|Publication number||US3756805 A|
|Publication date||Sep 4, 1973|
|Filing date||Oct 9, 1970|
|Priority date||Feb 3, 1970|
|Also published as||DE2012668A1, DE2065802A1|
|Publication number||US 3756805 A, US 3756805A, US-A-3756805, US3756805 A, US3756805A|
|Original Assignee||Ormaechea J|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (7), Classifications (9)|
|External Links: USPTO, USPTO Assignment, Espacenet|
p 4, 19-73 J. J. A. ORMAECHEA 3,756,805
METHOD OF PRODUCING LEAD-BEARING STEEL Filed Oct. 9, 1970 3 Sheets-Sheet 1 Sept. 4, 1973 J. J. A. ORMAECHEA 3,756,805
METHOD OF PRODUCING LEAD-BEARING STEEL 5 Sheets-Sheet 2 Filed Oct. 9, 1970 p 1973 J. J. A. ORMAECHEA 3,756,805
METHOD OF PRODUCING LEAD-BEARING STEEL I5 SheetsSheet 3 Filed Oct. 9, 1970 United States Patent Oihce 3,756,805 Patented Sept. 4, 1973 3,756,805 METHOD OF PRODUCING LEAD-BEARING STEEL Jose Joaquin Aguirre Ormaechea, Independencia 1,
Vitoria, Spain 7 Filed Oct. 9, 1970, Ser. No. 79,529 Claims priority, applgisatiosrg Spain, Feb. 3, 1970,
Int. or. can 39/54 US. (:1. 75 -58 5 Claims The present invention relates to an improved method of making steel and a product produced thereby.
The present invention. relates particularly to the manufacture of lead-bearing steels, having a lead content of between 0.10 and 0.8% which is distributed finely and homogeneously throughout the entire mass of the steel.
As is well known, lead-bearing steels have a greater machinability, when worked on chip-producing machinetools, than steels of the same basic composition that do not contain lead.
- can also be observed in a magnetoscope test for magnetic ,Known classical methods of producing lead-bearing steels are based upon the hiterto accepted supposition that lead is insoluble in steel. a
In order to produce, by classical methods, lead-bearing steels having an adequatedegree of homogeneity, it has been thought necessary to add the lead in the form of granules, just before the steel solidifies, with the object of avoiding segregation of the lead due to gravity and -'-as a result of the substantial difference between the density of steel and of lead Consequently, in the classical meth- 0d, the granules of lead are added to the molten material .at the moment atwhich it is poured into the mold.
Contrary to the method of the present invention, the classicalmethods require precise co-ordination of. the stream of granules and the stream of molten steel at the moment when addition takes place, and this calls for very great care as well as a high degree of professional skill on the part of the personnel in charge of the process of manufacture. I 1
Nevertheless, the principal drawback to the methods hitherto used-resides in the fact that, with these methods,
it is not possible to produce steels in which the lead is distributed in ahomogeneous manner. This segregation of "lead of varying intensity always occurs, as well' as agglomerations of this element, which break up the metallic structure and lower the quality of the steel.
The absence of homogeneity and the existence of segregations can be revealed by theWragge impression or particles, and by microscopic examination.
Because the above-mentioned deficiencies, steel manufactured by the classical methods have generally been used for the production of parts subjected to low or medium load when in service. 1
It is an object of the present invention to provide a method of making lead-bearing steel, avoiding the abovementioned disadvantages, and in which solid or liquid lead is added to a stream of molten steel as it is discharged from a melting furnace to a ladle. With this and other objects in view which will become apparent from the following detailed description, the present invention will be clearly understood in connection with the accompanying drawings in which:
FIG. 1 is a schematic vertical longitudinal section through a melting furnace, a ladle and the means for adding the lead at the moment at which the metal is poured into the ladle and the addition of lead is made;
FIG. 2 is a schematic vertical longitudinal section through the ladle showing one construction thereof according to the present invention of the ladle outlet; and
FIG. 3 is a schematic vertical longitudinal section through the ladle showing another ladle outlet construc tion.
Referring now to the drawings, and more particularly to FIG. 1, there is shown a melting furnace 1, from which a stream of molten steel 2 passes from the melting furnace 1 to a ladle 3. A feed means 4 feeds a solid or liquid lead into a duct 5 which carries the lead to the molten stream of metal with which it joins up at point 6.
The ladle outlet 7 is more particularly disclosed in FIGS. 2 and 3QFIG. 2 shows an arrangement in which a base 8 of the ladle has a projecting portion orupstanding rim9, whereby it israised above the opening ofitheladle outlet. In FIG. 3 there is shownianotherarrangement in which a sleeve 7 defining the ladle outlethas one end thereof raised above theflatnbase 8 of the ladle. A plug 10 is providedforopening and closing the'ladle outlet:
cient to permit theformation of lead-oxide, the vapour of which is solublein the molten steel. The lead-oxide formed has a low boiling point and causes bubbling of the steel bath which becomes saturated with this compound.
The bubbling caused by the lead-oxide" vapour which passesthrough the bath and saturates it, reduces the cori- 'tent of oxygen, hydrogen and other gases dissolved inthe steel, and thus indirectlyimproves the quality of'the 'steel.
The amount of reactive oxygen necessary for the formation of lead-oxide willdepend upon the composition of the steel, and'care is taken" not to add aluminium to the bath before the lead has been added. e
In the case of aluminium-killed "steelsfalumitiium 'is added to the metal in-the ladle in the finatst ages. This constitutes no drawback since it corresponds to normal manufacturing procedure.
Table No. 1 shows the solubility of lead-oxide as a function of the temperature of the bath, as established on the basis of numerous tests:
TABLE NO. 1
Percent Pb dissolved in the form of PbO Temperature of the bath in degrees C.:
The solubility of lead in steel is independent of the composition of the steel and is determined solely by temperature.
The temperature at which the metal is poured into the ladle should be greater than 1600 C. and is governed by the percentage of lead required in the steel, as shown in Table No. 1.
As can be seen from the table, when the temperature of the bath drops below 1600 C., as occurs in most cases when the steel is still in the ladle, the solubility of the lead in the steel is practically zero. Under these conditions lead-oxide is precipitated in the form of a fine and homogeneous dispersion, the particles of which do not settle by means of gravity, so that the lead is homogeneously distributed after solidification has taken place.
The remainder of the lead, insoluble in the steel at the temperature at which the addition is made, forms relatively large droplets, which each settle by gravity over a period of time not greater than 5 minutes, and are deposited on the base of the ladle. Thus, after the lead has been added, a minimum period of about 5 minutes should be allowed to elapse so that this deposition can take place before the steel is poured into the mold.
The quantity of lead added in solid or liquid form should be greater than that theoretically required, and preferably should be 40% greater than the quantity that it is desired to incorporate in the steel.
The lead is added at the feed point via means 4 (FIG. 1) at a rate equal to that required at the upper part 6 of the stream of molten steel.
The rate of supply of the lead needed at the feed point 4 in FIG. 1 can be determined by simple tests, the aim being to have a supply of solid or liquid lead reaching the stream of molten metal during practically the entire period during which pouring takes place. Nevertheless, the system does not call for a high degree of co-ordination in this operation, since, as previously indicated, if too much lead is added this does not become incorporated in the bath but is deposited on the base of the ladle.
The method of the present invention does not require any high capital cost equipment. The only requirement is that of positioning the ladle outlet 7 or a rim 9 in such a way that it projects upward of or beyond the plane of the base 8 of the ladle 3, thus preventing the lead, deposited on the base, from being entrained by the stream of steel which emerges through the mouth-piece 7 when casting takes place.
Despite the above-mentioned precautions, a small quantity of lead may be deposited directly on the surface of the ladle outlet. This lead can be eliminated simply by slight purging of the steel prior to casting it in the mold.
The method to which the present invention relates can be applied to all kinds of steel compositions and can be adopted in present-day steel-producing techniques.
The method of the present invention can be used in all the usual steel-making processes, for example, Siemens- Martin, electric furnace, L.D., continuous casting, or mold-casting by the siphon or direct methods.
These improvements result in advantages regarding an even and finely-dispersed distribution of the lead both at the top and the bottom of the ingot. Similarly, segregations do not occur either on the surface or in the middle of the ingot.
Consequently, ingots manufactured by the method of the present invention do not need to be end-cropped, as is the case with ingots manufactured by the classical methods.
In this connection, experience from numerous casting operations has shown that with the method of the present invention, an output can be obtained that is of the same order of magnitude as that obtained with steels of an identical basic compositions, but containing no lead.
The lead particles form a fine, homogeneous dispersion, the grain-size of which is often less than one micron.
Tests carried out so far using the new method in accordance with the present invention show that this particular method for the addition of lead has no adverse effect upon the fatigue behaviour of the steel or upon its mechanical properties.
While I have disclosed one example of the present invention, it is to be understood that this example is given by illustration only and not in a limiting sense.
1. A method of producing lead-bearing steel, containing a uniform distribution of lead, comprising the steps of discharging a stream of molten steel from a melting furnace into a ladle,
adding lead to said stream of molten steel at the moment as it is being discharged from said melting furnace between the latter and the ladle at temperatures above 1600 C. and controlling the temperature of the bath, and
dissolving oxygen in the bath in the ladle in order to favor the formation of lead-oxide.
2. The method, as set forth in claim 1, wherein sufficient lead is added to said stream of molten steel to provide a lead content of 0.10 to 0.80% by weight homogeneously distributed in said steel.
3. The method, as set forth in claim 1, further comprising the step of allowing the steel in said ladle to stand for at least 5 minutes before it is poured or tapped into a mold.
4. The method, as set forth in claim 3, further comprising the step of aluminium-killing said steel after it has been allowed to stand for at least 5 minutes and before it is poured or tapped.
5. The method, as set forth in claim 1, further comprising the step of preventing any deposited lead from being discharged from said ladle by catching said deposited lead in a projecting rim adjacent the discharge of the ladle.
FOREIGN PATENTS 4/ 1940 Great Britain -123 F L. DEWAYNE RUTLEDGE, Primary Examiner U.S. Cl. X.R.
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|US3917240 *||Oct 17, 1973||Nov 4, 1975||Sumitomo Metal Ind||Apparatus for projecting pieces of a deoxidizing agent into molten steel|
|US4203763 *||Nov 22, 1978||May 20, 1980||Scandinavian Lancers Aktiebolag||Method of manufacturing a lead alloy steel and a steel made according to the method|
|US4371395 *||Jul 6, 1981||Feb 1, 1983||Southwire Company||Technique for adding lead to steel|
|US4751047 *||May 26, 1987||Jun 14, 1988||Nippon Steel Corporation||Method of adding low-melting-point metal to molten steel|
|US4781887 *||Nov 5, 1987||Nov 1, 1988||Nippon Steel Corporation||Production of steels containing low melting point metals|
|US4848755 *||Oct 27, 1988||Jul 18, 1989||Inland Steel Company||Apparatus for adding liquid alloying ingredient to molten steel|
|US4849167 *||Mar 18, 1988||Jul 18, 1989||Inland Steel Company||Method and appartus for adding liquid alloying ingredient to molten steel|
|U.S. Classification||420/129, 266/216, 420/86|
|International Classification||C21C7/00, C22C38/60|
|Cooperative Classification||C21C7/0043, C22C38/60|
|European Classification||C22C38/60, C21C7/00D2|