CN107447079B - method for annealing medium-high carbon steel continuous casting billet - Google Patents
method for annealing medium-high carbon steel continuous casting billet Download PDFInfo
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- CN107447079B CN107447079B CN201610373079.1A CN201610373079A CN107447079B CN 107447079 B CN107447079 B CN 107447079B CN 201610373079 A CN201610373079 A CN 201610373079A CN 107447079 B CN107447079 B CN 107447079B
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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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Abstract
the invention relates to a method for annealing medium-high carbon steel continuous casting billets, which mainly solves the technical problem of high annealing cost of the existing medium-high carbon steel continuous casting billets. The technical scheme of the invention comprises the following steps: 1) measuring the temperature of the medium-high carbon steel continuous casting billet in the slab warehouse; 2) stacking medium-high carbon steel low-temperature billets at the temperature of 400-700 ℃ and medium-high carbon steel high-temperature billets at the temperature of 750-1000 ℃ on the ground paved with refractory bricks at intervals, and slowly heating the low-temperature billets for 2-2.5 h through heat conduction of the high-temperature billets; 3) covering a bottomless heat-preservation cover on the stack of the medium-high carbon steel continuous casting billets, preserving heat of the medium-high carbon steel continuous casting billets for 1-2 h, and then moving away the bottomless heat-preservation cover; 4) and (3) dismantling the stack of the medium-high carbon steel continuous casting billets at the temperature of less than or equal to 500 ℃, and finishing annealing of the continuous casting billets. The annealing method reduces the frequency of cracks, warping and breakage of the medium-high carbon steel casting blank in the stacking, improves the qualification rate of the steel blank, and has low annealing cost.
Description
Technical Field
the invention relates to a medium-high carbon steel continuous casting billet, in particular to a method for annealing the medium-high carbon steel continuous casting billet, and particularly relates to a method for stacking and annealing medium-high carbon steel casting steel at different temperatures.
Background
The billet is subjected to various external forces in the continuous casting process, such as friction force between a billet shell of a crystallizer and a copper plate, bulging force generated by molten steel static pressure, thermal stress, casting blank bending or straightening force, additional stress generated by misalignment of a supporting roller and phase change stress. These stress stacks constitute internal stresses in the ingot at different locations, which stresses generally increase with increasing alloying elements in the steel and with increasing ingot thickness. The continuously cast steel slabs may crack under the action of the wind scooping sand or the through-air in winter (thermal stress plus residual stress). In addition to causing cracking of the article, residual stresses can also cause shape and dimensional changes during subsequent processing, use and storage. For medium-high carbon steel casting blanks, even if the casting blanks are slowly cooled after casting, the risks of warping, cracking and even self-cracking still exist in the storage and transportation process.
annealing is often used to eliminate or reduce residual stresses. In the continuous casting-hot rolling section of the steel enterprise, because of the conditions of unmatched production rhythm and the like, the method of taking the cut slab off the line and placing the slab in the air for stacking and cooling is a common continuous casting billet cooling mode at present. The problems of cracks, casting blank fracture and the like of medium-high carbon steel continuous casting billets are frequently caused by the combined action of residual stress and low-temperature plasticity in the stacking and cooling process, the residual stress in the medium-high carbon steel casting blanks in the stacking needs to be reduced by annealing, the occurrence rate of the casting blank fracture is reduced, the production connection and matching are facilitated, and the production resources are saved. The factory design of the continuous casting-hot rolling section of the steel enterprise does not have equipment and a site for stress relief annealing, and the annealing modes of heating, heat preservation and cooling cannot be carried out on the cooled casting blanks so as to eliminate or reduce the residual stress in the casting blanks.
chinese patent application 200910300283.0, air cooling stacking method for hot rolled steel rail, discloses a method for reducing the curvature of steel rail by turning the rolled steel rail 180 ° and then stacking and cooling, chinese patent application 201320140040.7, a press plate for preventing buckling after stacking steel plates, discloses a press plate consisting of a cover plate and a support plate applied on the steel plates after stacking is completed, improves the heat dissipation condition of the steel plates at the stacking position to prevent buckling after stacking steel plates. The prior art can not realize low-cost annealing of medium-high carbon steel continuous casting billets.
Disclosure of Invention
the invention aims to provide a method for annealing medium-high carbon steel continuous casting billets, which mainly solves the technical problem of high annealing cost of the existing medium-high carbon steel continuous casting billets.
The technical scheme adopted by the invention is as follows: a method for annealing medium-high carbon steel continuous casting billets comprises the following steps:
1) Measuring the temperature of the medium-high carbon steel continuous casting billet in the continuous casting-hot rolling slab warehouse;
2) Completely transforming austenite into ferrite Ar at the temperature of 400-700 DEG C1Temperature) medium-high carbon steel low-temperature steel billets and medium-high carbon steel high-temperature steel billets at the temperature of 750-1000 ℃ are stacked on the ground paved with the refractory bricks at intervals, and the high-temperature steel billets conduct heat to the low-temperature steel billets and are slowly heated for 2-2.5 hours;
3) Covering a bottomless heat-preservation cover on the stack of the medium-high carbon steel continuous casting billets, preserving heat of the medium-high carbon steel continuous casting billets for 1-2 h, and then moving away the bottomless heat-preservation cover;
4) And (3) dismantling the stack of the medium-high carbon steel continuous casting billets at the temperature of less than or equal to 500 ℃, and annealing the medium-high carbon steel continuous casting billets.
further, the method of the invention also comprises the steps of producing medium-high carbon steel continuous casting billets in a batch mode by the slab caster;
The method of the invention is based on the following studies:
The quality problems of medium-high carbon steel continuous casting billets produced by a slab caster, such as cracks, casting blank warping, fracture and the like caused by residual stress in the high carbon steel continuous casting billets. There are two mechanisms for eliminating or reducing residual stress in high-carbon steel continuous casting billet by annealing: when the stress exceeds the yield limit, the stress is reduced or eliminated by plastic deformation; when the stress is less than the yield limit, the stress is relaxed by creep. The rapid release of residual stress at high temperatures is sometimes adversely affected. Because the stress is generally not uniformly distributed along the cross section and the length direction, the sudden release will break the balance of internal force and moment to cause the workpiece to warp. The greater the original residual stress, the greater the risk of warping. Therefore, it is desirable to relax the stress in a creep manner. Along with the increase of the temperature, the recrystallization of the steel phase change is carried out, the second type stress and the third type stress can disappear, and the first type stress is gradually relaxed and can be eliminated by more than 90 percent generally.
the annealing process consists of three stages of heating, heat preservation and cooling. Medium and high carbon steel has high brittleness and is easy to crack under the action of internal stress. Therefore, the casting blank is heated slowly, the temperature difference is small when the casting blank is heated at the speed of 50-100 ℃/h, and the thermal stress is small. The stress-relief annealing temperature of the continuous casting billet is selected mainly based on the principle of internal stress relief. The heating in each area of low temperature, medium temperature and high temperature has the function of removing internal stress, the adoption of higher temperature heating is favorable for quickly removing the internal stress and improving the productivity, but the heating temperature can not be too high, and the annealing heating temperature is selected to be at the critical point Ac of the transformation temperature of ferrite to austenite1Nearby. Experimental studies show that Ac is critical1slightly, the temperature is kept for a period of time to finish the stress relief annealing of the billet. No matter the phase change kinetics is required or the internal stress is removed, the heat preservation time is not too long, the actually required effective time is 1-2 h, the control of the stress-relief annealing cooling speed is very important, and the cooling speed is mostly 20-50 ℃/h.
The temperature of the medium-high carbon steel continuous casting billet produced by the slab caster is 750-1000 ℃ just after the billet is taken off the line, and a heat source is provided for annealing the low-temperature medium-high carbon steel continuous casting billet.
Compared with the prior art, the invention has the following positive effects: medium-high carbon steel cast steel stacks at different temperatures realize medium-high carbon steel casting blank stress relief annealing, and high-temperature steel blank waste heat is utilized to heat a low-temperature steel blank for heating; and a bottomless heat-insulating cover is adopted to insulate the stacked casting blank, and slow cooling of stress relief annealing is realized in a stacking mode, so that the residual stress of the medium-high carbon steel casting blank is reduced. By the method, the frequency of cracks, warping and breakage of the medium-carbon steel casting blank in stacking is reduced, the qualified rate of the steel billet is improved, and the annealing cost is low.
Detailed Description
A method for annealing medium-high carbon steel continuous casting billets comprises the following steps:
1) A slab caster produces medium-high carbon steel continuous casting billets in batch;
2) measuring the temperature of a medium-high carbon steel continuous casting billet in a continuous casting-hot rolling slab storage area;
3) completely transforming austenite into ferrite Ar at the temperature of 400-700 DEG C1temperature) medium-high carbon steel low-temperature steel billets and medium-high carbon steel high-temperature steel billets at the temperature of 750-1000 ℃ are stacked on the ground paved with the refractory bricks at intervals, and the high-temperature steel billets conduct heat to the low-temperature steel billets and are slowly heated for 2-2.5 hours;
4) Covering a bottomless heat-preservation cover on the stack of the medium-high carbon steel continuous casting billets, preserving heat of the medium-high carbon steel continuous casting billets for 1-2 h, and then moving away the bottomless heat-preservation cover;
5) and (3) dismantling the stack of the medium-high carbon steel continuous casting billets at the temperature of less than or equal to 500 ℃, and annealing the medium-high carbon steel continuous casting billets.
The mechanism of the method is as follows: the annealing comprises three stages of slow heating, heat preservation and slow cooling. After the high-carbon steel continuous casting steel billet which is produced and off-line is stacked for a certain time, the temperature of the steel billet is lower than Ar1The temperature of the medium-high carbon steel continuous casting billet of the just-down continuous casting production line is higher than Ac3and (completely converting ferrite into austenite), stacking the low-temperature medium-high carbon steel continuous casting billet and the high-temperature medium-high carbon steel continuous casting billet at intervals, and heating the low-temperature continuous casting billet by utilizing the residual heat of the high-temperature continuous casting billet through heat conduction between the continuous casting billets. The temperature difference between the high-temperature continuous casting billet and the low-temperature continuous casting billet is small,Slow heating can be achieved. The temperature of the high-temperature continuous casting steel billet is consistent with that of the low-temperature continuous casting steel billet after about 2 hours, a heat preservation cover is covered, and the temperature of the stacked high-temperature continuous casting steel billet and the stacked low-temperature continuous casting steel billet is more uniform. The thermal inertia and the covered thermal insulation cover are utilized to reduce heat loss so as to achieve the purpose of thermal insulation. And after heat preservation is carried out for 1-2 h, the stacked casting blanks are slowly cooled, after the temperature is reduced to 500 ℃, the stress relief annealing is completed, and the stack can be disassembled to continue the next procedure.
Example 1, a method of annealing a 55 steel billet comprising:
when the 55 steel cast blank in the stacking field of the continuous casting-hot rolling slab warehouse is cooled to below 600 ℃ (55 steel Ar)1The temperature is 690 ℃), stacking the steel billet with the surface temperature of 800 ℃ and the core temperature of 950 ℃ at intervals with a 55 steel billet of which the surface temperature is 800 ℃ of a continuous casting production line just below, stacking 12 steel billets on the upper surface of the steel billet; slowly heating the 55 steel casting blank at low temperature by heat conduction of the 55 steel casting blank at high temperature, wherein the heating speed is 60 ℃/h, the heating time is 2h, the temperature of the cold and hot 55 steel blanks tends to be 760 ℃ and is slightly higher than the Ac temperature of the 55 steel1temperature (727 ℃);
Covering a bottomless heat-preservation cover on the 55 steel continuous casting billet stack to reduce heat loss of stacked billets, enabling the temperatures of the high-temperature 55 steel continuous casting billet and the low-temperature 55 steel continuous casting billet to be more uniform, simultaneously carrying out heat preservation on the stacked 55 steel continuous casting billet by utilizing thermal inertia, and removing the bottomless heat-preservation cover after heat preservation is carried out for 2 hours;
and when the temperature of all 55 steel continuous casting billets is reduced to 500 ℃, the stress relief annealing of the 55 steel continuous casting billets is completed, compared with the cooling of a single 55 steel continuous casting billet, the stacking greatly reduces the cooling speed of the 55 steel continuous casting billets, the cooling speed is 20 ℃/h, and the annealing is completed.
Claims (2)
1. a method for annealing medium-high carbon steel continuous casting billets is characterized by comprising the following steps: the method comprises the following steps:
1) Measuring the temperature of the medium-high carbon steel continuous casting billet in the continuous casting-hot rolling slab warehouse;
2) stacking medium-high carbon steel low-temperature billets at the temperature of 400-700 ℃ and medium-high carbon steel high-temperature billets at the temperature of 750-1000 ℃ on the ground paved with refractory bricks at intervals, and slowly heating the low-temperature billets for 2-2.5 h through heat conduction of the high-temperature billets;
3) Covering a bottomless heat-preservation cover on the stack of the medium-high carbon steel continuous casting billets, preserving heat of the medium-high carbon steel continuous casting billets for 1-2 h, and then moving away the bottomless heat-preservation cover;
4) And (3) dismantling the stack of the medium-high carbon steel continuous casting billets at the temperature of less than or equal to 500 ℃, and annealing the medium-high carbon steel continuous casting billets.
2. The method for annealing the medium-high carbon steel continuous casting billet according to claim 1, which is characterized by comprising the following steps of: the method comprises the step of batch production of medium-high carbon steel continuous casting billets by a slab caster.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102861887A (en) * | 2012-09-21 | 2013-01-09 | 广东韶钢松山股份有限公司 | Hot loading method for medium-thick slabs |
| CN102876867A (en) * | 2012-10-17 | 2013-01-16 | 夏雨 | Heat treatment method of medium-high carbon steel |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102861887A (en) * | 2012-09-21 | 2013-01-09 | 广东韶钢松山股份有限公司 | Hot loading method for medium-thick slabs |
| CN102876867A (en) * | 2012-10-17 | 2013-01-16 | 夏雨 | Heat treatment method of medium-high carbon steel |
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