US2241187A - Alloy steel - Google Patents

Description

Patented May 6, 1941 I ALLOY STEEL Ralph P. De Vries, Menands, N. Y., assignor to Allegheny Ludlum Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Original application December 27,

1937, Serial No. 181,997.

Divided and this application May 24, 1939, Serial No. 275,460

4 Claims.

This application is a division of my co-pending application Serial No. 181,997, filed December 27,

f My inventionrelates to alloy steels and particularly to a composition principally useful for cutting tools and hot and cold work dies.

Until very recently it has been considered necessary, in order to obtain a high speed steel that can be satisfactorily hardened through a reasonably wide temperature range and which will function satisfactorily as a cutting tool at feeds and speeds which have come to be accepted as standard in the metal working industry, to incorporate about 18% of tungsten together with chromium, vanadium and other alloying elements in the composition. Althoughsuch steels with lower quantities of tungsten have been used, the reduction in tungsten content has always resulted inja substantial reduction in the cutting speeds and feeds obtainable with tools 'made therefrom;

Within the last few years high speed steels have been proposed in which molybdenum is the principal alloying'ele'ment instead of tungsten, but in which the molybdenum has been supplemented by the usual high speed elements carbon, chromium and vanadium," and either with or without a comparatively small quantity of tungsten. Such steels have attained results in cutting which approximate very closely the results attained with the usual high speed steels containing 18% of tungsten and other elements.

However, steels of this type containing molybdenum as the principal alloying ingredient are subject'to certain very serious limitations in that the range of hardening temperature within which the steel must be treated to give adequate service is extremely restricted. This hardening range is so narrow and critical that good and poor cutting results have been obtained from'approximately identical hardening treatments. In addition, these steels containing molybdenum as the principal alloying ingredient either decarburize or demolybdenumize to such an extent in the necessary heating operations for forging, annealing and hardening that they usually must be coated with borax or otherwise protected to prevent such losses of carbonand molybdenum.

I have discovered an alloy steel containing carbon, chromium, silicon, cobalt and vanadium, to-

gether with relatively small quantities of molyb denum and tungsten in certain critical proportions which not only has cutting qualities marl:- edly superior to any high 'speedsteels of which I am aware but in which the hardening difllculties heretofore encountered in steels of this general type have been eliminated.

The essential elements of my alloy steel and the proportions thereof, by weight, are as follows:

C .20 to 1.0

Cr 2.00 to 10.0

Si .50 to 2.0

Mo 2.50 to 5.0

W From more than 5 to under 8% Va .50 to 2.5

Go 0.1 to 2.0

Balance Iron While the tungsten and molybdenum may be used throughout the ranges given above, it is essential in all cases that the quantity of tungsten present in the composition be at least onethird greater than the quantity of molybdenum.

Where the alloy is to be used for high speed cutting tools, the chromium content should be maintained in the lower part of the range stated, say from 2% to 5%. However, where the alloy is used for hot and cold working dies, the higher chromium ranges may be employed. This is due to the fact that the temperatures from which hot and cold die steels are usually hardened lie from 200 F. to 300 F, below the temperatures which are suitable for hardening high speed steel, and in such a case the higher chromium contents do not produce austenite when the composition is hardened.

The above statements respecting the chromium content are especially true when considered in conjunction with hot and cold work die steels having a carbon content in the range of .20% to .60% which is lower than the usual carbon content of high speed steels.

It is Well known that additions of cobalt will improve the characteristics of any high speed steel, but the improvement may not be apparent in cutting all kinds of steel. However, in cutting certain particular types of steels which, although they may not be hard, are known as tough or mean steels to cut, the effect of cobalt additlons is very noticeable. Furthermore, I find that the addition of small quantities of cobalt, say up to about 2%, has a marked tendency to inhibit demolybdenumization or decarburization during the necessary heating operations of forging, annealing and hardening tools made therefrom. However, it has been noted that, with cobalt near the permissible upper limit, the best results are obtained with a vanadium content of from about 1.25% to about 1.75%, while if 00- bait is present only in a very small percentage, from about 1.5% to 2.0% of vanadium may be advantageously used.

Manganese in quantities up to about 2% may also be incorporated in my composition. Within this range manganese seems to increase the cutting qualities and also helps to prevent decarburization and demolybdenumization.

The preferred ranges of the various elements in my alloy when used for high speed cutting tools are as follows:

Comparative cutting tests of tools made from .my alloy with tools made from the following high-speed alloys 'now available, including a standard 1841 alloy used as a control, have been made.

High-speed alloys used for comparative tests Cr Si Mo W Va 00 Test #1 was made on a log of 1% carbon tool steel annealed to 179 Brinnell and run without a cooling lubricant. The depth of out was the tool feed 0.030 inch per revolution *of the log; and the rate of travel of the test logwith respect to the tool was 111 feet per minute. All tools were run to failure with the following results:

'lool made from heat No.

The tool made from Heat #T564A had not failed when it'had run the length of the test log after cutting 6300 inches thereon, and a second cut was then started on the log. Due to the decrease in diameter of the log by reason of the earlier cuts, however, the surface speed relative to the tool during the second cut was reduced to 107 feet per minute.

Operating on the second cut the tool made from Heat #T564A out 5600 inches before failure or, in all, a total of 11,900 inches.

Test #2 was made on a test log of SAE steel 2335, having a Brinnell hardness of 205. A soluble oil was used as a cooling medium; the depth of cut was A"; the tool feed per revolution of the log was 0.037 inch; and the rate of travel of the log with respect to the tool was 140 feet per Inches cut 7 minute. All tools were run to failure with the following results:

Tool made from beat No. Inches cut T517 2, 520 T544 13, 440 LXX 8, 820 T564A 12, 600

In test #3 a tool made from heat No. T464 was run at a surface speed of feet per minute against tools made from heat Nos. T470, T471 and L-XX. Except for the surface speed, all other conditions were the same as set forth in respect to test #2 above.

Tool made from heat N0. Inches cut T404 13, 600 T470 6, 000 T471 3, 900 L-XX 8, 400

Unless the tungsten content is maintained at least one-third greater than the molybdenum content, the effect on the cutting properties of the tool is very marked as will appear from the following tests. A tool made from heat #T532 of the following analysis:

when run against a tool made from heat #L-XX, used as a control, showed very poor results.

Both tools were run on a log of 1% carbon tool steel with a depth of out of and a tool feed of .030 inch per revolution of the log. No cooling lubricant was used and the tools were run at different surface speeds.

The tool made from heat #T532 failed after cutting only 3450" at a surface speed of 112 feet per minute, while the tool made from heat #L-XX (standard 18-4-1) when run on the same log at a surface speed of feet per minute, cut 5700" before failure.

That silicon has an important bearing on the cutting characteristics of tools made from my alloy is apparent from foregoing tests Nos. 1 and 2.

For example, a tool made from heat #T564A of my alloy is far better than a tool made from heat #T517 and containing only 0.15% of silicon, although the latter alloy not only contains tungsten and molybdenum within the limits and relative proportions of my invention but also 3.85% of cobalt.

That the percentages and relative proportions of the tungsten and molybdenum specified for my alloy are critical will be apparent from a consideration of the result of the test last above given and also test #3.

My alloy steel hardens very well for high speed cutting purposes from a temperature rangefof 2250 F.-2350 F., thus coming within the normal hardening ranges of high speed steel with a very much higher tungsten content. I consider this to be an outstanding advantage of this composi tion. After this heat treatment a secondary hardness is developed by drawing in a temperature range of 950 F.1050 F.

Where the alloy is to be used as a high speed steel, I prefer to keep the carbon somewhat higher than is the case where the steel is to be used for hot die purposes. In the latter case the carbon is preferably kept between .20% and .60%.

What I claim is:

1. An alloy steel adapted for tools and dies and containing carbon from 0.20% to 1.0%, chromium from 2% to 10%, silicon 0.50% to 2%, molybdenum from 2.5% to 5%, tungsten from more than 5% to substantially less than 8% and at least one-third greater than the molybdenum, vanadium from 0.5% to 2.5%, cobalt from 0.1% to 2% and the balance iron.

2. A high speed tool steel characterized by having a hardening temperature range of the order of 2250 to 2350 F. with comparatively low contents of tungsten and molybdenum; said steel containing a plurality of alloying elements of which the following are the only elements necessary to attain said characteristic: carbon from 0.60% to 1.0%, chromium from 2% to 10%, silicon from 0.50% to 2.0%, molybdenum from 2.5% to 5.0%, tungsten from over 5% to substantially less than 8% and at least one-third greater than the molybdenum, vanadium from 0.50% to 2.5%, cobalt from 0.1% to 2% and the balance iron.

3. A high speed tool steel characterized by having a hardening temperature range of the order of 2250 to 2350 F. with comparatively low contents of tungsten and molybdenum; said steel containing a plurality of alloying elements of which the following are the only elements necessary to attain said characteristic: carbon from 0.70% to .80%, chromium from 3.5% to 4.5%, silicon from 1% to 1.25%, molybdenum from 3% to 3.75%, tungsten from 5.25% to 6.00%, vanadium from 1.25% to 1.75%, cobalt from 1.25% to 2%, and the balance iron.

4. A high speed tool steel characterized by having a hardening temperature range of the order of 2250 to 2350 F. with comparatively low contents of tungsten and molybdenum; said steel containing a plurality of alloying elements