US2160423A - Alloy - Google Patents

Description

Patented May 30,1939

UNITED STATES PATENT OFFICE ALLOY California No Drawing.

18 Claims.

This invention relates to alloys and to that general class of alloys known as cobalt-chromiumtun'gsten alloys. It concerns such alloys as are highly suitable for use in welding rod form for hard facing and which may also be used in castings for various purposes. For many years cobalt-chromium-tungsten alloys have been used for hard facing and for casting and the characteristics of these alloys generally as to hardness, red hardness, toughness, weldability, corrosion resistance, and abrasion resistance are well known. In many instances, however, the use of cobalt-chromium-tungsten alloys is either impractical or prohibitive because of their expense due to the fact that the high cost of the component ingredients: cobalt, chromium, and tungsten; requires that the price of these alloys be relatively high.

In order to reduce the cost of cobalt-chromiumtungsten alloys, it has been proposed to dilute them with iron. However, when iron alone is introduced into alloys of cobalt, chromium and I tunsten in suflicient quantities so as to materially lower the cost, desirable characteristics of the cobalt-chromium-tungsten alloys are either lost or so vitally affected that the resulting composition has little value. We have discovered that it is possible to produce an alloy of iron, cobalt,

chromium and tungsten wherein there is a relatively large proportion of iron reducing the cost of the resulting composition, and that if other ingredients are added all of the desirable characteristics of cobalt-chromium-tungsten alloys can be retained and in some respects rendered superior to those of cobalt-chromium-tungsten alloys.

It is, therefore, an object of this invention to'provide an alloy which is highly suitable for use in welding rod form and which may be also suitably used in castings which while containing a relatively large amount of iron in conjunction with cobalt, chromium, and tungsten so as to reduce the cost of the composition will, by the addition of other ingredients, possess all the reasonably desirable characteristics as to hardness, red hardness, commensurate toughness, welda-w bility, castability, corrosion resistance, ,and abrasion resistance.

The situations where hard facing is used vary greatly and the same is true where the alloy is Application January 25, 1937, Serial No. 122,212

made into castings for various purposes. In some instances the hard facing and even castings are. subject to impact shocks as well as abrasion and, therefore, the alloy when used as a hard facing must be as tough as possible as well as hard and abrasion resistant. In the other extreme a hard facing may not be subject to impact or severe shock but to conditions requiring that it be extremely hard but not necessarily extremely tough. There are many situations between these two extremes where a hard facing is required to be as tough and as hard as it is possible to have these characteristics simultaneously present. As a general rule in hard alloys and in hard facing, extreme hardness results in increased'brittleness and reduced toughness and, conversely, increased toughness is obtained only from a sacrifice in hardness. It will, therefore, be understood that the welder or a person using an alloy for hard facing purposes is expected to exercise his judgment as to the proper hard facing alloy to use to fit the circumstances, that is, he is expected to judge from the proposed uses of the tool that he desires to hard face whether the hard facing should have a maximum toughness and yet be hard or a maximum hardness at a sacrifice of toughness or whether, it should be of medium hardness and commensurate medium toughness.

In order to satisfy varying conditions our invention is embodied in three preferred alloys which are preferably made in welding rod form for purposes of hard facing, or which may be in the form of ingots when the alloy is to be used for casting purposes. To these three alloys we have applied the trade names Stoodite Stoodite 54, and Stoodite 63 for purposes of distinguishing them. Typical chemical analyses of these three alloys embodying the invention are There may be present small amounts of impurities such as are frequently present in alloys of this general character, such as for example: manganese, silicon, phosphorus, and sulphur. But if these impurities are present at all in the preferred alloys the manganese content should not exceed one-half percent, the silicon content should not exceed one-half percent, the phosphorus content should not exceed one-tenth percent, and the sulphur content should not exceed one-tenth percent. While these alloys conceivably can be made up by mixing together proper percentages of their component ingredients and melting them together, we prefer to use the cheaper ferro alloys where possible. Our preferred method of making up the alloys is to thoroughly mix together charges of substantially the following proportions:

Stoodite Stoodite 54 Stoodite 63 Cobalt 3 lb. 3 lb. 2 lb. Ferrochromium (69.1 percent chromium) 2 lb. 8 oz. 2 lb. 8 oz. 1 lb. 7 oz. Forte-tungsten (82.16 percent tungsten) 1 lb. 4 oz. 1 lb. 4 oz. 2 lb. 8 oz. Farm-molybdenum (60.7 percent molybdenum) 2 oz. 10 oz. 1 lb. 7 oz. Ferro-vanadium (40.2 percent vanadium) 8 oz. 8 oz. 8 oz. Carbon 10 grams 1% oz. 3 oz. Iron 3 lb. 2 oz. 2 lb. 8 oz. 2 lb. 2 oz.

Each charge for each alloy is thoroughly mixed and then one or more charges of the mixture for the desired alloy is dumped into an electric furnace. The furnace that we have used successfully is eight inches in diameter and ten inches in depth. A two-inch carbon electrode is used and contact made between the electrode and the metal. When the metal becomes fully molten it is poured into chills.- We advantageously use for this purpose centrifugal chills to cash the alloy into welding rod form. During the melting operation in the furnace there are furnace losses of ingredients and these vary somewhat from time to time. The differences between the charge amount of an ingredient as noted above and the chemical analyses as above given are due to these furnace losses. Particularly noticeable is the molybdenum furnace loss in "Stoodite 63. How ever, after the furnace losses take place typical chemical analyses of the resulting alloys are as above given.

The Stoodite 45 has a hardness that varies somewhat, ranging usually from 40 to 48 on the C scale of the Rockwell hardness testing machine. As it is quite tough with relation to its hardness it is most suitably used where the hard facing is subject to impact and severe shock. Suitable uses for which Stoodite 45 is especially suited are to drop and trip hammer dies, hot trimming dies, valve seats, and in fact for virtually any tool that is subject to a great amount of impact shock as well as abrasion.

Stoodite 54 also has a varying hardness ranging usually between 53 and 58 on the C scale of the Rockwell. This alloy, having medium hardness and medium toughness, may be very advantageously used under a large variety of circumstances where maximum toughness together with maximum hardness are required. It may be very advantageously used for many types of machine tools for cutting all sorts of plain steels, cast irons, and for cutting alloy steels having hardness values up to 30 on the Rockwell C scale. It is excellent for surfacing lathe centers and it is also suitable for application to cert in typ s of dies where friction rather than severe impact is encountered.

Stoodite 63 has a hardness ranging from 62 to 69 and sometimes higher on the Rockwell C scale. It is extremely hard, being one of the hardest homogeneous alloys that can be successfully used for hard facing. It is even harder than most cobalt-chromium-tungsten alloys. However, as toughness has been sacrificed somewhat its use is restricted largely to situations where there is littleor no shock or impact. It may be very advantageously used on machine tools to machine high manganese steels (11 to 13% manganese), heat treated alloy steels, chilled cast iron and the like. It is not recommended for use where intermittent cutting is required.

It will be noted that the chemical composition of Stoodite 54 difiers from the chemical composition of Stoodite 45 most notably in the percentages of molybdenum, vanadium, carbon, and iron, and while these differences are small, a marked change in the hardness and a change in the toughness is present. The change in hardness is mostly attributable to the change in the carbon content and it would seem to logically follow that by merely increasing the carbon content above that in Stoodite 54 without materially changing the percentages of other ingredients we would produce an alloy having the hardness of Stoodite 63. Experiments in this direction disclose that by merely increasing the carbon content in the composition of Stoodite 54 we can secure an alloy having the hardness of Stoodite 63. However, when this increased hardness is accomplished by merely increasing the carbon, increased brittleness results. Therefore, when extreme hardness is desired, such as that which we secure in Stoodite 63, we find it advantageous, not only to increase the carbon content but to reduce the cobalt and chromium content and increase the molybdenum tungsten content and thus we can avoid increased brittleness in securing the desired hardness.

It is impossible to state with certainty the functions of each ingredient in the presence of the others in the proportions given. However, by comparison of the function that each ingredient has in other analogous alloys and by determining the effect where an ingredient is materially reduced or omitted from the proportions given, the following functions of the ingredients appear to be true:

The cobalt tends to make the rod run well in welding. As it lowers the melting point the-rod runs smoothly during the welding operation, producing smooth beads. The cobalt contributes to toughness and gives to the alloy the desired metallic color. If absent, the color of the surface of a welded bead of alloy is black or agreenish-black whereas when the cobalt is present the surface color is steely in appearance very much the same as that of fine grade alloy steels.

Chromium contributes to abrasion resistance, which is probably due to the formation of chromium carbides. These incidentally have some effect upon the hardness. Molybdenum is included primarily for the purpose of promoting fluidity of the alloy while it is molten and during the welding operation. By increasing the fluidity, very thin hard facing deposits may be made where occasion requires and thus the amuse able for casting such articles as dental plates,

die in a very thin deposit so that in subsequently grinding the hard facing to the finished surface very little grinding is necessary.

Molybdenum incidentally contributes to hardness. In this connection it is known that in many situations molybdenum is an equivalent of tungsten. Thus, where tungsten is present molybdenum will produce the effect of approximately twice its weight in tungsten. Such an effect is recognized in United States Letters Patent No. 1,937,334 issued November 28, 1933, to Emmons. Whether the molybdenum has such an effect in the present alloy we cannot definitely state but it is very likely that at least a portion of it does have this effect, thus enabling a smaller percentage of tungsten to be used although retaining desirable effects of larger amounts of tungsten. In this way an elevation of the melting point which tungsten produces is'somewhat avoided.

The tungsten ingredient contributes to hardness and red hardness. These alloys not only have the hardness as stated for them but in addition they are red hard in that they remain hard even though heated to quite high temperatures. We have experienced cutting tools faced with these alloys-continuing to out even when heated to temperatures estimated to be in excess of 1800 F. This characteristic enables these a1- loys to be very advantageously used where cutting or abrasion resistance must be performed under very high temperature conditions.

The vanadium contributes to toughness and also to red hardness. The vanadium also acts as a deoxidizer. While this ingredient could conccivably be omitted, its omission results in a marked decrease in toughness.

The carbon present functions very much th same as in most steels, that is, it combines with the carbide-forming ingredients to form carbides. The iron forms the body and if the alloy is considered as being a solid solution it acts as the solvent for the other ingredients. We find that the amount of iron used must be between 40 and 50 percent to obtain best results. Thus, a decrease in iron below 40 percent results in a marked increase in brittleness and, conversely, an

increase in iron above fifty percent results in a decrease in abrasion resistance.

Welding rods made from these alloys as above described can be readily applied by any welder experienced in hard facing. No particular skill or special technique is required for their use. The welder should use, however, a definitely carbonizing oxyacetylene welding flame and should exercise ordinary precautions to .work out all oxides that tend to form.

Welding rods formed of these alloys are not extremely brittle, In each instance it is possible to definitely bend the welding rod before it breaks. This characteristic is of great importance in casting the alloy in welding rod form by means of chills, particularly centrifugal chills. Due to the fact that the welding rods are susceptible of being bent before breaking, any tendency to warp on cooling in the chills does not result in broken rods in the chills. Where a rod is extremely brittle difficulty is experienced in recovering rods of full lengths from the'chills. No such difliculty is experienced in casting rods from the present alloys.

While the alloys as above described are highly suitable for use in hard facing when made in welding rod form we find that these alloys also produce very fine castings. The fine grain of the alloys is such as to render these alloys highly suitremovable bridge work, and like articles. This is especially true of the alloy identified herein as Stoodite 45. The hardness, corrosion resistance,

and the ability of the alloy to retain some degree of ductility enables its being advantageously used for this and analogous purposes.

While the described compositions preferably have the ingredients present in the percentages as above given the percentages of ingredients may vary. Variations in the percentages of the ingredients bring about small changes in the characteristics of the alloy. However, it does not necessarily follow that an increase or decrease in any given ingredient will necessarily increase or decrease the function attributed to it as above. From our experiments, many of the advantageous characteristics of the preferred composition may be retained even though the percentages of the ingredients may vary through the following We claim:

1. A welding rod composed of an alloy comprising iron between 40 and 50%, substantial amounts of cobalt, chromium, and tungsten aggregating between 40 and 50%, there being also present molybedenum, vanadium, and carbon.

2. A welding rod composed of an alloy comprising more than two-fifths iron; cobalt, chromium and tungsten aggregating more than two-fifths of the whole composition, and the balance mainly molybdenum, vanadium, and carbon.

3. A welding rod composed of an alloy comprising between 40 and 50% iron, substantial amounts of cobalt, chromium, and tungsten, with the cobalt present in greater amount by weight than either the chromium or tungsten, the cobalt, chromium, and tungsten contents aggregating more than two-fifths of the whole composition, there being also present molybdenum, vanadium, and carbon.

4. A welding rod composed of an allow comprising, roughly, two-fifths iron; cobalt, chromium, and tugnsten aggregating in amount slightly in excess of the iron content, the balance being mainly composed of molybdenum, vanadium, and

- carbon.

Per cent Caball- 26.28

- Chromi m 15.42

Molyb n m .32

Tungsten 9.51 Vanadium 1.83

Carbon 1.41

and the balance principally iron.

'1. A welding rod producing a welding deposit having a hardness of approximately 54 on the Rockwell C scale and containing the following ingredients in approximately the following percentages:

Per cent Cnhali' 26.06 Chromium 15.77 Molyhd Prmm 1,88 Tungst 10.04 Vanadium. 2.27 Carb 2.30

and the balance principally iron.

8., A welding rod producing a welding deposit having a hardness of approximately 63 on the Rockwell Crcale and containing the following ingredients in approximately the following percentages:

Per cent Coba 18.90 Chromium 9.88 Molybden 6.29 Tungs 18.11 Vanadi 2.05 Carbo 2.99

and the balance principally iron.

9. A welding rod composition producing a welded deposit having a hardness of approximately 45 on the Rockwell C scale and containing 10. A welding rod composition producing a welded deposit having a hardness of approximately 54 on the Rockwell C scale and containing the following ingredients within the following percentages:

Per cent Cobalt 15 to 40 Chromium 9 to Molyb 1 to 5 Tungsten 5 to 15 Vanadiu 1 to 3 Carb .50 to 3.5 Iron 40 to 50 11. A welding rod composition producing a welded deposit having a hardness of approximately 63 on the Rockwell C scale and containing the following ingredients within the following percentages:

12. A welding rod composed of an alloy comprising iron between 40 and 50%, chromium and tungsten aggregating about 26%, cobalt in excess of each of the chromium and tungsten ingredients and the balance being molybednum, vanadium, and. carbon.

13. A welding rod composed of an alloy com prising iron between 40 and 50%, cobalt and tungsten aggregating about chromium, molybdenum, vanadium, and carbon.

14. A welding rod composed of an alloy comprising iron between and cobalt and tungsten aggregating about 36%, chromium, molybdenum, vanadium, and carbon, the chromium content being in excess of the molybdenum content.

15. A welding rod composed of an alloy comprising iron between 40 and 50%, molybdenum, vanadium, and cobalt aggregating less than 20%, cobalt, chromium, and tungsten each being present in substantial amounts.

16. A welding rod composed of an alloy comprising iron between 40 and 50%, molybdenum, vanadium, and cobalt aggregating less than 20%, cobalt, chromium, and tungsten each being present in substantial amounts, with the cobalt present in excess of either of the chromium and tungsten ingredients.

17. A welding rod composed of an alloy comprising iron between 40 and 50%, molybdenum, vanadium, and cobalt aggregating less than 20%, cobalt, chromium, and tungsten each being present in substantial amounts, and each being present in excess of the molybdenum content.

18. A welding rod composed of an alloy comprising iron between 40 and 50%, molybdenum,

vanadium, and cobalt aggregating less than 20%,

cobalt, chromium, and tungsten each being present in substantial amounts, with the cobalt present in excess of either of the chromium and tungsten ingredients, and each of the cobalt, chromium, and tungsten ingredients being pres ent in excess of the molybdenum content.

JOHN R. SPENCE.

WINSTON F. STOODY.