US2195402A

US2195402A - Process of making cast tool steel

Info

Publication number: US2195402A
Application number: US179107A
Authority: US
Inventors: Baird Charles
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-12-10
Filing date: 1937-12-10
Publication date: 1940-04-02
Anticipated expiration: 1957-04-02

Description

Patented Apr. 2, 1940 PROCESS OF MAKING CAST TOOL STEEL Charles Baird, Detroit, Mich.

No Drawing.

16 Claims.

This invention relates to processes for preparing cast tool steel capable of being directly used for cutting tools such as tool bits without forging or metal working operations.

More specifically the invention relates to the production of cast high speed steel tool bits without forging or hot working the metal and without heating the bits above the critical temperature of the high speed steel by melting a high speed steel in an indirect are electric furnace, casting the molten metal in molds of the approximate tool size and grinding the castings to shape.

Metal cutting tool steels have a definite range of carbide particle size and grain size for best performance in a certain class of operation. If the carbide particles and grains of the metal have sizes that are too small, the tool will fail too rapidly at the cutting point as a result of the high temperatures combined with the abrasiveness of the metal machined. It is thus obvious that cutting steels with too small grain and carbide particle sizes are commercially inferior in certain operations to those having the larger sizes.

If the) grain and carbide particle sizes of the cutting steel are too large tobe within the definite range of carbide and grain particle sizes for cutting steel, the cutting tool will be too brittle, both at its cutting point or edge and at its holding or gripping end, for commercial use.

It has been the practice, in making cuttin tools, to cast high speed steels with a grain and carbide particle size too large to be included within the desired range for cutting tools. The cast steel has then been hot worked or forged to the desired grain size. This process, of course, is expensive and the hot working operations have some deleterious effect upon the steel.

The Langenberg U. S. Patent 1,492,567 discloses a process of making tool steels without forging or hot working the metal by melting a high speed steel, high in molybdenum content, in an electric or crucible furnace. The molten metal is cast in molds to the approximate desired tool size and the castings are then heated to temperatures from 900 to 1050 C., (1652 to 1922 F.) which temperatures are above the critical temperature of the steel. The castings are cooled and reheated to between 725 C. to 850 C. (133'7 to 1562 F.) until the molybdenum carbides are uniformly distributed throughout the mass. The castings are then ground to shape and given the usual heat treating cycle for high speed steels including another heating to above the critical point of the steel.

. quenched to room temperatures.

Application December 10, 1937, Serial No. 119,107

I have now found that the melting of a ferrous tool steel charge in an indirect arc rocking electric furnace has a. definite effect upon the grain and carbide particle size of the metal. Castings of high speed steel poured from the indirect are electric furnace have grain and carbide particle sizes within the range desired for cutting tools. If these castings are of the approximate tool size, the same need only be ground for direct use as cutting tools.

My process therefore not only avoids the heretofore necessary hot working, or forging operations but also renders unnecessary the heat treatment of high speed steels above their critical temperature.

The ferrous metal cast tool steels of this invention have longer tool life than the best heretofore known ferrous metal tools of similar composition.

I have also discovered that the cutting ability and resistance to impact of some ferrous metal high speed tool steels, such as steels of the 18-4-1 type, prepared according to this invention can be increased by subjecting the tools to a single or to a double draw heat treatment at temperatures below the critical temperature of the steel.

The single draw heat treatment comprises a heating of the castings to temperatures of from 1000 to 1150 F., for a period dependent upon the mass of castings, followed by a cooling in circulating air to room temperature. A heat treatment at 1000 to 1150 F. for thirty minutes to one hour is usually sufficient for tool bits. Thus a tool bit 8-10" in length and A square need only be heated for one hour. If temperatures above 1150 F., but below the critical temperature of the steel, are used in the heat treatment, the time may be decreased. Thus a heat treatment at 1650 F. for ten minutes might be sufflcient.

The double draw heat treatment includes heating the castings to temperatures around 1050" F. for a period dependent upon the mass of the castings as explained above, cooling the heated castings sufliciently slow to prevent formation of cracks and reheating the cooled metal to temperatures around 1050 F. The reheated metal is then eitherrapidly oil quenched or slowly air Cooling from the first heat treatment is preferably effected in circulating air since-this treatment is suficiently slow to prevent the formation of cracks.

Ferrous metal high speed steel alloys with an iron content of from 15% to 85%, a carbon con- I tent of from 0.6%to 2%, and the balance selected from the group comprising tungsten,

molybdenum, chromium, vanadium and cobalt are useful materials for the process of this invention. The steel alloys may also contain minor amounts of nickel and tantalum or other secondaryalloys. Steel alloys having a high iron content of from 60% to 80% and the balance one or more of the following elements: tungsten, molybdenum, chromium, vanadium and cobalt, are desired alloys for the process of this invention.

Specifically, high speed steel alloys of the 18-4-1 type (18% tungsten, 4% chromium, 1% vanadium, balance iron) are preferred for the process of this invention.

It is then an object of this invention to provide high speed tools wlthoutforging or hot working operations, and without heat treating the metal above its critical temperature.

Another object of this invention is to provide cast tool steels from high speed steels without hot working or heat treating the castings.

Another object of this invention is to convert high speed steels into a desired grain and carbide particle size for cutting tools without hot working the metal.

Another object of this invention is to utilize an indirect are electric furnace for producing a desired grain and carbide particle size in high speed steel.

A further object of this invention is to improve the hardness and resistance to impact of cutting tools by heat treating the same at temperatures below their critical points.

Other and further objects of this invention will become apparent to those skilled in the art from the following specific examples illustrating the invention. It should be understood that the examples are intended only to give specific data relating to processes already carried out and are not intended to limit the invention.

Example 1 A high speed toolsteel alloy of the following analysis:

. Percent Tungsten 18 Chromium 4 Vanadium 1 Carbon 0.84 Iron Balance was melted in an indirect arc electric furnace and poured into cold graphite molds of the approximate desired tool bit size at temperatures between 2845" F. and 2950 F. The furnace used was a Detroit Electric Furnace Company rocking type indirect are electric furnace. The furnace was lined with magnesite, the melting atmosphere in the furnace was non-oxidizing and predominately reducing, and the melt was agitated by a continuous and increasing rocking angle of the furnace. I

The casting was allowed to solidify and cool in the mold. The cooled casting was then stripped from the mold and directly ground and sharpened to form a cutting tool bit.

The resulting tool bit was then tested under fatigue conditions to determine its relative tool life as compared with standard commercial grade cutting tool bits. For this purpose a shaft of annealed S. A. E. 3140 steel was cut with the tool bit at a cutting speed of 166 feet per minute with a .0127 inch feed at a depth of .1000 inch. Under these conditions, the cast tool bit lasted 21.10 minutes before failure. No attempt was made to cool the tool bit during the cutting operation. I

A high speed steel tool bit of the identical analysis, but made according to the known process of hot working the metal to produce a tool bit of the exact shape as the cast cutting tool bit, only had a tool life of 5.06 minutes under the same conditions to which the cast tool bit was subjected.

Other commercial cutting tool bits now on the market were also subjected to the same'cutting tests to determine their tool lives. A cutting tool bit known as Dreadnaught" and having the following analysis: 1

Per cent Carbon .80 Manganese .28 Chromium 2.75

Tungsten 16.13 Vanadium 1.03

. Iron Balance had a tool life of 6.90 minutes under the same conditions.

A commercial tool bit now on the market known as Cyclops B-6 having the following analysis:

Per cent Chromium .l. 4 Tungsten 18 Vanadium 1, Carbon 0.65 Iron Balance had a tool life of 8.45 minutes under the same conditions.

Another commercial tool bit known as Blue Chip and having an analysis as follows:

- Per cent Carbon .70 Manganese .25 Chromium 4.00 Tungsten 18.00 Vanadium 1.00 Iron Balance had a tool life of 5.44 minutes under the same conditions.

The above comparisons clearly show that a high speed steel melted in an indirect are electric furnace and directly cast into the desired tool shape has a longer tool life than tool steels made by the usual forging operations.

Example 2 A high speed steel alloy of the following analysis:

was melted in an indirect are electric furnace and cast in cold graphite molds at temperatures.

between 2845 and 2950 F. The castings were allowed to cool in the molds, were then ground The tools;

The heat treated tools were tested under fatigue 6 conditions, to determine their tool life by using them to cut a shaft of S. A. E. 3140 normalized steel alloy at a speed of 126 feet per minute with a feed of .0127 inch and a cut depth of .1000 inch. The tool life in minutes under these fatigue conditions was 16 minutes. A tool. of Cyclops B-6 tool steel, when tested under the same conditions, only had a tool life of 2.21 minutes.

The tool as originally cast had a. Rockwell hardness of 60.5. After the one hour heat treatment, the Rockwell hardness was increased to 68.5.

Example 3 A high speed tool steel having the same analysis as the steel described in Example 2 was cast under the same conditions described in Example 2, subjected to a one hour draw at 1050 F. and was cooled in circulating air to room temperature. The resulting tool was then tested by cutting a heat treated shaft of Ford copper-silicon steel. The cutting conditions were as follows:

Speed a. feet per minute- 99.7 Feed inch .0127 Depth of cut do .1000

The one hour draw at 1050 F. increased the Rockwell hardness of the tool from 60 to 68. The tool life under the test conditions indicated was 9.55 minutes.

A cutting tool of Cyclops B-6 steel had a tool life under the same conditions of 2.40 minutes.

Example 4 A square tool bit having the same analysis of the tool of Example 2 was subjected to a. one hour draw at 1100 F. and was cooled in circulating air to room temperature. The tool was then tested under the same conditions outlined in Example 3.

The Rockwell hardness of the tool was increased from 61 to 67 by a one hour draw at 1100 F. The tool life under the conditions indicated was 10.48 minutes.

Example 5 A tool bit having the analysis of Example 2 was cast according to the same procedure of Example 2 and was heated for one hour at 1050 F., cooled in circulating air to room temperature and reheated to 1150 F.'f01' one hour. The reheated casting was then quenched in oil to room temperature.

The double draw heat treatment increased the Rockwell hardness of the tool from 61 to 68 and the tool had a life of 8.46 minutes under the,

conditions indicated in Example 3.

Example 6 I process of this invention results in cutting tools.

having several times as great a tool life as the heretofore known forged cutting tools or othergrades of ferrous metal cutting tools now on the market. The single or double draw heat treatments of this invention increase the Rockwell hardnesses of the cast tools but these heat treatments are'not necessary to produce high-grade cutting properties since, as indicated in Example 1, the unheat-treated cast tool of this invention has a much superior tool life than known commercial tools. However, the impact values and hardness of a tool steel, such as steel of the 18-4-1 group, when castfrom the furnace as described, were materially increased by single or double draw heat treatments, both treatments being at temperatures below the critical temperature of the steels.

By this means an improved cutting tool may be manufactured at a lower cost, it being unnecessary to heat, forge and reheat the tools to give them necessary physical properties.

I am aware that numerous details of the process maybe varied through a wide range without departing from the principles'of this invention,- and I, therefore, do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

I claim as my invention:

1. The process of making cutting tools without forging or heat treating the tools above their critical point which comprises melting a high speed steel in an indirect are electric furnace, agitating the melt, casting the molten steel into molds of the approximate tool size, allowing the castings to solidify in the molds, and grinding the castings to tool shape.

2. The process of making cutting tool bits without forging or heat treating operations which comprises melting a ferrous high speed steel alloy containing 18% tungsten, 4% chromium, 1% vanadium in an indirect are electric furnace until it is sufficiently molten to be readily poured, agitating the molten metal, casting the molten metal in molds of the approximate tool size, allowing the castings to solidify in the molds and grinding the castings to tool shape. 7

3. The process of making tool steel which comprises melting a high speed steel having an iron content of from 15% to 85%, a carbon content of from .6% to 2.0% and the balance consisting of at least one of the metals selected from the,

group comprising tungsten, molybdenum, chromium, vanadium and cobalt, in an indirect are electric furnace until the metal is sufficiently molten to be readily poured, agitating the molten metal, casting the molten metal into molds of the approximate desired tool size, allowing the metal to solidify in the molds and grinding the -casting the metal into cold molds of the approximate tool size, and grinding the castings to size and shape for use as cutting tools.

5. The process of making cutting tools without hot working or high temperature heat treatment which comprises melting a. high speed tool steel charge in an indirect are electric furnace, said tool steel charge comprising 18% tungsten, 4% chromium, 1% vanadium and the balance iron, rocking the furnace to agitate the melt, pouring the molten metal into molds of the approximate tool size and shaping the castings without hot working the metal to the tool size.

6. The process of making cutting tools from high speed steel alloys without forging or other metal working operations which comprises heating a high speed steel alloy in an indirect arc electric furnace to temperatures between 2845 and 2950 F., agitating the metal, pouring the molten metal into molds of the approximate tool size, allowing the metal to solidify in the molds, heating the resulting castings to temperatures above 1000 F., but below the critical point of the steel, and cooling the castings to room temperature.

7. The process of making cutting tools without forging or metal working operations which comprises melting a high speed steel alloy charge in an indirect arc electric furnace, agitating the melt, casting the molten metal into molds of the approximate tool size, allowing the metal to solidify in the molds, heating the castings to temperatures from 1000 to 1150 F. for about one hour. and cooling the castings to room temperature.

8. The process of making cutting tools without forging or heat treating the metal above its critical point which comprises melting a high speed steel alloy charge in an indirect are electric furnace, pouring the molten metal into molds of the desired tool size, allowing the metal to solidify in the molds, heating the castings to temperatures of about 1050 to 1100 F. for one hour, cooling the castings in circulating air to room temperature, reheating the cooled castings to temperatures of 1050 to 1150 F. for about one hour and quenching the reheated castings to room I, temperature.

9. The process of increasing the hardness, resistance to impactand cutting properties of a high speed tool steel containing 18% tungsten, 4% chromium, 1% vanadium which comprises preparing a melt of the steel in an indirect arc rocking type electric furnace, rocking the furnace to agitate the melt, casting the molten steel into a mold of approximate tool size, allowing the casting to cool, and subjecting the cooled casting to a combination low temperature heat treatment into a mold of the approximate tool size, allowing the casting to cool, and heating the cooled casting to 1050 F. for at least thirty minutes, quenching the casting in circulating air, reheating the quenched casting to 1050'1'. for at least thirty minutes and quenching the casting inoil.

11. The process of making castings adapted for use in preparing high speed tool bits without forging or other metal working operations which comprises heating a high speed tool steel in an indirect are electric furnace to superheat temperaturesbetween 2845" F. and 2950 F., agitating the metal, pouring the' molten metal into molds to form castings of the approximate tool bit size, heating the castings to temperatures above 1000 F. but below the critical temperature of the steel, cooling the heated castings to room temperature, reheating the castings to temperatures above 1000 F. but below the critical temperature of the steel and again cooling the castings to room temperature.

12. The process of making cast high speed steel tool bits without forging or heat treating above the critical temperature of the steel which comprises melting a high speed steel containing about 18% tungsten, 4% chromium and 1% vanadium with, the heat of an electric arc, agitating the molten steel, casting the molten steel into molds of the approximate bit size, allowing the castings to solidify in the molds and grinding the castings to tool bit shape.

13. A cast cutting tool comprising a high speed steel alloy cast directly from an agitated electric arc furnace melt into approximate tool size, said tool having high Rockwell hardness and prolonged tool life.

14. A cast high speed steel tool bit containing to iron, 0.6 to 2.0% carbon. and the balance consisting of at least one alloy metal selected from the group comprising tungsten, molybdenum, chromium, vanadium and cobalt, having a Rockwell hardness of from 60 to 68 and obtainable by casting directly into tool size from a rocked indirect are electric furnace melt.

15. A cast cutting tool comprising a high speed steel alloy containing about 18% tungsten, 4% chromium, 1% vanadium, and the balance substantially iron cast directly from an agitated indirect are electric furnace melt into molds of the approximate tool size and having a Rockwell hardness over 60.

16. A cast tool steel having a Rockwell hardness of about 67 comprising a high speed steel alloy containing 18% tungsten, 4% chromium, 1% vanadium and the balance substantially iron and obtainable by melting the steel alloy with an in-