US2212228A - Alloy steel - Google Patents

Description

Patented. Aug. 20, 1940 UNITED STATES PAT ENT OFFICE ALLOY STEEL No Drawing.

Refile oi abandoned application Serial No. 181,997, December 2'7, 1937. This application June 12,

3 Claims.

My invention relates to alloy steels'and particularly to a compositionprincipally useful for cutting tools and hot and cold work dies.

This application is filed in place of my forfeited 5 application Serial No. 181,997, filed December 1937, for Alloy steel, which was allowed'on February 4, 1939, and, except for this paragraph, is identical therewith.

Until very recently it has been considered necessary, in order to obtain a .high speed steel that can be satisfactorily hardened througha 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. Although such steels with lower quantitiesof tungsten have been used, the reduction in tungsten content has always resulted in a 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 element 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 so narrow and critical. that good and poor cutting results have been obtained from approximately identical hardening treatments. In addition, these steelscontaining molybdenum as 45 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 withborax or otherwise protected to pre- 50 vent such losses of carbon and molybdenum.

I have discovered an alloy steel containing carbon, chromium, silicon and vanadium, together with relatively small quantities of molybdenum and tungsten in certain critical proportion which 55 not only has cutting qualities markedly s perior is extremely restricted. This hardening range 1940, Serial No. 340,097

to any high speed steels of which I am aware but in which the hardening diiiiculties 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% Val", .50 to 2.5

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 one-third 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 austenitewhen the composition is hardened.

, The above statements respecting the chromium content areespecially 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 additions 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. Hence, it is to be understood that cobalt in quantities up to about 2% may be added to compositions of the above analysis. However, it has- .been noted that, with cobalt near the permissible 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 decar- 'burization and demolybdeniumization.

all, a total of 11900 inches.

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

.70 to .80 Cl" 3.50 to 4.50 Si. 1.00 to 1.25 M0 3.00 to 3.75 'W 5.25 to 6.00 Va 1.50'to 2.00 .75 to 1.25

The following are specimens of my alloy:

0 01' Si Mo W Va 00 Comparative cutting tests of tools made from my alloy with tools made from the following highspeed alloys now available, including a standard 18-4-1 alloy used-as a control, have been made.

v High-speed alloys used for comparative tests Heat N0. O Cr Si M0 W Va C0 Test #1 was made on a log of 1% carbon tool steel annealed to '179 Brlnell and run without a cooling lubricant. The depth of cut was the tool feed 0.030 inch per revolution of the log; and the rate of travel of the test log with respect to the tool was 111 feet per minute. All tools were run to failure with the following results:

Tool made from heat No. Inches cut T517 V v 4,400- T544 5,200 L-xx. 5,400 TW I 11,900

The 1:001 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 wasthen 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

Test #2 was made on a test log of SAE steel 2335, having Brinell hardness of 205. A soluble oil was used as a cooling medium; the depth of cut was the tool feed per revolution of the log was 0.037 inch; and the rate of travel of the log 7 with respect to the m1 was 140 feet per minute,

All tools were run to failure with the following results:

In test #3 a tool made from heat #T383A was run at a surface speed of feet per minute against a tool made from heat #L-XX which is a. standard 18-4-1 high-speed steel. All conditions except the surface speed of the tool were the same as in test #2 stated above. The results were as follows:

Tool made from heat No. Inches cut Irxx. 8, 280 Team 16,000

Tool made from heat No. Inches cut m 13, 600 T487 8, 800 T47 6, 000 T47 3, 900 L- 8, 400

Unless the tungsten content is maintained at 7 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 a heat #T532 of the following analysis C L. .77 C1; 4.19 Si .76 MO 4.99 W" 6.34 CO 1.07 Va--. .72

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 cut 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 asurface speed of 112 feet 1 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, out

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 #4.

My alloy steel hardens very well for high speed cutting purposes from a temperature range of 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 composition. 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 tungsten from more than 5% to less'than 8% and at least one-third greater than the molybdenum, vanadium from 0.5% to 2.5% 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 containinga 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 silicon from 0.50% to 2.0%, molybdenum from 2.5% to 5.0%, tungsten from over 5% to under 8% and at least one-third greater than the molybdenum, vanadium from 0.50% to 2.5%, 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 1.50% to 2.00%, and the balance iron.

RALPH P. DE VRIES.