CN111659731B - Pearlite spheroidizing method based on high-speed wire rod production line - Google Patents
Pearlite spheroidizing method based on high-speed wire rod production line Download PDFInfo
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- CN111659731B CN111659731B CN202010449897.1A CN202010449897A CN111659731B CN 111659731 B CN111659731 B CN 111659731B CN 202010449897 A CN202010449897 A CN 202010449897A CN 111659731 B CN111659731 B CN 111659731B
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- 229910001562 pearlite Inorganic materials 0.000 title claims abstract description 58
- 238000000034 method Methods 0.000 title claims abstract description 25
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 21
- 238000005096 rolling process Methods 0.000 claims abstract description 60
- 238000004321 preservation Methods 0.000 claims abstract description 39
- 238000001816 cooling Methods 0.000 claims abstract description 30
- 238000009987 spinning Methods 0.000 claims abstract description 19
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 19
- 238000009749 continuous casting Methods 0.000 claims abstract description 14
- 238000004513 sizing Methods 0.000 claims abstract description 14
- 238000010438 heat treatment Methods 0.000 claims description 22
- 229910052698 phosphorus Inorganic materials 0.000 claims description 8
- 229920000742 Cotton Polymers 0.000 claims description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 4
- 229910052804 chromium Inorganic materials 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 238000005098 hot rolling Methods 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 4
- 238000002791 soaking Methods 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 2
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 229910000831 Steel Inorganic materials 0.000 abstract description 61
- 239000010959 steel Substances 0.000 abstract description 61
- 229910000859 α-Fe Inorganic materials 0.000 abstract description 39
- 238000000137 annealing Methods 0.000 abstract description 17
- 230000009466 transformation Effects 0.000 abstract description 13
- 229910000954 Medium-carbon steel Inorganic materials 0.000 abstract description 8
- 230000000052 comparative effect Effects 0.000 description 22
- 229910052799 carbon Inorganic materials 0.000 description 17
- 229910001339 C alloy Inorganic materials 0.000 description 14
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 12
- 230000000694 effects Effects 0.000 description 9
- 238000010273 cold forging Methods 0.000 description 8
- 230000007547 defect Effects 0.000 description 8
- 239000006185 dispersion Substances 0.000 description 8
- 238000003860 storage Methods 0.000 description 8
- 238000012545 processing Methods 0.000 description 7
- 238000010583 slow cooling Methods 0.000 description 7
- 229910001566 austenite Inorganic materials 0.000 description 6
- 239000013078 crystal Substances 0.000 description 6
- 239000002253 acid Substances 0.000 description 5
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 4
- 238000004140 cleaning Methods 0.000 description 4
- 238000005261 decarburization Methods 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 4
- 239000011574 phosphorus Substances 0.000 description 4
- 238000007127 saponification reaction Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 238000007599 discharging Methods 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 238000007670 refining Methods 0.000 description 3
- 241000446313 Lamella Species 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 239000000498 cooling water Substances 0.000 description 2
- 230000007850 degeneration Effects 0.000 description 2
- 230000002035 prolonged effect Effects 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 230000001172 regenerating effect Effects 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 229910000915 Free machining steel Inorganic materials 0.000 description 1
- 229910000639 Spring steel Inorganic materials 0.000 description 1
- 229910001315 Tool steel Inorganic materials 0.000 description 1
- 238000005422 blasting Methods 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000009963 fulling Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 238000012797 qualification Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 230000006032 tissue transformation Effects 0.000 description 1
- UONOETXJSWQNOL-UHFFFAOYSA-N tungsten carbide Chemical compound [W+]#[C-] UONOETXJSWQNOL-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/16—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling wire rods, bars, merchant bars, rounds wire or material of like small cross-section
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
Abstract
The invention belongs to the technical field of high-speed wire rod steel rolling, and relates to a pearlite spheroidizing method based on a high-speed wire rod production line. After a continuous casting billet at 850-950 ℃ is subjected to rough and medium rolling and pre-finish rolling deformation, the temperature of the billet reaching the inlet of a finish rolling unit and a reducing and sizing mill unit is controlled at 700-760 ℃ by adjusting the water flow of a water tank, so that two-phase area controlled rolling is realized, and the spinning temperature is controlled at 720-780 ℃ by adjusting the water flow of the water tank after rolling; on the lengthened stelmor heat-preserving line, ferrite transformation continues to occur; through the reinforced heat preservation measure, the cooling rate reaches 0.01-0.1 ℃/s, and the pearlite transformation and online spheroidization are realized. By adopting the method, the proportion of ferrite in the obtained hot-rolled wire rod microstructure is greatly improved, the spheroidization rate of pearlite reaches more than 95%, and the grade of low-medium carbon steel spheroidization body can be rated by 4-5 according to JB/T5074-2007, and the microstructure is close to the structure after conventional spheroidization annealing.
Description
Technical Field
The invention belongs to the technical field of high-speed wire rod steel rolling, and relates to an on-line spheroidizing method of pearlite in a microstructure of a cold heading steel hot-rolled wire rod, in particular to a method for realizing spheroidization of pearlite on an elongated Steyr heat preservation line in the microstructure of the cold heading steel hot-rolled wire rod through a controlled rolling and controlled cooling production process based on a high-speed wire rod production line.
Background
The high-speed wire rod production line is characterized by high speed, single line, no torsion, micro tension, combined structure, tungsten carbide roll collar and high automation, can realize controlled rolling and controlled cooling, and has the characteristics of heavy coil weight, high dimensional precision, good surface quality of a coil rod and controllable microstructure and mechanical property of the hot-rolled coil rod.
The maximum rolling speed of the fifth generation of the Morgan finishing mill can reach 120m/s, and research shows that when the rolling speed of a steel rolled piece is more than 10m/s, the rolled piece is heated, and a multi-section water tank with strong cooling capacity is configured on a Morgan high-speed wire rod production line for realizing temperature control rolling. In order to realize controlled cooling after rolling, an ultra-long stelmor cooling control line is designed on the Morgan high-speed wire production line, and an ultra-high-power fan and a heat-insulating cover are configured on the cooling control line, so that quick cooling, slow cooling and random combination of hot-rolled wire rods can be realized. The Morgan high-speed wire production line can produce high-end wire products, such as spring steel, bearing steel, cord steel, hard wire steel, tool steel, free-cutting steel, cold-heading steel and the like.
Among the wire products of the Morgan high-speed wire production line, the digital cold heading steel has the most complex variety, the largest demand, the most extensive application and the most diversified processing technology. In the cold heading steel industry, cold heading steel with the C content lower than 0.25% is generally changed into low-carbon cold heading steel, and cold heading steel with the C content between 0.25% and 0.45% is called medium-carbon cold heading steel, so that the cold heading steel can be roughly divided into four types according to chemical components: low carbon cold heading steel (representative brand SWRCH6A, ML08Al, SWRCH15A, SWRCH22A), medium carbon cold heading steel (representative brand SWRCH35K, ML35, SWRCH38K, SWRCH45K), low carbon alloy cold heading steel (representative brand ML20Cr, ML20CrMo, ML20MnTiB, 10B21) and medium carbon alloy cold heading steel (representative brand 10B33, SCM435, ML40Cr, SCM 440). The cold heading steel has large demand, is mainly used for producing fasteners such as bolts, nuts, screws, rivets and the like, is widely applied to the fields of automobiles, trains, aviation, household appliances, mechanical equipment, industrial buildings and the like, and has strength grades of 4.8-6.8, 8.8, 10.9, 12.9 and above four grades. The cold forging steel processing technology has the characteristics of diversity, and the general processing technological process of the low-carbon cold forging steel and the common low-carbon alloy cold forging steel comprises the following steps: wire rod → acid pickling phosphorization (or shot blasting) → drawing → cold heading forming; the general processing technological process of the high-grade low-carbon alloy cold forging steel, the medium-carbon cold forging steel and the common medium-carbon alloy cold forging steel comprises the following steps: wire rod → spheroidizing annealing → acid cleaning → phosphorus saponification → drawing → cold heading forming → thermal refining; the general processing technological process of the high-grade medium carbon alloy cold heading steel comprises the following steps: wire rod → acid cleaning → phosphorus saponification → drawing → spheroidizing annealing → acid cleaning → phosphorus saponification → drawing → cold heading forming → thermal refining (even more demanding processing process flow is wire rod → spheroidizing annealing → acid cleaning → phosphorus saponification → drawing → cold heading forming → thermal refining).
According to the cold heading steel processing process, spheroidizing annealing and cold heading forming are important links, the cold heading forming is to obtain the shape of a final product, a cold heading steel wire rod is required to have lower deformation resistance and good plasticity, and the spheroidizing annealing is to prepare for a microstructure of the cold heading forming so as to spheroidize flaky pearlite in the microstructure of the cold heading steel, so that the strength and the hardness are reduced, the plasticity is improved, and the cold deformation capability is enhanced. If the original microstructure of the hot rolled wire rod of the cold heading steel is not good, it becomes difficult to achieve the desired effect by spheroidizing annealing, and the spheroidizing annealing time becomes long, particularly in high-grade medium carbon alloy cold heading steel (generally used for producing fasteners of grade 12.9 and above). Therefore, it becomes especially important to obtain a microstructure which is easy for spheroidizing annealing and cold heading forming when producing the cold heading steel hot rolled wire rod, so that the difficulty of spheroidizing annealing can be greatly reduced, and even one-time spheroidizing annealing can be reduced or annealing is avoided, thereby having important significance for improving the profit of a steel mill, saving the cost of a cold heading steel user and protecting the environment.
At present, when a Morgan high-speed wire rod production line produces cold heading steel hot rolled wire rods, a finishing mill group and a reducing sizing mill group are mostly rolled at the conventional temperature of 850-950 ℃ (in a complete austenite state), the heat preservation time on a stelmor heat preservation line is insufficient after spinning and looping, the proportion of ferrite in the microstructure of the obtained cold heading steel hot rolled wire rods is small, flaky pearlite is more, lamella is developed, no spheroidized body exists, the strength and the hardness are high, and the plasticity is poor. The invention discloses a controlled rolling and controlled cooling method for improving the ferrite proportion of a medium-carbon cold heading steel wire rod, which is disclosed by the Chinese patent with the patent number of CN 201911179037.4. Although the ferrite proportion can be remarkably increased to 85% or more, the spheroidizing effect of pearlite by this method is not good in terms of microstructure, and a large amount of lamellar pearlite exists in the microstructure, so pearlite spheroidizing is not specifically described in this patent.
The study on the test research on the non-spheroidizing annealed SWRCH35K cold forging steel and the study on the transformation behavior and the structure evolution of the non-spheroidizing cold forging steel SWRCH35KM study the influence of the rolling temperature and the cooling speed on pearlite spheroidization, and the results show that low-temperature rolling and slow cooling both contribute to pearlite spheroidization. However, the present inventors have made only studies on the mechanism of pearlite spheroidization, and have not provided a specific pearlite spheroidization method based on a high-speed wire rod production line, and particularly, it was concluded that adjustment to increase the spinning temperature and the like is contrary to the inventive concept of the present invention in the conclusion of "experimental study of spheroidization-free annealed SWRCH35K cold heading steel".
Therefore, in view of the above problems, there is a need to find a method for spheroidizing pearlite on a stelmor holding line in a hot-rolled wire rod microstructure of cold heading steel based on a high-speed wire rod production line.
Low-temperature controlled rolling is adopted to realize rolling in a two-phase region (alpha + gamma), a large amount of deformation induced ferrite is formed at a high strain rate, a large amount of dispersion defects and deformation storage energy are accumulated at the same time, and the formed deformation induced ferrite is inhibited from being re-austenitized; in addition, by matching with a slow cooling technology after rolling, the heat preservation time is prolonged on a stelmor heat preservation line after spinning and looping, ferrite transformation continues to occur, meanwhile, a large amount of dispersed carbide is formed in ferrite crystal by controlling the dispersion defect and deformation storage energy accumulated by rolling, so that the carbon content on the crystal boundary is reduced, the subsequent pearlite transformation is favorably reduced, the extremely low cooling rate is realized by a reinforced heat preservation measure, and the pearlite transformation is simultaneously spheroidized on line.
Disclosure of Invention
The invention aims to provide a pearlite spheroidization method based on a high-speed wire rod production line, which not only greatly improves the ferrite proportion in a hot-rolled wire rod microstructure by adopting the rolling process, but also enables the pearlite spheroidization rate in the hot-rolled wire rod microstructure to reach more than 95%, obtains a microstructure (4-5 grades can be evaluated according to JB/T5074-2007 low-medium carbon steel spheroidization body grades) which is close to the conventional spheroidization annealing, further enables the strength and hardness of the hot-rolled wire rod to be reduced, improves the plasticity, improves the cold heading performance, effectively solves the problems of long spheroidization annealing time and high die loss of a downstream user cold heading steel hot-rolled wire rod, and even can realize spheroidization annealing avoidance.
In order to achieve the technical purpose, the invention provides a pearlite spheroidization method based on a high-speed wire rod production line, which comprises the following steps: the method comprises the following steps of low-temperature heating of a continuous casting billet, low-temperature controlled rolling of a blank, low-temperature wire rod spinning and reinforced heat preservation of a hot rolled wire rod on a stelmor heat preservation line, and comprises the following steps:
(1) and (3) after the continuous casting slab is heated at a low temperature by a heating furnace, rolling at the temperature lower than 950 ℃, namely performing rough and medium rolling and pre-finish rolling deformation at the temperature of 850-950 ℃.
(2) Controlling the temperature of the blank at the inlet of a finishing mill group to be 700-760 ℃ by adjusting the water flow of a water tank;
(3) after the finishing mill set finishes rolling, controlling the temperature of blanks reaching the inlet of the reducing sizing mill set to be 700-760 ℃ respectively by adjusting the water flow of a water tank;
(4) after the final rolling of the reducing sizing mill set, controlling the spinning temperature of the wire rod to be 720-780 ℃ by adjusting the flow of a water tank;
(5) after spinning, hot rolling the wire rod on an elongated stelmor heat preservation line, closing all heat preservation covers, covering heat preservation cotton at gaps of the heat preservation covers, enabling the stelmor roller speed to be not more than 5m/min, the heat preservation time to be not less than 1800s, enabling the wire rod cover-discharging temperature to be not higher than 650 ℃, enabling the average cooling rate on the stelmor heat preservation line before discharging the wire rod cover to be 0.01-0.1 ℃/s, and naturally cooling the wire rod on a C-shaped hook after discharging the wire rod cover and performing tucking.
Further, the heating temperature of the continuous casting slab in the step (1) in a regenerative heating furnace is not more than 1050 ℃, so that the excessive growth of austenite grains is inhibited, the stability of austenite is reduced, the ferrite transformation is facilitated, and the decarburization of the continuous casting slab is reduced. More preferably: the first heating section is heated for 30-40 minutes at the temperature of 700-800 ℃, the second heating section is heated for 30-40 minutes at the temperature of 900-1000 ℃, and the soaking section is heated for 45-55 minutes at the temperature of 1000-1050 ℃.
Furthermore, the heating time of the continuous casting billet in the step (1) in the regenerative heating furnace is less than or equal to 2.5 hours, and the air-fuel ratio of the atmosphere in the furnace is less than or equal to 0.5, so that decarburization can be effectively inhibited, because the billet is easily decarburized when medium carbon steel and alloy steel are heated at high temperature for a long time, the decarburization reflected on a rolled material exceeds the standard, and the surface hardness of a subsequent machined part can be reduced.
Furthermore, the initial rolling temperature in the step (1) is not more than 950 ℃, so that the subsequent cooling is facilitated to realize low-temperature controlled rolling, and the accumulated deformation time is 50-120 s.
Further, the blank in the steps (2) and (3) is deformed at the temperature of 700-760 ℃ through a finishing mill group and a reducing sizing mill group respectively, so that rolling in a two-phase region (alpha + gamma) is realized, a large amount of deformation induced ferrite is formed at a high strain rate, and a large amount of dispersion defects and deformation storage energy are accumulated. The finishing rolling temperature of the finishing mill group and the reducing sizing mill group does not exceed 780 ℃, the low-temperature controlled rolling effect can be ensured, the dispersion defect and deformation storage energy accumulated by the low-temperature controlled rolling can not be eliminated due to temperature rise, and the formed deformation is inhibited to induce ferrite to be austenitized again.
Further, the hot rolled wire rod in the step (4) is subjected to low-temperature spinning at 720-780 ℃, so that the low-temperature controlled rolling effect can be ensured, the deformation induced ferrite can be preserved, re-austenitization of the deformation induced ferrite is prevented, dispersion defects and deformation storage energy accumulated by low-temperature controlled rolling due to temperature rise are avoided, and nucleation particles and diffusion energy are provided for forming point-shaped carbides, degenerating and spheroidizing pearlite in the subsequent tissue transformation process.
Further, immediately putting the wire rod on a stelmor heat preservation line for slow cooling after spinning in the step (5), wherein the temperature of the put wire rod in the cover is 700-780 ℃.
Further, the hot-rolled wire rod in the step (5) is arranged on the lengthened stelmor heat-preserving line, the heat-preserving cover adopts a sealing measure, the stelmor roller speed is not more than 5m/min, the heat-preserving time is not less than 1800s, ferrite transformation continues to occur, and meanwhile, a large amount of dispersed carbide is formed in ferrite crystal through the dispersion defect and deformation storage energy accumulated by controlled rolling, so that the carbon content on the crystal boundary is reduced, the subsequent pearlite transformation is favorably reduced, and the ferrite proportion in the microstructure is improved.
Further, the cover-removing temperature of the wire rod in the step (5) is not higher than 650 ℃, and the average cooling rate on the stelmor heat preservation line before the wire rod is covered can reach 0.01-0.1 ℃/s, and is further preferably 0.01-0.05 ℃/s, so that pearlite can be transformed and spheroidized on line at the same time, and the spheroidization rate of the pearlite is improved; if the cooling rate is too high, the corresponding spheroidizing effect is not achieved, and more lamellar pearlite is formed in the microstructure.
The wire rod comprises the following chemical components in percentage by mass: 0.18-0.48%, Si: 0.01 to 0.35%, Mn: 0.30-1.60%, P is less than or equal to 0.035%, S is less than or equal to 0.035%, Cr is less than or equal to 0.25%, Ni is less than or equal to 0.25%, Cu is less than or equal to 0.25%, Al: 0.010-0.045%, and the balance of iron and inevitable impurities.
According to the invention, through low-temperature heating of the continuous casting billet, excessive growth of austenite grains is inhibited, so that the stability of austenite is reduced, ferrite transformation is facilitated, decarburization can be effectively inhibited, and the blank can be ensured to pass through rough and medium rolling and pre-finish rolling deformation at a lower temperature, and then the blank can reach a lower temperature when reaching a finishing mill group and a reducing sizing mill group; low-temperature controlled rolling is adopted to realize rolling in a two-phase region (alpha + gamma), a large amount of deformation induced ferrite is formed at a high strain rate, a large amount of dispersion defects and deformation storage energy are accumulated at the same time, and the formed deformation induced ferrite is inhibited from being re-austenitized; in addition, by matching with a slow cooling technology after rolling, the heat preservation time is prolonged on a stelmor heat preservation line after spinning and looping, ferrite transformation continues to occur, meanwhile, a large amount of dispersed carbide is formed in ferrite crystal by controlling the dispersion defect and deformation storage energy accumulated by rolling, so that the carbon content on the crystal boundary is reduced, the subsequent pearlite transformation is favorably reduced, the extremely low cooling rate is realized by a reinforced heat preservation measure, and the pearlite transformation is simultaneously spheroidized on line.
Compared with the conventional production of the cold heading steel hot rolled wire rod (the finish rolling unit and the reducing sizing mill unit carry out conventional rolling in a complete austenite state, the heat preservation measure on a stelmor heat preservation line after spinning and looping is not strengthened, the heat preservation time is insufficient, the proportion of ferrite in the microstructure of the obtained cold heading steel hot rolled wire rod is small, flaky pearlite is more and lamella is developed, no spheroidized body exists, the strength and hardness are high, and the plasticity is poor). The proportion of ferrite in the hot-rolled wire rod microstructure is greatly improved, the nodulizing rate of pearlite is more than 95%, the microstructure which is close to that after conventional spheroidizing annealing is obtained (the grade can be evaluated by 4-5 according to JB/T5074-2007 low-medium carbon steel spheroidization grading), the strength and the hardness of the hot-rolled wire rod are reduced, the plasticity is improved, and the cold upsetting performance is improved.
Drawings
FIG. 1 is a microstructure of a medium carbon cold heading steel wire rod produced in example 1.
FIG. 2 is a microstructure view of a low carbon alloy cold heading steel wire rod produced in example 2.
Fig. 3 is a microstructure view of a medium carbon cold heading steel wire rod produced in comparative example 1.
Fig. 4 is a microstructure diagram of a medium carbon cold heading steel wire rod produced in comparative example 2.
FIG. 5 is a microstructure diagram of a low carbon alloy cold heading steel wire rod produced in comparative example 3.
FIG. 6 is a microstructure diagram of a low carbon alloy cold heading steel wire rod produced in comparative example 4.
Detailed Description
The invention is explained by combining a fifth generation Morgan high-speed wire rod production line and using continuous casting billets with 160mm multiplied by 160mm sections of medium carbon cold heading steel SWRCH35K and low carbon alloy cold heading steel 10B21 to roll hot rolled wire rods with phi 16.0mm finished product specifications.
Example 1
1. Heating of casting blanks
And (3) continuous casting billet component C: 0.35%, Si: 0.12%, Mn: 0.76%, P: 0.011%, S: 0.008%, Cr: 0.08%, Ni: 0.05%, Cu: 0.03%, Al: 0.031%.
The continuous casting billet with the section of 160mm multiplied by 160mm is heated in a heat accumulating type stepping heating furnace, the first heating section is heated for 35 minutes at the temperature of 700-800 ℃, the second heating section is heated for 35 minutes at the temperature of 900-1000 ℃, and the soaking section is heated for 50 minutes at the temperature of 1000-1050 ℃.
2. Low temperature controlled rolling
After blanks are subjected to rough and medium rolling and pre-finish rolling deformation at 850-950 ℃, the temperature of the blanks reaching the inlet of a finishing mill group and a reducing and sizing mill group is controlled to be 700-760 ℃ by adjusting the water flow of a water tank, and the finish rolling temperature is less than or equal to 780 ℃ by adjusting cooling water between frames.
3. Low temperature spinning
And after finishing rolling, controlling the spinning temperature of the wire rod to be 720-780 ℃ by adjusting the flow of the water tank.
4. After-rolling slow cooling
After spinning, hot rolling the wire rod on an elongated stelmor heat preservation line, closing all heat preservation covers, covering heat preservation cotton at gaps of the heat preservation covers, and controlling the temperature of the wire rod in the heat preservation covers to be 700-750 ℃. Preferably, the stelmor roller speed is 3m/min, the heat preservation time is not less than 1800s, the cover-removing temperature of the wire rod is lower than 650 ℃, the average cooling rate before the wire rod is removed from the cover can reach 0.01-0.05 ℃/s, and the preferred cooling rate in the embodiment 1 is 0.02 ℃/s.
FIG. 1 is the microstructure of a medium carbon cold heading steel SWRCH35K hot rolled wire rod produced in example 1. As can be seen from figure 1, the microstructure comprises ferrite, flaky pearlite, degenerated spheroidized pearlite and granular carbide, the proportion of the ferrite is more than 85%, the degenerated pearlite and spheroidizing effect is good, only a very small amount of flaky pearlite is contained, the spheroidization rate is more than 95%, and the microstructure is close to the structure after spheroidizing annealing, and the low-medium carbon steel spheroidized body can be graded by 5 according to JB/T5074-2007.
Example 2
1. Heating of casting blanks
And (3) continuous casting billet component C: 0.21%, Si: 0.05%, Mn: 0.86%, P: 0.013%, S: 0.006%, Cr: 0.13%, Ni: 0.02%, Cu: 0.04%, Al: 0.045%.
The continuous casting billet with the section of 160mm multiplied by 160mm is heated in a heat accumulating type stepping heating furnace, the first heating section is heated for 35 minutes at the temperature of 700-800 ℃, the second heating section is heated for 35 minutes at the temperature of 900-1000 ℃, and the soaking section is heated for 50 minutes at the temperature of 1000-1050 ℃.
2. Low temperature controlled rolling
After rough and medium rolling and pre-finish rolling deformation are carried out on the blank at the temperature of 850-950 ℃, the temperature of the blank reaching the inlet of a finish rolling unit and a reducing and sizing unit is controlled to be 700-760 ℃ by adjusting the water flow of a water tank, and the finish rolling temperature is less than or equal to 780 ℃ by adjusting cooling water between frames.
3. Low temperature spinning
And after finishing rolling, controlling the spinning temperature of the wire rod to be 720-780 ℃ by adjusting the flow of the water tank.
4. After-rolling slow cooling
After spinning, hot rolling the wire rod on an elongated stelmor heat preservation line, closing all heat preservation covers, covering heat preservation cotton at gaps of the heat preservation covers, and controlling the temperature of the wire rod in the heat preservation covers to be 700-750 ℃. Preferably, the stelmor roller speed is 3m/min, the heat preservation time is not less than 1800s, the cover-removing temperature of the wire rod is lower than 650 ℃, the average cooling rate of the wire rod can reach 0.01-0.05 ℃/s, and the cooling rate in the embodiment 2 is preferably 0.02 ℃/s.
Fig. 2 is a microstructure of a low carbon alloy cold heading steel 10B21 hot rolled wire rod produced in example 2. As can be seen from figure 2, the microstructure comprises ferrite, flaky pearlite, degenerated spheroidized pearlite and granular carbide, the proportion of the ferrite is more than 85%, the degenerated pearlite and spheroidized effect is good, only a small amount of flaky pearlite is contained, the spheroidization rate reaches 80%, and the grade of low-medium carbon steel spheroidized body can be rated as 4 according to JB/T5074-2007.
Comparative example 1
Comparative example 1 differs from example 1 mainly in that: the average cooling rate of 0.01-0.05 ℃/s in step 4 of example 1 is replaced by 0.2-0.3 ℃/s (the cooling rate of 0.25 ℃/s is preferred in comparative example 1), and the other conditions are the same as in example 1.
FIG. 3 is a microstructure of a medium carbon cold heading steel SWRCH35K hot rolled wire rod produced in comparative example 1. It can be seen from fig. 3 that although the microstructure includes "ferrite + lamellar pearlite + degenerated, spheroidized pearlite + particulate carbide" and the ferrite proportion is 85% or more, the pearlite degeneration and spheroidization effects are not as good as in example 1, relatively large lamellar pearlite is included, the spheroidization rate is less than 50%, and the low-medium carbon steel spheroidization rating can be rated only by 3 according to JB/T5074-2007.
Comparative example 2
Comparative example 2 differs from example 1 mainly in that: the inlet temperatures of the finishing mill group and the reducing and sizing mill group in the step 2 of the embodiment 1 are replaced by 860-920 ℃, the average cooling rate in the step 4 is replaced by 0.01-0.05 ℃/s to 0.2-0.3 ℃/s (the cooling rate is preferably 0.25 ℃/s in the comparative example 2), and the other conditions are the same as the embodiment 1.
FIG. 4 is a microstructure of a medium carbon cold heading steel SWRCH35K hot rolled wire rod produced in comparative example 2. It can be seen from fig. 4 that the microstructure only contains "ferrite + lamellar pearlite", the ferrite proportion is only 55%, and no degenerated and spheroidized pearlite exists.
Comparative example 3
Comparative example 3 compared to example 2, the main differences are: the average cooling rate of 0.01-0.05 ℃/s in step 4 of example 2 is replaced by 0.2-0.3 ℃/s (the cooling rate of 0.25 ℃/s is preferred in comparative example 3), and the other conditions are the same as in example 2.
Fig. 5 is a microstructure of a low carbon alloy cold heading steel 10B21 hot rolled wire rod produced in comparative example 3. As can be seen from fig. 4, although the microstructure includes "ferrite + lamellar pearlite + degenerated, spheroidized pearlite + particulate carbide" and the ferrite proportion is 85% or more, the pearlite degeneration and spheroidization effects are not as good as in example 2, large lamellar pearlite is included, the spheroidization rate is less than 30%, and the low-medium carbon steel spheroidization rating can be rated only by 2 according to JB/T5074-2007.
Comparative example 4
Comparative example 4 compared to example 2, the main differences are: the inlet temperatures of the finishing mill group and the reducing and sizing mill group in the step 2 of the embodiment 2 are replaced by 860-920 ℃, the average cooling rate in the step 4 is replaced by 0.01-0.05 ℃/s to 0.2-0.3 ℃/s (the cooling rate is preferably 0.25 ℃/s in the comparative example 4), and the other conditions are the same as the embodiment 2.
Fig. 6 is a microstructure of a low carbon alloy cold heading steel 10B21 hot rolled wire rod produced in comparative example 4. It can be seen from fig. 4 that the microstructure only contains "ferrite + lamellar pearlite", the ferrite proportion accounts for 75%, and pearlite without any degradation and spheroidization.
The pearlite spheroidization rate, the spheroidization grade, the ferrite proportion, the Rockwell hardness HRB, the tensile strength and the 1/4 cold heading in the wire rod microstructures of the example 1 and the example 2 of the invention and the comparative example 2 and the comparative example 4 are detected and compared as shown in the table 1.
TABLE 1
Compared with the conventional process, the proportion of spheroidized pearlite, spheroidized grade and ferrite in the microstructure of the cold heading steel wire rod obtained by the invention is greatly optimized, and the hardness and the strength are relatively reduced, so that the qualification rate of 1/4 cold heading is greatly improved.
The raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified. The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all modifications of the above embodiments made according to the technical spirit of the present invention are included in the scope of the present invention.
Claims (4)
1. A pearlite spheroidization method based on a high-speed wire rod production line is characterized by comprising the following steps: the method comprises the following steps:
(1) heating the continuous casting billet in a heating furnace at low temperature, and performing rough and medium rolling and pre-finish rolling deformation at 850-950 ℃; the low-temperature heating means that the continuous casting blank is heated for 30-40 minutes at the temperature of 700-800 ℃ in the first heating section, for 30-40 minutes at the temperature of 900-1000 ℃ in the second heating section, and for 45-55 minutes at the temperature of 1000-1050 ℃ in the soaking section;
(2) the temperature of the blank reaching the inlet of the finishing mill group and the inlet of the reducing sizing mill group are respectively controlled to be 700-760 ℃ by adjusting the water flow of the water tank;
(3) after finishing rolling, controlling the spinning temperature of the wire rod to be 720-780 ℃ by adjusting the flow of a water tank;
(4) and (3) after spinning, hot rolling the wire rod on a stelmor heat preservation line, closing all heat preservation covers, covering heat preservation cotton at gaps of the heat preservation covers, keeping the speed of a stelmor roller way at 3-5 m/min for at least 1800s, keeping the temperature of the wire rod out of the covers at not higher than 650 ℃, and keeping the average cooling rate at 0.01-0.05 ℃/s.
2. The pearlite spheroidization method based on the high-speed wire rod production line according to claim 1, characterized in that: the wire rod comprises the following chemical components in percentage by mass: 0.18-0.48%, Si: 0.01 to 0.35%, Mn: 0.30-1.60%, P is less than or equal to 0.035%, S is less than or equal to 0.035%, Cr is less than or equal to 0.25%, Ni is less than or equal to 0.25%, Cu is less than or equal to 0.25%, Al: 0.010-0.045%, and the balance of iron and inevitable impurities.
3. The pearlite spheroidization method based on the high-speed wire rod production line according to claim 1, characterized in that: the finishing temperature of the finishing mill group and the reducing sizing mill group does not exceed 780 ℃.
4. The pearlite spheroidization method based on the high-speed wire rod production line according to claim 1, characterized in that: the spheroidization rate of pearlite in the obtained hot-rolled wire rod microstructure reaches more than 95 percent.
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