US3423250A

US3423250A - Method of manufacturing a cast iron roll

Info

Publication number: US3423250A
Application number: US693025A
Authority: US
Inventors: Ichiro Morizumi; Yuichiro Sato; Kiyoshi Matsukura
Original assignee: Nisso Seiko KK
Current assignee: Nisso Seiko KK
Priority date: 1964-09-17
Filing date: 1967-12-22
Publication date: 1969-01-21
Anticipated expiration: 1986-01-21
Also published as: DE1287593B; GB1117025A; BE669695A

Description

Jan. 21, 1969 ICHIRO ,MORIZUMI E AL 3,423,250

METHOD OF MANUFACTURING A CAST IRON ROLL Original Filed May 5, '1965 Sheet of 4 Jan. 21, 1969 |H|RQ MQRIZUMI ETAL Y 3,423,250

METHOD OF MANUFACTURING A CAST IRON ROLL Original Filed May 5, 1965 Sheet 2 of 4 21, 1969 lcr-mo MORIZUMI ET AL 3,423,250

METHOD OF MANUFACTURING A CAST IRON ROLL Original Filed May 5, 1965 Sheet 3 of 4 F I g. 3

a E g (b) 3 45o (a Z 400 a: v 350 Jan. 21, 1969 lCHIRO MOR|ZUM| ETAL 3,423,250

. METHOD OF MANUFACTURING A CAST IRON ROLL Original Filed May 5. 1965 Sheet 4 of 4 Fig.4.

m Fig. 5.

United States Patent 3,423,250 METHOD OF MANUFACTURING A CAST IRON ROLL Ichiro Morizumi, Yuichiro Sato, and Kiyoshi Matsukura, Toyama, Japan, assignors to Nisso Seiko Kabushiki Kaisha, Tokyo, Japan, a Japanese corporation Continuation of application Ser. No. 453,355, May 5, 1965. This application Dec. 22, 1967, Ser. No. 693,025 Claims priority, application Japan, Dec. 2, 1964, Sho 39/67,436 US. Cl. 148-2 6 Claims Int. Cl. C21d 7/14 ABSTRACT OF THE DISCLOSURE Method of preparing castings having uniform white pig iron-like structure containing from 1.73.8% carbon, less than 2.5 silicon, alloying elements, and less than a 0.2% total of phosphorus, silver, copper, tin, arsenic, lead, antimony, bismuth and zinc which comprises hot-working the castings at temperatures of 900-1125 C., normalizing the heat-treated hot-worked castings, and heat-treating the normalized castings.

This application is a continuation of application Ser. No. 453,355 filed May 5, 1965, now abandoned.

This invention relates to a manufacturing method of rolls characterized by giving toughness in material quality by carrying out heat treatment on a roll formed by plastic deformation through hot working of a cast body which has an uniform structure of almost white pig iron up to .the interior of the cast body having composition range of hypoeutectic pig iron of high purity. Its object is to improve the roll quality drastically.

Generally considering from the condition of applications, toughness, wear resistance, anti-cracking property (anti-skin roughening property), resistance for spalling, feasibility for large angle of bite, and machinability are required for a roll. In addition to the above, uniform distribution of hardness within the roll and non-adhesiveness of scale are also required.

However among these qualities, some are contradictory to the others, and it is difiicult to satisfy all conditions at the same time. For example in order to given toughness to a roll, low carbon content is desired in general. On the other hand, to give wear resistance, it is necessary to get high hardness carbide suitably precipitated and dispersed in a roll by increasing carbon content. However, cracks formed on the surface of the roll (skin-roughening of the roll) are not necessarily avoided by high hardness of the roll. As can be seen from the above, toughness and wear resistance and the anti-skin roughening property which are required for a roll are contradictory to each other.

In rolls which are used at present for hot rolling purposes, there are cast iron series rolls such as ordinary chilled roll, alloy chilled roll, grain roll and cast steel series rolls such as cast steel roll, special cast steel roll, and graphite steel roll; besides there are adamite roll, ductile roll and others. However each roll has its own merit and demerit, and we can not find any roll which satisfies the prescribed three major conditions for the roll, namely, toughness, wear resistance and anti-cracking property at the same time.

Generally, cast iron series rolls have good wear resistance due to high carbon content, however in the as-cast "ice condition they are brittle in nature and readily develop internal defects such as segregation and others. Therefore in order to give toughness to cast iron series rolls, efforts are made to improve the cast structure by long period heat treatment or by addition of alloying elements. For example, adamite rolls of 1.42.4% carbon content are similar to white cast iron of low carbon content in the as-cast concondition, and have structures composed of eutectoid cementite and eutectic cementite in pearlite matrix. Since this structure is brittle, it is necessary to give ductility by long period heat treatment by which pearlite is made into grains, and needle like eutectoid cementite is broken up and is spherodized. However even when such heat treatment is carried out, eutectic cementite remains as a large block, therefore brittle nature of adamite roll can not be sufficiently improved. Ductile roll is produced by precipitating spheroidal free graphite in matrix by adding alloying elements which have the same effect as magnesium. Toughness is obtained by decrease of the internal notch effect of graphite. Ductile roll can improve wear resistance by increasing hardness through increase of free cementite in matrix, however by so doing the quality becomes brittle, and the anti-cracking property is worstened. In short, in adamite roll and ductile roll, toughness had to he sacrificed to maintain wear resistance. Heretofore in cast iron not having large amount of alloying elements, a large amount of cementite exists in a structure which appears almost like white pig iron, and such cast iron was considered to be very diflicult to plastically deform by hot working. However the present inventors, after investigations based on research resulting in Japanese patent application No. 3819,786, invented a cast iron alloy which can be hot worked, given in Japanese patent application No. 39- 52,890. This invention relates to a manufacturing method of cast iron series rolls having epoch making properties from such cast irons based on the prescribed two inventions.

The cast iron rolls described below include not only rolls made from a single casting but also sleeves used in composite type rolls.

The cast iron rolls manufactured by the method of this invention contain 1.7-3.8% carbon and below 2.5% silicon, and in order to make white pig iron like structure in the as-cast condition, alloying elements are limited to the following amounts; manganese content below 1.0%, chromium content below 2.0%, molybdenum content below 2.0%, vanadium content below 1.0%, tungsten content below 1.0%. The minimum amount of one or more of these elements are added, and total content of detrimental elements such as phosphorus, sulphur, copper, tin, arsenic, lead, antimony, bismuth, and zinc is limited to below 0.20%, and particularly below 0.15%. The method of manufacturing is characterized by combination of the following processes: a process of making a cast body of simple shape from a cast iron composition, a process in which this cast body is plastically hot deformed to make the roll shape, and the cast structure is destroyed, and carbide or graphite is made to be distributed in matrix as very fine structure, and a process in which heat treatment is carried out immediately after hot working to give toughness to a material degree.

The reason why the chemical composition of the cast body produced by the method of this invention is limited in the prescribed range is the following: first the reason why carbon content is limited to 1.7 to 3.8% is that as is generally known from the iron-carbon equilibrium diagram, this range belongs to hypoeutectic pig iron, and for a total carbon content below 1.7%, the precipitation amount of eutectic cementite is too small to get sufficient hardness and wear resistance, and for a carbon content above 3.8% hot workability of cast body becomes increasingly difficult and the mechanical roperties of roll become inferior. In the case of silicon, as the content increases, the strength of matrix is increased, and castability is improved, however when its content exceeds 2.5%, in the cast structure of the cast body, free graphite tends to be easily formed, and in order to make structure near the white pig iron structure, large additions of alloying elements such as manganese and chromium are required for graphitization prevention. It also worsens greatly the mechanical strength after hot working and heat treatment. However in order to prevent decrease of mechanical strength of roll-shaped formations after hot working and heat treatment without giving harmful effect on high temperature deformability of the cast body of this invention, silicon content should desirably be limited to the range of 0.41.5%.

Next the alloying elements to be added to the cast body of this invention such as manganese, chromium, molybdenum, vanadium and tungsten not only prevent the formation of free graphite in the as-cast condition, but also help to stabilize austenite and cemetite at high temperature. Particularly since the contents of detrimental elements are very small in the cast body of this invention, graphitization speed is fast, therefore additions 'of the prescribed alloying elements are asbolutely necessary. However since these elements have a very harmful effect on high temperature deformability of the cast body of this invention, the maximum allowable contents are limited to manganese 1.0%, chromium 2.0%, molybdenum 2.0%, vanadium 1.0%, and tungsten 1.0%. Moreover the invention is characterized by the least possible addition of one or more of these elements such that the structure near white cast iron is obtained in the as-cast condition based on iron carbon binary carbide.

In other words, the cast iron roll of this invention is characterized by the least :addition of alloying elements such as chromium, molybdenum, vanadium, and tungsten, while carbon content is increased to make the greatest use of iron-carbon binary carbide. In the case of high carbon iron forged rolls, large amounts of alloying elements such as chromium, molybdenum, vanadium and tungsten are added to form compound carbides of ironcarbon with these elements, thereby improving hot workability of the roll.

On the contrary, in the case of the cast iron roll of this invention, by decreasing the contents of detrimental elements to extremely small amounts, hot workability of the cast body is drastically improved, and compensates the defect of iron-carbon binary carbide which worsens hot workability greatly. These are the essential points of difference between this invention and the prescribed high carbon iron forged rolls.

Also in case of large contents of detrimental elements, chemical compounds such as oxides, sulphides and nitrides are formed, and complex compounds of these precipitate along the crystal boundaries as impurities. Since these complex compounds are harmful for high temperature deformability, it is necessary to limit their total content to below 0.20%, and particularly to less than 0.15%, lest they diminish hot deformability. Moreover when .a detrimental element exists independently of the others, the maximum allowable limit for phosphorus is 0.030% and for sulphur below 0.015% and particularly below 0.010% is desired. When phosphorus content exceeds 0.30%, ductility of the roll is decreased, and when sulphur content is increased, not only the hot deformability of cast body of this invention is badly affected but also the anticracking property of the roll is also badly affected. Moreover in order to avoid adverse effects on the hot workability of the casting and its anti-cracking properties, and toughness, it is desirable that the amount of arsenic be less than 0.30%.

Particularly when the total content of copper and tin exceeds 0.10%, hot deformability is very badly affected, this being observed during the tests by the inventors herein.

The first process of the manufacturing method of this invention is to cast the prescribed cast iron compositions into the cast body, and the second process is to obtain the cast iron formations by carrying out hot working due to forging after dispersion annealing and homogenization treatment as required. The heat treatment temperature and hot working temperature before hot working of the cast body of this invention should not exceed 1,125 C. If 1,125 C. is exceeded, partial melting is brought about. The hot working method of the cast body of this invention is most suitably done by press forging among various forging methods. After heating up to 50 C. lower than the solids line of the cast body of this invention, hot working in the temperature range of 1,125 C.900 C. is desirably carried out. Even within this range, hot working at the higher temperatures to obtain high deformability is desirable. The cast body of this invention has two or three phases existing together consisting of austenite and eutectic cementite or austenite, eutectic cementite and very small amount of graphite, but due to small contents of detrimental elements as previously described, plastic deformation is easy. Cementite, which is said t be hard and brittle in general, and exists as a network in the as-cast condition (since the ductility of the matrix is high) can be dispersed uniformly in the matrix, being easily broken up into fine grains by the process of hot working.

In the manufacturing method of cast iron roll, the reason for shaping into roll form by causing plastic deformation at high temperature is the following: ordinary cast iron rolls are cast in metal molds or in sand molds depending on roll shape in any case. However, in this invention regardless of the shape and size of roll and sleeve, we can make cast body of simple shape such as cylindrical, polygonal column or their hollow shapes. Moreover we can adopt any of the ordinary metal mold casting methods, sand mold casting methods and centrifugal casting methods. Further the production of one or more number of rolls or sleeves from one cast body is an outstanding characteristic of this invention.

The shaft part which requires the greatest strength for a roll is formed with much larger forging ratio than the barrel of the roll, therefore the strength can be made large also. In the case of caliber rolls, since the caliber part can be hot formed, the ability to use a large forging ratio for the part is another characteristic of this invention.

Further, although it is very difficult to adjust freely cementite in cast structure by any heat treatment, we can freely rearrange and disperse the cementite by carrying out hot working as is described in this invention. Thus we can increase toughness, anti-cracking property, and resistance for spalling while utilizing effectively the high hardness of cementite. Also We can remove various defects formed in the as-cast condition such as segregation and other by hot working.

The third process in the manufacturing method of cast iron roll related to this invention enables us to give various mechanical properties required in roll application by heat treatment of the cast iron formations and by machining. The cast iron formations after hot working are slowly cooled by the well known method in a furnace or in sand. The body is annealed in the temperature range of 700 C.- 850 C., and is kept at the temperature range of 850 C.- 950 C.; then quenching or normalizing is carried out; it is tempered in the temperature range of 400 C.700 C., then annealed in the temperature range of C.250 C. The cast iron formations can be made into the cast iron roll or the sleeve by subsequent machining.

An example of test results of mechanical properties and microscopic structures by various heat treatments carried out on samples taken from the cast iron roll manufactured by the method of this invention is given in the fol- (2) Dimension of the sample: diameter, 25 mmzp; length, 200 mm., forging ratio, 3.68. (This nomenclature is defined by the Japanese Industrial Standard [JIS] where iron roll manufactured by the method of this invention is shown in the following:

'(1) Chemical composition of the sample (percent):

C 3.02 Si 0.56 Mn 0.57 P 0.008 S 0.007 Cr 1.10 M0 0.39 Cu 0.012 Ti 0.005 V 0.007 As 0.008 Sn 0.009 A1 0.015 Pb Tr. Zn Tr. Sb Tr. Bi Tr.

(2) Dimension of the sample: diameter, mm b; length 200 mm., forging ratio 3.65.

(3) Mechanical properties after heat treatment and S is the diameter of the solid forging and the number is 25 microscopic structure:

Tensile Elonga- Hardness Strength, tion, (BHN) Structure kgJmm. percent Annealid 10 58.0 4. s 302 Cemenme' at 950 Extra fine graphite. (b) Air cooled after keepilg 40 min. at; 900

Eutectic cementite. Air cooled after keep 75 5 2 6 401 {Somme e pearlite. 6 at 630 Extra fine graphit Cooled alter keeping 60 min. at 180 C. (c) Air cooled after keepgig 40 min. at 850 Air cooled after keep- Eutectic cementite. ing 60 min. at 630 91. 7 2. 5 444 Extra fine graphite. C. Sorbitic. Air cooled after keep- Cing 60 min. at 180 the ratio, A/a, where A is the cross sectional area of the casting before forging and a is the cross sectional area of the casting after forging.)

(3) Mechanical properties and microscopic structure after heat treatment:

FIG. 3, FIG. 4, and FIG. 5 are the summary of many test results obtained on the relations among total content of detrimental elements, mechanical properties, cracking property, and Wear amount for the cast iron roll mannfactured by the method of this invention.

ing 60 min. at 630 C.

FIG. 1 shows a microscopic structure (magnification 100) of the above sample after heat treatment consisting of air cooling after keeping 40 minutes at 900 C. and air cooling after keeping 60 minutes at 630 C. In FIG. 1 a very fine graphite G dispersed in sorbitic pearlite matrix p is seen, and also eutectic cementite C, which is divided into fine structure by hot working, is observed.

FIG. 2 shows relations between carbon content and mechanical properties such as (a) hardness (BHN), (b) tensile strength, and (c) elongation after heat treatment of annealing and tempering of the cast iron roll (Cr, 0.9l.2%; Mo, 03-05%) manufactured by the method of this invention.

Further an example of mechanical properties due to These figures show the test results when the total content of detrimental elements is varied from 0.06%0.57% by arbitrarily adding the detrimental elements to a sample of basic chemical composition having C, 3.03.1%; Si, 0.550.58%; Mn, 0.56-0.57%; Cr, 1.05-1.10%; and Mo, 0.370.39%.

The method of preparation of the sample was the following: a 100 kg. sample piece was melted in a high frequency furnace, and cast into a cast block. This cast body was forged and hot worked "according to the method of this invention, and obtained the cast iron formation having forging ratio of 4.18.

Next heat treatment as above described was carried various heat treatment on a sample taken from other cast out on all samples, and test pieces of 25 mm. diameter and 200 mm. length were cut out from the samples, and various tests were carried out on these test pieces.

FIG. 3 shows relations between amount of detrimental element and mechanical properties such as (a) hardness (BHN), (b) tensile strength and (c) elongation.

FIG. 4 shows relations between amount of detrimental element and length of cracks developed. FIG. 5 shows relations between amount of detrimental element and wear amounts. As can be seen from the figures, when the total amount of detrimental elements exceed 0.15%, particularly 0.2%, mechanical properties and anti-cracking property become extremely bad.

Therefore as the necessary condition for giving superior quality to the cast iron roll of this invention, it is desirable to limit the total amount of detrimental elements to below 0.20%, particularly to below 0.15%.

In general cast iron series rolls, repeated bending stress and tors-ion stress at high application temperature act upon the roll in many cases. In hot rolling rolls thermal stress due to repeated heating and cooling is developed, and therefore fine cracks are formed by a kind of fatigue fracture. During rolling, due to abrasion between the roll surface and rolling materials, the roll is gradually worn out. Thus the roll is desirable to have toughness against pressure impact, temperature and wear at the time of rolling. However in the case of ordinary various cast iron rolls, it is diflicult to satisfy these conditions simultaneously.

The cast iron roll manufactured by the method of this invention has almost the same chemical composition as the general cast iron roll, however it has large toughness comparable to cast steel series rolls. Further it has a superior wear resistance which cannot be seen in the cast steel series rolls, and its anti-cracking property is extremely large. Therefore when its roll is used for particularly severe conditions such as when cast steel series roll is used by sacrificing wear resistance in place of strong toughness required, when strength is not sufficient although ductile roll and adamite roll are desirably used, or when roll breakage or breakage of caliber part are apt to occur due to deep and complicated shape of the caliber is required, the life of the roll of the invention is extremely prolonged due to its splendid characteristics.

Next several examples of actual application results of the cast iron roll of this invention and their methods of manufacturing are shown in the following:

EXAMPLE 1 The molten metal refined in a Hroult type electric steel making furnace was cast in the 11 tons octagonal ingot mold, and it was shaped by forging with a press at working temperature of 1110-930 C. for three high roughing roll for shape steel mill (barrel diameter 680 mm, barrel length 1,800 mm., total length 2,700 mm., weight 6,590 kg.).

The cast body had white pig iron-like structure with large amount of precipitated eutectic cementite, and had the following chemical composition (percent):

The total amount of detrimental elements except carbon, silicon, manganese, chromium, molybdenum and vanadium was not more than about 0.080%. This satisfies sufficiently the limiting value of 0.20%, and particularly of below 0.15% for the amount of detrimental elements in the cast iron roll of this invention. The forging ratio at the barrel part of the above-roll manufactured by this high purity cast iron body is 2,65.

After hot working, the cast body was kept for 10 hours at 900 C., and normalized, then after tempered at 650 C. for 15 hours, the cast body showed the following mechanical properties:

Yield point (kg./cm. 57.1 Tensile strength (kg./mm. 91.8 Elongation, percent 7.6 Reduction of area, percent 8.9 Charpy impact value (kg.m./cm. 0.8 Hardness (BHN) 298 When this roll was used as a roughing roll for channel mill of 180 x 90, the total rolling tonnage of 51, 2371 was obtained. This was 2.6 times larger than the result obtained for usual special cast steel roll (C, 1.03%; Cr, 0.98%; Mo, 0.30%

EXAMPLE 2 The molten metal refined in a Hroult electric steel making furnace was cast in the 5 t. octagonal metal mold, and the cast body was forged by a press at a working temperature of 1,080-980 C. for a three high medium roll for marchant bar (barrell diameter 330 mmrp, barrel length 1,000 mm., total length 1,570 mm., Weight 820 kg.).

This cast body had a white pig iron-like structure with large amount of precipitated eutectic cementite, and had the following chemical composition (percent):

The total amount of detrimental elements except carbon, silicon, manganese, chromium, molybdenum and vanadium was not more than about 0.078%, and satisfied sufliciently the upper limit 0.20% particularly below 0.15 for content of detrimental elements for the cast iron roll manufactured by the method of this invention.

After hot working, normalizing treatment was carried out after keeping it at 900 C. for 5 hours, and it was tempered at 630 C. for 8 hours; the mechanical properties obtained showed the following:

Yield point (kg./mm. 53.4 Tensile strength (kg./mm. 80.9 Elongation, percent 3.0 Reduction of area, percent 2.0 Charpy impact value (klg.m./crn. 0.5 Hardness (BHN) 331 Compared with the ordinarily used spheroidal graphite cast iron roll (C, 3.15%; Si, 1.98%; Mn, 0.60%; P, 0.077%; S, 0.008%; Cr, 0.33%; Ni, 0.80%; Mo, 0.35% the total rolling tonnage this roll showed the actual result 9 of 50,030 tons, amounting to about twice the amount for a spheroidal graphite cast iron roll.

EXAMPLE 3 The molten metal refined in a Hroult type electric steel making furnace was cast in a semi-chilled mold having a riser head of special cone shape, and forged by a press to form a finishing roll for a shaped steel mill (barrel diameter 340 mme, barrel length 1,000 mm., total length 1,570 mm., weight 1,040 kg.) at the working temperature of 1,100 -950" C.

This cast body had a white pig iron-like structure with a large amount of precipitated eutectic cementite, and its chemical composition was the following:

The total amount of detrimental elements except carbon, silicon, manganese, chromium, molybdenumand vanadium was not more than about 0.075%, and satisfied sufiiciently the upper limit of detriment-a1 elements 0.20% particularly below 0.15% for the cast iron roll manufact-ured by the method of the invention.

The forging ratio for the barrel part of the above described roll manufactured by this high purity roll material is 3.58. After keeping it for 5 hours at 900 C., and temper'ing it at 630 C. for hours, the mechanical properties obtained showed the following:

Yield point (kg./mm. 50.3 Tensile strength (kg./mm. 77.8 Elongation, percent 2.5 Reduction of area, percent 3.7 Charpy impact value (kg.m./cm. 0.7 Hardness (BHN) 379 When this roll was used as a finishing hot working roll of equal angles with round edge of 65 x 65, the total rolling tonnage was 27,850 t. Compared with the usual alloy grain roll (C, 3.02%; Si, 1.45%; Mn, 0.66%; Ni, 1.57%; Cr, 0.85%; Mo, 0.70%); this was about 4 times longer life.

EXAMPLE 4 The molten metal refined in a Hroult type electric steel making furnace was cast into a casting mold with a feeder head having special cone shape, and press forged at working temperature of 1,050-980 C. to make a finishing roll for a shaped steel mill (barrel diameter 327 mlmgb, barrel length 1,000 mm., total length 1,590 mm., weight 760 kg.).

This cast body had a white pig iron-like structure with a large amount of precipitated eutectic cementite, and had the following chemical composition (percent):

The total amount of detrimental elements except carbon, silicon, manganese, chromuirn, molybdenum, vanadium, and tungsten was not more than about 0.072%, and satisfied sufiiciently the upper limit of determintal elements, 0.20%, particularly below 0.15 for the cast iron roll produced by the method of this invention.

The forging ratio at the barrel part of the above roll manufactured from this hilgh purity roll material was 2.98.

After hot working, normalizing treatment was carried out after keeping it for 5 hours at 900 C., and the mechanical properties after tempering for 8 hours at 650 C. were the following:

Yield point (kg./mm. 50.2 Tensile strength (kg./mm. 79.5 Elongation, percent 2.1 Reduction of area, percent 3.5 Charpy impact value ....(kg.m./cm. 0.7

Hardness (BHN) 352 When this roll was used for the last finishing hot working roll for channel steel of 65 x 125, the total rolling tonnage was 25,100 t., and showed 4.0 times longer life compared with the usual double-poured cast iron roll (C, 2.84%; Si, 1.51%; Mn, 0.6 7%; P, 0.12%; S, 0.008%; Ni, 1.37%; Cr, 0.80%; Mo, 0.78%).

EXAMPLE 5 The molten metal refined in a Hroult type electric steel making furnace was cast into the cast body for cylindrical sleeve of 5 t. and this was hot forged, punched and mandrel forged to form a sleeve shape (outside diameter 630 mm., thickness mm., length 1,500 mm.) at the working temperature of 1,080 C.-900 C.

This cast iron sleeve had white pig iron-like structure and the following chemical composition (percent):

The total amount of detrimental elements except carbon, silicon, manganese, chromium, molybdenum, and vanadium was not more than about 0.085% and was within the limit of detrimental elements specified by the invention.

After this sleeve was kept at 900 C. for 6 hours, normalizing treatment was carried out, and it was tempered at 650 C. for 9 hours. The mechanical properties of the sleeve after annealing at 180 C. for hours were the following:

Tensile strength (kg./mm. 80.5 Yield point (kg./mm. 52.6 Elongation, percent 3.2 Reduction of area, percent 3.5 Charpy impact v-alue (kg.m./cm. 0.7 Hardness (BHN) 321 EXAMPLE 6 The molten metal refined in a Hroult type electric steel making furnace was centrifugally cast into the cast body for a 2-ton sleeve, and it was mandrel forged to form the sleeve shape (outside diameter, 349 mine; inside diameter, 80 mm.; length, 1,000 mm.) at the working temperature of 1,080 C.930 C.

This cast iron sleeve had white pig iron like structure and the following chemical composition (percent):

C 3.05 Si 0.62 Mn 0.54

P 0.007 S 0.006 Cr 1.03 Mo 0.65 Cu 0.015 Ti 0.006 V 0.52 As 0.008 Sn 0.009 Pb Tr. Zn Tr. Sb Tr. Bi Tr.

The content of derimental elements except carbon, silicon, manganese, chromium, molybdenum and vanadium was not more than about 0.066% and was within the limit of detrimental elements specified by the invention.

After this cast iron formation of sleeve shape was kept at 900 C. for 5 hours, normalization was carried out. The mechanical properties after tempering at 600 C. for 7 hours and annealing at 180 C. for 4 hours were the following:

Tensile strength (kg./mrn. 75.6 Yield point (kg./mm. 48.8 Elongation, percent 2.1 Reduction of area, percent 2.8 Charpy impact value (kg.m./cm. 0.5 Hardness (BHN) 444 This sleeve was shrunk on a forged steel shaft, normalized and tempered according to the steel kind SF 60 (a type of carbon steel forging defined by J IS), and the compound type cast iron roll (barrel diameter, 349 n1m;

barrel length, 1,000 mm.; total length, 1,590 mm.; weight, 1,060 kg.) was produced.

When this roll was used for a two high last finishing hot working roll for channel steel of 65 x 125, the total rolling tonnage of the roll was 27,300 tons which was about 4.3 times longer compared with the usual double-poured cast iron roll (C, 2.95%; Si, 1.58%; Mn, 0.67%; P, 0.13%; S, 0.008%; Ni, 1.35%; Cr, 0.80%; Mo, 0.82%).

EXAMPLE 7 The molten metal Hroult type electric steel making furnace was cast into a piece for a cylindrical sleeve of 3 tons, and this was hot forged, punched and mandrel forged to produce the compound type roll sleeve (outside diameter 750 111mg), thickness mm., length 700 mm.) at the working temperature of 1,100 C.950 C.

This cast iron body had white pig iron structure and the following chemical composition (percent):

Si 0.63 Mn 0.54 P 0.008 S 0.008 Cr 1.05 Mo 0.38 Cu 0.020 T1 0.006 V 0.006 As 0.007 Sn 0.008 A1 0.018 Pb Tr. Zn Tr. Sb Tr. B1 Tr.

The total amount of detrimental element except carbon, silicon, manganese, chromium, molybdenum and vanadium was not more than about 0.075%, and was within the limit of detrimental elements specified in this invention.

After this sleeve like cast iron body was kept at 850 C. for 6 hours, it was oil quenched and tempered at 650 C. for 9 hours. Its mechanical properties after being annealed at 180 C. for 5 hours were the following:

Tensile strength (kg./mm. 135.0

Elongation, percent 2.1 Reduction of area, percent 2.8 Hardness (BHN) 477 We produced from this sleeve a compound type cast iron roll (barrel diameter, 750 mm; barrel length, 700 mm.; total length, 1,864 mm.; weight, 3,060 kg.) by shrinking on to the forged steel shaft water quenched and tempered according to the steel kind S 45 C (a type of carbon steel defined by I IS for mechanical structural use).

When this roll was used for a four high cold rolling back up roll of alloy tool steel plates with thickness 10 mm. and width 60 mm., the total rolling tonnage of 5,850 tons was obtained, which was about 2.2 times larger than that of usual Ni-Cr-Mo steel forged sleeve compound type roll (C, 0.72%; Si, 0.25%; Mn, 0.65%; Cr, 1.03%; Mo, 0.35%; Ni, 0.65%).

We claim:

1. A method of manufacturing cast iron rolls which comprises preparing a casting having a uniform white pig iron-like structure from an iron composition consisting essentially of from about 1.7 to about 3.8 percent carbon, from about 0.4 to about 1.5 percent silicon, at least one alloying element selected from the group consisting of less than about 1.0 percent manganese, less than about 2.0 percent chromium, less than about 2.0 percent molybdenum, less than about 1.0 percent vanadium, and less than about 1.0 percent tungsten and containing less than about a 0.20 percent total of phosphorus, sulfur, copper,

tin, arsenic, lead, antimony, bismuth, and zinc and the balance iron; hot working the casting at temperatures in the range of from 900 C. to 1125 C. after heating to a temperature 50 below the solidus line to disperse cementite uniformly in the casting; heat treating the hotworked casting at 700 C. to 950 C., and tempering the heat-treated casting at 400 C. to 700 C.

2. A process according to claim 1 wherein the hot-working is carried out by forging.

3. A process according to claim 1 wherein the tempered casting is annealed in the range of 150 to 250 C.

4. A process according to claim 1 wherein the heattreated casting is subsequently machined to produce a roll.

5. A process according to claim 1 wherein the hot working is carried out by forging in the range of 900 to 1125 C. and the heat treatment comprises normalizing the forged casting in the temperature range of 850 to 950 C., annealing the tempered casting at a temperature in the range of 150 to 250 C., and subsequently machining the normalized, tempered, annealed casting to produce a roll.

6. A method according to claim 1 wherein the total of phosphorus, sulfur, copper, tin, arsenic, lead, antimony, bismuth, and zinc does not exceed 0.15 percent.

References Cited UNITED STATES PATENTS 1,999,153 4/1935 Gray l48138 2,241,270 5/1941 Nipper 14812 X 2,633,438 3/1953 Uhle 148l38 X CHARLES N. LOVELL, Primary Examiner.

US. Cl. X.R.