US2836527A - Method for producing flat solution heat treated titanium and zirconium alloy sheets - Google Patents

Description

United States Patent Gfiice 2,836,527 Patented May 27, 1958 lWETI-IOD FOR PRODUCENG FLAT SOLUTION HEAT TREATED TITANIUM AND ZIRCONIUM ALLOY SHEETS Harold D. Kessler, Las Vegas, and Raymond S. Richards,

Henderson, New, assignors to Titanium Metals Corporation of America, New York, N. Y., a corporation of Pennsylvania No Drawing. Application February 7, 1956 Serial No. 563,836

3 Claims. (Cl. 148-10) This invention relates to the heat treatment of metal sheets, and more particularly to solution heat treatment of sheets of refractory metals such as titanium and zirconium.

Heat treatment of metal sheets is employed to impart specific and desirable properties thereto. heat treatment the temperature of the sheet is raised sufiiciently to insure solution of certain alloy constituents, and the heating is generally followed by rapid cooling such as quenching. Such sequence of steps often results in distortion of the sheet so that it is no longer flat andmakes necessary an additional straightening operation to provide heat treated sheet in flat, useful form.

A principal object of this invention is to provide a simple, economical and rapid method for solution heat treating metal sheets. A further object'is to provide a method which will produce flat, solution heat treated metal sheets of refractory metals such as titanium and Zirconium. Another object is to provide a method for producing fiat, solution heat treated metal sheets in which scaling of the sheet surface is materially reduced. A still further object is to provide a rapid, combined method for flattening and solution heat treating metal sheets. These and other obiects of this invention will be apparent from the following detailed description thereof.

This invention, in its broadest aspects, contemplates a method for producing flat, solution heat treated sheets of metals such as titanium and zirconium in which the sheet is heated to the required temperature by passage of an electric current therethrough. During heating the sheet is maintained in a frame or other apparatus, preferably by clamping to two opposed edges. The clamps, suitably insulated, may serve as electrodes to conduct electric current through the sheet and also to grip the edges thereof for application of tension to stretch the sheet during the time it is at elevated temperature, thereby to insure flatness. After the sheet is at the desired temperature and has been stretched, it is then cooled, preferably quenched, for instance by treatment with water or brine sprays, and while quenching the sheet is maintained under tension so that contraction due to cooling will not result in distortion.

The tension maintained during quenching will generally be less than the yield strength of the sheet.

The method of this invention is particularly adapted to treatment of titanium and zirconium alloy sheets which have a relatively high electrical resistance. Such sheets may be of thickness from about 0.005 inch to about 0.2 inch. Since the method involves a straightening operation, it is not necessary that the original sheet be fiat. The sheet is held by clamps or jaws engaging opposing edges, preferably the ends, and the clamps maintain the sheet in suitable apparatus, which in and of itself forms no part of this invention, adapted to supply electric current to pass through the sheet and also to apply tension to the sheet between the clamps. The electrical and mechanical features of the apparatus may be of any suitable type to produce these effects, and may vary considerably depend- In a solution ing on the size, thickness and composition of the sheet to be treated, as Well as other factors which will be obvious to those skilled in the art.

Sufiicient electric current should be passed through the sheet to heat it rapidly to the required solution heat treatment temperature. This temperature will vary according to the composition of the alloy and the properties desired, but will generally lie within the range of 1300 to 1800 F. The sheet is maintained at solution heat treatment temperature for a short time to insure proper solution effect. However, this time should not be excessivel long, preferably not more than one minute and generally not more than ten minutes. Holding the sheet at solution heat treatment temperature longer than about ten minutes to to be avoided since this will result in heavy scale formation, which is not readily removed and which becomes a serious problem.

The sheet is stretched while it is at solution heat treatment temperature. The stretching is preferably accomplished towards the end of the period at which the sheet is maintained at such temperature. The sheet is stretched to eliminate unfiatness originally in the sheet, or caused by distortion during the heating step. Preferably the sheet is stretched longitudinally to an extent not more than about 5% of its original length. Elongation of 5% will be found to remove even gross unflatness, and less elongation may be employed when the condition of the sheet needs only a lesser amount to provide substantial flatness.

After stretching the sheet is rapidly cooled; preferably quenched by application of water sprays or other equivalent heat extracting means, which may include brine, cooled brine, and high velocity gases. During quenching the sheet is maintained under tension to prevent sagging or distortion due to the quenching operation, but the tension at this stage is suiiicient only to maintain the sheet flatness previously obtained and no additional stretching is necessary or desirable. Therefore, the tension maintained on the sheet during quenching should generally be less than the yield strength of the sheet, and preferably it will be substantially less. it may occur, primarily because of nonuniform quenching, that a slight additional stretching may be required during quenching. Under these conditions the tensile force applied at times during quenching may slightly exceed the yield strength of the sheet. The amount of work performed on the sheet should, however, be kept at "a minimum at this stage. Since the sheet will contract during cooling, the tension maintaining apparatus should include hydrauli controls or spring mechanisms to provide tensile relief to prevent contraction from increasing the force applied above that necessary or desirable. The quenched sheet will be found to be uniformly solution heat treated, fiat, and lightly scaled so that a simple, aqueous scale remover ap plied at relatively low temperature will restore an acceptable surface condition.

Flatne'ss in metal sheet products of the type to which this invention relates, is generally measured as a percentage figure obtained by placing a straight edge in any direction on the sheet and measuring the length between contact points and the distance from the straight edge to the material at the point of greatest deviation. The relation of the deviation expressed as a percentage of the distance between contact points is considered flatness. Since flatness is a relative quality, it will vary somewhat according to the use requirements and other factors. Specifications often call for flatness not exceeding two or three percent for some applications, while for other uses a seven or eight percent flatness maybe acceptable. Often rolled products Without straightening will show a serious unjiatness determined as high as 15% or higher flatness.

'to the sheet maintained by the clamps. direct currentele'ctric power was connected'to each of .formability inevitably result.

i The followingexample will illustrate the practice of an e b d en of t e ion.

Example 1 'An unflattened sheet (flatness 16% ZOinches by 30 inches; rolled from a titanium basef alloy'containing 6% aluminum and 4% vauadiumand of thickness .075" was clamped securely in a frame by its end edges. "One end of'the frame and its associated clamp was arranged to be movable with respect to the opposite clamp, and arranged to be' actuated by a hydraulic cylinder to apply tension A source of the clamps, which were insulated from the rest of the structure, and a current of 14,000 amperes and 10 volts was applied to the sheet. 'The temperature of the sheet was thereby raised to 1550" F. in about 30 seconds. On reaching this. temperaturethe power source was cut back to l0,000 amperes tomaintain'the sheet at 1550 for two minutes. Stretching'was initiated just prior to the endof the two minute holding period by application of a tensile force of 4,000 pounds. between the clamps until anelongation of 3%'in the length of the sheet was obtained. At this stage the sheet was essentially flat. The electric heating current was then turned oil and simultaneously water sprays were applied to quench the sheet. At the same time a relief valve in the hydraulic cylinder actuating the stretching mechanism perature accomplishes flattening under conditions which do not affect the mechanical properties of the sheet. In;

this respect the method of this invention is unique and does not introduce disadvantageous eiiects such as work 7 hardening which occurs when stretching is accomplished cold or at moderately elevated temperature such as 500 to 700 F. When metal-sheets are worked, as by stretching, at temperatures much below the solution heat treating temperature, appreciable and deleterious hardening, increasein' yield strength, and reduction in ductility and vention, however, since the deformation of the sheet is accomplished at solution heat treatment temperature,

these disadvantages are not encountered and the mechan- In the method of this in agents such as molten alkali applied at temperatures of;

the order of 800 F. or higher. Such treatment is expensive and difiicult to apply to thin sheets and, more.

over, exposure of the solution heat treated and quenched sheet again to a temperature as high as 800 F. or higher results in substantial change in mechanical properties. Since the heat treatment andiflattening operation, according to this invention, is carried out in anextremely short space of time, never longer than a few minutes; the scale formed under these conditions is of such character that it may be're'adilyremoved by anaqueous descaling agent at' temper'atures below that at which any deleterious effect on the sheet properties occur.

claim; 1 s L l. A method for producing flat, solution heat treated sheets of a metal selected from the' group consisting of titanium and zirconium base alloys, which comprises: heating said sheet by passage of an electric current therethrough until the temperature thereof :reachesibetween 1300 'F. and 1800 F.; maintaining said sheet at said temperature of a period not exceeding ten :minutes, stretching said sheetto provide an elongation thereof of not more than 5% in one direction during the time that said sheet is maintained at said temperature and quencha ing said sheet whilemaintaining it under tension.

2. A methodrfor producing flat, solution heat treated sheets of. a metal selected from the group consisting of titanium and zirconium base alloys which comprises: heating said sheet by passage of an electric current therethrough until the temperature thereof reachesbetween 1300 F. and 1800 F., maintaining said sheet at said temperature for a period not exceeding two;,minutes, stretching said sheet to provide an elongation thereof or not inore'than 5% in one direction towardrthe end of the time that said sheet is maintained at said temper: ature. and quenching said sheet while maintaining it under tension. 7 Y

3. A 'method'for producing flat, solution heat treated sheets of a metal selected from the group consisting of titanium and zirconium base alloys which comprises;

heating said sheet by passage-of an electric current there: through until the' temperature thereof reaches between 1300 F. and 1800 F., maintaining said sheet'at said temperature for -a period not exceeding ten minutes,-

ical propertiesof the solution heat treated sheet are 'essentially the same as ifit had not been subjected to any stretching or straightening work. p

The ability to heat treatand straighten thin metal sheets in an extremely short period of time is another important featureof this invention. Exposure to the atmosphere of alloys of thetype to which this invention relates at high temperatures inevitably results in scaling of the sheet surface. If the scaling is severe, it cannot 7 not more than 5% in one direction during the time that said sheet is maintained at said temperature and quench; mg said sheet while maintaining it under tension less than its yield strength.

References Cited the file of this patent V I UNITED STATES PATENTS OTHER REFERENCES V w. A. D. 0. Technical Report 53-26, April 1953,

vestigation of Heat Treatment of Commercial Titanium Base Alloys, page 6.

Claims (1)

1. A METHOD FOR PRODUCING FLAT, SOLUTION HEAT TREATED SHEETS OF A METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM BASE ALLOYS WHICH COMPRISES: HEATING SAID SHEET BY PASSAGE OF AN ELECTRIC CURRENT THERETHROUGH UNTIL THE TEMPERATURE THEREOF REACHES BETWEEN 1300*F. AND 1800*F., MAINTAINING SAID SHEET AT SAID TEMPERATURE OF A PERIOD NOT EXCEEDING TEN MINUTES, STRETCHING SAID SHEET TO PROVIDE AN ELONGATION THEREOF OF NOT MORE THAN 5% IN ONE DIRECTION DURING THE TIME THAT SAID SHEET IS MAINTAINED AT SAID TEMPERATURE AND QUENCHING SAID SHEET WHILE MAINTAINING IT UNDER TENSION.