US2604419A - Method of heat-treating surface hardened articles - Google Patents

Description

July 22, 1952 A. w. HERBENAR METHOD OF HEAT-TREATING SURFACE HARDENED ARTICLES Filed April 7, 1949 IN V EN TOR.

W44 fwc/r/vess 4/vra/v 1M 1905mm? Arman/5y w w as Patented July 22, 1952 METHOD OF HEAT-TREATING SURFACE I HARDENED ARTICLES Anton W. Herbenar, Ferndale, Mich, assignor to The Ohio Crankshaft Company, Cleveland, Ohio, a corporation of Ohio Application April 7, 1949, Serial No. 86,078

This invention pertainsto the art 'of metal heating and, more particularly, to the heating of metals for the purposes of drawing or tempering hardened layers or surf aces thereon.

An object of the present invention is to provide a new and improved method for drawing or tempering hardened layers or surfaces on metallic articles of manufacture which permits of ready control of the amount of draw, which permits of a substantially uniform draw throughout the entire hardened layer and which avoids the objections of the prior art.

Another object of the invention is ;to provide a new and improved method for drawing a hardened surface or layer on a metallic article of manufacture including the step of introducing, subsequent to the hardening operation, the heat for the drawing into the article on a side-remote from the hardened surface.

Another object is the provision of a new and improved method of drawing a hardened surface on a curved or flat metallic member having adjacent surfaces in the relatively unhardened state which comprises applying heat, subsequent to the hardening operation, as by electric inductionheating to the unhardened surface and allowing the heat to flow by conduction to the hardened surface.

The" invention is applicable to any metallic article having a surface portion or. layer which must be heated throughout its thickness uniformly and to a readily controlled amount.

The invention will be described as embodied in and applied to a cylinder liner which has an inner quench-hardened layer or surface, although it is equally applicable to other shapes of metallic articles either regular or irregular in shape or having continuous or discontinuous hardened surfaces.

Referring now to the drawings which are for the purposes of illustration only and not for limitation of the scope of the invention:

Figure 1 is'a side sectional view of a portion of i-arcylinder liner--having an inner hardened surface to bedrawn' to a lower hardness and an electric induction-heating head adjacent the hardened surface to supply the necessary heat;

-Figure 2 is a graph showing a group of typical curves of wall hardness plotted against cylinder wall thickness and showing the hardness variations resulting from the method of heating shown in Figure 1;

Figure 3 is a view similar to Figure 1 but with the inductor for supplying the drawing heat positioned adjacent a surface of the liner remote 3 Claims. (Cl. 148-215) from the hardened surface and embodying the present invention; and

Figure 4 is a view similar to Figure 2 but showing typical hardness curves obtainable by the present invention.

Referring now to Figure l, a portion of a cylinder liner I0 is shown formed of a material such as steel or the like having the characteristics which, in its initial unheat-treated state, is rela-' tively soft throughout but which can be hardened by heating above a critical temperature and interiorly of the liner and adjacent to the innerv surface, thus inducing high frequency electric currents to flow in the surface II to raise its temperature above the critical quench-hardening temperature. Subsequently, the surface is rapidly and forcefullyquenche'd by a quench head or the like not shown. v v j "Curve A of Figure 2 shows a typical hardness curve obtainable by using the above, described electric induction heating and quench method. As shown by this curve, the initial hardness of,

the metal of the cylinder wall was 10 Rockwell C. The quench-hardening operation increased the hardness on the inner surface of the liner to Rockwell C, which high hardness extendedfrom the inner surface of the liner outwardly for about a third of the thickness of the wall andthen dropped rapidly in a very short wall, thickness to;

the initial hardness of 10 Rockwell C. j

Such heat-treating methods oftentimes 'produce surfaces harder than are desiredor produce surfaces which have high internal stresses therein which must be remcvedeven at the.

sacrifice of some of the hardness of the surface. It is known that as the hardened surface or layer I I is reheated to sometemperature below the critical temperature, a softening of thehardened layer will result dependent on the temperature and the length of time that thelayer is held at that temperature together with a simultaneous,

very substantial relief of the internal stresses...

This operation is called a drawing or tempering operation. 1 I

To perform this drawing operation on cylin der liners for example, it has been conventional a method of supplying the heat for drawing oftentimes produces an undesirable final hardness pattern in that the absolute outer surface of the hardened layer draws to a greater degree than the portions of the hardened layer more a remote from the outer surface.

As an illustration of this fact, assume for example it is desired to draw the. surface, of the.

hardened layer to 44 Rockwell C. 'Curve B of 4 vention comprises introducing the heat into areas of the metal where overheating has no ill effects and allowing this heat to flow by conduction into the hardened area.

Thus, in the embodiment of the invention shown, the cylinder liner II] of Figure 1 with its internally hardened layer I I has the heat applied externally thereto; that is, on the side remote from the hardened layer I I and the heat is :allowed to flow into the hardened layer by conduction. This process is in contra-distinction to that shown in Figure 1 where the heat is generated in the hardened layer itself. In the embodirnent shown in, F ure 3, an induction-heating jjCOil I5 is positioned exteriorly of the cylinder liner in and is connected to a suitable source of high-frequency electric energy not shown. High- Figure 2 is typical of the hardness pattern which j will result. The surface area as shown by the curve will be, of the required hardness. ever portions intermediate the surface of the hardened layerand the unhardenedfportion I2 will be drawn to a lesser degree and will have a hardness somewhat between the desired {24 R0019,

well C and the initial hardness.

Assumefurther that it is desired to obtain a maximum, hardness of 44 Rockwell C through thehardened layerl I. Obviously, the temperatureofthe. hardened layer must be increased or thev layer must'be held at this temperature for. a longer period of time. Curve C of 'Figu're 2 represents typical results. While the maximum hardnessv has been reduc'ed to 44 Rockwell C, the hardness at the. surface of. the hardened layer .I I is substantially belowthat and is shown at 22 Rockwell C.

Without limitation on the scope of the invention bdt rather. to aid in an explanation thereof, applicant advancesthe following theory forthis variation in hardness pattern. As is known, high-frequency induced currents of the metallic article-arefconcentrated almost entirely at and immediately below the surface of the member adjacent the induction-heating head. For pro ducing hardened layers of shallow depth, this is extremely desirable but for drawing purposes, applicant advances the theory that this concentration of currents at the surface causes the variation in hardness pattern. cylinder-wall is to be heated through, it is obviousfroman examination of heat-flow theory that the source of the heat must be at some.

temperatureabove theportions of the wall to which the heat can flow by conduction. In the presentinstance, the source of the heat is interiorlyj'of the .metal itself but still adjacent a surface oppolsite theheating head. A temperature pattern somewhat as indicated by the curve t1 is ,believedjto occur, the elevated portions of theicurvebeing that where the currents themselves flow. It is believedthat this accounts for the increased draw adjacent the inner surfaces of i the cylinder liner.

The presentinvention contemplates a method of drawing 'metal articles having a hardened layer such as the cylinder of Figure 1 whereby. an evehtemperature and thus drawing of the. hardened layer II may be obtained throughout Generally speaking, 'the its entire thickness. 7 invention comprises generating the drawing heat or intro'ducing the drawing heat into the metal:- at a point remote from the hardened layer itself. and allowing the heat to flow thereinto by conuii a. Fplcillsn s s S aki ma How-.

As. the entire.

frequency heating currents still flow only adjacent the surface of the liner opposite from the induction-heating coil itself. No heating currents in the embodiment shown in Figure 3 will flow within the hardened layer. Thus, the heat is generated only in the soft portion I2 and flows to the hardened layer I I by thermal conduction, V A temperature curve such as that indicated by #2 will generally exist across the thicknessof the liner wall. It will be obvious from this curye that the temperature in the hardened'layer itself will be substantially uniform throughout its entire thickness, that the. higher temperatures generated in the wall are actually generated, in the layer I2, which is essentiallysoft'and will not be effected by heating to a temperaturebelow the critical. I

by heating externally. For example, ahigher rate of power can be applied initially resulting.

in the outer wall of the liner being atamo re; elevated temperature; for example, such-as ;that,

shown by curve ts- The flow of heat-by conduction soon levels out the temperature.-

It willbe appreciated that the induction-heap. ing coil I5 may be of any known type and may' be progressively moved along; the cylinder liner or may be held stationary.

Curve D of Figure 4 shows a typical hardnesspattern'resulting from the drawing operations following the teachings of this invention. .It will be noted that this curve shows a substantially uniform hardness obtained through the; hard,.

ened layer II after the drawing operation.

It will be obvious that the present invention is not limited to cylinder liners. It can beused on any other metallic articles having hardened; or other layers produced by any known means,

The hardened layersneed not be electrically .COIl-y ductive. It is sufficient that the heating be gen; erated elsewhere than in the hardened surface.

itself. Radiant heat in the embodimentshown in Figure 3 could be substituted for the inductionheating coil I5.

Other modifications will occur ;to others upon a reading and understanding of this specification. It is my intention-to cover all such modifi'-' cation insofar as they come within the'scope of the appended claims. Y Having thus described my invention, I claim: 1. The method of heat treating a metallic article of manufacture for the purpose of drawing a previously hardened surface layer portionthereof, said article having a body portion and; a surface layer portion on each side of said body portion, one of said surface layer portions being previously hardened, which comprises subse'- quently applying heat to said other surface layer It is possible to obtain a more; rapid heating,

which comprises subsequently applying heat to said other surface layer portion to raise the temperature thereof above the temperature of said other portions of said article. jto conduct said heat through said body portion and into said previously hardened surface layer portion to draw said last portion. 1-

3. The method of heat treating a metallic article of manufacture, said article having a body portion and a surface layer portion on each side of said body portion, which comprises heating one of said surface layer portions to quenchhardening temperature, quench-hardening said surface layer portion, subsequently applying heat to said other surface layer portion to raise the temperature thereof above the temperature of said other portions of said article to conduct said heat through said body portion and into said quench-hardened surface layer portion to draw said quench-hardened surface layer portion.

ANTON W. HERBENAR.

REFERENCES CITED The following references are of record in the file of this patent: v

UNITED STATES PATENTS N, b''r Name Date 2,295,272 Somer Sept. 8, 1942 2,303,467 Inskeep Dec. 1, 1942 FOREIGN PATENTS Number." Country Date 1 485,733 Great Britain May 19, 1938

Claims (1)

1. THE METHOD OF HEAT TREATING A METALLIC ARTICLE OF MANUFACTURE FOR THE PURPOSE OF DRAWING A PREVIOUSLY HARDENED SURFACE LAYER PORTION THEREOF, SAID ARTICLE HAVING A BODY PORTION AND A SURFACE LAYER PORTION ON EACH SIDE OF SAID BODY PORTION, ONE OF SAID SURFACE LAYER PORTIONS BEING PREVIOUSLY HARDENED, WHICH COMPRISES SUBSEQUENTLY APPLYING HEAT TO SAID OTHER SURFACE LAYER PORTION TO RAISE THE TEMPERATURE THEREOF ABOVE THE TEMPERATURE OF SAID OTHER PORTIONS OF SAID ARTICLE TO CONDUCT SAID HEAT THROUGH SAID BODY PORTION AND INTO SAID PREVIOUSLY HARDENED SURFACE LAYER PORTION TO DRAW SAID LAST PORTION.

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