US2672430A - Heat-treating metal objects - Google Patents

Description

March 16, 1954 Filed Feb. 1, 1950 A. SIMONS HEAT-TREATING METAL OBJECTS 2 Sheets-Sheet l INVENTQR ABRAHAM SIMONS BY C/ ATTORNEYS March 16, 1954 A. SIMONS 2,672,430

HEAT-TREATING METAL OBJECTS Filed Feb. 1, 1950 2 Sheets-Sheet 2 FIG. 2.

INVENTOR ABRAHAM SIMONS avz/ g k ATTORNEYS Patented Mar. 16, 1954 UNITED STATES PATENT OFFICE Abraham Simons, Monsey, N. Y.

Application February 1, 1950, Serial No. 141,785

6 Claims.

My invention relates to a new and-improved method for heat-treating metal objects, a new and improved mechanism for this purpose, and to new and improved heat-treated metal objects.

The invention relates particularly to the hardening of tools which are made of selfhardening or high-speed alloy steels, by means of heating and quenching. These tools include cutting and shaping and drilling tools of all kinds, as exemplified by lathe tools, planer tools, milling tools, milling cutters, taps, drills, etc.

The al oy steels, in addition to iron and carbon, contain one or more of many alloying elements. These alloying elements are exemplified by tungsten, vanadium, chromium, manganese, nickel, etc.

One example of a self-hardening or high-speed steel is an alloy which contains 18% of tungsten, 4% of chromium, 1% of vanadium, 0.5% of manganese, from 0.40% to 0.80% of carbon, the balance being iron.

Whie the invention relates particularly to the hardening of steel tools which are made of selfhardening or high-speed alloy steels, it also includes the hardening of steel tools which are made of steel which consists substantially wholly or wholly of iron and carbon.

The invention also includes the heat treatment of all steels and other metals and alloys, including non-ferrous metals and alloys, in which the tool or other object is cooled under conditions which produce internal strains in the tool or other object, which internal strains must be subsequently removed or lowered by subsequent heat treatment. This subsequent heat treatment is exemplified by drawing. annealing, etc.

For the purposes of a preliminary explanation of one aspect of the invention, reference is made to the hardening of a steel tool, to which the invention is particularly directed.

The general method of hardening steel is wellknown. For example, this general method is described in the 1920 edition of Machinerys Handbook published by The Industrial Press, at pages 1130-1138; and in the 1941 edition of Mechanical Engineers Handbook, published by McGraw-Hill Book Company, Inc., at pages 559-568.

In general, the steel is heated to a temperature which depends upon the composition of the respective steel. After heating to such temperature, the peariite form of the carbon in the steel.

is changed into martensite or hardening carbon during cooling. The steel is cooled with sulficient rapidity from its original high temperature to produce'the martensite in the cooled steel. The steel can thus be cooled by plunging it into a hardening or quenching bath. This bath may be of many differentrespective compositions, and it may be a fused metal or a fused alloy. The bath may be water, raw linseed oil, other oils, a solution of salt in water, a solution of acidin water, etc.

The martensite structure, while very hard; is

also very brittle, and a subsequent heat treatment of tempering or drawing is required, in order to increase the ductility of the steel. However, this tempering or drawing operation, in addition to increasing the cost of man facture, substantially lowers the original hardness of the steel. I

Also, uneven cooling produces a tool which has hard and soft places, and such tool hasa tendency to crack.

When a tool is thus quenched according to the old method at ordinary atmospheric pressure of 760 mm. of mercury, the outer layer of the tool is cooled and quenched while the interior portion of the tool is still hot'ancl plastic and deformable under pressure.

pressure upon the inner portion of the tool, while said inner portion cools below the critical point:

If the tool is of irregular shape and thickness, such as a drill, the quenching is not uniform,

so that the quenched tool is subject to high internal strains.

According to my invention, the heated tool is subjected to high pressure in the liquid quenching bath, as soon as the heated tool is immersed in the liquid quenching bath. This pressure is which is applied to the liquid bath may betas,

high as two hundred thousand pounds per square inch. When the heated tool is thus immersed it is at a high temperature, which may be close to its melting point. Thus, if the tool is made of high-speed tungsten steel, it may be at ,a ternperature of about 2300 F. when it is immersed in the bath, and it is cooled. in the bath to F.600 F. The external pressure which isap-i plied to the liquid bath and which is maintained The cooled and hardened outer layer exerts high and irregular during the cooling period, is preferably equal to or greater than the internal pressure which is created by the cooling and contraction of the tool, which cools and contracts inwardly from. its outer periphery.

I thus produce a quenched tool which is free from internal stresses, and which has sufiicient ductility and toughness so that the tool can be used with its original high quenched hardness, without drawing or tempering.

Even if the maximum preferred condition is not secured, and the quenched tool is under some internal stress, such internal stress is much less than under ordinary quenching conditions, and only a slight tempering or drawing is required, so

that the tool has much greater hardnes than lustrate the mechanism and method of my inr vention.

Fig. l is a vertical section, partially in elevation. It shows a chamber-member, a tool-form located above the chamber-member, and a vertical ram or plunger located above the tool-form.

Fig.2 is similar to Fig. 1. It shows the toolform immersed in the quenching bath which is provided in a chamber of the chamber-member, and it shows the ram or plunger in final pressureapplying position.

Fig. 3 is a vertical section, partially in elevation, which shows a detail of the ram or plunger.

The chamber-member i is made of any metal which can withstand the applied pressure. Said chamber-member I is provided with a chamber 5, which has a bottom wall Ba. Said chamber 5 has a liquid quenching bath L, which initially fills said chamber 6 to any selected level, as up to the line 1, before the tool-form S is immersed in the quench bath L.

For convenience, the longitudinal axis of chamber 6 is shown in the vertical position. The chamber 6 has a vertical cylindrical inlet throat 9. Optionally, a tapered part 3 is provided between chamber 5 and its throat 9. Optionally, an inwardly tapered junction-part 8 is provided between chamber 6 and its throat 9. The vertical wall of throat 9 is cylindrical up to the line 9a. Above the line 90., the throat 9 is outwardly tapered to provide a bell-mouth, in order to permit easy entrance of the ram or plunger R.

The liquid quenching bath L is maintained at the selected quenching temperature by means of fluid which is circulated through a regulating chamber 3, which has an inlet 4 and an outlet 5. This chamber 3 is provided by a supplemental wall 2.

The ram or plunger R is moved up-and-down by any conventional means. The ram B. may be the ram of a hydraulic press. Said ram R has a reduced cylindrical bottom extension Re, which has an external thread H. A ring or collar I ll has an internal thread, which engages thread H. Said ring or collar [9 is made of metal which is sufficiently yielding to provide a liquid-tight sliding closure against the cylindrical wall of throat 9. Said sliding closure is also optionally air-tight.

The lower part of ram R is cylindrical and it has a close sliding fit in the cylindrical wall of throat 9.

The operation is as follows:

The steel tool-form S, which has the shape and dimensions of the desired tool, is heated to the hardening temperature which is required for the respective steel composition, according to ordinary practice.

Optionally, the tool-form S may have an extension at its top or bottom or elsewhere for convenient gripping and handling. Such extension can be removed by grinding or by other mechanical operation, after the quenching.

Thus, the tool-iorm S may have such an extension at its top end, and the ram R may have gripping means at its bottom end, for gripping the tool-form S. Also, many tools have rear ends or butt-ends, and the ram R may grip such rear end or butt-end.

Also, the tool-form B may be held above the throat 9, in the position shown in Fig. 1, by any suitable releasable gripping means, prior to the downward movement of ram R. Such gripping means may be friction means or clamping means.

The ram R is moved down to immerse the heated tool-form S in the liquid L and to apply pressure to the liquid L. The downward move-'- ment of the ram R, to the position in which it contacts with liquid L to exert pressure on said liquid, should be very rapid, so that the tool-form S is immersed in the liquid L, while the tool-form S is at the required high initial temperature.

The immersion of tool form S in the liquid L, raises the level of liquid L, so that liquid L enters the throat 9 to any selected height, and ram-extension Rd and its ring [0 contact with liquid L in throat 9.

As above noted, the sliding closure between ring it and the cylindrical wall of throat 9 is liquid-tight, and said closure may or may not be air-tight. If said closure is air-tight, there will be a layer of compressed air between the bottom ends of ram-extension Rd and rin I 0 and the top of the liquid L in throat 9. This air layer will be of very small height, due to the high compression of the air. If the sliding closure between ring ID and the cylindrical wall of throat 9 is liquid-tight but not air-tight, the bottom ends of ram-extension Rd and ring Ill will contact directly with liquid L in throat 9.

The liquid L is optionally and preferably an oil which has a high flash point, and which is compressible under the applied pressure of ram R.

The volume of the pool of liquid L may be as large as desired, to provide a compression stroke of selected length of ram R, from the beginning of the compression of liquid L until it has been finally compressed to the maximum applied pressure. Said maximum pressure is also applied as quickly as possible, so that the immersed tool-form S is subjected to said maximum pressure, simultaneously with its cooling in the bath, or as soon as possible after such cooling begins. As above noted, the pressure is maintained at its maximum value, until the tool-form S has been uniformly cooled throughout its entire mass to the selected lower temperature which is suitable for the respective steel composition.

Fig. 2 shows that the tool-form S rests upon bottom wall 611. However. the tool-form S does not have a close fit against bottom wall So, so that the entire tool-form S is surrounded with liquid L under the applied pressure, which is transmitted equally to the entire periphery of tool-form S.

Also, if the top of tool-form S is gripped by ram R. during the cooling, the lower end oi tool form S is held above wall 6a during the quenching or cooling.

The ram R may have considerable weight. The kinetic energy of the downwardly movable ram is changed into heat when the downward movement of the ram R is stopped and such heat will raise the temperature of the liquid L.

However, by using a cooling medium which is circulated in sufiicient volume and with sufficient rapidity through chamber 3, the temperature of the liquid L can be regulated within a selected range or kept at a selected temperature.

There may be a sharp temporary increase of temperature of the liquid L, during each downward compression stroke of ram R. The wall of chamber-member I is made of metal which is a good conductor of heat.

The invention also includes the treatment of a tool-form or other body which has been heated to a forging temperature or other hot-working temperature, if said tool-form or body develops internal stresses due to progressive cooling from its exterior, when said tool-form or body is cooled below said hot-working temperature. Preferably, the body is plastic or deformable under pressure, when it is at its initial temperature.

As one illustration of the advantages of my invention, if a 0.45 per cent carbon steel is quenched in water in the usual manner, such steel has 600 Brinell hardness. Such steel then requires drawing or tempering it by heating it to 800 F. for one hour per each inch of thickness. The resultant finished steel has only a 444 Brinell hardness. According to my invention, the steel tool does not require any subsequent drawing or tempering, so that it retains its original 600 Brinell hardness. Even if the steel tool requires some drawing or tempering, this is much less than in the ordinary treatment, so that the final tempered steel tool has 90% or more of its original hardness after quenching according to my improved method.

Therefore, when I refer to a steel body or tool made according to my improved method, I include a steel body or tool which either does not require drawing or tempering, or which requires only moderate drawing or tempering, to retain at least 90% of the original hardness.

Without limitation thereto, in treating steel, I prefer to treat steel which has at least substantially 0.30% by weight of carbon, and which is in the forging grade of steel, with 0.30% to 0.60% by weight of carbon.

I claim:

1. A method .of treating a steel tool-body which develops a hard and brittle martensite structure upon quenching from an elevated temperature, said steel body having a selected shape which is substantially the shape of the selected tool, which consists in heating said steel body to a temperature which is sufliciently high to develop said martensite structure by subsequent quenching, said selected original shape being substantially maintained during said heating and quenching, said steel body being quenched by immersing it wholly in a pool of quenching liquid, applying pressure to said pool substantially simultaneously with the immersion of said steel body in said pool and transmitting said pressure substantially equally through said liquid to the entire periphery of said immersed body and maintaining said pressure during said quenching, said steel body normally developing internal quenching stresses in the absence of such pressure to require tempering for the reher of quenching stresses and to recover toughness and ductility, said pressure being suflicient substantially to eliminate such internal quenching stresses.

2. A method of treating a steel tool-body which develops a hard and brittle martensite structure upon quenching from an elevated temperature, said steel body having a selected shape which is substantially the shape of the selected tool, which consists in heating said steel body to a temperature which is sufficiently high to develop said martensite structure by subsequent quenching, said selected original shape being substantially maintained during said heating and quenching, said steel body being quenched by immersing it wholly in a pool of quenching liquid, applying pressure to said pool substantially simultaneously with the immersion of said steel body in said pool and transmitting said pressure substantially equally through said liquid to the entire periphery of said immersed body and maintaining said pressure during said quenching, said steel body normally developing internal quenching stresses in the absence or such pressure to require tempering tor the relief of quenching stresses and to recover toughness and ductility, said pressure being suiiicient substantially to eliminate such internal quenching stresses, and tempering said quenched body, said pressure being sufiiciently high to require tempering only to a point at which the hardness of the tempered body in the Brinell scale is at least of the hardness of said quenched body in the Brinell scale, said quenched body being tempered while retaining at least 90% of the hardness of said quenched body in the Brinell scale.

3. A method according to claim 1, in which said steel body is made of high-speed steel.

4. A method according to claim 2, in which said steel body is made of high-speed steel.

5. A method according to claim 1, in which said steel body is made of a forging grade of steel, which has substantially 0.30% to 0.60% by weight of carbon.

6. A method according to claim 2, in which said steel body is made of a forging grade of steel, which has substantially 0.30% to 0.60% by weight of carbon.

ABRAHAM SIMONS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 405,827 Button June 25, 1889 922,655 Wolle May 25, 1909 951,768 Kranz Mar. 8, 191 1,418,985 Stock June 6, 1922 1,500,571 Brandenburg July 8, 1924 1,723,769 Davis Aug. 6, 1929 1,960,219 Hayes May 22, 1934 2,056,708 Boecker Oct. 6, 19 2,074,312 Schraishumi Mar. 16, 1937 2,225,730 Armstrong Dec. 24, 1940 2,297,686 Burgess et al. Oct. 6, 1942 2,435,511 Rice Feb. 3, 1948

Claims (1)

1. A METHOD OF TREATING A STEEL TOOL-BODY WHICH DEVELOPS A HARD AND BRITTLE MARTENSITE STRUCTURE UPON QUENCHING FROM AN ELEVATED TEMPERATURE, SAID STEEL BODY HAVING A SELECTED SHAPE WHICH IS SUBSTANTIALLY THE SHAPE OF THE SELECTED TOOL, WHICH CONSISTS IN HEATING SAID STEEL BODY TO A TEMPERATURE WHICH IS SUFFICIENTLY HIGH TO DEVELOP SAID MARTENSITE STRUCTURE BY SUBSEQUENT QUENCHING, SAID SELECTED ORIGINAL SHAPE BEING SUBSTANTIALLY MAINTAINED DURING SAID HEATING AND QUENCHING, SAID STEEL BODY BEING QUENCHED BY IMMERSING IT WHOLLY IN A POOL OF QUENCHING LIQUID, APPLYING PRESSURE TO SAID POOL SUBSTANTIALLY SIMULTANEOUSLY WITH THE IMMERSION OF SAID STEEL BODY IN SAID POOL AND TRANSMITTING SAID PRESSURE SUBSTANTIALLY EQUALLY THROUGH SAID LIQUID TO THE ENTIRE PERIPHERY OF SAID IMMERSED BODY AND MAINTAINING SAID PRESSURE DURING SAID QUENCHING, SAID STEEL BODY NORMALLY DEVELOPING INTERNAL QUENCHING STRESSES IN THE ABSENCE OF SUCH PRESSURE TO REQUIRE TEMPERING FOR THE RE-

Images