US3391448A - Process for working metals and alloys and a composite billet for use therein - Google Patents

Description

PROCESS FOR WORKING METALS AND ALLOYS AND July 9, 1968 Bur. LANPHIER 3,391,

A COMPOSITE BILLET FOR USE THEREIN Filed Oct. 29, 1963 United States Patent 3,391,448 PROCESS FOR WORKING METALS AND ALLOYS AND A COMPOSITE BILLET FOR USE THEREIN Basil T. Lanpliier, Reading, Pa., assignor to The Carpenter Steel Company, Reading, Pa., a corporation of New Jersey Filed Oct. 29, 1963, Ser. No. 319,760 8 Claims. (Cl. 29-480) This invention relates to a process for working metals and alloys and more particularly to a process which is especially well suited for hot rolling or drawing alloys.

In the working of metals and alloys to produce bars, rods or similar shaped sections having a small cross sectional area, it is common in the art first to heat a billet or ingot of larger sectional area to a temperature at which the billet becomes plastic and then to pass the billet while hot through the rolls of a rolling mill thereby reducing the cross sectional area. The hot rolling process may be practiced by making a single pass through each of several mills, by making several passes through the same mill or by a combination of these methods. In any event the roll pass, i.e., the vertical distance between the working faces of the rolls, is usually decreased for each consecutive pass so that a reduction in cross sectional area is accomplished in each pass. If a relatively high number of passes is required to attain the desired final cross section or if time is lost between consecutive passes, it may be necessary to reheat the billet before further rolling can be done. Where a high degree of accuracy is required in the final cross section produced or where there is a requirement for a high quality surface, the hot rolled form may be cooled to room temperature, cleaned and then one or more passes taken in a cold mill. In either hot or cold rolling, it is obviously desirable for reasons of economy and productivity to perform the required reduction in as few passes as possible; also, unless required for other purposes, it is desirable to limit intermediate reheatings or annealings as much as possible. In the case of age hardenable alloys, it may be necessary to effect a certain minimum reduction between reheatings in order to provide the required microstructure of the finished product.

An object of the present invention is to obtain greater reductions per pass in rolling without the occurrence of rolling defects such as split ends, cold tears and the like than has been heretofore possible when rolling alloys having a high hot hardness.

Another object of the present invention is to enable rolling to be continued beyond the point where, in the prior practice, reheating would be necessary.

A further object of the invention is to enable hard to roll alloys to be rolled with heavy drafts while eliminating the risk of roll damage inherent in the prior practice.

A still further object of the present invention is to improve the yield of the rolled product when rolling hard to roll alloys by eliminating scrap at each end of the final rolled form.

A still further object of the present invention is to increase the productivity of mills when rolling hard to roll alloys by decreasing the time lag between each rolling pass.

Yet another object of the present invention is to produce rolled shapes from hard to roll alloys, having improved surface quality and microstructural uniformity over the products of the prior practice.

The practice of the process of the present invention comprises affixing to one or both ends of a prepared billet of a hard to roll metal or alloy a leader strip of relatively easily rollable material. Preferably, the easily 3,391,448 Patented July 9, 1968 ice rollable material, for example, ordinary stainless steel, is welded to each end of the billet of hard to roll alloy. After welding, in addition to normal surface preparation, the welded joint is ground to eliminate undesired irregularities resulting from the weld.

Further objects and advantages of this invention will be apparent from the following description and the accompanying drawings, in which:

FIGURES 1, 2 and 3 are diagrammatic elevational views showing a billet entering the working rolls of a rolling mill in accordance with the present invention.

In order to roll a billet or bar successfully, it is necessary to ensure that the billet enters the roll pass without undue difficulty. It will be appreciated that there are a number of factors which affect the ease with which a billet can enter the roll pass. These factors include (a) the amount of reduction that is to be taken in the pass, i.e., the draft, (b) the surface condition of the rolls, (0) the size of the rolls and (d) the nature and condition of the material to be rolled. It has been found that the problem of entering the material into the roll pass becomes more difiicult with an increase in the draft, with smoother rolls, with smaller rolls or with harder material. The problem of entering the billet into the mill is particularly difficult when it is desired to roll alloys having a high not hardness since the force required to cause plastic deformation of such alloys is high.

While in some cases it is possible to overcome the problem of entering the roll pass by decreasing the draft, it is apparent that this solution will require additional passes through the mill in order to attain the desired final cross section. Decreasing the draft not only increases the cost of production by lessening the productivity of the mill but also not enough heat may be generated in the billet during an individual pass to offset the loss of heat due to radiation and conduction. Thus, decreasing the draft may result in excessive losses in the temperature of the billet so that costly reheating is required. In addition, inadequate working between reheating will adversely affect the desired microstructure of the rolled product.

With respect to the roll surface, it is known that rough rolls will bite the entering material more effectively than smooth rolls but where it is desired to obtain a high quality surface on the rolled material, rough rolls may not be tolerated so that this method of solving the problem of roll pass entry is not entirely satisfactory.

Another approach to the problem involve increasing the size of the rolls but this solution also has its drawbacks since an increase in the roll size increases the rolling forces involved. In the rolling of hard metals and alloys, where the force required to deform the material is already high, it will be appreciated that an attempt to simplify entry which increases the rolling force is unsatisfactory.

According to the present invention, a leader strip of a relatively easily rollable material such as ordinary stainless steel is welded to one or both ends of a billet or bar of hard to roll alloy. Such a composite billet will enter the pass of a rolling mill in the same manner as will a billet of ordinary stainless steel with the initial contact between the billet and the rolls being substantially line contact. When the tip of the leader strip has been reduced by entering the roll pass, the contact between each of the working rolls and the leader strip is an extended surface. The effect of the increase in area of contact between the working rolls and the leader strip is to increase the frictional forces transmitted between the working rolls and the billet. As will be pointed out hereinafter, these frictional forces determine whether a mill, under given rolling condition, will bite the billet and also whether rolling can be continued.

Referring now to the drawings, workpiece comprises a main or central section 11 of an alloy which is extremely difficult to hot roll to which leaders 12 of easily hotrollable stock have been butt welded as indicated at 13. One alloy which is well known in the industry as being extremely difiicult to hot roll is Waspaloy, AISI No. 685 which has high hot hardness. With the main section 11 of Waspaloy, leaders 12 are formed of stainless steel to provide, in accordance with the present invention, troublefree hot rolling.

In FIGURE 1 are shown diagrammatically the forces involved in entering bar 10 into the roll pass. The billet or bar 10 enters the roll pass from the left and contacts the upper working roll 14 along a line indicated at point A. It is to be understood that the bar 10 simultaneously contacts the lower working roll 15 along a line indicated at point B. With the working rolls 14 and 15 having the same size, as is usually the case when the workpiece is rolled in a 2-high, 4-high, cluster or Sendzimir mill, the symmetry of the system results in similar forces at points A and B. In this analysis, consideration will be given only to the forces acting at point A, it being recognized that the forces at point B will not change the conclusions with respect to the problem of entry into the roll pass.

Since the bar 10 and the upper working roll 14 contact at point A, the forces between the two bodies act along the common normal at this point. This common normal extends along the radius of the upper working roll 14 at the point A and the force, which is a radial force, may be designated by the vector 16. The radial force 16 may be considered as the resultant of a force 17 which tends to push the bar 10 away from the roll pass and a compressive force 18. At point A, however, there is also a frictional force 19 acting along the common tangent between the bar 10 and the working roll 14 which may be considered as the resultant of a force 20 which tends to pull the bar 10 into the roll pass and a compressive force 21. The primary forces 19 and 16 are related inasmuch as the frictional force 19 is equal to the product of the radial force 16 and the coefficient of friction between the bar 10 and the roll 14. Manifestly, the bar cannot be brought into the roll pass unless the force 20 tending to draw the bar into the roll pass exceeds the force 17 which tends to prevent the entry of the bar into the pass.

It will be appreciated that as the point of contact A approaches the vertical line passing through the centers of the working rolls 14 and 15, the force 17 which tends to repel the bar 10 is reduced while the force 20 which tends to draw the bar into the roll pass is increased. This is the reason why, if the rolls will not bite the bar under a given set of rolling conditions, a reduction the draft to be taken may sometimes solve the problem.

It is also evident that even if the rolling conditions are such that entry of the bar into the roll pass can occur, it is essential that some horizontal force be applied to the bar 10 so that the radial and frictional forces can be developed.

Referring to FIGURE 2, it can be seen that the effect of the application of a horizontal force 22 to the bar 10 is to cause a deformation of the bar 10 so that it contacts the upper working roll 14 along an arc CD instead of the single point A shown in FIGURE 1. The magnitude of the arc CD depends, in part, on the magnitude of the horizontal force 22 applied to the bar. In spite of the fact that, at the point C, the frictional forces may be insufiicient to result in biting the bar 10, the frictional forces at the point D are such that biting of the bar 10 does occur. With the leader 12 formed of stainless steel, such as AISI type 304, the magnitude of the force 22 required to ensure deformation and biting as the leader enters the roll pass is relatively small and entry is easily accomplished. On the other hand. when it is contemplated to enter a workpiece having a high hot hardness, such as would be the case in the present instance, if the leader 12 where omitted, the magnitude of the force 22 reaches an objectionably high value before entry can be accomplished with the result that excessive roll damage and wear of the mill occurs. It may also be noted that while the amount of the local deformation varies with the applied horizontal force, a given horizontal force will produce less deformation with harder alloys than with softer alloys and less deformation with colder material than with hotter material.

As shown in FIGURE 2, entry of the workpiece 10 occurs in the usual way and without difficulty. Now, as the bar 10 advances between the working rolls 14 and 15, the surface area of the bar in engagement with the rolls becomes greater. As shown diagrammatically in FIGURE 3, the engagement of a given point on the surface of the working roll 14 with the upper surface of the bar 10 extends from an initial point of contact E to a final point of contact F. The area of contact between working roll 14 and billet 10 is an area bounded at its ends by arcs EF and having a lateral dimension equal to that of the billet 10. As was pointed out hereinabove in connection With FIGURE 1, the force 17 which tends to repel the billet 10 is reduced and the force 20 which tends to draw the billet into the roll pass is increased as the point of contact A approaches the vertical line passing through the centers of the working roll 14 and 15. Thus, as the main section 11 of hard to roll material enters the pass, a much greater force 20 tending to draw the bar into the roll pass acts on the billet because the point F is substantially on the vertical center line of the working rolls 14 and 15. The force 20 is sufficiently greater than the force 17 to ensure smooth entry of the main section 11, in spite of the fact that it may normally be extremely difficult or impossible to roll.

As an example of the practice of the present invention, the hot rolling of 7 inch round coil stock from 2% inch square Waspaloy billets about 6 -to 7 feet long weighing about to pounds will now be described in detail. The Waspaloy billets each contained by analysis in percent by weight: carbon 0.091%, manganese 0.05%, silicon 0.11%, phosphorus 0.002%, sulfur 0.004%, chromium 19.45%, molybdenum 4.42%, cobalt 13.58%, titanium 3.06%, aluminum 1.28%, zirconium 0.06%, boron 0.0049%, iron 1.30%, copper 0.03%, and nickel 56.19% forming the balance. This will be recognized as falling within the acceptable commercial range for Waspaloy (AISI No. 685) which contains in percent by weight: carbon 0.04 to 0.10%, manganese 0.10% maximum, silicon 0.15% maximum, phosphorus 0.015% maximum, sulfur 0.015% maximum, chromium 18 to 21%, molybdenum 3.50 to 5.00%, cobalt 12.00 to 15.00%, titanium 2.75 to 3.25%, aluminum 1.20 to 1.60%, zirconium 0.02 to 0.08%, boron 0.003 to 0.010%, copper 0.10% maximum, iron 2.0% maximum, nickel being the remainder. As published in the Metals Hand-book, volume 1, 8th edition, page 467, Waspaloy has a nominal composition of 0.1% carbon. 19% chromium, 14% cobalt, 4% molybdenum, 3% titanium, 1.3% aluminum, 1% iron, traces of boron and zirconium, and with nickel forming the remainder.

The billets of Waspaloy, after being solution treated for four hours at 1950 F. and water quenched, were then trim cut on each end so as to produce square ends. Leaders 12 formed of AISI No. 304 stainless steel each 8 inches long and 2% inches square with square ends were then welded to each of the opposite ends of the Waspaloy billets. In the present instance, the stainless steel leaders 12 were flash butt welded by an electrical resistance method to the Waspaloy billets. While best results and a sound weld over the entire cross section of the joints were achieved with the resistance welding method, other methods of welding may be used, such as fillet type arc-welding, filler-rod arc-welding or hand arc-welding.

After the leaders 12 were attached to the main Waspaloy sections 11, the composite billets were ground to provide the desired smooth surface at the welds and then heated in a furnace operated at a temperature of 2180 F. At the beginning of the first pass, the temperature of the billets, measured by optical means, ranged from about 2020 to 2040 F. Because of the presence of the leader strips 12 on each end of the billets, large drafts could be taken and this caused suflicient heat to be developed by internal friction so that the finishing temperature, again measured by optical means, ranged from 1875 to 1910 F. After rolling, the hardness was measured and found to be Rockwell 0-39 and microexamination of the as-rolled structure showed a uniform grain structure of equiaxed grains classified as ASTM No. 9.

For purposes of comparison, six 2% inch square billets of Waspaloy were prepared as described above from the same heat and thus had the same composition as the example described hereinabove. These billets received the same identical preparation as before except leaders 12 were not attached thereto. When these six billets were hot rolled, five developed split ends during rolling, and while the sixth billet was rolled, the presence of cold tears, slivers, and the like, on the surface required that it as well as the five other billets be rejected. An effort was made to hot roll four additional billets which were prepared for hot rolling in the same way as before and which also had the same composition. None of these last four billets could be successfully hot rolled because of difficulties encountered in entering the billets into the roll pass. The difficulties encountered in hot rolling billets formed of materials such as Waspaloy is in part caused by the extremely narrow hot working temperature range of Waspaloy which extends from about 1850 to 2150 F.

The present invention, for purposes of illustration, has been described in detail in connection with the hot rolling of Waspaloy billets. It is to be understood, however, that the present invention is useful and provides unique advantages in connection with other alloys which normally present difliculty in hot rolling or drawing. The invention is also applicable to the cold rolling or drawing of alloys as well. Stainless steel leader strips formed of AISI 304 are preferred in connection with the hot rolling of Waspaloy billets and provide best results. However, other materials may be used for forming the leader strips. In connection with the selection of such other materials, it is to be noted that it should be relatively easy to roll and compatible with the hard to roll alloy. The leader strips must be weldable so that a substantially uniform junction of high strength between the main section and the leader strips is obtained. In the case of hot rolling, the leader strip material must be capable of withstanding the temperatures required to hot work the hard to roll alloy and must also have s-ufiicient alloy content to withstand the preheating temperature to which it may be necessary to subject the hard to roll alloy.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

I claim:

1. In a process for working hard-to-work alloy billets, the steps of forming a composite billet by welding a leader section of easier-to-work alloy to the end of a main section formed of said hard-to-work alloy in endto-end relation with both sections adjacent to said weld and the weld joint between them having substantially the same cross section, the length of said leader section being such that when said composite billet is entered between the opposed rolls of a rolling mill a portion of said leader section is engaged by said rolls substantially along a line passing through the centers of said opposed rolls when said rolls engage said main section, heating the composite billet to an elevated temperature, and while the composite billet is at an elevated temperature Working the same including entering the leader section followed by the main section into a rolling mill and hot rolling them in that sequence to form a product having a smaller cross sectional area.

2. The process of claim 1 in which the welding step comprises butt welding by the electrical resistance method.

3. The process of claim 1 in which the alloy of the leader section is trimmed from the product.

4. The process of claim 1 in which said hard-to-work alloy is AISI No. 685 and said easier-to-work alloy is AISI 304.

5. A composite billet, comprising a main section of a hard-to-work metal, a leader section of an easier-towork metal, and said leader section being welded at one end thereof to one end of said main section, both sections adjacent to said weld and the weld joint between them having substantially the same cross section, the length of said leader section being such that when said composite billet is entered between the opposed rolls of a rolling mill a portion of said leader section is engaged by said rolls substantially along a line passing through the centers of said opposed rolls when said rolls engage said main sections.

6. A composite billet, comprising a main section of an alloy having high hot hardness, a leader section of an alloy having lower hot hardness, and one end of said leader section being welded to one end of said main section, both sections adjacent to said weld and the weld joint between them having substantially the same cross section, the length of said leader section being such that when said composite billet is entered between the opposed rolls of a rolling mill a portion of said leader section is engaged by said rolls substantially along a line passing through the centers of said opposed rolls when said rolls engage said main section.

7. In a process for working hard-to-work alloy billets, the steps of forming a composite billet by welding a leader section of easier-to-work alloy to the end of a main section formed of said hard-to-work alloy in end-to-end relation with both sections adjacent to said weld and the weld joint between them having substantially the same cross section, the length of said leader section being such that when said composite billet is entered between the opposed rolls of a rolling mill a portion of said leader section is engaged by said rolls substantially along a line passing through the centers of said opposed rolls when said rolls engage said main section, and working said composite billet including entering the composite billet into said rolling mill with said leader section leading so that the leader section and main section are rolled in that sequence to form a product having a smaller cross-sectional area.

8. The process of claim 7 in which, after completion of rolling, the alloy of the leader section is trimmed from the product.

References Cited UNITED STATES PATENTS 290,002 12/1883 Dodge 29480 1,940,939 12/ 1933 Coryell 29480 3,150,936 9/1964 Hunt 29----1 87.5 3,017,697 1/1962 Wlodek 29552 2,382,045 8/1945 Flowers 29552 3,092,470 6/1963 Ripling 29187 2,812,573 11/1957 May 29187 OTHER REFERENCES Harris: Steel Jacket Protects Beryllium During Extrusion Process, July 7, 1960, Iron Age, vol. 186.

CHARLIE T. MOON, Primary Examiner.

H. BIZOT, Examiner.

R. O. DEAN, I. CLINE, Assistant Examiners.

Claims (1)

1. IN A PROCESS FOR WORKING HARD-TO-WORK ALLOY BILLETS, THE STEPS OF FORMING A COMPOSITE BILLET BY WELDING A LEADER SECTION OF EASIER-TO-WORK ALLOY TO THE END OF A MAIN SECTION FORMED OF SAID HARD-TO-WORK ALLOY IN ENDTO-END RELATION WITH BOTH SECTIONS ADJACENT TO SAID WELD AND THE WELDL JOINT BETWEEN THEM HAVING SUBSTANTIALLY THE SAME CROSS SECTION, THE LENGTH OF SAID LEADER SECTION BEING SUCH THAT WHEN SAID COMPOSITE BILLET IS ENTERED BETWEEN THE OPPOSED ROLLS OF A ROLLING MILL A PORTION OF SAID LEADER SECTION IS ENGAGED BY SAID ROLLS SUBSTANTIALLY ALONG A LINE PASSING THROUGH THE CENTERS OF SAID OPPOSSED ROLLS WHEN SAID ROLLS ENGAGE SAID MAIN SECTION, HEATING THE COMPOSITE BILLET TO AN ELEVATED TEMPERATURE, AND WHILE THE COMPOSITE BILLET IS AT AN ELEVATED TEMPERATURE WORKING THE SAME INCLUDING ENTERING THE LEADER SECTION FOLLOWED BY THE MAIN SECTION INTO A ROLLING MILL AND HOT FOLLING THEM IN THAT SEQUENCE TO FORM A PRODUCT HAVING A SMALLER CROSS SECTIONAL AREA.

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