US3623850A

US3623850A - Composite chill cast iron rolling mill rolls having increased resistance to the spalling

Info

Publication number: US3623850A
Application number: US810025A
Authority: US
Inventors: Paul J Horvath Jr
Original assignee: Bethlehem Steel Corp
Current assignee: Bethlehem Steel Corp
Priority date: 1969-03-24
Filing date: 1969-03-24
Publication date: 1971-11-30
Anticipated expiration: 1988-11-30
Also published as: FR2039871A5; SE349061B; DE2013728C3; BE747828A; DE2013728B2; JPS4837495B1; GB1271185A; AT320568B; CA922938A; DE2013728A1

Abstract

A COMPOSITE CHILL CAST IRON ROLL IN WHICH THE CHILL AREA HAS A COMPOSITION OF ABOUT 3.20% TO ABOUT 3.40% CAR1.45% TO ABOUT 1.65% SILICON, ABOUT 4.00% TO ABOUT 4.40% NICKEL, ABOUT 0.90% TO ABOUT 1.10% CHROMIUM, ABOUT 0.50% TO ABOUT 0.70% MOLYBDENUM AND ABOUT 0.03% TO ABOUT 0.08% MAGNESIUM, ABOUT 0.07% PHOSPHORUS, ABOUT 0.02% SULFUR, THE REMAINDER IRON AND INCIDENTAL IMPURITIES AND THE CORE IS A LOW ALLOY CAST IRON COMPOSITION OF ABOUT 3.40% TO ABOUT 3.50% CARBON, ABOUT 0.50% TO ABOUT 0.60% MANGANESE, ABOUT 1.25% TO ABOUT 1.35% SILICON, ABOUT 0.30% TO ABOUT 0.50% CHROMIUM, ABOUT 0.75% TO ABOUT 1.25% NICKEL, ABOUT 0.15% PHOSPHORUS, ABOUT 0.10% SULFUR, THE REMAINDER IRON AND INCIDENTAL IMPURITIES.

Description

United States Patent US. Cl. 29-1961 4 Claims ABSTRACT OF THE DISCLOSURE A composite chill cast iron rollin which the chill area has a composition of about 3.20% to about 3.40% carbon, about 0.55% to about 0.65% manganese, about 1.45% to about 1.65% silicon, about 4.00% to about 4.40% nickel, about 0.90% to about 1.10% chromium, about 0.50% to about 0.70% molybdenum and about 0.03% to about 0.08% magnesium, about 0.07% phosphorus, about 0.02% sulfur, the remainder iron and incidental impurities and the core is a low alloy cast iron composition of about 3.40% to about 3.50% carbon, about 0.50% to about 0.60% manganese, about 1.25% to about 1.35% silicon, about 0.30% to about 0.50% chromium, about 0.75% to about 1.25% nickel, about 0.15% phosphorus, about 0.10% sulfur, the remainder iron and incidental impurities.

BACKGROUND OF THE INVENTION Composite chill cast iron rolls have found limited use as work rolls in severe applications, for example in the latter strands of cold rolling mills. While the rolls have good resistance to Wear and high hardness on the surface they are brittle and therefore susceptible to spalling and have insufiicient toughness to resist bruising when contacted by the stock being worked. The stock is marked causing it to be rejected and decreasing the product yield. The bruise is many times a focal point for the beginning of a spall. The rolls must be removed from the mill and the surface reground to below the bruised area, thereby decreasing the life expectancy of the rolls.

Cold rolling blackplate requires rolls which will take a highly polished surface finish and which have high surface hardness, good resistance to spelling, good resistance to bruising, suflicient strength to resist deflection stresses and which will not mark the sheet being processed.

Cold rolling sheet for exterior automotive body parts requires rolls which, in addition to the above mentioned qualities, have a surface which will take and retain a blast pattern having a finish of about 55 microinches to about 70 microinches. This finish is necessary to impart a finish of about 40 microinches to about 60 microinches on the surfaces of the sheet being rolled. Heretofore the above mentioned operations required the use of expensive forged steel rolls which required elaborate heat treatments to obtain the desired properties. However, the rolls are susceptible to marking and spalling and have relatively short service life. The rolls of this invention resist marking and bruising and, when required, clean up with less metal removal than the other old prior art rolls.

It is an object of this invention to provide composite chill cast iron rolls having a reduced tendency to surface marking and spalling.

It is a further object of this invention to provide composite chill cast iron rolls which may be reconditioned with comparatively light dressing.

It is a further object of this invention to produce composite chill cast iron rolls which will have good resistance to wear, high hardness, sutficient strength to resist deflection stresses and increased resistance to spalling.

Patented Nov. 30, 1971 The composite chill cast iron working rolls of the invention contain about 3.20% to 3.40% carbon, about 0.55% to 0.65% manganese, about 1.45% to about 1.65% silicon, about 4.00% to about 4.40% nickel, about 0.90% to about 1.10% chromium, about 0.50% to about 0.70% molybdenum, about 0.03% to about 0.08% magnesium, not more than .07% phosphorus and not more than 0.02% sulfur and the remainder iron and incidental impurities. Rolls having a composition within the above specified ranges have good resistance to wear, high surface hardness, improved resistance to bruising, increased resistance to spalling and suflicient strength to resist deflection stresses and will not mark the material being rolled. By a composite chill cast iron roll I mean a roll having a chill portion and a core, said chill portion having a composition as heretofore described and said core being a low alloy cast iron composition as is well known in the art. Such a composition may contain about 3.40% to about 3.50% carbon, about 0.50% to about 0.60% manganese, about 1.25% to about 1.35% silicon, about 0.30% to about 0.50% chromium, about 0.75% to about 1.25% nickel, about 0.15% phosphorus, not more than 0.10% sulfur, the remainder iron and incidental impurities.

The composition of the rolls must be balanced to obtain the optimum mechanical properties. The carbon content in the surface of the rolls must be suflicient to impart the hardness necessary for the surface to resist deformation when rolling cold sheet products. However the carbon content must be low enough to provide sufficient depth of the chill in the roll. Therefore, I use a carbon content of between about 3.20% to about 3.40%, but I prefer a carbon content of between about 3.25% and 3.35%. The manganese must be sufficient to prevent mottling of the iron in heavy sections, that is, about 0.55% to about 0.65%. Nickel in the iron suppresses pearlite formation and favors formation of martensite and also aids in refining carbides. The nickel should be from about 4.00% to about 4.40%, but I prefer to limit the the upper range of the nickel to 4.20%. Chromium within a range of about 0.90% to about 1.10% will be suflicie-nt to stabilize the carbides and to suppress graphite formation. However I prefer to use a range of 0.95% to about 1.05%. Molybdenum in the range of about 0.50% to about 0.70% will increase the resistance of the chill surface to spalling, however, I prefer to use a range of 0.55% to about 0.65%. While silicon aids in graphite formation, and increases the strength, the ductility and the bend test energy to fracture, too high a silicon will increase the amount of graphite formed and decrease the depth of chill. I, therefore, control the silicon content Within a range of about 1.45 to about 1.65%, however, I prefer to use a range of 1.50% to about 1.60%. Magnesium is added to the chill cast iron to promote the formation of nodular graphite. For this purpose I prefer to control the magnesium content within a range of about 0.03% to about 0.08% and prefer a magnesium content of 0.05% to 0.07%. There may be a distinct line of demarcation between the chill and core areas in composite rolls, because of the sudden transition from nodular to flake graphite. In the past, this has been of great concern since this line is a metallurgical notch and may become a focal point for spalling. It has been found to be of no consequence in the rolls of the invention since the transition of graphite from nodular to flake has been found to be gradual through this area because of the comparatively low sulfur content of the chill area and core of the rolls.

3 The above mentioned microstructure may be obtained by subjecting the rolls to a stress-relief treatment. Two such treatments are listed below:

Cast molten iron and cool to about 100 F., Stress relieve at 500 F.,

Hold 1 hour/ inch of thickness,

Cool to ambient temperature.

Rolls treated by the above methods were found to have a surface hardness of Rockwell C 57.0 to 59.0, an ultimate bend strength of about 86,000 to 90,000 p.s.i., a total deflection on bend test of about 0.040 to 0.045 inch and a bend to fracture strength of about 1.10 ft. lbs. to about 1.15 ft. lbs. and about 11.3% retained austenite in the microstructure. The bend test used to determine the ultimate bend strength, total deflection and toughness (bend to fracture strength) is described in International Nickel Company, Inc., Technical Paper 541-CP dated Nov. 3, 1967, by F. K. Kies and R. D. Schelleng.

Rolls having a standard white cast iron composition and treated as above had a surface hardness of Rockwell C 54.0 to 56.5, an ultimate bend strength of 77,000 to 78,000 p.s.i., a total deflection on bend test of 0.037 to 0.040 inch and a bend to fracture strength of .92 to 1.03 ft. lbs., and 18% retained austenite in the microstructure of massive continuous carbide network, martensite, nodule graphite and eutectic austenite. It must be understood that where percent retained austenite is noted such percent is by volume.

EXAMPLE 1 Percent 0 Mn P S Si Ni Cr Mo Mg Chill 3. 29 0. 56 0. 06 0. 012 1. 54 4. 10 0. 98 0. 61 0. 07 Core 3. 44 0. 48 0. 09 0. 04 1. 33 1. 22 O. 54

The casting was cooled in the mold to about 300 F., shaken from the mold and cooled to ambient temperature. The roll was placed in a furnace and heated to 850 F. held for 4 hours, cooled at 50 F./hour to 100 F., reheated to 500 F., held for 4 hours and cooled to ambient temperature. Test specimens from the casting had a surface hardness of Rockwell C 58, an ultimate bend strength of 88,410 p.s.i., a total deflection on bend test of 0.042 inch and a bend to fracture strength of 1.15 ft. lbs. Microscopic examination of the test specimens showed the roll to have finely-divided well dispersed nodules of primary graphite, fine primary and eutectic martensite, fine austenite-martensite grains, a secondary precipitation of fine carbides in areas of former austenitic grains, a discontinuous carbide network and 11.3% retained austenite.

The roll was mated with a standard white cast iron roll in the No. 5 stand of a 5 stand, 4 high, 48" cold mill rolling tinplate. The pair of rolls rolled 5,252 tons of tinplate. The standard roll was bruised four times and had to be redressed to prevent marking the sheet. The roll of the invention was also redressed so as to mate with the standard roll although it had not shown evidence of bruising nor did it mark the sheet.

EXAMPLE 2 In another specific example of the invention, 2 composite tats-Q05? Chill cast iron work rolls 21 x 78" were 75 4 processed in a conventional manner. The chill and core were found to have the following chemical compositions:

Percent 0 Mn P S Si Ni Cr Mo Mg Chill 3. 34 0.47 0. 06 0.011 1.60 4.15 1.01 0. 64 0.07 Core 3. 42 0.54 0. 023 1. 26 0.92 0.41

The rolls were processed in the manner described in Example 1 above and were found to have a similar microstructure as the roll in Example 1. The rolls were ground to a finish of 20 microinches and shot-blasted to a finish of 75 microinches. The rolls were placed in a 78 inch 4 high temper mill and were used to process sheet for use in forming exterior automotive body parts. The rolls processed 8 coils of sheet before redressing was required.

Rolls of the invention may be used as work rolls in the final stands of a tandem mill to cold roll blackplate and in a temper mill to cold roll sheet from which exterior automotive body parts are formed. Rolls of the invention when used in this application have processed as many as 9 coils of sheet before requiring redressing due to wear of the blast pattern, while standard forged rolls process about 3 to 4 coils before requiring dressing. The rolls of the invention may be redressed by removing less metal than rolls heretofore used in these applications and therefore have a longer life expectancy than prior art rolls.

In this specification and claims wherever percentages are referred to such percentages are by weight unless otherwise noted.

I claim:

1. A composite work roll for cold rolling sheet stock, said roll having a low alloy cast iron core consisting of:

Carbon: about 3.40% to about 3.50% Manganese: about 0.50% to about 0.60% Phosphorus: not more than about 0.15% ulfur: not more than about 0.10% Silicon: about 1.25% to about 1.35% Nickel: about 0.75 to about 1.25% Chromium: about 0.30% to about 0.50%

remainder iron and incidental impurities and a chill surface area consisting essentially of:

Carbon: about 3.20% to about 3.40% Manganese: about 0.55% to about 0.65% Phosphorus: not more than 0.07%

Sulfur: not more than 0.02%

Silicon: about 1.45% to about 1.65% Nickel: about 4.00% to about 4.40% Chromium: about 0.90% to about 1.10% Molybdenum: about 0.50% to about 0.70% Magnesium: about 0.03 to about 0.08%

the remainder iron and incidental impurities, the microstructure in said chill area comprising finely divided, welldispersed nodules of graphite, finer than normal primary and eutectic martensite and martensite-austenite grains not more than 15% retained austenite, a secondary precipitation of carbides in areas of former austenitic grains, and a discontinuous carbide network and characterized by having an ultimate bend strength of about 86,000 psi. to about 90,000 p.s.i.

2. The composite work roll of claim 1 having a gritblasted surface of a roughness of between 55 microinches to about microinches.

3. A composite work roll for cold rolling sheet stock, said roll having a low alloy cast iron core consisting of:

Carbon: about 3.40% to about 3.50% Manganese: about 0.50% to about 0.60% Phosphorus: not more than about 0.15% Sulfur: not more than about 0.10% Silicon: about 1.25% to about 1.35% Nickel: about 0.75% to about 1.25% Chromium: about 0.30% to about 0.50%

remainder iron and incidental impurities and a chill sur- 4. The composite work roll of claim 3 having a gritface area consisting essentially of: blasted surface of a roughness of between 55 microinches Carbon: about 3.25% to about 3.35% to about 70 microinches' Manganese: about 0.55% to about 0.65%

Phosphorus: not more than 0.07% 5 References Cited Sulfur: not more than 0.02% UNITED STATES PATENTS Silicon: about 1.50% about 1.60% 1,910,034 /1933 Mitchell et al 75128 X Nickel: about 4.00% to a o t 1,988,910 1/1935 Merica et a1. 75128 X Chromium: about 0.95% to about 1.05% 2,097,709 11/1937 Walters 75-128 X Molybdenum: about 0.55% to about 0.65% 2,105,968 1/1938 Castle 7s 128 Magnesium: about 0.04% to about 0.08% 3, 71 1 1944 d k 148--35 X the remainder iron and incidental impurities, the micro- 2,516,524 7/1950 Minis- 2,771,358 11/1956 Spear 14835 X structure in said chill area comprising finely divided, welldispersed nodules of graphite, finer than normal primary 15 and eutectic martensite and martensite-austenite grains, not more than 15% retained austenite, a secondary pre- CHARLES LOVELL Pnmary Examiner cipitation of carbides in areas of former austenitic grains, U S Cl X R and a discontinuous carbide network and characterized by having an ultimate bend strength of about 86,000 p.s.i. 75123, 128; 148-34,

to about 90,000 p.s.i.

3,273,998 9/1966 Knoth.