US1898390A - Chilled iron roll - Google Patents

Description

Patented Feb. 21, 1933 UNITED STATES PATENT; OFFICE WALTER H. IPFEIL, F READING, PENNSYLVANIA, ASSIGNOR TO BIBDSBORO STEEL FOUNDRY AND MACHINE COMPANY, OF. BIRDSBORO, PENNSYLVANIA, A COBPUHAU TION OF PENNSYLVANIA No Drawing.

My invention relates to chilled cast iron rolls for use in rolling mills and it has for its general object to provide a chilled roll consisting of an iron alloy of a composition such that chilled rolls made thereof will have greater strength, greater hardness, better wearing qualities and greater resistance to fire cracking than the ordinary chilled cast iron rolls heretofore in use.

A further characteristic of a chilled iron roll consisting of an alloy embodying my invention is that deep grooves may beformed therein without the excessive depth of chill which is required in the case of ordinary chilled rolls.

A further purpose is to make a chilled cast iron roll containing chromium and copper, and at the same time to avoid the undesirable characteristics imparted to the roll by effective quantities of molybdenum.

A further purpose. of my invention is to form a chilled roll of an iron alloy having a carbon content within the cast iron range, containing an effective amount of chromium but not more than 2.00%, an ehective amount of copper but not more than 1.50%, and no molybdenum or at least not more than 10% of molybdenum.

In the present day practice in ,rolling 3 mills, chilled cast iron rolls are subjected to great stresses and strains and altogether undergo very hard usage. Heretofore this condition has been met in some cases by increasing the sizes of the rolls in order to chtain the requisite strength and in others by the employment of very expensive allo s. But this is objectionable and it is highly esirable to obtain the requisite strength and ruggedness without the necessity of 1ncreas-- ing the. dimensions or sizes of the rolls and without the employment of very expensive alloys.

By my invention I am enabled to employ rolls of smaller diameter, to perform certain kinds of work, than would be required if ordinary chilled rolls were employed. In other words, I am enabled to perform work on smaller mills that otherwise would require the use of larger and more expensive mills.

I Application filed January 5, 1932. Serial No. 584,901.

It is a further purpose of my invention to provide a chilled cast iron roll in which the primary or outer chill is very thin; that is to say, 1s very light and merges into the sec ondary or inner chill without any apprecia i ble line of demarkation. By. providing chilled rolls with this characteristic feature of construction, I am enabled to provide deep grooves in the same for the purpose of giving the shapes desired to beams, rods and the like, which are passed betweenv adjoin- In a. roll having the composition of my invention, the surface hardness and hardness of metal toward the cent-er of the roll differ but slightly. However, there is a gradual decrease in hardness, the hardness of the outer surface portion of the roll merging gradually into the secondary chill and in terior portion of the roll, as already indicated. Thus a homogeneous, dense and very strong structure is produced, due primarily to the new composition employed by me in the manufacture of my roll.

In the manufacture of ordinary chilled iron rolls, it heretofore has been the practice to employ silicon, manganese, sulphur, phos phorus, carbon and iron, the percentages of these materials varying with the character of roll desired. My reference to the character of roll desired is meant to refer to the char actor of work for which the roll is to be employed.

It may be noted that the mixture of pig iron, scrap and alloys used in the manufacture of chilled iron rolls is usually melted in an air-furnace, but might also be made by (iii the use of an open-hearth, electric or cupola i i that it must be altogether absent, and in fact in the normal case some very small quantity of molybdenum will be present in the roll of my invention, due to the almost inevitable presence of molybdenum in the scrap. I mean to imply, however, that molybdenum will not be present in an effective quantity, that is, that its percentage will not rise above a fraction of I find that rolls made in accbrdance with my invention may have very deep grooves without the necessity for excessive or great depth of chill, as has been required in the prior art.

Chilled rolls of ordinary cast iron lack the strength necessary to enable them to perform many kinds of work which they are called upon to perform. This is particularly true where very deep chill is required.

roll produced by the use of chromium and copper, without effective quantities of molybdenum, has been found by me to be much superior to the same roll containing the chromium and copper along with an effective quantity of molybdenum.

'line molybdenum tends to cause the precipitation of graphitic carbon in the chilled section of the roll. It appears that the presence of molybdenum undesirably favors the reachingof equilibrium during chilling; in other words, molybdenum opposes the formation of the grain structure which is most desirable in rolls of this type. Due

to the grain visible in photomicrographs of the chilled sections of rolls of the kind to which am referring, such rolls are comy known in the trade as grain rolls. I therefore find it most desirable to preserve the grain structure in its most pronounced form by omitting molybdenum in ill effective quantities.

il hcre molybdenum is not present in effective quantities, the grain structure is not only more pronounced, but it is also more uniform and more homogenious in the chilled section.

l requcntly during the casting of rolls, cracks and incipient cracks develop which either cause rejection of the casting at the foundry or else lead to failure in service and u timate replacement.

il here molybdenum is present, the tendency of the roll to crack is thereby increased. I have observed that the percentage of rejections of castings has decreased markedly in instances where effective quantities of molybdenum have been omitted, as compared with those cases in which efiective quantities of molybdenum have been used.

From the standpoint of furnace practice and casting, it will be obvious, and it is the actual experience, thatthe alloy containing the four effective components iron, carbon, chromium, and copper is much more easily handled than the five component alloy having the additionalelement.molybdenum in effective percentage.

An additional feature of wide commercial importance is thelower cost of my roll as compared with the roll in which molybdenum is used. By avoiding the use of effective quantities of molybdenum, I avoid the need for the most costly alloy ingredient of the three components chromium, copper and molybdenum. For example, on the basis of the alloyingredierit the cost of molybdenum is approximately $1.00 per pound, as against per pound for chromium and 9 per pound for copper. Furthermore, I find that the percentages of chromium and copper need be no higher when molybdenum is absent than when it is present.

In effect, I have discovered that the molybdenum, which was formerly considered highly desirablein grain rolls, is in fact a deleterious ingredient if it is present to an extent of more than 10%. All of the advantages previously attributed to the molybdenum in the combination may be obtained by using the chromium and copper alone in the cast iron.

In making up my alloy I ordinarily charge the furnace with scrap and also with pig iron. The scrap, especially when obtained from previously used rolls of a type not embodying my invention frequentl contains a relatively high content of molybdenum, as for example, .50% or more, and I therefore dilute this high molybdenum scrap by melting with it or adding to it pig iron or other ferrous material low in molybdenum or lacking in molybdenum. In this manner the total molybdenum content of the resultant molten charge will be below that which is considered an effective quantity of molybdenum.

A certain oxidation of oxidizable ingredients present in the charge, such as chromium, is inevitable during melting and during furnace operation. I therefore find it necessary to add chromium even when the chromium content of the charge as calculated from the content of the solid raw materials was initially correct. I also find it necessary in most cases to add copper to enrich the charge. During the additions of alloying ingredients, especially chromium and copper, I am careful to avoid any addition of molybdenum, as

I desire to limit the molybdenum content to the lowest amount consistent with the use of the scrap available. For convenience I have referred to additions of copper and chromium from the standpoint of the enrichment of the charge in these metals. My alloy as prepared in my furnace is primarily intended'for casting and chilling, since its composition is controlled by my desire to "avoid the possibility of cracks during casting and chilling and of subsequent cracking during service. I find the alloy disclosed well suited to form a thin surface chill'and that there is less danger of cracking with a thin chill and a progressively changing backing than with a thick chill with dependence upon the thickness of the chill in that event, rather than the flexibility.

The percentage of copper and chromium to be used vary or differ for difier'ent sizes and kinds of rolls. As already suggested, it is meant by kinds of rolls to refer to the nature of the work it is expected that they shall be required to do.

In the production of an alloy in accordance with my invention I propose to employ the ingredients heretofore indicated, including chromium and copper, in percentages 30 somewhat as follows:

Carbon 2.50% to 4.00% Chromium .75% to 2.00% Copper 25% to 1.50% 35 Molybdenum 0.00% to .10%

Silicon 50% to 2.00% Manganese 25% to 1.25% Sulphur 025% to 20% Phosphorus 025% to .50%

the remainder sufiicient to make up 100% consisting of'iron.

As has been indicated previously herein the percentages of the ingredients enumerated may be varied in order to produce rolls having characteristics which will best fit them for operations under the conditions heretofore indicated.

It may be noted that the casting of rolls of a composition embodying my invention is carried out in the manner usually employed in the casting of ordinary chilled rolls, chill pass, and rolls in which condensing chills are used; hence it is deemed unnecessary to refer in detail to the manner or way in which the casting operation is performed.

I desire to get the full benefit of the copper and chromium ranges of content indicated, which are of real value but which have been clouded in previous teachings by effective and therefore objectionable contents of other ingredients, of which one of the most objectionable is molybdenum.

By reason of the very powerful effect of.

molybdenum as an alloying ingredient, even effective and therefore objectionable. For example, in a previous alloy the good efiects of the presence of copper and chromium have been negatived by the presence of an efiective quantity of molybdenum, indicated as being present in as low a quantity as .10%. It will be evident that the benefit of my invention is to be measured by maintenance of the content of molybdenum below that which becomes eiiective, rather than upon any given and definite percentage of molybdenum. My own experience agrees with the teaching of the prior art that molybdenum to be efiective must be approximately 10%. I

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain part or all of the benefits of my invention without copying the structure shown, and I, therefore, claim all such in so far as they" fall within the reasonable spirit and scope of my invention.

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

1. A chilled cast iron roll wherein there is no distinct line of demarcation between the primary chill and the secondary chill,containing between 0 and 10% of molybdenum and comprising as essential ingredients of the composition thereof chromium and between about .7 5% and 2.00% and copper between about 25% and 1.50%.

2. A chilled cast iron roll containing and comprising as essential ingredients in the composition of the matenal of which the roll consists chromium and copper, the percentage of chromium ranging from about .75%

10% of molybdenum and comprising as essential ingredients chromium which may range from about .7572; to about 2.00% and copper which may range from about 25% to about 1.50%, the said roll being further characterized in that it offers relatively great resistance to fire cracking.

4:- A chilled cast iron roll wherein the outside primar chill is thin and merges into the secondary chill without any appreciable line of demarcation and wherein also the surface hardness and hardness of the metal toward the center of the roll differ but slightly, the composition of which consists of carbon which may range from about 2.50% to about 4.00%, chromium'from about .75% to about 2.00%, copper from about 25% to about 1.50%, molybdenum from to about 10%, silicon from about .50% to about 2.00%, manganese from about 25% to about 1.25%, sulphur from about 025% to about 20%, phosphorus from about 025% to about 50%, and iron sufficient to make a total of 100%.

5. A chilled cast iron roll characterized in that the surface thereof is hard, dense and resistant to abrasion and in which the said surface portion merges gradually into the inner portions of said rolls Without a definite line of demarcation, the said roll offering relatively great resistance to fire cracking, containing between 0 and .10% of molybdenum and comprising and containing as essential ingredients in its composition chromium and copper, the former in proportions which may range from .75% to about 2.00% and the latter in proportions which may range from about to about 1.50%, the presence of the specified characteristics of said roll being due to the casting thereof against a chilling medium.

WALTER H. PFEIL.