US2115465A - Rolling mill roll - Google Patents

Description

April 26, 1938; w. J. MERTEN 2,115,465

ROLLING MILL ROLL Fil ed March 22, 1957 2 Sheets-Sheet l INVENTOR William I M erfen April 26, 1938. w. J. MERTEN ROLLING MILL ROLL 1957 2 Sheets-Sheet 2 Filed March 22 INVENTOR William JMeJ-ten OFFICE UNITED STATES PATEN BOILING ILL norm,

-Wllliam J. Merton, Pittsburgh, Pa., assignor to Pittsburgh Rolls Corporation, Pittsburgh, Pa., a corporation of Vir a Application March 22, 1937, Serial No. 132,257

16 Claims. (Cl. 80-58) This invention relates to rolling mill rolls and by thermal treatment in the solid state, and after provides a ferrous base roll having outstanding the proper thermal treatment has been effected qualities either for hot or cold rolling and for use the roll is remarkably fine grained and uniform. either as a working roll or as a pressure roll in In the accompanying drawings illustrating a backed-up mills. While'the invention is applipresent preferred embodiment of the invention, 5 cable either to ironor steel rolls, it is herein Figure 1 is a vertical section, largely diagramparticularly described as applied to steel rolls. matic, showing a mold with my improved roll cast Certain problems and conditions of use therein; peculiar to rolling mill rolls have long been Figure 21s a photo'micrograph showing the steel 7 known in the art and a number of. schemes, some in the cast state; 10 metallurgical in their nature and others having Figure 3 is a view showing a fracture of the to do with processes of manufacture, have been steel in the cast state; proposed. Despite the large amount of study Figure 4 is aview corresponding to Figure2 but which has been given to the problem the life of showing the steel after it has been homogenized;

rolls in use has been distressingly short and has v Figure 5 is a view corresponding to Figure 3 15 been reflected in higher manufacturing costs. but showing a fractured section of the homo- The problem has. become one of-increasingimgenized steel; portance as the rolling art has progressed in Figure 6 is a view corresponding to Figure 2 operations which, because of their nature, imbut showing the fracture after annealing;

O pose particularly great hardships on the rolls. Figure '7 is a view corresponding to Figure 6 Examples are alloy sheets and high speed wide but showing the steelafter annealing; strip mills. Figure 8 is a view corresponding to Figure 2 Rolls of this sort should have great physical but showing the steel after air quenching and strength and toughness, should be relatively free tempering and in condition to be used.

from fire cracking, spalling and roughening, and Figure 9 is a photomicrograph corresponding to 25 should be susceptible of taking and retaining a Figure 8 but to a higher degree of magnification; high surface finish. As heretofore made, how- Figure 10 is a view corresponding to Figure 3 ever, such rolls have suffered from the limitations but showing a fracture of the material after air indicated to a greater or less degree and with inquenching; and 7 3o creases in mill loads have shown an increasing Figure 11 is a corresponding view showing a tendency to fracture under the alternating fracture of the material after tempering.

stresses to which rolls are inevitably subjected. In the illustratedembodiment of the invention By the present invention I provide a roll which the roll is a steel casting within the following in practice has beenconclusively shown to have composition range: Percent.

a much longer life than rblls as heretofore made; Carbon to 09 35 to be substantially or entirely free of the defects 2 1,035 which result in fractures, and to be vastly superior Chromium 25 to 5 to ordinary rolls in respect of the features above Mdybdenu; 0.4 to enumerated. I cast my improved roll from an 40 ,11 containing b n, manganese, chromium, The balance is substantially iron except for 40 molybdenum and a killing agent, preferably silim a m n s or th mp dsa d d f r con, although titanium or aluminum may be used. d xidi ns and degaslfying the e S as a These several elements are so proportioned as to element of the group S n, titanium, um-

give the qualities above referred to. Preferably I Pr f r to add Silicon in n amount sufllcient to their proportions aresuch that the alloy has a obtain in the solid metal a silicon content of 0.2 45 very short period of primary crystallization reto 0.35 percen Amore p i range w hm y sulting in freedom from coarse dendritic freezing be conveniently followed and whiclnI have found or segregation. I believe my alloy to be a eutectic particularly desirable 18 a fo ows or of quasi-eutectic composition Despite the Percent. fact that the alloy contains an unusually large Carbon .5 to ..'l 50 amount of manganese much beyond the figure Manganese 2 to 2.5 generally regarded as the limit for steel rolls, Chromium 3 to 3.5 my composition is such that the coarsening effect Molybdenum .4 to .5 of the manganese is limited. In fact, the alloy Silicon .3 to .35

is markedly responsive to structural mcation Balance principally iron 7 w A specific analysis which I have employed with great success is as follows:

Balance iron The phosphorus and sulphur are undesirable impurities and should be kept as low as is practical in open hearth or electric furnace practice.

The relationship between the manganese and the chromium content is of importance and should be carefully maintained if the best results are to be secured. I prefer to keep the chromium content in excess of the manganese content, preferably by 0.5 percent or more. It will be found that if this relationship is observed the carbon content of the roll can be varied over quite wide limits. The chrome-manganese relationship is also of importance in that it makes the roll soften more readily during the heat treatment.

Figure 1 illustrates a conventional mold comprising a base 2 and a flask 3 for the casting of the roll R. The mold'is in accordance with customary foundry practice in the manufacture of cast rolls and is bottom poured through a spout 4. The gate 5 is tangentially arranged so as to impart'a swirling motion to the steel. A melt of the specific analysis above given may be successfully pouredat a temperature of 2650-2750 F. I endeavor to have the metal at a temperature of As is usual in the casting of rolling mill rolls, the mold is several feet higher than the desired roll length, thus insuring sound metal in the roll itself. After the pour has'been completed, the top of the mold is covered as with kieselguhr to prevent heat loss.

On cooling, several important facts will be noted. The transition from the liquid, phase to the solid phase is of quite short duration. The

metal, while perfectly fluid and free-running at the pouring temperature, has the important property of changing promptly to thesolid stage with but little temperature drop. This is of special importance in the casting of rolling mill rolls.-

Such rolls, as cast, are frequently of very large size, for example, up to 12 feet or more in length and 4 feet or more in diameter. Such a mass of metal in cooling undergoes considerable shrinkage and in most steel alloys gives rise to fissures,

cracks or cavities in the body of the casting. In the casting of ordinary rolls the last zone or portion of the metal to freeze is located approximately as indicated at '6 in Figure 1, and the consequence almost invariably is that the metal is discontinuous thereabouts. Since a roll is always fiexed to some degree in use, the rotation of the roll brings about an alternating stress therein and in practice it is quite common for rolls of ordinary composition to break at a place corresponding to the location of the point 6. Rolls made of my, improved alloy appear to be free of this defect. Certainly experience with the same up to the present time indicates no such weakness. Iattribute this important advantage to the uniform solidificationor non-dendritic freezing of the alley or substantially perfect liquid solution practically down to the solidus temperature. As stated, I believe the alloy to be a eutectic or of quasi-eutectic composition.

A second important point to be noted in the casting of my improved alloy is the characteristic shape of thesinkhead. This is indicated at l in Figure 1. In ordinary roll casting practice, the sinkhead cavity is of steeply tapering conical form, the point of the cone extending deep into the riser. The sinkhead cavity formed after casting my alloy is more generally cylindrical in form, being of almost the same diameter at the bottom as at the top and the bottom being much in the form of a shallow dish. My studies indicate that the alloy possesses the property of retaining its fluidity to a marked degree in the initial cooling and of shrinking uniformly and without severe dendritic segregation during the change from the liquid to the solid state, being 'in these respects far superior to the alloys generally used -in making rolls. In consequence a sound casting isinsured and the possibility of imperfections in the working portion of the roll is greatly reduced. This is a matter of large commercial importance because of the fact that rolls of this sort are periodically dressed down and any imperfection in the metal for a considerable distance below the cylindrical surface of the roll must be eliminated.

After the casting has solidified, it is removed from the mold, the gate and the riser are cut off, and the roll is then heat treated. In the following description of the heat treatment reference will be made to Figures 2 to 11 as illustrative of the structure at different stages. These views were made from a disc cut from the top of a casting of approximately the analysis above set forth and subjected to the same heat treatment as the roll from which it was cut.

Figures 2 and 3 represent the cast structure. As shown by the photomicrograph Figure 2, the steel is martensitic. As shown by the fracture specimen Figure 3, the steel is coarse grained There is some difierence in grain size of the .metal from the outside toward the center,

although this difierence is not as much as in steels ordinarily used for rolls. The cast metal is substantially free from streaks and ghost lines which, of course, are optical evidence of segregation; This uniformity of cast structure is one reason for the unique and ready response of the structure to thermal treatment for the formation of a desired structure which is substantially heat was then cut off, the doors were opened, and

air was allowed to circulate freely through the furnace until the metal was brought down to nor mal temperature. Figures 4 and 5 illustrate the resulting structure. It will be noted from Figure 5 that the grains have been greatly refined and instead of the coarse crystal structure of Figure 3'the structure shows a smooth and silkyappearance.

Following the homogenizing treatment, the roll 4 is annealed by heating it to 1450 F., followed by .slow cooling. This annealing was given to make the cast roll machinable for the rough tumlng operation. The grain structure is shown in Figure 6 and the fracture is illustrated in Figure 7.

It will be noted that there is a slight coarsenin of the crystal structure.

The roll is now extremely tough and the release of strain hardening by the tempering operation results in higher physical properties.

Figures 8 and 9 show the micro structure of the finished roll. Figure 8 is to the same degree of magnification as Figures 2, 4, and 6 (100 diameters in the original drawing, not reduced for reproduction), while Figure 9 is to a greater degree ofmagnification (1000 diameters in the original drawing, not reduced for reproduction). As will be particularly apparent from Figure 9, there has been considerable spheriodizing.

The following tabulation gives the physical properties of the roll in the cast condition and after the above described heat treatment:

As homogenized Heat treated Yield point 90,00039/511. in. 125,000#/sq. in. Ultimate tensile strength 120,000#/sq. in. 182,000#/sq. in; Elongation 12% Reduction of area.- 21% 17% Hardness-Brinell. 248 302 Hardness-scleroscope B 38 47 Due to the relatively high percentages of chromium, manganese and molybdenum, the alloy is quite resistant to oxidation or heavy scaling at temperatures considerably above those employed in the heat treatment. In consequence, only a fire cracking. Fire cracking has heretofore been a limiting factor on the length of time that a roll might be used without redressing, and fire cracks frequently progress to such a point as to cause failure of the roll or to show tears and bad marking on the surface of the work. In any event, deep fire cracking requires heavy dressing of the rolls, thus reducing the tonnage obtainable from them. My improved rolls have a much reduced tendency toward fire cracking and surface markingand such of it as does take place is shallow. Experience proves that it can be eliminated by comparatively light dressing.

In either hot or cold work spelling of rolls has also been a factor. It takes place either in working rolls or in backing rolls due to deep cold work occasioned either by contact with the work itself in the case of a wormng roll, or by contact with the working roll in the case of a backing roll. My improved roll is remarkably free of this defect. It is also quite free from any tendency to roughen in service, thus indicating an unusually high intergranular or cohesive strength.

I have illustrated and described the present preferred embodiment of my invention. It will be understood, however, that this is by way of example only and that the invention may be otherwise embodied within the. scope of the following claims:

I claim:

1. A-steel roll for rolling mills comprising carbon 0.3 to 0.9 percent, manganese 2. to 3.5 percent, chromium 2.5 to 5. per cent, molybdenum 0.4 to 0.75 percent, a small quantity of a degasify ing and deoxidizing element of the group silicon, titanium, aluminum, the balance being principally iron. I

2. A steel roll for rolling mills comprising carbon 0.3 to 0.9 percent, manganese 2. to 3.5 percent, chromium 2.5 to 5. percent, molybdenum 0.4

to 0.75 percent, silicon 0.2 to 0.35 percent, the

balance being principally iron.

- 3. A steel roll for rolling mills comprising carbon .5 to .7 percent, manganese 2. to 2.5 percent,

chromium 3. to 3.5 percent, molybdenum .4 to .5 percent, silicon .3 to .35 percent, the balance being principally iron.

4. A steel roll for rolling mills comprising carbon .5 to .7 percent, manganese'2. to 2.5 percent, chromium 3. to 3.5 percent, molybdenum .4 to .5 percent, a small quantity of a degasifying and deoxidizing element of the group silicon, titanium, aluminum, the balance being principally iron.

5. A steel roll for rolling mills having approximately the composition carbon .58 percent, manganese 2.5 percent, chromium 3.31 percent, molybdenum .44 percent, silicon .35 percent, the balance being principally iron.

6. A steel roll for rolling mills comprising carbon 0.3 to 0.9- percent, manganese 2. to 3.5 percent, chromium 2.5 to 5. percent, molybdenum 0.4 to 0.75 percent, a small quantity of a degasifying and deoxidizingelement of the group silicon,

titanium, aluminum, the balance being 'principally iron, the several elements being so propor tioned that the alloy is a eutectic or quasi-eutectic.

'7. A cast steel roll for rolling mills comprising carbon 0.3 to 0.9 percent, manganese 2. to 3.5 percent, chromium 2.5 to 5. percent, molybdenum 0.4 to 0.75 percent, a small quantity of a degasifying and deoxidizing element of the group silicon, titanium, aluminum, the balance being principally iron, and characterized by a generally cylindrical sinkhead cavity on casting.

8. A homogenized, annealed and tempered cast steel roll for rolling mills comprising carbon 0.3 to 0.9 percent, manganese 2. to 3.5 percent, chr mium 2.5 to 5. percent, molybdenum 0.4 to 0.75 percent, a small quantity of a degasifying and deoxidizing element of the group silicon, titanium,

aluminum, the-balance being principally iron, characterized by relative freedom from fire cracking and spelling.

9. An annealed and tempered cast steel roll for rolling mills comprising carbon 0.3 to 0.9 percent, manganese 2. to 3.5 percent, chromium 25* to 5. percent, molybdenum 0.4 to 0.75 percent, a small quantity oi. a degasifying and deoxidizing element of the group, silicon, titanium, aluminum, the balance being principally iron, characterized by relative freedom from fire cracking and spalling.

10. A steel" roll for rolling mills comprising carbon 0.3 to 0.9 percent, manganese 2. to 4.5 percent, chromium 2.5 to 5 percent, the balance being principally iron, characterized by substantially uniform grain structure throughout,

11. A heat treated cast steel roll for rolling mills comprising carbon 0.3 to 0.9 percent,'manganese 2. to 4.5 percent, chromium 2.5 to 5. percent, the balance being principally iron, characterized by having a substantially uniform finegrained structure throughout.

12. A steel rollfor rolling mills comprising carbon 0.3 to 0.9 percent, manganese 2. to 3.5

percent, chromium 2.5 to 5. percent, the chromium content exceeding the manganese content by at least about 0.5 percent, molybdenum 0.4 to .75 percent, the balance being principally iron.

13. A ferrous base roll for rolling mills comprising carbon in essential amount, manganese 2. to 3.5 percent, chromium 2.5 to 5. percent, the chromium content exceeding the manganese content by at least about 0.5 percent, molybdenum 0.4 to .75 percent, the balance being principally iron.

14. A ferrous ,base roll for rolling mills comprising carbon in essential amount, manganese 2. to 3.5 percent, chromium 2.5 to 5. percent, the chromium being in excess of the manganese, molybdenum 0.4 to 0.75 percent, a small quantity of a degasitying and deoxidizing element of the group silicon, titanium, aluminum, the balance being principally iron.

15. A ferrous base roll for rolling mills comprising carbon in essential amount, manganese 2. to 3.5 percent, chromium 2.5 to 5. percent, the chromium being in excess of the manganese, molybdenum 0.4 to 0.75 percent, a small quantity of a degasifying and deoxidizing element or the group silicon, titanium, aluminum, the balance being principally iron, the several elements being so proportioned that the alloy is a eutectic or quasi-eutectic.

16. A ferrous base roll for rolling mills comprising carbon in essential amount, manganese 2. to 3.5 percent, chromium 2.5 to 5. percent, the

chromium being .in excess of the manganese,

molybdenum 0.4 to 0.75 percent, a small quantity of a degasifying and deoxidizing element of the :4. J. mania.

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