Graphite-containing high-chromium cast iron roller and production method and application thereof

Abstract

The invention discloses a graphite-containing high-chromium cast iron roller and a production method and application thereof, and relates to the technical field of hot rolling, the graphite-containing high-chromium cast iron roller is used for hot rolling of plates, strips, rods, wires and profiles, the production process is simple, only common equipment such as an intermediate frequency furnace, a centrifugal casting machine and a heat treatment furnace is needed, and production cost is low. The metallographic structure mainly comprises high-hardness martensite, and further comprises 20-30 vol% of high-hardness eutectic carbide and 1-3 vol% of graphite. According to the prepared graphite-containing high-chromium cast iron roller, the hardness of the roller can reach 53-56 HRC, the tensile strength is 465-580 MPa, and the impact toughness is 3.5-4.0 J / cm < 2 >. According to the graphite-containing high-chromium cast iron roller, a small amount of flaky or nodular graphite is separated out from a matrix structure of the working layer of the roller, cracking, stripping and fragmentation are avoided in the using process, the abrasion resistance is good, the graphite-containing high-chromium cast iron roller is suitable for rollers of various pre-finishing mills of a hot rolling mill, and the steel rolling amount is three times or above that of original medium-high nickel-chromium-molybdenum bainite nodular cast iron; and the produced rolled material is smooth in surface and stable in size.

Description

Technical Field

[0001] The invention relates to the technical field of hot rolling, in particular to a graphite-containing high-chromium cast iron roll and a production method thereof, which can be applied to a working roll of a hot rolling mill. Background Art

[0002] Hot-rolled seamless steel pipes require steel pipe mills, of which the reducing mill is used to reduce the diameter of the steel pipe. The reducing mill is divided into two types according to the number of rolls in the main frame: three-roller type and two-roller type. The three-roller type is widely used because the three-roller rolling deformation distribution is more uniform, and the cross-sectional wall thickness of the pipe is uniform. For the same nominal roll diameter, the spacing between the three-roller mill frames can be shortened by 12% to 14%; the two-roller mill is mainly used for thick-walled pipes with a wall thickness greater than 10 to 12 mm. The existing reducing rolls are composed of a roll ring and a mandrel set, and the mandrel can be reused to reduce the production cost of the rolls.

[0003] At present, the rollers and rings of various reducing mills in steel tube rolling mills are mainly made of centrifugal casting or integral casting of nickel-chromium-molybdenum infinitely chilled ductile iron. Although the reducing rollers made of this material have the characteristics of good toughness, they have the problems of low hardness, poor red hardness and poor wear resistance.

[0004] There are some alloy ceramic roller rings with good wear resistance in the prior art, such as: Chinese patent document CN1174764A discloses an alloy ceramic roller ring with good wear resistance, which uses tungsten carbide (WC) as the main component, and is expensive. This roller ring must be formed by hot pressing and sintering, and the production process is complicated. In addition, non-metallic ceramics (aluminum oxide, zirconium oxide) are added to the roller ring, which damages the toughness of the roller ring and causes the roller ring to break during use. In addition, since the working conditions of the reducing rollers of the steel pipe mill are different from those of the high-speed steel rollers of the wire or bar mill, the high-speed steel rollers of the traditional wire or bar mill are not suitable for the working conditions of the reducing rollers of the steel pipe mill. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a graphite-containing high-chromium cast iron roll and its production method and application, which has the advantages of suitable hardness, strength and toughness, good red hardness and wear resistance to meet the working conditions of hot-rolled plates, strips, bars and wire profiles.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a graphite-containing high-chromium cast iron roll, the chemical composition (wt%) of which is as follows:

[0008] C: 2.30~2.55;

[0009] Si: 1.0~2.0;

[0010] Mn: 0.4~1.0;

[0011] P ≤ 0.05;

[0012] S≦0.05;

[0013] Ni: 3.0~5.0;

[0014] Cr: 10.0~13.0;

[0015] Mo: 0.7~1.5;

[0016] Nb: 0.5~1.5;

[0017] Al≦0.3;

[0018] Ti: 0.05~0.10;

[0019] Y: 0.05~0.15;

[0020] Ce: 0.05~0.15;

[0021] N≤0.30;

[0022] The balance is Fe;

[0023] The metallographic structure of the graphite-containing high-chromium cast iron roller is mainly high-hardness martensite, and also contains 20-30 Vol% of high-hardness eutectic carbide and 1.0-3.0 Vol% of graphite.

[0024] The composition of the graphite-containing high-chromium cast iron roll is designed as follows:

[0025] C: Too much C content will increase the brittleness of the material. When the hot rolling work roll is working and connecting with the red hot billet, if the C content is too high, the risk of cracks on the roll surface will increase, which will eventually lead to the breakage of the roll. The test results show that the strength and thermal stability of the roll are good when the C content is controlled at 2.30-2.55%.

[0026] Si: Si is an indispensable reducing agent and deoxidizing element in the smelting process. Si can be dissolved in austenite to increase the yield strength and elastic limit of the matrix, improve the oxidation resistance of the matrix, and reduce the appearance of ring marks after the use of the roll. However, excessive Si content will reduce the hardenability of the matrix. In order to precipitate 1.0-3.0Vol% of graphite in the matrix structure, the Si addition amount is controlled at 1.0-2.0%.

[0027] Mn: Mn element strongly hinders graphitization. When its content is high, it will cause serious segregation. Therefore, it is better to keep it as low as possible while meeting the performance requirements. Therefore, its content is controlled below 1.0%.

[0028] P: P has a low melting point and solidifies last. It will precipitate phosphorus eutectics along the grain boundaries, making the matrix structure brittle. Its content should be strictly controlled, so its content is controlled below ≤0.05%.

[0029] S: S is an anti-spheroidizing element. When its content is high, it is easy to produce low-melting-point Fe distributed on the grain boundaries, reducing strength and toughness. The content should be strictly controlled, so its content is controlled below ≤0.05%.

[0030] Ni: Ni is a non-carbide forming element, mainly dissolved in the matrix, improving the matrix toughness, so that the matrix provides good support for carbides, preventing carbides from peeling off during high-temperature wear, and is beneficial to improving the wear resistance of graphite-containing high-chromium cast iron. However, if the Ni content is too high, the residual austenite in the quenching structure will increase, resulting in an increase in the number of roll tempering, so it is controlled at 3.0-5.0%.

[0031] Cr: Cr exists in M7C3 type carbides when Cr / C is ≥4.0 in high chromium iron, and about 40% exists in the matrix. M23C6 type carbides containing Cr are completely dissolved at a lower quenching temperature. Cr also makes high chromium iron have higher hardenability and hardenability. Therefore, considering comprehensively, its content is controlled at 10.0-13.0%.

[0032] Mo: Mo is added to high chromium cast iron to increase hardenability and high temperature red hardness. At the same time, Mo dissolved in tempering can prevent carbides from precipitating along grain boundaries, thus improving the strength and toughness of high chromium cast iron. Mo is controlled at 0.7-1.5%.

[0033] Nb: High chromium cast iron contains more alloying elements such as Cr and Mo, and the density of these elements and the carbides they form is very different. Under the action of centrifugal force, segregation is easy to occur, which reduces the wear resistance of the roll. Adding Nb can form MC-type composite carbides with higher density, reduce the density difference between carbides and melts, reduce segregation, and improve the wear resistance of the roll. However, Nb increases the quenching temperature of iron and reduces the temperature at which the secondary hardness peak appears, so its content is controlled at 0.5-1.5%.

[0034] Al: Al dissolves in the matrix and can improve the tempering stability, hardness and red hardness of high chromium cast iron. It also improves the oxidation resistance of high chromium iron rolls, so its content is controlled below 0.3%.

[0035] Ti: Ti can refine the grains of high chromium cast iron and improve its strength, toughness and wear resistance. Taking all factors into consideration, its content is controlled at 0.05-0.10%.

[0036] Y: Y can refine the grains of high-speed steel, limit dendrite segregation, improve mechanical properties, oxidation resistance and wear resistance, and its content is controlled at 0.05-0.15%.

[0037] Ce: Ce is a strong component supercooling element in steel alloys. During the solidification process, it is enriched in the melt at the front of the primary austenite growth through solute redistribution, causing component supercooling and refining the austenite dendrites. Due to the refinement of austenite dendrites, the eutectic steel liquid pool formed by segregation between austenite dendrites becomes smaller in the later stage of solidification, thereby refining the eutectic carbide and improving the strength and toughness of high-speed steel; therefore, its content is controlled at 0.05-0.15%.

[0038] The present invention also provides a method for producing the graphite-containing high-chromium cast iron roll, comprising the following steps:

[0039] S1. Mix ordinary scrap steel, high chromium iron chips, pig iron, ferromolybdenum, ferrochrome and nickel plates according to the above composition requirements and put them into a medium frequency electric furnace for smelting;

[0040] S2. When the temperature in front of the furnace rises to 1550-1600°C, ferroniobium particles are added to melt, and then 0.1-0.3% of the weight of the molten steel is added as an aluminum deoxidizer for alloying treatment;

[0041] S3, after drying, cerium silicate, yttrium iron and titanium iron are placed at the bottom of the ladle, and the molten steel is subjected to composite modification by the flushing method, and the chemical composition in the molten state is stabilized within the set range, and the components are adjusted in front of the furnace and then discharged from the furnace;

[0042] S4, forming the reducing roller ring by centrifugal casting;

[0043] S5. After the outer layer of high-chromium molten iron is poured, an antioxidant is sprinkled on the inner surface, and the mixture is centrifugally rotated for 8 to 10 minutes. Then, an inner layer of ductile iron molten iron at 1350 to 1380°C is poured, and the mixture is centrifugally rotated for 20 to 30 minutes. After the inner surface temperature is below 1050°C and the centrifuge is stopped, the casting mold is lifted out of the centrifuge, and the mold is directly turned over and buckled with the base sand mold. The upper neck sand mold and the core filling funnel are installed, and the core filling is completed with core filling ductile iron molten iron at 1350 to 1380°C. Then, the casting is placed in an insulation box for high-temperature annealing, and rough machining is performed after annealing;

[0044] S6. After rough machining, the roller ring is subjected to high temperature quenching treatment. During quenching, the roller ring is heated to 950-980℃ with the furnace and then kept warm for 2-6 hours. Then, it is quickly cooled to the martensite transformation temperature by mist cooling, and then medium temperature tempering treatment is carried out.

[0045] S7. Before finishing, the residual stress on the roller ring surface and the shallow surface residual austenite are tested. The residual austenite is controlled below 5% before rolling on the machine and is obtained after finishing.

[0046] Furthermore, in step S2, ferroniobium particles with a particle size of 2 mm are added.

[0047] Furthermore, in step S3, cerium silica with a particle size of 10 mm and containing 30% cerium, yttrium iron with a particle size of 10 mm and containing 60% yttrium, and titanium iron with a particle size of 10 mm and containing 30% titanium are added.

[0048] Furthermore, in step S4, the rotation speed n of the centrifuge during casting is determined according to the following formula:

[0049]

[0050] Where G is the gravity coefficient, which ranges from 30 to 100; R is the inner radius of the casting thickness.

[0051] Furthermore, in step S4, the mold material is 20 cast steel or heat-resistant ductile iron, the wall thickness is 100-150 mm, the preheating temperature is 150-200°C, and at this temperature, a 2-5 mm thick layer of coated sand is lined on the inner surface of the mold. After the mold is dried, it is installed on a horizontal centrifuge and waits for pouring. During pouring, the mold temperature is 80-120°C, the molten steel pouring temperature is 1380-1420°C, and the molten steel pouring speed is 2-8Kg / s.

[0052] Furthermore, in step S5, the antioxidant includes but is not limited to O-type glass slag.

[0053] Furthermore, in step S5, after the high temperature annealing treatment is performed for more than 24 hours, the roller ring is hoisted out and placed in a slow cooling pit for slow cooling. The hardness of the roller ring after annealing is 25HRC to 35HRC.

[0054] Furthermore, in step S6, the medium-temperature tempering treatment is repeatedly performed at least three times.

[0055] The present invention also provides application of the graphite-containing high-chromium cast iron roll, which is applied to a working roll of a hot rolling mill.

[0056] Compared with the prior art, the present invention has at least the following advantages:

[0057] (1) The graphite-containing high-chromium cast iron roll of the present invention is used for hot rolling of plates, strips, rods, wires and profiles. The production process is simple and only requires common equipment such as a medium-frequency furnace, a centrifugal casting machine and a heat treatment furnace. The metallographic structure is mainly high-hardness martensite and also contains 20-30 Vol% of high-hardness eutectic carbides and 1-3 Vol% of graphite.

[0058] (2) The high chromium cast iron roll containing graphite prepared by the present invention has a roll hardness of 53-56 HRC, a tensile strength of 465-580 MPa, and an impact toughness of 3.5-4.0 J / cm 2 .

[0059] (3) The high-chromium cast iron roll containing graphite of the present invention has a small amount of flaky or dotted graphite precipitated in the matrix structure of the working layer of the roll, and does not crack, peel or break during use and has good wear resistance. It is suitable for various pre-finishing mill rolls of hot rolling mills, and the steel rolling capacity is more than 3 times that of the original medium-high nickel-chromium-molybdenum bainitic ductile iron, and the produced rolled material has a smooth surface and stable dimensions. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 Metallographic image of a high chromium cast iron roll containing graphite prepared in Example 1. DETAILED DESCRIPTION

[0061] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] The specific implementation of the present invention will be clearly and completely described below in conjunction with the embodiments and drawings.

[0063] Example 1

[0064] This embodiment provides a method for manufacturing a high-chromium cast iron roll containing graphite, comprising the following steps:

[0065] S1. Mix ordinary scrap steel, high chromium cast iron chips, pig iron, ferromolybdenum, ferrochrome and nickel plate according to the roll composition requirements of Example 1 in Table 1 and put them into a medium frequency electric furnace for melting;

[0066] S2, when the temperature in front of the furnace rises to 1600°C, add 2mm ferroniobium particles to melt, then add 0.3% aluminum by weight of the molten steel for deoxidation and alloying before taking out of the furnace;

[0067] S3, drying the cerium silica with a particle size of 10 mm and containing 30% cerium, the yttrium iron with a particle size of 10 mm and containing 60% yttrium, and the titanium iron with a particle size of 10 mm and containing 30% titanium at 100°C or above to remove moisture, and placing them at the bottom of the ladle, and subjecting the molten iron to a composite modification treatment by a flushing method, so that the contents of all element components in the molten state after smelting are stabilized within the content range of the roll components described in Example 1 in Table 1 below, and the components are adjusted in front of the furnace and qualified before being discharged from the furnace;

[0068] S4. The reducing roller ring is formed by centrifugal casting. The speed n of the centrifuge during casting is determined by the following formula:

[0069]

[0070] Where, G is the gravity coefficient, which ranges from 30 to 100; R is the inner radius of the casting thickness;

[0071] In the specific implementation, the mold speed is selected to be 500-900 rpm according to the inner radius of the roller ring in this embodiment;

[0072] In this embodiment, the mold material is 20 cast steel or heat-resistant ductile iron, with a wall thickness of 80-150 mm, a preheating temperature of 160 ° C, and at this temperature, a layer of 2-5 mm coated sand is lined on the inner surface of the mold. After the mold is dried, it is installed on a horizontal centrifuge to wait for pouring. During pouring, the mold temperature is 85 ° C, the molten iron pouring temperature is 1400-1420 ° C, and the molten steel pouring speed is 4 Kg / s;

[0073] S5. After the outer layer of high chromium molten iron is poured, the inner surface is sprinkled with anti-oxidation O-type glass slag, and the centrifugal rotation is performed for about 8 to 10 minutes. Then, the inner layer of ductile iron molten iron at 1350 to 1380°C is poured. After the centrifugal rotation is continued for 20 to 30 minutes, the inner surface temperature is below 1050°C. After the centrifuge stops and stops steadily, the casting mold is lifted out of the centrifuge, and it is directly turned over and buckled with the base sand mold. The upper neck sand mold and the core filling funnel are installed. The core is filled with core-filled ductile iron molten iron at 1350 to 1380°C. It is placed in a non-electric insulation box for high-temperature annealing. After more than 24 hours, it is lifted out and placed in a slow cooling pit for slow cooling. The hardness of the roller ring after annealing is 28HRC, and it is roughly processed under this condition;

[0074] S6. After rough machining, the roll is subjected to high temperature quenching treatment. During quenching, the roll is heated to 950-980°C with the furnace and then kept at this temperature for 2-4 hours. Then, it is rapidly cooled to the temperature before the martensitic transformation temperature by mist cooling, and then subjected to medium temperature tempering treatment (sufficient isothermal time). The tempering treatment is repeated at least three times.

[0075] S7. Before finishing, the residual stress on the roller surface and the shallow surface retained austenite are tested to control the retained austenite to less than 5% before rolling on the machine;

[0076] S8. Finishing to obtain rollers with dimensional accuracy and surface finish that meet the requirements.

[0077] The performance of the roll manufactured in this example is shown in Example 1 in Table 2 below.

[0078] Example 2

[0079] This embodiment provides a method for manufacturing a high-chromium cast iron roll containing graphite, comprising the following steps:

[0080] S1. Mix ordinary scrap steel, high-chromium iron chips, pig iron, ferromolybdenum, ferrochrome and nickel plate according to the roll composition requirements of Example 2 in Table 1 and put them into a medium frequency electric furnace for melting;

[0081] S2. When the temperature in front of the furnace rises to 1550°C, 2mm ferroniobium particles are added to melt, and then 0.3% aluminum by weight of the molten steel is added to deoxidize and alloy the molten steel before taking it out of the furnace;

[0082] S3, drying the cerium silica with a particle size of 10 mm and containing 30% cerium, the yttrium iron with a particle size of 10 mm and containing 60% yttrium, and the titanium iron with a particle size of 10 mm and containing 30% titanium at 100°C or above to remove moisture, and placing them at the bottom of the ladle, and subjecting the molten steel to a composite modification treatment by a flushing method, so that the contents of all element components in the molten state after smelting are stabilized within the content range of the roller ring components described in Example 2 of Table 1 below, and the components are adjusted in front of the furnace and qualified before being discharged from the furnace;

[0083] S4. The reducing roller ring is formed by centrifugal casting, and the speed n of the centrifuge during casting is 500-900 rpm;

[0084] In this embodiment, the mold material is 20 cast steel or heat-resistant ductile iron, with a wall thickness of 80-150 mm, a preheating temperature of 200 ° C, and at this temperature, a layer of 2-5 mm coated sand is lined on the inner surface of the mold. After the mold is dried, it is installed on a horizontal centrifuge to wait for pouring. During pouring, the mold temperature is 120 ° C, the molten iron pouring temperature is 1400-1420 ° C, and the molten iron pouring speed is 6 Kg / s;

[0085] S5. After pouring, sprinkle the inner surface with anti-oxidation O-type glass slag. After the molten iron is poured and enters the eutectic solidification platform, pour in the inner layer of ductile iron at 1350-1380℃, continue centrifugal rotation, and wait until the inner layer solidifies and enters the eutectic solidification platform at 1080-1100℃, then stop the centrifugal machine, and then lift the centrifugal cold mold and assemble it with the base sand mold buckle box, put the upper sand mold tooling buckle on the upper cold mold mouth, buckle the riser sand box and the core filling pipe, and start filling the core with 1350-1380℃ ductile iron molten iron. When the mold is cooled to about 450℃, open the box hot and take out the ≤900℃ hot rolling roller directly into the non-electrical insulation box for high temperature annealing. After more than 24 hours, lift it out and place it in the slow cooling pit for slow cooling. The hardness of the roller ring after annealing is 34HRC, and it can be roughly processed under this condition;

[0086] S6. After rough machining, the roll is subjected to high temperature quenching treatment. During quenching, the roll is heated to 950-980°C with the furnace and then kept at this temperature for 2-4 hours. Then, it is rapidly cooled to the temperature before the martensitic transformation temperature by mist cooling, and then subjected to medium temperature tempering treatment (sufficient isothermal time). The tempering treatment is repeated at least three times.

[0087] S7. Before finishing, the residual stress on the roller surface and the shallow surface retained austenite are tested to control the retained austenite to less than 5% before rolling on the machine;

[0088] S8. Finishing to obtain rollers with dimensional accuracy and surface finish that meet the requirements.

[0089] The performance of the roller ring manufactured in this embodiment is shown in Example 2 in Table 2 below.

[0090] Example 3

[0091] This embodiment provides a method for manufacturing a high-chromium cast iron roll containing graphite, comprising the following steps:

[0092] S1. Mix ordinary scrap steel, high chromium iron chips, pig iron, ferromolybdenum, ferrochrome and nickel plate according to the roll composition requirements of Example 3 in Table 1 and put them into a medium frequency electric furnace for melting;

[0093] S2. When the temperature in front of the furnace rises to 1580°C, ferroniobium particles with a particle size of 2 mm are added to melt, and then aluminum accounting for 0.3% of the weight of the molten steel is added for deoxidation and alloying before being taken out of the furnace;

[0094] S3, drying the cerium silica with a particle size of 10 mm and containing 30% cerium, the yttrium iron with a particle size of 10 mm and containing 60% yttrium, and the titanium iron with a particle size of 10 mm and containing 30% titanium at 100°C or above to remove moisture, and placing them at the bottom of the ladle, and subjecting the molten steel to a composite modification treatment by a flushing method, so that the contents of all element components in the molten state after smelting are stabilized within the content range of the roller ring components described in Example 2 of Table 1 below, and the components are adjusted in front of the furnace and qualified before being discharged from the furnace;

[0095] S4. The reducing roller ring is formed by centrifugal casting, and the speed n of the centrifuge during casting is 500-900 rpm;

[0096] In this embodiment, the mold material is 20 cast steel or heat-resistant ductile iron, with a wall thickness of 80-150 mm, a preheating temperature of 200 ° C, and at this temperature, a layer of 2-5 mm coated sand is lined on the inner surface of the mold. After the mold is dried, it is installed on a horizontal centrifuge to wait for pouring. During pouring, the mold temperature is 120 ° C, the molten iron pouring temperature is 1400-1420 ° C, and the molten iron pouring speed is 6 Kg / s;

[0097] S5. After pouring, sprinkle the inner surface with anti-oxidation O-type glass slag. After the molten iron is poured and enters the eutectic solidification platform, pour in the inner layer of ductile iron at 1350-1380℃, continue centrifugal rotation, and wait until the inner layer solidifies and enters the eutectic solidification platform at 1080-1100℃, then stop the centrifugal machine, and then lift the centrifugal cold mold and assemble it with the base sand mold buckle box, put the upper sand mold tooling and buckle it on the upper cold mold mouth, buckle the riser sand box and the core filling pipe, and start filling the core with 1350-1380℃ ductile iron molten iron. When the mold is cooled to about 450℃, open the box hot and take out the hot rolling rollers ≤900℃ and directly put them into the insulation box without electricity for high temperature annealing. After more than 24 hours, lift them out and place them in the slow cooling pit for slow cooling. The hardness of the roller ring after annealing is 30HRC, and it can be roughly processed under this condition;

[0098] S6. After rough machining, the roll is subjected to high temperature quenching treatment. During quenching, the roll is heated to 950-980°C with the furnace and then kept at this temperature for 2-4 hours. Then, it is rapidly cooled to the temperature before the martensitic transformation temperature by mist cooling, and then subjected to medium temperature tempering treatment (sufficient isothermal time). The tempering treatment is repeated at least three times.

[0099] S7. Before finishing, the residual stress on the roller surface and the shallow surface retained austenite are tested to control the retained austenite to less than 5% before rolling on the machine;

[0100] S8. Finishing to obtain rollers with dimensional accuracy and surface finish that meet the requirements.

[0101] The performance of the roller ring manufactured in this embodiment is shown in Example 3 in Table 2 below.

[0102] Table 1: Roller ring composition

[0103]

[0104] Table 2: Roller ring performance

[0105]

[0106] In summary, the present invention provides a high-chromium cast iron roll containing graphite, and a production method and application thereof. The high-chromium cast iron roll has the advantages of suitable hardness, strength and toughness, good red hardness and wear resistance, so as to meet the working conditions of hot-rolled plate, strip, rod and wire profiles. The production process of the present invention is simple, and only ordinary equipment such as a medium-frequency furnace, a centrifugal casting machine, and a heat treatment furnace are required. The high-chromium cast iron roll containing graphite prepared by the present invention can have a roll hardness of 53 to 56 HRC, a tensile strength of 465 to 580 MPa, and an impact toughness of 3.5 to 4.0 J / cm 2 .

[0107] The above are only preferred embodiments of the present invention, and only describe the implementation methods of the present invention. They do not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A high chromium cast iron roll containing graphite, characterized in that: The mass fractions of its chemical composition are as follows: C：2.30～2.55； Si: 1.0~2.0; Mn: 0.4~1.0; P≦0.05； S≦0.05； Ni: 3.0~5.0; Cr：10.0～13.0； Mo: 0.7~1.5; Nb: 0.5~1.5; Al≦0.3； Ti: 0.05~0.10; Y：0.05～0.15； Ce: 0.05~0.15; N≤0.30； The balance is Fe; The metallographic structure of the graphite-containing high-chromium cast iron roller is mainly high-hardness martensite, and also contains 20-30 Vol% of high-hardness eutectic carbide and 1.0-3.0 Vol% of graphite.

2. The method for producing a graphite-containing high-chromium cast iron roll according to claim 1, characterized in that: The following steps are involved: S1. Mix ordinary scrap steel, high chromium iron chips, pig iron, ferromolybdenum, ferrochrome and nickel plates according to the above composition requirements and put them into a medium frequency electric furnace for smelting; S2. When the temperature in front of the furnace rises to 1550-1600°C, ferroniobium particles are added to melt, and then 0.1-0.3% of the weight of the molten steel is added as an aluminum deoxidizer for alloying treatment; S3, after drying, cerium silicate, yttrium iron and titanium iron are placed at the bottom of the ladle, and the molten steel is subjected to composite modification by the flushing method, and the chemical composition in the molten state is stabilized within the set range, and the components are adjusted in front of the furnace and then discharged from the furnace; S4, forming the reducing roller ring by centrifugal casting; S5. After the outer layer of high-chromium molten iron is poured, an antioxidant is sprinkled on the inner surface, and the mixture is centrifugally rotated for 8 to 10 minutes. Then, an inner layer of ductile iron molten iron at 1350 to 1380°C is poured, and the mixture is centrifugally rotated for 20 to 30 minutes. After the inner surface temperature is below 1050°C and the centrifuge is stopped, the casting mold is lifted out of the centrifuge, and the mold is directly turned over and buckled with the base sand mold. The upper neck sand mold and the core filling funnel are installed, and the core filling is completed with core filling ductile iron molten iron at 1350 to 1380°C. Then, the casting is placed in an insulation box for high-temperature annealing, and rough machining is performed after annealing; S6. After rough machining, the roller ring is subjected to high temperature quenching treatment. During quenching, the roller ring is heated to 950-980℃ with the furnace and then kept warm for 2-6 hours. Then, it is quickly cooled to the martensite transformation temperature by mist cooling, and then medium temperature tempering treatment is carried out. S7. Before finishing, the residual stress on the roller ring surface and the shallow surface residual austenite are tested. The residual austenite is controlled below 5% before rolling on the machine and is obtained after finishing.

3. The method for producing a graphite-containing high-chromium cast iron roll according to claim 2, characterized in that: In step S2, ferroniobium particles with a particle size of 2 mm are added.

4. The method for producing a graphite-containing high-chromium cast iron roll according to claim 2, characterized in that: In step S3, cerium silica with a particle size of 10 mm and containing 30% cerium, yttrium iron with a particle size of 10 mm and containing 60% yttrium, and titanium iron with a particle size of 10 mm and containing 30% titanium are added.

5. The method for producing a graphite-containing high-chromium cast iron roll according to claim 2, characterized in that: In step S4, the rotation speed n of the centrifuge during casting is determined according to the following formula: Where G is the gravity coefficient, which ranges from 30 to 100; R is the inner radius of the casting thickness.

6. The method for producing a graphite-containing high-chromium cast iron roll according to claim 2, characterized in that: In step S4, the mold material is 20 cast steel or heat-resistant ductile iron, the wall thickness is 100-150 mm, the preheating temperature is 150-200 ° C, and at this temperature, a layer of 2-5 mm coated sand is lined on the inner surface of the mold. After the mold is dried, it is installed on a horizontal centrifuge to wait for pouring. During pouring, the mold temperature is 80-120 ° C, the molten steel pouring temperature is 1380-1420 ° C, and the molten steel pouring speed is 2-8 Kg / s.

7. The method for producing a graphite-containing high-chromium cast iron roll according to claim 2, characterized in that: In step S5, the antioxidant includes but is not limited to O-type glass slag.

8. The method for producing a graphite-containing high-chromium cast iron roll according to claim 2, characterized in that: In step S5, after high temperature annealing treatment for more than 24 hours, the roller ring is hoisted out and placed in a slow cooling pit for slow cooling. The hardness of the roller ring after annealing is 25HRC to 35HRC.

9. The method for producing a graphite-containing high-chromium cast iron roll according to claim 2, characterized in that: In step S6, the medium-temperature tempering treatment is repeated at least three times.

10. Use of the graphite-containing high chromium cast iron roll according to any one of claims 1 to 9, in working rolls of a hot rolling mill.

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