US2208117A - Ferrous alloy - Google Patents

Description

July 16, 1940. T, AP ET AL 2,208,117

FERROUS ALLOY Original Filed Sept. 6, 1938 Y r Cr- 30 Nl AREA 20 N? B AREA 57 X 6 8 I070 Ni INVENTORS ART/10R Z CAPE BY CHARLES ll FfigSTE/P ATTO EY- Patented July 16, 1940 1 UNITED STATES PATENT OFFICE FERROUS ALLOY Arthur T. Cape and Charles V. Fcerster,

Santa Cruz, Calif.

2 Claims. (01. 12s) This invention relates to ferrous alloys, but has reference more particularly to ferrous alloys which are especially adapted for hard-facing purposes and for utilization in the form of castings.

It is perhaps well-known that there are, in general, three types of hard-facing metals, which, briefly, are the hard carbides, the non-ferrous type, and the compounds of ferrous materials. In facing a base metal with the hard carbides, the retaining metal flows onto the metal to befaced and becomes welded to it, the carbides not being melted. This type of hard facing alloy is highly resistant to abrasion but it cracks badly and rapidly under repeated impact, and, consequently, its service is limited. Non-ferrous types of hard facing alloys have a relatively good wear resistance, although not as good as the carbides, but are decidedly tougher. The hard-facing alloys of the ferrous type vary greatly and it can be said that the effectiveness of the material can generally be indicated by the market price thereof. In other words, the cheaper the hard facing metals of the ferrous type are, the lower is their effectiveness. That is, these cheaper materials are too soft and they wear rapidly. On the other hand, the more expensive the hard facing alloy of the ferrous type, the greater tendency they have to be brittle, although they are reasonably resistant to wear.

A primary object of the present invention is to provide ferrous alloys for hard-facing and casting purposes which not only have a high resistance to wear and abrasion, but have high resistance, as well, to heavy and repeated impacts, that is to say, they possess high mechanical strength.

Another object of the invention is to provide ferrous. alloys for hard-facing and casting purposes, which are resistant to chemical corrosion, to oxidation at high temperatures, and possessing strength at high temperatures.

A further object of the invention is to provide ferrous alloys of the hard-facing type which also possess the quality of being capable of forming a sound bond with the base metal.

A still further object of the invention is to provide ferrous alloys of the hard-facing type, which have a viscosity, in the molten condition, such as to permit exceedingly easy application of the alloys to the base metal.

Other objects of the invention, together with some of the advantageous features thereof, will appear from the following description of the preferred and other embodiments of the invention. It is to be understood, however, that we do not limit'ourselves to the embodiments described, since our invention, as defined in the appended claims, can be embodied in a plurality and variety of forms.

The alloys with which we are principally concerned' fall into two groups, the alloys in each group having certain properties in common with those of the other group, but having other properties distinct from those of the latter. In order to more clearly visualize these groups, reference may be had to the accompanying drawing, forming a part of the present applicat.on, and in which appears a graph containing two curves, all points of which have as their abscissae percentages of nickel, and as their ordinates percentages of chromium.

Referring more particularly to this graph, it maybe noted that the graph contains two sets of rectangular coordinates, one set consisting of the axes of 0X(a:-axis) and 0Y(y-axis), and the other consisting of the axes 0X1(a:1-axis) and 0--Y1(y1-axis), that is, both sets have a common origin (0), but the sci-axis is inclined at an angle of 60 degrees, measured in a counterclockwise direction, to the :v-axis. The :c-axis denotes percentages of nickel and the y-axis denotes percentages of chromium.

The graph also contains two curves, designated A and B. Curve A is a parabola, whose principal axis is the sci-axis and whose equation or formula is w10y1 =a, where a and c are constants, with a=2.7 and 0:0.9. To reduce this formula or equation to concentrations of percentages of chromium and nickel, the following is established:

x1-cy1 must be greater than a, which equals 2.7, where 2 plus .217y and y minus .4332:

and :1: equals the percentage of nickel and y equals the percentage of chromium. The parabola defined in terms of concentration of chromium and nickel is plus .217y minus 4% minus .433:::) equals a.

Of the two principal groups which have been referred to, the preferred group comprises all those alloys which lie within the area designated No. l in the graph, this area being bounded by the parabola A and the lines representing 10% nickel and 30% chromium. The other group comprises all of those alloys which lie within the area designated No. 2 in the graph, this area being bounded by the curves A and B and the lines representing 10% nickel and 30% chromium. The curve B is generally parabolic, and somewhat parallel with curve A. No attempt will be made to give the formula or equation of this curve, but it is to be noted that the curve is a dividing line between alloys of different characteristics.

The curve A passes through points or values where there is a critical change of hardness from the austenitic to the ferritic or more magnetic state. The curve B passes through points or values where the effect of the critical change represented by curve A no longer exists and the hardnesses begin to decrease rapidly. The critical change in hardness from compositions above A to those lying between A and B is accompanied by changes in the magnetic values, from a value of 3 inside the curve to 4 just below curve A, such values being arbitrary but reproducible.

The method. used for determining these arbitrary values consists in balancing the metal to be tested, bringing a magnet to a fixed point and noting the deflection. Such a test readily designates the general physical characteristics of an unknown chromium nickel composition or a known composition to which other alloying elements have been added. 7

The alloys lying within area N0. I are especially adapted for hard-facing applications, where softness from the point of view of indentation hardness is of advantage, for resistance to impact.

At the same time, the complex chromium carbideplates distributed through the matrix in alloys of this group, plus the fact that the matrix itself is austenitic, and therefore hardens assoon as any work is done, imparts to this group a resistance to wear which is remarkable. In practice, we have been able to lay down deposits as soft as 30 Rockwell C (approximately 290 Brinell) which are file hard. A preferred alloy of this group contains about 4.20% carbon, about 14%-18% chromium, about 4%-6% nickel and about 40% vanadium. This alloy is particularly useful in the form of weld rods for hard facing applications for cement mill machinery, agricultural equipment, brick, clay and tile machines, including muller tires; hammer mill parts, and coke handling equipment.

The alloys lying within area No. 2 have asubstantially greater initial indentation hardness than the alloys in area No. i, this being (mate the tendency of such alloys to change from the austenitic to the ferritie states. In other words, some of the austenite formed at higher temperatures decomposes during cooling, and the critical precipitation of carbides gives increased hardness. This occurs in the cast material, and does not require heat treatment to bring it about. Just how critically the hardness values change will appear from the graph, wherein, for example, an alloy containing 10% chromium and 4% nickel has a hardness of 57 Rockwell C, while an alloy containing 8% chromium and 4% nickel has a siderable interest.

type contains about 4% carbon, about 16% chromium, about 2% nickel, about 8% molybdenum and about 1% vanadium. Typical uses of this alloy are valve seat inserts and valves, hot shear knives, steel mill guides, forging dies, tobacco and ensilage cutters, etc. The vanadium, which may be added in quantities of from about .20% to about 1%, apparently imparts to the alloy increased toughness, and, in the welding rod, a degree of stickability, which is definitely the property or ability of the weld metal, deposited by the melting welding rod, to resist separation from the base metal, under severe impact.

Titanium may be added in amounts of from plications as Bradley pulverizer rings, Grlmn rings, etc.

In manufacturing the aforesaid alloys, it is desirable to produce sound castings or good welding material. For this purpose, the original charge in the furnace must be kept free from silicon, or as reasonably low in silicon as is possible, and also free from titanium. Additions of silicon and titanium should be made as close to the end of the melting operations as possible. If these conditions are not observed, the material, whether used as castings or as acetylene welding rods, is porous. For arc welding, these factors are not quite as important, because the gases present in the welding rod are removed during the arc welding process. In order to control the acetylene welding property of the material and also to some extent the arc welding characteristics, a small quantity of alkaline earth or alkali metal is added to the melt. The addition of minutely small quantities of these elements increases the wetting properties of all of the varieties. Without them, during acetylene welding, the metal tends to form into balls, the surface is improperly covered and the adherence is not satisfactory. With an immeasurably small amount of sodium, potassium or calcium, the metal melted by the acetylene torch spreads over the surface and covers it excellently. This is a most valuable property, and distinguishes the present alloys from all other welding materials. The addition of calcium to the metal is preferably as calcium silicide. The addition of these elements increases the fluidity of the metal, as Well as merely changing the surface tension. The quantity of calcium silicide used is about .07 ounce per pound of metal. The amount used is Well in excess of that required.

' The arc welding rods are coated with a mixture of plumbago and sodium silicate, to which a small quantity of Bentonite sometimes is added, or they may be coated with a mixture of graphite (in the form of crushed arc furnace electrodes) and sodium silicate, to which Bentonite sometimes is added. The use of these coatings is of con- Where the rods are coated with plumbago, the deposits are soft; where the rods are coated with graphite, the deposits are hard. Differences as great as 30 Rockwell C to 55 Rockwell C can be produced by the selective use of these coatings. The normal mixtures employed in these coatings are as follows, the rods being coated by simply dipping them in the mixture and drying them:

This peculiar effect of plumbago as against graphite is of interest not only in connection with the present alloy, but also in connection with the coating of'welding rods formed of other ailoys and compositions.

It has been found that where the problem of porosity arises, the addition of fluoride eitherto the metal itself in the case of castings, or as a thin layer over the graphite coating of the welding rod can be used effectively in eliminating the gas pockets. in removing gases from the molten metal and in the event of unduly humid conditions causing an absorption of the gases can be eliminated during the freezing process by the addition of the fluoride to the molten metal. In many cases where it is necesary to weld on dirty or gassy cast iron or cast steel the addition of fluoride either with the graphite or plumbago coating,

All of the fluorides are efiective or as a thin layer superimposed upon the coating, will prevent porosity in the welded deposit.

The alloys should be kept as free from elements other than those described, as possible. In other words, silicon (except where specifically required), manganese, phosphorus and sulphur should be kept to a minimum. For certain specific uses the addition of manganese and phosphorus may have an advantage and these will be described in a later application.

The alloys can be increased in hardness by beating them to 1650 F. and up and cooling them fairly slowly. This is a true precipitation hardening phenomenon.

This application is a division of our co-pending application Serial No. 228,528.

We claim:

1. A ferrous alloy consisting oi more than 3% but not more than about 5% carbon, nickel in amounts of from about 25% to about 10%, chromium in amounts of from about 4% to about 30%, molybdenum in amounts of from about 6% to about 10%, and vanadium in amounts up to about 1%, the balance being iron.

2. A ferrous alloy consisting of about 4% carbon, about 16% chromium, about 2% nickel. about 8% molybdenum and about 1% vanadium, the balance being iron.

ARTHUR T. CAPE. CHARLES V. FOERSTER.

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