> 170 <SEP> 55.30
<tb> 2241 <SEP> 0.03 <SEP> 0.75 <SEP> 0.05 <SEP> 0.153 <SEP> 0.010 <SEP> 0.020 <SEP> 183 <SEP> 57.05
<tb> Base $ <SEP> 0.04 <SEP> 0.90 <SEP> 0.09 <SEP> 0.176 <SEP> 0.012 <SEP> 0.008 <SEP> 150 <SEP> 49.70
<tb> 2246 <SEP> 0.03 <SEP> 0.87 <SEP> 0.05 <SEP> 0.172 <SEP> 0.055 <SEP> ----- <SEP> .159 <SEP> 53.06
<tb> 2247 <SEP> 0.04 <SEP> 0.97 <SEP> 0.07 <SEP> 0.173 <SEP> 0.114 <SEP> ----- <SEP> 163 <SEP> 56.70
<tb> 2248 <SEP> 0.07 <SEP> 0.99 <SEP> 0.10 <SEP> 0.174 <SEP> 0,

  207 <SEP> ----- <SEP> 187 <SEP> 63.00
<tb>
 $ Average of three lots: Nos. 2242, 2243 and 2245.



   The relationship between increases in nitrogen and phosphorus content and ease of work is shown in Table V-A in which steels from Table V were used for testing. For comparison purposes, Table V-A shows the tests carried out for ease of working on a series of steels containing lead,

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 but having the same basic composition as those to which nitrogen or phosphorus have been added.



   Table V-A- Effect of nitrogen and phosphorus on ease of work
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<tb>
<tb> Steels <SEP> Nitrogen <SEP> Phosphorus <SEP> Lead <SEP> Indices <SEP> of
<tb> N <SEP>% <SEP>% <SEP>% <SEP> Sawing <SEP> drilling
<tb> Base <SEP> 0.008 <SEP> 0.012 <SEP> - <SEP> 1.11 <SEP> 0.81
<tb> 2255 <SEP> 0.014 <SEP> 0.012 <SEP> - <SEP> 1.07 <SEP> 0.84
<tb> 2241 <SEP> 0.020 <SEP> 0.012 <SEP> - <SEP> 1.11 <SEP> 0.85
<tb> Base <SEP> 0.008 <SEP> 0.012 <SEP> - <SEP> 1.11 <SEP> 0.81
<tb> 2246 <SEP> 0.008 <SEP> 0.055 <SEP> - <SEP> 0.98 <SEP> 0.83
<tb> 2247 <SEP> 0.008 <SEP> 0.114 <SEP> - <SEP> 0.98 <SEP> 0.83
<tb> 2248 <SEP> 0.008 <SEP> 0.207 <SEP> - <SEP> 0.95 <SEP> 0.95
<tb> Base <SEP> 0.008 <SEP> 0.012- <SEP> 1.11 <SEP> 0.81
<tb> 2256 <SEP> 0.008 <SEP> 0.012 <SEP> 0.04 <SEP> 1.04 <SEP> 0.79
<tb> 2257 <SEP> 0.008 <SEP> 0.012 <SEP> 0.10 <SEP> 0.86 <SEP> 0.75
<tb> 2258 <SEP> 0,

  008 <SEP> 0.012 <SEP> 0.18 <SEP> 0.79 <SEP> 0.77
<tb>
 
The information in Tables V and V-A show the relative effects of nitrogen, phosphorus and lead on ease of work. By increasing the lead content from 0.04 to 0.18%, the hardness of the hot-rolled or cold-drawn bars was not increased and, on the contrary, it was slightly reduced. Thus, it is evident that in the practice of this invention, it may be desirable in some cases to modify the composition of the base steel to obtain the desired hardness and strength by adjusting the carbon, phosphorus, manganese, silicon and nitrogen.

   When the

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 Desired mechanical properties have been obtained, lead is then added to improve the ease of working, and it is found that the addition of lead has only a relatively small effect on the mechanical properties.



   In order to manufacture the machining steels according to the invention, the steels are preferably cold drawn in order to further increase the ease with which they can be worked. This not only improves the ease of work. but favors obtaining dimensional characteristics meeting the relatively severe tolerances normally imposed by users.



   As indicated above, the invention is mainly aimed at steel. The Applicant particularly envisages its application to ferrous alloys containing carbon contents of less than 1.7%. As stated above, the invention is applicable to any steel, including special steel with a high content of alloying elements which is intended to be machined. The invention contemplates the application of lead contents of between 0.03 and 1% for these steels.



  The invention is also advantageously applicable to machining steels in which sulfur is present in an amount of 0.05 to 0.3, given that it has been observed that the presence of percentages of lead between 0.03 and 1 % markedly improves the machining characteristics of these steels.



   With particular reference to machining steels of the kind indicated, it will be seen that extremely important and novel results have been obtained by the application of lead in appropriate amounts. In fact, the invention makes it possible to manufacture a steel containing only simple traces of sulfur or the quantities of this element which are inevitable.

 <Desc / Clms Page number 20>

 and, at the same time, which can be worked easily enough to fall directly into the class of machining steels, as regards the adaptability of steel to similar uses. In addition, the application of lead with a view to obtaining this better workability avoids all the disadvantages which could result from the use of relatively large quantities of sulfur.

   In other words, the application of lead as a replacement agent for sulfur results in a steel which can be worked easily without causing adverse effects on the physical properties of the steel.



   It is further understood that the desired ease of work can be obtained by introducing lead into a steel which also contains substantial amounts of sulfur.



  As a result, it is possible to obtain better results, from the point of view of ease of work, than those which were possible to date, when one relied mainly or entirely on sulfur and without at the expense of the necessary or desired physical properties of the steel. In fact, the application of lead, with or without sulfur, makes it possible to produce a steel which is not only a machining steel, but also has physical properties superior to an equivalent steel from the point of view of ease of work but in which this facility is mainly provided by sulfur.



   In addition, it is seen that, thanks to the application of lead in order to improve here the ease of working of the steel,

 <Desc / Clms Page number 21>

 it also becomes possible to manufacture a steel which lends itself better to hot working. It can be worked hot at lower temperatures without it becoming brittle, that is to say without reducing the mechanical resistance of the steel to the wheel. In addition, this obviates the need to increase the manganese content of the steel, as has hitherto been necessary to compensate for the tendency of this alloy to be red brittle as a result of relatively sulfur content. big.

   It follows that a wide variety of machining steels can be produced in which one relies primarily or entirely on lead to achieve the desired ease of work.



   Additional research carried out by the Applicant has shown that lead can be used to increase the ease of working of steels of very varied contents both in carbon and in alloying elements. Likewise, it has been found that lead improves the workability of steels after heat treatment without reducing the desired mechanical properties.

   Thus the steels of the compositions indicated in Table VI given below were cast, forged and rolled to give 2.5 cm bars which were then heat treated and subjected to sawing tests with a view to determining their ease of work.

 <Desc / Clms Page number 22>

 
 EMI22.1
 rrii: 3.L'd V'I -Com osition, ae steel batch e;

  .Quality
 EMI22.2
 
<tb>
<tb> Steel <SEP> Chemical-composition <SEP>% <SEP>
<tb> N
<tb> 0 <SEP> Mn <SEP> Si <SEP> P <SEP> S <SEP> Cr <SEP> Ni <SEP> Mo <SEP> Pb
<tb> 3494 <SEP> 0.15 <SEP> 0.54 <SEP> 0.09 <SEP> 0.024 <SEP> 0.025 <SEP> - <SEP> zero
<tb> 3495 <SEP> 0.17 <SEP> 0.85 <SEP> 0.11 <SEP> 0.025 <SEP> 0.025 <SEP> - <SEP> --- <SEP> - <SEP> 0 , 07
<tb> 3496 <SEP> 0.47 <SEP> 0.74 <SEP> 0.09 <SEP> 0.027 <SEP> 0.025 <SEP> - <SEP> zero
<tb> 3497 <SEP> 0.46 <SEP> 0.80 <SEP> 0.17 <SEP> 0.024 <SEP> 0.025 <SEP> - <SEP> - <SEP> 0.197
<tb> 3498 <SEP> 0.88 <SEP> 0.74 <SEP> 0.16 <SEP> 0.022 <SEP> 0.024 <SEP> - <SEP> - <SEP> -
<tb> 3499 <SEP> 0.88 <SEP> 0.82 <SEP> 0.15 <SEP> 0.02j <SEP> 0.025 <SEP> - <SEP> - <SEP> 0.183
<tb> 3502 <SEP> 0.48 <SEP> 0.74 <SEP> 0.14 <SEP> 0.022 <SEP> 0.017 <SEP> 0.72 <SEP> 1.42 <SEP> 0.16
<tb> 3503 <SEP> 0.49 <SEP> 0.77 <SEP> 0.15 <SEP> 0,

  024 <SEP> 0.015 <SEP> 0.75 <SEP> 1.84 <SEP> 0.17 <SEP> 0.158
<tb> 3569 <SEP> 0.14 <SEP> 0.62 <SEP> 0.46 <SEP> 0.010 <SEP> 0.012 <SEP> 17.2 <SEP> 7.86 <SEP> -
<tb> 3570 <SEP> 0.14 <SEP> 0.59 <SEP> 0.42 <SEP> 0.010 <SEP> 0.013 <SEP> 17.7 <SEP> 7.78 <SEP> 0.08
<tb>
 
The compositions indicated in this table are the results of analyzes, carried out in the laboratory, of samples taken from the bars produced using the various castings: and from the bars which were actually used for the tests to determine the ease. by Lravail. Note that 34-94 steel does not contain lead, while 3495 steel contains 0.07% lead.

   Lead was added to these castings as an oxide, so that the sulfur content
 EMI22.3
 was not increased as it would have been increased if galena had been used. Likewise for the other steels of Table VI, one of the steels ae each pair received no addition of lead, while the other contained the quantity indicated.



   The results of the mechanical tests to which the
 EMI22.4
 Thermally processed bars were submitted are shown in Table VII given below.

 <Desc / Clms Page number 23>

 TABLE VII- Thermal treatment and physical properties of experimental castings
 EMI23.1
 Castings Pb Treatment Limits Char-esD Allon! Trio-lesi Dux? % thermal elas- de breaking J # J:

  all related links
 EMI23.2
 
<tb>
<tb> ticity <SEP> -bure <SEP>% <SEP>% <SEP> ces <SEP> BriKg / mm2 <SEP> Kg / mm2 <SEP> (Char- <SEP> nell
<tb> py)
<tb> 3494 <SEP> - <SEP> (870 -1 <SEP> er- <SEP> 31.43 <SEP> 43.575 <SEP> 40 <SEP> 66.5 <SEP> 50 <SEP> 114
<tb>) re <SEP> cooled
<tb> 3495 <SEP> 0.07 (<SEP> to <SEP> air <SEP> 31.325 <SEP> 45.605 <SEP> 40 <SEP> 67 <SEP> 50.9 <SEP> 121
<tb> 3496 <SEP> - <SEP> (814 <SEP> 1 <SEP> er- <SEP> 43.085 <SEP> 66.045 <SEP> 28.5 <SEP> 50.6 <SEP> 22.8 < SEP> 179
<tb>) ne <SEP> cooled
<tb> 3497 <SEP> 0.197 (<SEP> to <SEP> air <SEP> 45.325 <SEP> 68.53 <SEP> 28.5 <SEP> 52 <SEP> 23.8 <SEP> 179
<tb> 3498 <SEP> - <SEP> (779 <SEP> 1 <SEP> er- <SEP> - <SEP> 99.05 <SEP> 10.5 <SEP> 20 <SEP> 5.3 <SEP> 269 <SEP>
<tb>) re <SEP> cooled
<tb> 3499 <SEP> 0.183 (at <SEP> air <SEP> - <SEP> 97.615 <SEP> 12.3 <SEP> 23.4 <SEP> 5,

  3 <SEP> 277
<tb> 3502 <SEP> - <SEP> (814 <SEP> 1 <SEP> er- <SEP> - <SEP> 86,695 <SEP> 22 <SEP> 55 <SEP> 20 <SEP> 235
<tb>) re <SEP> cooled
<tb> 3503 <SEP> 0.158 (at <SEP> oven <SEP> 103.46 <SEP> 17.5 <SEP> 44.9 <SEP> 15 <SEP> 262
<tb> 3502 <SEP> - <SEP> (Quench <SEP> to <SEP> the <SEP> - <SEP> - <SEP> - <SEP> - <SEP> - <SEP > 341
<tb>) oil <SEP> to <SEP> by-
<tb> (shot <SEP> from <SEP> 814
<tb>
 
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 3503 0.158) Reverted to 538 - - - - - 341
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<tb>
<tb> (<SEP> 2 <SEP> hours
<tb> 3569 <SEP> - <SEP> (Tempering <SEP> to <SEP> 68.11 <SEP> 60 <SEP> 68.4 <SEP> 69.7 <SEP> 158
<tb>) <SEP> Water <SEP> to <SEP> by-
<tb> 3570 <SEP> 0.08 <SEP> (shot <SEP> from <SEP> 1093 <SEP> 68.60 <SEP> 57 <SEP> 66.7 <SEP> 68.0 <SEP> 159
<tb>
 The values indicated are the means of two tests.



   It can be seen from Table VII that the addition of about 0.1 to 0.2% lead did not adversely affect the mechanical properties of steels.



   Tests have been carried out to determine the ease with which these steels can be worked after having heat treated the test pieces (whether containing lead or not) so as to give them approximately the same Brinell hardness.



  The results of these tests are given in Table VIII.

 <Desc / Clms Page number 24>

 Table VIII - Effect of lead on ease of scia, se
 EMI24.1
 
<tb>
<tb> Steel <SEP> Carbon <SEP> Lead <SEP> Hardness <SEP> Index <SEP> of <SEP> Improvement <SEP> contribution <SEP>% <SEP>% <SEP> Brinell <SEP> Sawing <SEP > tee <SEP> to <SEP> the <SEP> facility
<tb> from <SEP> work
<tb>
 
 EMI24.2
 ¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
 EMI24.3
 
<tb>
<tb> 3494 <SEP> 0.15 <SEP> ---- <SEP> 114 <SEP> 0.93
<tb> 3495 <SEP> 0.17 <SEP> 0.07 <SEP> 121 <SEP> ci, 73 <SEP> 21
<tb> 3496 <SEP> 0.47 <SEP> ---- <SEP> 179 <SEP> 0.68
<tb> 3497 <SEP> 0.46 <SEP> 0.17 <SEP> 179 <SEP> 0.51 <SEP> 25
<tb> 3498 <SEP> 0.88 <SEP> ---- <SEP> 269 <SEP> 0.72
<tb> 3499 <SEP> 0.88 <SEP> 0.183 <SEP> 277 <SEP> 0.56 <SEP> 22
<tb> 3502 <SEP> 0.48 <SEP> ---- <SEP> 210 <SEP> 0.64
<tb> 3503 <SEP> 0.49 <SEP> 0,

  158 <SEP> 210 <SEP> 0.55 <SEP> 14
<tb> 3502 <SEP> 0.48 <SEP> ---- <SEP> 341 <SEP> 0.73
<tb> 3503 <SEP> 0.49 <SEP> 0.158 <SEP> 341 <SEP> 0.58 <SEP> 21
<tb> 3569 <SEP> 0.14 <SEP> ---- <SEP> 158 <SEP> 1.55
<tb> 3570 <SEP> 0.14 <SEP> 0.08 <SEP> 159 <SEP> 1.38 <SEP> 11
<tb>
 
 EMI24.4
 $ Lots of special low-carbon steel 811ie @ 18 + 8 stainless steel
It appears from this table that the addition of lead improved in each case the ease of work, the improvement.
 EMI24.5
 ration varying from 11%, for steel with 18% Cr and 8% Ili, quenched from 1095, to 25) il for normalized S. E. 1050 steel.

   The low alloy steel was improved by 14%, after tempering to a Brinell hardness of 210, but when the hardness was higher (Brinell 341), the ease of work was improved by 21 %.



   Tests were also carried out on steels rich in manganese Gels such as that called "manganese steel

 <Desc / Clms Page number 25>

 estenic or "Hadfield manganese" steel. This steel contained approximately 1.25% carbon and 13-14% manganese, one of the castings containing no lead, the other having added 0.5% lead. The rolled bars of the approximate compositions above were heated to 1028, allowed to stand for one hour and then soaked in water. Machiners observed that specimens from steel with the addition of lead were easier to work and gave a finished machined surface with fewer "chatter" marks.



   From the information given above, it appears that the steels listed in Table VI would have been even easier to work if the lead addition had been greater.



   Lead steel ingots were fabricated in a steel plant for the production of billets and bars. These steels were of the low carbon type and all had essentially the same composition except that steels E and F contained 0.1% lead. The tests carried out have shown that these steels have essentially the same yield strengths, breaking loads, elongations, strictures, Brinell hardnesses and Charpy strengths. These tests gave the following results:

   
 EMI25.1
 
<tb>
<tb> Steels <SEP> Lead <SEP> I <SEP> n <SEP> d <SEP> i <SEP> c <SEP> e <SEP> s <SEP>
<tb> N <SEP>% <SEP> of <SEP> sawing <SEP> of <SEP> drilling <SEP> Combinas
<tb> 0, l10 <SEP> 66 <SEP> 75 <SEP> 70
<tb> F <SEP> 0.10 <SEP> 68 <SEP> 74 <SEP> 71
<tb> G <SEP> zero <SEP> 85 <SEP> 98 <SEP> 91
<tb>
 

 <Desc / Clms Page number 26>

 
The procedure adopted for performing the workability testing was the same as that previously described, and it is evident that the addition of 0.1% lead significantly improved the workability.



   It is understood that the invention is not only applicable to machining steels and to steels used for similar works, but also to steels intended to be stamped or drawn, steel sheets, forged steels and carburized steels in general, whether it is ordinary or special steels.



   Applicants' various tests indicate that the addition of suitable quantities of lead to cast irons and low carbon steels which are "greasy" when machined also improves the ease with which these materials, generally difficult to machine, let themselves work. Thus, they indicate that one can greatly improve the ease of working of irons and steels which contain a trace of 0.1% carbon, a trace of 0.2% manganese, a trace 0.2% phosphorus, a 0.2% trace of silicon and a 0.2% trace of sulfur by the addition of 0.05 to 1% lead, improving their is made being beautiful that their ease of work becomes at least substantially equivalent to that of normal machining steels.



   It can be seen from the foregoing that the applicant's research has shown that lead can be used to improve the ease with which carbon steels and special steels can be worked, whether these steels are low or rich in carbon, which 'they are poor or rich in alloying elements. This research indicates that steel containing alloying elements such as manganese,

 <Desc / Clms Page number 27>

 silicon, nickel, copper, chromium, molybdenum, vanadium, tungsten, zirconium, titanium, columbium and tantalum can be improved by the incorporation of various percentages of lead.


    

Claims (1)

SUMMARY This invention relates to irons, ordinary steels and special steels suitable for their machining and is mainly characterized by the following points, together or separately: 1. They contain effective amounts and up to 1.7% carbon, less than 0.5% sulfur and 0.03 to 1% lead. 2. Their structure is characterized by the fact that lead is dispersed throughout the mass of the alloy. 3. Their sulfur content is less than 0.2-0.3%. 4. Their lead content is preferably between 0.21% and 1%. 5. They may also contain: a) Mn: traces at 2% b) Si: traces at 1% c) P: traces at 0.2% 6. The composition of a preferred alloy is as follows C effective quantities up to 1.7% Ion traces - 0.2% to 2% P traces - 0.1% to 0.2% S traces - 0.03 to 0.3% If traces - 0.01 to 1% Pb at least 0.03 to 1% Fe substantially the rest. <Desc / Clms Page number 28> 7. To the iron specified in 6 may be added one or more of the following alloying elements: nickel, copper, chromium, molybdenum, vanadium, tungsten, zirconium, titanium, columbium, tantalum and aluminum, the total of iron and this or these elements being included in the expression "substantially the remainder".