US1999790A - Process for hardening gray and mottled cast iron - Google Patents

Description

April 30, 1935. v H SHAW ET AL 1,999,790

PROCESS FOR HARDENING GRAY AND MOTTLED CAST IRON Filed Aug. 18, 1950 INVENTORS Howard. I. 511 aw Nawi'cm ELI- maple want M ATTOR N EYS.

Patented Apr. 30, 1935 h UNITED STATES PATENT OFFICE PROCESS FOR HARDENING GRAY AND MOTTLED CAST IRON Howard I. Shaw and Newton S. Hoerle, Muskegon, Mich.

.Application August 18, 1930, Serial No. 476,164 3 Claims. (01. 148-3) This invention relates to improvements in procdrawing. The mould chamber II in this case is esses or methods for the hardening of gray and shaped to form a valve tappet l2 consisting of a mottled cast iron. disc-shaped head 13 and an integral shank or The primary object of the invention is the stem M, as shown in the drawing. The molten 5 provision of an improved method for the produciron is chilled at the time of pouring, using con- 5 tion of cast iron parts, such as valve ta-ppets and ventional cast iron chill plates or the like. In the cam shafts, which will materially harden the cast specific instance a chill plate 15 is provided, upon iron parts during formation, to produce the neceswhich the head I3 may be formed, for the pursary physical properties and wear resisting, pose of chilling and hardening the same. The strengthening, and toughening characteristics depth of the chillplate can of course be varied. 10 which will permit of the economical, durable and Other means may be provided for chilling the efficient formation and use of the parts. cast iron as it is poured into the mould, such as In the drawing, forming a part of this specifithe use of a metallic mould kept cool by circulacation: tion of water or the like. This chilling operation Figure 1 is a view in elevation of a valve tappet is used to produce extreme and localized hard- 18 in a mould, portions of the mould being in verness, particularly in the head portion of the spetical section. ciflc tappet shown. The depth of the chill can of Figure 2 is a viewin elevation of the cast iron course be varied within limits. The chilled portappet removed from the mould. tion of the article is hardened to a state or con- 29 Figure 3 is a similar view of the finished valve stituent known as cementite, whichis of course 20 tappet, partly in elevation and partly in section iron carbide. This gives the extreme wear resistto show characteristics thereof. ing qualities to the article, which are so essential While the invention is particularly directed to in the case of a tappet head. the provision of a durable and economically pro- Next, the casting, after it has solidified in the duced one-piece cast iron valve tappet, yet the mould and dropped to a temperature below 700 25 method is not to be limited to the provision of F. may be removed, although the casting from the such parts. mould may be removed at any time after it has We may use ordinary gray or mottled cast iron cooled sufficiently and it is then quickly heated of conventional composition in the cupola and if in a suitable furnace to a temperature ranging 0 desired may have suitable alloys to increase wear between 1550 F. and 1700 F. preferably to a resisting and other qualities and properties. We temperature of 1650 F. which we have found to be have found that good results are obtained by usbest. The statement that the casting is to be ing a composition consisting of: heated quickly means that the cast iron article Cupola charge should not be held at the temperatures above set 20% steel forth for any great length of time, since by so pig iron doing would break up the combined carbon or 40% foundry return scrap cementite into ferrite and graphite. Therefore Ladle additionsthe heating of the article after casting is very l%# ferro molybdenum carefully carried out, preferably by heating the 40 ferro vanadium furnace previous to introduction of the article Analysis of ferro vanadiumto 1650" F. When the article is placed in the 37.90% contained furnace the temperature in the furnace, due Analysis of ferro molybdenum to the cold casting, will naturally drop. The 57% contained castings-are heated to, a temperature of 1650 Since the analysis of constituents of the cast iron 'F. as quickly as possible, and when the furnace 45 have influence on the physical properties and has again reached the desired temperature, prefhardness, we do not restrict ourselves to the above erably 1650 F. the castings are removed and formula. Indeed, we have used a higher per cent quenched in oil, water, or any, other suitable of steel scrap than that listed in the cupola quenching medium. The castings are permitted charge, and the percentage of vanadium varies to remain in the quenching bat until cold, or 59 between .15 and 25%. The alloy additions may until the castings have reached he same tem or may not be used, as desired. perature as the quenching medium. The tem The molten iron, at a temperature ranging from perature of the quenching bath preferably ranges 2500 F. to 2700 F. is poured from the cupola from to F. The heating and quenching 55 into sand moulds, shown at H) in Figure 1 of the produces a very uniform structure and uniform 55 tension hardness, probably caused by the fact that some of the carbon is thrown back into solid solution with the iron and held therein thru the cooling stage during quenching. A uniform martensitic-troostitic structure is produced with a corresponding hardness of approximately 600 Brinell, which structure can be broken down to a sorbiticpearlitic structure and corresponding decrease of hardness by regulating the time and temperature of heating at the time of drawing the temper.

After the quenching operation the castings are drawn" to relieve internal strains produced during the quenching operation. The immediate step after quenching is to place the castings in a furnace and heat them to approximately 500 to 600 F. holding them approximately one hour for each inch of cross section of the article. For a valve tappet, fifteen to twenty minutes will suffice. This temperature reduces the hardness somewhat; relieving internal strains caused by quenching, and it should be borne in mind that the temperature of re-heating must be regulated according to the hardness desired.

If desired, the chilling of the iron during moulding may be eliminated, since the subsequent steps will produce a very uniform structure, with resulting uniform hardness throughout the article cast. In normal gray cast iron there is an uneven distribution of carbons. However,with our improved heat treatment, a. very uniform structure is produced, having a uniform distribution of carbon. This'particularly applies to castings of uneven eliminating softand weak spots in the casting, and giving greater hardness with increased physical properties, and especially giving better wearresisting qualities and greater strength and toughness. This refers particularly to iron which has not been chilled, and if desired the chilling step may be included to render particular partsof the casting harder than others, for instance, thehead in the particular tappet shown. The casting shotihFwhen it comes from the mould, will have a Brinell hardness ofaround 180 to 200 on the unchilled portion. The subsequent heating and quenching will raise the hardness to from 400 to 450 Brinell. On the chilled head or section, however, the Brinnell hardness will be approximately '600.

As before noted the addition of alloys, such as the use of approximately 1% molybdenum will materially improve the physical properties and wear resisting qualities of the casting.

In order to bring out the importance of the invention it should be noted that cast iron parts hardened by means of chilling alone have certain inherent defects, namely, brittleness, lack of controlled hardness and strength. In the case of chilled tappets, which are not subject to the heating and quenching steps as mentioned herein, the stem is too soft and gauls where the tappet bearing is disposed; the threads strip, and the heads are too brittle, very often breaking in service. Therefore, it can readily be understood that the specific heat treatment, quenching and drawing of our invention produces a casting which is tough, durable, wear-resistant and hard without resulting brittleness.

It should be noted that the castings are left in the mould until they are black, or at the temperature above mentioned, and after taking out they are rough-machined before heating to 1650 F.

Various changes in the steps of the method and process herein outlined, and the application of the same to the formation of various articles and parts may be made to the invention herein shown and described, without departing from the spirit of the invention or the scope of the claims.

We claim:

1. The steps in the method of treating cast iron which consists in chilling the cast iron at the time of pouring to produce an extreme localized hardness, quickly heat treating the cast iron after removal from the mould to a temperature of substantially 1650 F., said heat treating at said temperature continuing over a period of time suflicient to increase the hardness of the unchilled portion and insufficient to soften and reduce the hardness of the chilled portion, said period being considerably less than one hour, and quenching the then heated parts in a quenching bath.

2. The method of producing cast iron valve tappets, having a hardened head portion and a relatively softer stem, which consists in casting the valve tappet and chilling the head portion of the tappet at the time of pouring to produce an extreme localized hardness there, subsequently quickly heat treating the cast tappet to approximately 1650 F., for a sufilcient time to materially harden the unhardened portion of said tappet said last mentioned time being insufficient to affect the chilled head portion materially, and immediately thereafter quenching the casting.

3. Those steps in the method of producing a chilled cast iron article which consists in treating a casting having a Brinell hardness of between 180 to 200 of a portion of said casting and a Brinell hardness substantially greater of another portion of said casting, by subjecting said casting to a temperature of substantially 1650 1",, bringing said casting to substantially said temperature and immediately quenching said casting, whereby the hardness of. the softer portion is raised to substantially 450 Brinell and a hardness of substantially 600 Brinell is maintained by the harder portion.

HOWARD I. straw. NEWTON S. HOERLE.

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