US2370959A - Method of heat treatment for wire drawing - Google Patents

Description

. dies, where" w a, 194s Manson or WIRE HEAT TREATMENT FOR paawmo F. Holden, Northford, Conn.

No' Drawing. Applicatlon March 4, 1942,. Serial no. 433,291

1 Claim. The present invention relates broadly to metallurgy and more especially to a salt bath method for treating metals, especiallyferrous metals,

during wire drawing operations.

In order that the present inventionmay be I more clearly understood, a description of the present method of treating metals, particularly 'steel, during wire drawing operations, is presented. In the common practice of wire drawing, thevork is. unwound from coils on reels and is heated to a temperature between 1500 F. and 1700" F. either in lead baths on'open air'furnaces as the fii step, and then as a second step. the metal passes through air to a lower temperature stageusually referred to as a quenching stage in which the temperature is lowered to between 900 F. and 1100 F. and this operation may also be carried out either in a lead bath or in an air furnace. The steel is then submitted'to a third quenching operation, which may be by the use of a water spray, but more usually merely by permitting it to cool in air. The temperature of the metal on leaving this third stage, is normal atmospheric temperature or, slightly higher. After passing the third stage, the steel is recoiled on mechanical reels. The coils are removed from p the reels and are submersed in an acid pickling 'bath where they.v remain until the deep oxide or scale which is formed on the metal is removed.

The fifth step is to submerge the coils in a washing bath to remove the acid pickle,and the sixth step.is to submerge the coil in a boiling water lime" solution which is in the nature 'of a thick creamy liquid- The coils are taken, in the seventh step, from the llme ba'th to a baking oven which is heated to a suiilcient temperature, .usually about 350 F., to quickly evaporate the water and to leave a lime deposit on the wire. The coil is again set onfa suitable reel from which the material on the coil is unwound-as it is pulled through a,drawing die. Preceding the drawing die is a container for suitable grease through which the wire or rod, depending on the diameteroftheworlaisdrawn. Thelimecoatingon' the work neutralizes the acid pickling bath and .the lime residue deposited on theworkpicksup and carries with the greas used for lubricaa .the drawing operation. I the drawing The drawing ot the metal through there' is a. substantial-reduction in also, changes the characteristics of the metal and heat treatment isrequired prior to the next suc-, drawing operation." Therefore, theusual practice is to repeat all the foregoing operations prior to each drawing operatiomwith the tion of preceding the 'nnal and (Tiaw. The final and last draw is a finishing. operation the heat treatment step is, therefore, usually omitted prior to the final and last draw; and usually r there is no heat treatment after the final and last drawing operation. a

The present method comprises the use of salt baths which have related characteristics in such which remains on the work is not',substantially removed by thesucceeding'batfi. Thus, the hot stock is completely coated after the stock or work leaves the high temperature bath and until it is cooled suillc ntly to prevent uncontrolled oxidation' due to oxygen picked up from the air. i

In the present invention, the wire stock, after leaving the reel, is first heated in a bath, operating at a temperature between 1500 F. and 1700 F. comprising alkali metal chlorides andan alkali metal fluoride. This bath may comprise 25% to 45% potassium chloride, 35% to 55% sodium chloride, and 1% to 5% sodium fluoride; the preferred specific amounts being 43% potassium chloride, 55% sodium chloride, and 2% sodium fluoride. The work'then proceeds to the second bath which comprises an alkalimetal hy- 4 droxide, an alkali metalchlorlde, an alkali metal carbonate, an alkali metal fluoride, and an alkali metal cyanide, the preferred range of proportions being 25% to 50% sodiumhydroxlde, 5%- to 10% to'1 7% sodium fluoride and 7% to 20% sodium cyanide; the preferred speciflcproportions being 40% sodium hydroxide or potassium hydroxide, 10% sodiumchlorlde, 25% sodium can. bonate, 13%,sodium'fiuorlderand 11% sodium cyanide.

The second bath is intended to operate at temperatures between 900 F. and 1100? F." and the work in passing the" second bath does not lose in any substantial t e material f duetotheiact that the first bathmelts at a gher temperature than the second bath and'also due to the. chemioi. the two aths. The advantage of carrying the first bath the second bath is to. prevent contamination or the second bath by the first bath, and to-keep the work completely .50 coveredbysaltswhile themetalishot.

linthethirds entheworkiscarrledthrougha water bath. Since the ingredients of the first,

two baths are solublein water, the water bath charged'wlth the materials of the first 58 secondbathandtheeooled stockleamthe wherein the reduction in size is very slight and I manner that the material of the preceding bath sodium chloride, 15% to 35% sodium carbonate,

isoo'r'. to 1700' F.- Where the lead bathis used. therewillbeaveryslightoxidationoithework water bath wetted with a watersoiution containing the salts'ot the two preceding baths. The

watershouldcontainnotlessthan4oa.to6oz.-

of the salts per gallon of watc -and in starting it may be desirable to dissolve some ofthe salts in the water. .Therefore, as the water evaporates,

a small proportion of these salts remains upon the stock when it is reeled into coils after pass-- ing through the baths specified- These treated coils ofwirearenowreadyforadrawing operation without the pickling, liming or baking steps previously referred to in the old well-known ordinary methods. I'hechemicals remaining on the wire, in accordancewith the present invention, are suflicient to act as carriers for the lubricant specified-may be slightly modified by using a clear water wash which is flowed or sprayed at a sufficient rate to completely wash all of the'salts from the wire after the stock has passed the second bath. The. material may then be subjected to a very hot lime bath so that when the stock leaves the lime bath it may-be of sufllcient temperature to dry the lime on the stock without baking, or if desired, the baking step may be included. In any eveniithe pickling of the wire is omitted according to the present invention.

Whenwire stockissubmittedtothesteps specifled comprising the present invention, the stock is without oxide and is clean, bright metal.

I Asa furthervariaflonofpossible treatment, in accordance with the present invention, after the stock haspassed salt bath and has beenwashedcleanof thefirsttwobaths specifled, the stock may be passedthrough abath comprising a nitrate bath which maybe made up of 50% sodimn nitrate and 50% potassium ni- I trate, or 50% hydroxide and 50% sodium nitrate heated to a temperature suihcient to produce a definitely controlled, extremely thin oxide filmonthewire. Thisfilmi'ssothinthatitcan-;

not be measured by ordinary methods. The potassium nitrate-sodium nitrate bath should be run at a temperature of from 600 F. tb 900 F.

and would produce a thin film of oxide of a blueblack colon-while the sodium-hydroxide-sodium nitrate bath, when heated .from 900 F. to 10001 F. produces a black oxide. The nitrate bath works 55 very quickly so, therefore, the stock may be passed quickly through this. bath in order-to obtain the particular controlled oxide desired. This oxide acts as a carrier for a lubricant during the sucstituting the old lead bath for the first salt bath,

, and the lead bath at temperatures of before the work reaches the second bath which is the salt bath; Since this second bath is a reducing bath, the work leaves the second rbath bright and clear of oxide.

The bath No. 1 comprising potassium chloride, sodium chloride, and sodium fluoride may be varied by substituting either potassium carbonate l0 orsodium carbonate for the potassium chloride or the sodium chloride or both. The bariumfiuoride-or calciumhuoride may-be substituted for the sodium fluoride. These substances, however,

' comprise chemical compounds which may tend to contaminate the secondbath, and, therefore,

are not as desirable as the preferred forms given above.

The second bath may be varied by omitting the alkali metal chloride, and the alkali metal carbonate. When this is done, the bath is more liable to fume and, therefore, the preferred formula is better for the purpose intended.

melting point of the second bath may be lowered by the addition of potassium hydroxide 5 but the preferred temperatures above specified are thosewhich are most desirable.

One of the prime objects of the present invention is that the stock, after having been heated to the higher temperature, remains coated by on chemicals which are inert to the stock until the temperature has been reduced to normal or room temperature, thereby avoiding a heavy film of oxides on the stock which may result in scale which is undesirable.

no Iclaim:

The method 5f preparing ferrous wire for drawing which comprises progressively. passing said wire througha salt bath having a temperature of between 1500 and 17.00 F. and a composition consisting essentially of from to potassium chloride, 35% to sodium chloride and 1% to 5% sodium fluoride which leaves a ferrous-oxidation inhibiting drag-out coating of said salts thereon, thence progressively passing '45 saidthuscoatedwirethroughasaltbathhaving a temperature of between 900 and I F. and

a composition comiisting essentially of from 25% -to 50% sodium hydroxide, 5% to 20% sodium chloride, 15% to 35% sodium carbonate, 10% to upon the wire, thence passing the two-bath coated wire through anaqueous saline bath containtration of not less than 4 ounces per gallon to provide upon said wire a thin aqueous coating of the salts of said first two baths, drying said aqueous coating in situ upon said wire to proceeding drawing operation but the metal, after (to vide a very thin oxidation-protective lubricantleaving the drawing die, is substantially clear and. clean and the oxide has disappeared. I A further slight modification comprises subwettable adherent salt coating thereon, and

tained by said salt coating.

F. HOLDEN;

17% sodium fluoride and 7% to 20% sodiumcyanide which leaves a ferrous-oxidation inhibiting drag-out coating'of the salts from both baths ing dissolved salts .of said baths in a .6oncen-'