US3136665A - Alloy steel - Google Patents

Description

United States Patent Jersey. No Drawing. Filed Aug. 17, 1960, Ser. No. 50,084 1 Claim. (Cl. 14836) This invention relates to alloy steel and more particularly to a tool and die steel having improved room temperature impact properties.

This application is a continuation-in-part of my application Serial No. 662,805, filed May 31, 1957, now Patent No. 2,950,968, August 30, 1960, and assigned to the assignee of the present application. In that application there is described an invention by means of which unexpected and unique results are achieved in providing a tool and die steel which is susceptible of deep hardening in large sections and which has outstanding toughness or impact properties at room temperature. These results are attained by the use of copper as an alloying element in carefully controlled amounts in proportion to the carbon and manganese content of the composition.

The tool and die steels of said application are commonly identified as cold work tool steels and are air or oil hardening. There are numerous instances when a composition having the outstanding properties of that set forth in said copending application is not required but where improved impact properties with better toughness is required than was hitherto available. In the case of the shock resisting tool steels, it has been the usual practice to rely upon a relatively low carbon content in attaining better toughness. In this connection it may be noted that products such as tools and dies which are normally subjected to impact loading are best produced from a composition having high impact strength. The present invention stems from the discovery that a water hardening tool steel may be provided having improved impact properties without the sacrifice in the maximum attainable as-hardened and tempered hardness usually associated with the conventional practice of improving the impact properties by reducing the carbon content.

The foregoing as well as additional advantages of the present invention are achieved by providing an alloy steel consisting essentially of about 0.3% to 0.9% carbon, about 1.0% to 4.0% copper, about 0.2% to 1.5% silicon, up to about 1.5 molybdenum and the remainder substantially iron. As will be more fully pointed out, the maximum amount of carbon for any given total content of the alloying elements is limited to a value which does not exceed the eutectoid forming quantity of carbon in the composition for that alloy content. It is not intended to exclude elements which may be present from the standpoint of good melting practice, which are normally present in varying amounts in commercial steels or which may be added without adversely affecting the room temperature impact properties of the composition.

Thus, residual amounts of manganese from about 0.2% to about 0.6% may be present. Somewhat more manganese may be included to take advantage of its beneficial effect on the hot workability of the steel. As a further example, up to about 0.5% vanadium may be included for the purpose of grain refinement.

Carbon to a large extent affects the attainable as-hardened and tempered hardness of the composition. A minimum of about 0.3% carbon is usually necessary to attain the minimum hardness desirable in a tool steel and a minimum of about 0.45% carbon is preferably used to insure a minimum hardness of Rockwell C-55. When carbon is present not in excess of amounts corresponding to its eutectoid proportions for this composition, copper, which must be in solid solution, is effective to provide the desired beneficial results. The eutectoid carbon content ranges from about 0.7% to about 0.9% depending upon the alloy content, the eutectoid alloy contaimng less carbon as the content of the alloying elements in the composition increases, and preferably the carbon content is no more than about 0.6%. As the carbon content is increased over that in the eutectoid then even the larger copper contents are ineffective to provide the desired improvement in room temperature toughness.

When copper is present in amounts above about 4%, such undesirable metallurgical phenomena as precipitation of the copper are likely to occur when the alloy is hardened and drawn. Furthermore, in processing and treating my composition after it has been subjected to a hardening treatment, care is taken to avoid such treatment, particularly at elevated temperatures, as may be likely to result in precipitation of the copper out of solid solution. Within the ranges specified copper is readily retained in solid solution so long as the composition is not maintained at temperatures of about 700 F. or above for any appreciable length of time. Thus the duration of any treatments carried out at elevated temperatures after hardening is eflected in a short time, about ten minutes.

I preferably limit the silicon content to the amount required, approximately 0.5%, to attain desirable deoxidation and to maintain fluidity in the melt. While I may include as much as 1.5% silicon I find that better impact properties are achieved with smaller amounts of silicon.

Up to about 1.5 molybdenum is included in order to achieve desirable hardenability properties in the composition. Preferably a minimum of about 0.5 and no more than about 1.0% molybdenum is included in the composition.

The examples whose analyses are shown in Table I, below, were prepared to demonstrate the improved properties of this composition and specimens which were tested had been forged from ingots which were processed by forging and rolling and were heated at a temperature of about 1600 F. for about ten minutes and then were water quenched. This was followed by drawing or soaking at 300 F. for one hour. The results of standard notched bar impact tests on these specimens, A" x A" x 2 /2", processed and tested in accordance with the standard established by the American Society for Testing Materials are recorded under impact strength. These recordmgs are the average of two tests.

Table I Impact Ex. No. 0 Mn Si Mo Cu av. of2

tests The results of the impact tests recorded in Table I represent a range of improvement of about 3 to 6 times as is evident from a comparison with results achieved with a tool and die steel having analyses as indicated for 3 Examples 10 and 11 in'Table II below and to which copper has not been added.

The specimens having the composition of Examples 10 and 11 were prepared and processed as indicated in connection with the examples of Table I. Notched bar impact tests, the results of which are shown in Table II as the average of two tests on identical specimens, were carried out in the same manner and under the same conditions as was done with Examples 1-9.

In order to achieve the improved impact strength in my composition the total content of the alloying elements should not exceed about 6% and preferably is kept below about by weight of the composition to achieve the best impact properties. V

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:

An alloy steel article consisting essentially of about 0.45% to 0.6% carbon, about 0.4% to 0.6% manganese, about 0.4% to 0.6% silicon, about 0.5% to 1% molybdenum, about 1% to 4% copper, the remainder being iron with incidental impurities, the combined content of the alloying elements being less than 6%, said article being water hardened and tempered at a temperature below about 700 P. so as to retain said copper in solid solution, and said article having a hardness of at least about Rockwell C- and good toughness as indicated by impact tests.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES The Journal of the Iron and Steel Institute (British),

" volume No. 2, 1907, pages 4, l4, and 17.

Alloys of Iron and Copper, page 195, by Gregg and Daniloif, published in 1934 by the McGraw-Hill Book Company, New York.