US3012880A

US3012880A - Iron-base alloy

Info

Publication number: US3012880A
Application number: US71993A
Authority: US
Inventors: Jerome K Elbaum; Russel P Culbertson
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1960-11-28
Filing date: 1960-11-28
Publication date: 1961-12-12
Anticipated expiration: 1978-12-12
Also published as: GB917154A; DE1209756B; DE1209756C2; CH406649A

Description

Dec. 12, 1961 J. K. ELBAUM ErAL 3,012,880

IRON-BASE ALLOY Filed Nov. 28, 1960 INVENTORS JEROME K. ELBAUM RUSSEL F? CULBERTSON "F WA. Fwy.

A T TOR/gr pea 3,012,880 RON-BASE ALLOY Jerome K. Elbaum and Russel P. Culbertson, Kokonlo,

Ind, assiguors to Union Carbide Corporation, a corporation of New York Filed Nov. 28, 1960, Ser. No. 71,993 8 Claims. (Cl. 75--126) This invention relates to an iron-base alloy having high hardness and wear resistance and characterized by excellent fabricability.

Wear-resistant iron-base alloys are currently designed according to their intended uses. The uses may vary from cast wear-resisting articles to wear resistant surfaces applied to softer metals by welding and metal spraying techniques. It would be invaluable to have one ironbase alloy having all the properties needed for each of these specialized applications.

One very important use of wear-resistant materials is in surfacing valves and valve lifters used in internal combustion engines.

FIG. 1 is a partially-sectioned front elevation view of a valve lifter. A valve lifter 10 is subject to severe conditions of service including friction, wear, impact and heat, particularly in the face area 11. When the face area becomes worn the entire lifter must be replaced or the face area can be resurfaced with a wear-resistant metal. One method for resurfacing such parts is by grinding a depression 12 into which is placed powdered metal. The part is then heated in an upright position until the metal powder melts aind metallurgically bonds to the article. After cooling the fused deposit may be finished by grind- 1111".

FIG. 2 shows an exhaust valve in a partially sectioned front elevation view. The exhaust valve 13 is particularly subject to wear in the valve area 14. Such a part is resurfaced by first grinding away a recess at the seat area15. A ring-like dam 16 is positioned around the seat area and metal powder 1'7 is placed in the pocket thus formed. Heat is applied to fuse and metallurgically bond the metal powder to the recessed area. After cooling, the dam is removed and the valve restored to its desired shape by grinding away the excess resurfacing metal.

Diiilculty arises in these resurfacing processes in that the high temperatures, 2200 F. to 2400 F., required to fuse the metal powders sometimes tend to distort the article being resurfaced and may even cause local melting of the part. The class of alloys available for such use as surfacers generally have depositing temperatures in this range.

it is the primary object of this invention, therefore, to provide an iron-base alloy which is easily cast and also producible as prealloyed powder for spray hard facing applications, which alloy is hard, wear-resistant and low in cost.

It is also an object of this invention to provide an ironbase wear resistant alloy especially suited for surfacing valve lifters and valves used in internal combustion engines as well as other parts which must resist abrasion, corrosion and impact.

Other aims and advantages of the invention will be apparent from the following description and the appended claims.

In accordance with these objects an iron-base alloy is provided consisting essentially by weight of from 13 to 21 percent chromium, from 12 to 19 percent in the aggregate of molybdenum and tungsten, up to 10 percent cobalt, up to 4 percent vanadium, up to 1.75 percent maximum of nickel, from 0.2 to 1.8 percent boron, from 1.8 to 4 percent carbon, from 0.4 to 1.8 percent silicon,

3,12,880 Patented Dec. 12, lfifil the boron, carbon, and silicon contents having the following relationship B+0.25C+0.5Si=from 0.85 to 3.70

wherein B is the percent boron, C is the percent carbon, and Si is the percent silicon, and the balance substantially all iron in a minimum amount of about 38 percent and incidental impurities. The relationship of boron, carbon, and silicon contents is hereinafter called the balance factor.

In a preferred embodiment of the invention the alloy consists essentially by weight of from 15.5 to 18.5 percent chromium, from 14.5 to 17.5 percent in the aggregate of molybdenum and tungsten, from 5.25 to 7.25 percent cobalt, from 1.6 to 2.1 percent vanadium, up to 1.75 percent maximum of nickel, from 0.5 to 1 percent boron, from 2.85 to 3.25 percent carbon, from 0.6 to 1 percent silicon, the boron, carbon, and silicon contents having the following relationship B+0.25C+0.5Si=from 1.51 to 2.31

vention are shown along with alloys not within the range of the invention. All of the alloys shown in Table 1 have a chromium content of 17 percent by weight and a molybdenum content of 16 percent by weight and the balance iron. The alloy compositions were deposited on mild steel by a hard facing operation and were ground level for hardness testing. Since there was some dilution of the alloy by the iron of the steel base, the hardnesses are less than those of the undiluted alloy.

The molybdenum content of the alloy contributes to strength and hardness. A broad range of 12 to 19 percent tungsten plus molybdenum is allowed but 16 percent molybdenum is preferred. Molybdenum or tungsten contents over 20 percent do not appreciably improve the hardness or strength.

The chromium content serves to improve corrosion resistance. As the chromium content is increased, corrosion resistance is increased; however, chromium contents much above 22 percent tend to decrease weldability of the alloy and are to be avoided. The chromium content is 17 percent in the preferred alloy composition.

Wear resistance of the alloys is enhanced by the addition of vanadium as a carbide former. Additionally the vanadium promotes a finer grain structure. For uses where such considerations are important a vanadium content of from 1.65 to 2.1, and specifically 1.9 percent, is preferred. In applications where grain size is not a critical characteristic, vanadium may be replaced by iron. In Table 1 alloy E contains no vanadium, but still has desirable hardness characteristics.

Cobalt serves as a high-temperature strengthener and promotes hot hardness retentivity of the alloys. The preferred cobalt content is up to 10 percent and specifically about 6.25 percent. In those applications where hot hardness is not critical and where cobalt is undesirable, the cobalt content may be replaced in whole or part by iron. Alloy G of Table 1, which contains no cobalt is seen to possess as high a room temperature hardness as cobalt-containing alloys A or D.

TABLEI Al y o po i on Constituents, percent by- Alloy Alloy Alloy Alloy Alloy Alloy Alloy weight A B O F G 6. 25 6. 25 9. 80 6. 25 6. 25 nil 2.92 1.75 1.75 1.75 1.75 1.75 1.9 1.9 1. 9 nil 1.9 1.9 2. 98 3.00 2. 04 2.76 3.0 3.0 .03 .80; .63 .78 .80 .80 1.08 56 72 l. 53 nil 75 Balance Factor 2. 28 1. 73 1. 67 2. 01 1.15 1 9 Hardness, Rockwell 0,. 67 6 57 69 66. G8 60 67 Melting Range, "F

Liquidus- 2, 130 2, 160 2, 075 ,110 Depositing Temperature,

F; Minimum. 2,090 2,090 2, 000 2, 090 2,000 2,190 2, 090 Heat Treatment required for Maximum Hardness none none none none none 1 yes none 1 Max. 2 1,950 F. for 1 hour. Rapid Air 0001.

of the alloy. Higher carbon contents promote'the forma tion of embrittling massive carbides and/or graphite. Furthermore the boron content must be within the range 0.2 to 1.8 percent to increase the hardness, lower themelting point, increasethe fluidity of the molten metal and, as the principal fluxing agent, to promote fusion and Weldability. The boron-freealloy F of Table 1 does not possess adequate hardness although the constituents other than boron are in the-prescribed ranges. Boron then is an essential ingredient of the alloy'and is preferably present in an amount from 0.5 to 1 percent. Silicon serves to lower the viscosity of theliquid metal, lower the melting point, promote alloying and, as a fluxing agent, promotes the removal of oxygen from the liquid metal. It is the combined effects of the carbon, boron, and silicon in the alloy which impart the desired characteristics of the liquid metal. Although there is a range for each of these elements the total content must be controlled to satisfy the relationship:

B+0.25C+0.5Si=from .85 to 3.7 and preferably from 1.5 to 2.3

This balance factor is based on the atomic relationshipof the elements asthey interact-in the alloy. AS3311 ex: ample of the less than satisfactory properties produced in an alloy when the required range of these elements and the balance factor are not satisfied, reference is made to alloy F with a balancefactor of 1.15 and no boron; This alloy possesses inferior'hardness because of the boron deficiency and a higher melting range anddeposic' ing temperature than the other examples. Alloy C, which possesses about the same carbon and silicon contentsas alloy F, has a relatively low boron content of 0.56 percent. This boron content is lower than the preferred boron content of 0.75 but is sufficient to lower the melting range and depositing temperature. This is evidenced by the increase in the balance factor of alloy C to 1.73 compared to 1.15 for alloy F. Boron is given a full value in the balance factor compared to lesser values for carbon (0.25) and silicon (0.5) thereby reflecting the greater effectiveness of boron in this regard. This example serves to demonstrate the effectiveness of the balance factor in the designof this alloy. While in the prior-art fluidity and decrease its melting range, it is seen here.

that definite relationships exist. To merely increase the carbon content or silicon content to lower the melting point of the alloy would not necessarily produce thedee sired effectunless the relationship expressed inthe balance factor were followed.

The preferred boron, carbon and silicon contents are about 0.75 percent boron, about 3 percent carbon; and about 0.8 percent silicon giving a balance factor of 1.9. The preferred alloy composition therefore consists essentially by weight of about 17 percent chromium, about 16 percent molybdenum, up to about 6.25 percent cobalt, up to about 1.9 percent vanadium, a maximum of 0.75 percent of nickel, about 0.75 percent boron, about 3 percent carbon, about 0.8 percent silicon, and thebalance substantially all iron and incidental impurities.

The combined properties of low melting point, high fluidity, and good fluxing characteristics make the alloy of this invention very castable. The alloy may be cast to shape by the usual casting methods, including sand casting, shellmold techniques, lost wax process, metal mold, etc. These castings are especially useful for applications requiring resistance to wear, abrasion and corrosion at temperatures up to 1500 F.

Cast welding or hard facing rods of the alloy may be made by the usual methods employed in the art. Composite-filler rods may also be made from the alloy.

The alloy is especially suited for the hard facing of valves and valve lifts according to the processes outlined above and shown in the drawings. A quantity of pro-alloyed metal powder is placed either in the-depression of the valve lifter or in spacebetween the dam and the groundout valve. The article is thenplaced in a furnace operating within the range 2085" F. to 2ll5 F.

with an oxygen-free reducing atmosphere, preferably of hydrogen, for a period of 10 to 40 minutes depending on the size andconfiguration of the article. The furnace temperature, when slightly above the solidus point of the alloy, 2075 F., fuses the alloy powder and causes it to metallurgically bond with the article. The article is then removed from the furnace and cooled. The now metallurgically sound alloy may be finished to the required dimensions. Nofurther heat treatment is necessary to develop the required hardness and wear resistance. Table 2 shows the properties of the heat-treated alloy compared to the as-cast alloy. Specimens from ten heats of the preferred composition of the alloy without heat treatment were testedfor hardness and impact resistance and 6 specimens were heat treated as shown and similarly tested. The results are shown in Table 2..

TABLE 2 Eflect of heat t eatment Average compo- Average eomposltion i 6 heats; Composition sltion of 10 heats; 1 hour heat treatno heat treatment at 1950 F.,

ment followed by 1 hour at 375 F.

Cr 15. -18. 5 15. 5-18. 5 Mo 14. 5-17. 5 14. 5-17. 5 G0 5. 25-7. 25 5. 25-7. 25 V 1 1. 65-2. 1. 65-2. 10 Ni 1 1. 75 1 1. 75 B 0. 5-1. 0 0. 5-1. 0 C 2. 85-3. 25 2 85-3. 25 Si 0.6-1.0 0.6-1.0 Fe Bal. Bal. Impact Strength, Charpy impact,

unnotched, ft.-lb.:

Range 4-8 4-8 Average 6 6 Hardness, Rockwell Range. 64-70 64-70 Average 67. 5 67. 5

1 Max.

The results of Table 2 show that no heat treatment is necessary with this alloy. Other alloys, now used in the art must be heat treated to attain maximum hardness. Additionally these alloys must be applied at higher temperatures, 2200 F. to 2400 F., than the alloy of this invention. These higher application temperatures are undesirable because they tend to distort the parent article, may cause local melting of the article and require more heating power.

In another method for applying a hard surfacing, pellets of the prealloyed metal powder are prepared by compaction. These pellets are placed on the area to be hardfaced and then the article is heated in a furnace with a reducing atmosphere at about 2100 F. This method is especially suited for automatic production methods.

The alloy may be fused to the article to be hard faced by tungsten-arc inert gas methods, the atomic hydrogen process, oxy-acetylene welding methods and other usual methods. Fusion may also be accomplished by utilizing induction heating coils.

What is claimed is:

1. An iron-base alloy consisting essentially by weight of from 13 to 21 percent chromium, from 12 to 19 percent in the aggregate of molybdenum and tungsten, up to 10 percent cobalt, up to 4 percent vanadium, up to about 1.75 percent maximum of nickel, from 0.2 to 1.8 percent boron, from 1.8 to 4 percent carbon, from 0.4 to 1.8 percent silicon, the boron, carbon and silicon contents having the following relationship B+0.25C+0.5Si=from 0.85 to 3.70

wherein B is the percent boron, C is the percent carbon, and Si is the percent silicon, and the balance substantially all iron in a minimum amount of about 38 percent and incidental impurities.

2. An iron-base alloy consisting essentially by weight of from 15.5 to 18.5 percent chromium, from 14.5 to 17.5 percent in the aggregate of molybdenum and tungsten, from 5.25 to 7.25 percent cobalt, from 1.6 to 2.1 percent vanadium, up to about 1.75 maximum of nickel, from 0.5 to 1 percent boron, from 2.85 to 3.25 percent carbon, from 0.6 to 1 percent silicon, the boron, carbon and silicon contents having the following relationship:

B+0.25C+0.5Si=from 1.51 to 2.31

wherein B is the percent boron, C is the percent carbon and Si is the percent silicon, and the balance substantially all iron and incidental impurities.

3. An iron-base alloy consisting essentially by weight of from 13 to 21 percent chromium, from 12 to 19 percent in the aggregate of molybdenum and tungsten, up to 4 percent vanadium, up to about 1.75 percent maximum of nickel, from 0.2 to 1.8 percent boron, from 1.8 to 4 percent carbon, from 0.4 to 1.8 percent silicon, the boron, carbon, and silicon contents having the following relationship B+0.25C+0.5Si=from 0.85 to 3.70

wherein B is the percent boron, C is the percent carbon, and Si is the percent silicon, and the balance substantially all iron and incidental impurities.

4. An iron-base alloy consisting essentially by weight of from 15.5 to 18.5 percent chromium, from 14.5 to 17.5 percent in the aggregate of molybdenum and tungsten, from 1.6 to 2.1 percent vanadium, up to about 1.75 percent maximum of nickel, from 0.5 to 1 percent boron, from 2.85 to 3.25 percent carbon, from 0.6 to 1 percent silicon, the boron, carbon and silicon contents having the following relationship B+0.25C+0.5Si=from 1.51 to 2.31

5. An iron-base alloy consisting essentially by weight of about 17 percent chromium, about 16 percent molybdenum, about 6.25 percent cobalt, up to about 1.9 vanadium, up to about 0.75 percent maximum of nickel, from 0.5 to 1 percent boron, from 2.85 to 3.25 percent carbon, from 0.6 to 1 percent silicon, the boron, carbon and silicon contents having the following relationship B+0.25C+0.5Si=from 1.51 to 2.31

6. An iron-base alloy consisting essentially by weight of about 17 percent chromium, about 16 percent molybdenum, about 6.25 percent cobalt, up to about 1.9 percent vanadium, up to about 0.75 percent maximum of nickel, about 0.75 percent boron, about 3 percent carbon, about 0.8 percent silicon, and the balance substantially all iron and incidental impurities.

7. An iron-base alloy consisting essentially by weight or" about 17 percent chromium, about 16 percent molybdenum, up to about 1.9 percent vanadium, up to about 0.75 percent maximum of nickel, about 0.75 percent boron, about 3 percent carbon, about 0.8 percent silicon, and the balance substantially all iron and incidental impurities.

8. An iron-base alloy consisting essentially by weight of about 17 percent chromium, about 16 percent molybdenum, up to about 0.75 percent maximum of nickel, about 0.75 percent boron, about 3 percent carbon, about 0.8 percent silicon, and the balance substantially all iron and incidental impurities.

References Cited in the file of this patent UNITED STATES PATENTS 2,220,084 Golyer Nov. 5, 1940 2,224,448 Schlumpf Dec. 10, 1940 2,967,103 Baldwin Jan. 3, 1961

Claims

1. AN IRON-BASE ALLOY CONSISTING ESSENTIALLY BY WEIGHT OF FORM 13 TO 21 PERCENT CHROMIUM, FROM 1I TO 19 PERCENT IN THE AGGREGATE OF MOLYBDENUM AND TUNGSTEN, UP TO 10 PERCENT COBALT, UP TO 4 PERCENT VANADIUM, UP TO ABOUT 1.75 PERCENT MAXIMUM OF NICKEL, FROM 0.2 TO 1.8 PERCENT BORON, FROM 1.8 TO 4 PERCENT CARBON, FROM 0.4 TO 1.8 PERCENT SILICON, THE BORON, CARBON AND SILICON CONTENTS HAVING THE FOLLOWING RELATIONSHIP