US2327209A - Alloy steel article and process of producing the same - Google Patents

Description

O. M. OTTE Aug. 17, 1943.

ALLOY STEEL ARTICLE AND PROCESS OF PRODUCING THE SAME Filed May 23, 1941 2 Sheets-Sheet l B P J INVENTOR Otho ill. Otte BY 6/ 4 r %a 7 ATTORNEYS O. M. OTTE Aug 17, 1943.

2,227,209 ALLOY STEEL ARTICLE AND PROCESS OF PRODUCING THE SAME 2 Sheets-Sheet 2 Filed May 23, 1941 INVENTOR 0tho M. Otbe 1 726$ ATTORNEYS Patented'Aug.17, 1943 UNITED STATES PATENT OFFICE h i 2,321,209 v ALLoY STEEL ARTICLE'AND PROCESS or PRODUCING r m SAME Otho M. Otto, Tarentum, Pa. Application May 2:, 1941, Serial No. 394,871

3 Claims.

This invention relates .to rolled steel articles and to a method of preparing th same. It particularly relates to alloy steel ingots, bars, slabs,

and the lighter sections of sheetsstrip and plates, and to the method of preparing the same. In the preparation of rolling articles as above mentioned, it frequently happens that relatively small pieces or areas of the surface of the steel or metal when in a hot state, become partly sep arated from the main body of the metal at one or more points and the rolling pressures cause these surface segregations to curl up, fold back or spread out thinly. Since these pieces are but partially attached to the main body of metal, they appear like shingles or chips on the surface of the metal. Such separation occurs during the back and forth rolling operations, and especially is this fracturing of the surface likely to occur during the deformation of ingot into bloom, slab or bar. Once chipping starts, the number of chips or defects are progressively enlarged or areas increased in the further rolling of the metal, so that a very serious surface problem results.

Heretoiore, once the surface of the metal ruptured, scaled, laminated or chipped to any appreciable extent, it was necessary to subject the whole mass to an expensive refinishing of surface by grinding or similar operation, during which suificient metal was removed to present a smooth surface for subsequent rolling.

Surface fracture and similar defects created during rolling deformation, are most noticeable in steels containing substantial. quantities of hardening elements, and particularly inalloy steels, which have substantial toughness andhammer-weld withdifiiculty, or in such steels which do not hammer-weld'especially those containing chromium, molybdenum, nickel or the like.

It is the object of the presentinvention to provide a method for rolling steels wherein the amount of surface defects and the frequency of ing technique.

It is a further object of the present invention to provide a steel having modified grain. structure and improved characteristics obtained by perfected grain orientation in combination with annealing temperatures best suited to develop the particular physical properties sought.

It is a further object of this invention to provide steel in sheet or strip form having improved surface characteristics, and improved tensile strength. a

their occurrence is largely reduced through roll- Other objects will be apparent from the following description of the invention as illustrated in the accompanying drawings, in which:

Figure '1 is 'a schematic elevational view showing the steps of the first pass of asuitable in through the cogging or blooming mill;

Fig. 2 is a schematic view showing the positions occupied by the metal duringthe second pass through the cogging or blooming mill;

Fig. 3 is a further diagrammatic view showing the position occupied by the ingot in the third or subsequent passes through the mill rollsto form a slab or bar of the desired shape;

Fig.4 is a diagrammatic view showing one section cut from a bar or slab in such a manner as to readily designate theproper entry end for further operations;

Fig. 5 is a diagrammatic elevational view of the metal of Fig. 3 during further steps in its're- .tive movement of the various portions of the metal of Fig. '7 when it is given one pass in the opposite direction;

Fig. 9 shows a portion of an unrolled piece of a steel of a single crystal thickness and shows a hypothetical arrangement of the grain crystals sep arated by impurities, eutectic, or the like;

Fig. 10 illustrates a portion of steel of Fig. 9.

showi g the efiects on the crystal shapes of one-'- .or two passes in a single sense;

Fig. 11 illustrates the metal of Fig. 10 after it has been given one -or two passes in the reverse direction, showing the efiect of thereverse rolling on the structure of the grains; and

Fig. 12 illustrates steel of Fig. 10 which has been reduced entirely ina single sense according to the present invention.

In my prior application, Serial No. 275,696, filed May 25, 1939, nowPatent No. 2,260,397,

, dated Oct. 28, 1941, of which the .present application is a continuation-in-part, I disclosed a method for producingsilicon steel sheets or strips having improved magnetic properties by roliine them from ingot to final thickness in a single sense, that is, by reducing the metal of the ingot to the desired thickness by rolling it in a single longitudinal direction by" always entering the the original ingot was first same end. of the metal being rolled into rolls when obtaining efifective elongation.

It has'now been found that not only silicon steel but that other steels, particularly those conreduction in thickness oi the metal is caused when the end portion A of the metal first enters be trimmed inthe usual manner and, if the quan- ..tity of metal is'too great for further handling,

.proved properties'and improved crystal struc-' tures. They haveg'reateistrength and improved surface characteristics 'when the are rolled from ingot to slab in the same manner a described in my prior application for silicon steel.

According to the present invention, the metal cast in the form of an ingot is reduced in the bldomingmill and in subsequent mills, buteach pass is made unidirectionally, i. e., in the same sense. Thus. if the end of the ingot first presented for reduction to the blooming mill is designated A, and the opposite end is designated B, the metal of the-ingot is always introduced for reducing passes through subsequent reducing the slabs S or the bar, as the case may be, may be cut as desired into sections of the desired size or weight. In such cases, however, it is desirable to designate the end portions A and B of the various sheared sections, tomak it-easy for the operator to determine .the proper, end .of each section of the slab or bar to be introduced into the rolls, so that subsequent reduction takes place in the sense of A to B.

-The slab or bar S, diagrammatically indicated as S inFig. 3, may be further reduced to produce rolls in the direction of A to B, so that it passes therethrough in the same sense, i. e., from A to B. The backandforth rolling of the metal even in the blooming mill affects thegrain arrangement and crystal structure in the final article to such an extent that the highest tensile strength and best oriented grain structure is not obtained.

In this application the term "sense .is being used to mean in one longitudinal direction. In. other words, in the making of reducing passes, to

reduce the metal from the ingot to-the desired final thickness, the ingot, slab, bar, sheet or strip, as may in turn be prepared, is presented to the rolls'in the same relative position end-to-end as presented to blooming millrolls. f'

Re ferring to the drawings, the-ingot I of steel, which has been stripped in the usual manner from the ingot mold and reheated in the usual manner in a soaking pit to obtain a uniform temperature throughout, and having end'portions A and B, respectively, is passed betweenthe rolls I and 2 of the blooming mill to elongate it as desired to form the reduced ingot M having. end

portions A and B, corresponding with portions designated A and B of the ingot. The metal M is then returned to the position shown in Fig. 2,

so. that the end A may again enter the bite of the rolls 1 and 2 of the blooming mill. The return of .the metal M from the position of Fig. '1 to that. of Fig. 2 may be accomplished by raising roll I of the blooming or cogging mill to allow a dead pass of the metal M therethrough, and using the table rolls to cause the metal to'return to the initial position. If the metal is causedto pass through the rolls l and 2 in a sense from'B to A, all pressure should beremoved from the rolls, So that noreduction of metal takes place. Other suitable means, such as providing a shunt or by-pass around the blooming mill, may beused to ensure the presentation of the proper end of the metal to the rolls.

The elongated metal M may be'further passed between theiolls I and 2 a suitable number oftimes to produce the bloom P of Fig. 2, and the bloom may be reduced by further hot rolling between the rolls I and 2' -to the slab S of Fig. 3, or to a bar. of suitable size, if desired, havingjend portions A and B which respectively correspond to' the end portions A and B of the'ingot.

It is'to be noted that. in all passe through the rolling mills after the hot ingot has been initially introduced into the first hotroll mill, 3

may be identified as mentioned above, in order that the sections'may be rolled longitudinally in the same sense as the original ingot was rolled, i. e., from Ato B.

The slab S is particularly adaptable for the rolling of long strips of metal.' To accomplish this, the slabS, if large, may be divided into sections of the proper size or weight to give the desired length of a strip of given width and thickness. I

In cutting the slab S into sections of the desired weight it is preferable to have the cut so made that the cut itself will designate theA and B ends of the sections. various ways, a very convenient method of doing it being to use a wide angle V-shaped shear blade cut therefrom, the .cut 8 being in the form of a wherein any reduction in thickness takes place,

Wide angle V, the pointed endbeing designated A, and the other end B. I

The material from the rolls .i' and 2,, which has beenreduced to a suitable size and shape, is s then further reduced through rolling mills. For

example, astand of three or more pairs of rolls, having proper screw reduction, may be used in line, if desired. In such rolling operations,

the end portion designated A is the one entered between the rolls.

The slab or bar S is received-from the slabbing mill at relatively-high temperature, and subsequent heating is usually unnecessary befo'reit is presented to the continuous hot rolls. As shown in Fig'."5, there are three pairs'of reducing rolls. The rolls 3 and 4 are preferably spaced so as to producea relatively high reduction in the thickness of the bar S, and rolls 5 and 6, and 1 and 8,.

are preferably spaced so as to provide a medium reduction and a. low reduction, respectively, in the thickness of the strip'material.

The relative-speeds-of the rolls 3 and 4,5 and 5, and I and .8, 'are preferably adjusted to compensate for the elongation produced, and during the rolling procedure the material may be passed.

This can'be accomplished in of the drawings.

reduction in the same'sense.

- rangement.

, grain arrangement seems to be characteristic of purities, or

of Fig. 9 are given a aszmoo tinuous hot mill is of suitable thickness for use,

it may be wound upon a formhaving the desired shape, such as that of a coil.

Effects of unidirectional rolling, or rolling in one sense, and effects of back and forth rolling are diagrammatically illustrated in Figs. 6 to 12 In Fig. 6 the unrolled'ingot metal l8, having vertical identifying lines l9 thereon, which are spaced uniformly so that flowof the metal may be indicated, is shown as the ingot is passed between reducing rolls in a direction from A to B to reduce its thickness. The straight identifying lines become curved, as shown at Ma. In Fig. 7 the metal which was reduced in Fig. 6 is shown when given a further I It may be seen that this further reduction causes the flow of the metal to continue in the same relative direction as in Fig. 6, with the result that the flow lines 19a become more sharply curved, asshown at l9b, and th s becomes-more pronounced on further reductions.

In Fig. 8 is illustrated metal from Fig. 6, which is reduced to the same extent as in-Fig. '7, by rolling it in the opposite sense. The flow lines l9a become d storted andfreversed, asat l'9c, showing a reversal of flow of the metal, which destroys the most desirable crystal shape with resulting infe- .rior properties.

Thus, Figs. 6 and '7 diagrammatically indicate the movement of metal when subjected to compression rolls in two rolling operations. From the rolling of the ingot to the finished strip, however, there are usually more than fifteen or more such passes and as such passes are made while the metal is hot, the repeated elongations of the metal in-the same sense tend to produce a more uniform crystal axis orientation .or grain ar- Such crystal axis orientation or metal treated in this manner. and such metal possesses very desirable finish and improved;

strength in the direction 'of the grain or rolling.

Fig. 8 illustrates the detrimental effects of a single pass back and forth, which obviouslgtends to cause .a non-uniform or heterogeneous structure, and such structure is emphasized when further back and forth passesare made, resultin in less desirable properties.

- Although it is known that even thin sheets strips of steel usually have a thickness greater ducing rolls they will have substantially the shape of the grains shown in Fig, 10, characterized by the elongated portions of the grains continuously converging towards the ends thereof. If the partially reduced steel of Fig. 10 is now further reduced in the same sense instead. of by back and forth reduction, as has always been the'practice heretofore, the tongue X of Fig. 10 will be further elongated in length, as shown in Fig. 12, so that the grains are characterized by the elongated portions continuously converging toward their ends, with the grains 1 being oriented and having a sharply cur'ved edge. if the partially reduced steel of Fig, 10'

is now rolled in the reverse direction, the metal ofthe tongue X flows in the opposite direction to the previous flow and the general thickness of the tongue is increased in the vicinity of Y, so that the grains have substantially the form shown in Fig. 11, and although reduced in thickness they are less pointed, shorter and generally of a flatter shape than when they are rolled enthegrains of tirely in a single sense, as were- Fig. 10. Such reciprocally rolled grains do not continuously converge toward their ends. Although the reduction of the metal is the same in Figs. 11 and 12, it is readily seen that the grainsin the steel produced according to of the metal rolled in a single sense are much longer in the direction of rolling than are the grains in the metal of Fig. 11.

It is well known that steels, suchas bolts, rods, etc., which are rolled in a back and forth direction without crosswise rolling are much stronger in the direction of their rolling than in the perpendicular direction. This is undoubtedly due to the fact that the grains'in steel so produced are elongated solely in the direction of rolling. It is found in accordance with the present invention that the tensile strength is still further improved. Probably this improvement takes place for the same reason, as it will be readily seen, that'since thegrain are elongated still more when all the rolling, including that of the blooming mill, is in the same sense.

It has also been found that since the grains thepresent invention havegreatly increased inter-grain adhesion surfaces with the lengthof grain face oriented to the common line of elongation and in the same sense, that the mass presents greatly increased resistance to parting or rupture, which individual grain body exposed and these grains than the thickness of a single grain, it is believed that the reason for the improvement obtained by applicant can best be explained by considerin the effects of rolling in a single direction and the rolling back and forth on a hypothetical sheet having a thickness of one grain, as is illustrated in Fig. 9. The effects on ness are representative of theeflects' on thicker metal and the drawing is much simplified;

In Fig. 9 the grains G. are shown prior to rollthe metal of "such thickalong the boundary therefore forces of break or fracture. occurs lines between grains, and

stretching or tensile force applied parallel to' the axis of rolling elongation may be materially increased over like metal and mass that has been formed by first rolling in one direction the. opposite direction.

Onthe surface of the are accordingly more tals or grainsterniinating at the surface of the metal are elongated from their pointof strongest attachment and at no time. are these ends.

ing of thesteel, 'separated by the usual slag, im-

other ingredients designated 25, and usually present between the boundaries of the separate grains of the metal.

single pass through the-re- When the grains havoc in the preparation of molybdenum steels forcedin the direction of such point of strongciable tendency for scuffingthe ends. from the est" attachment. There is,therefore, no appremainbody of metal and so-called shingling or which occasionally causes so much including armor plate, and in the preparation firmly interlocked with each other and the next underlying surfaces. 'When the elongation of the metal is in one sense, as above-explained; any thin ends of crysforming the slab or bar.

of other low silicon alloy and stainless steels, is

reducedand usually entirely eliminated.

-As the heavier reductions in thickness usually take place in the blooming or slabbing'mills, a. reverse pass on these mills is usually more deleor bar of a suitable thickness for further proc-.

essing into a sheet or strip the reductions'in thickness for a given rolling pass are, of course, considerably less in amount than those for Even in the further processing, the metal should .be rolled in a single I sense to obtain the best'properties, and particu lar-ly for the heavier reductions in thickness' In the reduction of the steel as above described, it is contemplated that it be given coatings of insulating material, such as magnesium oxide, before it is coiled. It is alsocontemplated that, after thesteel has been reduced to a suitable thickness, several laminae of the material may, if desired, be superimposed and giv en the final'reduction in thesuperimposed condition to produce sheet or strip.

always entering the same end of the metal being ro1led into the rolls when obtaining effective be utilized in various ways, numerous modifications and alterations being contemplated, it

being understood that the embodiments shown in the drawings and described above are given merely ior purposes of explanation and illustration; without intending to limit-the scope' of the claims to the specific, details disclosed.

. What I claimis:

15A process of forming molybdenum steel wherein the amount of surface chipping is substa'ntlally reduced, which comprises reducing a molybdenum steel ingot to the desired form by rolling it in a single longitudinal direction by elongation, whereby molybdenum steel having all eiiective elongation in a single sense is produced.

2. A process for producing alloy steels other than silicon steels containing at least one member of the group consisting of chromium, molyb- 'denum and nickel, in which process the amount of surface chipping is substantially reduced, said process comprising casting an ingot of' the desired metal, and reducing the-metal of the ingot to the desired thickness by rolling it in a In. my above-designated, copending application, now Patent 2,260,397, I disclosed a process for producing relatively thin silicon steel of improved magnetic properties; Silicon steel is defined in Chambers Technical Dictionary, published by The Maximilian Company of- New York in 1940, on page 770, as: Iron or low car- -bon steel to which .0'.75-4.0% silicon has been added. It is not my intention to claim herein silicon steel according tothe above definition.

The principles of the present invention may' single longitudinal direction by always entering the same end of the metal being rolled into the rolls when obtaining eifective elongation, whereby alloy steels having all effective elongation in a single sense are produced.

'3. A molybdenum steel article substantially free from surface chipping,- having the grains of metal elongated in a single longitudinal direction by always entering the same'end of the metal being rolled into the rolls when obtaining effective elongation, said article being characterized by having the elongated portions of the grains continuously converging toward the ends thereof, the ends being sharply curved.

' OTHO M. OTTE.

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