US2204283A - Tool steel - Google Patents

Description

15 ness.

upon for this purpose, but in present practice Patented June 11,

UNITED STATES 5 PATENT ori-" cs V TOOL STEEL Allen D. Potts, 'Lockport, N. Y., and Daniel Simonds, Hollis, N. 11., assignors to Simonds Saw and Steel 00., Fitchburg, Mass, a corporation of Massachusetts No Drawing. Application March 15,. 1938,

, Serial No. 195.956

3 Claims.

This invention relates to improved tool steels, and more particularly to improved alloy tool steels for metal-cutting and metal-shearing.

tools. 1

Predominant among the characteristics of tool steel are hardness, toughness, and wear-resisting properties. A steel must possess a certain minimum hardness in order to be classified'as tool steel, and it must possess adequate toughness and 10 wear-resistance. Other properties vary somewhat accordingto commercial practice.

Tool steels. are also characterized by a carbon content in excess of prescribed minimums, in

order to impart to thesteel the desired hard- In earlier times, carbon alone was relied used at the present time is known as high-carbon,

high-chromium steel and ordinarily contains 30 about 1.40 to 2.25 percent. carbon and Ito 18 per cent. chromium. This steel has enjoyed wide favor in cutting and shearing tools, but -it.has been observed that when this steel is used in cutting tools, foninstance'in saws for cutting comparatively soft metals, such ascopper or a generated during the cutting operation. This difliculty has restricted the use of otherwise satls-= factory steel in high speed cutting tools.

The present invention is based upon the discovery that the effectiveness of such alloy tool 4 steels can be markedly increased by incorporating' in the steel during manufacture a substan tial percentage of sulfur. This can be accomplished without substantially changing the usual manufacturing operations, and without undesirm ably affecting the hardness of the finished product.

By way of an example illustrating the nature of the invention there is set forth the following analysis of a steelwhich is markedly superior to .asteel madeinthesamewayandhavingthe In some cases molybdenum is used same analysis, but containing only the usual trace of sulfur:

Per cent by weight Carbon 1.47 Phosphorus, .03 Sulfur .28. Silicon .31 Manganese .30 Chromium 11.12 Vanadium .20 Molybdenum .71 Iron Balance Total 100.00

This steel is characterized by a high-carbon, high-chromium content, and is useful in cutting tools, such as saws and machine tools, as

.well as in shearing tools which operate continuously, or practically so, with the consequent generation of much heat. The improved steel may be manufactured by the same methods employed for making known tool steels, so that no additional operations are required. That is to say, it

may be cast, hot worked to shape, and heat treated in the usual way to impart the required hardness to the finished. product. Those skilled in the art will understand that the sulfur may.

be added to the other ingredients at the proper stage during the melting. The required amount of sulfur may be present, in some cases, in the iron used.

It will be understood that the phosphorus in the above specific example is a normal impurity, and that the silicon, manganese, vanadium and molybdenum are optional.

Although it has been recognized that a few hundredths of a per cent. of sulfur are not objectionable in tool steel, it has been customary to regard this element merely as an impurity. In accordance with the present invention thesulfur is employed substantially in excess of .15 per cent., and preferably in' amount from .20 to .75 per cent. Although even more sulfur may be used, possibly as much as 1 to 2 per cent., there appear to be no additional advantages, and some objections, to using more than .75 per cent. In

place of sulfur other similar elements may be used, particularly the closely related metalloids selenium and tellurium.

Although the invention is not to be restricted -to any particular theory of operation, it appears that the sulfur provides some lubricting action, perhaps by imparting to the tool what may be 2 acoaaea termed greasiness. This is rather remarkable because the amount of sulfur employed is so extrmely small as compared to the large volume of metal which is subjected to the action of the tool.

Although the invention was developed in connection with and is peculiarly applicable to alloy tool steels having a high-chromiumcontent, it will be appreciated that it is also applicable to other tool steels. For instance, the invention in its broader aspects may be applied to the class of tool steels which is characterized by a carbon content of from .50 to 2.50 per cent., particularly those steels which contain substantial amounts of chromium or tungsten or'chromium in conjunction with tungsten or molybdenum. These alloy tool steels may contain from 3 to 22 per cent. of tungsten or from about 4 to 12 per cent. of molybdenum. When tungsten or molybdenum is employed the chromium content usually lies in the lower portion of the range specified; and when chromium alone is relied upon to improve the hardenability of the steel it preferably ranges from 6 per cent. to a maximum of 28 per cent. It will-be understood that such alloy tool steels may contain vanadium or other known alloying elements, in addition to the usual silicon and manganese. These tool steels, as mentioned, are especially adapted for high-speed metal-cutting and metal-shearing tools and saws which operate continuously, or practically so, and which generate large amounts of heat.

Steels constituting the product of the present invention, and tools manufactured from these steels, are characterized by a hardness of from Rockwell C43 to Rockwell C66. However, the higher figure is given for purposes of illustration, and is not intended to exclude from the scope of the invention any steel which may have an even greater hardness.

Since alloy tool steels of the character described often contain small amounts of silicon and manganese, impurities such as phosphorus, and alloying elements such as those mentioned in the specific example, it will be understood by those skilled in the art that the expression the balance of said steel being iron" is intended to cover such alloy tool steels in accordance with the invention.

When the term sulfur is used in the claims it includes metalloids of the sulfur group, e. g., selenium and tellurium.

Tool steels according to the present invention possess, as indicated, a number of advantages. For one thing, it is possible to manufacture them without departing from the usual manufacturing procedure, except by the addition of a comparatively large proportion of sulfur or the like. The cutting or shearing action of such tools when used in continuous operation, with the generation of considerable heat, is markedly improved over the cutting action of similar tools without the added surfur or the like. And, the addition of the relatively large proportion of sulfur or the like produces the improvement in cutting action without adversely afiecting the desired hardness, toughness and wear-resisting properties of the tool steel.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described, or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. As an article of manufacture, a high-speed cutting or shearing tool, the working edge of which is composed of a high-carbon, high-chromium alloy steel containing from 7 to 18% of chromium, from 1.40 to 2.25% of carbon, and sulfur in amount more than .15% and less than about 2%, the balance being iron, and said steel having a hardness in excess of Rockwell C43.

2. As an article of manufacture, a high-speed cutting or shearing tool, the working edge of which is composed of a high-carbon, high-chromium alloy steel containing from '7 to 28% of chromium, from .50 to 2.50% of carbon, and sulful in amount more than .15% and less than about 2%, the balance being iron, and said steel having a hardness in excess of Rockwell C43.

3. As an article of 'manufacture, a high-speed cutting or shearing tool, the working edge of which is composed of steel containing a member of the group consisting of chromium, in the range of 7 to 28%, tungsten, in the range of 3 to 22%, and molybdenum in the range of 4 to 12%; and carbon in the range from .50% to 2.50%; the balance of said steel being iron; and said steel being characterized by a sulfur content of more than 20% and less than about 2%, and having a hardness in excess of Rbckwell C43.

ALLEN D. POTTS. DANIEL SIMONDS.