CN101265547A - A kind of high chromium manganese cast iron roll and preparation method thereof - Google Patents

Abstract

A high-chromium-manganese cast iron roll and a preparation method thereof belong to the technical field of steel rolling. The production cost of the existing high-chromium cast iron roll is high. The chemical composition and weight percentage of the roll in the present invention are C2.7～3.3, Cr15.0～22.0, Mn4.2～5.0, Si0.3～1.2, N0.05～0.15, Ti0.4～0.8, Te0. 006～0.012, Bi0.02～0.06, Cu0.5～1.5, W0.6～1.2, and 5.0<Cr/C<7.0, the rest are Fe and trace impurities. In the invention, high chromium manganese cast iron rolls are obtained through smelting and centrifugal casting, first heat treatment at 510-550°C and second heat treatment at 475-500°C. The invention has the advantages of high roll hardness, good wear resistance, long service life, low production cost, simple preparation method and the like.

Description

A kind of high chromium manganese cast iron roll and preparation method thereof

technical field

The invention belongs to the technical field of steel rolling, and in particular relates to a hot roll and a preparation method thereof, in particular to a high-chromium-manganese cast iron roll and a preparation method thereof.

Background technique

Rolls are the main consumable spare parts in steel rolling production. The quality of rolls directly affects the production rate of rolling mills, the output and quality of rolled products, and the production cost of rolled products. The development of new roll materials to meet the needs of steel rolling production is a topic that roll developers continue to pay attention to. Because high-chromium cast iron contains M7C3 carbides with high hardness, and the carbides are distributed in the matrix in the form of blocks, the continuity of the matrix is enhanced, so high-chromium cast iron has good strength and toughness and excellent wear resistance. High-chromium cast iron It is used in the manufacture of hot rolls and has a good use effect. Chinese invention patent CN1854328 discloses an improved composite high-chromium cast iron roll, which is characterized in that the composition of the working layer of the roll is C2.5-3.0%, Si0.5-1.2%, Mn0.6-1.2%, Ni1.0-1.5%, Cr12～20%, Mo0.5～3.5%, V0.05～0.5%, W0.2～1.5%, A10.03～0.3%, N0.03～0.1%, P≤0.04%, S≤0.04%, The rest is iron and impurities. After heat treatment, its structure is mainly tempered martensite with high surface hardness + carbide + a small amount of retained austenite, which effectively reduces the hardness unevenness of the working layer and the hardness unevenness of the working layer of the roll. Less than 3HSD. Chinese invention patent CN101015836 also discloses cast high-chromium iron or cast high-chromium steel rolls for welded steel pipes. The components of the cast high-chromium iron rolls are: C: 1.8-2.8%, Si: ≤ 1.0%, Mn: ≤1.0%, P: ≤0.05%, S: ≤0.05%, Cr: 12～22%, Ni: 0.5～3.0%, Mo: 0.8～3.0%, Ii: 0～0.3%, V: 0～1.0% , Cu: 0-1.0%, RE: 0.01-0.5%, and the rest is Fe; the invention adopts high-chromium iron or high-chromium steel and adopts casting process to produce, and the material structure of the roll product is uniform inside and outside, with excellent wear resistance and toughness. It is greatly improved. Due to the adoption of casting molding, the processing procedure is shortened, the processing amount is reduced, and the material utilization rate can reach 70% or even 80%. Japanese patents JP58116911-A and JP86016334-B disclose a high chromium white cast iron composite roll, the roll outer layer contains C 2.0-3.2%, Si 0.5-1.5%, Mn 0.5-1.5%, P<0.08%, S< 0.06%, Ni 1.0-2.0%, Cr 10-25%, Mo 0.5-1.5%, the balance is Fe, and the roll hardness is Hs 70-80. U.S. Patent US5183518-A also discloses a high-chromium white cast iron roll whose chemical composition is 2.4-3.8% C, 0.4-2% Mn, 0.2-1.9% Si, 0-3% Cu, 1.5-4.5% Ni , 12 ~ 29Cr, the balance is Fe. The above-mentioned high-chromium cast iron roll materials all contain expensive alloy elements such as molybdenum and nickel, and the production cost is relatively high.

Contents of the invention

The object of the present invention is to provide a chemical composition of a high chromium manganese cast iron roll and a preparation method thereof. The invention adopts a high-chromium-manganese cast iron to make the working layer of the roll body, uses cast iron or cast steel to make the roll core, and adopts a centrifugal composite casting method to compound the roll core and the roll body working layer. Its main feature is that the roll body does not contain expensive alloy elements such as nickel and molybdenum. In addition to containing high chromium, it also contains more manganese. The as-cast structure of the roll is mainly austenite and contains a small amount of martensite. , the roll does not require high-temperature quenching treatment, but only needs to be subjected to sub-temperature heat treatment at 510-550 ° C to precipitate secondary carbides in the as-cast austenite, reduce the stability of the as-cast austenite, and lose stability when it is subsequently air-cooled Austenite transforms into martensite, which has higher hardness and better wear resistance.

The purpose of the present invention can be achieved through the following technical solutions.

The chemical composition and weight percentage of the roll of the present invention are: C: 2.7-3.3%, Cr: 15.0-22.0%, Mn: 4.2-5.0%, Si: 0.3-1.2%, N: 0.05-0.15%, Ti: 0.4～0.8%, Te: 0.006～0.012%, Bi: 0.02～0.06%, Cu: 0.5～1.5%, W: 0.6～1.2%, and 5.0<Cr/C<7.0, the rest is Fe and unavoidable trace Impurities.

Roll of the present invention is smelted in an electric furnace, and its manufacturing process steps are:

① Preparation of ordinary steel scrap, carbon ferrochrome, copper plate, ferrotungsten, pig iron or graphite, ferrosilicon, ferromanganese, tellurium, bismuth, ferrotitanium and ferrochrome nitride according to the weight percentage of the chemical composition in the target product, C: 2.7～3.3%, Cr: 15.0～22.0%, Mn: 4.2～5.0%, Si: 0.3～1.2%, N: 0.05～0.15%, Ti: 0.4～0.8%, Te: 0.006～0.012%, Bi: 0.02 ~0.06%, Cu: 0.5~1.5%, W: 0.6~1.2%, and 5.0<Cr/C<7.0, the rest is Fe and unavoidable trace impurities;

②Heating and melting ordinary steel scrap, carbon ferrochrome, copper plate, and ferrotungsten, adding carbon with pig iron or graphite, adding ferrosilicon and ferromanganese after the molten iron is melted;

③ After adjusting the ingredients in front of the furnace, raise the temperature of the molten iron to 1540-1580°C, add 0.08-0.20% of the weight of the molten iron to deoxidize aluminum, add ferro-titanium, ferrochromium nitride, tellurium and bismuth after deoxidation, and obtain high-chromium-manganese cast iron molten iron , and then released;

④ High chromium manganese cast iron molten iron is poured into the rotating mold on the centrifuge after the slag removal treatment, when the temperature is 1390-1420 °C;

⑤After 10-20 minutes of pouring, measure the temperature of the inner layer of the roll body with a non-contact thermometer. When the temperature is 1220°C-1280°C, pour cast iron molten iron or cast steel molten steel into the roll core. The pouring temperature of the cast iron molten iron on the roll core is 1330℃～1350℃, the pouring temperature of molten steel for roller core casting is 1480～1520℃;

⑥ Unpack the roll after pouring for 8 to 20 hours, place the roll in the holding furnace or slow cooling pit, then cut the pouring riser, and clean the residual roots, flashes and burrs;

⑦ Carry out the first heat treatment of the roll at 510-550°C for 6-10 hours, then air cool to room temperature, then conduct the second heat treatment at 475-500°C for 12-15 hours, and then furnace cool to After 150°C, it is air-cooled after being released from the furnace, and finally processed to the specified size.

The performance of the alloy material is determined by the metallographic structure, and a certain structure depends on the chemical composition and heat treatment process. The chemical composition of the present invention is determined as follows:

C: C is an important element in high chromium cast iron. The excellent wear resistance of high chromium cast iron comes from the high hardness carbides in the structure, and C has the greatest influence on the number of carbides. C, Cr and carbides (K%) The content can be calculated according to the following formula:

K%＝12.33(C%)+0.55(Cr%)-15.2 (1)

However, too much C is added, because the excessive amount of carbides increases the brittleness of the material, and the roll is easy to crack and peel off during use. Considering its advantages and disadvantages, the C content is controlled at 2.7-3.3%.

Cr: In addition to partly forming carbides and increasing wear resistance, part of Cr dissolves in the matrix to increase the hardenability and oxidation resistance of the matrix, and promotes the formation of dense oxide films during the use of high-chromium cast iron rolls, which is beneficial to Improving the wear resistance of the roll and preventing the steel sticking phenomenon during the use of the roll are also beneficial to improving the surface quality of the rolled material. The average Cr content in the matrix can be calculated as follows:

%Cr(m)＝1.95Cr/C-2.47, m means matrix (2)

It can be known from formula (2) that the average Cr content of the matrix is also related to the C content of the material (C consumes part of Cr). Therefore, in order to ensure an appropriate Cr content in the matrix, the Cr content is controlled at 15.0-22.0%, and 5.0<Cr/C<7.0

Mn: Mn is an element that expands the austenite phase region. When added to high-chromium cast iron, except for a small part entering carbide, most of it dissolves in the matrix, which can improve the hardenability of the roll. If the amount of Mn added is too much, it will increase The roll tends to crack, so the Mn content is controlled at 4.2-5.0%.

W: Part of W enters the carbide, and part enters the matrix. The W entering the matrix has the effect of improving hardenability and tempering stability. The appropriate amount of W added is 0.6-1.2%.

Cu: Cu is a non-carbide forming element, which dissolves in the matrix and can significantly improve the hardenability of the roll. In addition, the addition of Cu can also refine the grains. If too much Cu is added, it will precipitate at the grain boundary, which will improve the performance of the roll. Unfortunately, the appropriate amount of Cu added is 0.5-1.5%.

Ti: Ti is a strong carbide forming element. It is easy to form fine and evenly distributed TiC when added to high chromium cast iron. TiC can be used as the nucleation core of primary M ₇ C ₃ carbides, which can hinder the growth of carbides and refine them. The primary M ₇ C ₃ type carbide is beneficial to improve the casting cracking resistance of high chromium cast iron and increase the strength and toughness of high chromium cast iron. After the addition of 0.8%, the trend of further refinement of carbide is not obvious, and the appropriate addition of Ti The amount is 0.4 to 0.8%.

N: Adding N to steel, in addition to reacting with Ti, produces fine TiN with high melting point, which is beneficial to promote the refinement of solidification structure. Part of N dissolves in the matrix, which can improve the hardenability of the matrix. If the amount is too much, pores are prone to appear in the roll. , the appropriate amount of N added is 0.05-0.15%.

Te: Te has a strong effect of promoting the whitening of cast iron. Adding a small amount of Te to the high-chromium-manganese cast iron roll can easily obtain pure white structure and improve the wear resistance of the roll. In addition, Te is added to the high chromium manganese cast iron roll to make the carbide change from a long sheet with strong direction to a plate shape, which is beneficial to improve the strength and toughness of the high chromium manganese cast iron roll. The brittleness of large high-chromium-manganese cast iron rolls will damage the strength and toughness of the rolls. The appropriate amount of Te added is 0.006-0.012%

Bi: Adding a small amount of Bi to the high-chromium-manganese cast iron roll can increase the hardness and depth of the white layer of the roll at the same time, and the hardness gradient of the section is gentle. In addition, the addition of Bi can also increase the microhardness of carbides, which is beneficial to the increase of the macrohardness of the roll and the improvement of wear resistance. The appropriate amount of Bi added is 0.02-0.06%

Si: Si is a smelting and deoxidizing element. Adding an appropriate amount of Si can prevent the oxidation of other alloying elements, but Si is a non-carbide forming element, which is mainly dissolved in the matrix and reduces hardenability. Considering its advantages and disadvantages, the Si content is controlled at 0.3~ 1.2%.

Unavoidable trace impurities are brought into the raw materials, including P and S, both of which are harmful elements. In order to ensure the strength, toughness and wear resistance of the roll, the P content is controlled below 0.05%, and the S content is controlled at 0.04%. the following.

The performance of high chromium-manganese cast iron rolls is also directly related to the heat treatment process. The basis for its formulation is: the rolls are first heat-treated at 510-550°C. The main purpose is to reduce the cast austenite by precipitating secondary carbides Increase the content of alloying elements in the matrix structure, increase the Ms point, and transform the as-cast austenite matrix into high-hardness martensite during subsequent air cooling, which is conducive to increasing the hardness of the roll and improving the wear resistance of the roll. The second heat treatment of the roll at 475-500°C is mainly to eliminate the internal stress remaining in the roll when austenite transforms into martensite, so as to ensure that the roll will not be deformed and cracked during use.

The present invention has the following beneficial effects:

①The high-chromium-manganese cast iron roll prepared by the present invention has a simple production process, and the microstructure contains more than 20% of high-hardness M ₇ C ₃ carbides, and the roll has a high macroscopic hardness of 82-85HS, and has excellent wear resistance sex.

② After the high chromium manganese cast iron roll is treated with Ti and N, the solidification structure is fine and the carbides are obviously refined, resulting in a significant improvement in the mechanical properties of the roll. The bending strength exceeds 850MPa and the impact toughness is greater than 10J/cm ² .

③High-chromium-manganese cast iron rolls do not require high-temperature heat treatment, and the heat treatment process is simple and reduces energy consumption.

④ High chromium manganese cast iron rolls do not contain nickel, molybdenum and other precious alloy elements, and the production cost is more than 30% lower than nickel and molybdenum high chromium cast iron rolls, and more than 15% lower than high nickel chromium infinite chilled cast iron rolls.

⑤ The service life of the high-chromium-manganese cast iron roll of the present invention is equivalent to that of the high-chromium cast iron roll containing nickel and molybdenum, and is more than 50% higher than that of the high-nickel-chromium infinite chilled cast iron roll.

The present invention will be further described below in combination with specific embodiments.

Detailed ways

Example 1

The high-chromium-manganese cast iron roll prepared by the present embodiment is produced in an intermediate frequency induction furnace with a capacity of 500 kilograms, and its manufacturing process steps are:

①Heat and melt ordinary steel scrap, carbon ferrochrome, copper plate, and ferrotungsten, add carbon with pig iron, add ferrosilicon and ferromanganese after the molten iron is melted;

② After adjusting the ingredients before the furnace, the temperature of the molten iron is raised to 1563°C, adding 0.15% of the weight of the molten iron to deoxidize aluminum, and after deoxidation, add ferro-titanium, ferrochromium nitride, tellurium and bismuth, and then release it from the furnace;

③ High chromium manganese cast iron molten iron is poured into the rotating mold on the centrifuge after the slag removal treatment, when the temperature is 1402°C;

④After 15 minutes of pouring, measure the temperature of the inner layer of the roll body with a non-contact thermometer. When the temperature is 1258°C, pour the cast iron molten iron into the roll core, and the pouring temperature of the cast iron molten iron is 1339°C;

⑤ Unpack the roll after pouring for 15 hours, place the roll in a slow cooling pit, then cut the pouring riser, and clean the residual roots, flashes, and burrs;

⑥ Carry out the first heat treatment of the roll at 538°C for 7 hours, then air cool to room temperature, then conduct the second heat treatment at 490°C for 14 hours, then furnace cool to 150°C and leave the furnace for air cooling, and finally process to Specified size. The composition of the roll is shown in Table 1, and the mechanical properties of the roll are shown in Table 2.

elements C Cr Mn Te Si Cu W content 3.05 18.37 4.94 0.008 0.68 0.71 0.96 elements N Ti S Bi P Fe Cr/C content 0.08 0.60 0.032 0.04 0.040 Surplus 6.02

Table 1 roll chemical composition and content (weight %) Hardness/HS Bending strength/MPa Impact toughness/J.cm ^-2 84.2 881.5 11.6

Table 2 Roll Mechanical Properties

Example 2

The high-chromium-manganese cast iron roll prepared by the present embodiment is produced in an intermediate frequency induction furnace with a capacity of 1500 kilograms, and its manufacturing process steps are:

①Heat and melt ordinary steel scrap, carbon ferrochrome, copper plate, and ferrotungsten, add carbon with graphite, and add ferrosilicon and ferromanganese after the molten iron is melted;

② After adjusting the ingredients before the furnace, the temperature of the molten iron is raised to 1542°C, adding 0.08% of the weight of the molten iron for deoxidation, adding ferro-titanium, ferrochromium nitride, tellurium and bismuth after deoxidation, and then out of the furnace;

③ High chromium manganese cast iron molten iron is poured into the rotating mold on the centrifuge after the slag removal treatment, when the temperature is 1393°C;

④ 18 minutes after the pouring is completed, measure the temperature of the inner layer of the roll body with a non-contact thermometer. When the temperature is 1267°C, pour the molten steel for casting the roll core, and the pouring temperature of the molten steel for casting the roll core is 1498°C;

⑤ Unpack the roll after pouring for 18 hours, place the roll in the holding furnace, then cut the pouring riser, and clean the residual roots, flashes and burrs;

⑥ Carry out the first heat treatment of the roll at 515°C for 10 hours, then air cool to room temperature, then conduct the second heat treatment at 480°C for 15 hours, then furnace cool to 150°C and air-cool, and finally process to Specified size. The composition of the roll is shown in Table 3, and the mechanical properties of the roll are shown in Table 4.

elements C Cr Mn Te Si Cu W content 3.28 21.80 4.58 0.006 0.44 1.37 0.71 elements N Ti S Bi P Fe Cr/C content 0.14 0.76 0.029 0.05 0.041 Surplus 6.65

Table 3 roll chemical composition and content (weight %)

Hardness/HS Bending strength/MPa Impact toughness/J.cm ^-2 84.9 859.6 10.7

Table 4 Roll Force Performance

Example 3

The high-chromium-manganese cast iron roll prepared by the present embodiment is produced in an intermediate frequency induction furnace with a capacity of 1000 kilograms, and its manufacturing process steps are:

①Heat and melt ordinary steel scrap, carbon ferrochrome, copper plate, and ferrotungsten, add carbon with pig iron, add ferrosilicon and ferromanganese after the molten iron is melted;

② After adjusting the ingredients in front of the furnace, the temperature of the molten iron is raised to 1577°C, adding aluminum accounting for 0.19% of the weight of the molten iron for deoxidation, adding ferro-titanium, ferrochromium nitride, tellurium and bismuth after deoxidation, and then out of the furnace;

③ High chromium manganese cast iron molten iron is poured into the rotating mold on the centrifuge after the slag removal treatment, when the temperature is 1416°C;

④After 15 minutes of pouring, measure the temperature of the inner layer of the roll body with a non-contact thermometer. When the temperature is 1235°C, pour the cast iron molten iron into the roll core, and the pouring temperature of the cast iron molten iron is 1332°C;

⑤ Unpack the roll after pouring for 18 hours, put the roll in the slow cooling pit, then cut the pouring riser, and clean the residual root, flash and burr;

⑥ Carry out the first heat treatment of the roll at 545°C for 7 hours, then air cool to room temperature, and then conduct the second heat treatment at 495°C for 13 hours, then cool it to 150°C and leave the furnace for air cooling, and finally process it to Specified size. The composition of the roll is shown in Table 5, and the mechanical properties of the roll are shown in Table 6.

elements C Cr Mn Te Si Cu W content 2.74 15.61 4.23 0.011 1.16 0.58 1.19 elements N Ti S Bi P Fe Cr/C content 0.05 0.45 0.033 0.02 0.039 Surplus 5.70

Table 5 roll chemical composition and content (weight %)

Hardness/HS Bending strength/MPa Impact toughness/J.cm ^-2 82.3 897.2 12.0

Table 6 Roll Force Performance

The high chromium-manganese cast iron roll of the present invention has carried out installation operation assessment on the front stand of the finishing stand of the bar mill with a speed of 11m/s and the finishing stand of the wire rod mill with a speed of 25m/s. The results show that the high-chromium-manganese cast iron roll of the present invention is safe to use, Reliable, no peeling, no cracking during use, uniform wear of the rolling groove, the service life of the high chromium manganese cast iron roll of the present invention is equivalent to that of nickel and molybdenum high chromium cast iron rolls, and is more than 50% higher than that of high nickel chromium infinite chilled cast iron rolls . The high-chromium-manganese cast iron roll of the present invention does not contain expensive alloy elements such as molybdenum and nickel, has low production cost, simple production process, does not require high-temperature heat treatment, and has low energy consumption. The popularization and use of the high-chromium-manganese cast iron roll of the present invention has good economical and economic benefits. social benefits.

Claims (2)

1. A high-chromium-manganese cast iron roll, characterized in that the chemical composition and weight percentage of the roll are: C: 2.7-3.3%, Cr: 15.0-22.0%, Mn: 4.2-5.0%, Si: 0.3-1.2% %, N: 0.05～0.15%, Ti: 0.4～0.8%, Te: 0.006～0.012%, Bi: 0.02～0.06%, Cu: 0.5～1.5%, W: 0.6～1.2%, and 5.0<Cr/C <7.0, the rest is Fe and unavoidable trace impurities. 2. A method for preparing a high-chromium-manganese cast iron roll according to claim 1, characterized in that it comprises the following steps: ① Preparation of ordinary steel scrap, carbon ferrochrome, copper plate, ferrotungsten, pig iron or graphite, ferrosilicon, ferromanganese, tellurium, bismuth, ferrotitanium and ferrochromium nitride according to the weight percentage of the chemical composition in the target product, C: 2.7～3.3%, Cr: 15.0～22.0%, Mn: 4.2～5.0%, Si: 0.3～1.2%, N: 0.05～0.15%, Ti: 0.4～0.8%, Te: 0.006～0.012%, Bi: 0.02 ~0.06%, Cu: 0.5~1.5%, W: 0.6~1.2%, and 5.0<Cr/C<7.0, the rest is Fe and unavoidable trace impurities; ②Heating and melting ordinary steel scrap, carbon ferrochrome, copper plate, and ferrotungsten, adding carbon with pig iron or graphite, adding ferrosilicon and ferromanganese after the molten iron is melted; ③ After adjusting the ingredients in front of the furnace, raise the temperature of the molten iron to 1540-1580°C, add 0.08-0.20% of the weight of the molten iron to deoxidize aluminum, add ferro-titanium, ferrochromium nitride, tellurium and bismuth after deoxidation, and obtain high-chromium-manganese cast iron molten iron , and then released; ④ High chromium manganese cast iron molten iron is poured into the rotating mold on the centrifuge after the slag removal treatment, when the temperature is 1390-1420 ℃; ⑤After 10-20 minutes of pouring, measure the temperature of the inner layer of the roll body with a non-contact thermometer. When the temperature is 1220°C-1280°C, pour cast iron molten iron or cast steel molten steel into the roll core. The pouring temperature of the cast iron molten iron on the roll core is 1330℃～1350℃, the pouring temperature of molten steel for roller core casting is 1480～1520℃; ⑥ Unpack the roll after pouring for 8 to 20 hours, place the roll in the holding furnace or slow cooling pit, then cut the pouring riser, and clean the residual roots, flashes and burrs; ⑦ Carry out the first heat treatment of the roll at 510-550°C for 6-10 hours, then air cool to room temperature, then conduct the second heat treatment at 475-500°C for 12-15 hours, and then furnace cool to After 150°C, it is air-cooled after being released from the furnace, and finally processed to the specified size to obtain a high-chromium-manganese cast iron roll.