US1963403A - Locally hardened molybdenum steel article of manufacture - Google Patents

Description

June 19,1934. Y F. T. DANIELS 1,963,403

LOCALLY HARbENED MOLYBDENUM STEEL ARTICLE OF MANUFACTURE Filed Jan. 26, 1933 Patented June 19, 1934 UNITED STATES PATENT OFFICE LOCALLY HARDENED MOLYBDENUM STEEL ARTICLE OF MANUFACTURE I Fred C. T. Daniels, Pittsburgh, Pa. Application January 26, 1933, Serial No. 653,629 1 claim. (Cl. 148-21) gree of hardness of the surface itself. I havefound, for example, that the depth of hardness in such carbon steels varies at least from onesixteenth of an inch to three-sixteenths of an inch under approximately the same heating conditions and varies in degree of hardness from 40 to 65 scleroscope.

I am also aware that it has been attempted with more or less success to surface harden steels in other ways. For example, it is known to casecarbonize or case-harden carbon steels or articles by impregnating the surfaces of initially low carbon steels after which the articles or the steels are quenched from the carbonizing heat or re-heated, quenched and drawn. Such treatment, however, alters the chemical composition of the surface tobe hardened and, while it is capable of certain general localization, it is not possible to obtain true local surface hardening with any degree of accuracy or control.

In addition, such case-carbonization or casehardening introduces considerable distortion into the pieces with the result that subsequent grinding or machining is required to restore trueness. Further than this, such case-carbonized or casehardened articles require complete heating after machining and case carbonizing and then liquid quenching. In case-carbonizing also the case must of necessity follow the whole contour of the outer surface yielding as much hardness and consequent weakness at the properties at that point being unnecessary and harmful. Such case-carbonized or hardened articles develop at most a hardness of only about to '70 scleroscope, depending upon the size 5 and other factors. For the same heating conditions the depth of hardening is uncontrollable and varies from to In what is known as the full hardened articles, steels or alloy steels are machined for finishing 50 purposes on the hardened parts and then furnace heated to quenching temperature and then subjected to a'liquid quench. In articles of the larger sizes particularly the hardness obtainable is verylimited being not over about 40 to 60 scleroscope. This may be in part explained by base, both of which- .the fact that in the larger articles the mass of thearticle is so great or the variability of crosssection is so marked that drastic quenching is impossible.

In contradistinction to the foregoing, I have obviated all the defects and disadvantages of such prior procedure and such accordingly constitutes one of the objects of my present invention.

Another object of my invention is to so correlate the composition of the steel and the hardening procedure that I obtain an article having an especially hard surface and in which the line of demarcation between the hardened and unhardened areas is so sharp that it does not extend in either direction as much as one one-hundredth (1/100) of an inch.

A further object of my invention is the provision of' local surface hardening for steels or articles of the kind hereinafter set forth wherein the line of demarcation between the hardened and unhardened areas does not follow the crystal boundaries but takesv a direct course on a straight line regardless of grain boundaries, therefore cutting through some grains.

An additional object of my invention is to so locally surface harden molybdenum steel containing for example over about .2 up to about 5% molybdenum that the temperature at which the hardening may be carried out falls within a relatively wide and convenient range and further in which the depth of hardening can be accurately controlled.

A still further object of my invention is a molybdenum steel article or piece having a hardened surface of predetermined and controllable depth and having a hardness equivalent to about to scleroscope.

Other and further objects and advantages will either be pointed out hereinafter or will be understood by those skilled in this art. 95

13y way of illustration I have shown in a comparative manner the effect and product of the present invention as applied in a manner consistent therewith and wherein: V

Figure 1 represents a cross-section of an unhardened molybdenum steel bar or article; and

Fig. 2 represents the bar or article of Fig. 1 after it has been hardened in accordance with the principles of the present invention.

In Figs. 1 and 2, the numeral 10 indicates the unhardened portion of the molybdenum steel, bar or article to which the method of thepresent invention has not yet been applied and 11 represents the hardened portion after subjecting the bar or article 10 to my method of the present invention. The numeral 12 indicates the boundary line or line of demarcation between the unhardened area 10 and the hardened area 11. It will be understood that the figures are more or less diagrammatical and to that extent'must be so considered merely as indicative. It will be noted further that the hardened area 11 is of much finer grain structure than unhardened area 10 but insofar as I am aware there has been no chemical change brought about by my method primarily due to the fact that I do not use any chemicals or hardening agents other than heat itself. Insofar as it is possible to show the same in asimple drawing it will be further observed that the boundary line or line of demarcation 12 is a sharp one so that the areas 10 and 11 do not appreciably cross this line and by suitable tests I have discovered that the' line 12 is so sharp that the areas 10 and 11 do not overlap even to one onehundredth of an' inch. Moreover, by micro study I have discovered that this line 12 is not only of the sharpness indicated but it does not follow the crystal boundaries which would have the effect of rendering the line 12 of a more or less jagged or saw-tooth type, but on the contrary the line travels in a true straight line and thus crosses or intersects certain of the grains and boundaries with the degree of sharpness above pointed out.

In carrying out the'present invention I either start with molybdenum steel containing from about .2 to .5% molybdenum or to available on satisfactory low carbon steels I add such an amount of molybdenum in suitable form at a suitable stage in the manufacture thereof as willproduce in the finished steel about .2 to .5% molybdenum. In some cases I need merely remelt the steel and add the proper amount of molybdenum thereto, but in other cases where I am making up a batch of steel I add the molybdenum in any of the recognized stages of manufacture and in desired form such as ferro-molybdenum, elemental molybdenum and the like or equivalent.

Having obtained the steel .of the desired molybdenum content with or without other elements such as nickel, chromium, vanadium, etc. in small amounts to impart any desired physical properties to the steel or article when finished, I then carryout the local surface hardening in any selected one of the following ways according to the circumstances and conditions involved in. any

particular batch or article. The precise, hardness in any. given case'varies somewhat with the percentage of carbon and the percentages of other elements in the steel. I

One preferred way of carrying out the surface hardening is by means to a torch such as an oxy-' acetylene welding torch which may have either one tip or two tips so that double width harden ing may be. simultaneously produced or so that (when the tips are arranged at angles to each other) I may harden simultaneously two surfaces, such as both sides of a gear or'pinion tooth, at one time. Such torch is adjusted so that the flame is of a character which will make possible a rapid input ofheat to the molybdenum steel article.

-stood by those skilled in this art.

Assuming a bar or article of the general nature illustrated in the drawings, I torch hard-' important result and advantage is that insteadof being forced to carry out the hardening at a specific temperature without appreciable variation-uthereabove or therebelow I find that I no longer need to maintain such close and commercially impractical control over the temperature,

but that uniform hardness can be obtained merely by maintaining the temperature of the hardening heat within the general limits of about 1250 and 1700 F. Not only this, but I find that the depth of hardening is proportional to the time of application of the hardening heat-the longer the time, the greater the depth, other factors being the same,-so that by subjecting the material or article to the hardening heat within the temperature range stated for a predetermined time, I may obtain the hereinabove pointed out results. Furthermore, the line of demarcation between the hardened and unhardened areas is exceedingly distinct and much sharper than anything heretofore obtained by any method of hardening insofar as I am afare.. As above indicated the line of demarcation is so sharp that the hardened and unhardened areas do not overlap even to the extent of one one-hundredth of an inch insofar as I am able to determine by available tests. This sharp line furthermore does not follow the crystal boundaries but proceeds in a true straight line irrespective of grain boundaries.

, In the particular sample illustrated in the drawing I have obtained by the present invention a hardened area having a hardness of 90 to 100 scleroscope.

the rate of cooling is appreciably slower I have obtained a hardness of the order of to scleroscope and in some instances I find that the minimum hardness is about 70 to 80 scleroscope under less favorable conditions due'to the nature of the article or for other reasons under- I have made many tests andfind that the sharp line of demarcation is not a line of weakness. By no test have I been able to cause a partition at this line of juncture. I have'even pounded the article while cold under a steam'hammer until it was reduced one-eighth in thickness without In some larger articleswhre' damaging the hardened surface in anyway, and without causing it to spall or fiake ofl, indicating a perfect bondbetween the hardened and unhardened areas. The samples are file-hard and will frequently scratch glass.

As I have stated above, the molydenum content may vary from about .2% to about .5%,

the intention beingthat these percentages are typical rather than limitative, and the remaining elements of the steels may also vary as will be understood. In general, the sulphur, phosphorus, manganese and silicon are within the usual limits found in steel making practice, thatis, are within amounts classified as impurities and are so small as to have no appreciable influencing effect on the alloy.

The following .ranges of elements approximate- I e I l v 1,903,408 a Iy' define. successful practice according to the composition of the hardened surfaceto any degree a m r M e mmmm mm vttfl u. I

d m m m mm m M Mmm mm H m mm mw m mm mmmym m n w m ss mam w mm mm mmmwwMmm mnmmmm c v manna m h M m w u. MwmmC articular area to be hardened. Unusually good wearing surfaces are thus obtained.'

.10- .75 quench the p Molybdenum and, when present: I

Nickel Chromium ..-a

duc- The precise form of such apparatus f my I may, if desired; carry out the heating by a suitably constructed and arranged electrical apsuch as one of the resistance or con forms, no part ofthe present invention. The type of heat seems to have no real influence v I upon the results obtainable by the present inven- Mg tion and it is accordingly within the Scope 0 invention to utilize'heat generated electrically in suitable manner.

m m m w a mammmme. mm m n fiwm mm u 1 m n rm 0 n e e A m Wm M m m a n m n u r u m m M a m H m m .m m M m .m n m n km W 1 m m mmmmm 3 1 m 0. n t w mmim m wmmw u 3 mm a z I t s wasmauwaaamaaawawnmmm umber of open paratus ggivi th bove 'tion type.

Manama was mmfiwnsmae L .LLL LLL Tani?" i i r L tels rig ea and the balance substantially all iron, said article of of manufacture being characterized by having a hardened surface produced by rapidly heating the same by subjection to a flame to 1250-1700 1". and then quenching; and further characterized by flame hardened'portion has a the foregoing process hearth heats:

owing Table 11 represents a num than the above open The following TableI gives a n hearth heats illustrative of s e Vanadium results when subjected to the hardening proceai described:

o w M The toll other steels hardened by 40 other portion is the same as the unhardened portion, the hardened and unhardened portions are relatively sharply delimited from one another, the The present invention is not limited, however. depth of hardness is fully under control and is teeth but applies equally well directly proportional to the time during which pulverizer hammers, the hardening applied, and a uniform rings, pinions, gears, hardness of 'l0-100 scleroscope is readily atbevel gears, shovel points. tained. g FREDQ'LDANIELB. nymyinventionldonotaltertheehemical guides, couplings. punches, etc.

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