US2399730A - Method of producing alloyed iron rolls - Google Patents

Description

Fatented May 7, 1946 Q METHOD OF PRODUCING more mom ROLLS Albert Paul Gagnebln, Red Bank, and Edmund Merriman Wise, Westiield, N. J., asslgnors to The International Nickel Company, linc., New York, N. Y., a corporation of Delaware No Drawing. Application May 4, 1942, Serial No. 441,726

14' Claims.

The present invention relates to rolls and more particularly to hard alloyed cast iron rolls having a hard body and machinable necks and the like.

It is well known that the more fully alloyed cast iron rolls of the chilled type possess certain advantages but these rolls suffered from th disadvantage that when cooled from the cast condition in the conventional manner the necks of the rolls, i. e., the parts of the rolls which rest in chucks or hearings, were unmachinable. This necessitated the use of slow expensive operations to shape the roll necks, usually by grinding. These operations were necessary because the composition of the roll is governed by the requirements of the chilled body where a very hard, mirror-like surface is required. The amounts of alloying elements in the cast iron are usually controlled at a sufficiently high level to produce a hard martensitic matrix structure in the roll body. As a result, the necks also developed a martensitic matrix structure and were also hard and unmachinable. Attempts have been made to soften the martensitized roll necks by heating them but this treatment often results in cracking or weakening the material near the junction between the neck and the body of the roll and is also very slow, about 4 to 6 days being required for accomplishing this treatment. Due to the inherently unsatisfactory nature of this process, the necks are frequently left hard and are ground to dimensions, which,while slow and costly, about $600 per pair of rolls or more than 15% of the total cost, avoids the hazards of the reheating process. To avoid this slow and costly grinding operation it has been proposed to use. a process which consists'in the mold with the regular roll alloy, waiting Ior'fa short time to permit the. formation of a shell in the chilled body, then draining out the molten portion of the roll alloy and refilling the mold with a less alloyed composition or plain iron which would provide a soft neck which could be machined. While this method has been tried in certain types of rolls, it had several disadvantages. The most serious of these was that the chilled body shell frequently cracked and, besides the obvious mechanical diiliculties involved in this production method, the roll suffered some loss in scrap value because its average composition was unknown. This method required very exact timing, perfect control of pouring tern; peratures, extreme care in pouring and other accurately controlled conditions and, as far as known, attempts to use it have been abandoned in the United States.

a An outgrowth of the above process is the scheme of pouring in enough metal to fill the mould for the lower neck and the roll bodyand then to follow this with a small amount of bottom poured plain cast iron which dilutes the metal in the lower neck and renders it less hard and more or less simultaneously pouring in a small amount of plain cast iron into the top of the mould to form the neck at the upper end of the roll casting. 'This too requires great skill and very accurate control of the volumes of hot metal, but the worn rolls. and the compositions of the necks are not identical and their properties are somewhat variable depending, as they do, on the amount of mixing that has occurred, both features being objectionable. Attempts were also made to soften martensitic roll necks by reheating them while the roll body was kept cool enough to avoid softening it. However, severe thermal stresses were set up in the brittle martensite which initially constitutes both the neck and the body of the roll with the result that cracks often developed in a new roll which would cause the necks to break of! when lifted with a crane or still worse. the high stresses or minute cracks, in the weak region near the junction of the body of the roll and the neck, would cause failure during use which would result in the shut down of a whole continuous strip mill.

Great effort has been made to mitigate these difi'iculties and whil considerable progress has been effected this treatment is inherently precarious due to the brittleness of the martensite and the large thermal stresses which are set up by the diilerential heating of a mass of meta] weighing from l0000..to 20000 lbs. It is also slow, some 4 to 6 days being required to perform it.

Although'many attempts have been made to remedy the foregoing shortcomings, none, as far as we are aware was entirel successful when carried into practice on an industrial scale. We have discovered that a roll can be obtained having the same composition in the neck as in the body and having a machinable neck and a hard face or chill on the body by a special treatment which'involves arresting the cooling of the necks after casting for a period of time in a range of elevated temperatures. While diamonds and perhaps some of the special carbide tools may cut the martensitic irons, we consider that machinability with reference to roll necks means that the neck can be cut in a practical manner with tools made of good high speed steel.

It is an object of the present invention to provide a method of producing an alloyed cast iron roll having a body with a hard martensitic face, and: integral with it, one or more necks having the same composition as the body, and comprising a machinable substantially nonmartensitic structure, whereby the roll neck may be machined.

It is another object of the present invention to provide a method of treating cast.iron rolls which would have unmachinable necks after conventional cooling from casting solidification temperatures to render said necks machinable and at the same time to retain a hard face or chill on the body of said rolls.

Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description.

Broadly stated, the invention comprises casting an alloyed martensitic cast iron roll-having a body and necks; cooling the metal in said 'cast roll from solidification temperatures; arresting the cooling of the metal in said necks within the range of about 500 F. to slightly below the temperature at which austenite is stable. The latter temperature, as is well known in the art, varies with the composition of the austenite but normally will not exceed 1400 F. even in compositions containing appreciable chromium and like elements. The rate of decomposition of austenite is very slow just below the temperature at which austenite is stable but becomes more rapid as the temperature is lowered, reaches a maximum rate and again becomes slow as temperatures of the order of 500 F. are approached. We therefore arrest the cooling at a temperature at which austenite transforms at a reasonable rate; i. e., a temperature normally below 1400 F. and generally below 1300 F. and preferably 900 F. to 1100 F., while continuing the cooling of the metal in the body of said roll. The invention further comprises maintaining said necks within said temperature ran e for a period of time suflicient to transform the necks to a machinable In actual practice, the roll is ordinarily cast vertically, in accordance with preferred commercial procedure, in a mold with chillers around the body and sand around the necks. After the roll, (plus its necks) has been poured it may be allowed to cool in the mold or may "be stripped from the mold, e. g., at about black or dull red heat, and be placed in an annealing oven, e. g., at about 1000 F., to cool or may be covered with a heat insulating medium to retard the cooling depending upon the type of hard iron employed, stripping and oven cooling being preferred with the high chromium type of irons sold under the trade-mark Ni-Hard" to avoid cracking, while mold cooling is satisfactory for the low chromium type of iron sold under the trade mark Ni- Hard and allied roll compositions. Stripping from the vmold followed by'air cooling is employed in a few instances with rolls of low alloy content. The invention may be applied to rolls stripped from the molds and cooled in air or to rolls cooled in the molds, as well as in ovens, furnaces, pitS, etc. In accordance with the present invention the entire roll is not then slowly cooled to atmospheric temperatures but, on the contrary, the necks of the roll are maintained at temperatures within the range set forth hereinbefore for transforming the necks to a machinable structure, e, g., at a temperature within the range of about 850 F. to about 1200 F., say at about 1000 F., for the specified period of time, e. g., about 10 to 50 hours, whilst the body of the roll is slowly cooling. The necks of the roll are maintained at the desired temperature or temperatures within the specified range by the local application of heat to the roll necks. Where rolls are to be cooled in the mold, which ourrently is the most generally employed method,

' s'istance heating is ordinarily most convenient,

structure, say for a period of time generally exceeding one hour, (which would only be useful for a rapidly transforming low alloy composition) but generally about 10 to about 200 hours, preferably about 10 to about hours, while continuing the cooling of the metal in said roll body; and thereafter cooling the thus treated metal of said necks and cooling the metal of said body to a temperature low enough for the body to transform to martensite, whereby an alloyed cast iron roll is obtained having a hard martensitic body face and integral therewith machinable necks of the same composition as said roll body. By martensite we mean a structure resulting from the decomposition of austenite at or below about 500 F. and generally above about 200 F. It is a feature of the present invention that the cooling of the necks is interrupted during the original cooling from casting without first cooling to room temperatures, which would result in the production of martensite, and then reheating, and that the isothermal treatment of the roll necks occurs while the roll body-is still above atmospheric temperatures, preferably whilethe roll body is still .in the austenitic condition and before the body or body face transforms to marten site, which usually takes place in the range of about 500 F. to about 200 F.

induction heating can be employed if desired. Hollow coils may also be employed as described below.

Where rolls are stripped from the mold while hot, a satisfactory method of heating the necks comprises placing heating coils about them, e. g., placing a tube or sleeve furnace about each neck to be treated, and placing the entire assembly into an annealing oven, pit, or other apparatus adaptable for the conventional slow cooling of rolls. Gas flames can be used for heating the necks but are not preferred. Any source of heat may be used, e. g., resistance furnace, induction heating, etc., and hollow coils may be employed so that an appropriate cooling medium can be blown through them to accelerate the attainment of the desired temperature in the neck. Heat is then applied to the necks, e. g., through the heating coils,

to maintain the necks at substantially constant temperatures, 1. e., at temperatures within the range specified herein, while the roll body is cooling slowly in the conventional manner. In commercial practice rolls cooling in chillers in the mold cool rapidly at high temperatures and more slowly as the temperature falls. and the cooling rate will decrease somewhat with an increase in the diameter of the roll. As a typical example it may be'noted that a 26" roll will cool at the rate of about 40 F./hour at 1000 F. and about 20 F./hour at 700 F; In rolls that are stripped and placed in a furnace the cooling rate can be reduced as may be required to avoid cracking. It is preferred to so control the slow cooling of the roll body that the isothermal transformation of the roll necks is substantially completed while the body of the roll is still austenitlc. The necks are We are of the opinion that the lowest residual stress-Will result if the temperature of the roll neck is slightly above rather than below that Of the body of the roll at the time the latter marten-' sitizes as the volume of the roll increases when it martensitizes.

The hardness of roll necks produced by slow cooling in the conventional manner will depend on the proportion of carbide and graphite even though the matrix is martensitic. The difference in hardness of the neck after having been given the isothermal treatment as compared to the hardness of the neck obtained on continuous slow cooling will be roughly the sameregardless of the degree of mottle (proportion of graphite to carbide) However, the length of time required to complete the isothermal transformation of the necks will vary inversely with the degree of mottle.

After the prescribed isothermal treatment, the roll necks are then slowly cooled to temperatures approaching atmospheric temperatures While the slow cooling of the roll body is continued. After the body of the roll has cooled low enough to permit martensitization to occur, the roll is pref- 'erably given the usual stress relieving treatment. e. g., heating at-about 400 F. to 600 F. followed by slow cooling. Alloyed cast iron rolls produced in accordance with the foregoing are characterized by a hard martensitic face or chill on the roll body and by machina ble roll necks integral therewith and of the same composition as the roll body.

As an illustrative example, we may consider the isothermal treatment of the metal of a roll neck having the composition suitable for definite chill rolls, and sold under the trade-mark of Ni- Hard. When the isothermal treatment of such a roll neck is conducted at temperatures of bout 1000 F. to about 1200 F. for about 10 to about '50 hours the hardness of the roll neck is lowered as much as from about 175 to 230 points Brinell below the hardness which would be secured by continuous slow cooling from solidification temperatures. While somewhat softer structures may be obtained in rolls made of the composition sold under the trade-mark of "Ni-Hard by treatment at about 1100 F. and about 1200" F.,.the time required for transformation of the metal in the neck is greater than at approximately 1000 F. and it is preferred to use the latter approximate temperature in interrupting the cooling of the roll. neck for the isothermal transformation thereof. It has been found: that the structure of the metal has a more important effect upon machinability than the hardness. Thus, irons having a matrix structure .madeup of peariitic and closely related transformation products with hardnesses up, to about 510 Brinell could be machined while irons having a heavily mottled, martensitic structure with about 375 Brinell hardness could not be machined. The aim in isothermally treating the roll necks is primarily to obtain a structure. on the part of the roll neck to be machined, which is machinable rather than merely to obtain minimum hardness which is not always desirable as it may reduce the strength unduly.

The matrix structures developed in the necks will depend upon the temperature and time used for the isothermal treatment as well as the composition of the roll and neck, as those skilled in the art will readily understand. High temperatures will result in coarse pearlite, lower temv peratures in fine pearlite and still lower temperatures in acicular intermediate transformation products including some types which may be called Bainite. All of these structures can be machined although with increasing difficulty in the order named. The desired matrix structure of the neck is defined to include any machinable austenite decomposition product such as coarse or fine pearlite and other intermediate transformation products including all which are developed upon cooling or holding at suitable intermediate temperatures above about 500 F. We desire to exclude martensite and tempered martensite which may be called sorbite. the transformations described herein are incomplete and while a large amount of pearlite is desirable in the matrix, satisfactory machinability of the necks can be securedwith about 50% pearlite or allied intermediate austenite decomposi-' tion product, the remainder may be martensite or some related structure. The usual carbides and graphite will be embedded in this matrix. It "is to be observed that the matrix microstructure obtained by the present invention is different from that .obtained by reheatingmartensitized roll necks to the temperature which would be used for the, isothermal transformation or other temperature at which tempering could-be accomplished. The face or chill of the body of rolls produced in accordance with the present invention is generally martensitic, i. e., the microstructure has a martensitic matrix, plus the usual carbides embedded in the matrix; Grain rolls will also contain some graphite in the face of the roll. The martensitic matrix of the hard face or chill may, and usually does, extend deep into the roll body. In depth the 'microstructure is' usually made up of graphite in a martensitic matrix. In addition to graphite, carbides may also be present in some instances. While the matrix usually willbe largely martensitic; other products may also be present. The change in 'microstructure from neck to roll body is gradual and may extend over a few inches, usually into the body of the roll. The transition zone usually contains less and finer pearlite as it blends into the structure of the roll proper, thus assuring greater strength at the. junction between the roll and the neck.

The isotherlrialtreatment contemplated by the present invention may be accomplished in various manners. Thus, for rolls that are :to be cooled inthe mold, a helix of electric resistance wire may be embedded. in the sand aroundthe neck when ramming the mold. When the neck of the cast roll has cooledto about l000 F., as

determined by a thermo-coupleembedded in the sand around the neck, the helix may be connected toa sultable'source of electrical power and the temperature of the neck controlled at say about 1000" F. for the time required to develop the desired machinable structure. An alternative method comprises placing tube furnaces over the necks after the roll is stripped from its mold to maintain the desired constant temperature in the necks until the isothermal transformation has occurred therein. It is usually necessary, however,

Generally to protect ,the body from too fast a cooling rate which may be done in various ways, for example, by placing the roll and its neck furnaces in a preheated furnace so as to allow the body of the roll to cool very gradually, while the tube furnace is holding the temperature of the neck at about 1000 F. or any other desired transformation temperature. Also, the cooling rate of the body can be slowed up by covering the body of the roll with some insulating material, such as infusorial earth or fine sand.

It shouldbe noted that the present invention differs radically from cooling the body and neck of theroll to room temperature, which results in. martensitizing both portions, and then heating the neck to soften it for machining. The

latter process sets up very high stresses between the hot roll neck and the cold martensitic roll body and produces a weak transition zone which frequently cracks or breaks when such rolls are put into service. In the present invention the pearlite transformation of the rollneck is preferably accomplished while the roll body is in the plastic austenitic condition when it is better adapted to withstand the stresses set up at or near the junction of the body and neck than is a brittle martensitic roll body. However, with small rolls, which can be cooled safely at somewhat higher rates than large rolls, and with rolls which contain a sub-normal amount ofalloying elements and as a result must be cooled at various high rates to develop adequate hardness, the isothermal transformation of the roll neck may not be completed prior to the martensitization of the body of the roll, a result which,

while not so desirable as that outlined above, is

permissible under the circumstances and yields a reasonably good product; in any event it is superior to the old process where the roll body and the necks are cooled to a sufficiently low temperature to transform to mazrtensite and then the necks are reheated to soften them.

Another, although less preferred procedure, in accordance with the. present invention, involves accelerating the cooling of the necks tothe desired temperature for the isothermal transformation, for example, about 1000" F., by blowing air thereon, for example through a surrounding coil which later could be employed to supply heat, and then holding the neck at about this temperature while the roll body cools at any desired rate. In this procedure, the neck would be held for a maximum percentage of the total cooling time in the temperature range where the isothermal transformation occurs at the highest rate. After the transformation of the necks has proceeded sumciently to yield the desired machinable structure, the necks may be cooled to approximately the temperature of the roll, preferably by passing air roll are cooled together. This procedure, while slightly more invol may be expected to give the minimum stres at the junction of the roll body and the neck. Under some circumstances, the accelerated cooling of the neck in the early part of the above cycle may lead to the retention of slightly more carbon in solid solution which may render the isothermal transformation more sluggish but the various other advantages of the modification ofthe process are frequently more important than this effect. Under some circumstances the accelerated cooling will only be applied after' the isothermal transformation with the object of bringing the neck and roll to apascenao proximate temperature equality at the time of martensitization of the roll body.

While the invention has been described in con- Junction with roll necks, it is to be clearly understood that the present invention is equally applicable not only to roll necks but to extensions of roll necks such as wobblers and to other parts integrally cast with the roll body and subsequently machined and we use the term "necks in its broad sense to include such extensions of roll necks and similar constructions which are to be machined. Similarly, while there are usually two necks, with or without extensions, etc., on each roll which must be machined or dressed it will be apparent that the invention is applicable also to the treatment of one roll neck where it is desired to machine only one neck and where reference is made to roll "necks it is not intended to exclude treatment of a single roll neck to render it machinable. shaped by turning, there are numerous other machlning jobs on necks depending on the type of .roll, such as drilling operations, keying, etc.,

is likely to be hotter than the cope neck if all the metal required to fill the mold is poured through thebottom gate or the cope neck may be hotter than the drag neck if pouring is interrupted to fill the riser with metal from the pouring ladle. The temperature differential between roll body and roll necks usually increases with increasing ratios between diameters of necks and bodies. It is to be understood that such variations and differentials in temperatures are within the scope of the present invention and are to be considered within the temperature ranges set forth herein. The present invention has been described in conjunction with rolls and it is to be understood that the terms "roll and rolls are intended to include the rough unfinished roll casting as well as the finished roll.

The present invention is applicable broadly to all alloyed cast iron rolls which are sufliciently alloyed that in conventional or normal cooling after casting and solidification are characterized by a martensitic matrix structure at the face of the roll body and neck. The invention includes rolls having any combination of alloy elements producing unmachinable structures, such as martensitic and related products, on slow cooling, and capable of being isothermally transformed in a reasonable time to machinable austenite decomposition products. As an illustrative example, alloyed cast irons which have been used in the manufacture of such martensitic rolls include those sold under the trade-mark and falling within the range of about 2.75% to 3.75% carbon, about 0.25% to 1.75% silicon, about 0.15% to 1.65% manganese, about 3.5% to 6.5% nickel, and about 0.5% to 2.25% chromium. In tive amount up to about 2.5% tungsten or vanadium, of boron,

of molybdenum, and/or up to about 0.15% or more, may also be present. Other While roll necks, etc., are

addition, a small but eifec- An illustrative example of a definite chill type roll is one made of an alloy cast iron containing from about 3.2% to 3.5% carbon, about 0.5%

silicon, about 4.5% nickel, about 1% chromium, and about 0.25%-manganese. This composition is widely employed and is normally allowed to'cool in the mold. Another example of definite chill type roll is one made of an alloy cast iron containing about 3.2% carbon, about 0.6% silicon, about 0.3% phosphorus, about 0.1% sulfur, about 0.25% manganese, about 4.75% nickel, 0.75% chromium, and about 0.4% vmolybdenum. -An illustrative example of an indefinite chill type or grain type roll-is one made of an alloy cast iron containing about 3.2% carbon, about 1 to 1.5% silicon, about 4.5% nickel, about 2% chromium, and about 1.25 to 1.5% manganese. This composition normally is stripped from the mold while hot and cooled in afurnace. Another example of an indefinite chill type roll is one made of a high manganese type of alloy cast iron containing about 3.4% carbon, about 0.9% silicon. about 0.2% phosphorus, about 0.06% sulfur. about 4.5% nickel, about 1.85% chromium and about 1.4% manganese. An indefinite chill type roll made of a low manganese type'of alloyed cast iron has the same composition except that the manganese content is about 0.3%. By-raising the silicon content of the preceding high manganese composition and low manganese composition to about 1.5% a grain type rollis obtained.

While the type of rolls having the composition sold under the trade-mark ,of Ni-Hard comprises a substantial proportion of all the commercial alloy working rolls made, other alloy combinations are not excluded from the scope of this invention. In general, martensitic alloyed cast iron rolls will contain at least an effective amount of one or more stabilizing alloy elements. Thus, one or more of the following elements. nickel, manganese, molybdenum, vanadium, copper, chromium, tungsten, boron, tellurium, in amounts up to about ten percent total may be added to a cast iron base composition of about 2 to 3.75% carbon,- about 0.3 to 2% silicon, about 0.2 to 0.7%

manganese with the usual impurities and incidental or minor elements, including sulfur and phosphorus. to produce hard rolls. For example one combination which has been-proposed for commercial application is carbon about 3.2%, silicon about 0.5%, manganese about 0.4%, nickel about 2.5%, molybdenum about 2.5%, and chromium about 0.5% and another is carbon about 3%, silicon about 0.6%, manganese'about- 4.5%, copper about 4%, and molybdenum about The invention includes any alloy combination which produces hard martensitic rolls which are susceptible to isothermal treatment to improve the machinability of the necks.

The alloy cast iron rolls provided by the present invention are of the chill type and are characterizedby a roll body having a hard martensitic face or chill and, integral with the roll body, roll necks of the same composition as the face or body having a machinable structure contain- 70 ing pearlite and/or allied subcritical transformation products whereby said'necks may be satisiactorily machined in commercial practice without necessitating costly grinding operations except possibly for final surfacing and the like. It 75 is understood that in addition to martensite in the roll body, carbides are always present, at least in the face or chill, and in the so called grain rolls some graphite is also intentionally present in the chilled face.

The present invention is particularly applicable to the production of large diameter rolls used in industry, including steel mill rolls, rolls for rolling non-ferrous materials, crushing rolls,

paper mill rolls, and to other castings'made of m martensitic matrix irons which have extensions which must be made machinableand softened.

Although the present invention has been described in connection with preferred embodiments, it isto be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as

those skilled in the art will readily understand.

Such variations and modifications are considered to be Within the purview and scope of the appended claims.

We claim:

l. A method of producing alloyed cast iron rolls having a hard martensitic body and machinable necks of the same composition as the body which comprises pouring into a mold an al-' loyed cast iron roll having a body and necks which would be martensitic on being allowed to cool at a rate at least as slow as cooling in air, slowly cooling said-roll from solidification temperatures and while still hot from its original heat of castingv to temperatures above 500 F. and below the critical temperature, holding said necks at said temperatures while still hotirom 3 their original heat of casting for more than one of pearlite and hour to transform the structure of the necks to at least one constituent from the group consisting intermediate transformation products while the slow cooling of said body is continued, slowly cooling the thus-treatednecks and transforming the matrix structure of at least the face of the body below 500 F. to unmachinable martensite while said body is still hot from its original heat of casting.

2. A method of producing alloyed cast iron rolls having a hard martensitic face and machinable necks of substantially the same composition as the body which comprises casting an alloyed cast iron roll having a body and necks which would be martensitic on being allowed to cool in the mold in which said roll is cast, slowly cooling said roll from solidification temperatures and while still hot from its original heat of casting, interrupting the slow cooling of thenecks from solidification temperatures and while still hot" 1 from their original heat of casting at temperatures below the temperature at which austenite is stable but above 500 F., treating said necks while still hot from their original heat of casting between said temperatures ,for more than about 10 hours while the slow cooling of said body metal containing about 2% to 3.75% carbon,

0.3% to 2% silicon, a. small but effective amount j up to 10% of at least one element from the group consisting of nickel, manganese, molybdenum,

, vanadium, copper, chromium. tungsten, boron and tellurium, and the balance substantially all iron, slowly cooling said cast roll and arresting the slow cooling of the necks from solidification temperatures and while still not from their original heat of casting at temperatures within the range of 500 F. to 1300 F., treating said necks still hot from their original heat of casting within said range for about 10 to about 200 hours while the slow cooling of the body is continued, slowly cooling the thus-treated necks and transforming the matrix structure of the body below 500 F. to martensite while said body is still hot from its original heat of casting, whereby an im= proved roll is obtained having a hard body containing martensite and integral with said body machinable necks of the same composition.

4. A method of producing martensitic alloyed cast iron rolls having machinable necks of the same composition as the body which comprises casting a cast iron roll having a body and necks which would be martensitic on being allowed to cool to atmospheric temperatures in the mold in which said roll is cast, slowly cooling said cast roll while still hot from its original heat of casting from solidification temperatures to temperatures within the range of 500 F. to 1300 F., interrupting the slow cooling of the necks from solidification temperatures and while still hot from their original heat of casting within said range of temperatures, maintaining the necks of said roll while still hot from their original heat of casting within said temperature range while the'slow cooling of the body is continued to transform at least 50% of the structure of the neck to machinable austenite decomposition products,

said transformed structure being substantially devoid of tempered martensite,slowly cooling the thus-treated necks and transformingthe matrix structure of the body below 500 F. to martensite while said body is stil1 hot from its original heat of casting, and thereafter subjecting said roll to a stress relief treatment.

5. A method of producing martensitic alloyed cast iron rolls having machinable necks'ot the same composition as the body which comprises pouring a cast iron roll having a body and necks which would be martensitic on being allowed to cool to atmospheric temperatures in the mold in which said roll is cast, slowly cooling said roll from solidification temperatures and while still hot from its original heat of casting to temperatures within the range of 900 F. to 1100 F., maintaining the necks of said roll within said temperature range while still not from their original heat of casting for about 10 to about 50 hours while the slow cooling oi the bodyis continued, slowly cooling the thus-treated necks and transforming the matrix structure of at least the face of the body below 500 F. to unmachinable martensite while said body is still but from its original heat 01' casting, whereby an improved martensitic roll is obtained having machinable necks of the same composition as the body and integral therewith.

6. .A method of producing martensitic alloyed cast iron rolls having machinable necks of the same composition as the body which comprises pouring a roll having a body and necks from moltencast iron containing about 2% to 3.75% carbon, 0.3% to 2% silicon, a small but eifective amount upto 10% of at least one element from the group consisting of nickel, manganese, molybdenum, vanadium, copper, chromium, tungsten, boron and tellurium, and the balance substantially all iron, slowly cooling said roll while still aseavso hot from its original heat of casting from solidification temperatures to temperatures within the range of 900 F. to 1100 F., maintaining the necks oi. said roll still hot from their original heat of casting within said temperature range for about 10 to about 50 hours while the slow cooling of the body is continued, slowly cooling the thus -treated necks and transforming the matrix structure of at least the face of the body below 500 F. to unmachinable martensite while said body is still hot from its original heat of casting, and thereafter subjecting said roll to stress relieving treatment within the range of 400 F. to 600 F., whereby an improved martensitic roll is obtained having machinable necks of the same composition as the body and integral therewith.

7. A method of producing alloyed cast iron rolls having a body with a hard unmachinable martensitic face and machinable necks of the same composition as the body of the roll from cast iron which would be martensitic at least at the face-of said roll when allowed to cool in the mold in which the roll is cast which comprises casting and slowly cooling the roll made of said cast iron, arresting the slow cooling of the necks from solidification temperatures while still hot from their original heat of casting a ove. 500 F. but below 1400 F. and holding said necks be-' tween said temperatures to transform at least 50% of the matrix structure of the neck from austenite to atleast one constituent selected from the group consisting of pearlite and intermediate transformation products while slowly cooling the body of the roll, and transforming'the face of said slowly cooled body from austenite-to martensite below 500 F. while said body is still hot from its original heat of casting.

8. A method of producing alloyed cast iron I rolls having a body with a hard martensitic face and having machinable necks of the same composition as the body of the roll which comprises casting a roll from cast iron' having a composition within the range of about 2% to 3.75% carbon, 0.3%v to 2% silicon, and a small but efiective amount up to 10% of at least one element from the group consisting of nickel, manganese, mo-

lybdenum, vanadium, copper, chromium, tungsten, boron, and tellurium, slowly cooling said roll while still hot from its original heat of casting from solidification temperatures to below 1400" F. but above 500 F., maintaining said necks 01 said roll below 1400 F. but above 500 Fl while still hot from their original heat ofjcasting for over one hour to transform at least 50% of the matrix structure of said necks from austenite to at least one constituent from the group consisting of pearlite and intermediate transformation products formed above 500 F. while slowly cooling the body of the roll, and transforming at least the face of said slowly cooled body below 500 F. from austenite to martensite while said body is still hot from its original heat of casting. V

9. A method of producing alloyed cast iron rolls having a body with a hard unmachinable martensitic face and machinable necks of the same composition as the body of the roll which comprises casting a roll from cast iron containing about 2% to 3.75% carbon, 0.3% to 2% silicon, a small but effective amount up to 10% from the group consisting of nickel, manganese, molybdenum, vanadium, copper, chromium, tungsten,

. boron and tellurium, and the balance substantialcation temperatures and while still hot from their original heat of casting at a temperature below I the critical temperature but above 500 F., main- .lected from the group consisting of pearlite and intermediate transformation products while the slow cooling of the body is continued, slowly cooling the thus-treated necks and transforming the matrix structure of at least the face of the slowly cooled body below 500 F. to unmachinable mar"- tensite while said body is still hot from its origthe said slowly cooled body from austenite to martensite at temperatures below 500 F. while said'body is still hot from its original heat of casting.

10. A method of producing an alloyed cast iron roll having a body with 'a hard martensitic face andmachinable necks of the same composition as the body of the roll which comprises pouring into a mold an integral roll made of alloyed cast iron which would have a martensitic structure at the face'of the roll on being allowed to cool at a rate at least as slow as cooling in air and then conducting the slow cooling of the necks and the slow cooling of the body from solidification temperatures in a manner to transform the structure of the roll necks, while still hot from their original heat 'of casting,'between 1400 F. and 500 F. from austenite to a machinable matrix product and to transform the structureof the face of the roll body,'while still hot from its original heat of casting, 7 below 500 F. from austenite to a martensitic unmachinable product.

11. A method of producing an alloyed cast iron roll having a body with a hard, unmachinable martensitic face and machinable necks ofthe same composition as the body of theroll which neck-like extension of lesser diameter and of the inal heat of casting. v

13. A method of producing an alloyedcast iron casting having a body with a hard martensitic face and integral with said body a'machinable same composition as the body which comprises pouring said casting'from molten cast iron havtension while still but from its original heat of casting at elevated temperatures below 1400 F. but above 500 F. for over one hour and up to 200 hours to at least partially transform said necklike extension from austenite to at least one machinable' decomposition product of austeniteselected-from the group consisting of pearlite. and

I intermediate transformation products while the comprises pouring and slowly cooling an integral 7 alloyed cast iron roll, arresting the slow cooling of the necks from solidification temperatures above '500? F. but below 1300 F. while the necks are still hot from their original heat of casting, holding said necks between said temperatures while still hot from their original heat of casting tegral with the body of the roll which comprises slowly cooling said martensitic alloyed cast iron roll from solidification temperatures and while still hot from its original heat of casting, arresting the slow cooling of the necks while still hot from their original heat-of casting at temperatures within the range of 1300 F. to 500 F., maintaining said necksv for more than one hour within said range of temperatures while still hot from their original heat of casting to transform at least of the austenitic structure of the necks to austenite decomposition products se body of the casting continues to cool slowly, and transforming the matrix structure of at least the face of said slowly cooled body below 500 F. from austenite to a hard martensitic product while said body is still hot from its original heat of casting.

' 14. A method of producing an alloyed cast iron 1 element from the group consisting of nickel, manganese, molybdenum, vanadium, copper, chromium, tungsten, boron and tellurium, slowly cooling said cast roll, arresting the slow cooling of the necks from solidification temperatures while still hot from their original heat of casting at, elevated temperatures below the critical temperature but above 500 F. to at least partially transform said necks from austenite to at least one' machinable decomposition product of austenite selected from the group consisting of pearlite and intermediate transformation products while the body of the roll slowly cools, and transforming at least the face of said slowly cooled body below 500 F. from austenite to a hard martensitic prod-