High-quality special steel bar and wire direct rolling process technology

Abstract

The invention discloses a high-quality special steel bar wire direct rolling technology and belongs to the field of metal material machining. According to the method, a 200 * 200 mm square section continuous casting billet or a round continuous casting billet with the equivalent section is adopted, direct rolling is achieved, a traditional heating furnace is omitted, and a rolling mill production line is set on the basis of multi-strand continuous casting in combination with the pulling speed of a continuous casting machine; the production process of continuous casting, fixed-length cutting, induction heating temperature compensation, high-temperature roller way hot delivery and rolling is adopted. The continuous casting billet is subjected to heat preservation and hot delivery at the high temperature, the surface temperature is rapidly increased through induction heating, and surface cracks are avoided; and the alloy elements stay in the high-temperature heat preservation roller bed for enough time, so that segregation of the alloy elements is relieved, and the problem that the segregation affects the product quality can be solved in combination with subsequent rolling under large pressure and large compression ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of steel rolling, and in particular to a high-quality steel bar and wire direct rolling process technology (SSRDR). Technical Background

[0002] China is a large steel producer with an annual output of more than 1 billion tons. Among them, rod and wire products account for more than 43%, and more than 90% of the more than 40 million tons of rod and wire products per year are building materials. As the scale of national infrastructure is reduced, the demand for building materials is gradually decreasing, and the structure of steel products is changing. The rod and wire field generally follows the route of "general to high-quality, high-quality to special". The state encourages the conversion of converters to electric furnaces.

[0003] There are currently two technologies for direct rolling of bars and wires at home and abroad, both of which serve ordinary carbon steel building materials products. The first is that the continuous casting billet is quickly sent to the rolling mill for direct rolling by a hot delivery roller with an insulation cover. In a few cases, electric induction heating is used to make up the temperature. This is a purely domestic technology, with a balanced output of multi-stream continuous casting and a rolling line, an annual output of 800,000-1.6 million tons, a continuous casting machine pulling speed of 3-4m / min, and a billet cross-section of 150x150mm-165x165mm; the second is the Mida technology of Danieli Company in Italy, with a balanced output of first-class continuous casting and a rolling line, an annual output of 600,000-800,000 tons, a continuous casting machine pulling speed of 6-8m / min, and a billet cross-section of 190x220mm.

[0004] The high-quality steel production line has the following three characteristics: first, the continuous casting machine has a slow pulling speed and a fast surface temperature drop; second, because the high-quality steel bar and wire products have special requirements for the compression ratio of the billet, the billet cross-section is larger than that of ordinary carbon steel; third, the carbon and alloy element content in the billet is high, and segregation is easy to occur during the continuous casting process. It needs a certain diffusion time in the high-temperature furnace to uniform the composition. The traditional production process is continuous casting-fixed length cutting-bill cooling-collection-reloading-heating-rolling, and the high-temperature heat energy of the continuous casting billet is wasted. The cold billet enters the heating furnace and is first slowly heated to the highest temperature, and then stays in the equalizing section of the heating furnace for a sufficient time to uniformly organize the structure. Direct rolling technology eliminates the heating furnace, utilizes the high-temperature heat energy of the continuous casting billet, reduces the billet cooling, collection, reloading, and reheating links, reduces production costs, and complies with the national energy conservation and emission reduction policy. Summary of the invention

[0005] The present invention aims to solve the direct rolling problem of high-quality steel bar and wire production line, and improves the rolling technology for small and medium-sized bars Ф16-90mm (including Ф16-40mm large coils) and Ф5-25mm wire products with a market share of more than 80%.

[0006] A high-quality steel bar and wire direct rolling technology comprises the following steps:

[0007] 1) Use 200x200mm square continuous casting billet or round continuous casting billet of equivalent cross section to realize direct rolling, eliminate the traditional heating furnace, based on multi-strand continuous casting, and combine the continuous casting machine speed to match the rolling mill production line;

[0008] 2) The production process is continuous casting - fixed-length cutting - induction heating - high-temperature roller hot delivery - rolling.

[0009] Furthermore, the continuous casting-cutting to length-induction heating and temperature compensation stage described in step 2) is that after being cut and formed at the continuous casting machine, the steel is passed through a heat preservation roller and a gathering roller to be combined into one line, and then straightened by a straightening roller before entering the induction heating and temperature compensation device.

[0010] Furthermore, the continuous casting billet enters the electric induction heating device to heat the surface of the continuous casting billet, and then enters the high-temperature insulation roller; the high-temperature insulation roller consists of 3 sections, the first section is fixed, and the second and third sections are movable, which is convenient for transferring the continuous casting billets from two lines to one line and entering the rough rolling unit.

[0011] Furthermore, a cold billet removal stand and roller table are provided in front of the rough rolling mill; the continuous casting billet enters the rough rolling mill to roll out a square intermediate billet with a cross-section of 120x120mm or a circular intermediate billet with an equivalent cross-section. The intermediate billet is detached on the intermediate roller table, and then sent to the subsequent medium and finishing rolling mills by the intermediate roller table to produce bars and large coil products.

[0012] Furthermore, in order to reduce the temperature drop, the intermediate roller table is usually provided with a heat insulation cover.

[0013] Furthermore, the bars and large coil products produced by the finishing mill then enter the subsequent wire rod finishing mill and wire rod sizing mill to produce wire rod products.

[0014] Furthermore, cold billets usually appear during the rolling process. Cold billets usually occur when the rolling mill is shut down for a short period of time due to rolling accidents, replacement of pass types, guides and rollers, but the continuous casting is not stopped. There are two ways to handle cold billets, one is take-out; the other is to set up a small heating furnace next to the rolling line to heat and roll the cold billets when the continuous casting machine is shut down. When the cold billet is moved out of the cold billet stand and roller table, it is sent to the heating furnace by the furnace discharge roller table, and the cold billet is moved from the entrance to the heating furnace entrance through the backward stepping beam in the heating furnace, and then sent to the furnace entry roller table for collection. The cold billet loading-furnace entry-heating-furnace discharge-lateral movement-rolling execution procedure is opposite to the cold billet collection, and the equipment is all reversible.

[0015] Furthermore, the small heating furnace can be electrically heated or gas heated, and can only be used for heating a small amount of cold billets, and can also be used as an emergency buffer for the rolling line. If a small amount of cold billets are sold out, the small heating furnace can be omitted, and only a cold billet collection stand can be installed.

[0016] As mentioned above, the direct rolling technology of high-quality steel bars and wires,

[0017] For a continuous casting machine with a casting speed of 1.3m / min, if four strands are used for one rolling line, the hourly output is 96 tons and the annual output of the rolling line is 600,000 tons; if six strands are used for one rolling line, the hourly output is 140 tons and the annual output of the rolling line is 800,000 tons.

[0018] For the 600,000-ton rolling line to produce high-quality steel bars and wires,

[0019] The specific steps are as follows: The direct rolling production process is continuous casting-cutting to length-induction heating-high-temperature roller hot delivery-rolling. As shown in the attached figure, the 200x200mm cross-section continuous casting billet is formed at the continuous casting machine, cut into 8m long fixed length by hydraulic shears, and sent to the gathering roller by the insulation roller to combine the two streams of continuous casting billets into one line, and then enter the straightening roller, and the auxiliary continuous casting billet enters the electric induction heating device to heat the surface of the continuous casting billet, and then enters the high-temperature insulation roller behind. The high-temperature insulation roller consists of 3 sections. The first section is 18m long and is fixed. The second and third sections are both 10m long and are mobile, which is convenient for the two-line continuous casting billet to be transferred to one line and enter the rough rolling mill behind. A cold billet removal stand and roller are set in front of the rough rolling mill. The continuous casting billet enters the rough rolling unit composed of 6 large-reduction rolling mills to roll out the intermediate billet with a square section of 120x120mm (or a round intermediate billet with an equivalent section). The intermediate billet is removed on the intermediate roller. In order to reduce the temperature drop, the intermediate roller is usually equipped with a heat-insulating cover. Then, it is sent to the middle and finishing rolling units behind, that is, 18 continuous rolling mills (including 4 sizing units) to produce bars and large coils. It can also enter the 8 wire finishing mills and 4 wire sizing units behind to produce wire products.

[0020] The technical features of this invention are mainly reflected in three points: First, induction heating compensation, induction heating can increase the low-temperature layer with a surface depth of about 10mm from 950℃ to more than 1150℃. Insulation covers are set before and after the hydraulic shear to ensure that the internal temperature of the continuous casting billet is not lower than 1150℃. The high-temperature billet is compensated by induction heating, which eliminates the factors that cause cracks in the process of cooling the continuous casting billet from high temperature to room temperature and then sending it to the heating furnace to heat it to high temperature in the traditional production mode; second, the high-temperature insulation roller adopts a special structural design, and the roller is made of Cr28Ni48 material, which is resistant to high temperature of 1200℃. The roller insulation cover is heated by high-temperature resistance belt to ensure that the temperature inside the cover reaches 1200℃. Under normal circumstances, 7 billets are guaranteed to be in the roller, which is equivalent to each billet being heated and evenly heated in the high-temperature insulation roller for about 11 minutes, and the alloy elements are well diffused; third, two lines are combined into one line. In order to balance the production capacity, only a two-line high-temperature insulation roller design can be adopted, and the billets on one line outside the rolling line can be transferred to the rolling line by moving the roller. The position and switching rhythm of the steel billet in the roller table are controlled by automatic instruments and PLC.

[0021] The quality problems of high-quality steel bars and wires caused by billets are mainly surface cracks, internal segregation, shrinkage cavities, bubbles, and inclusions. Inclusions can be eliminated by improving the smelting level; shrinkage cavities and bubbles can be pressed together by large reduction and large compression ratio rolling. Although electromagnetic stirring is added during the continuous casting stage, it is difficult to completely eliminate the segregation of alloy elements. This is why the traditional technical route requires the billet to stay in the equalizing section of the heating furnace for a sufficient time to diffuse. Of course, large reduction and large compression ratio rolling can also eliminate some segregation. Surface cracks mainly come from two aspects. One is that they are generated in the second cooling section of the continuous casting process; the other is that the continuous casting billet cools too quickly during the cooling from high temperature to room temperature, and no slow cooling measures are adopted or the cold billet is heated too quickly when heated in the heating furnace. The surface cracks caused by the continuous casting process have been basically solved by optimizing the cooling system.

[0022] For high-strength alloy steel containing niobium, the hot delivery direct rolling process is more suitable. If the traditional process is used, niobium will precipitate in large quantities during the cooling process of the continuous casting billet. When the continuous casting billet enters the heating furnace for reheating, niobium cannot be dissolved into the grain boundary, and the niobium fine grain strengthening effect cannot be achieved, which is equivalent to wasting the role of niobium. The direct rolling process preserves niobium, and niobium plays a role in fine grain strengthening in the subsequent rolling process, effectively utilizing niobium.

[0023] Through the above analysis, the production of high-quality steel bars and wires can be completely realized by abandoning traditional heating furnaces and adopting direct rolling technology.

[0024] The advantages of the present invention are as follows: the continuous casting billet is heat-insulated and hot-transported at high temperature, and the surface temperature is quickly increased by induction heating, thereby avoiding the generation of surface cracks; the billet stays in the high-temperature heat-insulating roller for a sufficient time, so that the segregation of alloy elements can be alleviated, and combined with subsequent large reduction and large compression ratio rolling, the influence of segregation on product quality can be solved.

[0025] Economic benefit calculation: The power of the first line induction heating is about 1200KW, and the power of the three sections of high-temperature insulation roller heating is 400+200+200=800KW, totaling 2000KW. The two lines have a total of 4000KW. The normal production consumes 4000 degrees of electricity per hour, calculated at 0.5 yuan per degree, that is, 2000 yuan / hour. The rolling mill output is 96 tons / hour, and the heating cost per ton of steel billet is 20.8 yuan. Considering daily maintenance, it is calculated at 25 yuan. Compared with the heating cost of 50-70 yuan per ton of steel billet in traditional heating furnaces, the cost savings are about 30 yuan / ton on average, with an annual output of 600,000 tons of products and an annual benefit of 18 million yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the plan layout of the direct rolling process of continuous casting billet of high-quality steel bars and wires;

[0027] Among them: 1-continuous casting machine, 2-hydraulic shear, 3-insulating roller, 4-gathering roller, 5-straightening roller, 6-induction heating device, 7-high temperature insulation roller, 8-cold billet removal stand and roller, 9-roughing mill, 10-intermediate roller, 11-medium and finishing mill, 12-outlet roller, 13-small heating furnace, 14-inlet roller. DETAILED DESCRIPTION

[0028] Embodiment: For the production of high-quality steel bars and wires by a 600,000-ton rolling line, the specific steps are as follows: the direct rolling production process is continuous casting-cutting to length-induction heating-hot delivery by high-temperature rollers-rolling. As shown in the attached figure, the 200x200mm cross-section continuous casting billet is formed at the continuous casting machine 1, cut into 8m long fixed length by the hydraulic shear 2, and sent to the gathering roller 4 by the insulation roller 3 to combine the two streams of continuous casting billets into one line, and then enter the straightening roller 5, and the auxiliary continuous casting billet enters the electric induction heating device 6 to heat the surface of the continuous casting billet, and then enters the high-temperature insulation roller 7 behind. The high-temperature insulation roller 7 consists of 3 sections, the first section is 18m long and is fixed, the second and third sections are both 10m long and are mobile, which is convenient for the two-line continuous casting billet to be transferred to one line and enter the rough rolling unit 9 behind. A cold billet removal stand and roller 8 are set in front of the rough rolling mill. The continuous casting billet enters the rough rolling unit composed of 6 large-reduction rolling mills to roll out the intermediate billet with a square section of 120x120mm (or a round intermediate billet with a similar section). The intermediate billet is removed on the intermediate roller table 10. In order to reduce the temperature drop, the intermediate roller table is usually equipped with a heat-insulating cover. Then, the intermediate billet is sent to the middle and finishing rolling unit 11, i.e., 18 continuous rolling mills (including 4 sizing units) to produce bars and large coils. It can also enter the 8 wire finishing mills and 4 wire sizing units to produce wire products.

[0029] Cold billets usually occur when the rolling mill is shut down for a short period of time, such as for rolling accidents, replacement of pass types, guides and rollers, but continuous casting is not stopped. There are two ways to handle cold billets: one is to sell them out; the other is to set up a small heating furnace next to the rolling line to heat and roll the cold billets when the continuous casting machine is shut down. When the cold billets are removed from the cold billet removal stand and roller 8, they are sent to the heating furnace 13 by the furnace discharge roller 12. The cold billets are moved backwards through the stepping beam in the heating furnace, and then sent to the furnace entry roller 14 for collection. The cold billet loading-furnace entry-heating-furnace discharge-lateral movement-rolling execution procedure is opposite to the cold billet collection, and the equipment is reversible. The heating furnace 13 is a small heating furnace that can be heated by electricity or gas. It is only used for heating a small amount of cold billets, and can also be used as an emergency buffer for the rolling line. If a small amount of cold billets are sold out, the small heating furnace does not need to be installed, and only a cold billet collection stand is required.

Claims

1. A high-quality steel bar and wire direct rolling technology, characterized in that: The steps include: 1) Use 200x200mm square continuous casting billet or round continuous casting billet of equivalent cross section to realize direct rolling, cancel the traditional heating furnace, and set the rolling mill production line based on multi-strand continuous casting and combined with the continuous casting machine pulling speed; 2) The production process is continuous casting - fixed-length cutting - induction heating - high-temperature roller hot delivery - rolling.

2. The high-quality steel bar and wire direct rolling technology according to claim 1 is characterized in that: The continuous casting-cutting to length-induction heating and temperature-replenishing stage described in step 2) is that after being cut at the forming part of the continuous casting machine, the steel is passed through a heat preservation roller and a gathering roller to be combined into one line, and then is straightened by a straightening roller and then enters the induction heating and temperature-replenishing device.

3. The high-quality steel bar and wire direct rolling technology according to claim 1 is characterized in that: The continuous casting billet enters the electric induction heating device, and the surface of the continuous casting billet is heated and supplemented, and then enters the high-temperature insulation roller; The high-temperature insulation roller table consists of three sections. The first section is fixed, and the second and third sections are movable, which facilitates the transfer of continuous casting billets from two lines to one line and enters the rough rolling unit.

4. The high-quality steel bar and wire direct rolling technology according to claim 3 is characterized in that: A cold billet removal stand and roller table are provided in front of the rough rolling mill; the continuous casting billet enters the rough rolling mill to roll out a square intermediate billet with a cross-section of 120x120mm or a round intermediate billet with an equivalent cross-section. The intermediate billet is removed on the intermediate roller table and then sent to the subsequent medium and finishing rolling mills by the intermediate roller table.

5. The high-quality steel bar and wire direct rolling technology according to claim 4 is characterized in that: The intermediate roller table is provided with a heat-insulating cover.

6. The high-quality steel bar and wire direct rolling technology according to claim 4 is characterized in that: The bars and large coil products produced by the finishing mill then enter the subsequent wire finishing mill and wire sizing mill to produce wire products.

7. The high-quality steel bar and wire direct rolling technology according to claim 1 is characterized in that: As described above, cold billets will appear during the rolling process. Cold billets occur when rolling accidents occur, the pass type is changed, the guides and rollers are stopped for a short time while the continuous casting is not stopped. Cold billet treatment is to set a small heating furnace next to the rolling line to heat and roll the cold billets when the continuous casting machine is stopped. When the cold billet is removed from the cold billet stand and the roller table, it is sent to the heating furnace by the furnace discharge roller table, and the cold billet is moved backward by the walking beam in the heating furnace, and then sent to the furnace entry roller table for collection. The cold billet loading - entering the furnace - heating - exiting the furnace - lateral movement - rolling execution procedure is opposite to the cold billet collection, and the equipment is reversible.

8. The high-quality steel bar and wire direct rolling technology according to claim 7 is characterized in that: The small heating furnace is heated by electricity or gas, and is only used for heating a small amount of cold billets, or as an emergency buffer for the rolling line.

9. The high-quality steel bar and wire direct rolling technology according to claim 1 is characterized in that: For a continuous casting machine with a casting speed of 1.3m / min, if four strands are used for one rolling line, the hourly output is 96 tons and the annual output of the rolling line is 600,000 tons; if six strands are used for one rolling line, the hourly output is 140 tons and the annual output of the rolling line is 800,000 tons. For the 600,000-ton rolling line to produce high-quality steel bars and wires, the specific steps are as follows: the direct rolling production process is continuous casting - fixed-length cutting - induction heating and temperature compensation - high-temperature roller hot delivery - rolling. 200x200mm cross-section continuous casting billets are formed at the continuous casting machine, cut into 8m long fixed lengths by hydraulic shears, and sent to the gathering roller by the insulation roller to combine the two streams of continuous casting billets into one line, and then enter the straightening roller. The auxiliary continuous casting billets enter the electric induction heating device to heat and compensate the surface of the continuous casting billets, and then enter the high-temperature insulation roller behind. The high-temperature insulation roller table consists of 3 sections. The first section is 18m long and is fixed. The second and third sections are both 10m long and are movable, which is convenient for transferring the continuous casting billets from two lines to one line and entering the rough rolling mill at the back. A cold billet removal stand and roller table are set in front of the rough rolling mill. The continuous casting billets enter the rough rolling unit composed of 6 large reduction rolling mills to roll out intermediate billets with square sections of 120x120mm or round intermediate billets with equivalent sections. The intermediate billets are detached on the intermediate roller table, and the intermediate roller table is equipped with an insulation cover. Then, they are sent to the intermediate and finishing rolling units at the back, that is, 18 continuous rolling mills including 4 reducing and sizing units to produce bars and large coil products. They can also enter the 8 wire finishing mills and 4 wire reducing and sizing units at the back to produce wire products.

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