CN116287592A - Heat treatment method for high-carbon steel wire rod - Google Patents
Heat treatment method for high-carbon steel wire rod Download PDFInfo
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- 229910000677 High-carbon steel Inorganic materials 0.000 title claims abstract description 129
- 238000010438 heat treatment Methods 0.000 title claims abstract description 107
- 238000000034 method Methods 0.000 title claims abstract description 56
- 150000003839 salts Chemical class 0.000 claims abstract description 106
- 238000010791 quenching Methods 0.000 claims abstract description 37
- 230000000171 quenching effect Effects 0.000 claims abstract description 37
- 230000009466 transformation Effects 0.000 claims abstract description 20
- 230000007704 transition Effects 0.000 claims abstract description 18
- 230000008569 process Effects 0.000 claims abstract description 17
- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Chemical compound [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 claims description 38
- 238000005422 blasting Methods 0.000 claims description 27
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 claims description 20
- 235000010333 potassium nitrate Nutrition 0.000 claims description 19
- 239000004323 potassium nitrate Substances 0.000 claims description 19
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 15
- 229910000831 Steel Inorganic materials 0.000 claims description 15
- 229910052799 carbon Inorganic materials 0.000 claims description 15
- 239000010959 steel Substances 0.000 claims description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 13
- 235000010344 sodium nitrate Nutrition 0.000 claims description 10
- 239000004317 sodium nitrate Substances 0.000 claims description 10
- 230000005855 radiation Effects 0.000 claims description 2
- 239000002245 particle Substances 0.000 claims 1
- 229910001563 bainite Inorganic materials 0.000 abstract description 12
- 229910001566 austenite Inorganic materials 0.000 abstract description 9
- 229910001562 pearlite Inorganic materials 0.000 abstract description 9
- 229910000734 martensite Inorganic materials 0.000 abstract description 7
- 238000004781 supercooling Methods 0.000 abstract description 6
- 239000002344 surface layer Substances 0.000 abstract description 6
- 238000011534 incubation Methods 0.000 abstract description 5
- 238000009792 diffusion process Methods 0.000 abstract description 4
- 230000015572 biosynthetic process Effects 0.000 abstract description 3
- 230000002035 prolonged effect Effects 0.000 abstract description 3
- 230000000052 comparative effect Effects 0.000 description 29
- 229910001335 Galvanized steel Inorganic materials 0.000 description 25
- 239000008397 galvanized steel Substances 0.000 description 25
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 18
- 238000001816 cooling Methods 0.000 description 13
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 12
- 230000008859 change Effects 0.000 description 12
- 239000010410 layer Substances 0.000 description 8
- 238000012797 qualification Methods 0.000 description 8
- 230000003746 surface roughness Effects 0.000 description 8
- FBPFZTCFMRRESA-JGWLITMVSA-N D-glucitol Chemical compound OC[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO FBPFZTCFMRRESA-JGWLITMVSA-N 0.000 description 7
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- 239000007789 gas Substances 0.000 description 6
- 229910052757 nitrogen Inorganic materials 0.000 description 6
- 238000004321 preservation Methods 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 238000005261 decarburization Methods 0.000 description 3
- 238000001514 detection method Methods 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 230000018109 developmental process Effects 0.000 description 3
- 238000001000 micrograph Methods 0.000 description 3
- 238000005096 rolling process Methods 0.000 description 3
- 230000032683 aging Effects 0.000 description 2
- 239000003153 chemical reaction reagent Substances 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000006911 nucleation Effects 0.000 description 2
- 238000010899 nucleation Methods 0.000 description 2
- LPXPTNMVRIOKMN-UHFFFAOYSA-M sodium nitrite Chemical compound [Na+].[O-]N=O LPXPTNMVRIOKMN-UHFFFAOYSA-M 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 238000004804 winding Methods 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 230000003749 cleanliness Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000005501 phase interface Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000012266 salt solution Substances 0.000 description 1
- 235000010288 sodium nitrite Nutrition 0.000 description 1
- 238000010025 steaming Methods 0.000 description 1
- 230000035882 stress Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
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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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/34—Methods of heating
- C21D1/44—Methods of heating in heat-treatment baths
- C21D1/46—Salt baths
-
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
- C21D1/20—Isothermal quenching, e.g. bainitic hardening
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Crystallography & Structural Chemistry (AREA)
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Abstract
The invention discloses a heat treatment method of a high-carbon steel wire rod, which comprises the following steps: the austenitized high-carbon steel wire rod is subjected to a heat treatment process of quenching and isothermal phase transformation in a salt bath in sequence; the quenching temperature is 400-450 ℃, and the quenching time is 10-20s; the isothermal phase transition temperature is 550-590 ℃, and the isothermal phase transition time is 3-5min. In the heat treatment method, quenching is firstly carried out to cool the high-carbon steel wire rod to 400-450 ℃ so as to quickly reach deep supercooling, and the supercooling mode is adopted, so that the atomic diffusion capacity is reduced at low temperature, the phase transformation incubation period is prolonged, and when the temperature is kept for 10-20 seconds, supercooled austenite is still in the phase transformation incubation period, the supercooled austenite cannot undergo low-temperature phase transformation, the formation of bainite is avoided, the section structure of the high-carbon steel wire rod obtained by the heat treatment method is uniform, no low-temperature bainite and martensite structures are formed, and both the surface layer and the core structure are pearlite.
Description
Technical Field
The invention relates to the technical field of material heat treatment, in particular to a heat treatment method of a high-carbon steel wire rod.
Background
In recent years, along with the demands of economic development in China, the number of super-span suspension bridges is rapidly increased on the steaming day of traffic infrastructure. With the increase of span and lane number, the main cable steel wire of the suspension bridge at home and abroad is in the ultra-high strength development stage, the tensile strength of the steel wire is continuously improved to become the development trend of bridge cables, and the strength and the tissue uniformity of the raw material wire rods corresponding to the steel wire are also required to be greatly improved.
The existing high-speed wire rod rolling and stelmor air cooling technology is used for cooling the air-cooled wire rod, the sorbite rate is not high, and the wire rod is not uniform in tissue performance due to the fact that a joint point exists when the wire rod is cooled, and on the other hand, the air-cooled wire rod is limited in cooling capacity, so that the strength of the wire rod is hardly improved greatly. Therefore, in order to further improve the strength and the tissue uniformity of the wire rod, the wire rod needs to be processed by adopting a post-rolling heat treatment mode without changing the existing production line.
The salt bath is one of the prior heat treatment modes after wire rod rolling, and when the high-strength cable steel wire rod is subjected to the salt bath heat treatment, the wire rod is often austenitized and then subjected to isothermal transformation at a lower temperature so as to refine pearlite sheets and improve the strength of the wire rod. However, most heat treatment salts are nitrate salts, which are composed of two or three of potassium nitrate, sodium nitrate and sodium nitrite, have low heat exchange efficiency with wire rods and insufficient cooling capacity, but in order to control the actual phase transition temperature, the salt temperature is lower than the actual phase transition temperature by more than 60 ℃, the fluidity change of molten salt can be caused, the convective heat exchange efficiency is affected, meanwhile, the effective phase transition section is too short, incomplete phase transition of the wire rods is easily caused, residual austenite is converted into a low-temperature bainite or martensite structure after the wire rods are discharged from a salt tank, the plasticity of the wire rods is reduced by the bainite and the martensite, stress concentration is easily generated at a tissue phase interface due to different tissue deformability, the generation probability of the inside of the material is increased, the drawing fracture is caused, the wire breakage rate in the drawing process is increased, and the torsion performance of the steel wires is reduced. Patent CN110205473a discloses a heat treatment method for improving the uniformity of the wire rod structure for ultra-high strength cables, which adopts three-stage isothermal salt bath heat treatment, firstly carries out salt bath heat treatment at 470-500 ℃, then raises the temperature to 510-540 ℃ and ensures that the retained austenite is converted into pearlite. However, the cooling capacity of the salt bath is limited, the production requirements of the wire rod with the carbon content of more than 0.95 percent and the specification of more than 14mm on high strength and high toughness cannot be met, the application is limited, and more bainite tissues still exist in the wire rod after heat treatment.
Disclosure of Invention
Therefore, the technical problem to be solved by the invention is to overcome the defects that the application is limited and low-temperature bainite and martensite structures are easy to form when the high-carbon steel wire rod for the high-strength cable steel is subjected to off-line heat treatment, so that the heat treatment method for the high-carbon steel wire rod is provided.
In order to achieve the above purpose, the present invention provides the following technical solutions:
a method of heat treating a high carbon steel wire rod, comprising: the austenitized high-carbon steel wire rod is subjected to a heat treatment process of quenching and isothermal phase transformation in a salt bath in sequence;
the quenching temperature is 400-450 ℃, and the quenching time is 10-20s;
the isothermal phase transition temperature is 550-590 ℃, and the isothermal phase transition time is 3-5min.
When the quenching temperature is 400-450 ℃, and the quenching time is more than 10s, the high-carbon steel wire rod and molten salt in salt bath can realize rapid heat exchange, so that the high-carbon steel wire rod is rapidly supercooled to a lower temperature, the atomic diffusion speed is reduced, the supercooled austenite is kept in a stable state in a short time, and the core and surface temperatures of the high-carbon steel wire rod tend to be consistent; when the quenching time is less than 20s, the high-carbon steel wire rod can be rapidly supercooled to a lower temperature, the core and the surface temperature tend to be consistent, and the supercooled austenite can be ensured to be continuously in the incubation period and not to undergo phase change due to the shorter time, so that the formation of low-temperature bainite can be avoided; when the high-carbon steel wire rod returns to the isothermal phase transition temperature from the low-temperature quenching temperature, the phase transition latent heat released in the phase transition process can be taken away rapidly due to the strong cooling capacity of the salt solution, the molten salt temperature is consistent with the actual phase transition temperature of the wire rod, and the high-carbon steel wire rod can undergo isothermal phase transition at a stable temperature. Meanwhile, the high-carbon steel wire rod enters an isothermal phase transformation area after exiting the quenching area, the driving force stored under deep supercooling can obviously improve isothermal transformation nucleation rate, the size of pearlite groups can be obviously thinned, the plasticity of the wire rod is greatly improved, the high-carbon steel wire rod is subjected to phase transformation at 550-590 ℃, small and uniform sorbite tissues of the sheet layers can be obtained, and the phase transformation time is set to 3-5min, so that the phase transformation can be fully carried out.
Preferably, the austenitized high carbon steel wire rod is also subjected to shot blasting treatment before austenitizing heating.
Preferably, in the shot blasting treatment step, the granularity of the adopted steel shot is 1.2-2.0mm, and the roughness Ra of the high-carbon steel wire rod after shot blasting is 6.3-8.0 mu m. Shot blasting is performed on the hot rolled wire rod, so as to remove a surface rust layer and an oxide skin. The shot blasting process mainly controls the surface cleanliness and roughness, and therefore, the granularity of the used steel shot is 1.2-2.0mm, and the surface roughness after shot blasting reaches 6.3-8.0 mu m. The scale is not removed cleanly or the surface roughness is larger, so that not only the fluidity of molten salt on the surface of the wire rod is poor, but also the heat conduction between the wire rod and the molten salt is poor, and the heat exchange strength is reduced.
Preferably, the process for obtaining the austenitized high carbon steel wire rod comprises the following steps: and heating the high-carbon steel wire rod by adopting heat radiation, wherein the heating temperature is 940-980 ℃, and the heating time is 6-10min.
Preferably, the austenitized high-carbon steel wire rod is obtained by heating in a reducing atmosphere, and the carbon potential in the furnace is more than or equal to 0.96%.
Preferably, the salt bath adopts a fused salt of potassium nitrate and sodium nitrate.
Preferably, the mass fraction of potassium nitrate in the molten salt is 40-60%.
Preferably, water is also added to the molten salt; the water accounts for 0.2-0.5% of the total mass of the water and the molten salt.
Preferably, the molten salt is immersed in the high carbon steel wire rod transmission area in a spring mode.
Preferably, the frequency of the spring is 38-42Hz, and the direction of the spring is opposite to the movement direction of the wire rod.
The technical scheme of the invention has the following advantages:
1. a method of heat treating a high carbon steel wire rod, comprising: the austenitized high-carbon steel wire rod is subjected to a heat treatment process of quenching and isothermal phase transformation in a salt bath in sequence; the quenching temperature is 400-450 ℃, and the quenching time is 10-20s; the isothermal phase transition temperature is 550-590 ℃, and the isothermal phase transition time is 3-5min. In the heat treatment method, quenching is firstly carried out to cool the high-carbon steel wire rod to 400-450 ℃ so as to quickly reach deep supercooling, and the supercooling mode is adopted, so that the atomic diffusion capacity is reduced at low temperature, the phase transformation incubation period is prolonged, and when the temperature is kept for 10-20 seconds, supercooled austenite is still in the phase transformation incubation period, the supercooled austenite cannot undergo low-temperature phase transformation, and the formation of bainite is avoided; and then carrying out isothermal phase transformation, wherein the quenching of the high-carbon steel wire rod in the first stage salt bath is completed, the core temperature tends to be consistent, and when the high-carbon steel wire rod enters the second stage salt bath for subsequent isothermal exchange, the influence on the molten salt temperature is extremely small, the isothermal phase transformation can be completed within the preset temperature of the molten salt, and the surface layer is consistent with the core temperature, so that the austenitic structure is converted into pearlite, and no bainite structure is generated on the surface layer. Meanwhile, as the high-carbon steel wire rod is subjected to a deep supercooling step, a large amount of driving force is stored, so that the nucleation rate in isothermal phase transition is improved, the size of pearlite clusters is thinned, and the plasticity of the wire rod is improved; the plasticity is improved, so that the wire rod with higher plasticity can be obtained without natural aging treatment, the aging treatment of downstream clients can be avoided, the service cycle is shortened, and the time cost is saved;
the high-carbon steel wire rod obtained by the heat treatment method has uniform section structure and no low-temperature bainite and martensite structures, the tensile strength of the final high-carbon steel wire rod is more than or equal to 1600MPa, the surface shrinkage is more than or equal to 35%, the sorbite proportion is more than or equal to 97%, the average lamellar spacing is less than or equal to 70nm, the average pearlite colony size is less than or equal to 2 mu m, and the torsion of the produced galvanized steel wire is more than or equal to 18 circles.
2. In the heat treatment method provided by the invention, the high-carbon steel wire rod is subjected to off-line heat treatment, and compared with on-line salt bath heat treatment, the off-line heat treatment does not need to modify a Steyr wire, has low cost, and can meet the requirement of simultaneous production of a plurality of wires.
3. In the heat treatment method provided by the invention, the high-carbon steel wire rod is heated to above the austenite temperature before salt bath heat treatment; because the high-carbon steel wire rod is basically sorbite structure, the lamellar cementite needs to be dissolved for a certain time, and the carbon element can be uniformly diffused, therefore, the heating time is preferably 6-10min. The austenitizing heating temperature is lower than 940 ℃, so that the movement of carbon and alloy elements is weaker, and the homogenization of component diffusion is not facilitated; when the heating temperature exceeds 980 ℃, the growth speed of the crystal grains is high, coarsening phenomenon occurs, coarse crystal grains delay pearlite transformation, the phase change time is prolonged, and the production efficiency is reduced; therefore, the present invention further preferably controls the heating temperature to 940-980 ℃.
4. In the heat treatment method provided by the invention, the decarburization and the oxidation of the surface of the wire rod are strictly controlled in the heating process of austenitizing, the atmosphere in the furnace is controlled to be a reducing atmosphere, and the carbon potential in the furnace is more than or equal to 0.96%. The carbon potential in the furnace is higher than the carbon content of the wire rod, so that the surface can be slightly carburized, and decarburization generated in the hot rolling process of the wire rod is counteracted. The heating time is controlled to be 6-10min, and surface carburetion caused by long-time carburization is avoided. By controlling the temperature, time and carbon potential of austenitizing heating, the wire rod components are further homogenized, no obvious decarburization or carburetion exists on the surface, and the components of the whole section tend to be consistent.
5. In the heat treatment method provided by the invention, two factors of melting point and viscosity are mainly considered in the selection of the molten salt component, the lowest quenching temperature is determined by the melting point, and the influence of the viscosity on the cooling speed is larger. In order to meet the use temperature of salt bath heat treatment and improve the cooling speed as much as possible, the medium selected by the technology is mixed molten salt of potassium nitrate and sodium nitrate, and the potassium nitrate accounts for 40-60 percent, so that the requirement of the use temperature of 350-600 ℃ can be met. In addition, a certain amount of water is added into the molten salt, so that the viscosity can be reduced, the fluidity of the molten salt is improved, the cooling capacity of the molten salt is enhanced, and the cooling speed of the wire rod is improved. The addition amount of water is matched with the temperature of the molten salt, and the maximum cooling capacity can be achieved by adding 0.2-0.5% of water in the preset temperature of the molten salt. The invention also adopts the fountain type salt tank, so that the stability of the liquid level can be maintained, and the temperature uniformity can be promoted by stirring the fountain; the stirring frequency is 38-42Hz, and the flow of molten salt in the salt tank can be controlled to meet the cooling requirement. The flow direction of the molten salt is opposite to the movement direction of the wire rod, so that the relative movement speed of the high-carbon steel wire rod and the molten salt can be increased, and the heat exchange efficiency is improved. The parameters are combined to ensure that the cooling speed and the efficiency of the wire rod in molten salt are optimal.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a microstructure micrograph of a high carbon steel wire rod of example 1 after salt bath heat treatment;
FIG. 2 is a microstructure micrograph of the high carbon steel wire rod of example 1 after salt bath heat treatment;
FIG. 3 is a microscopic image of the surface layer structure of the high carbon steel wire rod of comparative example 1 after heat treatment in a single salt bath;
FIG. 4 is a microstructure micrograph of a high carbon steel wire rod of comparative example 1 after heat treatment in a single salt bath.
Detailed Description
The following examples are provided for a better understanding of the present invention and are not limited to the preferred embodiments described herein, but are not intended to limit the scope of the invention, any product which is the same or similar to the present invention, whether in light of the present teachings or in combination with other prior art features, falls within the scope of the present invention.
The specific experimental procedures or conditions are not noted in the examples and may be followed by the operations or conditions of conventional experimental procedures described in the literature in this field. The reagents or apparatus used were conventional reagent products commercially available without the manufacturer's knowledge.
The criteria for the yield in the following examples and comparative examples were: the tensile strength of the finished galvanized steel wire is more than or equal to that of the target bridge cable galvanized steel wire, the elongation after breaking is more than or equal to 6%, and the number of torsion turns is more than or equal to 12.
Example 1
The embodiment provides a heat treatment method for a high-carbon steel wire rod, wherein the weight percentage composition of the high-carbon steel wire rod is shown in table 1, the specification is 14mm, and the heat treatment method specifically comprises the following steps:
1) Shot blasting is carried out on the high-carbon steel wire rod by using steel shots with granularity of 1.2mm, rust layers and oxide scales on the surface of the high-carbon steel wire rod are cleaned, and the surface roughness Ra of the high-carbon steel wire rod after shot blasting is 6.5 mu m;
2) Uncoiling the high-carbon steel wire rod subjected to shot blasting in the step 1), then feeding the high-carbon steel wire rod into a gas heating furnace with controllable atmosphere for austenitizing heating, and introducing nitrogen and methanol into the furnace to adjust the furnace to be in a reducing atmosphere and adjust the carbon potential value to be 0.97%, wherein the heating temperature is 961 ℃, and the heating time is 8min;
3) And (2) sending the high-carbon steel wire rods heated by austenitizing in the step (2) into a two-stage salt bath tank for salt bath treatment, wherein molten salt in the salt bath tank is mixed salt of potassium nitrate and sodium nitrate, the mass fraction of the potassium nitrate in the molten salt is 43%, and water with the mass fraction of 0.2% is added into the molten salt. Immersing the high-carbon steel wire rod in molten salt in a spring mode, wherein the spring frequency is 40Hz, and the spring direction is opposite to the wire rod movement direction. The high-carbon steel wire rod sequentially passes through a quenching area and an isothermal phase change area in a salt bath, wherein the temperature of the quenching area is 415 ℃, the quenching time is 18s, the temperature of the isothermal phase change area is 572 ℃, the heat preservation time is 4min, and the wire rod is wound.
The high carbon steel wire rod heat-treated in the above example was sampled, and the metallographic and mechanical properties were measured, and the test results are shown in tables 2 and 3, respectively, and the microscopic diagrams of the surface layer structure and the core structure of the high carbon steel wire rod heat-treated in the present example are shown in fig. 1 and 2, respectively.
The high-carbon steel wire rod heat-treated by the embodiment is used for producing 7mm2100MPa bridge cable galvanized steel wire, no wire breakage occurs in the drawing process, the tensile strength of the finished galvanized steel wire is 2140-2176MPa, the elongation after breakage is 8.5%, the number of torsion turns is 26-34, the use requirement of 2100MPa galvanized steel wire is met, and the qualification rate is 100%.
Example 2
The embodiment provides a heat treatment method for a high-carbon steel wire rod, wherein the weight percentage composition of the high-carbon steel wire rod is shown in table 1, the specification is 15mm, and the heat treatment method specifically comprises the following steps:
1) Shot blasting is carried out on the high-carbon steel wire rod by using steel shots with granularity of 1.7mm, rust layers and oxide scales on the surface of the high-carbon steel wire rod are cleaned, and the surface roughness Ra of the high-carbon steel wire rod after shot blasting is 7.5 mu m;
2) Uncoiling the high-carbon steel wire rod subjected to shot blasting in the step 1), then feeding the high-carbon steel wire rod into a gas heating furnace with controllable atmosphere for austenitizing heating, and introducing nitrogen and methanol into the furnace to adjust the furnace to be in a reducing atmosphere and adjust the carbon potential value to be 0.99%, wherein the heating temperature is 980 ℃, and the heating time is 6min;
3) And (3) sending the high-carbon steel wire rods heated by austenitizing in the step (2) into a two-stage salt bath tank for salt bath treatment, wherein molten salt in the salt bath tank is mixed salt of potassium nitrate and sodium nitrate, the mass fraction of the potassium nitrate in the molten salt is 55%, and water with the mass fraction of 0.5% is added into the molten salt. Immersing the high-carbon steel wire rod in molten salt in a spring-gushing mode, wherein the spring-gushing frequency is 42Hz, and the spring-gushing direction is opposite to the moving direction of the high-carbon steel wire rod. The high-carbon steel wire rod sequentially passes through a quenching area and an isothermal phase change area in a salt bath, wherein the temperature of the quenching area is 445 ℃, the quenching time is 12s, the temperature of the isothermal phase change area is 558 ℃, the heat preservation time is 5min, and the wire rod is wound.
The high carbon steel wire rods heat-treated in the above examples were sampled, and metallographic and mechanical properties were measured, and the measurement results are shown in tables 2 and 3, respectively.
The high-carbon steel wire rod heat-treated by the embodiment is used for producing the 7mm2200MPa bridge cable galvanized steel wire, no wire breakage occurs in the drawing process, the tensile strength of the finished galvanized steel wire is 2237-2281MPa, the elongation after breakage is 8%, the number of torsion turns is 25-32, the use requirement of the 2200MPa galvanized steel wire is met, and the qualification rate is 100%.
Example 3
The embodiment provides a heat treatment method for a high-carbon steel wire rod, wherein the weight percentage composition of the high-carbon steel wire rod is shown in table 1, the specification is 14mm, and the heat treatment method specifically comprises the following steps:
1) Shot blasting is carried out on the high-carbon steel wire rod by using steel shots with granularity of 1.2mm, rust layers and oxide scales on the surface of the high-carbon steel wire rod are cleaned, and the surface roughness Ra of the high-carbon steel wire rod after shot blasting is 6.3 mu m;
2) Uncoiling the high-carbon steel wire rod subjected to shot blasting in the step 1), then feeding the high-carbon steel wire rod into a gas heating furnace with controllable atmosphere for austenitizing heating, and introducing nitrogen and methanol into the furnace to adjust the furnace to be in a reducing atmosphere and adjust the carbon potential value to be 0.96%, wherein the heating temperature is 940 ℃, and the heating time is 10min;
3) And (2) sending the high-carbon steel wire rods heated by austenitizing in the step (2) into a two-stage salt bath tank for salt bath treatment, wherein molten salt in the salt bath tank is mixed salt of potassium nitrate and sodium nitrate, the mass fraction of the potassium nitrate in the molten salt is 40%, and water with the mass fraction of 0.2% is added into the molten salt. Immersing the high-carbon steel wire rod in molten salt in a spring mode, wherein the spring frequency is 38Hz, and the spring direction is opposite to the wire rod movement direction. The high-carbon steel wire rod sequentially passes through a quenching area and an isothermal phase change area in a salt bath, wherein the temperature of the quenching area is 400 ℃, the quenching time is 20s, the temperature of the isothermal phase change area is 550 ℃, the heat preservation time is 5min, and the wire rod is wound.
The high carbon steel wire rods heat-treated in the above examples were sampled, and metallographic and mechanical properties were measured, and the measurement results are shown in tables 2 and 3, respectively.
The high-carbon steel wire rod heat-treated by the embodiment is used for producing 7mm2100MPa bridge cable galvanized steel wire, no wire breakage occurs in the drawing process, the tensile strength of the finished galvanized steel wire is 2151-2186MPa, the elongation after breakage is 8.8%, the number of torsion turns is 22-30, the use requirement of 2100MPa galvanized steel wire is met, and the qualification rate is 100%.
Example 4
The embodiment provides a heat treatment method for a high-carbon steel wire rod, wherein the weight percentage composition of the high-carbon steel wire rod is shown in table 1, the specification is 14mm, and the heat treatment method specifically comprises the following steps:
1) Shot blasting is carried out on the high-carbon steel wire rod by using steel shots with the granularity of 2.0mm, rust layers and oxide scales on the surface of the high-carbon steel wire rod are cleaned, and the surface roughness Ra of the high-carbon steel wire rod after shot blasting is 8.0 mu m;
2) Uncoiling the high-carbon steel wire rod subjected to shot blasting in the step 1), then feeding the high-carbon steel wire rod into a gas heating furnace with controllable atmosphere for austenitizing heating, and introducing nitrogen and methanol into the furnace to adjust the furnace to be in a reducing atmosphere and adjust the carbon potential value to be 0.97%, wherein the heating temperature is 961 ℃, and the heating time is 8min;
3) And (3) sending the high-carbon steel wire rods heated by austenitizing in the step (2) into a two-stage salt bath tank for salt bath treatment, wherein molten salt in the salt bath tank is mixed salt of potassium nitrate and sodium nitrate, the mass fraction of the potassium nitrate in the molten salt is 60%, and water with the mass fraction of 0.5% is added into the molten salt. Immersing the high-carbon steel wire rod in molten salt in a spring-gushing mode, wherein the spring-gushing frequency is 42Hz, and the spring-gushing direction is opposite to the moving direction of the high-carbon steel wire rod. The high-carbon steel wire rod sequentially passes through a quenching area and an isothermal phase change area in a salt bath, wherein the temperature of the quenching area is 450 ℃, the quenching time is 10s, the temperature of the isothermal phase change area is 590 ℃, the heat preservation time is 3min, and the wire rod is wound.
The high carbon steel wire rods heat-treated in the above examples were sampled, and metallographic and mechanical properties were measured, and the measurement results are shown in tables 2 and 3, respectively.
The high-carbon steel wire rod heat-treated by the embodiment is used for producing 7mm2100MPa bridge cable galvanized steel wire, no wire breakage occurs in the drawing process, the tensile strength of the finished galvanized steel wire is 2130-2158MPa, the elongation after breakage is 9.6%, the number of torsion turns is 25-36, the use requirement of 2100MPa galvanized steel wire is met, and the qualification rate is 100%.
Comparative example 1
The comparative example provides a heat treatment method for a high-carbon steel wire rod, wherein the weight percentage composition of the high-carbon steel wire rod is shown in table 1, the specification is 14mm, and the heat treatment method specifically comprises the following steps:
1) Shot blasting is carried out on the high-carbon steel wire rod by using steel shots with the granularity of 2.2mm, rust layers and oxide scales on the surface of the wire rod are cleaned, and the surface roughness Ra of the high-carbon steel wire rod after shot blasting is 8.5 mu m;
2) Uncoiling the high-carbon steel wire rod subjected to shot blasting in the step 1), then feeding the high-carbon steel wire rod into a gas heating furnace with controllable atmosphere for austenitizing heating, and introducing nitrogen and methanol into the furnace to adjust the furnace to be in a reducing atmosphere and adjust the carbon potential value to be 0.97%, wherein the heating temperature is 931 ℃, and the heating time is 8min;
3) And (3) feeding the high-carbon steel wire rods heated by austenitizing in the step (2) into a single salt bath tank for salt bath treatment, wherein molten salt in the salt bath tank is mixed salt of potassium nitrate and sodium nitrate, the mass fraction of the potassium nitrate in the molten salt is 50%, the temperature of the molten salt is 515 ℃, the heat preservation time is 8min, and winding is carried out.
The high carbon steel wire rod heat-treated in the above comparative example was sampled, and metallographic and mechanical properties were measured, and the measurement results are shown in tables 2 and 3, respectively, and microscopic images of the surface layer structure and the core structure of the high carbon steel wire rod heat-treated in the present comparative example are shown in fig. 3 and 4, respectively.
The high-carbon steel wire rod subjected to heat treatment in the comparative example is used for producing a bridge cable galvanized steel wire with the thickness of 7mm and the thickness of 2200MPa, the wire breakage rate is 1.3 times/ton in the drawing process, the tensile strength of the finished galvanized steel wire is 2173-2191MPa, the elongation after breakage is 5%, the number of turns is 4-18, and the finished product qualification rate is only 41%.
Comparative example 2
The comparative example provides a heat treatment method for a high-carbon steel wire rod, wherein the weight percentage composition of the high-carbon steel wire rod to be treated is shown in table 1, the specification is 14mm, and the heat treatment method specifically comprises the following steps:
1) Shot blasting is carried out on the high-carbon steel wire rod by using steel shots with the granularity of 3.0mm, rust layers and oxide scales on the surface of the high-carbon steel wire rod are cleaned, and the surface roughness Ra of the high-carbon steel wire rod after shot blasting is 11.5 mu m;
2) Uncoiling the high-carbon steel wire rod subjected to shot blasting in the step 1), then feeding the high-carbon steel wire rod into a gas heating furnace with controllable atmosphere for austenitizing heating, and introducing nitrogen and methanol into the furnace to adjust the furnace to be in a reducing atmosphere and adjust the carbon potential value to be 0.97%, wherein the heating temperature is 985 ℃, and the heating time is 5min;
3) And (2) sending the high-carbon steel wire rods heated by austenitizing in the step (2) into a two-stage isothermal phase change salt bath tank for salt bath treatment, wherein molten salt in the salt bath tank is mixed salt of potassium nitrate and sodium nitrate, the mass fraction of the potassium nitrate in the molten salt is 45%, the temperature of the first-stage molten salt is 492 ℃, the isothermal time is 30s, the temperature of the second-stage molten salt is 534 ℃, the isothermal time is 5min, and the winding is carried out.
The high carbon steel wire rod subjected to heat treatment in the comparative example is sampled, metallographic and mechanical properties are detected, and detection results are shown in tables 2 and 3 respectively.
The high-carbon steel wire rod subjected to heat treatment in the comparative example is used for producing 7mm2100MPa bridge cable galvanized steel wire, the wire breakage rate is 0.8 times/ton in the drawing process, the tensile strength of the finished galvanized steel wire is 2073-2151MPa, the elongation after breakage is 6.5%, the number of turns is 10-25, and the finished product qualification rate is only 63%.
Comparative example 3
The comparative example was different from example 3 in that the quenching temperature was adjusted to 400℃and the quenching time was adjusted to 23s, and the other conditions were the same as example 3.
The high carbon steel wire rod subjected to heat treatment in the comparative example is sampled, metallographic and mechanical properties are detected, and detection results are shown in tables 2 and 3 respectively.
The high-carbon steel wire rod subjected to heat treatment in the comparative example is used for producing 7mm2100MPa bridge cable galvanized steel wire, the wire breakage rate is 1.3 times/ton in the drawing process, the tensile strength of the finished galvanized steel wire is 1982-2146MPa, the elongation after breakage is 5.1%, the number of turns is 8-26, and the finished product qualification rate is 95.2%.
Comparative example 4
The comparative example was different from example 4 in that the quenching temperature was adjusted to 450℃and the quenching time was adjusted to 7s, and the other conditions were the same as example 4.
The high carbon steel wire rod subjected to heat treatment in the comparative example is sampled, metallographic and mechanical properties are detected, and detection results are shown in tables 2 and 3 respectively.
The high-carbon steel wire rod subjected to heat treatment in the comparative example is used for producing 7mm2100MPa bridge cable galvanized steel wire, the wire breakage rate is 1.8 times/ton in the drawing process, the tensile strength of the finished galvanized steel wire is 2151-2185MPa, the elongation after breakage is 4.7%, the number of turns is 7-16, and the finished product qualification rate is 96.1%.
Table 1 chemical compositions of high carbon steel wire rods of examples 1-4 and comparative examples 1-4
Table 2 metallographic examination results of high carbon steel wire rods of examples 1 to 4 and comparative examples 1 to 4
TABLE 3 results of mechanical property test of high carbon steel wire rods of examples 1-4 and comparative examples 1-4
| Tensile strength/MPa | Face shrinkage/% | |
| Example 1 | 1613-1680 | 38-42 |
| Example 2 | 1625-1702 | 36-40 |
| Example 3 | 1629-1691 | 35-39 |
| Example 4 | 1606-1657 | 40-42 |
| Comparative example 1 | 1712-1761 | 15-22 |
| Comparative example 2 | 1570-1647 | 28-34 |
| Comparative example 3 | 1528-1662 | 27-38 |
| Comparative example 4 | 1613-1706 | 24-42 |
As is clear from tables 1 to 3 and examples 1 to 4 and comparative examples 1 to 4, the heat-treated high carbon steel wire rods of comparative examples 1 to 4 had bainite or martensite, the partial area shrinkage was less than 35%, the sorbite transformation rate was less than 97%, the average sorbite lamellar spacing was 60 to 108. Mu.m, and the wire breakage problem was found in the drawing process for producing 7mm2200MPa and 7mm2100MPa galvanized steel wires, and the elongation after breakage and the percent of pass were not high. The high-carbon steel wire rod subjected to heat treatment in the embodiment 1-4 has uniform cross-section structure, no low-temperature bainite and martensite structures, tensile strength of more than or equal to 1600MPa, surface shrinkage of more than or equal to 35%, sorbite proportion of more than or equal to 97%, average lamellar spacing of less than or equal to 70nm, average pearlite cluster size of less than or equal to 2 mu m, and the produced galvanized steel wire with the level of 7mm2200MPa and 7mm2100MPa is twisted for more than or equal to 18 circles, so that the structure performance and the mechanical property are excellent.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the invention.
Claims (10)
1. A heat treatment method of a high carbon steel wire rod, comprising: the austenitized high-carbon steel wire rod is subjected to a heat treatment process of quenching and isothermal phase transformation in a salt bath in sequence;
the quenching temperature is 400-450 ℃, and the quenching time is 10-20s;
the isothermal phase transition temperature is 550-590 ℃, and the isothermal phase transition time is 3-5min.
2. The heat treatment method according to claim 1, wherein the austenitized high carbon steel wire rod is further subjected to a shot blasting treatment before austenitizing heating.
3. The heat treatment method according to claim 2, wherein in the shot blasting step, the steel shot has a particle size of 1.2-2.0mm, and the roughness Ra of the high carbon steel wire rod after shot blasting is 6.3-8.0 μm.
4. A heat treatment method according to any one of claims 1 to 3, wherein the austenitizing high carbon steel wire rod is obtained by: and heating the high-carbon steel wire rod by adopting heat radiation, wherein the heating temperature is 940-980 ℃, and the heating time is 6-10min.
5. The heat treatment method according to any one of claims 1 to 4, wherein the austenitized high carbon steel wire rod is obtained by heating in a reducing atmosphere, and the carbon potential in the furnace is not less than 0.96%.
6. The heat treatment method according to any one of claims 1 to 5, wherein the molten salt used in the salt bath is a mixed salt of potassium nitrate and sodium nitrate.
7. The heat treatment method according to claim 6, wherein the mass fraction of potassium nitrate in the molten salt is 40 to 60%.
8. The heat treatment method according to claim 6 or 7, characterized in that water is further added to the molten salt; the water accounts for 0.2-0.5% of the total mass of the water and the molten salt.
9. The heat treatment method according to any one of claims 6 to 8, wherein the molten salt is submerged in the high carbon steel wire rod transfer area by a spa method.
10. The heat treatment method according to claim 9, wherein the frequency of the spring is 38-42Hz, and the direction of the spring is opposite to the direction of the wire rod movement.
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