CN111482568B - Control method of net-shaped carbide of hot-rolled bearing steel - Google Patents
Control method of net-shaped carbide of hot-rolled bearing steel Download PDFInfo
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- CN111482568B CN111482568B CN202010321519.5A CN202010321519A CN111482568B CN 111482568 B CN111482568 B CN 111482568B CN 202010321519 A CN202010321519 A CN 202010321519A CN 111482568 B CN111482568 B CN 111482568B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/20—Controlling or regulating processes or operations for removing cast stock
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
- B22D11/225—Controlling or regulating processes or operations for cooling cast stock or mould for secondary cooling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D11/00—Process control or regulation for heat treatments
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
Abstract
The invention relates to a control method of steel network carbide of a hot rolling bearing, belonging to the technical field of bearing steel hot rolling process. In order to solve the problem that the service life of a bearing is influenced by the existence of reticular carbide in bearing steel, the invention provides a control method of the reticular carbide in hot rolling bearing steel, which comprises the steps of firstly adopting low superheat degree casting and controlling a continuous casting process to obtain a prepared structure with a low power carbon segregation index of 0.95-1.05; further improving the carbide distribution by controlling a high-temperature diffusion heating process; and finally, controlling the cooling speed of the steel billet in the rolling and cooling process, controlling the temperature of the steel billet in the finish rolling pass to be 700-800 ℃, and reducing the temperature of the finally rolled steel to be 630-680 ℃ by using through water cooling. The bearing steel hot-rolled round steel for the rolling body produced by the control method has the central carbide net less than or equal to 5.3, the carbide net less than or equal to 5.1 at 1/2R, the width of the chilling layer is 5mm, and the central and chilling layers are pearlite structures.
Description
Technical Field
The invention belongs to the technical field of bearing steel hot rolling processes, and particularly relates to a control method of a steel-mesh carbide of a hot-rolled bearing.
Background
The bearing steel belongs to hypereutectoid steel, and a large amount of carbide exists in the product necessarily. In bearing use, wear failure is not the only fatigue failure, and therefore carbide is unlikely to exist, and it is critical to try to improve carbide size and distribution. The used structure of the bearing should be martensite in a quenched-tempered state, fine grained carbides and a small amount of retained austenite. In order to obtain an ideal final structure, the steel material must have a good spheroidizing annealing preliminary structure, i.e., a fine lamellar pearlite structure in which the precipitation of network carbides at grain boundaries is suppressed, before spheroidizing annealing. In the cooling process of the bearing steel in an austenite state after rolling, secondary carbides are separated out and form network carbides at austenite grain boundaries, which has great influence on the service life of the bearing. Therefore, how to reduce the level of the net-shaped carbide is a problem to be solved in the hot rolling process of the bearing steel.
Disclosure of Invention
The invention provides a control method of net-shaped carbide of hot-rolled bearing steel, aiming at solving the problem that the net-shaped carbide of the bearing steel influences the service life of a bearing.
The technical scheme of the invention is as follows:
a control method of a net-shaped carbide of hot-rolled bearing steel comprises the steps of firstly adopting low superheat degree casting and controlling a blank drawing speed, a secondary cooling parameter and an electromagnetic stirring parameter in a continuous casting process to obtain a preparation structure with a low-power carbon segregation index of 0.95-1.05; further improving the carbide distribution by controlling the heating temperature and the heating time of the high-temperature diffusion heating process; and finally, controlling the cooling speed of the steel billet by adopting a three-section water-through cooling process in the rolling and cooling process, controlling the temperature of the steel billet in the finish rolling pass within the range of 700-800 ℃, and then reducing the temperature of the finally rolled steel to 630-680 ℃ by utilizing water-through cooling.
Further, the continuous casting blank type adopted by the low superheat degree casting is a square blank of 250mm multiplied by 280mm, and the liquidus temperature is 1454 ℃; the degree of superheat is controlled to be 25-35 ℃.
Further, the blank drawing speed in the continuous casting process is 0.50-0.62 m/min; the specific water amount in the secondary cooling parameters is 0.18; the distribution ratio of the secondary cooling water is 38/38/24; the water quantity of the crystallizer is 2450L/min; the electromagnetic stirring parameters are M-EMS: 500A/2 Hz; F-EMS: 400A/18 Hz.
Furthermore, the heating temperature of the high-temperature diffusion heating process is divided into four stages of a preheating stage, a heating 1 stage, a heating 2 stage and a soaking stage in sequence, and the total heating time is not less than 390 min.
Further, the heating temperature of the preheating section is less than or equal to 800 ℃, and the heating time of the preheating section is not less than 75 min; the heating temperature of the heating section 1 is 900-1120 ℃, and the heating time of the heating section 1 is not less than 100 min; the heating temperature of the heating 2 sections is 1200-1220 ℃, and the heating time of the heating 2 sections is not less than 110 min; the heating temperature of the soaking section is 1200-1220 ℃, the heating time of the soaking section is not less than 115min, the discharging temperature of the steel billet after the high-temperature diffusion heating process is ended is 1120-1200 ℃, and the stepping period of the steel billet in the high-temperature diffusion heating process is 2-3 min.
Further, in the rolling and cooling process, the steel blank sequentially passes through a primary rolling unit, first water through cooling, a middle rolling unit, second water through cooling, a finishing mill and third water through cooling.
Further, the rolling and cooling process is sequentially provided with a primary rolling unit consisting of 16 rolling mills, a first water-through cooling device consisting of a 1# water tank and a 2# water tank, a middle rolling unit consisting of 4 rolling mills, a second water-through cooling device consisting of a 3# water tank, a KOCKS finishing mill, and a third water-through cooling device consisting of a 4# water tank and a 5# water tank; the distance from the 16 th rolling mill of the initial rolling unit to the 1# water tank is 2.8m, the distance from the 1# water tank to the 2# water tank is 4m, the distance from the 2# water tank to the 17 th rolling mill of the intermediate rolling unit is 9.2m, the distance from the 20 th rolling mill of the intermediate rolling unit to the 3# water tank is 2m, the distance from the 3# water tank to the KOCKS finishing mill is 19.2m, the distance from the KOCKS finishing mill to the 4# water tank is 4.2m, and the distance from the 4# water tank to the 5# water tank is 2.8 m.
Further, the lengths of the No. 1 water tank, the No. 2 water tank, the No. 3 water tank, the No. 4 water tank and the No. 5 water tank are all 5m, and the maximum flow rates of the water tanks are all 320m3And h, the rolling speed in the rolling and cooling process is 1.0-13 m/s.
Further, the initial rolling temperature of the initial rolling unit is 1120 ℃; the water outlet pressure of the No. 1 water tank is 2bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 1 water tank is 950 ℃; the outlet water pressure of the No. 2 water tank is 1bar, the air pressure is 1bar, and the temperature of the steel billet outlet No. 2 water tank is 850 ℃; the water outlet pressure of the No. 3 water tank is 1bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 3 water tank is 830 ℃; the finishing temperature of the finishing mill is 700-800 ℃; the water outlet pressure of the No. 4 water tank is 2bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 4 water tank is 800 ℃; the water outlet pressure of the No. 5 water tank is 1bar, the air pressure is 1bar, and the temperature of the No. 5 water tank from the steel billet is 630-680 ℃.
The invention has the beneficial effects that:
according to the invention, low superheat degree casting is adopted, the carbon segregation of the continuous casting billet is controlled by controlling a continuous casting process, a good preparation structure with a low-power carbon segregation index of 0.95-1.05 is provided for a rolled material, and the small continuous casting segregation is beneficial to carbide control. The invention adopts a high-temperature diffusion process, the total heating time is not less than 390min, the temperature of the core part of the billet and the temperature of the surface tend to be consistent, the carbide diffusion is facilitated, and the carbide diffusion is reduced. According to the invention, the cooling speed of the steel billet is controlled by a three-section water-through cooling process, the temperature of the finish rolling pass is controlled within the range of 700-800 ℃, so that a large amount of carbide is prevented from being precipitated, and then the finally rolled steel is subjected to water cooling by utilizing the third water-through cooling, so that the finally rolled steel rapidly passes through the temperature range of 500-700 ℃, the precipitation of the carbide is strongly inhibited, the proportion of cementite in pearlite is increased, and the grade of the reticular carbide is reduced.
Compared with the special quality level of the existing high-carbon chromium bearing steel, the bearing steel hot-rolled round steel for rolling bodies obtained by controlling the net-shaped carbide by adopting the control method provided by the invention has the advantages that the purity is higher, the carbide is more uniform, the net shape of the central carbide is less than or equal to 5.3, the net shape of the carbide at 1/2R is less than or equal to 5.1, the carbide liquation is 0 grade, the low-power density is uniform, the depth of a chilling layer is 5mm, and the center and the chilling layer are both fine lamellar pearlite structures.
Drawings
FIG. 1 is a macroscopic photograph of a cross-sectional structure of hot-rolled round steel for a bearing steel for rolling bodies prepared in example 1;
FIG. 2 is a macroscopic photograph of a cross-sectional structure of hot-rolled round steel for a bearing steel for rolling bodies prepared in example 3;
FIG. 3 is a photograph of a metallographic microscope showing examination of nonmetallic inclusions in hot-rolled round steel of bearing steel for rolling bodies prepared in example 1 at a magnification of 100 times;
FIG. 4 is a photograph of a metallographic microscope showing examination of nonmetallic inclusions in hot-rolled round steel of bearing steel for rolling bodies prepared in example 1 at a magnification of 100 times;
FIG. 5 is a bright field image, which is acquired under a metallographic microscope, of 500 times magnified reticular carbides at the most severe central part of the hot-rolled round steel of the bearing steel for rolling bodies prepared in example 1;
FIG. 6 is a bright field image, which is acquired under a metallographic microscope, of the band-shaped carbide at the most serious central part of the hot-rolled round steel of the bearing steel for rolling bodies prepared in example 1, and which is magnified by 100 times;
FIG. 7 is a bright field image of carbides amplified by 100 times after spheroidizing annealing of a bearing steel hot-rolled round steel sample for rolling bodies prepared in example 1;
FIG. 8 is a bright field image of a pearlite structure at the center of hot rolled round steel of bearing steel for rolling bodies prepared in example 1, which is collected under a metallographic microscope;
FIG. 9 is a bright field image of a chill layer pearlite structure of hot-rolled round steel of bearing steel for rolling bodies prepared in example 1, which is acquired under a metallographic microscope;
fig. 10 is a schematic view showing the hardness test positions of hot-rolled round steel for bearing steel for rolling bodies prepared in example 1.
Detailed Description
The technical solutions of the present invention are further described below with reference to the following examples, but the present invention is not limited thereto, and any modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Example 1
The embodiment provides a control method of a net carbide of hot-rolled bearing steel, which comprises the following specific steps:
(1) casting with low superheat degree and controlling a continuous casting process:
the continuous casting blank type adopted by the low superheat degree casting is a square blank of 250mm multiplied by 280mm, and the liquidus temperature is 1454 ℃; controlling the degree of superheat to be 25-35 ℃; the blank drawing speed in the continuous casting process is 0.50 m/min; the secondary cooling specific water amount is 0.18; the distribution ratio of the secondary cooling water is 38/38/24; the water quantity of the crystallizer is 2450L/min; the electromagnetic stirring parameters are M-EMS: 500A/2 Hz; F-EMS: 400A/18 Hz.
The withdrawal speed in the continuous casting process is an important factor influencing the growth of columnar crystals, and the withdrawal speed is controlled to be 0.50m/min in the embodiment, so that the component segregation can be reduced.
The secondary cooling technology has important influence on the surface quality and the internal quality of a casting blank, the formation of center segregation and shrinkage porosity is closely connected with the secondary cooling technology, if the secondary cooling strength is not enough, the surface temperature of the casting blank is higher, the liquid core of the casting blank is lengthened, the bulging deformation capability of a blank shell caused by hydrostatic pressure of molten steel is weakened, the formation and the development of the center segregation and the shrinkage porosity are promoted, in the actual production, the sufficient cooling strength is ensured, and the cooling water distribution is reasonable. The secondary cooling technology adopted by the embodiment can reduce the formation and development of center segregation and shrinkage porosity.
The electromagnetic stirring technology breaks the columnar crystal by stirring the molten steel, and then the columnar crystal is mixed with the molten steel to be used as the core of the isometric crystal; on the other hand, the flow of molten steel is increased, the heat transfer between solidification phases is improved, the superheat degree is favorably reduced, the temperature gradient of the solidification front is reduced, the directional enlargement of columnar crystals is inhibited, and the formation of isometric crystals is promoted. Meanwhile, the change of the temperature field causes the change of the solidification rate, and when the electromagnetic field is applied, the solidification rate is small at the beginning stage and is large at the end stage of solidification.
In the embodiment, the crystallizer electromagnetic stirring and tail end electromagnetic stirring processes are adopted, the segregation of the continuous casting billet is controlled, and a good preparation structure is provided for a rolled material. The ratio of the mean value of the carbon contents of the two central points to the mean value of the carbon contents of the four points with the half radius is adopted to calculate the low-power carbon segregation of the continuous casting billet, and the result is shown in the table 1:
TABLE 1
| Inspection position | Center-1 | Center-2 | 1/2R-2 | 1/2R-3 | 1/2R-4 | 1/2R-5 | Mean of centers | Mean value of radius | Index of segregation |
| Heat 1 | 0.99 | 1 | 0.99 | 1.02 | 1.02 | 1.02 | 1.0 | 1.01 | 0.98 |
As can be seen from Table 1, the low-power carbon segregation index of the continuous casting slab is 0.98, the carbon segregation of the continuous casting slab is small, and carbide control in a subsequent treatment process is facilitated.
(2) Controlling a high-temperature diffusion heating process:
the heating temperature of the high-temperature diffusion heating process is divided into four stages of a preheating stage, a heating 1 stage, a heating 2 stage and a soaking stage in sequence, and the total heating time is not less than 390 min.
Wherein the heating temperature of the preheating section is 800 ℃, and the heating time of the preheating section is 75 min;
the heating temperature of the heating 1 section is 1120 ℃, and the heating time of the heating 1 section is 100 min;
the heating temperature of the heating 2 section is 1220 ℃, and the heating time of the heating 2 section is 110 min;
the heating temperature of the soaking section is 1220 ℃, and the heating time of the soaking section is 115 min.
In the high-temperature diffusion heating process in the embodiment, the billet stepping period is 2-3 min, and the tapping temperature of the billet is 1200 ℃.
Uneven carbides formed in the steel blank in the steel-making and casting process can be relieved or eliminated by heating and high-temperature diffusion in the rolling process. The main influencing factors of high-temperature diffusion are heating temperature and heat preservation time, and generally, the higher the heating temperature is, the longer the heat preservation time is, the better the high-temperature diffusion effect is. However, the prolonged heating time will result in the reduction of production efficiency, and the too high heating temperature is liable to cause equipment or quality accidents. Therefore, the determination of reasonable heating temperature and holding time is a necessary condition for ensuring the sufficient diffusion of carbide. The total heating time of the high-temperature diffusion heating process set in the embodiment exceeds 390 minutes, so that the temperature of the core part of the billet and the temperature of the surface of the billet tend to be consistent, the diffusion distribution of carbide is facilitated, the carbide segregation is reduced, and meanwhile, a good low-power effect can be obtained. The macroscopic structure of the whole section of the material is fine and uniform, a chilling layer with the depth of about 5mm exists at the edge of the sample, the center is loose by 0.5 level, the loose is generally 0 level, and the ingot type segregation is generally 0 level.
(3) Controlling the rolling and cooling process:
in the embodiment, three-section water cooling process is adopted to control cooling, and the temperature of the finally rolled steel is rapidly reduced to 630-680 ℃ by using water cooling.
The controlled rolling is a new rolling process which combines thermoplastic deformation and solid phase transformation to obtain fine grain structures by reasonably controlling a metal heating mechanism, a deformation mechanism and a temperature system in the hot rolling process so that the steel has excellent comprehensive mechanical properties. For low carbon steel and low alloy steel, the controlled rolling process is mainly adopted to refine and deform austenite grains by controlling the rolling process parameters, and refined ferrite grains and smaller pearlite pellets are formed through the phase change from austenite to ferrite and pearlite, so that the aims of improving the strength, toughness and welding performance of the steel are fulfilled.
The controlled cooling is to control the cooling speed of the rolled steel to achieve the purpose of improving the structure and the performance of the steel. Due to the action of hot rolling deformation, the transformation temperature of deformed austenite to ferrite is promoted to be increased, ferrite grains after phase transformation are easy to grow up, and the mechanical property is reduced. The controlled cooling process is used in order to refine ferrite grains, reduce pearlite interlamellar spacing, and prevent carbide precipitation at high temperatures to enhance precipitation strengthening effects.
In the rolling and cooling process, the steel billet in the embodiment sequentially passes through a primary rolling unit, a first water-through cooling unit, a middle rolling unit, a second water-through cooling unit, a KOCKS finishing mill and a third water-through cooling unit at the rolling speed of 8 m/s. The number of continuous rolling units of the rolling process of the embodiment is 20, wherein the number of the initial rolling unit is 16, and the number of the middle rolling unit is 4; the first time water-through cooling passes through 1# water tank and 2# water tank in proper order, and the second time water-through cooling passes through 3# water tank, and the third time water-through cooling passes through 4# water tank and 5# water tank in proper order.
In this embodiment, the lengths of the five water tanks are 5m, the distance from the 16 th rolling mill of the blooming train to the 1# water tank is 2.8m, the distance from the 1# water tank to the 2# water tank is 4m, the distance from the 2# water tank to the 17 th rolling mill of the intermediate rolling train is 9.2m, the distance from the 20 th rolling mill of the intermediate rolling train to the 3# water tank is 2m, the distance from the 3# water tank to the KOCKS finishing mill is 19.2m, the distance from the KOCKS finishing mill to the 4# water tank is 4.2m, and the distance from the 4# water tank to the 5# water tank is 2.8 m.
In this embodiment, the maximum flow rates of the water tanks are all 320m3H is used as the reference value. The initial rolling temperature of the initial rolling unit is 1120 ℃; the water outlet pressure of the No. 1 water tank is 2bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 1 water tank is 950 ℃; the outlet water pressure of the No. 2 water tank is 1bar, the air pressure is 1bar, and the temperature of the steel billet outlet No. 2 water tank is 850 ℃; the water outlet pressure of the No. 3 water tank is 1bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 3 water tank is 830 ℃; the finishing temperature of the KOCKS finishing mill is 700-800 ℃; the water outlet pressure of the No. 4 water tank is 2bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 4 water tank is 800 ℃; the water outlet pressure of the No. 5 water tank is 1bar, the air pressure is 1bar, and the temperature of the No. 5 water tank from the steel billet is 630-680 ℃.
The distance from the 3# water tank to the KOCKS finishing mill can ensure that the steel billet has enough time for temperature equalization and re-reddening before entering a finish rolling pass, and the temperature of the finish rolling pass during the hot rolling of the steel billet is controlled within the range of 700-800 ℃ so as to avoid the precipitation of a large amount of carbides. And (3) carrying out water cooling on the finally rolled steel by utilizing third water cooling, so that the finally rolled steel rapidly passes through the temperature range of 500-700 ℃, the precipitation of carbide is strongly inhibited, and the proportion of cementite in pearlite is increased.
The embodiment combines the controlled rolling and the controlled cooling process, so that two strengthening effects of the hot rolled steel are added, the strength and toughness of the steel are further improved, and reasonable comprehensive mechanical properties are obtained. Meanwhile, the cooling speed is controlled in the rolling process, the carbide precipitation is controlled, the size and the distribution state of the carbide are improved, and the level of the net-shaped carbide is reduced.
Example 2
This example provides bearing steel hot-rolled round steel for rolling stock prepared by controlling the network carbide by the method for controlling the network carbide of hot-rolled bearing steel provided in example 1.
(1) The chemical composition of the hot rolled round steel for bearing steel in this example is shown in table 2:
TABLE 2
| Furnace number | C％ | Si％ | Mn％ | P％ | S％ | Ni％ | Cr％ | Ca％ | Mo％ |
| 1# | 0.97 | 0.27 | 0.42 | 0.014 | 0.002 | 0.05 | 1.54 | 0.0003 | 0.02 |
| Cu％ | Al％ | Ti％ | As％ | Sn％ | Pb％ | Bi％ | Hydrogen ppm | Oxygen ppm | Nitrogen ppm |
| 0.08 | 0.017 | 0.0008 | 0.005 | 0.006 | 0.001 | 0.001 | —— | —— | —— |
(2) In the embodiment, a macroscopic structure photomicrograph of the cross section of the bearing steel hot-rolled round steel is shown in fig. 1, the macroscopic structure of the whole cross section of the material is fine and uniform, a chilling layer with the depth of about 5mm exists at the edge, the center is loose by 0.5 level, the center is loose by 0 level, and the ingot type segregation is 0 level.
(3) The results of examination of nonmetallic inclusions in the hot-rolled round steel for bearing steel of this example are shown in Table 3, and photographs of examination of nonmetallic inclusions at a magnification of 100 times under a metallographic microscope are shown in FIGS. 3 and 4:
TABLE 3
As can be seen from table 3, fig. 3 and fig. 4, the non-metallic inclusions of the hot rolled round steel of bearing steel prepared by controlling the network carbide according to the control method provided by this embodiment are small in size, and the steel material has high purity, so that the tensile strength, the blank strength and other properties of the steel material can be further improved.
(4) The grades of the net-shaped carbide and the strip-shaped carbide at the center and 1/2R positions of the bearing steel hot-rolled round steel in the embodiment are checked according to GB/T18254-2016 standard and SEP1520 standard, and figures 5 and 6 are respectively bright field images which are acquired under a metallographic microscope and are magnified by 500 times of the most serious net-shaped carbide and strip-shaped carbide at the center of the bearing steel hot-rolled round steel for the rolling body provided by the embodiment; selecting 1 sample, carrying out spheroidizing annealing, and then inspecting the decarburization condition of the carbide, wherein FIG. 7 is a bright field image of the carbide amplified by 100 times after the spheroidizing annealing of the bearing steel hot-rolled round steel sample for the rolling body in the embodiment;
the results are shown in Table 4:
TABLE 4
| Heart net | 1/2R net | Heart belt | 1/2R belt | Liquid chromatography | Decarburization of carbon |
| 2/5.3 | 1/5.1 | 1.5/7.2 | 1/7.0 | 0 | 0.1 |
As can be seen from Table 4, the hot rolled round steel for bearing steel provided in this example had a net shape of carbide at the center of 5.3 or less, a net shape of carbide at 1/2R of 5.1 or less, a band shape of carbide at the center of 7.2 or less, a band shape of carbide at 1/2R of 7.0 or less, a carbide liquation of 0 grade, and decarburization of 0.1.
(5) The center and the chilled layer of the low-power test sample of the hot-rolled round steel of the bearing steel in the embodiment are inspected, and as shown in fig. 8 and 9, the center and the chilled layer of the hot-rolled round steel of the bearing steel are both fine lamellar pearlite structures, so that the use requirement of the rolling body of the bearing steel can be completely met.
(6) The hardness of the hot-rolled round steel of the bearing steel in this embodiment was tested according to the testing positions shown in fig. 10, and the hardness of the 5 testing positions were 32.7HRC, 35.1HRC, 33.3HRC, 33.5HRC and 34.8HRC, respectively, which indicates that the round steel of the bearing steel in this embodiment has uniform hardness, extremely poor hardness of 2.4HRC, good toughness and good comprehensive mechanical properties.
Example 3
The embodiment provides a control method of a net carbide of hot-rolled bearing steel, which comprises the following specific steps:
(1) casting with low superheat degree and controlling a continuous casting process:
the continuous casting blank type adopted by the low superheat degree casting is a square blank of 250mm multiplied by 280mm, and the liquidus temperature is 1454 ℃; controlling the degree of superheat to be 25-35 ℃; the blank drawing speed in the continuous casting process is 0.62 m/min; the secondary cooling specific water amount is 0.18; the distribution ratio of the secondary cooling water is 38/38/24; the water quantity of the crystallizer is 2450L/min; the electromagnetic stirring parameters are M-EMS: 500A/2 Hz; F-EMS: 400A/18 Hz.
The withdrawal speed in the continuous casting process is an important factor influencing the growth of columnar crystals, and the withdrawal speed is controlled to be 0.62m/min in the embodiment, so that the component segregation can be reduced.
The ratio of the mean carbon content of the two points at the center to the mean carbon content of the four points at half radius is adopted to calculate the low-power carbon segregation of the continuous casting billet, and the result is shown in table 5:
TABLE 5
| Inspection position | Center-1 | Center-2 | 1/2R-2 | 1/2R-3 | 1/2R-4 | 1/2R-5 | Mean of centers | Mean value of radius | Index of segregation |
| Heat 1 | 1.01 | 0.99 | 1.00 | 1.02 | 1.03 | 1.00 | 1.0 | 1.01 | 0.99 |
As can be seen from Table 5, the low-power carbon segregation index of the continuous casting slab is 0.99, and the carbon segregation of the continuous casting slab is small, so that the control of carbides in the subsequent treatment process is facilitated.
(2) Controlling a high-temperature diffusion heating process:
the heating temperature of the high-temperature diffusion heating process is divided into four stages of a preheating stage, a heating 1 stage, a heating 2 stage and a soaking stage in sequence, and the total heating time is 460 min.
Wherein the heating temperature of the preheating section is 750 ℃, and the heating time of the preheating section is 90 min;
the heating temperature of the heating section 1 is 900 ℃, and the heating time of the heating section 1 is 115 min;
the heating temperature of the heating 2 section is 1200 ℃, and the heating time of the heating 2 section is 125 min;
the heating temperature of the soaking section is 1200 ℃, and the heating time of the soaking section is 130 min.
In the high-temperature diffusion heating process in the embodiment, the billet stepping period is 2-3 min, and the tapping temperature of the billet is 1200 ℃.
(3) Controlling the rolling and cooling process:
in the embodiment, the cooling is controlled by adopting a three-section water-through cooling process, so that the temperature of the re-reddening of the cooled steel billet is lower than 730 ℃.
In the rolling and cooling process, the steel billet sequentially passes through a primary rolling unit, a first water-through cooling unit, a middle rolling unit, a second water-through cooling unit, a finishing mill and a third water-through cooling unit at a rolling speed of 5 m/s. The number of continuous rolling units of the rolling process of the embodiment is 20, wherein the number of the initial rolling unit is 16, and the number of the middle rolling unit is 4; the first time water-through cooling passes through 1# water tank and 2# water tank in proper order, and the second time water-through cooling passes through 3# water tank, and the third time water-through cooling passes through 4# water tank and 5# water tank in proper order.
In this embodiment, the lengths of the five water tanks are 5m, the distance from the 16 th rolling mill of the blooming train to the 1# water tank is 2.8m, the distance from the 1# water tank to the 2# water tank is 4m, the distance from the 2# water tank to the 17 th rolling mill of the intermediate rolling train is 9.2m, the distance from the 20 th rolling mill of the intermediate rolling train to the 3# water tank is 2m, the distance from the 3# water tank to the KOCKS finishing mill is 19.2m, the distance from the KOCKS finishing mill to the 4# water tank is 4.2m, and the distance from the 4# water tank to the 5# water tank is 2.8 m.
In this embodiment, the maximum flow rates of the water tanks are all 320m3H is used as the reference value. The initial rolling temperature of the initial rolling unit is 1120 ℃; the water outlet pressure of the No. 1 water tank is 2bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 1 water tank is 950 ℃; the outlet water pressure of the No. 2 water tank is 1bar, the air pressure is 1bar, and the temperature of the steel billet outlet No. 2 water tank is 850 ℃; the water outlet pressure of the No. 3 water tank is 1bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 3 water tank is 830 ℃; the finishing temperature of the KOCKS finishing mill is 700-800 ℃; the water outlet pressure of the No. 4 water tank is 2bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 4 water tank is 800 ℃; the water outlet pressure of the No. 5 water tank is 1bar, the air pressure is 1bar, and the temperature of the No. 5 water tank from the steel billet is 630-680 ℃.
The distance from the 3# water tank to the KOCKS finishing mill can ensure that the steel billet has enough time for temperature equalization and re-reddening before entering a finish rolling pass, and the temperature of the finish rolling pass during the hot rolling of the steel billet is controlled within the range of 700-800 ℃ so as to avoid the precipitation of a large amount of carbides. And (3) carrying out water cooling on the finally rolled steel by utilizing third water cooling, so that the finally rolled steel rapidly passes through the temperature range of 500-700 ℃, the precipitation of carbide is strongly inhibited, and the proportion of cementite in pearlite is increased.
Example 4
This example provides bearing steel hot-rolled round steel for rolling bodies prepared by controlling the network carbide by the method for controlling network carbide of hot-rolled bearing steel provided in example 3.
(1) The chemical composition of the hot rolled round steel for bearing steel in this example is shown in table 6:
TABLE 6
| Furnace number | C％ | Si％ | Mn％ | P％ | S％ | Ni％ | Cr％ | Ca％ | Mo％ |
| 1# | 0.96 | 0.28 | 0.42 | 0.017 | 0.002 | 0.05 | 1.53 | 0.0004 | 0.02 |
| Cu％ | Al％ | Ti％ | As％ | Sn％ | Pb％ | Bi％ | Hydrogen ppm | Oxygen ppm | Nitrogen ppm |
| 0.08 | 0.017 | 0.0010 | 0.006 | 0.006 | 0.001 | 0.001 | 0.6 | 5.4 | 46 |
(2) In the embodiment, a macroscopic structure photomicrograph of the cross section of the bearing steel hot-rolled round steel is shown in fig. 2, the macroscopic structure of the whole cross section of the material is fine and uniform, a chilling layer with the depth of about 5mm exists at the edge, the center is loose by 0.5 level, the center is loose by 0 level, and the ingot type segregation is 0 level.
(3) The grades of the net carbides and the ribbon carbides at the center and 1/2R positions of the hot rolled round steel of the bearing steel in the embodiment were examined according to GB/T18254 standard and SEP1520 standard, and 1 sample was selected for spheroidizing annealing, and then the decarburization of the carbides was examined, and the results are shown in Table 7:
TABLE 7
| Heart net | 1/2R net | Heart belt | 1/2R belt | Liquid chromatography | Decarburization of carbon |
| 2/5.3 | 1/5.1 | 1.5/7.2 | 1/7.0 | 0 | 0.1 |
As can be seen from Table 4, the hot rolled round steel for bearing steel provided in this example had a net shape of carbide at the center of 5.3 or less, a net shape of carbide at 1/2R of 5.1 or less, a band shape of carbide at the center of 7.2 or less, a band shape of carbide at 1/2R of 7.0 or less, a carbide liquation of 0 grade, and decarburization of 0.1.
Claims (2)
1. A control method of hot rolling bearing steel network carbide is characterized in that firstly, casting with low superheat degree is adopted, and the blank drawing speed in the continuous casting process is controlled to be 0.50m/min, and the specific water amount in secondary cooling parameters is 0.18; the distribution ratio of the secondary cooling water is 38/38/24; the water quantity of the crystallizer is 2450L/min; the electromagnetic stirring parameters are M-EMS: 500A/2 Hz; F-EMS: 400A/18Hz, and obtaining a preparation structure with a low power carbon segregation index of 0.98;
further improving the carbide distribution by controlling the heating temperature and the heating time of the high-temperature diffusion heating process; the heating temperature of the high-temperature diffusion heating process is divided into four stages of a preheating stage, a heating 1 stage, a heating 2 stage and a soaking stage in sequence, wherein the heating temperature of the preheating stage is 800 ℃, and the heating time of the preheating stage is 75 min; the heating temperature of the heating 1 section is 1120 ℃, and the heating time of the heating 1 section is 100 min; the heating temperature of the heating 2 section is 1220 ℃, and the heating time of the heating 2 section is 110 min; the heating temperature of the soaking section is 1220 ℃, and the heating time of the soaking section is 115 min; the step period of the steel billet in the high-temperature diffusion heating process is 2-3 min, and the tapping temperature of the steel billet is 1200 ℃ after the high-temperature diffusion heating process is finished;
finally, in the rolling and cooling process, a three-section water-through cooling process is adopted to control the cooling speed of the steel billet, the temperature of the steel billet in the finish rolling pass is controlled within the range of 700-800 ℃, and then the temperature of the finally rolled steel is reduced to 630-680 ℃ by water-through cooling; in the rolling and cooling process, the steel blank sequentially passes through a primary rolling unit, a first water-through cooling unit, a middle rolling unit, a second water-through cooling unit, a finishing mill and a third water-through cooling unit;
the rolling and cooling process is sequentially provided with a primary rolling unit consisting of 16 rolling mills, a first water-through cooling device consisting of a 1# water tank and a 2# water tank, a middle rolling unit consisting of 4 rolling mills, a second water-through cooling device consisting of a 3# water tank, a KOCKS finishing mill, a third water-through cooling device consisting of a 4# water tank and a 5# water tank; the distance from the 16 th rolling mill of the initial rolling unit to the 1# water tank is 2.8m, the distance from the 1# water tank to the 2# water tank is 4m, the distance from the 2# water tank to the 17 th rolling mill of the intermediate rolling unit is 9.2m, the distance from the 20 th rolling mill of the intermediate rolling unit to the 3# water tank is 2m, the distance from the 3# water tank to the KOCKS finishing mill is 19.2m, the distance from the KOCKS finishing mill to the 4# water tank is 4.2m, and the distance from the 4# water tank to the 5# water tank is 2.8 m;
the length of 1# water tank, 2# water tank, 3# water tank, 4# water tank and 5# water tank is 5m, and the maximum flow of water tank is 320m3H, the rolling speed in the rolling and cooling process is 8 m/s;
the initial rolling temperature of the initial rolling unit is 1120 ℃; the water outlet pressure of the No. 1 water tank is 2bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 1 water tank is 950 ℃; the outlet water pressure of the No. 2 water tank is 1bar, the air pressure is 1bar, and the temperature of the steel billet outlet No. 2 water tank is 850 ℃; the water outlet pressure of the No. 3 water tank is 1bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 3 water tank is 830 ℃; the finishing temperature of the finishing mill is 700-800 ℃; the water outlet pressure of the No. 4 water tank is 2bar, the air pressure is 1bar, and the temperature of the steel billet discharged from the No. 4 water tank is 800 ℃; the water outlet pressure of the No. 5 water tank is 1bar, the air pressure is 1bar, and the temperature of the No. 5 water tank from the steel billet is 630-680 ℃.
2. The method for controlling the net-like carbide of the hot rolled bearing steel as claimed in claim 1, wherein the low superheat degree casting uses a continuous casting billet with a 250mm x 280mm square billet and a liquidus temperature of 1454 ℃; the degree of superheat is controlled to be 25-35 ℃.
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| CN112536321B (en) * | 2020-11-23 | 2023-03-14 | 山东钢铁股份有限公司 | Cold control method for small-specification bearing steel |
| CN112916611B (en) * | 2020-12-29 | 2022-03-25 | 南京工程学院 | Hot rolling process for improving ingot segregation form of large-section hot-rolled round steel |
| CN113084110B (en) * | 2021-03-04 | 2022-07-12 | 天津荣程联合钢铁集团有限公司 | Method for reducing carbon segregation of alloy steel |
| CN113088639B (en) * | 2021-03-30 | 2023-05-23 | 江西红睿马钢管股份有限公司 | Bearing steel pipe inspection quality control method for cold rolling and expanding bearing |
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