US2109746A - High speed alloy steel - Google Patents

Description

Patented Mar. 1, 1938 UNITED STATES PATENT OFFICE HIGH SPEED ALLOY STEEL Alvin J. Herzig, Detroit, Mich., assignor to Climax Molybdenum Company, a corporation of Delaware No Drawing. -Application September 12, 1935, Serial No. 40,254

8 Claims.

This invention relates to alloy steels and parresistant to decarburization of the surface thereof during the manufacture of the steel and the fabrication of tools and wearing parts therefrom when the steel is necessarily subjected to elevated temperatures as in forging, rolling, hardening, drawing, etc.

As is well known to those skilled in the art, many steel alloys, commonly referred to as steels, are subject to the phenomenon of decarburization, rendering them unfit for service in many .applications. This is especially true of those steels which are used in the manufacture of cuttingtools and wearing parts where extremely high surface hardness is required, which hardness cannot be obtained if carbon is lost from the surface of the tool by decarburization even to the small extent of such depth as fractions of a thousandth of an inch.

A steel is sa d to decarburize when, by reason of. the conditions to which it is subjected, a lowering of the carbon content on the surface takes place. This lowering of the carbon content on the surface is accompanied by a change in the micro-structure which, in the case of many important tool steels, results in a soft skin.

The rate of decarburization depends upon the rate at which carbon is oxidized at the surface zone and the rapidity with which the underlying carbon diffuses into the surface oxidization zone. It has been suggested in the prior art to overcome this phenomenon of decarburization by protecting the steel, when at elevated temperatures, from decarburizing atmospheres by means of coatings. These coatings may consist of electrodeposited metal or may be formed by dipping the steel into molten salts or solutions of salt. It has also been suggested that the phenomenon of decarburization may be overcome by controlling the composition of the atmosphere to which the steel is subjected at elevated temperatures. All of these methods afford a certain amount of protection but possess many objections either by Way of being prohibitively costly, incompletely protective, or hazardous in commercial practice. For example, the use of controlled atmospheres cannot be economically applied to prevent decar- .burization during forging or rolling. Electrodeposited coatings cannot always be conveniently employed by reason of the expense of equipment involved, in a great many places where tool steels are treated. The use of solutions of salt or molten salt, while effective in the forging operation as well as in the heat treating operation, bring about an undesirably messy condition in the heating furnace and considerably complicates the com,- mercial handling of the steels through the fabricating processes.

' As is also well known to those familiar with the art, the presence of molybdenum in high speed steels, by virtue of its inherent characteristics when alloyed with iron, promotes the rate of diffusion of carbon when the steels are subjected to elevated temperatures. It has been universally observed that molybdenum containing high speed steels are particularly subject to the phenomenon of decarburiz'ation and this objection alone prevents the universal use of compositions which otherwise are superior from the standpoint of cost and performance to compositions now widely used. Accompanying thisdecarburization it has been noted that molybdenum containing steels when subjected to elevated temperatures for forging, rolling, or heat treating operations emits copious white fumes which are molybdic oxide. This invention not only prevents decarburization of such steels at elevated temperatures but eliminates or materially reduces the loss of molybdenum in the surface layer through emission of this molybdic oxide.

, This invention, therefore, relates to the discovery of alloy additions to high speed steels containing molybdenum, which additions overcome the effect of molybdenum in promoting decarburization. By theuse of these alloy additions molybdenum containing high speed steels may be subjected to elevated temperatures without protection against oxidizing atmosphere such as ordinarily'occur in furnaces, without loss of carbon from the surface and without formation .of a soft skin.

More specifically, it has been found that the 4 addition of copper in amounts of 1.5%. to 5% to a h gh speed steel containing molybdenum, markedly retards the rate of diffusion of carbon and makes it possible to expose the high speed steel containing molybdenum and copper to oxid'zing' atmospheres at elevated temperatures without suffering decarburization and without the formation of the so-called soft skin. Furthermore, it has been found that the addition of copper in the above amounts may be made without sacrificing the cutting properties prevalent in high speed steel containing molybdenum but not containing copper.

The high speed steel of the present inventio may be substantially that disclosed in United States Patent No. 1,937,334 issued November 28, 1933 to Joseph V. Emmons on Steel alloy and articles made therefrom, with the addition of copper and, if desired, other elements thereto. Additionally, as will hereinafter be pointed out, substitution of the molybdenum. element in the steel covered by the above patent may be made in whole or part by tungsten, within the spirit of the present invention. As an example of the present invention the steel of the following composition has been found satisfactory.

Per cent Carbon 0.80 Manganese 0.50 Silicon 0.30 Chromium 4.00 Molybdenum 8.50 Vanadium 1.00 Copper 3.00 Iron and usual impurities Remainder These elements may vary in percentages according to the following limits depending upon the particular characteristics desired.

It has also been found that .02% to .50% of boron may be added to the above disclosed composition with more or less satisfactory results. 0.20% of boron gives very satisfactory results. Likewise 0.20% to 2.00% of titanium may be added to the above described composition with more or less beneficial results and 0.50% is quite satisfactory. In addition tungsten may be added to the above disclosed composition with certain beneficial results. 2.00% tungsten has been found quite satisfactory. Either one, two or all three of the last mentioned elements may be added in the amounts stated, if desired. Ordinarily it will be found that tungsten will have about the same final result as the molybdenum but that approximately twice as much tungsten is required as molybdenum to obtain the desired results. In other words, if a particular composition of the steel described contained 1% of molybdenum and it was desired to entirely replace it by tungsten, 2% of tungsten would be required to obtain the same effect as the molybdenum. Tungsten does not have the effect of promoting as rapid diffusing of the carbon in the steel as molybdenum, but the addition ofcopper to high speed steels of approximately the above disclosed composition, except that tungsten is employed to replace the molybdenum in part or in whole, is found to be extremely beneficial. Accordingly, in the broader aspects of the present invention it will be understood that tungsten may be emplcyed to replace either part or all of the molybdenum content set forth, so much of the molybdenum which is replaced by the tungsten be- It has been found that steels of the above disclosed compositions will not develop the soft skin or bark while being heated for forging and during the forging, operation, that it will not decarburize during the heating operation for hardening or during hardening, and that its properties as a, cutting tool are equal to, or better than, a steel of similar composition but not containing copper. It has also been found that this steel forges more readily and with less danger of cracking than a steel of similar composition but not containing copper.

It will be understood that it is within the province of the present invention to add to the above described composition elements whose additions thereto will result in well understood and expected results, and in proportions commensurate with the degree of modification desired thereby and, accordingly, it will be understood that formal changes may be made in the specific composition herein set forth without departing from the spirit or substance of the broad invention, the scope of which is commensurate with the appended claims.

What I claim is:

1. An alloy steel containing the following ele ments: carbon about 0.50% to 1.30%, manganese about 0.30% to 0.8%, silicon about 0.10% to 0.75%., chromium about 0.20% to 10.00%, molybdenum about 6.00% to 15.00%, vanadium about 0.20% to 3.00% and copper about 1.50% to 5.00%, said steel having high speed properties and being characterized by its resistance to surface decarburization at forging and rolling temmratures in ordinary atmospheres.

2. An alloy steel containing the following elementsz ca'rbon about 0.50% to 1.30%, manganese 'about 0.30% to 0.80%, silicon about 0.10% to 0.75%, chromium about 0.20% to 10.00%, molybdenum about 6.00% to 15.00%, vanadium about 0.20% to 3.00%, boron about 0.02% to 0.50%, and copper about 1.50% to 5.00%, said steel having high speed properties and being characterized by its resistance to surface decarburization at forging and rolling temperatures in ordinary atmosphere.

3. An alloy steel containing the following elements: carbon about 0.50% to 1.30%, manganese about 0.30% to 0.80%, silicon about 0.10% to 0.75%, chromium about 0.20% to 10.00%, molybdenum about 6.00% to 15.00%, vanadium about 0.20% to 3.00%, tungsten about 2.00%, and copper about 1.50% to 5.00%, said steel having high speed properties and being characterized by its resistance to surface decarburization at forging and rolling temperatures in ordinary atmospheres.

4. An alloy steel containing the following elements: carbon about 0.50% to 1.30%, manganese about 0.30% to 0.80%, silicon about 0.10% to 0.75%, chromium about 0.20% to 10.00% molybdenum about 6.00% to 15.00%,wanadium about 0.20% to 3.00%, boron about 0.02% to 0.50%, tungsten about 2.00%, and copper about 1.50% to 5.00%, said steel having high speed properties and being characterized by its resistance to surface decarburization at forging and rolling temperatures in ordinary atmospheres.

5. An alloy steel comprising the following elements: carbon about 0.80%, manganese about 0.50%, silicon about 0.30%, chromium about 4.00%, molybdenum about 8.50%, vanadium about 1.00%, and copper about 3.00%; said steel being characterized by having high speed properties and by being resistant to surface decarburization at forging and rolling temperatures in ordinary atmosphere.

6. An alloy steel comprising the following elements: carbon about 0.80%, manganese about 0.50%, silicon about 0.30%, chromium about 4.00%, molybdenum about 8.50%, vanadium about 1.00%, boron about 0.20% and copper about 3.00%; said steel being characterized by having high speed properties and by being resistant to surface decarburization at forging and rolling temperatures in ordinary atmospheres.

7. An alloy steel comprising the following elements: carbon about 0.80%, manganese about 0.50%, silicon about 0.30%, chromium about molybdenum about 8.50%, vanadium about 1.00%, boron about 0.20%, tungsten about 2.00%, and copper about 3.00%; said steel being characterized by having high speed properties and by being resistant to surface decarburization at forging and rolling temperatures in ordinary atmospheres.

8. An alloy steel comprising the following essential elements: carbon about 0.50% to 0.85%, chromium about 4.00%, molybdenum about 8.50%, copper about 3.00%, and boron 0.03% to