CN109022709B - Heating process for eliminating thermal stress of steel billet - Google Patents
Heating process for eliminating thermal stress of steel billet Download PDFInfo
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- CN109022709B CN109022709B CN201811137367.2A CN201811137367A CN109022709B CN 109022709 B CN109022709 B CN 109022709B CN 201811137367 A CN201811137367 A CN 201811137367A CN 109022709 B CN109022709 B CN 109022709B
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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
- C21D1/26—Methods of annealing
- C21D1/30—Stress-relieving
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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
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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
- C21D6/00—Heat treatment of ferrous alloys
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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Abstract
The invention relates to the technical field of metallurgy, and particularly discloses a heating process for eliminating thermal stress of a steel billet. The heating process for eliminating the thermal stress of the steel billet provided by the invention is characterized in that a differential heating process is formulated according to the charging temperature of the steel billet, the heating process is divided into a preheating section, a heating section and a soaking section in the heating furnace along the charging-in and discharging direction of the steel billet, the heating section and the soaking section are divided into 3-6 sections along the length direction of the steel billet, and the temperature control is respectively carried out, so that the consistency of the temperature of the steel billet along the length direction when the steel billet enters a blooming mill is realized, and the steel billet is free of thermal stress, cracking and good in plasticity in the heating and rolling processes.
Description
Technical Field
The invention relates to the technical field of metallurgy, in particular to a heating process for eliminating thermal stress of a steel billet.
Background
Heating is a necessary process for high-speed wire rod rolling, and the quality of heating quality plays a decisive role in the quality of the final wire rod. In the heating process of the steel billet, because of the heat resistance of metal, the internal temperature and the external temperature difference inevitably exists, the surface temperature is increased faster than the internal temperature, the surface expansion is larger than the central expansion, so that the surface of the steel billet is stressed by compression stress, the central stress is stressed by tension, and the temperature stress, namely the thermal stress is generated in the steel billet. If the temperature gradient of the steel billet in the heating furnace is too large, the expansion deformation of each part of the steel billet is not uniform, and the thermal stress generated by mutual constraint causes the problems of steel billet thermal stress concentration, steel billet bending, cracking and the like. Therefore, the heating control of the steel billet in the production process is very important, the target temperature and the soaking degree of discharging are ensured, and the small full-length temperature fluctuation and the uniform head-tail temperature of the steel billet are ensured when the steel billet enters the blooming mill. However, the existing billet heating process generally takes the principle of ensuring the billet to be fully heated, and has the following main problems: (1) a production workshop adopts a constant heating temperature system; (2) the generation of thermal stress in the heating process of the billet steel cannot be well eliminated due to the problem of temperature setting; (3) the temperature uniformity of the billet in the time direction during rolling cannot be ensured.
Disclosure of Invention
Aiming at the defect that the existing heating process of the steel billet cannot effectively eliminate the thermal stress, the invention provides the heating process for eliminating the thermal stress of the steel billet.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a heating process for eliminating the thermal stress of a steel billet comprises the following steps:
the method comprises the following steps of sequentially dividing a steel billet heating furnace into a preheating section, a heating section and a soaking section according to the conveying direction of steel billets, and controlling the temperature of each section respectively, wherein the specific temperature control method comprises the following steps:
when the temperature of the steel billet is less than or equal to 100 ℃, controlling the temperature of the preheating section to be 650-700 ℃;
when the temperature of the steel billet is more than or equal to 500 ℃, controlling the temperature of the preheating section to be 830-880 ℃;
the heating section and the soaking section are respectively and sequentially divided into 3-6 temperature zones along the conveying direction of the steel billet and are respectively subjected to temperature control, the temperature of each temperature zone is sequentially increased along the conveying direction of the steel billet, and the temperature difference between the heating section and the preheating section is 150-250 ℃; the temperature of the first soaking zone of the soaking section is 1080-1120 ℃, and the temperature difference between the last soaking zone and the first soaking zone is 35-40 ℃.
Compared with the prior art, the heating process for eliminating the thermal stress of the steel billet has the following advantages:
(1) in order to adapt to the production rhythm, different heating processes are set aiming at different temperatures of the steel billets entering the furnace, different preheating temperatures are set for the cold steel billets and the hot steel billets respectively, the difference value between the temperature of the preheating section and the temperature of the steel billets is reduced, the difference value between the temperature of the preheating section and the temperature of the heating section is controlled within a certain range, and the problems of thermal stress concentration and cracking caused by too fast temperature rise in the processes of entering the furnace and heating the cold billets are reduced.
(2) The heating section and the soaking section are respectively set to be 3-6 areas, the temperature control in the areas is carried out, the temperature difference of the same area of the billet between the heating section and the soaking section is reduced, and the risk of stress concentration and cracking of the billet is reduced.
(3) The heating process realizes the consistency of the temperature of the billet in the length direction when the billet enters the blooming mill by controlling the temperature of the billet in the length direction, and has no thermal stress, no cracking and good plasticity in the heating and rolling processes.
Preferably, the heating section and the soaking section are equally divided into 3-6 sections along the length direction of the billet, and the temperature control is carried out respectively.
Preferably, the temperature difference between every two adjacent soaking zones is the same between every two soaking zones.
The soaking sections are divided into 3-6 zones along the length direction of the steel billet, the temperature difference between the last soaking zone and the first soaking zone is controlled to be 35-40 ℃, and the temperatures of the zones are distributed in an equal difference mode, namely the temperature difference between every two adjacent soaking zones is 7-20 ℃. Because tapping and entering the blooming mill are at constant speed, the temperature difference between soaking zones is set to be 7-20 ℃, the temperature drop generated by each section of the billet can be just compensated in the process of entering the blooming mill after tapping, the temperature consistency of the billet when entering the blooming mill is ensured, the internal stress generated in the billet in the deformation process due to the uneven temperature in the compression deformation process is avoided, and the risk of billet cracking is reduced.
Preferably, in the heating section of the heating furnace, the temperature difference between the first heating zone and the last heating zone is 20-25 ℃.
The temperature difference range of the heating section is controlled to be 20-25 ℃, so that the temperature difference between the front part and the tail part of the billet steel in a high-temperature area of the heating furnace can be reduced, the thermal stress of the billet steel is small, and the plasticity is good.
Preferably, the temperature difference between each zone of the heating section and the adjacent two heating zones is the same.
The temperature of the preheating section is not controlled in a partitioning mode, the heating section is set to be 3-6 sections for partition control, preparation can be made for partition control of the soaking section, otherwise, the temperature difference between the head and the tail of the billet is too large due to the fact that the billet directly enters the partition control of the soaking section, and the billet is bent. The temperature between the heating sections is arranged in an equal difference mode, the temperature difference between the heating sections and the soaking sections in the same areas of the steel billets can be reduced, and the risks of thermal stress concentration and cracking of the steel billets are reduced.
Preferably, when the temperature of the steel billet is more than or equal to 500 ℃, the temperature of the first heating zone of the heating section is controlled to be 1000-1030 ℃, the temperature difference between the first heating zone and the last heating zone is 20-25 ℃, and the temperatures of the rest heating zones are arranged in an equal difference mode along the length direction of the steel billet.
The optimal temperature control method can reduce the temperature difference among the heating section, the preheating section and the soaking section, prepare for the partition control of the billet entering the soaking section, reduce the temperature difference between the heating section and the soaking section in the same area and furthest reduce the occurrence of the problem of thermal stress concentration.
Preferably, when the temperature of the steel billet is less than or equal to 100 ℃, the temperature of the first heating zone of the heating section is controlled to be 850-950 ℃, the temperature difference between the first heating zone and the last heating zone is 20-25 ℃, and the temperatures of the rest heating zones are arranged in an equal difference mode along the length direction of the steel billet.
The charging temperature of the steel billet is influenced by the production rhythm and is divided into two conditions of charging the hot billet (more than or equal to 500 ℃) and the cold billet (less than 100 ℃). If the heating systems of the cold billet and the hot billet are completely the same, the temperature gradient of the billet per se and the furnace temperature in the heating section of the cold billet just entering the furnace has larger difference, and the cold billet is easy to form thermal stress and even crack. Therefore, different heating systems are made according to the charging temperature of the steel billet, great convenience is provided for production, and thermal stress caused by overlarge temperature gradient in the heating process is avoided.
The preferred cold billet heating process reduces the occurrence of billet thermal stress concentration problems.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1:
the charging temperature of the square billet is 21 ℃, the heating furnace is divided into three sections for control, the first section is a preheating section, the second section is a heating section, the third section is a soaking section, the square billet is heated to 700 ℃ by the preheating section, and then entering a heating section, wherein the temperature control of the heating section is equally divided into a front end region, a middle region and a rear end region along the length direction of the square billet, the temperature of the front end region is set to 950 ℃, the temperature of the middle region is set to 960 ℃, the temperature of the rear end region is set to 970 ℃, the front end, the middle region and the rear end of the square billet enter a soaking section after reaching the set temperature, the temperature control of the soaking section is also equally divided into the front end region, the middle region and the rear end region along the length direction of the square billet, the temperature of the front end region is set to 1100 ℃, the temperature of the middle region is set to 1120 ℃, the temperature of the rear end region is set to 1140 ℃, and the front end, the middle region and the rear end of the square billet are.
Example 2:
the method comprises the following steps of controlling a feeding temperature of a square billet to be 85 ℃, dividing a heating furnace into three sections, controlling the first section to be a preheating section, the second section to be a heating section and the third section to be a soaking section, heating the square billet to be 650 ℃ in the preheating section, then feeding the square billet into the heating section, controlling the temperature of the heating section to be equally divided into four regions along the length direction of the square billet, setting the temperature of a front end region to be 850 ℃, setting the temperature of a middle section to be 857 ℃ and 864 ℃, setting the temperature of a rear end region to be 871 ℃, enabling each part of the square billet to enter the soaking section after reaching the set temperature, controlling the temperature of the soaking section to be equally divided into four regions along the length direction of the square billet, setting the temperature of the front end region to be 1080 ℃, setting the temperature of the middle section to be 1090 ℃ and 1110 ℃, setting the temperature of the.
Example 3:
the charging temperature of the square billet is 550 ℃, the heating furnace is divided into three sections for control along the charging and discharging directions of the square billet, the first section is a preheating section, the second section is a heating section, the third section is a soaking section, the preheating section heats the square billet to 830 ℃, then the square billet enters the heating section, the temperature control of the heating section is equally divided into three sections of a front end, a middle part and a rear end along the length direction of the square billet, the temperature of the front end region is set to 1000 ℃, the temperature of the middle part region is set to 1012 ℃, the temperature of the rear end region is set to 1024 ℃, the front end, the middle part and the rear end of the square billet enter the soaking section of the third section after reaching the set temperature, the temperature control of the soaking section is equally divided into three sections of the front end, the middle part and the rear end along the length direction of the square billet, the temperature of the front end region is set to 1120 ℃, the temperature of the middle region is, The rear ends of the rolling stands are driven by the motor to the rolling mill for rolling production after reaching the set temperature.
Example 4:
the charging temperature of the square billet is 620 ℃, the heating furnace is divided into three sections along the charging and discharging directions of the square billet for control, the first section is a preheating section, the second section is a heating section, the third section is a soaking section, the preheating section heats the square billet to 880 ℃, then the billet enters a heating section, the temperature control of the heating section is equally divided into six regions along the length direction of the billet, the temperature of the front end region is set to be 1030 ℃, the temperatures of the middle four sections along the length direction of the billet are 1034 ℃, 1038 ℃, 1042 ℃ and 1046 ℃, the temperature of the rear end region is set to be 1050 ℃, all parts of the billet enter a soaking section after reaching the set temperature, the temperature control of the soaking section is also equally divided into six regions along the length direction of the billet, the temperature of the front end region is set to be 1100 ℃, the temperatures of the middle four sections along the length direction of the billet are 1107 ℃, 1114 ℃, 1121 ℃ and 1128 ℃, the temperature of the rear end region is set to be 1135 ℃, all parts of the billet reach the set temperature and then are driven to a rolling mill.
Comparative example 1:
the feeding temperature of the square billet is 21 ℃, the heating furnace is divided into three sections for control, the first section is a preheating section, the second section is a heating section, the third section is a soaking section, the preheating section heats the square billet to 850 ℃, then the square billet enters the heating section, the temperature is set to be 1000 ℃, the square billet enters the third soaking section after reaching the set temperature, the temperature of the soaking section is set to be 1100 ℃, and the square billet is driven to a rolling mill by a motor to be rolled and produced after reaching the set temperature.
Comparative example 2
The temperature of the square billet in the furnace is 85 ℃, the heating furnace is divided into three sections to be controlled along the directions of charging and discharging the square billet, the first section is a preheating section, the second section is a heating section, the third section is a soaking section, the square billet is heated to 850 ℃ by the preheating section and then enters the heating section, the temperature of the heating section is set to be 1000 ℃, the square billet enters the soaking section of the third section after reaching the set temperature, the temperature control of the soaking section is also equally divided into three regions of a front end, a middle part and a rear end along the length direction of the square billet, the temperature of the front end region is set to be 1100 ℃, the temperature of the middle part region is set to be 1120 ℃, the temperature of the rear end region is set to be 1140 ℃, and the front end, the middle part and the rear end of the square billet are.
Comparative example 3:
the feeding temperature of the square billet is 620 ℃, the heating furnace is divided into three sections for control, the first section is a preheating section, the second section is a heating section, the third section is a soaking section, the preheating section heats the square billet to 850 ℃, then the square billet enters the heating section, the temperature is set to be 1000 ℃, the square billet enters the third soaking section after reaching the set temperature, the temperature of the soaking section is set to be 1100 ℃, and the square billet is driven to a rolling mill by a motor to be rolled and produced after reaching the set temperature.
Comparative example 4:
the charging temperature of the square billet is 620 ℃, the heating furnace is divided into three sections to be controlled along the charging and discharging directions of the square billet, the first section is a preheating section, the second section is a heating section, the third section is a soaking section, the preheating section heats the square billet to 850 ℃, then the square billet enters the heating section, the temperature of the heating section is set to be 1000 ℃, the square billet enters the soaking section of the third section after reaching the set temperature, the temperature control of the soaking section is also equally divided into three regions of a front end, a middle part and a rear end along the length direction of the square billet, the temperature of the front end region is set to be 1100 ℃, the temperature of the middle part region is set to be 1120 ℃, the temperature of the rear end region is set to be 1140 ℃, and the front end, the middle part and the rear end of the square billet are driven by.
The billets produced in examples 1 to 4 and comparative examples 1 to 4 were hot rolled to specification
And (4) taking 1000 wire rod samples of the specification, and performing surface quality acid pickling test and 1/2 cold heading test. The surface pickling crack rate and the 1/2 cold heading crack rate are shown in Table 1:
TABLE 1
| Surface pickling rate | 1/2 cold heading cracking rate | |
| Example 1 | 0.3％ | 0.1％ |
| Example 2 | 0％ | 0％ |
| Example 3 | 0.1％ | 0％ |
| Example 4 | 0％ | 0％ |
| Comparative example 1 | 7.5％ | 6.3％ |
| Comparative example 2 | 4.3％ | 4.9％ |
| Comparative example 3 | 2.2％ | 2.8％ |
| Comparative example 4 | 1.1％ | 1.2％ |
As can be seen from Table 1, the products prepared in examples 1-4
Hot-rolled wire rod of specification and those prepared in comparative examples 1 to 4
The hot rolled wire rods of the specifications were significantly reduced in both the surface pickling crack rate and the 1/2 cold heading crack rate as compared to the hot rolled wire rods of examples 1 to 4.
In summary, the heating system for eliminating the thermal stress of the steel billet provided by the invention can effectively eliminate the thermal stress of the steel billet in the heating process by performing differential temperature control on the cold billet and the hot billet and performing zone control on the heating section and the soaking section along the length direction of the steel billet, and realizes uniform temperature consistency of the steel billet when entering the blooming mill, no thermal stress, no cracking and good plasticity in the heating and rolling processes.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (5)
1. A heating process for eliminating the thermal stress of a steel billet is characterized in that a steel billet heating furnace is sequentially divided into a preheating section, a heating section and a soaking section according to the conveying direction of the steel billet, and each section is respectively subjected to temperature control, and the specific temperature control method comprises the following steps:
when the temperature of the steel billet is less than or equal to 100 ℃, controlling the temperature of the preheating section to be 650-700 ℃;
when the temperature of the steel billet is more than or equal to 500 ℃, controlling the temperature of the preheating section to be 830-880 ℃;
the heating section and the soaking section are respectively and sequentially divided into 3-6 temperature zones along the conveying direction of the steel billet and are respectively subjected to temperature control, the temperature of each temperature zone is sequentially increased along the conveying direction of the steel billet, and the temperature difference between the heating section and the preheating section is 150-250 ℃; the temperature of the first soaking zone of the soaking section is 1080-1120 ℃, the temperature difference between the last soaking zone and the first soaking zone is 35-40 ℃, and the temperature difference between every two adjacent soaking zones is the same.
2. The heating process for relieving the thermal stress of the steel billet according to claim 1, wherein the temperature difference between the first heating zone and the last heating zone in the heating section of the heating furnace is 20 to 25 ℃.
3. The heating process for relieving thermal stress of a steel slab of claim 2 wherein the temperature difference between adjacent heating zones is the same between each zone of said heating section.
4. The heating process for relieving the thermal stress of the steel billet according to claim 3, wherein the temperature of the first heating zone of the heating section is controlled to be 850-950 ℃ when the temperature of the steel billet is less than or equal to 100 ℃.
5. The heating process for relieving the thermal stress of the steel billet according to claim 3, wherein the temperature of the first heating zone of the heating section is controlled to be 1000 to 1030 ℃ when the temperature of the steel billet is more than or equal to 500 ℃.
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