US2135495A - Alloy - Google Patents

Description

Patented Nov. 8, 1938 UNITED STA'TES PATENT orries No Drawing. Application December 5, 1936,

Serial No. 114,370

2 Claims.

The present invention relates to a ferrous base alloy containing molybdenum and boron as well as certain other alloy elements.

The object of the present invention is to pro- 5 vide an alloy which is entirely or substantially free from carbon and which has a combination of advantageous physical properties and characteristics rendering-it particularly valuable for use as metal cutting tools.

The type of alloy tool steel, usually classified as high speedsteel which has heretofore been in general use contains tungsten as the principal alloy element; the'standard 18-4-1 high speed steel being substantially an alloy of iron with 8% tungsten, 4% chromium, 1% vanadium,

" 0.50% to 0.75% carbon and minor percentages of manganese and silicon. Various modifications have been proposed, such as steels containing approximately four times as much molybdenum as tungsten, e. g., from 6% to 8% molybdenum and from l.5% to 2.5% tungsten; and steels containing from 6% to 12% molybdenum without tungsten.

All of the previously known high speed steels,

irrespective of whether they contain tungsten or molybdenum as the principal alloy element, de-

pend upon the presence of an appreciable amount of carbon to impart the degree of hardness necessary for metal cutting tools. An examination of any of the previously known types of high speed steel discloses grains or. particles of an excess constituent comprising a complex compound of carbon, tungstenand iron, or carbon, molybdenum and iron, as the case may be. This constituent is commonly designated as the carbide segregate.

. It is well known that a minimum carbon content of 0.50% is necessary for the development of the requisite hardness and cutting efficiency in high speed steel; the usual carbon content of such steel being from 0.60% to 0.70%.

I have discovered that by combining appreciable amounts of molybdenum, boron, chromium and vanadium in a ferrous alloy entirely free from carbon that I can produce a composition which has a cutting eiliciency superior to previously known high speed steels containing appreciable percentages of carbon. Furthermore, 50 by reason of the freedom from carbon the alloy of the present invention is amenable to a method of thermal treatment which is markedly difierent from that required for heretofore known tool steels. By means of such thermal treatment 55 hardness and other physical properties and characteristics determining cutting eillciency can be accurately regulated over a wide range.

The essential components of the alloy of my present invention are molybdenum, boron, chromium, vanadium and iron. Manganese and sili- 5 con are usually present in minor amounts. Phosphorous and sulphur, as well as certain other elements commonly found in alloy steels, are usually present in ineffective amounts in the nature of incidental impurities. 10

The alloy of the present invention comprises molybdenum 6% to 15%, boron 0.30% to 2.25%,

chromium 1% to 5%, vanadium 0.70% to 4% and the remainder principally iron. Manganese and silicon will usually be present in amounts not 15 exceeding approximately manganese 1.10% and silicon 1.20%.

I prefer to have the alloy entirely free from carbon as when this element is absent the composition is not only more amenable to thermal 20 treatment but, in general, has greater cutting efliciency. However, by reason of the fact that certain of the materials used in the preparation of the alloy frequently contain varying amounts of carbon I have found that when my alloy is 25 manufactured under ordinary commercial conditions it will frequently contain from about 0.03% to 0.06% carbon in the nature of an 1 incidental impurity. I have found that such incidental carbon can be present in an amount 30 as highas approximately 0.10% without materially decreasing the valuable physical characteristics possessed by the carbon free alloy.

The presence of 0.45% or more carbon in high speed steels containing tungsten or molybdenum 35 as the principal alloy elements results in the formation of the carbide constituent or segregate referred to hereinabove. A relatively large portion of such constituent occurring in cast ingots is in comparatively massive form, which can be 40 reduced in size and distributed throughout the steel only by mechanical working. Only the smallest particles of the carbide constituent can be dissolved in the matrix by means of heating. Consequently, a relatively large proportion of the primary carbide constituent persists through all of the thermal treatments to which such steels are subjected. Therefore, the regulation of particle size and distribution of a major portion of the complex carbide constituent forming the segregate is entirely dependent upon mechanical working. This does not provide a satisfactory method of control of the physical structure of the aggregate.

I have previously proposed the use of boron as principal alloy element. I have found that such bore-carbide compounds are extremely hard and brittle and that relatively coarse particles of this constituent cannot be appreciably fragmented by mechanical working without rupturing the steel.

I have also discovered that such bore-carbide constituents are only partially dissolved in the matrix by thermal treatment. It will be apparent, therefore, that the presence of an appreciable proportion of such complex boro-carbides produces a steel in which the particle size and dissemination of the hard constituent cannot be closely regulated by thermal treatment.

' In the alloy of the present invention the segregate of the cast structure appears to be essentially a complex compound of boron, molybdenum and iron. This segregate can be more or less readily fragmented by mechanical working, or it can be largely or entirely dissolved in the matrix by heating the cast aggregate.

Examples of alloys which I have found particularly useful for metal cutting tools contained molybdenum 9.25%, boron 0.85%, chromium 3.80%, vanadium 1.75%,' manganese 0.60%, silicon 0.40% and the balance principally iron; molybdenum 11%, boron 0.93%, chromium 4%, vanadium 2%, manganese 0.55%, silicon 0.55%, carbon 0.04% and the balance principally iron.

I have found that the hardness and other physical properties and characteristics of the alloy of the present invention can be accurately controlled by means of suitable thermal treatment. As an illustration, one satisfactory method consists essentially of heating an aggregate of the alloy to a temperature in excess of 1000 C. maintaining the aggregate at this temperature for a sufficient period of time to dissolve an appreciable proportion of the molybdenum-ironboron compound in the matrix; quenching the aggregate to substantially retain the solid solution; subsequently heating the aggregate to a temperature substantially lower than that at which the solid solution was formed for a suiflcient period of time to produce precipitation of molybdenum-iron-boride particles from the solid solution. I have found that in carrying out the primary heating for effecting solid solution it is not necessary to dissolve all of the molybdenumiron-borlde constituent in the matrix. After the alloy has been quenched from the primary heating temperature it will usually have a hardness of approximately Rockwell C compared to a hardness of from to 69 Rockwell C which can be developed by precipitation of the boron containing constituent during the secondary heating. It will beapparent that by regulating the temperatures and periods of heating the ratio of precipitated boron compound to matrix constituent, or to primary boron compound may be ac: curately controlled. The precipitated boron compound is uniformly disseminated throughout the aggregate.

I have found that the boron containing constituent of the present alloy is not only extremely hard, but is relatively strong. The presence of boron imparts high impact strength to the al- 10y, particularly at temperatures generated in the tip of a metal cutting tool. Such boron containing compounds are also highly resistant to oxidation at such temperatures, and consequently the injurious effect of decarburization, which occurs in carbon containing tools, is entirely eliminated.

Although the greatest scope of usefulness for this alloy appears to be in cast or wrought forms as cutting tools, I have found that it may be utilized for many other industrial applications such as forming dies, wearing parts, etc.

I claim:

1. An alloy containing molybdenum 6% to 15%, boron 0.30% to 2.25%, chromium 1% to 5%, vanadium 0.70% to 4%, manganese not exceeding approximately 1.10%, silicon not exceeding approximately 1.20% and the remainder iron.

2. An alloy containing molybdenum 6% to 15 boron 0.30% to 2.25%, chromium 1% to 5%, vanadium 0.70% to 4%, carbon not exceeding approximately 0.10%, manganese not exceeding approximately 1.10%, silicon not exceeding approximately 1.20% and the remainder iron.

ANTHONY G. DI: GOLYER.