US3001897A

US3001897A - Steels and method of processing same

Info

Publication number: US3001897A
Application number: US617270A
Authority: US
Inventors: Elliot S Nachtman
Original assignee: Lasalle Steel Co
Current assignee: Lasalle Steel Co
Priority date: 1956-10-22
Filing date: 1956-10-22
Publication date: 1961-09-26
Anticipated expiration: 1978-09-26

Description

Ute Stes Pater 3 001 897 STEELS AND Mnrnoi) 6F PROCESSING SAMIE Elliot S. Nachtman, Park Forest, 111., assignor to La Salie Steel Company, Hammond, Ind., a corporation of Delaware No Drawing. Filed Oct. 22, 1956, Ser. No. 617,270 11 Claims. (Cl. 148-12) This invention relates to a new and novel cold finishing method for producing steels having improved physical and mechanical properties.

It is an object of this invention to produce and to provide a method for producting steels having improved physical and mechanical properties, and it is a related object to provide a method of processing steels in a cold finishing operation to improve the physical and mechanical properties of the steel.

More specifically, it is an object of this invention to provide a method applicable to steels of the nonaustenitic type or which strain harden and which harden by some mode of precipitation during working at elevated temperature to improve the mechanical and physical properties of the steel in the cold finishing of such steels, and it is a related object to produce steels having new and improved physical and mechanical properties.

This application is an improvement of the copending applications Serial No. 518,411, Serial No. l8,412,'Serial No. 518,413 and Serial No. 518,414, filed June 27, 1955, now Patents No. 2,767,837, No. 2,767,835, No. 2,767,836, and No. 2,767,838, respectively.

In the aforementioned copending applications, description is made of a new and improved method for use in the cold finishing of steels wherein the steel in the form of a bar, red, tube or wire is worked, as by means of extrusion or drawing, to eifect reduction in cross-sectional area by advancing the steel througha die while at a temperature in excess of 200 F. but below the lower critical temperature for the steel composition. Depending upon the temperature of the steel being worked, or upon its chemistry or upon the percent reduction taken, various properties, both physical and mechanical, can be beneficially infiuenced to produce a wide range of values in the steel.

In accordance with the teachings of the aforementioned copending applications, improvements in tensile strength, yield strength, machineability, hardness, ductility and other physical and mechanical properties of the steel are secured, although some of these properties are maximized in certain temperature ranges as compared to others. For example, as defined in applications Serial No. 518,411 and Serial No. 518,413, improvements in machineability and in mechanical properties such as tensile strength, yield strength, proportional limits, impact strength and hardness, and physical properties such as surface roughness, are secured by advancing the steel through a die to eflect reduction in cross-sectional area while the steel is in a temperature range between 450 and 850 F. Within this range, machineability, tensile strength, proportional limits and yield strengths are maximized when the steel is drawn while at a temperature within the range of 450- 600 F. Improvements in plastic properties, as represented by elongation and impact strength, are more noticeable when the steel is advanced through the die While at a temperature within the range of 600-850 F.

In addition to the improvement in mechanical and physical properties of steel, the processes described in the aforementioned copending applications can be employed Patented Sept. 26, 1961 to control the residual stresses available in the steel to tailor the steel for certain applications. For example, in the aforementioned copending application Serial No. 518,- 412, the development of residual stresses in steel can be minimized and the type or magnitude of the residual stresses in steel can be controlled to reduce warpage values and to reduce the development of cracks in products fabricated of such steels by advancing the steel through a die to effect reduction in cross-sectional area while the steel is at a temperature in excess of 650 F. and preferably at a temperature within the range of 850 F. to the lower critical temperature for the steel composition.

The marked reduction in warpage values which occurs when the steel is advanced through a die to eiiect re duction in cross-sectional area at a temperature above 650 F. and preferably above 850 F. permits the production of steel products having improved physical and mechanical properties with the residual stress values as low or lower than values which have heretofore resulted from processing subsequent to drawing, as by heat treatment. High compression stresses, instead of tensile stresses, can be formed in the outer portions of the steel if the steel is advanced through the die to elfect reduction in cross-sectional area at a temperature in excess of 800- 850 F. followed almost immediately by rapid cooling, as by quenching, for example, in water or oil. Such high compressive stresses in the surface portions of the steel are extremely advantageous in'increasing the torsional fatigue value of the steel at any particular strength value.

Thus, it has become possible, in accordance with the teachings of the aforementioned copending applications, to produce steels having properties tailor-made for particular uses by the proper selection of the steel from the standpoint of chemistry, by proper selection of the amount of reduction, and by proper selection of the temperature of the steel advanced through the die to effect reduction in cross-sectional area.

It has now been found, in accordance with the practice of this invention, that, by a new combination of steps which makes use of the cold reduction step prior to the reduction step at elevated temperature, as described in the aforementioned copending applications, still further or other improvements can be secured. In some instances greater uniformity of properties from heat to heat can be produced. A wider range of properties can be made available with a given chemistry and some of the physical and mechanical properties of the steel can be still further increased. The improvement which makes use of a cold reduction step in advance of the passage of the steel through a die at elevated temperature to effect a reduction in cross-sectional area is somewhat independent of the amount of reduction that is taken in the earlier cold reduction step, but the degree of improvement, especially in the tensile and yield strength properties of the steel, is somewhat proportional to the amount of reduction that is taken in the cold reduction step. For example, the tensile strength properties and the yield strength properties of the steel, as well as the proportional limits, are maximized by advancing the steel through a die to take a heavy reduction as compared to a light reduction at room temperature prior'to advancement of the steel through a. die to take a subsequent reduction while the steel is' at elevated temperature.

The improvement in physical and mechanical properties securedby the combination of steps described is available when, in the subsequent elevated reduction step, the

steel is advanced through the die to eifect reduction in cross-sectional area while at a temperature within the range of 200 F. up to the lower critical temperature for the steel composition, as in the aforementioned copending applications, but the improvements are maximized, especially in tensile strength and yield strength, when the temperature at which the steel is advanced through the die in the subsequent elevated reduction step is in the range of 450-850 F. and preferably within the range of 500-750 F. -While. subsequent processing, as by slow cooling in air or by rapid cooling as by means of a water quench or oil quench has some effect on the stresses developed in the processed steel and on some of the mechanical and physical properties, such subsequent cooling does not materially affect the improvements in the physical and mechanical properties developed by the combination of cold reduction with reduction at elevated temperature.

Steels capable of use in the practice of this invention are characterized by the ability to strain harden and harden by some mode of precipitation or other rearrangement when worked at elevated temperature within the ranges described, as by drawing or extrusion or rolling to effect reduction in cross-sectional area. Thus steels which may be employed in the practice of this invention can be distinguished over other steels, such as the hard-to-draw high-speed steels or carbon tool steels of the types described in the Kronwall Patent No. 2,400,866.

Advancement through a die to effect reduction in crosssectional area is intended to include the advancement of the steel through a draw die in a drawing operation to effect reduction in cross-sectional area. It includes the advancement of the steel through an extrusion or roller die to effect reduction in cross-sectional area. While not equivalent from the process standpoint, many of the properties described have been found capable of being developed when the described steels are processed by other processes for reduction in cross-sectional area, such as in a rolling process.

As used herein, the term percent reduction is meant to relate to the true reduction as represented by the formula D D D where D is the original hot roll diameter of the steel, D is the final diameter of the steel.

Most of the terms herein employed are well known to the art. The following will define some of the lesser known terms or terms upon which a special meaning is placed, and the following will also define some of the abbreviations which will hereinafter be employed in the more specific illustration of this invention.

The term proportional limi corresponds to the point in the stress-strain curve where the greatest stress that the material is capable of sustaining without deviation from the law of proportionality of stress to strain occurs (Hookes law). This point is of particular importance in steel and, in practically every instance, is measurably increased to heretofore unobtainable high values when the steels of the non-austenitic type are produced, as by drawing or extrusion at elevated temperatures within the range defined in the aforementioned copending applications.

Residual stress is related to the warpage values secured in the finished steel. The warpage value is an indication of the concentration and character of the longitudinal stresses present in the steel. The residual stress is obtained by means of a warpage test whereby the length of the test piece is determined as being five times the diameter plus 2 inches. The test pieces are slotted through a diameter for a distance five times the diameter. The length of the slot is recorded and the maximum diameter perpendicular to the slot is also recorded. The differences between the diameter before slotting and after slotting comprise the flare caused by the presence of residual stresses. The flare is considered positive, indicating tensile stresses in the outer area of the material, if the bar expands on slotting. The flare is considered negative, indicating compressive stresses in the outer area of the material, if the ends move towards the cut which is made through the diameter. The warpage values determined for evaluation are calculated with the following equation:

(Ls), X100 Warpage factor:

where The pull load is determined by recording the average hydraulic pressure reading of the chain drag at idling speed and while drawing the bar stock at the rate of 25 feet per minute on a 30,000 pound Waterbury-Farrell hydraulic draw bench. The corrected hydraulic pressure reading of the drawing load minus chain drag was converted to pounds pull by multiplying by a factor of 22.9. The factor 22.9 was obtained from the slope of a calibration curve of Waterbury-Farrell hydraulic pressure versus Tinius-Olson tensile testing machine pound pull.

Where Izod impact is mentioned, the values in foot pounds was obtained by averaging the impact results from three equidistant 45 degree notches (0.130 deep) at F. on a 0.45" diameter round it 4 /2 long specimen.

As used herein, the term hardness corresponds to the Diamond Pyramid Number (DPN) or Vickers Hardness measured on a Gries Reflex hardness testing machine employing 136 Pyramid Diamond at a 50 kg. load.

The abbreviations used in the following tables are as follows:

ETD (A)=elevated temperature drawing with air cooling after drawing ETD(W) or (0) =elevated temperature drawing with a water quench or an oil quench after the final drawing operation L =light reduction at room temperature H =a moderate to heavy reduction at room temperature The concepts of this invention will hereinafter be illustrated with four steels taken as representative of the class of steels which may be employed. These representative steels will hereinafter be referred to as C-1018, C-1 144, C-1080 and 4140. The following is a ladle analyses of these steels in which the major ingredients other than iron are set forth:

Chemistry 5 5 Grade 0 Mn 1? S 81 Or Mo G1018. 18 .88 015 037 C-1l44 45 1. 51 018 28 .22 O1080 86 79 010 031 20 0 4140 43 .88 018 020 26 .86 18 The procedure for processing the steels in the development of the data set forth for the support of the invention is as follows:

(A) HOT ROLLED PREPARATION The data was developed on hot rolled bar stock of the following dimension:

The hot rolled bar stock as received was descaled by pickling in sulphuric acid and limed to prevent rusting.

5 HEATING PROCEDURE FOR THE ELEVATED DRAWING STEPS All of the bars, except those cold drawn at room temperature, were heated to the desired temperatures in a gas-fired furnace and the bars were lubricated prior to drawing.

(C) DRAFTING PRACTICE The cold reduction steps were carried out by advancing the steel bar through a draw die to effect the desired reduction in cross-sectional area while the steel was at room temperature. Reduction at elevated temperature was carried out by advancing the steel bars through the draw die to effect the desired reduction in cross-sectional area While the steel was at a desired elevated temperature.

The data in the following tables sets forth the physical and mechanical properties of the hot rolled steels; the same steels drawn at room temperature; the same steels drawn at elevated temperature (ETD) as described and claimed in the aforementioned copending applications; the same steels in which a light reduction was taken at room temperature prior to reduction at elevated temperature (L +ETD); and the same steels in which a heavy reduction was taken at room temperature prior to reduction at elevated temperature (H -PET D). The last two represent the improved practice of this invention. In the development of the data, the same steels of the same composition were employed in the various tests. The amount of reduction was held as nearly the same as possible and the data set forth was from a comparable temperature range, as indicated in each of the tables.

The data set forth in the following tables is not intended to provide a comparison for distinguishing the instant invention over the invention described and claimed in the aforementioned copending applications, although some of the data will indicate the development of improvements in some properties over the properties developed in the same steel by reduction at elevated temperature. It should be understood that the combination of steps which combines a cold reduction step in advance of a reduction at elevated temperature permits the development of certain properties in steel incapable of being secured by conventional methods of cold finishing steel or, in some instances, even by reduction at elevated temperature.

TABLE I -1018 STEEL Loo 8% Hon Hot roll CD ETD +ETD 31%+ 26% 18% ETD Tensile strength, p.s.i. 68, 375 98, 500 109,750 120, 750 128,000 Yield strength, psi. 46, 875 97, 500 107, 500 116,500 122,000 Elongation, percent. 36.0 14. 12. 13.0 12. 5 s 13, 168 11, 450 9, 733 7, 443 Izod impact, ft lbs 87.0 9. 3.7 2.7 7.0 Hardness, DPN.-. 151 220 249 271 266 Warpage factor 021 331 264 472 623 TABLE II 0-1018 STEEL Lap 8% Hon Hot roll OD ETD +ETD 31%+ 26% 18% ETD 98, 000 109,250 112, 500 128,750 97, 500 107, 500 108, 750 122, 500 12. 5 9. 5 13.0 11.5 13, 168 11, 450 9, 733 7, 443 12.0 3.0 3. 7 4.0 216 249 245 266 Warpage factor 319 288 399 566 CD=0old drawn at room temperature. ETD=Drawn at 650700 F.

Table I=Results air cooled.

Table II=Results water or oil quench.

TABLE III 0-1144 STEEL Loo Hen Hot roll OD ETD 4.5 21.5%

22% 22% +ETD +ETD 17.5% 15.5%

Tensilestrength, p.s.i-.. 108,000 132,750 150, 250 152,000 172, 500 Yield strength, p.s.i 70, 500 118,750 145, 000 146, 000 172,500 Elongation, percent 23.0 13.0 9. 5 8. .6. 0 11, 450 9, 8, 588 9, 733 18. 0 4. 0 4. 4. 7 266 318 301 356 Warpage factor 732 661 803 008 TABLE IV Lon Hon Hot roll OD ETD 4.5% 21.5%

22% 22% +ETD +ETD Tensile strength, p.s 1 108,000 133,000 152, 250 155, 000 172, 500 Yield strength, p.s. 70, 500 127, 500 147, 500 150,000 172, 500 Elongation, percent 23.0 9. 8. 7. 6.0 s 11,450 9,160 8, 588 9, 733 Izod impact ft lb 32. 7 22. 3 3. 4. 0 4. 0 Hardness, DPN- 220 258 324 307 336 Warpage factor- 004 789 639 782 031 OD=Cold Drawn room temperature. ETD=Drawn at 600-650" F. Table III= Results air cooled. Table IV=Results water or 011 quench.

TABLE V C1080 Steel Leo Hon Hot CD ETD 5.5% 22% Roll 22% 22% +ETD +ETD Tensile strength, p.s.i. 144, 500 168, 250 180, 000 170, 250 183, 000 Yield strength, p.s i 76, 000 136. 000 154, 500 140, 000 140, 000 Elongation, percen 12. 2. 3. 9. 3. 6 Pull, lbs -1 16, 603 11, 450 12, 595 7, 443 Izod impact, It. 4. 7 3. 3 4. 4. 3 4. 7 Hardness, DPN 296 324 364 343 356 Warpage factor..- 023 0 063 087 TABLE VI 0-1080 Steel oo Hon Hot OD ETD 5.5% 177 r011 22% 22% +ETD +1216) Tensile strength, p.s.i--. 144, 500 167, 000 178, 000 170, 500 168,500 Yield strength, p.s.l 76, 000 129,000 151, 500 139, 000 135, 500 Elongation, percent 12. 5 5. 6. 4 5. 0 3. 6 lbs 16, 603 11, 450 12, 595 7, 443 Izod impact, ft. lbs 4. 7 3.0 4.0 3. 3 4. 7 Hardness, DPN- 296 330 304 7 350 350 Warpage factor; 025 007 007 048 087 CD=Cold drawn at room temperature. ETD=Drawn at 800 F.=l=50 F. Table V=Results air cooled. Table VI-- Results water or oil quench.

TABLE VH 4140 Steel oo Hon Hot OD ETD 5% 20% Roll 20% 20% +ETD +ETD Tensile strength, p.s.i.-. 140, 000 165,000 189, 500 194, 250 211, 750 Yield strength, p.s.l- 105, 750 182,000 189,000 188, 750 206, 000 Elongation, percent--- 15. 9.0 9. 5 9.0 7. 0 Pull, lbs 18, 320 14, 885 24, 045 14, 026 Izod impact, ft. lbs 9.0 4. 3 5. 3 2. 0 4. 0 Hardness, DPN... 307 336 394 378 402 Warpage factor 004 083 057 971 +1. 172

CD=Co1d drawn at room temperature. ETD=Drawn at 600 F.:l=25 F.

Table VII= Results air cooled.

Table VIII=Results water or oil quench.

TABLE XII C-1144 steel cold drawn to take a 21.6 percent reduction and drawn at elevated temperature to take a 15.6 percent reduction followed by air coo g Tensile Yield Elonge- Warpage Tcmp. of draw, F. strength, strength, tlcn, factor p.s.i. p.s.l. Percent TABLE XIII C-1080 steel cold drawn to take a 5.5 percent reduction and drawn at elevatgd temperature to take a 17.4 percent reduction followed by oil queue The following tables present data developed to show Tensile Yield Elongm warpage the wide range of propertles which are secured by draw- Temp ofdmw, o strength, strength, r n, factor ing at an elevated temperature within the range described, Percent as compared to room temperature, but after the steels 1 144, 500 76,000 12. 5 025 have first been given either a light or a heavy cold re 140,500 97,500 M +392 duction. 100, 000 120, 000 4. a 055 883 129888 ti 1 182, 19 TABLE IX 100,000 183,000 2.9 -.0s7 19288 132283 2'8 "823 (3-1018 steel cold drawn at room temperature to take an 8.2 percent reduction and drawn at elevated temperature to take an 18.0 percent 153'500 no'ooo reduction followed by water quenching TABLE XIV Pull, Tensile Yield Warpage (3-1080 steel cold drawn to take a 22 percent reduction and drawn at Temp. of draw, F. lbs. etc. strength, strength, factor elevated temperature to take a 17 percent reduction followed by air p.s.i. p.s.i. cooling 68,375 46,875 +.021 Tensile Yield Elonga- Warpage 95, 000 92, 500 454 Temp. of draw, F. strength, strength, tlon, factor 95, 750 95. 000 p.s.i. p.s.i. Percent 124, 500 120, 000 116,500 113,000 112, 500 108, 750 169, 000 133, 000 1. 4 341 95, 000 82, 500 178,000 144, 500 2. 1 350 750 79, 000 183, 000 140, 000 3. 6 087 157, 000 126, 000 10. 0 044 TABLE X TABLE XV C4018 steel cold drawn at room temperature to take a 31.2 percent reduction and drawn at elevated temperature to take a 17.7 percent reduction followed by water quench Pull, Tensile Yield Werpage Temp. of draw, F. lbs. etc. strength, strength, factor p.s.i. p.s.i.

TABLE XI C-1l44 steel cold drawn to take a 4.6 percent reduction and drawn at elevuelted temperature to take a. 17.7 percent reduction followed by air coo g 4140 steel cold drawn to take a 4.8 percent reduction and drawn at elevated temperature to take a 16.1 percent reduction followed by air coo mg Tensile Yield Elongo- Warpage Temp. of draw, F. strength, strength, tion, factor p.s.i. p.s.i. Percent TABLE XVI 4140 steel cold drawn to take a 20.3 percent reduction and drawn at elevated temperature to take a 17.7 percent reduction followed by air cooling Tensile Yield Elongu- Warpage Temp. of drew, F. strength, strength, tiou, factor p.s.i. p.s.i. Percent As illustrated by the foregoing data, steels having different mechanical and physical properties can be produced by the combination of steps which makes use of a cold reduction step in advance of taking a reduction at elevated temperature within the range of 200 F. to the lower critical temperature for the steel composition. From the standpoint of the strength properties of the steels, it will be apparent that for most of the steels, the tensile strengths and yield strengths are maximized when the steels, which have first been subjected to a cold reduction, are subsequen y reduced when heated to a temperature within the range of about 400-900 F.

From the foregoing, it will be apparent that I have provided a process used in combination with the elevated temperature systems described and claimed in the previously mentioned copending applications to improve the physical and mechanical properties of steel. While I have discussed the improvements as found in the increase in tensile and yield strength, others of the properties of the steels are also enhanced by the combination of the steps which includes a cold reduction step in advance of reduction at elevated temperature. These other properties include surface finish, impact strength, machineability, pull load and the like physical and mechanical properties.

As used herein and in the claims, the term bar is intended to include and includes rounds, flats, tubing, wire, rod and the like steels subjected to cold finishing operations. The term cold as used in combination with reduction is meant to relate to ambient temperatures but will include temperatures up to about 200 F.

It will be understood that changes may be made in the details of the chemistry of the steel, the amounts of reductions, and the means by which the reductions are carried out, without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. The metallurgical process for the improvement of mechanical and physical properties of steel of the nonaustenitic type having a pearlitic structure in a matrix of free ferrite, consisting of the following combination of steps in the order specified of extruding the steel through an extrusion die to elfect reduction in cross-sectional area in a cold reduction step, and extruding the cold reduced steel through an extrusion die to eflect a further reduction in cross-sectional area while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition.

2. The metallurgical process for the improvement of mechanical and physical properties of steel of the nonaustenitic type having a pearlitic structure in a matrix of free ferrite, consisting of the following combination of steps in the order specified of advancing the steel through a die to effect reduction in cross-sectional area in a cold reduction step, and, without any intermediate heat treatment, extruding the cold reduced steel through an extrusion die to effect a further reduction in cross-sectional area while the steel is at a temperature within the range of 400900 F.

3. The metallurgical process for the improvement of mechanical and physical properties of steel which steel strain hardens and which hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature of the steel composition, consisting of the following combination of steps in the order specified of advancing the steel through a die to effect reduction in cross-sectional area in a cold reduction step, and, without any intermediate heat treatment, advancing the cold reduced steel through a die to effect a further reduction in cross-sectional area while the steel is heated to a temperature within the range of 200 F. to the lower critical temperature for the steel composition.

4. The method as claimed in claim 3 which includes the additional step of air cooling the steel after advancement through the die at elevated temperature.

5. The method as claimed in claim 3 which includes the additional step of quenching the steel in a bath formed of a liquid selected from the group consisting of oil and water after advancement through the die at elevated temperature.

6. A steel product produced by the method of claim 3.

7. The metallurgical process for the improvement of mechanical and physical properties of steel which strain hardens and which hardens by some mode of precipitation when worked at a temperature between 400900= F., consisting of the following combination of steps in the order specified of advancing the steel through a die to effect a cold reduction in cross-sectional area, and, without any intermediate heat treatment, advancing the cold reduced steel through a die to effect a further reduction in cross-sectional area while the steel is heated to a temperature within the range of 400-900 F.

8. The metallurgical process for the improvement of mechanical and physical properties of steel which steel strain hardens and which hardens by some mode of precipitation when worked at a temperature between 400- 900 F. consisting of the following combination of steps in the order specified of drawing the steel through a draw die in a cold reduction step to eifect reduction in crosssectional area, and, without any intermediate heat treatment, drawing the cold reduced steel through a draw die to effect a further reduction in cross-sectional area while the steel is heated to a temperature within the range of 400900 F.

9. The metallurgical process for the improvement of mechanical and physical properties of steel which strain hardens and which hardens by some mode of precipitation when worked at a temperature between 200 'F. and the lower critical temperature for the steel composition, consisting of the following combination of steps in the order specified of advancing the steel through a die to effect reduction in cross-sectional area in a cold reduction step, and, without any intermediate heat treatment, advancing the cold reduced steel through a draw die to effect reduction in cross-sectional area in a drawing operation while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition.

10. The metallurgical process for the improvement of,

mechanical and physical properties of steel which strain hardens and which hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition, consisting of the following combination of steps in the order specified of advancing the steel through a die to effect reduction in cross-sectional area in a cold reduction step, and, without any intermediate heat treatment, advancing the cold reduced steel through an extrusion die to effect reduction in cross-sectional area in an extrusion operation while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition.

11. The metallurgical process for the improvement of mechanical and physical properties of steel which strain hardens and which hardens by some mode of precipitation when worked at a temperature between 200 F. and they lower critical temperature of the steel composition, consisting of the following combination of steps in the order specified of working the steel to effect a reduction in crosssectional area in a cold reduction step, and rolling the cold reduced steel to effect a further reduction in cross-sectional area in a rolling operation while the steel is at a temperature within the range of 200 F. to the lower critical temperature for the steel composition.

References Cited in the file of this patent

Claims

3. THE METALLURGICAL PROCESS FOR THE IMPROVEMENT OF MECHANICAL AND PHYSICAL PROPERTIES OF STEEL WHICH STEEL STRAIN HARDENS AND WHICH HARDENS BY SOME MODE OF PRECIPITATION WHEN WORKED AT A TEMPERATURE BETWEEN 200*F. AND THE LOWER CRITICAL TEMPERATURE OF STELL COMPOSITION, CONSISTING OF THE FOLLOWING COMBINATION OF STEPS IN THE ORDER SPECIFIED OF ADVANCING THE STEEL THROUGH A DIE TO EFFECT REDUCTION IN CROSS-SECTIONAL AREA IN A COLD REDUCTION STEP, AND, WITHOUT ANY INTERMEDIATE HEAT TREATMENT, ADVANCING THE COLD REDUCED STEEL THROUGH A DIE TO EFFECT A FURTHER REDUCTION IN CROSS-SECTIONAL AREA WHILE THE STEEL IS HEATED TO A TEMPERATURE WITHIN THE RANGE OF 200*F. TO THE LOWER CRITICAL TEMPERATURE FOR THE STEEL COMPOSITION.