US 2880855 A
Description (OCR text may contain errors)
United States Patent 2,880,855 METHOD OF PROCESSING STEEL Elliot S. Nachtman, Park Forest, 11]., assignor to La Salle Steel Company, Hammond, 11111., a corporation of Delaware No Drawing. Application November 29, 1955 Serial No. 549,862
3 Claims. (Cl. 205-21) This invention relates to steels and to methods for processing same while in the form of bars, rods, tubing, sheets and the like, to improve the physical and mechanical properties thereof and to effect reduction in cross-sectional area.
This invention is a continuation-in-part of my copending application Serial No. 286,039, filed May 3, 1952, now abandoned, and entitled Method of Treating Steel for Drawing.
It is anobject of this invention to produce steels of the type described and to provide a method for the processing of same to introduce better physical and mechanical properties and to'effect reduction in cross-sectional area of the steel.
As used herein, the term steel is meant to include steels in the form processed by a cold finishing mill, such as rods, bars, tubing, sheets, flats and the like which are advanced through a die to effect reduction in crosssectional area and to provide a desirable surface finish on the steel for use in the manufacture of various products. For the most part, the steels processed through such a cold finishing mill represent hot rolled steels of the nonaustenitic type having a pearlitic structure in a matrixof free ferrite. Included also are low alloy steels.
It has been found that improvements are securedin physical and mechanical properties of such steels when advanced through a die to effect reduction in cross-sectional area while the steel is at an elevated temperature I within the range of 250 F. up to the lower critical temperature for the steel, such as at a temperature within the range of 250 to 1150" F. and preferably within the range of 550 to 850 F. for non-austenitic steels having a pearlitic structure in a matrix of free ferrite. For a detailed description with respect to the improvements secured in the physical properties and inmechanical properties at various temperatures, reference may be had to the co-pending applications Serial Nos. 518,411, 518,412, 518,413 and 518,414, filed June 27, 1955. Y
Ordinarily in processing steel for passage through a die to effect reduction in cross-sectional area and to provide a finish on the surface of the steel, as by advancing the steel through a draw die or an extrusion die, the steel is first processed through various steps such as descaling,
washing, liming or phosphating and lubricating to 'remove the oxide scale that forms on the surfaces of the steel and then to prepare the surface-for passage through the die. Heating to raise the temperature of the'steel not only introduces a further step in the processing of such steels through a die to effect reduction in crosssectional area, but the elevated temperatures employed introduce additional problems with respect to lubrication under the temperature conditions existing and the method to the die, and without increasing the load required to .efiect the desired deformation of the steel.
of application of such lubricants without interfering with w the continuity and smoothness of the operation, without causing variation in the temperature of the steel advanced "ice to provide a method whereby the scale can be removed from the steel, whereby a suitable lubricant can be applied to the surface of the steel for lubrication of the steel heated to an elevated temperature for passage through the cold finishing process, whereby improved lubrication at the surface of the steel is obtained, whereby the steel is heated uniformly to atemperature within the range of 250 F. to the lower critical temperature of the steel for passage through the die, and whereby a steel having improved surface finish is secured upon passage through the die, and whereby all of these conditions can be made available in a continuous process, and whereby descaling, lubrication and heat of the steel to the desired temperature is achieved in a single step as distinguished from the three or four separate and individual steps which would heretofore have 'been required. 1
In accordance with the practice of this invention, steel having the usual scale on the surface thereof is advanced through a bath of metal hydroxide present in combination with a reducing agent and heated to molten condition at elevated temperature. The steel is advanced directly from the molten bath of the reducing agent and metal hydroxide through the die, such as a draw die, to effect reduction in cross-sectional area.
In the molten bath of the metal hydroxide having a small amount of reducing agent therein such as a metal hydride, the scale present principally as the oxides naturally formed of the metal is removed. Removal of the oxides leaves a porous surface which is capable of retaining substantial amounts of the metal hydroxide, whereby the metal hydroxide in combination with the porous surface operates as an excellent lubricant during subsequent deformation of the steel upon passage through the die.
No one before, to the best of applicants knowledge, has recognized the advantage which accrues from the use of a metal hydroxide in combination with a reducing agent in a molten bath for descaling and as a lubricant for steel in the subsequent deformation or drawing operations by permitting the metal hydroxide to remain in the high concentration in the porous surface of the descaled steel, thereby to provide for descaling and improved lubrication in a single operation.
Numerous advantages not heretofore contemplated or capable of existence in other systems have been found to result from the treatment of steel in a bath of molten metal hydroxide and reducing agent without removal of the metal hydroxide prior to deformation or drawing.
By the use of the one-step process made possible in ac cordanee with the practice of this invention, the various steps of descaling, washing, liming or phosphating and lubricating are avoided, and marked improvements are secured in the operational characteristics in the subsequent finishing steps of the steel as well as improvements-in the physical properties of the product that is formed.
In addition, the surface which is secured by the treatment of the hot rolled and non-au-stenitic steels of the type described by immersion in a bath of a reducing agent and metal hydroxide at molten condition is far superior to that formed by normal acid pickling. The surface formed by the molten bath is not only scale-free but it embodies a porosity which permits retention of considerably greater amounts of the metal hydroxide and reducing agent for use as a lubricant than would otherwise have been possible to have retained on the surface as a lubricant for drawing.
It is believed that the porosity formed on the surface of the steel permits the use of reduced drawing loads and heavier drafts can be achieved while still increasing the usable life of the drawing die. While the explanation for the phenomenon secured has not, as yet been made available, it has been found that the surface of the steel through a die, after the porous surface has been formed thereon by the described treatment in a molten bath of the reducing agent and metal hydroxide, has superior finish and a higher degree of smoothness than has heretofore been secured with similar metals processed in accordance with the treating steps that have heretofore been employed. The porosity developed on the surface, possibly because of reactions which take place with the oxide scale, permits the molten metal hydroxide to become intimately associated with the surface where it can function more ably as a lubricant.
As the metal hydroxide, it is preferred to make use of an alkali metal hydroxide such as sodium or potassium hydroxide. Though not equivalent to sodium hydroxide or potassium hydroxide, use can be made of zinc hydroxide, iron hydroxide, or lead hydroxide, alone, but preferably combinations with sodium hydroxide or potasa s'iur'n hydroxide are'more desirable. 7 Use can also be made of salts of alkali metals, such as sodium palmitate,
.sodium acetate, sodium orthophosphate, and sodium sul- Any conventional reducing agent compatible with the molten metal hydroxide can be used but where rapid descaling in combination with lubrication is desired, it is preferred to introduce a strong reducing agent such as nascent hydrogen into the bath. This may be accomplished by the inclusion of a small amount of a salt such as sodium or potassium hydride. Rapid descaling may also be achieved by arranging the metal to be descaled as the cathode in an electrolytical bath containing the molten metal hydroxide and reducing agent as the electrolyte so that the descaling operation can be achieved at the same time that the porous surface is formed on the metal to retain sufficient amounts of the metal hydroxide for useas a lubricant during the subsequent deformation of the steel.
By proper selection of temperature and materials used in the molten bath .of the reducing agent and metal hydroxide and by controlling the speed of travel or time of immersion of the meta'l in the bath, the metal can, simultaneously with the descaling and lubricating operation, be heated to a temperature in the range of 250 F. to below the lower critical temperature for the steel for deformat-ion at elevated temperature to secure specific improvements in physical and mechanical properties, as well steel for deformation as by the formation of a porous layer on the surface of the steel, to lubricate the steel and to heat the steel to a desired elevated temperature, and then immediately advance the steel from the molten bath of the metal hydroxide to the die for deformation or reduction in cross-sectional area without removal of the molten metal hydroxide, without subsequent treatment of the surface, and while the steel is heated from the'molten bath of metal hydroxide and reducing agent to the desired temperature for working, as by drawing or extrusion. By the combination of steps described, it is possible uniformly to condition the surface of the steel for deformation and also uniformly to heat the steel substantially throughout its length 'to the desired temperature for drawing or deformation, whereby an improved product is secured.
The-following examples of the practice of this invention will be given by way of-illustration and not byway of'limitation.
Example I ,Hatrollcd steel-bar con ni gl owing i dd fian toiron.
, 0.1.17 perc nt carbon :75 percentma 0-9. P rcent phosphorus 0.04 percent sulphur 0.08 percent silicon 0.005 percent nitrogen are fed through a molten bath of sodium hydroxide containing from 1 to 5% by Weight sodium hydride. The bath is heated to a temperature within the range of 650 to 725 F. The baris advanced through the bath for immersion in the molten metal hydroxide for a time ranging up to about 30 minutes, depending upon the temperature of the steel introduced, the size of the bar, and the temperature to which it is desired to heat the steel for drawing at elevated temperature. From the molten bath the descaled, lubricated and heated steel bar is advanced directly through a draw die to effect reduction in cross-sectional area, such as to eifect a reduction of from 15 to 35%. A stream of molten sodium hydroxide may be directed onto the bar at the die to maintain the desired temperature level and further to aid in the lubrication thereof for deformation. After passing through the die, the surface of the steel can be washed with water and/or dilute acid to neutralize and to remove the excess metal hydroxide and to expose the surface finish which is of high luster and considerably better than that which is capable of being secured by present p qs s es- 0 Example 11 Hot rolled steel rods containing the following'matcrials-in addition to iron.
0.48 percent carbon 1.5 percent manganese 0.03, percent phosphorus 0.27 percent sulphur 0.3 percent silicon 0.005 percent nitrogen and having no previous cleaning treatments are passed through a molten bath of sodium orthophosphate con taining from 1 to 5% by weight of potassium hydride heated to a temperature within the range of 650 to 850 F. and wherein the rod is arranged as a cathode in an electrolytic cell in which the molten salt bath constitutes the electrolyte. The rod is descaled during immersion in the molten salt bath as the cathode and after the rod has been heated to a desired elevated temperature, it is then passed directly from the molten salt bath through a draw die where heavy reductions can be taken and where a superior finish is formed on the surface of the steel upon drawing. As in the previous example, the salt remaining on the surface of the steel after passage through the draw die can be removed by washing with water. preferably having a small amount of acid therein.
Example 111 Bars of hot rolled non-austenitic steel having a pearlitic and ferritic structure are advanced without any pre; vious cleaning step through a molten bath of sodium formate and potassium hydroxide present in equal amounts by weight containing from 1 to 10% by weight of areducing agent and heated to a temperature of about 000 F. The bars are arranged as a cathode for descal mg and allowed to remain in the bath for sufficient time to raise the temperature of the steel to about 750 F, The steel is passed directly from the molten bath to the extrusion die to effect reduction in cross-sectional area while the steel is at the described elevated temperature. After passing through the extrusion die, the steel is washed with aqueous medium to remove the salt and expose a superior finish.
Example IV ds of a s i -an em a; st el onta ni g the w in aterials addition to iron and other rhino rim.- pml gg v :08 P rc n ca 0.75 percent manganese -1. per en phos hor s 0.27 percent sulphur are advanced in continuous fashion to a drawing die to effect a reduction in cross-sectional area. Immediately prior to entrance into the die block, potassium hydroxide containing 2% by weight sodium hydride and heated to a molten state at a temperature of about 675 to 750 F. is poured over the surface of the steel to descale the steel and to lubricate the steel as the metal passes through the drawing die. After the metal emerges from the drawing die, it is washed with aqueous medium to remove the soluble salts and to expose a bright surface finish.
Example V A non-austenitic low allow steel having a pearlitic structure in a matrix of free ferrite and of the following composition .42 percent carbon .87 percent manganese .016 percent phosphorus .026 percent sulphur .29 percent silicon .87 percent chromium .20 percent molybdenum was processed by drawing through dies to effect a reduction in cross-sectional area, as by the reduction of a /8 inch steel bar to about inch. In advance of the drawing step, the steel is submerged in a bath of a molten potassium hydroxide having from 1 to 10% by weight of potassium hydride or other reducing agent and in which the bath is maintained at a temperature of about 800 F. The steel is submerged in the molten bath for a time sufficient to raise the steel to a temperature of 650 to 725 F. During immersion in the bath, the oxide scale which normally forms on the steel upon standing is removed and a porous surface is formed on the steel. The steel is advanced directly from the molten bath to the draw die to effect the desired reduction in cross-sectional area While the steel is at a temperature corresponding to that to which it has been raised in the molten bath, and with potassium hydroxide present in substantial amounts on the porous surface of the steel for use as a lubricant which enables the desired reduction to be effected during passage through the draw die at a reduced load. After passage through the die, the surface of the steel is rinsed with an aqueous medium preferably containing a small amount of acid to remove metal hydroxides remaining on the surface and to expose the surface of the steel which will be smooth and have a luster considerably brighter than that which is capable of being produced by processes heretofore employed.
It will be understood that other combinations of reducing agents and metal hydroxides or salts, with or without electrical current, may be used in accordance with the practice of this invention to effect descaling, lubrication, and to heat the steel to a desired elevated temperature for an improved drawing operation in a single step, that some of the reducing agent will be carried with the molten metal hydroxide retained on the porous surface of the steel as a lubricant, and that the compositions of the bath may be varied to provide the desired temperature conditions and other characteristics, and that other techniques may be used for reacting the surface of the steel 6 with the molten metal hydroxide prior to passage of the steel through the die for deformation.
It will be further understood that the described improvements can be made available in other metal finishing operations wherein the metal is worked, as in rolling or the like, to effect reduction in cross-sectional area, and that other changes may be made in the details of formulation and operation without departing from the spirit of the invention, especially as defined in the following claims.
1. A method for heating, descaling and lubricating steel in conjunction with a working operation to effect reduction in cross-sectional area at temperatures of 250 F. to the lower critical temperature for the steel comprising reacting the surface of the steel with a molten alkali metal hydroxide containing a reducing agent concurrently and in a single step to descale the steel to lubricate the steel and to heat the steel to the elevated temperature for the elevated temperature reduction step and then working the steel as a continuous operation following treatment with the molten alkali metal hydroxide and with the molten alkali metal hydroxide present as a lubricant on the surface thereof and while the steel is at an elevated temperature responsive to heating by the molten alkali metal hydroxide to effect a reduction in crosssectional area while the steel is at a temperature within the range of 250 F. to the lower critical temperature for the steel.
2. A method for heating, descaling and lubricating steel in conjunction with a reduction step wherein the steel is advanced through a die to take a reduction in cross-sectional area while the steel is at a temperature within the range of 250 F. to the lower critical temperature for the steel comprising reacting the surface of the steel with a molten alkali metal hydroxide containing a reducing agent simultaneously to descale the steel to lubricate the steel and to heat the steel to elevated temperature for the elevated temperature reduction step, and then advancing the steel through the die as a continuous operation with the reaction step and with molten alkali metal hydroxide present as a lubricant on the surface thereof and while the steel is at an elevated temperature responsive to heating by the molten alkali metal hydroxide to effect a reduction in cross'sectional area while the steel is at a temperature within the range of 250 F. to the lower critical temperature for the steel.
3. The method as claimed in claim 2 in which the reducing agent comprises a metal hydride present in an amount of 1-10 percent by weight of the treating composition.
References Cited in the file of this patent UNITED STATES PATENTS 1,399,044 Bellis Dec. 6, 1921 2,059,468 Lyon Nov. 3, 1936 2,074,224 Johnson Mar. 16, 1937 2,338,045 Leonard Dec. 28, 1943 2,370,959 Holden Mar. 6, 1945 2,377,876 Gilbert June 12, 1945 2,448,262 Gilbert Aug. 31, 1948 2,479,979 Spence et a1. Aug. 23, 1949