US1680937A - Treatment of alloy steel - Google Patents

Description

Patented Aug. 14, 1928.

UNITED STATES PATENT OFFICE.

ARTHUR C. DAVIDSON, OF BRONXVILLE, NEW YORK, ASSIGNOR TO 1). 00., INC.,

NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TREATMENT OF ALLOY STEEL.

No Drawing.

This invention relates to treatment of alloy steel, and has for its object to produce castings more especially for milling cutters, reamers, countersinks, bar stock for lathe 5 tools, end mills, etc., which will be tough, homogeneous, free from blow holes, gases and other impurities to such an extent as to be adapted for use after finishing and heat treatment without the necessity of rolling, forging or hammering. By this 1nvent-ion, it is possible to produce a wide range of alloy steels in the form of castings at a great saving in cost as well as improvement in quality, especially in semi and high speed alloy steels, as compared with the best forged, rolled or hammered tool steels now on the market.

I have discovered that the ordinary scavenging treatment with silicon, manganese, etc., for removing impurities inelectric furnace or crucible steel just before pouring, is ineffective. This is evidenced by the weakness and lack of uniformity of the castings due to blow holes, slag, carbon,

other impurities and crystallization due to rapid solidification foundin cast steel tools heretofore produced, variation of analysis in different parts of the same casting, and loss of expensive alloying metals used.

Thus for vanadium, there is ordinarily a loss of one-half and upward, whereas by this process, the loss can be kept between one-fifth and three-tenths, which effects a decided saving v.inthis expensive material.

Again, the percentage of usable castings from a melt is important, because alloy steel is expensive at best, and a high percentage of loss increases the cost of the remainder. Furthermore, these figures are affected by the amount of metal lost from a usable casting in the head and risers, so

that it is desirable to reduce this loss as much as possible.

By this process, day to day results in a commercial foundry producing form tools such as milling cutters, reamers, countersinks, etc., in sand molds, show over 90% usable castings, with 30% or less for the heads, as compared with ordinary steel foundry practice using a head equal to or greater than the casting and having a much lower percentage .of good castings. In many castings I do away with risers entirely. As

far as I am aware, I am the first to produce uniform cast alloy steel form tools Application filed October 28, 1919. Serial No. 383,966.

in quantity on a commercial basis, which excels the best forged tools in the most difficult kinds of work.

The process of this invention enables these results to be obtained by producing a tough, dense and homogeneous steel when set, and of ext-remeffluidity when poured. The tools may be cast within .015 inch on surfaces, enabling finishing to be by grinding, with a large saving in laborcost, and can be heat treated according to usual practice.

I make up the melt such as of iron, tungsten and chromium in any desired manner so as to secure complete amalgamation. These materials melt at about 2900 degrees F., from which the temperature is raised to 3300 degrees F. and continued for thirty minutes or more. A quantity of scavenging deoxidizing mixture is now added to remove oxides, sulphur, phosphorus, etc. This mixture will amount to about 35% of the melt, containing some or all of silicon, titanium, vanadium, maganese, aluminum, etc., as desired. Alloying metals such as cobalt, zirconium, molybdenum, uranium,

etc., which would otherwise be volatilized or oxidized and lost, can now be added. The vanadium used .at this time is for scavenging, and not for alloying, as alloying vanadium is added later so as not to be oxidized. In ordinary practice, the melt would now be kept at 3100 to 3200 degrees F. for a few minutes and then cast in an ingot mold, but could not produce satisfactory or uniform cast tools. Cast ingot steel of suitable analysis is then hammered or rolled and annealed, and finally machined intotools at considerable expense. For cast form tools or bar'cuttin-g stock, additional refinement is necessary to eliminate oxides, gases and other impurities.

After the last mentioned alloys such as cobalt etc. are added, oxidation of the alloys is prevented by another treatment with 1 the same scavenging deoxidizing mixture, while holding at or above 3400 degrees F. during 30 minutes or more. The temperature is now dropped to about 3200 degrees F. and a charge of iron, tungsten and chro- 105 mium similiar to that before used is employed except that it is somewhat less than one-half as much, and contains .some iron scale". Tantalum amounting to .1% of the melt is preferably added to this charge. 110

These charges are in packages tied to iron rods so as to be inserted by the melter at the bottom of the electric furnace or crucible. The melt immediately becomes more fluid and quiets down as the heat is raised to above 3200 degrees F. to about 3400 degrees F. and maintained for 10 minutes.

Alloying vanadium can now be added, with only an allowance for loss, as stated, of 20% to 30%, as compared with over 50% for previous practice, while maintaining say 3300 degrees F.. for about 10 minutes.

The bath is now quiet, and appears to be free of impurities, but such is not the case, as I have found by experience. The addition of further scavenging materials at this time would have some effect, but I have discovered that chemical action alone will not completely clear a bath of this character at this high temperature without risk of removing some of the valuable alloying metals desired in the final analysis. I have found that a violent, almost explosive action is required, which acts mechanically as well as chemically to expel the residue of oxides, occluded gases, slag, fragments of brick from the furnace lining (which sometimes adhere to the side of the crucible or the furnace below the surface of the bath), sulphur and phosphorus. The treatment at this time also has the function of increasing the fluidity of the bath and must be of such character as not to introduce objectionable matters therein.

After holding the temperature at about 3300 degrees F. to 3500 degrees F., I add a mixture of alloys, namely silcon, manganese, aluminum, titanium and magnesium, together with a small percentage of iron oxide, amounting in all to about .62 percent of the charge, this mixture being composed partly of finely powdered alloys and part y of lumps, and varying in composition according to necessity and the analysis. More exact directions can not be given, as the best results have to be determined by experiment according to the anal sis desired. As a general rule lumps of about the size of nuts will be about 50 per cent, and the metallic aluminum will preferably be in small lumps. The action of this mixture of lumps and powder may perhaps be explained by assuming that as soon as the covering of the package is consumed the powder goes off first with a comparatively violent reaction, which is immediately followed by the larger reac tion due to the mass of the lumps, the whole resulting in what is practicall an explosion at the bottom of the pot or urnace, which not only violently disturbs the bath causing occluded gases to pass out, but also carries away any solid impurities and thoroughly mixes the entire bath. Heretofore in alloy steel casting it has been diflicult to obtain large castings of uniform analysis owing to the different specific gravities of iron, tungsten, chromium and vanadium, but after this explosive scavenging action, there is not only a substantial freedom from sulphur, phosphorus, oxides, gases, slag and other impurities, but there is a complete amalgamation into a homogeneous alloy. If an electric furance is being used, the bath can now be poured from the furnace into pre-heated ladles at about 3500 degrees F. and then given a final treatment in the ladle or pouring crucible with a smaller amount of alloys of silicon, manganese or aluminum, with or without metallic aluminum amounting in all to about 25% to 45% of the bath in the crucible, for the purpose of removing any oxides or gases induced by pouring from the furnace, or in taking a crucible out of a furnace and slagging off, it being understood that there may be some slag in the pouring crucible from the furnace, to be removed, and the slag in a melting crucible is not removed until the crucible is taken out of the furnace just before pouring. After the slag is removed from the melting crucible this last treatment is applied.

In the specific explosive mixture, powdered magnesium may be used to advantage for both its mechanical and chemical effect, and other agents for chemically reducing a mechanical stirring up of the ath may be used, as I have had satisfactory results bv using a small percentage of gunpowder. It is impossible to specify percentages of ingredients of these treatments because of the variation of the material used in making up the bath and also the temperatures obtainable. The temperatures herein specified are considerably higher than previous practice in alloy steel castings, some authorities having considered that such high temperatures burn the metal or tend to cause it to become too stiff when poured to properly fill out the molds caused on account of rapid cooling from such high temperatures. Due to the exothermic action of the explosive scavenging treatment, the temperature may rise as high as 3600 degrees F, without any damage to the metal.

The metal is now poured into the molds, which are ordinarily of sand in the case of milling cutters, reamers, countersinks, bar stock, dies, special form tools, etc., and the metal is so fluid and so completely follows the mold that the surfaces are cast within .015 inch, and in most instances only requirin to be finished by sand blasting or very lig t grinding. Where cutting surfaces are to be ground to finish, it is referable to allow somewhat more. As a ove stated, in many instances risers are omitted entirely where heretofore universally required, and the heads are made very small, because the metal in setting in the mold has an unusually prolon ed period of solidification or semi-solidification, without a fineness and fiber .unlike other steels,-

either cast or forged, having similar analysis. A, peculiar herring-bone formation has frequently been observed which is quitedistinct from anything heretofore observed in cast steels. 7 There is little or no variation between the outer and the interior structure of the casting, nor variation in the cutting eificiencyibetween material at the outside of the casting and that at the interior, the bath when poured seeming to be wholly free of impurities and producing a non-changing homogeneous stee Castings of alloy steel for cutting tools,

' etc., are annealed, rough ground to size after being bored for the arbor, heat treated, hardened, etc., according to standard practice. A; further advantage of the process is that uniformity of analysis is obtained and a durability, toughness and longevity obtained considerably in excess of steels made from ingots and then forged or hammered, machined down to size and then heat 7 treated and h hardened. These ordinary steels will sometimes show surface checks if ground at too high a temperature, but steel made by this process does not show such effect even at red heat caused by grinding. There is considerable loss in heat treating forged steels due to cracks caused by strains, which does not occur with my steel. -Where specific metals or materials are mentioned, alloys of like properties may be used, or equivalents without specific mention of each equivalent in each case. The broad features of the invention are applicable to refining all steels and many other metals, although described by way of example as applied to high speed steel for cutting tools.

What is claimed is: a L

1. Process of producing high speed steel consisting in melting iron, chromium and tungsten, scavenging ,to remove oxides, etc., adding cobalt, scavenging, adding vanadium in less than 50% excess over the desired analysis, adding an explosive material, and casting at above 3-200 F.

2. Process of producingxhigh speed steel consisting in melting the base metals, scavenging, adding vanadium, adding an explosive material, and casting at above 3200.

Signed at the=city of New York, in the county of New 'York and State of New -York, this 24th day of October, A. D. 1919.

ARTHUR C. DAVIDSON.