US2908565A - High temperature alloy - Google Patents

Description

Oct.;13, 1959 J. A. NELSON 2,908,565

HIGH TEMPERATURE ALLOY Filed Aug. 29,1956

7. COPPER N 0 Q l 2 3 4 5 6 7 I 8 9 [0 II I2 l3 l4 l5 COBALT INVENTOR. Jaw/y #52500 United States Patent HIGH TEMPERATURE ALLOY John A. Nelson, Braeburn,Pa., assignor to Continental Copper & Steel Industries, Inc. (Braeburn Alloy Steel Division), New York, N.Y.,' a corporation of Delaware Application August 29, 1956, Serial No. 610,042

6 Claims. (Cl. 75-125) The present invention relates to alloys for high temperature application and it particularly relates to free machining precipitation hardening alloys. The present invention will'be particularly described in regard to novel free machining cobalt-copper hardening alloys for high temperature applications which are involved in connec: tion with die casting dies, plastic molds, extrusion dies, and forging dies. r

-It,' has been found quitediflicult .to providemost'satisfactory alloys which maybe made at moderate costs and at commercial selling prices which will provide great resistance to softening under heat, while at-the same time providing ready machinability, even, though having high hardness values, and it isfamo-n'g the primaryobjects -of the present invention to provide die steel alloys of moderate costs which will combine vhigh machinability, even though very hard, with high resistance to softening under heat.

It isa further object of the present invention to pro vide novel cobalt-copper low carbon alloy steels which have a particular application for hot work applications and which will be highly resistant to heat checking, which will;be subject to aminimum distortion on heat treatment, which will be abrasion resistant,- which will have a minimum tendency to stick or solder to thework, which may be polished tojhigh mirror finish,- and, which will be highly resistant bothto corrosion and heat checking.

A particular object of the present invention is to provide novel, free machining, precipitation hardening alloy steels for high temperature applications which may be most desirability utilized for dies for such hot work applications as die casting, extrusions, forgings, and moulded plastics Stillfurther objects and advantages will appear in the more detailed description set forth below, it being understood, however, that this more detailed descriptionis given byway. of illustration and explanation only and not-by way of limitation, since various changes therein may be made by those skilled in the art without departing from the scope and spirit of the present invention.

In accomplishing the above objectsit has been found that at least 2 /2 of cobalt and desirably about 4 to 6% cobalt is eflfective. Copper in amounts ranging from about A to /2 of the cobalt content is also effective in contributing to precipitation hardening and free machining qualities.

While the addition of copper is efiective and is included in the preferred analysis, desirable properties for some applications can be obtained with cobalt alone in the absence of copper.

' In the preferred alloy the carbon content is low, desirably less than about .15 Chromium and molybdenum is added with or without tungsten and nickel.

The essential feature of the present invention is to provide novel, free machining, precipitation hardeningfalloys ICC peratures up to about 1500 F.,Machining is usually done after suitable solution heat treatment. Upon age hardening, hardnesses up to about 50 Rockwell C are obtained with. a negligible or a minimum amount of distortion from heat treatment.

It is found that the alloy has the desirable proper-ties which are most effective when there is a substantial absence in the alloy of sulphur, lead, selenium, tellurium or silver, and when there is also-substantially absent, or in very low amounts, carbon, manganese, silicon and "vanadium inquantities less than 0.5% and desirably not'exceeding 0.2%, and when any nickelthat maybe present is.in amounts less than 1% and desirably in theneighborhood of 0.5% or less. 1 The drawing is a diagrammatic chart disclosing the preferred range and the widest specified range in cobalt and copper to obtain the desired effect.

These alloys in addition have excellent polishability and freedom from heat checking in use. V

The most important feature of thepresent invention resides in the discovery-that cobalt above about 2%% .and' less than about 8%, and preferably with copper in minor proportion will give these unusual and desirable properties. 7

The copper should preferably be added in amounts at least in excess of its solid solubility in the steel.

Cooper in amounts less than about /z% is not most effective in imparting free machining characteristics. Above 4 or 5%, hot working difliculties are encountered. The preferred range of copper in the alloy should be from /2% to 2%%.

With the addition ofl to 3% of copper, cobalt in the preferredrange 4 to 6% will result in hardnesses up to about 5'0 Rockwell C after suitable solution and aging treatments.

Nickel may be added up to about 1% to enhanceage a hardening and to improve forgea'bility. The nickel conplications. Said alloys are particularly useful at temtent should be about half of the copper content for max imum eifectiveness in avoiding cracking on forging or other hot working operations.

For maximum age hardening characteristics. thelcarbon should, be kept low,'preferably less than about'.15%.f

With over'.30% carbon substantially lower hardness will result on age hardening. t

,Cobalt should be added in amounts inexcess of about 2 /z% and, preferably in the range of about 4 to 6%.

, Copper in amounts less than /z% is relatively inefiective and copper in the preferred analysis is added in amounts ranging from about 1 /2 to 2%%. The ratio of copper to cobalt should be in the range of 1:5 to 1:2.

Molybdenum with or without tungsten constitutes an important addition. Molybdenum in excess of about 3% results in alloy steels which are less machinable and the molybdenum content therefore should be lessthan about 3 /2%. Also, if tungsten is included it should vdesirably be less than the molybdenum content. Suitable results areobtained with the ratio of molybdenum 'to tungsten substantially in the ratio of 5:4 or 4:3.

Chromium contributesto age hardeningand may-be present up to about 6%. 'Best machining characteristics are achieved where the chromium content exceeds the molybdenum content and preferably the excess of chromiumover molybdenum should be in the ratio of 5:4 or greater.

Vanadium should be kept relatively low, less than 1%. Likewise manganese and silicon are kept relatively low, not over about 1%. Vanadium, manganese, and

silicon are not of critical importance and may be present in somewhat larger amounts than the preferred range cited without detracting from the advantageous properties of the alloy.

Phosphorusand sulphur do not normally exceed about I Patented Oct. 13, 1959 .03% each, and in this range their effect is minor. Aluminum may be added in small amounts up to about 5% Aluminum acts as a deoxidizer in melting and also contributes somewhat to age hardening. A

Example 1 Preferred Range Broad Range Less than about .15%. Less than about .60% Less than about 60%-.

Below about .30%. Below about 1.00%. Below about 1.00%.

About 2 to 4% Below about 6%. About 1 to 2% Below about 3%. About .75 to 2.75% Below about 5%. Less than about .50% Below about 1%. About 4 to 6% About 2% to 8%.

Below about 2%.

About .50 About 1% to 2%% About to 4%.

Balance substantially iron. I

All'percentages by weight. p

The above alloy steels have excellent machinability at high'hardness and retention of hardness at elevated temperatures. They may. also include other" ferrite forming alloying elements such as titanium or columbium in restricted amounts without detrimentally afiecting the machinability.

As set forth above, the molybdenum should be below' but desirably it should be keptless than Il /2% sincev if the percentage is in excess of 3 /2%, the steel is less machinable. The preferred .range of molybdenum is .75 to 2.75%. I

Preferably the cobalt should be present in a minimum percentage of 2% but in most instances the minimum percentageshould preferably be 2 /2% of cobalt.

On the other hand, the copper, nickel and tungsten should be present in a maximum percentage of 4 /2 3 and 5% respectively, with the preferred maximum of each of these elements not exceeding in the preferred alloy 4%, 2% and 3%.

In respect to the combined cobalt and copper, it should at all 'times be in the range of 2 to 15%, although preferably it'should be in the range of 2 /2 to 12%.

Example II Asa specific steel alloy melted and tested according to the present'invention, the following is cited:

Balance substantially iron.

- Steels conforming to these proportions possess characteristics which-are outstanding for hot work die steels for die casting, extrusion, metal forming and other high temperature applications. These steels are precipitation hardening and may be furnished in a variety of -conditions. Such steels can'be solution treated at tempera- 4 tures about 1850 F. followed by air cooling to a hardness in the range of about 40/45 Rockwell C. In this condition the steels are very readily machinable.

After machining the die may be aged or tempered at about between 1000 F. and 1050 F. for a Rockwell C hardness of about 50. The distortion on heat treating is negligible and is much less than is found on steels which harden by the formation of martensite from austenite.

Example III As a third example the following percentages by weight may be included:

These steels machine very well in the as forged condition at about 41 to 44 Rockwell C, following which they may be aged or tempered to desired hardnesses up to about 50 Rockwell C.

Another variation in heat treating consists in hardening andv tempering to about 41 to 44 Rockwell C after which the impression may be machined by the consumer and then the die is used without further tempering.

Secondary hardening or aging takes place by the heat imparted to the die surfaces from contact with hot metal in use. This develops hard surface at about 50 Rockwell C and a softer core to withstand shock at about 43 Rockwell C.

Side rake angle degrees 8 Back rake angle do 5 Side relief angle do 6 End relief'angle do 8 End cutting edge angle do 12 Nose radium I inches..- 5

Surface R.p.m Depth of Cut Speed, Result .Imin.

212 .050 of an inch 176 Cut without failure. 328 .010 of an inch 257 Do. 328 .025 of an inch"... 215 Do.

As a further example of the excellent machinability of this steel at 42 Rockwell C, drill tests were conducted using a %4-ll'l0h diameter drill at 500 r.p.m. The material drilled very easily with very little generation of heat.

The present invention dilfers from high cobalt, low carbon machinable steels disclosed in US. Patent No. 2,598,714, issued to John A. Nelson and Charles W. Sch'uck, in the provision of copper in combination with cobalt.

Whereas the low carbon steels disclosed in US. Patent No. 2,598,714 contain about 16 to 30% cobalt together with. Smaller amounts of chromium, molybdenum, vanadi- 5 am, and tungsten and may be hardened up to a maximum of about 62 Rockell C, the alloy steels of the present invention are used at substantially lower hardnesses in the range up to about 5 Rockwell C and have a considerably lower cobalt content.

It will be noted that the present invention achieves free machining properties without sulphur, lead, selenium, tell urium or silver, all of which have been proven unsatisfactory for many purposes.

For example, sulphur makes the steel hot short increasing greatly the difliculties on hot working. Sulphur also adversely affects the transverse impact strength and contributes to pitting and surface blemishes on die cavities which are highly polished such as plastic molds or die casting dies.

Lead :gives rise to toxic fumes and because of its high specific gravity as compared with steel, the lead tends to segregate and give uneven and ununiform steels, particularly in large sections.

Selenium and tellurium also give toxic fumes. Silver has never proved practicable for free machining characteristics.

Surprisingly by use of cobalt, copper combinations, a novel steel composition is provided which has the un usual characteristics of a free machining precipitation hardening alloy which is substantially free from distortion on heat treating. It may be agedor tempered at 1050 F. after solution treating to give a hardness of about Rockwell C 50.

As many changes could be made in the above high temperature alloys, and many widely difierent embodiments of this invention could be made without depart ment from the scope of the claims, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

Having now particularly described and ascertained the nature of the invention, and in what manner the same is to be performed, what is claimed is:

1. A free machining precipitationhardening cobaltcopper alloy die steel, and capable of being polished to high mirror finish and capable of being aged and tempered at about or above 1,000 F. to a Rockwell C hardness of about 50, composed principally of iron alloyed with cobalt, nickel, carbon and copper, the cobalt and copper together ranging from 2 to 15% and the cobalt being present in about three times the quantity of the copper, nickel being included in amount ranging up to about one-half the percentage of the copper, balance principally iron.

2. A free machining precipitation hardening cobaltcopper alloy die steel, and capable of being polished to high mirror finish and capable of being aged and tempered at about or above 1,000 F. to a Rockwell C hardness of about 50, composed particularly of iron not over about .25 carbon, about 1 to 6% chromium, not over 3% tungsten, not over 5% molybdenum, about 2 to 8% cobalt, about /2 to 4%% copper and not over 3% nickel, the copper being present in an amount approximately one-third of the cobalt content and the ratio of molybdenum to tungsten being about 5 :4, balance principally iron.

3. A tree machining precipitation hardening cobalthigh mirror finish and capable of being aged and tem-,

pered at about or above 1,000 F. to a Rockwell C hardness of about 50, composed particularly of iron and less than about .25% carbon, about 1 to 6% chromium, about 2 to 8% cobalt, less than 4% tungsten, less than 5% molybdenum and copper in an amount in excess of its solid solubility in said steel but not over about 4 /2% and the remainder iron, the copper being present in an amount approximately one-third of the cobalt content and the ratio of molybdenum to tungsten being about 5:4.

5. A free machining precipitation hardening cobaltcopper alloy die steel, and capable of being polished to high mirror finish and capable of being aged and tempered at about or above 1,000" F. to a Rockwell C hardness of about 50, composed particularly of iron and not over about .25 carbon, about 1 to 6% chromium, about 2 to 8% cobalt, about /2 to 4 /2 copper, l to 5% tungsten, 1 to 5% molybdenum, in which the ratio of molybdenum to tungsten is 5 :4, and copper in an amount approximately one-third of the cobalt content, balance principally iron.

6. A free machining, precipitation hardening cobaltcopper alloy die steel capable of being polished to a high mirror finish and capable of being aged and tempered at about or above 1000 F. to a Rockwell C hardness of about 50, comprising principally iron, carbon, cobalt and nickel in the following proportions by weight:

Cobalt, 2 /2 to 6%.

Copper, A to of the cobalt content Carbon, less than about 0.15%

Chromium, up to 6% Vanadium, less than 1% Manganese, less than 1% Silicon, less than 1% Molybdenum, less than 3 .6%

Tungsten in a ratio of between 5:4 and 4:3 to the molybdenum Balance principally iron.

References Cited in the file of this patent UNITED STATES PATENTS 2,197,098 Davis et al. Apr. 16, 1940 2,565,264 Payson Au 21, 1951 2,697,035 Clarke D c. 14, 1954 FOREIGN PATENTS 677,967 France 2. Dec. 19, 1929 OTHER REFERENCES Gregg et al.: Alloys of Iron and Copper, pages 97 and 160, 1934. Published by McGraw-Hill, New York, NY.

Claims (1)

1. A FREE MACHINING PRECIPITATION HARDENING COBALTCOPPER ALLOY DIE STEEL, AND CAPABLE OF BEING POLISHED TO HIGH MIRROR FINISH AND CAPABLE OF BEING AGED AND TEMPERED AT ABOUT OR HAVE 1,000* F. TO A ROCKWELL C HARDNESS OF ABOUT 50, COMPOSED PRINCIPALLY OF IRON ALLOYED WITH COBALT, NICKEL, CARBON AND COPPER, THE COBALT AND COPPER TOGETHER RANGING FROM 2 TO 15% AND THE COBALT BEING PRESENT IN ABOUT THREE TIMES THE QUANTITY OF THE COPPER, NICKEL BEING INCLUDED IN AMOUNT RANGING UP TO ABOUT ONE-HALF THE PERCENTAGE OF THE COPPER, BALANCE PRINCIPALLY IRON.

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