US3836359A - Method of producing leaded steel - Google Patents
Method of producing leaded steel Download PDFInfo
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- US3836359A US3836359A US00264012A US26401272A US3836359A US 3836359 A US3836359 A US 3836359A US 00264012 A US00264012 A US 00264012A US 26401272 A US26401272 A US 26401272A US 3836359 A US3836359 A US 3836359A
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
Definitions
- ABSTRACT High lead content of uniformly dispersed finely divided particles is obtained in cast steel through a programmed addition of lead to molten steel in a vessel and control of other process factors, such as temperature, agitation and slag cover, affecting dissolution and retention of lead in molten steel.
- an initial quantity is introduced to the steel, large with respect to the time during which it is added as compared with the total lead added relative to the total time span of lead addition, and subsequently additional led is added, the total sufficient to produce a lead content in the steel greater than 0.15 percent by weight and no greater than 0.26 percent by weight.
- the total lead is introduced as three to five discrete additions at time intervals of one to fifteen minutes.
- the present invention is an improvement over that of North et al. referred to above, in that it overcomes the shortcomings of the previously known processes in the manner of North et al. and assures the production of steel in which the lead content in cast billets or ingots is essentially uniformly dispersed and finely divided, yet in addition achieves a significantly higher level of lead content.
- the present process comprises a combination of steps that make effective use of solubility of lead in steel at temperatures above the liquidus. Upon solidification of the steel, the dissolved lead is rejected, resulting in the formation of a uniform, fine, dispersion of lead in the steel.
- programmed lead additions made under specific process conditions materially increase the level of lead solubility over that heretofore obtainable with a single addition (from the previous .15 percent lead of the North et al. process to a presently obtainable 0.24 to 0.26 percent by weight) without disadvantageous gross segrega tion of lead or appearance of large lead particles in the steel characteristic of typical prior art processes that provide a high lead content.
- This higher lead solubility and the improved leaded steel product having highlead content, uniformly and finely dispersed without macrosegregation, is obtained by (a) adding lead to the steel in a vessel from which leaded steel containing essentially only dissolved lead is subsequently removed while molten to a casting mold, (b) establishing a minimum temperature of the molten steel at the time the lead is added that is significantly above the liquidus temperature of the unleaded steel, (0) introducing the lead to the steel by adding an initial quantity large with respect to the time for addition as compared with the total lead added relative to the total time span of lead additions and subsequently adding additional lead to reach a solubility level between 0.15 and 0.26 percent lead by weight, and preferably by adding the lead to the steel in a plurality but relatively limited number of discrete quantities or additions with a significant time interval therebetween, and also between the last addition of lead to the steel and the casting of the steel, (d) adding a limited excess of lead over the target quantity desired in the steel, (e)
- a principal object of this invention is to achieve an increased level of dissolved lead in steel in a commercially practical process for producing cast leaded steel that assures a uniform dispersement of small finely divided lead particles and an absence of macrosegregation of lead and surface or subsurface streaks or blobs of lead.
- FIG. 1 is a flow diagram illustrating both a general method of adding lead to steel in accordance with the present invention and a more specific process for the continuous casting of steel;
- FIG. 2 is a diagrammatic illustration showing apparatus used in a process of FIG. 1;
- FIGS. 3, 4A, 4B, 5 and 6 are graphs showing the content of dissolved lead in molten steel as a function of time under various conditions.
- molten steel from a furnace such as a BOF, electric arc furnace, or the like
- a vessel such as a ladle
- a slag cover is applied to the steel in the vessel and the vessel is placed in a stirring apparatus such as an induction stirrer of a degasser, and the steel is stirred.
- Lead in divided form is added to the steel during stirring in multiple additions at significant intervals.
- the total quantity of lead added through the multiple additions is greater than the quantity desired in the final product by an amount at least as great as the anticipated lead losses, as through volatilization, occlusion in the slag and refractory materials and settling.
- the amount and form of lead added, the number and size of the lead additions, the time interval between additions, the stirring, slag cover and melt temperature, are all controlled to obtain desired results.
- the present process relies upon and utilizes the solubility of lead in molten steel and the insolubility of lead in solidified steel to obtain a uniform dispersion of fine particles of lead in cast, i.e., solidified, steel.
- a target or aimed lead content in the steel is selected consistent with a determined solubility limit of lead in the steel at the temperature when added to assure that the lead contentatll 2,854,716.
- process variables in the present invention affect the solubility level attainable, i.e., the maximum target amount permissible if macrosegregation and large particle size of lead is to be avoided, a significantly higher upper limit of lead content for practical purposes has been found to be 0.24 to 0.26 percent by weight.
- the present invention is applicable to the attainment of a lead content in steel of between 0.15 percent and 0.25 percent by weight, the process of a single lead addition being suitable to 0.15 percent but essentially inapplicable therebeyond regardless of the excess lead introduced in the one addition.
- the actual lead added during the process must be greater than the target amount.
- the amount greater depends upon the level of lead desired within the 0.15 to 0.25 percent range, as well as upon process variables, such as stirring, temperature, etc. Where the process variables are controlled consistent with the entire process contemplated herein, the recovery in solution of the lead added to the steel ranges from a low of about 42 percent at the maximum solubility level of this process of 0.25 percent lead (thus requiring an excess of 140 percent over the target amount) to 56 percent at a solubility level of 0.18 percent (requiring an excess of 77 percent over the target amount).
- Experimental data illustrative of the above and showing the total amount of lead added to steel to provide the indicated amount actually obtained, based on 200 pound leaded steel heats, is set forth in Table I.
- target level will have been in solution at the time of casting and will be precipitated in a uniformly distributed fine dispersion upon solidification.
- the actual amount of lead added to the steel is selected to assure that the target amount is obtained at the time of casting.
- the actual amount comprises the target amount plus an excess, based on anticipated lead losses during and after lead addition and prior to casting, due essentially to volatilization, occlusion of lead in the refractory container and the covering slag, and settling of undissolved lead.
- solubility limit of lead in low carbon (less than 0.10 percent carbon) steel may be as high as 0.43 percent, only a 0.15 percent dissolved lead content level has been attainable under practical conditions with the North et al.
- the excess lead over the target amount added to the steel melt takes into account lead losses in the molten steel bath which occur during handling and casting.
- the lead losses result in primarily five ways: (1) lead volatilization, (2) lead oxidation forming volatile lead oxides, (3) lead taken into the refractories, (4) lead taken into the slag that covers the melt, and (5) lead that settles without dissolving, especially as the solubility limit is approached.
- excesses of lead over the amounts needed to compensate for the above losses in obtaining the desired level of dissolved lead can be added if subsequently separated or purposefully allowed to escape so as not to become a part of the steel that is cast, but such excess represents an unnecessary inefficiency rather than a required excess and necessary part of the process.
- the lead additions specified herein are applicable to steel alloys typified by AISI types 1020, l 1 18,41 18 and 4140, among others. It will be appreciated that the upper limit of lead that can be attained in accordance with this process, based on actual solubility, is influenced by differences in the steel composition, because of the effect of certain elements upon the solubility of lead.
- a controlled variable rate of continuous lead addition is regarded as equivalent to discrete lead additions in the broad sense, if programmed to produce the same general effect of initially establish-
- the time interval between discrete lead additions can vary from I to 15 minutes and typically will vary between 1 to 7 minutes.
- the specific time depends upon the utilization rate of the lead, i.e., the rate at which it dissolves, and the rate at which losses occur.
- the solution rate depends upon factors such as the stirring rate, melt temperature and cooling rate, and others, and the rate of lead loss depends upon the slag cover, the solubility of lead in the refractory of the vessel containing the melt, and the like.
- a lead content of 0.20 to 0.25 percent by weight lead is achieved in the preferred practice by utilizing three to five lead additions spaced apart one to seven minutes.
- the graph of FIG. 3 depicts the lead content with re spect to the time from a first lead addition in the five 200 pound steel heats (A181 4118 steel) for which Table I tabulates certain data, and indicates the time interval between lead additions.
- the lower two curves are illustrative of the prior process disclosed in the aforementioned co-pending application, in which only a single addition of lead is made.
- the other three curves show the lead content at different times for melts having final lead levels of 0.18 percent, 0.20 percent and 0.25 percent. Additional details are included in the examples below.
- the steel is contained in a vessel such as a ladle prior to teeming.
- a vessel such as a ladle prior to teeming.
- One principal reason is that in the event the actual lead losses are less than anticipated or some settling of undissolved lead occurs, especially where the target amount of lead is near or at the solubility limit, excess undissolved lead will or can be segregated within the vessel and steel containing only dissolved lead can be removed from the vessel and cast.
- the steel can be conveniently stirred before, during and after lead addition, and adequate time can be provided for dissolution of the lead in the steel prior to casting.
- the steel When Lead Added To obtain leaded steel in a fine dispersion and uniformly distributed in accordance with this invention, the steel must be at least ten degrees Fahrenheit above the liquidus temperature of the steel. This limit is arbitrary to the extent that there is no sharp break in the solubility curve at that temperature, but is a realistic and necessary limitation from a practical standpoint in assuring adequate solubility. Optimum conditions for obtaining maximum solubility and maximum lead content require still higher temperatures above the liquidus.
- optimum lead solubility in low carbon (i.e., less than 0.10 percent carbon) steel is obtained by adding lead to the steel bath with the steel bath at a temperature as high as mill practice will permit, which is seldom higher than 3,000 degrees Fahrenheit and typically 75 to 135 degrees Fahrenheit above liquidus.
- the temperature of the melt at the time of lead addition would advantageously be 2,850 to 2,910 degrees Fahrenheit. This may be referred to as the optimum temperature for this steel and is that temperature of the melt necessary to attain the maximum solubility of lead in the molten steel, optimum ingot quality, and/or optimum casting practice.
- the lead will be in contact with molten steel prior to being cast, for a time of about five to 30 minutes, i.e., from the first lead addition to the start of casting.
- the steel is at a temperature substantially above the liquidus, especially in the process of continuous casting, where the steel temperature when introduced to the ladle .is about 50 to 150 degrees Fahrenheit higher than the temperature normally used for ingot casting.
- the solution rate of lead in molten steel depends significantly upon stirring, i.e., mechanical mixing of the steel and added lead.
- stirring must be maintained for a period during and after each lead addition.
- a stirring action is maintained throughout the period of time during which multiple lead additions are made and is continued for a time after the last addition.
- a minimum total stirring time of five minutes is required and most desirably the stirring time will be fifteen to thirty minutes in commercial practice, assuming a generally constant, somewhat intense or vigorous, stirring rate. For maximum dissolution and efficiency, the stirring rate should be maximized.
- a suitable stirring rate will cause an obvious, visible, flow of metal in the vessel, which when created by induction, as in a small induction furnace, is sufficient to cause an upward bulging of the metal top surface.
- Stirring is continued after the last addition of lead, preferably for a period of time somewhat in excess of the -stirring time provided between lead additions, because of the greater difficulty in dissolving lead as the dissolved lead content of the melt increases and approaches the solubility limit.
- the stirring of the melt cleanses the steel of undissolved lead in instances where some excess of lead may exist above the solubility limit.
- the undissolved lead is rapidly settled from the steel within the ladle or other vessel, assuring that with proper pouring or teeming techniques no undissolved lead will be removed with the steel.
- the quantity of lead comprising each addition be in a divided form to provide a high surface area-to-volume ratio and may be added in the form of small lead chunks, lead shot, leadsteel pellets, or lead-iron pellets, which increase the degree of immediate dispersion and decrease the time required for dissolution and dispersion.
- a small lead particle size enhances the possibility of reaching maximum lead solubility and increases the solution rate.
- the lead additive can be in the form of steel capsules and be submerged beneath the bath surface, or lead shot or capsules can be poured through a tube in which the lower end is submerged beneath the bath surface. Lead shot or capsules can also be injected pneumatically or otherwise projected into the bath.
- Slag Cover A slag cover over the molten steel is necessary to inhibit the loss of lead through volatilization and serves to increase the dissolved lead content in the melt. By trapping lead vapor, the slag effectively increases the time available for lead dissolution and enhances the lead supersaturation of the melt.
- the solution reaction can proceed for a longer time, until the vaporization reaction becomes predominant due to gradual dissipation of the higher lead partial vapor pressure initially built up between the melt and the slag cover after a lead addition.
- Any typical slag is satisfactory, for example, vermiculite or bauxite-lime, but the more viscous the slag the more effectively it traps lead vapor over the melt and reduces the rate of gaseous diffusion.
- the slag cover must be present immediately after lead addition, and preferably is present initially and pushed aside to expose a portion of the bath surface to which the lead is added. Tests have indicated that lead loss for heats without slag cover averaged 0.006 percent per minute. With slag cover, the loss is reduced to an average of 0.0013 percent per minute, measured when the bath was under heavy stirring from induction heating.
- the lead content will remain relatively constant throughout a normal teeming operation.
- Leaded Steel Products The present process is contemplated for use with a composition of steel to which lead can be added and is especially useful in producing free machining steels.
- the steel can be produced in billet form by continuous casting. Alternatively, the process is also applicable to the casting of ingots or the like.
- the product produced is a steel alloy having enhanced machinability over a conventional steel without lead, but which will not have drawbacks, i.e., defects, as in conventionally leaded steel, which defects include surface and subsurface streaks of lead and blobs of lead.
- the product is characterized by an absence of macrosegregation of lead.
- Multiple lead additions are utilized to produce a product having a lead content of between 0.15 percent to 0.24-0.26 percent lead by weight in which the predominant lead particle size will be no greater than 10 microns and the maximum lead particle size will be no greater than 30 microns.
- the distribution of lead throughout the product is extremely uniform, generally varying no more than 0.01 to 0.03 percent lead by weight. While nonuniformity beyond this range has been experienced, it has been attributable to the presence of undissolved lead resulting from inadequate stirring, spill-over during pouring, low melt temperature, etc.,; i.e., a failure to observe the process requirements.
- FIG. 11 A flow diagram illustrative of the general process embodying the present invention is shown in FIG. 11 of the drawings, with more specific steps utilized in a continuous casting process being illustrated in broken lines. Apparatus for practicing the process is shown in FIG.
- molten steel such as low carbon steel
- a steel-making furnace such as a BOF or other furnace
- the ladle may typically hold 100 to 200 tons of steel, indicated at 12.
- a layer of slag 13 is applied to the steel 12 in a conventional manner, to retain heat, reduce fuming and lead loss after lead addition, and increase the level to which lead will dissolve in the steel. Approximately a two-inch layer of slag is adequate.
- the slag may be applied to the steel in the vessel immediately after the first addition of lead.
- the vessel such as the ladle i0, is then transferred to stirring apparatus, such as a degasser 114, which provides an enclosed chamber MA and induction stirring apparatus MB.
- stirring apparatus such as a degasser 114, which provides an enclosed chamber MA and induction stirring apparatus MB.
- the temperature of the steel in the vessel is as high as mill practice will allow, at least 10 degrees Fahrenheit above the liquidus temperature of the steel at the time the lead is initially added, and typically at a temperature of between 2,850 and 2,910 degrees Fahrenheit for best results, considering the type of steel, the solubility of lead, and good casting practice. To achieve this temperature level, the temperature of the steel at the time it is tapped from the furnace may be approximately 3,000 degrees Fahrenheit. Vigorous stirring by induction is begun and is maintained at a substantially constant rate.
- Lead to be added is in subdivided form, for example, in the form of small chunks, shot, or lead-steel pellets. When in finely divided form, such as shot, the lead may be advantageously wrapped in a steel sheet.
- the quantity of lead to be added depends upon the target amount desired in the cast steel. While the exact excess to be added over and above the target amount varies with process conditions, Table 1 above is a guide. As indicated therein, lead in the amount of 140 percent of the target amount was used to achieve the maximum solubility level.
- the lead is added in multiple additions with a time interval between.
- a total of 0.60 percent lead by weight is added to the steel in three to five distinct additions of 0.20 to 0.12. percent by weight lead, respectively, one to seven minutes apart, with constant stirring during and after each lead addition, for a total time of five to 30 minutes.
- the additional lead above the target amount allows for the anticipated loss of lead from the melt during addition and dissolution through lead volatilization, lead oxidation forming volatile lead oxides, lead taken into the refractories, lead taken into the slag, and settling.
- Lead is added by thrusting lead chunks or lead shot wrapped in steel sheet through the slag layer.
- the time interval between lead additions is selected so as to timely replenish the melt with lead as that previously added is dissolved and lost.
- the lead is added to the steel in a vessel, such as the ladle 10, any lead that does not dissolve in the steel melt, refractory or slag, or volatilize, but rather settles, can be retained in the vessel so that only steel containing dissolved lead is removed from the vessel and is cast. This is accomplished either through the pouring technique or through a particular vessel con struction.
- the ladle is constructed to prevent any excess lead not dissolved in the steel from being teemed during the continuous casting process, by utilizing a nozzle 18 projecting upward from the bottom of the ladle a short distance so that the bottom of the ladle acts as a reservoir to retain any settled excess undissolved lead.
- a rod 20 within the ladle functions as a stopper for the ladle and is moved vertically to open and close the nozzle by a lever 22.
- the uniformity of lead content makes practical the continuous casting of high lead content steel.
- This continuous casting process is accomplished by teeming the steel containing only dissolved lead from the ladle 10 into a tundish 24, which provides a uniform flow of steel to a continuous casting mold 30.
- the steel in the tundish is covered by a protective layer of slag 25.
- a ventilation tube 26 is provided adjacent the top of the tundish to withdraw any volatilized lead.
- the tundish serves to provide a substantially uniform pressure head and, hence, flow rate of the steel, which flows from the tundish through a fused silica nozzle 20 to the continuous casting mold 30, where it is solidified and advanced as a continuous formed billet 32.
- the continuous casting mold is typically a water cooled copper mold.
- a special low fusion point slag material 34 is utilized over the steel in the continuous casting mold to reduce lead fuming from the molten leaded steel poured into the mold and to lubricate the mold surfaces to avoid sticking of the solidified steel to the mold walls.
- a ventilation tube 36 is provided at the top of the mold 30 to withdraw any volatilized lead.
- a series of heats were made of five pounds and two hundred pounds in an induction furnace.
- the fivepound heats were made under an atmosphere of argon and the two hundred pound-heats were made under an atmosphere of air.
- the melt temperature in both cases was maintained at approximately 2,900 degrees Fahrenheit, each melt as completely covered with a fluid lime-bauxite slag in a ratio of 60 percent lime, 40 percent bauxite.
- the base composition of the heats was AISI 4118 steel, as follows, in percent by weight (all proportions herein being expressed in percent by weight of the steel melt unless otherwise noted):
- lead was added to separate heats in different forms. In each heat, five additions of lead in the amount of 0.12 percent by weight of the melt were added, except in the case of lithium lead compound, where the amount of lead was 0.20 percent by weight.
- the lead was added to molten steel as (a) lead-1008 steel (AISI designation) compacted pellets, (b) lead compacted pellets, free lead shot wrapped in thin protective foil (steel sheet or aluminum), (d) lead sulfide powder wrapped in protective foil, and (e) lithium lead compound wrapped in protective foil.
- the lead additions were made to each melt over a period of time of approximately minutes with continuous induction stirring.
- FIGS. 4A and 4B of the drawings The lead content at various times during the process, as determined by spectrographic analysis of melt samples (so-called pin samples) are shown in FIGS. 4A and 4B of the drawings.
- a lead content in solution of approximately 0.25 percent by weight was achieved in the trials shown in FIG. 4A. It can be seen from the graph of FIG. 48, that the lead content achieved through the use of lead sulfide powder leveled off at 0.20 percent, apparently due to a variation in stirring and temperature.
- the lead content of the melt to which the lithium lead compound was added went beyond the solubility limit because of the excess lead added over the 0.60 percent by weight of the other examples.
- Solubility limit To determine the solubility limit of lead in steel, lead was added to two additional five-pound heats of AISI 4] 18 steel prepared above and at a temperature of 2900 degrees Fahrenheit. Dissolved lead content is defined for the present purpose as the lead content determined by spectrographic analysis from pin samples of the heats when the lead particles in the solidified steel are evenly distributed and all are essentially one to 10 microns in size. It has been found that once pin samples indicate a consistent lead content after a certain level of lead addition, a further increase in the lead content results in a loss of uniformity of lead distribution in the ingot, and the lead solubility limit in molten steel can be assumed to have been reached and surpassed.
- a graph is shown in FIG. 5, indicating points at which lead additions were made to the two heats referred to above and showing the lead content at different times as determined by spectrographic analysis of pin samples.
- ten additions of 0.20 percent lead by weight were made in the same manner.
- the content of dissolved lead reached a plateau at 0.24 to 0.26 percent by weight.
- the lead content of the molten steel became greater than 0.26 percent by weight and inconsistent lead content was noted.
- the solubility limit had been surpassed.
- Three 200 pound heats of AISI 41 18 steel were prepared as set forth above in a 250 pound induction furnace operated at 50 kilowatts, which stirred the melt vigorously.
- a first lead addition was made to the steel, which was at a temperature of 2900 degrees Fahrenheit, in an amount of 0.20 percent by weight.
- the total lead addition made to each melt is shown in Table I above.
- the lead additions comprised lead shot wrapped in steel sheet and thrust through a slag cover over the melt.
- the second lead addition to each heat was added 2 /2 minutes after the first.
- a third lead addition was made 2 /2 minutes after the second.
- the second and third additions in the 0.25 percent lead heat contained lead in the amount of 0.20 percent by weight of the melt.
- the 0.19 and 0.20 percent ingots were made by making five equal additions of lead in the amount of 0.12 percent by weight and the 0.15 percent lead ingot was made by making 15 equal additions of lead in the amount of 0.04 percent by weight.
- Lead content in each instance was determined spectrographically to an accuracy of 10.01 percent by weight.
- the three 72 pound ingots were cut transversely at locations adjacent the top, middle and bottom and lead content was determined at three points along a radius from the center.
- the fivepound ingots were cut transversely only at one location and lead content was determined at two peripheral locations diametrically opposite each other and at three central locations.
- the lead was considered as nonsegregated (all resulting from dissolved lead in the melt) except for that in the 72 pound ingot having a lead content of 0.25 percent by weight, in which undissolved lead spilled from the vessel containing the steel near the end of the pour, accounting for the greater variation in lead distribution and the higher content of the lead at the center top portion of the ingot.
- leaded steel having a substantially uniform dispersion of finely divided lead particles varying in the amount present throughout major portions of the steel by no more than 0.03 percent by weight, the predominant size of said particles being no greater than about 10 microns in diameter and essentially all of the lead in said steel having been dissolved in the steel when molten, including the steps of adding lead to molten steel in a vessel while the steel is at least 10 degrees Fahrenheit above the liquidus temperature of the steel, providing a slag cover over the steel in the vessel and stirring the steel after the lead is added, the improvement comprising introducing the lead as at least two substantially discrete additions, each having a lead content greater than one-fifteenth of the total amount of lead added but no greater than 9.35 percent by weight of the molten steel and added lead and spaced apart in time by at least one minute, the total additions together containing an amount of lead sufficient to produce a lead content in the steel greater than 0.15 percent by weight and no greater than 0.26 percent by weight.
- the improvement comprising introducing the lead in at least three and no more than five substantially discrete additions none of which contains lead in an amount exceeding .35 percent by weight of the molten steel and added lead separating each addition from the next by a time interval at least one minute and no more than fifteen minutes, the total amount of lead added being less than 1 percent by weight of the molten steel and added lead.
- a process of adding lead to steel to assure a uniform distribution of only finely dispersed lead particles the largest of which are no greater than about 10 microns in diameter including the steps of first adding lead to steel in a vessel and then removing the leaded steel from the vessel to a mold, such as an ingot mold or a continuous casting mold or the like, wherein the temperature of the steel is at least 10 degrees Fahrenheit above the liquidus temperature of the steel when the lead is added, two to 15 discrete additions of lead are made at time intervals of at least one minute, a cover layer of slag is provided over the steel in the vessel, the steel is stirred within the vessel for at least one minute after each lead addition and for a total time of at least five minutes, and essentially all of the lead in the steel removed from the vessel is in a dissolved state.
- a mold such as an ingot mold or a continuous casting mold or the like
- a process of continuously casting steel containing a uniform distribution of finely dispersed lead particles the predominant size of which is less than microns in diameter and the largest of which are no greater than 30 microns in diameter including the steps of: containing molten steel to which lead is to be added in a vessel at a temperature at least 75 degrees Fahrenheit above the liquidus temperature of the steel; adding an initial quantity of lead to the steel in the vessel and subsequently adding an additional quantity, said initial quantity of lead being a greater percentage of the total lead added than any subsequent addition, the total lead added being sufficient to produce a lead content solidified shape of leaded steel.
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Abstract
Description
Claims (12)
- 2. In a process of producing leaded steel having a lead content greater than 0.15 percent by weight and no greater than 0.26 percent by weight in the form of a substantially uniform dispersion of finely divided lead particles varying in the amount present throughout major portions of the steel by no more than 0.03 percent by weight, the predominant size of said particles being no greater than about 10 microns in diameter and essentially all of the lead in said steel having been dissolved in the steel when molten, including the steps of adding lead to molten steel in a vessel while the steel is at least 10 degrees Fahrenehit above the liquidus temperature of the steel, providing a slag cover over the steel in the vessel and stirring the steel after the lead is added, introducing an initial quantity of lead to the steel and subsequently introducing additional lead, said initial quantity of lead being a greater percentage of the total lead added than any subsequent addition, the total lead added being sufficient to produce a lead content in the steel greater than 0.15 percent by weight and no greater than 0.26 percent by weight.
- 3. In a process of producing leaded steel having a substantially uniform dispersion of finely divided lead particles essentially all of the lead in said steel having been dissolved in the steel when molten, including the steps of adding lead to molten steel in a vessel while the steel is at least 10 degrees Fahrenheit above the liquidus temperature of the steel, providing a slag cover over the steel in the vessel and stirring the steel after the lead is added, the improvement comprising introducing the lead as at least two substantially discrete additions, each having a lead content greater than one-fifteenth of the total amount of lead added and spaced apart in time by at least one minute, the total additions together containing an amount of lead sufficient to produce a lead content in the steel greater than 0.15 percent by weight and no greater than 0.26 percent by weight.
- 4. A process as set forth in claim 3 wherein the first of said at least two substantially discrete lead additions has a lead content at least as great as any subsequent lead addition.
- 5. In a process of producing leaded steel having a substantially uniform dispersion of finely divided lead particles varying in the amount present throughout major portions of the steel by no more than 0.03 percent by weight, the predominant size of said particles being no greater than about 10 microns in diameter and essentially all of the lead in said steel having been dissolved in the steel when molten, including the steps of adding lead to molten steel in a vessel while the steel is at least 10 degrees Fahrenheit above the liquidus temperature of the steel, providing a slag cover over the steel in the vessel and Stirring the steel after the lead is added, the improvement comprising introducing the lead as at least two substantially discrete additions, each having a lead content greater than one-fifteenth of the total amount of lead added but no greater than 0.35 percent by weight of the molten steel and added lead and spaced apart in time by at least one minute, the total additions together containing an amount of lead sufficient to produce a lead content in the steel greater than 0.15 percent by weight and no greater than 0.26 percent by weight.
- 6. A process as set forth in claim 5 wherein the first of said at least two substantially discrete lead additions has a greater lead content than any subsequent addition.
- 7. In a process of producing leaded steel having a substantially uniform dispersion of finely divided lead particles essentially all of the lead in said steel having been dissolved in the steel when molten, including the steps of adding lead to molten steel in a vessel while the steel is at least 10 degrees Fahrenheit above the liquidus temperature of the steel, providing a slag cover over the steel in the vessel and stirring the steel after the lead is added, the improvement comprising introducing the lead in at least three and no more than five substantially discrete additions none of which contains lead in an amount exceeding .35 percent by weight of the molten steel and added lead, separating each addition from the next by a time interval at least one minute and no more than fifteen minutes, the total amount of lead added being less than 1 percent by weight of the molten steel and added lead.
- 8. A process as set forth in claim 7 wherein the first of said discrete additions has a lead content at least as great as any subsequent lead addition and the time interval between additions is no greater than seven minutes.
- 9. In a process of producing leaded steel having a lead content greater than 0.15 percent by weight and no greater than 0.26 percent by weight in the form of a substantially uniform dispersion of finely divided lead particles varying in the amount present throughout major portions of the steel by no more than 0.03 percent by weight, the predominant size of said particles being no greater than about 10 microns in diameter and essentially all of the lead in said steel having been dissolved in the steel when molten, the steps comprising containing molten steel in a vessel at a temperature of between 10 and 135 degrees Fahrenheit above the liquidus temperature of the steel, providing a slag cover over the steel in the vessel, introducing an initial quantity of lead in divided form to the steel and thereafter introducing additional lead to the molten steel, said initial quantity of lead being a greater percentage of the total lead added than any subsequent addition, the total lead added being sufficient to produce a lead content in the steel greater than 0.15 percent by weight and no greater than 0.26 percent by weight, stirring the molten steel in the vessel during and after the addition of lead for a total time period of between five and thirty minutes, removing steel containing lead essentially only in the dissolved state from the vessel, and solidifying the steel removed from the vessel.
- 10. A process as set forth in claim 9 wherein the lead is introduced as at least two substantially discrete additions, each discrete addition having a lead content greater than one-fifteenth of the total amount of lead added but not greater than 0.35 percent by weight of the steel and spaced apart in time by at least one minute and not more than 15 minutes, and the total lead added being less than 1 percent by weight of the steel.
- 11. A process as set forth in claim 10 wherein the first of said at least two substantially discrete lead additions has a greater lead content than any subsequent addition.
- 12. A process of adding lead to steel to assure a uniform distriBution of only finely dispersed lead particles the largest of which are no greater than about 10 microns in diameter, including the steps of first adding lead to steel in a vessel and then removing the leaded steel from the vessel to a mold, such as an ingot mold or a continuous casting mold or the like, wherein the temperature of the steel is at least 10 degrees Fahrenheit above the liquidus temperature of the steel when the lead is added, two to 15 discrete additions of lead are made at time intervals of at least one minute, a cover layer of slag is provided over the steel in the vessel, the steel is stirred within the vessel for at least one minute after each lead addition and for a total time of at least five minutes, and essentially all of the lead in the steel removed from the vessel is in a dissolved state.
- 13. A process of continuously casting steel containing a uniform distribution of finely dispersed lead particles the predominant size of which is less than 10 microns in diameter and the largest of which are no greater than 30 microns in diameter, including the steps of: containing molten steel to which lead is to be added in a vessel at a temperature at least 75 degrees Fahrenheit above the liquidus temperature of the steel; adding an initial quantity of lead to the steel in the vessel and subsequently adding an additional quantity, said initial quantity of lead being a greater percentage of the total lead added than any subsequent addition, the total lead added being sufficient to produce a lead content in the steel greater than .15 percent by weight and no greater than 0.26 percent by weight; applying a slag cover to the steel in the vessel; inductively stirring the steel in said vessel for a total time of at least five minutes after the addition of lead; teeming steel containing lead essentially only in a dissolved state from said vessel to a tundish and flowing said steel from the tundish to a continuous casting mold; and continuously casting a solidified shape of leaded steel.
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US00264012A US3836359A (en) | 1972-06-19 | 1972-06-19 | Method of producing leaded steel |
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US00264012A US3836359A (en) | 1972-06-19 | 1972-06-19 | Method of producing leaded steel |
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US4203763A (en) * | 1977-12-21 | 1980-05-20 | Scandinavian Lancers Aktiebolag | Method of manufacturing a lead alloy steel and a steel made according to the method |
US4371395A (en) * | 1981-07-06 | 1983-02-01 | Southwire Company | Technique for adding lead to steel |
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