US1496980A - Alloy steel for metal-cutting tools - Google Patents

Description

?atented nlune 10, 1924.

PERCY A. E. ARMSTRONG, OF LOUIDONVILLE, NEW YORK.

ALLO'Y STEEL FOR METAL-CUTTING TOOLS.

No Drawing.

To all whom it may concern:

Be it known that I, PERCY A. E. ARM- STRONG, a subject of the King of Great Britain, and a resident of Loudonville,

county of Albany, and State of New York,

have invented a new and useful Improvement in Alloy Steel for Metal-Cutting Tools, of which the following is a specification.

This invention relates to alloy steel for 1 metal cutting tools, having properties generally intermediate between carbon steel and high speed steel.

For small metal cutting tools, such as drills, taps, reamers and the like, carbon steel answers sufficiently well, takes a keen cutting edge and produces smooth finished work, but is limited in its application, because under heat it softens and dulls rapidly.

High speed steel, which is commonly used for somewhat larger drills and similar tools, which have to withstand greater heat, is not, of course, rapidly softened by frictional heat, but, in addition to its high price, has the objection that the 'work produced is not so smooth and well finished as can be obtained by sharp edge carbon steel tools, for example, and a subsequent separate finishing operation is usually required. For example, drilled holes require finish reaming to produce satisfactory work. Furthermore, in the case of taps, for example, the teeth of the tap are often injured by the high temperatures required for heat treatment of high speed steel.

The present invention relates to the provision of an alloy steel having the desirable properties of both carbon steel and high speed steel, that is, which will retain a hard, keen cutting edge and which is very strong,

40 and at the same time will not soften to an injurious extent when drawn to medium temperatures, such 500700 F.

The steel of the present invention contains, chromium, vanadium, and molybdenum, and also contains silicon considerably in excess of the usual silicon content of steel, silicon being present "iii my improved alloy steel preferably to the extent of from about .5% to 2.5%. This steel is hard and strong and holds a keen cutting edge which is not materially softened, so as to become dulled,

Application fi1ed. January 5, 1922. Serial No. 527,224.

An important feature of the invention re-- lates to the employment of silicon as one of the components of the alloy. The silicon appears to serve as a sort of solvent for other components, and causes them to form a chemical combination with one another and produce an alloy steel having improved properties. A second function of the silicon is to raise the transformation point of the resulting alloy, thus imparting to the alloy steel the very valuable property of hardening at relatively high temperatures. A

third function of the silicon is to enhance the air hardening properties of the alloy. Silicon enables the chromium and molybdenum in combination "tvithtlie carbon and iron to take on a tremendously enhanced air hardening property. It also prevents the breaking down of this hard state when being drawn at temperatures which would cause a straight chromium, carbon or chromium-molybdenum-carbon steel to soften.

According to another feature, an alloy steel is provided having as one of its components a predetermined proportion of tungsten. This alloy steel has an increased red hard property. The use of tungsten also creates a lag to transformation, that is to say, when the steel is re-heated for a very short. period after being quenched for hardening, it is given the quality of having a lag to the breaking down of the solid solution produced in quenching. Consequently, cutting tools made of the alloy so made can withstand overheating of their cutting edges for limited times without destruction of their cutting ability. One example of a composition for an alloy steel in accordance with the present invention is as follows:

1900 F. without quenching in oil or water. Variations'in manganese in this alloy will require inversely proportional variations in the temperature to which the alloy is heated; for example, if the manganese is increased to 1% the temperature should be changed to substantially 1500 F., while if the manganese is increased to 1.5% the temperature should be reduced to substantially 14.50 F.

Another example of an alloy made in accordance with the present invention is of about the following composition:

. Per cent. Carbon 1 Chromium 2 Molybdenum 2 Manganese 4O Silicon 1 Tungsten 3 Vanadium 1 Cobalt 1 Balance iron with small amounts of phosphorus and sulfur.

In order to harden this alloy it should be heated as quickly as possible to substantially 1800 F., and quenched in oil or water. Variations in manganese require variations 'in the heatdzreatment temperature as in the preceding example.

A third example of an alloy made in accordance with the present invention is oi about the following composition Per cent. Carbon 1.50 Chromium 2 Molybdenum 2' Manganese 40' Silicon 2 Tungsten 2 Vanadium 50 Cobalt 2 Balance iron with small amounts of phosphorus and sulfur.

The heat treatment of this alloy consists of heating to substantially 1800 F., as quickly as possible and quenching in oil or water. Selection of the heat treatment temperature is made in accordance with variations in percentage of manganese as in the preceding examples.

Another example of alloy made in accordance with the present invention is of about the following composition:

Per cent. Carbon Chromium 10 Molybdenum 5. 7 5 Manganese 40 Silicon 2. 5 Vanadium 2 Tungsten 5 Cobalt 2 Balance iron with small amounts of phosphorus and sulfur.

In the heat treatment of this alloy heat should be applied until the alloy has a tem perature of substantially 2100 F. The alloy should then be cooled in the air. This alloy may be cast for use in forming cutting tools.

More or less variation is possible without.

any substantial detriment to the desirable qualities of the material and good. results are obtained with varying quantities of the several components within substantially the following range:

Balance iron with small amounts of phosphorus and sulfur.

This represents about the outside range. Good results can be obtained with somewhat lesser proportions of some of the components within the following more limited range: carbon 25-2 0, molybdenum .50-2%, silicon .50-2%, chromium .502%, vanadium under 1%, manganese under 1%, cobalt under 1%, and tungsten .252%, and the balance principally iron.

I have found that good results are obtained with heat treatment of alloys made in accordance with the present invention, which consists of heating the alloy to a temperature of approximately 1800 F, in as short a time as possible, after which the alloy may be air hardened or quenched in oil or water. It is preferably not held at this temperature more than a half-minute or so longer than necessary to heat the piece throughout. Holding the temperature at the point specified for too long a period promotes grain growth, which although not affecting the cutting powers of the completed tool, may reduce its strength.

A preferred example of alloy made in accordance with the present invention is of about the following composition:

Balance iron with small amounts of phosphorus and sulfur.

In the heat treatment of this alloy, heat.

should be applied until the alloy has a temperature of substantially 1850 F., and held at this temperature only so long as it is necessary to heat thoroughly the material, preferably not to exceed-a half-minute. It is then quenched in oil and drawn to a temperature of substantially 500 F.

All of the alloys described in the present application, particularly the preferred form just described, give their maximum cutting efficiency when run hot at about the temperatures between 500 and 600- F. Furthermore, the efficiency of this steel from a metal removing point of View appears to be greatest when the cutting tool is running at a higher cutting speed and feed per minute than are usually employed for a straight carbon steel of about the same carbon. Generally speaking, the cutting speed and feed should be at least double that of carbon steel. n

A modified allov made in accordance with the present invention may comprise, for example, components within substantially the following range:

Percent.

Carbon .25 2 Molybdenum .50- 5.75 Silicon .50- 2. 5

Chromium 5010 Manganese 0 1.5 Tungsten .25- 5 Balance iron with small amounts of phosphorus and sulfur.

Heat treatment substantially as given for previously described alloy steels.

The steel works well in the mill, is substantially free from seams and can b castinto very smooth ingots. In rolling the temperature should not be carried unduly high and should preferably be kept under 2100 F. After rollin the steel should preferably be cooled slow y as, for example, in

. lime, thereby removing strains which may result from rapid cooling. This becomes more import-ant as the alloying constituents are increased. The steel will anneal and become quite easy to machine when properly annealed. There is very little tendency for this alloy combination towmove, that is to say, to exhibit tendency to warping, or other malformation upon heating up and quenching, which is a feature of great advantage in heat treatment of tools.

I claim: r

1. As a new composition ofmatter, an alloy steel of analysis substantially as follows: carbon 1.50 0, chromium 2%, molybdenum 2%, silico 2%, mangan se 40%, vanadium 50%, tungstenl2%,cobaft 2%, and the principal part of the remainder iron.

2. As a new composition of matter an alloy steel of analysis having substantially the following range: carbon .252%, chromium 50-10%, molybdenum 50 517 5%, silicon 50-25%, vanadium 0 2%, manganese 04.5%, tungsten .25 5%, cobalt0-2%, and the principal part of the remainder iron.

8. Metal. cutting tools made from alloy steel as claimed in claim 1.

4. Metal cutting tools made from alloy steel as claimed in claim2.

. 5. Drills for drilling metal made from alloy steel as claimed in claim 1.

6.- Drills for drilling metal made from alloysteel as claimed in claim 2.

7. An air hardening .alloy steel adapted to withstand temperatures ofabout 500 700 degrees F. without material softening, and containing upon analysis substantially carbon .25% to 2%, chromium, 50% to 2%, Jmolybdenum 50% to 2%, silicon 50% to molybdenum 50% to 2%,- silicon .50% to 2%, tungsten 25% to 2%, an appreciable quantity up to 1% of vanadium and of manganese, an appreciable quantity up to 2% of coba t, and the principal portion of the remainder iron.

11. Metal cutting tools made from alloy steel as claimed in claim 10.

12. Drills for drilling metal made from alloy steel as claimed in claim 10. i

In testimony whereof, I have signed my name hereto.

* PERCY A. E. ARMSTRONG.