US2681874A

US2681874A - Method of preferentially heat treating steel articles

Info

Publication number: US2681874A
Application number: US252629A
Authority: US
Inventors: Robert J Linney
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-04-28
Filing date: 1951-10-23
Publication date: 1954-06-22
Anticipated expiration: 1971-06-22

Description

i June 22, 1954 METHOD OF PREFERENTIALLY HEAT TREATING STEEL ARTICLES Original Filed April 28, 1948 2 Sheets-Sheet 1 fig INVENTOR.

ROBERT J3 Ll/V/VEY R. J. LINN EY 2,681,874

' 2 Sheets-Sheet 2 June 22, 1954 METHOD OF PREFERENTIALLY HEAT TREATING STEEL ARTICLES Original Filed April 28, 1948 VENTOR. Z/NNEY IN IEOBEIE'T J BY RIC HEY, WA rrs, Ease-Prom? MCNFN/V) Patented June 22, 1954 UNITED STATES ATENT OFFICE METHOD F PREFERENTIALLY HEAT TREATING STEEL ARTICLES 23,693. Divided and this application October 23, 1951, Serial No. 252,629

6 Claims. 1

This invention relates generally to the art of metal heat treatment, and particularly to an improved method of the tempering of ferrous metal objects, especially drill bits.

In the manufacture of certain metal articles: it is quite important that they should be properly tempered, that is, so cooled from a heat-treating temperature that they will possess the desired properties. For example, steel bits used with drilling machines for drilling holes in hard rock should be properly and uniformly tempered. Frequently a plurality of bits of progressively decreasing size are used in drilling a single hole, the largest drill being used first and the smaller ones following thereafter in the decreasing order of their sizes. If one of the bits should be improperly tempered, for example, if it should be softer than the succeeding bits, it will not make a hole of the desired size for succeeding bits and may stick in the hole. Hence, it is important that each bit of a set of drill bits should be properly and uniformly tempered, but it is also important that all bits whether intended for use in a certain set or not should be properly and uniformly tempered.

So far as I know, it was not possible, prior to the present invention, automatically to temper steel drill bits properly and uniformly or to insure that the tempering will be proper and uniform from bit to bit. By the present invention I am able not only to temper steel drill bits and also other metal objects properly, but also to insure that all the objects of the same composition will be tempered properly and substantially Llll'iformly.

The present invention is predicated on the discovery that proper and uniform tempering may be attained by cooling highly heated metal objects with a predetermined amount of cooling liquid maintained at substantially constant temperature, or by exposing the highly heated ob jects to the cooling effect of a substantially uniform temperature coolant for a predetermined length of time, then transferring the thus partially cooled objects, without substantial decrease in their temperature, to a second cooling liquid maintained at a lower temperature and allowing the objects to cool to the temperature of that liquid.

In the drawings accompanying and forming a part of this specification,

Fig. l is a top plan view of one form of apparatus embodying the present apparatus invention and with which the present method invention may be practiced;

Fig. 2 is an elevational view taken from the chute side of. the apparatus of Fig. 1; and

Fig. 3 is an elevational view taken from the left side of Fig. 1.

In the drawings the reservoir I is provided with a drain pipe 2 controlled by a valve 3 and an overflow pipe l. Liquid is maintained in reservoir I to the level indicated by line 5. Liquid may be brought into reservoir I through pipe 5 which is equipped with a thermostatically controlled valve "I. In this case the thermostat 8 is of the electrical type and is connected through lead ii, panel I!) and lead II to an electrical device I2. The thermostat 8 and the device I2 may be, respectively, the well-known Mercoid thermostat control and Mercoil magnetic valve. When the temperature of the liquid in reservoir I rises above a predetermined point the thermostat 3 actuates the valve I2 and opens valve I, thereby admitting cold liquid through pipe 6. Since the discharge end of pipe 6 is remote from the thermostat 8, the incoming fluid will continue to flow for some little time before the thermostat 8 will be actuated by a lowering of the temperature of the liquid in reservoir I to ole-energize the valve control device and close the valve 1 against further entry of cold liquid.

Adjacent to the thermostat 8 is disposed a pump I3 which communicates with the interior of the reservoir I and serves to withdraw liquid therefrom and to force it through pipe I l and into the top of a hollow shaft presently to be described. The pump I3 is actuated by a motor I5.

Two upright beams I 6 are disposed on opposite sides of reservoir I and are connected together at their upper ends by a channel I"? and at a point some little distance above the top of reservoir I by a pair of channels I8. An upright leg or beam I9 also located outside of reservoir I is connected at its upper end to one or more channels 20 which extend horizontally toward and connect to one of the channels I8. A plate or platform 25 rests on channels 2!] and is secured to channels [8 and 2t and serves as a support for a power unit consisting of a motor 23 and a reduction gearing device 23. Panel It, above mentioned, is secured to channel II, to one of the uprights Iii and, to plate 2I.

The plate 2 I supports a thrust bearing 25 which, in turn, rotatably supports the hollow shaft 28 above mentioned. This shaft passes through a pillow block or bearing 21 on channel IT. A sprocket 28 is keyed to shaft 2% and is connected to the reduction gearing device 23 by a driving of tank 30, and an enlarged upper end 33 proi vided with a screen on which an object to be tempered may be placed. It will be understood that when pump 13 withdraws liquid from l and forces it through pipe I4 into hollow shaft 25, such liquid will fill the tank and will flow out through pipes 32 and up through the perforations in the screen and against an object on the screen. It will also be understood that when the motor 22 is actuated the chain 29 will rotate shaft 25, tank 30 and members 3! and that by varying the speed of rotation of the shaft objects on those members may be subjected for various lengths of time to cooling liquid flowing thereagainst through said members.

A magnet is mounted on supports ii which are connected to reservoir I by arms 52. This magnet is adjustably positioned relative to metallic articles on the spray-heads, so that vhen en-- ergized the magnet may attract to itself and thereby remove from an adjacent spray-head a magnetic metal article on the latter. The magnet 40 is alternately energized for a short period of time and then is de-energized for another short period of time. The top of tank 30 is provided with a plurality of pegs 15 positioned radially inward of the respective spray-heads 3i. These pegs are so disposed as to make contact with the switch closing member :lfi of a limit switch il which is connected to a suitable source of electric current and also to the windings of magnet 4|]. When one of these pegs 45 closes the contacts of the limit switch 4? the electrical current energizes magnet 49 and the magnet in turn attracts to itself a metal object on the spray-head adjacent the magnet. When the peg 65 moves on and permits the contacts of the limit switch 41' to separate, the current to magnet it is interrupted and the metal object which had been attracted to the magnet is allowed to fall. Hi this way the magnet is energized for a short time and then is de-energized for another short time, and the energization occurs when a spray-head is adjacent to the magnet.

An inclined chute 59 is disposed with its upper end in position to receive metal articles which r fall from the de-energized magnet 40. The lower end of this chute 50 is disposed above a stationary tank 5| so that metal articles dropping from magnet 40 may slide into that tank. An opentop screen-basket 52 is provided in tank 5! to receive such articles. This tank also contains a cooling liquid which may be maintained at above a predetermined temperature by means of a heat ing unit 53 which may be of any suitable construction, for example, the well-known Calrod immersion heating unit.

The general operation of the above described apparatus will be understood from the foregoing description. However, when it is to be operated to temper steel drill bits for hard rock drilling it may be operated substantially as follows: The motor [5 is energized and pump I3 circulates coolant from reservoir I through pipe [4, shaft 26, tank 30 and spray-heads 3! and brings the level of coolant in tank 30 to above the tops 4 of heads 3| so that the coolant will overflow the heads and return to reservoir I. The motor 22 is energized and tank 30 is rotated. Then steel drill bits which have been heated to the proper temperature, which may be about 1440 F. for one particular kind of steel, are removed from the heating furnace and are placed one at a time points down on the spray-heads when they reach the position indicated by the letter X in Fig. l and while tank 30 is rotating. As tank 30 rotates, the pressure exerted on the cooling liquid is so regulated that the liquid bubbles up through the spray-heads and to a predetermined distance thereabove which is sufiicient to cover only the 1- drilling points of the bits or about for the average size jack bit. This liquid is maintained at a temperature under 75 F. preferably at about 72 F. The liquid thus regulated as to pressure and temperature cools the points from the time they leave point X until they reach the position indicated by the letter Y in Fig. 1. When a bit reaches that position, a peg 45 several stations behind that spray-head will close the circuit through limit switch 41, thereby energizing magnet 40. When energized this magnet attracts to itself the drill bit on the spray-head at station Y and when de-energized drops that drill bit onto chute 50 and the bit slides into tank 5|.

It will be understood that during the time of about 53 seconds which elapses between the placing of a bit on a spray-head at station X and the time the drill bit is removed therefrom at station Y, the liquid coming into contact with the drill bit will have lowered the temperature of the drill bit considerably, for example, from about 1440 F. to about 900 F., that the bit will then be at a temperature within the magnetic temperature range of the steel, and that the temperature of the drill bit will not sensibly decrease between the time it is removed at station Y and the time it arrives in tank 5!. The speed of r0- tation of tank 30 should be so adjusted for bits of different sizes that the bits are cooled through the just mentioned range during one revolution of the tank. Higher or lower speeds may, of course, be used when smaller or greater decreases in temperature are desired.

Drill bits of the type referred to herein are composed of steel which can be made quite hard by treatment. While drill bits are made from steels of different S. A. E. numbers, the compositions which are suitable contain between about 370% and 86% of carbon, between about 40% and of manganese, about 133% maxi mum of sulfur and of phosphorous, with the remainder being iron containing small amounts of other impurities but without any substantial amounts of alloying elements. The cutting edges are often formed on these bits when the carbides in the steel are in a spherodized condition and the steel is soft and machinable as a result thereof. Then the steel is heated to such a temperature as will result in a complete solution of the carbides which in this case is about ll40 F. Then the dissolved carbides in the cutting edge portions are precipitated as very fine grain martensite more or less uniformly throughout those portions by quenching the cutting edges of the bit with resultant hardening of those portions. This quenching step is carried out by quickly lowering the temperature of the cutting edge portions from about 1440" F. to about 900 F. in a short space of time as by bubbling water at about 72 F. to about 75 F. over the cutting surfaces for about 51 seconds on the average.

The entire bit is cooled by the extraction of heat from the body of the bit through the surfaces in contact with the water but the cooling rate of the metal beyond the cutting edge portions is less rapid and hence the body part of the bit is more ductile and resistant to breakage than the cutting edges. The thus quickly cooled article is transferred, preferably magnetically, when at a temperature of about 900 F. into a body of water maintained, for example, at about 192 F. where it is allowed to cool for about minutes. If desired, the bit may be reheated to a drawing temperature to reduce the brittleness of the cutting edge portions.

Since the cooling rate of the drill bits in tank 5| should not be too rapid, the temperature of the liquid is maintained above a predetermined minimum temperature by the heating unit 53.

Various cooling liquids may be used in reservoir l and stationary tank 5|, as desired. Water may be used in reservoir l but its temperature should not be permitted to rise beyond a certain point for if it becomes too highly heated, due to heat extracted from the bits, it will not cool the bits below their non-magnetic range and hence the magnet 40 will not attract them to it. When the liquid in reservoir I is maintained at a temperature not in excess of about 75 F. and the speed of rotation of tank and the rate of liquid flow through the spray-heads are properly adjusted, tool bits having a temperature of about 1440" F. when placed on the spray-heads will be cooled to below their non-magnetic temperature range before they reach the magnet and hence will be attracted to the magnet and removed from the spray-heads. By suitably setting the thermostat 8 the temperature of the coolant in reservoir may be maintained substantially constant, as above mentioned.

The coolant preferred in tank 5| is Water and its temperature is preferably maintained close to its boiling point by the heating unit in the bottom of the tank, 192 F. having been found to be satisfactory.

Each bit cools to about the temperature of the water in tank 5| within about 10 minutes and may then be removed for subsequent treatment.

While the foregoing detailed description is specific to the tempering of drill bits, it will be understood that other articles may be tempered through the use of the above-described apparatus in accordance with the method of this invention, and that by adjusting the speed of rotation of tank 30 and the temperature of the coolant in reservoir 1 and the rate or amount of coolant flow through spray-head 3|, various metal objects may be cooled throughout various temperature ranges and to various temperatures, depending on the characteristics desired in the objects and obtainable by such variations in the time, rate and nature of the tempering action. It will be understood that by varying the kind and temperature of the coolant in tank 5|, the rate of cooling of metal articles therein may be varied with some variation in the properties of the articles cooled under those conditions.

This application is a division of my application Serial No. 23,693, filed April 28, 1948, now Patent No. 2,596,493 which was a continuationin-part of my application Serial No. 499,398, now abandoned.

Having thus described the present invention so that others skilled in the art may be able to understand and practice the same, I state that 6. what I desire to secure by Letters Patent is defined in what is claimed.

What is claimed is:

1. The method of heat treating and preferentially hardening surfaces and making ductile the remainder of steel articles containing between about .70% and about of carbon, between about 40% and about .60% of manganese, less than about .03 of phosphorus and of sulphur, the remainder being iron with the usual amounts of other impurities which comprise the steps of exposing to the atmosphere such an article which is at a temperature of about 1440 F. and has its carbides in solution, flowing water at a temperature of about 75 F. against part of the surface of said article and thereby quenching such surface, precipitating the carbides therein as finegrained martensite and hardening said surface, and thereupon completing the cooling in water near its boiling temperature.

2. The method of heat treating and preferentially hardening surfaces and making ductile the remainder of steel articles containing between about .'70% and about .90% of carbon, between about .40% and about .60% of manganese, less than about 03% of phosphorus and of sulphur, the remainder being iron with the usual amounts of other impurities, which comprise the steps of exposing to the atmosphere such an article which is at a temperature of about 1440 F. and has its carbides in solution, flowing water at a temperature of about 75 F. against surfaces at one end of said article and thereby quenching said surfaces, precipitating the carbides therein as finegrained martensite, hardening said surfaces, and reducing the temperature of the article to about 900 F., then immediately transferring said article magnetically to a bath of water at a temperature of about 192 F. and removing the article from said bath after it has been cooled to the bath temperature.

3. The method of heat treating and preferentially hardening surfaces and making ductile the remainder of steel articles containing between about 370% and about .90% of carbon, between about .40% and about .60% of manganese, less than about 03% of phosphorus and of sulphur, the remainder being iron with the usual amounts of other impurities which comprise the steps of exposing to the atmosphere such an article which is at a temperature of about 1440 F. and has its carbides in solution, flowing water at a temperature of about 75 F. against surfaces at one end of said article until the article has been cooled to about 900 F., thereupon transferring the article magnetically into a bath of water at a temperature near its boiling temperature, and cooling the article in said 'bath to about the temperature of the water.

4. A method of heat treating and preferentially hardening the cutting surfaces and making ductile the shanks of high carbon steel drill bits which comprises the steps of heating the bit at a temperature of about 1440 F. until the carbides therein have dissolved, exposing the thus heated article to the atmosphere, quenching and cooling the drill surfaces of the bit from a temperature of about 1440 F. to about 900 F. by flowing water at a temperature of about 75 F. against said surfaces while the remainder of the article is exposed to the atmosphere and is cooled at a lower rate, and then cooling the entire article to about 192 F. by immersing it in water at about that temperature.

5. A method of heat treating and preferentially hardening the cutting surfaces and making ductile the shanks of high carbon steel drill bits which comprises the steps of heating the bit at a temperature of about 1440 F. until the carbides therein have dissolved, exposing the thus heated article to the air While flowing water at a temperature of about 75 F. against the drill surfaces of the bit and cooling said surfaces to about 900 F., While the remainder of the article is exposed to the air and is cooled at a slower rate, thereupon transferring the bit magnetically to a bath of water maintained near its boiling temperature and cooling the entire bit in the bath to about the water temperature.

6. The method of heat treating and preferentially hardening the cutting surfaces and making ductile the shanks of steel drill bits containing between about .70% and about .90% carbon, between about .40% and about .60% of manganese, less than about .03% of phosphorus and of sulphur, and the remainder being iron with the usual amounts of other impurities, which comprises the steps of heat treating the bit at a temperature of about 1440 F. until the carbides therein have dissolved, exposing the thus heated article to References Cited in the file Of this patent UNITED STATES PATENTS Number Name Date 2,441,628 Grifiiths et al May 18, 1948 FOREIGN PATENTS Number Country Date 580,728 Great Britain Sept. 18, 1946 OTHER REFERENCES High Speed Steel, by Grossman & Bain, page 68, 1931.

Tool Steels, by Gill et al., pages 219 and 220, 1944.

Claims

1. THE METHOD OF HEAT TREATING AND PREFERENTIALLY HARDENING SURFACES AND MAKING DUCTILE THE REMAINDER OF STEEL ARTICLES CONTAINING BETWEEN ABOUT .70% AND ABOUT .90% OF CARBON, BETWEEN ABOUT .40% AND ABOUT .60% OF MANGANESE, LESS THAN ABOUT .03% OF PHOSPHORUS AND OF SULPHUR, THE REMAINDER BEING IRON WITH THE USUAL AMOUNTS OF OTHER IMPURITIES WHICH COMPRISE THE STEPS OF EXPOSING TO THE ATMOSPHERE SUCH AN ARTICLE WHICH IS AT A TEMPERATURE OF ABOUT 1440* F. AND HAS ITS CARBIDES IN SOLUTION, FLOWING WATER AT A TEMPERATURE OF ABOUT 75* F. AGAINST PART OF THE SURFACE OF SAID ARTICLE AND THEREBY QUENCHING SUCH SURFACE, PRECIPITATING THE CARBIDES THEREIN AS FINEGRAINED MARTENSITE AND HARDENING SAID SURFACE, AND THEREUPON COMPLETING THE COOLING IN WATER NEAR ITS BOILING TEMPERATURE.