US1997004A - Method of preparing and nitriding a ferrous article - Google Patents

Description

April 9, 1935. A, w. MoRRs 9 9 METHOD OF PREPARINCT AND NITRIDING A FERROUS ARTICLE Filed Dec. 17, 1931 r: I E (C. 14 `I` I A C C I 7 v i ;i I If MG o o G q y l f Z e/ofuj/i I B I 'J /////J////////// Patented Apr. 9, 1935 I I 1997,

UNITED SITA'TES PATENT OFFICE METEO!) OF PBEPABING AND NITRmlNG A FERROUS ARTICLE Albert w. Mon-is, Springfleld, Masa., assignor to Moore Drop Forgng Company, Sprlngeld, Masa., a corporation of Massachusetts Application December 17, 93, seiai No. 581,? 01 4 Claims. (CI. 148-16) This invention relates to a new method of prean electric current through the molten bath and paring and nitriding a ferrous article. y the ferrous article. Any one or more of these Heretofore, so far as I am informed, in presubsidiary steps may be used in practicing the paring a ferrous article for surface nitrogenizamethod.

5 tion, all the metal in the article has been made The improved method may be carried out by 5 of the same mixture or alloy. In other words, to many forms of apparatus, one of which is shown get a surface suitable for nitridation, the entire in the accompanying sheet of drawing formin piece has been made of a nitridable alloy or of the part of this application for patent. same composition throughout its mass. Referring to the drawing:-

o This generally is a disadvantage, first because Fig. 1 is a sectional elevation, and

of the cost, and second because the elements in- Fig. 2 is a cross sectional view of the apparatus cluded in the article to make it nitridable are shown in Fig. l. usually detrimental to the texture of the article Referring more speciflcally to the drawing in and often interfere with or prevent heat treatwhich like reference numerals indicate like parts, ment. A designates a heating chamber, and B a suit- 15 My improved method consists in impregnating able crucible which 'can be placed in the chamthe surface of the ferrous article to be treated ber A, the crucible having lugs G which positionto a suitable depth with a metal or alloy having the same in the heating chamber. Gas pipes afllnity for'nitrogen. The article thus treated is D-D extend through the walls of the chamber 4 then subjected to the action oi* nitrogen so that a A and a. mixture of air and gas may be led 20 hard nitrided surface will be obtained on the through these pipes, tangentially into the annuarticle and whereby the core or 'center of the lar space between the heating chamber and article will be practically untreated and will recrucible so that the metal in the crucibie can be tain the characteristics due to its original comkept in molten condition and at a suitable temposition or alloy. perature. 25

By my method almst any ferrous alloy hav- E designates a cover plate which is adapted ing good properties of strength and that will be to rest upon the top rim of the crucible B. This insensible to tempering brittleness can be used, cover plate may be tightly clamped to the'top thus ensuring better castings, forgings and perof the crucible by screws F', which are pivoted ao mitting heat treatment of ferrous articles hav- ,in the lugs G on crucble and which screws ing nitrided surfaces. fit between ears (U ormed. on the rim of the My method may be carried out as follows:- cover plate E, huta H being threaded on the After making the ferrous article in the form screws F. desired, either by casting or forging I immerse A packing or bear-ing washer may be placed on or dip it, while hot and preferably heated to a top of the c'ucible. The cover plate E may be 35 temperature above 12007 Fahrenheit, in a bath provided with a. stumng box I through which a oi' molten metal having aflinity for nitrogen. plunger J can be reciprocated for purposes here- This bath is preferably molten aluminum either matter described. This plunger may be made pure or alloyed with zirconium, titanium, of graphite or may have its surface coated with 40 chromium, vanadium, magnesium, beryllium, graphite. Extending from the cover plate is a 40 silicon, nickel, molybdenum, manganese, or any notched flange K for holding the ferrous articles desred combination of these, known in the art to be treated.. for alloying with iron to make up a nitridable Practically any ieri-aus article can be treated in the apparatus above described. As shown a I have found by thus treating a ferrous article umbe of aut mobil rank shafts L are being 4: that there will be a surface impregnation thereof treated. with the above described apparatus, to a co ab d p by e metal or alloy the crank shafts L after being shaped either by havin aflinity for nitrogen. forging or casting are placed in the notches in I have also found that I can increase both the flange K,

60 the depth and amount of the impregnation of Care should be taken to keep the articles from ferrous article either by subjecting the bath of touching each other, while in the bath, as such molten metal having aflinity for nitrogen to touching would hinder impregnation of the artihydrostatic pressure, by agitating the bath durcles at the `points of contact and would result ing impregnation, by removing the air and using in thin spots in the coating.

nitrogen on the surface of the bath, or by passing These crank shafts or ferrous articles to be 55 treated when placed in position should be very` hot, preferably heated to a temperature above 1200 Fahrenheit. This temperature can be obtained by taking the articles while they are hot from forging or casting or they can be heated to the desired temperature before being placed in the notches.

The crucible is filled with a bath of molten metal or alloy having afllnity for nitrogen. The metal 'or alloy thus employed is preferably alumi- .num or any alloy that is known in the art as useful for effecting nitrogenization.

This bath is kept at the proper temperature by the gas jets D-D previously described.

The cover plate is then placed in position on the crucible and tightly clamped thereto so that the hot ferrous articles will be immersed or dipped in the bath of molten metal. The articles are kept, in the bath a suitable length of time.

During the treatment in the bath, care should be used'to see that the surface of the ferrous articles to be impregnated is clean and free from scale.

I 'found that under these conditions, the metal or alloy having afllnity for nitrogen will penetrate to a suflicient depth into the surface of the ferrous articles being treated to permit them to be nitrided after being machined to size.

This impregnation is accelerated by depressing the plunger J to create a hydrostatic pressure between the bath and the articles, or by reciprocating the plunger to agitate the bath during impregnation.

After this treatment the cover plate is removed and the ferrous articles are allowed to cool. They then may be subjected to-a flnishing process the only surfaces which will be hardened or nitrided will be the bearings and the crank pins or journals;

The nitrogen will unite with the metal having an afiinity for nitrogen which has impregnated 'into the surface of the ferrous article.

Thus a ferrous article will be produced having any desired ferrous .composition in its core and having a 'hard nitrided surface or surfaces. This article will thus have' the. advantages previously many other forms of apparatus may be devised V whereby the surface impregnation, which is the principal feature of my invention, can be practiced. i

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:-

1. The method of nitriding a ferrous article which consists in heating the article to a temperature of at least 1200 F. and immersing the article while heated in a bath of molten metal having amnity for nitrogen and composed at least in part of aluminum, and agitating the molten metal by applying and removing a hydrostatic pressure on the bath, to obtain a surface impregnation of the ferrous article with said metal, removing the article from the bath and thereafter hardening the surface thereof by nitridation. i

2. The method of treating a ferrous article which consists in heating the article to a temperature of at least 1200" F. and in immer'sing the article while heated in a bath of molten metal having afllnity for nitrogen and composed at least in part of aluminum, placing the bath under a hydrostatic pressure to obtain a surface impregnation of the ferrous article with said metal, removing the article from the bath and thereafter hardening the surface thereof by nitrldation.

3. The method of. treating a ferrous article, which consists in heating the article to a temperature of at least 1200 F. and in immersing the article while heated in a bath of molten metal having afllnity for nitrogen and composed at least in part of aluminum, agitating the molten metal to obtain a surface impregnation of the ferrous article with said metal, removing the article from the bath and thereafter hardening the surface thereof by nitridation.

4. The method of nitriding a ferrous article, which consists in heating the article to a temperature over 1200 E., and immersing the article while eo heated in a bath of molten metal having amnity for nitrogen and composed at least'in part of aluminum, to obtain a surface impregnation of the ferrous article with said metal and thereafter removing the article from ,the bath and subiecting the-impresnated article to hardenlns by nitrldation.

ALBERT W. NORRIS.

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