CN117165866A - Graphite high-speed steel for rolling stand roller in high-speed wire rod and heat treatment process thereof - Google Patents
Graphite high-speed steel for rolling stand roller in high-speed wire rod and heat treatment process thereof Download PDFInfo
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- 238000005096 rolling process Methods 0.000 title claims abstract description 101
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 72
- 229910002804 graphite Inorganic materials 0.000 title claims abstract description 72
- 239000010439 graphite Substances 0.000 title claims abstract description 72
- 229910000997 High-speed steel Inorganic materials 0.000 title claims abstract description 71
- 238000010438 heat treatment Methods 0.000 title claims abstract description 60
- 238000000034 method Methods 0.000 title claims abstract description 53
- 230000008569 process Effects 0.000 title claims abstract description 45
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- 238000005496 tempering Methods 0.000 claims description 42
- 238000010791 quenching Methods 0.000 claims description 31
- 230000000171 quenching effect Effects 0.000 claims description 30
- 238000000137 annealing Methods 0.000 claims description 15
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- 238000005266 casting Methods 0.000 claims description 9
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 8
- 229910052750 molybdenum Inorganic materials 0.000 claims description 7
- 238000003723 Smelting Methods 0.000 claims description 5
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- 229910052786 argon Inorganic materials 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 4
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- 229910052748 manganese Inorganic materials 0.000 claims description 3
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- 239000010959 steel Substances 0.000 description 11
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
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Abstract
The invention discloses graphite high-speed steel for a rolling stand roller in a high-speed wire rod and a heat treatment process thereof, wherein the toughness of a matrix is increased by designing material components so as to meet the low-temperature rolling requirement of the rolling stand roller in the high-speed wire rod; meanwhile, by adopting a matched heat treatment process, the mechanical properties of the graphite high-speed steel for the rolling stand roller in the high-speed wire rod at normal temperature and high temperature are comprehensively improved, and particularly, the high-temperature toughness, oxidation resistance and thermal cracking resistance are greatly improved, so that the problems of breakage, short service life, peeling and the like of the rolling stand roller in use are solved, the production efficiency is improved, and the production cost is reduced.
Description
Technical Field
The invention belongs to the field of high-speed steel materials, and particularly relates to graphite high-speed steel for a rolling stand roller in a high-speed wire rod and a heat treatment process of the graphite high-speed steel.
Background
Reform of the wire industry began with the introduction of Morgan company 1 set of 50m/s high speed torsion-free wire rolling mill in the second steel mill in 1985 and the introduction of horse steel into SMS company 85m/s wire rolling mill in 1987; the small bar industry starts with a semi-continuous small bar mill manufactured by spanish, five steel mills in 1989, 1 set of KUPP company in germany, and a pacifying steel mill in 1992, 1 set of 24-frame fully continuous small alloy steel bar mill in italian Pomini company. The high-speed wire rolling mill has the characteristics of high rolling speed, high product quality, high equipment efficiency and the like, and provides guarantee conditions for high product yield and large range of product specifications; therefore, the revolutionary change of the wire rod field is caused as soon as the occurrence, and the strong cyclone is also generated in the wire rod production field in China; starting from the beginning of the construction of the first high-speed wire rolling mill in China at the end of 1986, the production line of the high-speed wire in China reaches 73 in 2003, and China becomes the country with the largest production line and the highest yield of the high-speed wire.
In recent years, a wire rod production line adopts a short stress line rolling mill, and a way of development of high speed, no torsion and no tension is adopted to develop endless rolling and low temperature rolling technologies; as the specifications of wire rod production lines are more diversified, the demands of small-size products are continuously increased, and the mechanical properties of the processing devices are continuously improved, the mechanical properties of the processing devices are required to be continuously improved, and the high-speed wire rod production lines realize full-line low-temperature tapping and low-temperature controlled rolling, so that the microstructure, yield strength and toughness of the obtained products are simultaneously improved; the ductile cast iron roller of the original rough middle rolling mill set has low rolling quantity of a single groove and frequent roller changing times become the bottleneck for further improving the productivity; this requires that the toughness and wear resistance of the working layer of the roughing mill train rolls also be substantially improved while the substrate remains relatively tough.
The materials used for rolling stand rollers in the prior high-speed wire rods mainly comprise semisteel, graphite steel and the like, and the specific conditions are as follows: publication No. CN101537428A discloses a semisteel roll and a preparation method thereof, the semisteel roll has reasonable chemical composition, the hardness of the roll body of the semisteel roll can reach 55-58HS, the tensile strength can reach 900-950MPa, and the impact toughness can reach 10-12J/cm 2 The service life is prolonged; publication number CN101892374a discloses a heat treatment method for a high-hardness semisteel roll, which changes the common heat treatment method for semisteel rolls, and breaks through the concept that semisteel and cast iron materials cannot be subjected to oil cooling treatment by properly controlling the oil cooling time and the cooling temperatures at different stages; the roller is cooled at a certain cooling speed by controlling the air quantity and the air blowing intensity, and the hardness of the high-hardness large-scale semisteel roller reaches more than 55HSD by effectively matching the two cooling methods of oil cooling and air cooling; publication number CN102628146A discloses a high nickel-chromium alloy semisteel roll and a manufacturing method thereof, and the semisteel roll prepared by the method has higher wear resistance and stronger toughness, is not easy to peel off, has good hot cracking resistance, and has the greatest characteristics that the working layer has almost no hardness drop, the working efficiency can be greatly improved, and the rolling cost is saved; the above technologies are all developed as semisteel rolls; the semisteel roller has good wear resistance, and the hardness in the working layer is reduced less, but the heat crack resistance is poor; with the development of low-temperature rolling technology of a high-speed wire production line, higher requirements on the hot cracking resistance and the toughness of the roller are put forward. Therefore, the semisteel roll cannot meet the mechanical property requirement of the roll stand roll in the high-speed line.
Publication No. CN1070600A discloses a production method of a centrifugal composite spheroidal graphite cast iron roller, which is mainly characterized in that the outer layer and the core part of the centrifugal composite cast roller are spheroidal graphite cast iron. The service life of the roller is prolonged by more than one time compared with that of the magnesium spheroidal graphite cast iron roller which is integrally cast; CN101654734a discloses a method for manufacturing alloy spheroidal graphite cast iron roller of universal rolling mill, which comprises the steps of pre-perforating grooves on the roller, performing high-temperature austenitizing and homogenizing on the roller, rapidly cooling, refining matrix structure, refining groove bottom and side matrix structure of the grooved roller, and greatly improving wear resistance of groove bottom and side surface of the roller; the ductile iron roller developed by the technology has good heat transfer performance and heat crack resistance, but with the continuous improvement of the quality of high-speed wire products, the wear resistance of the ductile iron roller cannot meet the rolling requirement of the high-performance products.
Publication No. CN106676408A discloses a preparation method of a novel high-carbon graphite steel roller, which is compared with a common section steel roller, and is characterized in that the product is cultivated and distributed uniformly, the hardness is high, special fine grain carbide with good toughness and spherical graphite with lubricating property is easy to break during hot friction extrusion of rolled pieces, thereby improving the yield and surface quality of the rolled pieces and prolonging the service life of the roller; however, the toughness of the graphite steel roller is improved compared with that of the spheroidal graphite cast iron roller, but the difference is not large, and the rolling requirement of high-performance products of a rolling stand in a high-speed line cannot be met
The application number CN98121315.4 discloses a high-speed steel part produced by a powder metallurgy method, and the high-hardness and high-wear resistance combination is obtained by compositely adding W, mo, V, co and other elements, in particular to the high-hardness and high-wear resistance steel part at high temperature; the application number CN90103207.7 discloses low-alloy high-speed steel, which has the main innovation points of reducing alloy elements, improving Si and increasing N elements and improving the secondary hardening performance of the high-speed steel, thereby reducing the production cost and improving various performances of the high-speed steel; in the use process of the high-speed steel roller developed by the technology, an oxide film is required to be formed on the surface, and the wear resistance of the roller can be effectively exerted; practice proves that the high-speed wire rod production line has high rolling speed due to small contact area between the wire rod and the roller groove, and an effective oxide film is difficult to form in the rolling process.
In view of the above, development of a new material having the advantages of high wear resistance, small turning amount, high single-groove rolling amount and the like and a middle rolling stand roll manufactured by the same is desired.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide graphite high-speed steel for a rolling stand roller in a high-speed wire rod and a heat treatment process thereof, and the toughness of a matrix is increased by designing material components so as to meet the low-temperature rolling requirement of the rolling stand roller in the high-speed wire rod; meanwhile, by adopting a matched heat treatment process, the mechanical properties of the graphite high-speed steel for the rolling stand roller in the high-speed wire rod at normal temperature and high temperature are comprehensively improved, and particularly, the high-temperature toughness, oxidation resistance and thermal cracking resistance are greatly improved, so that the problems of breakage, short service life, peeling and the like of the rolling stand roller in use are solved, the production efficiency is improved, and the production cost is reduced.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the invention provides graphite high-speed steel for a rolling stand roller in a high-speed wire rod, which comprises the following components in percentage by weight: c:3.0 to 3.6 percent of Si:0.2 to 1.8 percent of Mn:0.3 to 0.9 percent, less than or equal to 0.10 percent of P, less than or equal to 0.015 percent of S, and Cr:1.0 to 3.5 percent of W:1.0 to 2.8 percent of Mo:2.0 to 5.6 percent, V:1.0 to 3.0 percent, RE:0.12 to 0.26 percent, N:0.10 to 0.80 percent, and the balance of Fe and other unavoidable impurities;
wherein, W and Mo satisfy: w: mo=1:2, 5% < (w+2mo) <14%.
Preferably, the tensile strength of the graphite high-speed steel for the rolling stand roller in the high-speed wire rod at normal temperature is 800-850 MPa, and the impact energy is A KU2 3.0 to 4.0J, and the hardness HSD is 70 to 75.
In a first aspect, the present invention provides a heat treatment process for graphite high-speed steel for rolling stand rolls in high-speed wire rods, wherein the graphite high-speed steel for rolling stand rolls in high-speed wire rods is cast into a roll blank by adopting the components of the graphite high-speed steel for rolling stand rolls in high-speed wire rods, and the heat treatment process comprises annealing treatment, quenching treatment and tempering treatment in the cooling process of the roll blank.
Preferably, the roller blank is made by the following process: the graphite high-speed steel for the rolling stand roller in the high-speed wire rod is prepared by proportioning the components, smelting, inoculating, modifying and casting.
Preferably, the annealing treatment process is as follows: when the temperature of the roller blank is cooled to 930-960 ℃, carrying out furnace-following heat preservation treatment for 2-3 hours, then slowly cooling to 600-620 ℃ along with the furnace, and then discharging and air cooling to room temperature.
Preferably, the quenching treatment process is as follows:
(1) Carrying out primary temperature equalization treatment, namely heating the roller blank subjected to annealing treatment at a heating rate of 200-230 ℃/h, and carrying out temperature equalization heat preservation treatment at 600+/-10 ℃ for 8-10 min;
(2) The second temperature equalization treatment, namely heating the roller blank continuously at the heating rate of 200-230 ℃/h, and carrying out the temperature equalization heat preservation treatment for 8-10 min at 800+/-10 ℃;
(3) Quenching, namely continuously heating the roller blank to 1150-1250 ℃ for quenching and preserving heat for 45-60 min, cooling to 800-830 ℃ along with a furnace, preserving heat for 15-20 min, then blowing argon for cooling, controlling the cooling speed to be 4-5.5 ℃/s, cooling to below 300 ℃, discharging, air-cooling to room temperature, and tempering within 2-3 h.
Preferably, in the tempering treatment, the roller blank after quenching treatment is heated at a heating rate of 200-230 ℃/h, then is insulated for 110-120 min at a tempering temperature of 580-660 ℃, is cooled to 200-210 ℃ along with a furnace, and is discharged from the furnace for air cooling to room temperature; the tempering treatment is repeated for 2 to 3 times.
Preferably, the tensile strength of the graphite high-speed steel for the rolling stand roller in the high-speed wire rod at normal temperature is 800-850 MPa, and the impact energy is A KU2 3.0 to 4.0J, and the hardness HSD is 70 to 75.
The design principle of each element in the graphite high-speed steel for the rolling stand roller in the high-speed wire rod provided by the invention is as follows:
c: the C element is an important carbide forming element, the C content is required to be matched with the alloy content, and proper C content can form proper amount of primary and secondary carbides in a matrix, so that the properties of red hardness, wear resistance and the like of the roller are ensured; test results show that in the graphite high-speed steel roller for the high-speed line rolling stand, when C is less than 3.0%, alloy elements in a matrix cannot fully play a role, and various mechanical properties of the roller are difficult to ensure due to less carbide; when C >3.6%, the matrix will precipitate M3C type carbide, resulting in an increased propensity for matrix overheating; therefore, the content of C is 3.0 to 3.6 percent.
Si: the purpose of adding Si element is to increase the toughness of the middle rolling stand roller so as to adapt to the high strength and shock resistance required by low-temperature rolling; research results show that Si element can improve the solid solution quantity of alloy elements in a matrix during quenching, can promote M2C eutectic carbide to be decomposed into fine MC+M6C carbide, increases the quantity of carbide precipitated during tempering, refines carbide, and is beneficial to the stability of quenching and tempering performance. Therefore, the content of Si element is controlled to be 0.2 to 1.8%.
Mn: in order to control the cost, the invention adopts low-cost Mn to replace noble metal Ni of rare resources in China; meanwhile, mn element can improve the thermoplasticity of the matrix, is easy to combine with harmful elements such as S and the like to form MnS, and reduces the harmful effect of S. The test result shows that when Mn is more than 0.3%, mn element and Fe are infinitely dissolved, so that the Mn element and Fe can be dissolved in a matrix and exist in the form of carbide, the strength of the matrix is improved, and the risk of breakage of a roller during low-temperature rolling is reduced; but when Mn is more than 0.9%, the Ms point can be obviously reduced, the content of retained austenite after roller quenching is increased, and the roller breakage risk is increased; therefore, the Mn content is controlled to be 0.3 to 0.9%.
Cr: cr element is a strong carbide forming element, part of Cr element can be dissolved in carbide in a solid solution way, and the majority of Cr element is dissolved in a matrix in a solid solution way, so that the effect of solid solution strengthening is achieved, and meanwhile, the hardenability, tempering hardness and oxidation resistance of the roller can be improved; however, when the Cr content is too large, the thermoplasticity of the matrix is affected, and thus the Cr content is controlled to be 1.0 to 3.5%.
Mo: mo is also a strong carbide forming element, so that the stability of austenite and the hardenability of a matrix can be improved, the second-class tempering brittleness is prevented, and test results show that in the invention, when the Mo content is controlled to be 2.0-5.6%, a better effect is obtained, wherein about 46% of Mo forms M6C type carbide, the stability of MC type carbide and the tempering resistance of the matrix are improved, and the occurrence of thermal cracks of a roller in the use process can be inhibited; about 28% of the carbide is added into M7C3 carbide, which can effectively improve hardness, wear resistance and service life; in addition, about 26 percent of the material is dissolved into the matrix, so that the hardenability of the material is obviously improved.
W: the W element can improve the high-temperature decomposition stability of martensite, so that the matrix can still keep the lattice property of the martensite at high temperature, carbide formed by alloy elements W and C is not easy to gather and grow, grains of a roller can be thinned, the carbide is dissolved in the matrix in a solid solution mode during quenching, carbide with tiny dispersion distribution is separated out during tempering, and the carbide tiny dispersion distribution can still be kept at 600+/-10 ℃, namely the high-temperature softening resistance of the matrix is kept, so that the functions of improving the toughness, the red hardness, the wear resistance and the hot cracking resistance of the roller are achieved.
Since 1% w works quite well with 2% mo, the W, mo element ratio is designed to be 1:2. The research result shows that when (W+2Mo) >5, enough tungsten and molybdenum carbide exists in the roller matrix, so that the high-temperature hardness, red hardness and wear resistance of the matrix are ensured; when (w+2mo) >14, excessive ledeburite eutectic carbide is formed in the roll matrix, which deteriorates the hot working plasticity and hot cracking resistance of the roll, so that the roll is easily cracked during manufacturing and use. Therefore, the W content is designed to be 1.0-2.8%, the Mo content is designed to be 2-5.6%, and 5% < (W+2Mo) <14% is satisfied.
V: v is a strong carbide forming element, and the V element and the C element form VC, belong to a face-centered cubic interstitial phase, and can control the grain size of a roller during quenching so as to improve the wear resistance of a matrix; when the V content exceeds 3%, grindability of the matrix is lowered. Therefore, the V content is controlled to be 1.0-3.0%.
Re, N: re and N are residual inoculant added during smelting; the inoculation and deterioration technology is not used as the content of the patent of the invention, but experiments show that when the inoculant and the modifier with the optimal contents are used, the Re content in the finished product roller can be detected to be 0.12-0.26%, and the N content is detected to be 0.8-0.28%. The N element can promote the decomposition and transformation of M2C eutectic carbide to form fine carbide, can inhibit the growth of crystal grains of the matrix during quenching, and enables the matrix to be quenched at a higher temperature, thereby ensuring that as many alloy elements as possible are dissolved in the quenched matrix, generating the maximum secondary hardening effect during tempering, simultaneously maintaining the structure with finer crystal grains and better toughness, and having good effect on the toughness of the roller. Re content is controlled to be 0.12-0.26%, and N content is controlled to be 0.10-0.80%.
The graphite high-speed steel for the rolling stand roller in the high-speed wire rod and the heat treatment process thereof provided by the invention have the following beneficial effects:
1. according to the graphite high-speed steel for the rolling stand roller in the high-speed wire rod and the heat treatment process thereof, the material components are designed, so that the toughness of a matrix is increased, and the low-temperature rolling requirement of the rolling stand roller in the high-speed wire rod is met; meanwhile, by adopting a matched heat treatment process, the mechanical properties of the graphite high-speed steel for the rolling stand roller in the high-speed wire rod at normal temperature and high temperature are comprehensively improved, and particularly, the high-temperature toughness, oxidation resistance and thermal cracking resistance are greatly improved, so that the problems of breakage, short service life, peeling and the like in use of the rolling stand roller in the middle rolling stand are solved, the production efficiency is improved, and the production cost is reduced;
2. the graphite high-speed steel material for the high-speed wire rod mill stand roller and the heat treatment process thereof, which are designed for solving the problems of low-temperature rolling requirements and existing rollers, and the high-speed wire rod mill stand roller prepared from the graphite high-speed steel material, have excellent toughness, wear resistance and heat crack resistance, can solve the difficult problem of low-temperature rolling of a wire rod production line, and have good popularization and application prospects.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
FIG. 1 is a graph showing the annealing temperature in the heat treatment process of graphite high speed steel for rolling stand rolls in high speed wire rods according to the present invention;
fig. 2 is a graph showing the temperature profile of the quenching treatment and tempering treatment in the heat treatment process of the graphite high-speed steel for rolling stand rolls in the high-speed wire rod according to the present invention.
Detailed Description
In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below with reference to examples.
The invention provides graphite high-speed steel for a rolling stand roller in a high-speed wire rod, which comprises the following components in percentage by weight: c:3.0 to 3.6 percent of Si:0.2 to 1.8 percent of Mn:0.3 to 0.9 percent, less than or equal to 0.10 percent of P, less than or equal to 0.015 percent of S, and Cr:1.0 to 3.5 percent of W:1.0 to 2.8 percent of Mo:2.0 to 5.6 percent, V:1.0 to 3.0 percent, RE:0.12 to 0.26 percent, N:0.10 to 0.80 percent, and the balance of Fe and other unavoidable impurities; wherein W and Mo satisfy: w: mo=1:2, 5% < (w+2mo) <14%.
The tensile strength of the graphite high-speed steel for the rolling stand roller in the high-speed wire rod is 800-850 MPa at normal temperature, and the impact energy is A KU2 3.0 to 4.0J, and the hardness HSD is 70 to 75.
The graphite high-speed steel for the rolling stand roller in the high-speed wire rod is made of the designed material, and the toughness of the matrix is specially increased so as to meet the low-temperature rolling requirement. Because of the conventional heat treatment process of the high-speed steel material of the traditional middle rolling stand, the aim is to obtain martensite, and the matrix meets the normal-temperature rolling of 900-1100 ℃; along with the development of production, the rolling temperature is reduced to 800-860 ℃, the low-temperature rolling technology is continuously popularized, and the rolling yield is increased. Therefore, the graphite high-speed steel for the roller of the middle-speed wire rod mill frame needs to adopt a matched process, namely, the graphite high-speed steel roller for the middle-speed wire rod mill frame adopts a casting roller blank to carry out stress relief annealing, discharging, re-quenching and tempering in the cooling process; in addition, pearlite cannot appear in the matrix after the heat treatment process, the content of residual austenite also needs to be strictly controlled, and the final structure is controlled to be martensite, carbide and a small amount of residual austenite.
The heat treatment process of the graphite high-speed steel for the rolling stand roller in the high-speed wire rod adopts the same component as the graphite high-speed steel for the rolling stand roller in the high-speed wire rod to cast into a roller blank (the casting of the roller blank can be carried out by proportioning raw materials according to the component of the graphite high-speed steel for the rolling stand roller in the high-speed wire rod, and casting the raw materials into the roller blank after smelting, inoculating and modifying or other roller blank preparation methods), and then the heat treatment is carried out in the roller blank cooling process, wherein the heat treatment process comprises annealing treatment, quenching treatment and tempering treatment.
(1) Annealing: immediately carrying out furnace-following heat preservation treatment for 2-3 hours when the temperature of the roller blank is cooled to 930-960 ℃, then slowly cooling to 600-620 ℃ along with a furnace, then discharging and air cooling to room temperature, wherein the temperature curve in the annealing treatment process is shown in figure 1;
in the annealing treatment process, firstly eliminating residual stress generated in the casting process; secondly, high-temperature annealing and a slightly long heat preservation time are adopted to ensure that a large amount of large-size ledeburite and pearlite contained in a graphite high-speed steel cast structure are decomposed, and netlike carbide in a matrix structure is scattered to form intermittent netlike carbide, so that the non-uniformity of the carbide is eliminated, the mechanical property of the matrix is adjusted, the function of alloy elements is fully exerted, and preparation is made for the next quenching and tempering; and one of the most remarkable characteristics of the invention is that the cooling annealing treatment technology after casting is adopted, so that not only is the better annealing performance obtained, but also the production cost of time, energy sources and the like is saved.
(2) Quenching treatment
And (3) primary uniform temperature treatment: heating the annealed roller blank at a heating rate of 200-230 ℃/h, and carrying out temperature equalization and heat preservation treatment at 600+/-10 ℃ for 8-10 min;
and (3) secondary uniform temperature treatment: continuously heating the roller blank at a heating rate of 200-230 ℃/h, and carrying out uniform temperature and heat preservation treatment for 8-10 min at 800+/-10 ℃;
quenching: continuously heating the roller blank to 1150-1250 ℃ for quenching and preserving heat for 45-60 min, cooling to 800-830 ℃ along with a furnace, preserving heat for 15-20 min, then blowing argon for cooling, controlling the cooling speed to 3-5 ℃/s, cooling to below 300 ℃, discharging, cooling to room temperature in an air way, and tempering in time (within 2-3 h).
In the heating process of quenching treatment, two times of temperature equalization and heat preservation are needed, because the heating speed is high, and when the quenching temperature is high, the roller can be heated uniformly by short-time temperature equalization and heat preservation; therefore, in the quenching treatment, the temperature is kept at 600.+ -. 10 ℃ and 800.+ -. 10 ℃ for 8-10 min twice. Then quenching at 1150-1250 deg.c, homogeneous spheroidizing carbide at 800-830 deg.c and cooling at 4-5.5 deg.c/s to obtain martensite, avoid pearlite and control austenite content.
Since graphite high-speed steel roll stock contains a large amount of high-melting-point carbide. Wherein MC is carbide of V, precipitates during eutectic transformation or precipitates from austenite, the initial solid solution temperature is 1100-1150 ℃, and VC particles are fine and uniformly distributed. M6C is carbide of W and Mo, is dissolved in austenite at 1050-1250 ℃, is quite stable, is not easy to gather and grow up, and can increase the hardness and wear resistance of the die. M7C3 is Cr carbide, which is a primary eutectic carbide or a secondary carbide precipitated from austenite, and can be dissolved into elements such as W, mo, V and the like, thereby increasing the wear resistance and reducing the friction coefficient. Dissolving secondary M7C3 into austenite at 980-1180 ℃; M23C6 is another carbide of Cr, and is solid-dissolved at 1020-1050 ℃ and at 1150-1200 ℃ when it is completely solid-dissolved in austenite. Therefore, a relatively high quenching temperature of 1150-1250 ℃ is necessary to sufficiently dissolve the carbide into the matrix.
The high-speed graphite steel has reticular hypoeutectic carbide formed during casting and graphite inoculation and dispersed and intermittent carbide with tips. The temperature is kept for a short time at 800-830 ℃, and the small blocky carbide with the tip has obvious spheroidizing effect; when the carbide is in a dispersion sphere shape, the carbide cannot become the origin of cracks, and meanwhile, if the crack is expanded to a circular carbide, the crack expansion can deflect at the moment, so that the crack expansion path is prolonged, the crack expansion energy is consumed, and the crack is prevented from being quickly expanded to the roll surface to cause roll breakage.
A large number of experiments show that the austenitizing temperature of alloy elements in the matrix can be increased by adopting a higher quenching temperature of 1150-1250 ℃, more alloy can be dissolved in the matrix, the quantity of twin martensite is reduced, and the quantity of dislocation martensite is increased; the matrix can obtain more dispersed spheroidized carbide by short-time heat preservation at 800-830 ℃. Meanwhile, when the quenching cooling speed is controlled to be 3-5 ℃/s, a martensitic structure can be obtained, pearlite is avoided, and the austenite content is controlled to be within 3%. Therefore, the toughness and thermal fatigue resistance of the matrix are improved, the thermal cracking initiation time is delayed, and the crack growth speed is also reduced.
(3) Tempering: heating the quenched roller blank at a heating rate of 200-230 ℃/h in combination with a temperature curve in the tempering treatment process shown in fig. 2, then preserving heat for 110-120 min at a tempering temperature of 580-660 ℃, cooling to 200-210 ℃ along with a furnace, and discharging and air-cooling to room temperature; the tempering treatment is repeated for 2 to 3 times.
In the tempering treatment process, a higher tempering temperature is adopted, and on one hand, the higher quenching temperature is matched with the higher tempering temperature; and the higher tempering temperature can ensure that the roller blank has excellent thermal cycle stability and tempering resistance, and the roller manufactured subsequently meets the requirement of low-temperature rolling. On the other hand, the graphite high-speed steel roller blank contains more alloy carbide, and a large number of experiments show that MC type and M type in the graphite high-speed steel roller blank 7 C 3 The carbide is separated out in the high-temperature tempering cooling process at the temperature of 550-650 ℃, the dispersivity is large, the secondary hardening effect is generated, the hardness and the wear resistance are increased, and the tempering stability is improved. M is M 23 C 6 At a tempering temperature of 450-550 ℃ or higher, fe saturated with Cr 3 C is converted from the alloy, is not easy to gather and grow greatly, and the precipitation can slightly increase the tempering hardness. When the tempering temperature is higher than 660 ℃, the final hardness of the roller blank is lower, and when the tempering temperature is lower than 580 ℃, the quantity of precipitated carbide is insufficient, and the strength of the roller blank is insufficient; therefore, the tempering temperature is required to be ensured to be between 580 and 660 ℃, and the tempering heat preservation time is controlled to be between 110 and 120 minutes, so that the high-speed steel hardness of the graphite is ensured to meet the requirements, and the high-speed steel has high strength, toughness and crack initiation resistance.
Through the heat treatment method, the finally obtained graphite high-speed steel for the rolling stand roller in the high-speed wire rod is comprehensively improved in mechanical properties at normal temperature and high temperature, and particularly, the high-temperature toughness, oxidation resistance and thermal crack resistance are greatly improved. Then the high-speed wire rod middle rolling mill roll prepared by adopting graphite high-speed steel as materialThe method also has the following characteristics: the area size of the working layer matrix of the roller is less than 5-6 mu m 2 The carbide accounts for about 85 percent, the quantity of carbide particles dispersed in the matrix is also large, and the minimum particle area is 0.03-0.08 mu m 2 Between them; the graphite size is controlled to be about 1.5 μm. The hardness of the working layer is 70-75 HSD, the tensile strength of the roller body is 800-850 MPa, and the depth of the hardening layer is 55mm on one side. The change of the content of graphite and carbide in the working layer is small, and the microstructure is controlled stably and consistently, so that the hardness drop is small. The hardness drop in a working layer with a single side of 55mm is only about 1.5HSD, and the good hardness drop ensures that the rolling performance stability of the graphite high-speed steel roller is improved in the whole service life. The test result of the upper machine shows that the use of the graphite high-speed steel upper machine meets the requirement of low-temperature rolling, and the wear resistance is 2-3 times of that of an infinite chilled ductile iron material roller (ICDP).
The graphite high-speed steel for the high-speed wire rod middle rolling stand roller is compared with the normal-temperature and high-temperature mechanical properties of spheroidal graphite cast iron which is the original middle rolling stand material, and the graphite high-speed steel is shown in the table 1:
TABLE 1 comparison of mechanical Properties at Normal and high temperatures
The graphite high-speed steel for rolling stand rolls in high-speed wire rods and the heat treatment process thereof according to the present invention are further described below with reference to specific examples.
Examples
In the composition range of graphite high-speed steel for rolling stand roller in high-speed wire rod, adopting different proportions, smelting, inoculating and modifying, casting into roller blank, heat-insulating for 2h when the roller blank is cooled to 940 ℃, stopping heating, cooling to 610 ℃ along with furnace, and discharging and cooling to room temperature.
Heating at a heating rate of 200 ℃/h, and carrying out uniform temperature insulation for 8min at 600 ℃; continuously heating at a heating rate of 200 ℃/h, and carrying out uniform temperature insulation for 8min at 800 ℃; quenching at 1200 ℃, preserving heat for 45min, cooling to 820 ℃ along with a furnace, preserving heat for 20min, then blowing argon for cooling, controlling the cooling speed to be 4.5 ℃/s, cooling to below 200 ℃, discharging, air-cooling to room temperature, and tempering in time (within 2-3 h). Heating at a heating rate of 200 ℃/h, tempering and preserving heat at 600 ℃ for 110min; cooling to 200 ℃ along with the furnace, discharging and air cooling to room temperature. The tempering process is repeated for 2 to 3 times, and the graphite high-speed steel and high-speed wire rod rolling stand roller is prepared, wherein specific chemical compositions are shown in table 2, and specific normal-temperature mechanical properties are shown in table 4.
TABLE 2 Components (wt%) of examples 1-5
TABLE 3 mechanical Properties at Normal temperature for examples 1-5
| R m /MPa | A KU2 /J | HSD | |
| Example 1 | 801 | 3.6 | 70 |
| Example 2 | 805 | 3.5 | 71 |
| Implementation of the embodimentsExample 3 | 808 | 3.7 | 72 |
| Example 4 | 812 | 3.8 | 74 |
| Example 5 | 816 | 4.0 | 75 |
As shown in tables 2 and 3, the high-speed graphite steel of examples 1 to 5 and the high-speed wire rod prepared from the same have a tensile strength of 800 to 820MPa at normal temperature and an impact energy of A KU2 3.5 to 4.0J, and the hardness HSD is 70 to 75.
The average single-pass average wear of the rolling stand rolls in the high-speed wire rod prepared by the method is shown in table 4. When the graphite high-speed steel roller is used in 13 frames, the single-time single-groove average rolling quantity 7500t is improved by 3 times compared with the single-time single-groove rolling quantity 2500t of the original nodular cast iron roller; when the graphite high-speed steel roller is used for 14 frames, the single-time single-groove average rolling quantity 9000t is improved by 3 times compared with the single-time single-groove rolling quantity 3000t of the original nodular cast iron roller.
Table 4 comparative table of average rolling amount of graphite high-speed steel and spheroidal graphite cast iron on single pass
With the development of the mechanical properties of wire rod products, the low-temperature rolling technology is gradually popularized, so that new requirements are put forward on the mechanical properties of the roller, and the original mechanical properties of the roller cannot meet the requirement of low-temperature rolling. With the increase of the quantity of low-temperature rolling production, the production line almost has no available rolls. The graphite high-speed steel and the roller made of the graphite high-speed steel, which are designed aiming at the low-temperature rolling requirements and the problems existing in the existing roller, have excellent toughness, wear resistance and hot cracking resistance, solve the difficult problem of low-temperature rolling of a wire production line, and have better popularization and application prospects.
It will be appreciated by persons skilled in the art that the above embodiments are provided for illustration only and not for limitation of the invention, and that variations and modifications of the above described embodiments are intended to fall within the scope of the claims of the invention as long as they fall within the true spirit of the invention.
Claims (8)
1. The graphite high-speed steel for the rolling stand roller in the high-speed wire is characterized by comprising the following components in percentage by weight: c:3.0 to 3.6 percent of Si:0.2 to 1.8 percent of Mn:0.3 to 0.9 percent, less than or equal to 0.10 percent of P, less than or equal to 0.015 percent of S, and Cr:1.0 to 3.5 percent of W:1.0 to 2.8 percent of Mo:2.0 to 5.6 percent, V:1.0 to 3.0 percent, RE:0.12 to 0.26 percent, N:0.10 to 0.80 percent, and the balance of Fe and other unavoidable impurities;
wherein, W and Mo satisfy: w: mo=1:2, 5% < (w+2mo) <14%.
2. The graphite high-speed steel for high-speed wire rod mill stand rolls according to claim 1, wherein the graphite high-speed steel for high-speed wire rod mill stand rolls has a tensile strength of 800 to 850MPa at normal temperature and an impact energy of a KU2 3.0 to 4.0J, and the hardness HSD is 70 to 75.
3. A heat treatment process of graphite high-speed steel for rolling stand rolls in high-speed wire rods, characterized in that a roll blank is cast from the composition of graphite high-speed steel for rolling stand rolls in high-speed wire rods according to claim 1, and heat treatment is performed in the course of cooling the roll blank, and the heat treatment process comprises annealing treatment, quenching treatment and tempering treatment.
4. A process for heat treatment of graphite high speed steel for rolling stand rolls in high speed wire according to claim 3, characterized in that the roll bloom is made by the following process: the graphite high-speed steel for the rolling stand roller in the high-speed wire rod is prepared by proportioning the components, smelting, inoculating, modifying and casting.
5. A heat treatment process of graphite high-speed steel for rolling stand rolls in high-speed wire rods according to claim 3, wherein the annealing process comprises the following steps: when the temperature of the roller blank is cooled to 930-960 ℃, carrying out furnace-following heat preservation treatment for 2-3 hours, then slowly cooling to 600-620 ℃ along with the furnace, and then discharging and air cooling to room temperature.
6. The heat treatment process for graphite high-speed steel for rolling stand rolls in high-speed wire rod according to claim 5, wherein the quenching treatment process comprises the following steps:
(1) Carrying out primary temperature equalization treatment, namely heating the roller blank subjected to annealing treatment at a heating rate of 200-230 ℃/h, and carrying out temperature equalization heat preservation treatment at 600+/-10 ℃ for 8-10 min;
(2) The second temperature equalization treatment, namely heating the roller blank continuously at the heating rate of 200-230 ℃/h, and carrying out the temperature equalization heat preservation treatment for 8-10 min at 800+/-10 ℃;
(3) Quenching, namely continuously heating the roller blank to 1150-1250 ℃ for quenching and preserving heat for 45-60 min, cooling to 800-830 ℃ along with a furnace, preserving heat for 15-20 min, then blowing argon for cooling, controlling the cooling speed to be 4-5.5 ℃/s, cooling to below 300 ℃, discharging, air-cooling to room temperature, and tempering within 2-3 h.
7. The heat treatment process of graphite high-speed steel for rolling stand rolls in high-speed wire rods according to claim 6, wherein in the tempering treatment, the quenched roll blank is heated at a heating rate of 200-230 ℃/h, then is kept at a tempering temperature of 580-660 ℃ for 110-120 min, is cooled to 200-210 ℃ along with a furnace, and is discharged for air cooling to room temperature; the tempering treatment is repeated for 2 to 3 times.
8. The heat treatment process for a graphite high-speed steel for rolling stand rolls in a high-speed wire rod according to any one of claims 3 to 7, wherein the graphite high-speed steel for rolling stand rolls in a high-speed wire rod has a tensile strength of 800 to 850MPa at ordinary temperature and an impact energy of a KU2 3.0 to 4.0J, and the hardness HSD is 70 to 75.
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