A processing method for continuous billet opening of large square billets and intermediate billets obtained by processing the same

Abstract

The present invention discloses a processing method for continuous billet opening of large square billets, comprising: heating large square billet billets; descaling the surface of the heated billet with high-pressure water; opening the descaled billet by continuous rolling in 9 passes with alternating vertical and horizontal positions to obtain an intermediate billet; and at the same time, the parameters of the rolling pass in the 9-pass continuous rolling opening are disclosed. The present invention also discloses the intermediate billet obtained by the above processing method. The present invention improves the uniformity of the deformation of the corners of the large square billet by optimizing the billet opening rolling pass and reasonably matching the pass parameters, thereby preventing the excessive deformation of individual passes; at the same time, the heating temperature and the water pressure during descaling are controlled to avoid excessive temperature drop at the corners of the billet, improve the deformation characteristics of the corners, thereby reducing the generation of rolling cracks at the corners of the large square billet, and significantly reducing the grinding ratio of the intermediate billet, and even achieving no grinding, which effectively reduces the production cost and improves the yield rate of large square billets; the present invention has a simple process and can be industrialized after the parameters are limited.

Description

Technical Field

[0001] The invention relates to the field of casting billet rolling, and in particular to a method for continuously blanking a large square billet and an intermediate billet obtained by the blanking. Background Art

[0002] At present, bars and wires are divided according to the continuous casting billets used for rolling, mainly into small square billets, medium billets and large square billets.

[0003] Among them, small square billet refers to the continuous casting billet with a cross-section of ≤180mm×180mm; large square billet refers to the continuous casting billet with a cross-section of ≥220mm×220mm (including rectangular billet and round billet); the continuous casting billet with a cross-section between small square billet and large square billet is called medium billet.

[0004] In the process of using large square billets to produce rods and wires, they generally have to go through a billet opening process, which is to roll the large square billets into square billets of (140-180) mm × (140-180) mm, and then roll the square billets into rod and wire products. The square billets obtained by billet opening are the intermediate process products in the process of producing rods and wires from large square billets, and those in this field call them intermediate billets. Billet opening is a very important production process. If the production parameters of the billet opening process are not designed reasonably, it will directly lead to surface defects on the surface of the intermediate billet, such as rolling cracks, ear shapes, etc. In order to prevent the surface defects of the intermediate billet from being inherited to the rods and wires, the intermediate billet needs to increase the grinding process or even be directly scrapped.

[0005] During the billet opening process, the corners of the billet are deformed greatly and have low temperatures, which is a typical low-temperature rigid-plastic deformation zone. This makes it easy for the corners to produce rolling cracks. In order to eliminate rolling cracks, the traditional method is to add a mechanical grinding process to the intermediate billet, which will increase production costs and reduce the yield rate of large square billets.

[0006] There have been many studies on rolling crack control in the prior art. Chinese patent document CN201186286Y discloses a roller pass structure that avoids wrinkles on the surface of large-sized hot-rolled round steel. The technical solution adopted by the patent is that the width dimension B of the bottom of the roller pass groove of the first pass of the rough rolling mill and the width dimension b of the billet after heating should satisfy the relationship of Bb=3-5mm. The patent notes the influence of the rolling pass on the surface quality of the rolled piece, but only considers the influence of the first pass of rough rolling. Chinese patent document CN104209318A aims at the surface crack problem that occurs when large-sized round steel with a diameter of φ100-φ180mm is rolled with large rectangular continuous casting billets. By designing the rough rolling pass and the rough rolling process, the metal particles in the rheological instability area can enter the safe zone, thereby avoiding the generation of surface cracks. However, the rough rolling pass of the patent has 3-5 box-shaped holes, and the finished product is hot-rolled round steel.

[0007] The existing technology for controlling rolling surface cracks is mainly focused on the rolling process of round steel or wire. During the rolling process of round steel or wire, after the rough rolling of the ingot, the cross-sectional shape is rolled from square to elliptical, and the corners disappear. The corners of the ingot do not run through the entire rolling process, and subsequent rolling will not produce rolling cracks. The subsequent rolling reduction can eliminate rolling cracks to a certain extent. The rolling opening of large square billets is just the opposite. The rolling hole type is a box-shaped hole. The corners of the ingot always exist during the opening process. Rolling cracks are more difficult to control and the technical difficulty is greater. At present, there are few studies and reports on the control of rolling cracks during the rolling opening process of large square billets. Summary of the invention

[0008] Therefore, the technical problem to be solved by the present invention is that in the existing billet opening process, rolling cracks are easily generated at the corners, which increases production costs and reduces the yield rate of large square billets, thereby providing a processing method for continuous billet opening of large square billets and an intermediate billet processed therefrom.

[0009] To this end, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for continuously forming a large square billet, comprising the following steps:

[0011] S1: heating the large square billet;

[0012] S2: Descaling the surface of the heated blank using high pressure water;

[0013] S3: The descaled billet is subjected to 9-pass continuous rolling in alternating vertical and horizontal positions to obtain an intermediate billet;

[0014] In the 9-pass continuous rolling process of alternately setting the vertical and horizontal positions, the rolling pass types are all box-shaped holes, and the rolling sequence is the first rolling pass type, the second rolling pass type, the third rolling pass type, the fourth rolling pass type, the fifth rolling pass type, the sixth rolling pass type, the seventh rolling pass type, the eighth rolling pass type and the ninth rolling pass type;

[0015] Among them, the elongation coefficients of the first to ninth rolling hole profiles are 1.05±0.01, 1.26±0.01, 1.23±0.01, 1.21±0.01, 1.21±0.01, 1.27±0.01, 1.20±0.01, 1.29±0.01, and 1.19±0.01 respectively; the inner fillet radii of the first to ninth rolling hole profiles are 30±2mm, 30±2mm, 34±2mm, 30±2mm, 28±2mm, 26±2mm, 23±2mm, 20±2mm, and 20±2mm respectively.

[0016] Furthermore, the bite angles of the first to ninth rolling holes are 18±1°, 28±1°, 32±1°, 25±1°, 30±1°, 27±1°, 27±1°, 25±1°, and 23±1° respectively; the filling degrees of the rolling holes are 92±1%, 94±1%, 89±1%, 90±1%, 88±1%, 93±1%, 90±1%, 86±1%, and 89±1% respectively.

[0017] Furthermore, in step S1, the bloom is heated to 1200-1250°C.

[0018] In step S2, the pressure of the high-pressure water used for descaling is 15-20 MPa.

[0019] In step S3, the final rolling speed is 0.80-0.85 m / s.

[0020] Preferably, the cross-sectional dimensions of the large square billet before processing are (300-320 mm)×(380-400 mm), the corner radius is 20±3 mm, and the carbon content is 0.05-0.92 wt%;

[0021] The cross-sectional dimensions of the intermediate billet obtained are (140-160 mm)×(140-160 mm).

[0022] The present invention also provides an intermediate billet, which is obtained by subjecting a large square billet to the above-mentioned continuous billet opening processing method.

[0023] The technical solution of the present invention has the following advantages:

[0024] (1) The present invention improves the uniformity of the corner deformation of the large square billet by optimizing the billet rolling pass and reasonably matching the deformation amount, bite angle and filling degree, thereby preventing excessive deformation in individual passes; at the same time, the heating temperature and the water pressure during descaling are controlled to avoid excessive temperature drop at the corner of the billet, improve the corner deformation characteristics, and thus reduce the generation of rolling cracks at the corner of the large square billet. The grinding ratio of the intermediate billet is significantly reduced, and even grinding-free is achieved, which effectively reduces the production cost and improves the yield rate of the large square billet.

[0025] (2) The rolling pass of the present invention is limited to 9 times, the main purpose of which is to take into account both production cost and rolling crack control; if the rolling passes are less than 9 times, the elongation coefficient of one or more rolling holes will be too large, resulting in large corner deformation and serious rolling cracks; if the rolling passes are more than 9 times, although the elongation coefficient of each rolling hole is small, which is beneficial to rolling crack control, the equipment investment of the rolling mill is large, the rolling efficiency is low and the energy consumption is high, resulting in a surge in production costs, which is not conducive to the market promotion of the product.

[0026] (3) The present invention limits the parameters of the rolling hole type, wherein the elongation coefficient represents the rolling deformation of the billet. Since the corner is the position with the largest deformation on the cross section of the billet, by controlling the elongation coefficient, the excessive deformation of the corner in individual rolling passes can be prevented. The inner fillet of the hole type is mainly beneficial to the metal rheology of the corner. Sufficient metal rheology at the corner can reduce the generation of rolling cracks. In addition, the rolling deformation of the corner can be uniform. In order to improve the metal rheology at the corner, the radius of the inner fillet of the hole type should be larger than the corner fillet of the rolled billet. If the bite angle is too large, rolling will stop or pile up steel, interrupting production; if the bite angle is too small, the elongation coefficient of the hole type will be too small, and a rolling mill with a larger roller diameter will have to be used or the number of rolling mills will be increased, which will increase production costs; if the filling is too large, ear-shaped will be generated, and the intermediate billet needs to be repaired or scrapped; if the filling is too small, the billet will be twisted, which is not conducive to rolling stability and surface quality control. By designing these hole parameters, the uniformity of the corner deformation of the large square billet is improved, while ensuring smooth production of the billet and preventing the occurrence of other rolling defects such as ear shape.

[0027] (4) The present invention limits the parameters of the blank rolling, wherein the final rolling speed is limited. A too high final rolling speed will lead to large stress at the corners, poor plasticity, and rolling cracks; while a slow final rolling speed will lead to a large temperature drop in the blank, which will lead to a low deformation temperature at the corners and rolling cracks. The pressure of the high-pressure water used for descaling is limited. Too high a pressure will cause the temperature drop of the blank to be too large and the deformation temperature of the corners to be too low; too low a pressure will make it difficult to remove the iron oxide on the surface, resulting in the presence of oxide scale pressed into the surface of the intermediate blank, which requires an additional grinding process to remove it. The heating temperature is limited. Increasing the heating temperature can increase the deformation temperature at the corners, which is beneficial to the control of rolling cracks. However, too high a heating temperature will lead to severe decarburization of the blank, coarse grains, and affect product performance. These blank rolling parameters cooperate with each other to improve the corner deformation characteristics, and further cooperate with the restrictions on the hole parameters, thereby reducing the occurrence of rolling cracks at the corners of large square billets.

[0028] (5) The process of the present invention is simple, and industrial production can be carried out after the parameters of the rolling hole and the blank rolling parameters are defined. DETAILED DESCRIPTION

[0029] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0030] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0031] The large square billet used in the embodiments and comparative examples is a 300 mm×390 mm large square billet produced by the BOF-LF-CC process, with a corner radius of 20 mm, and the size of the rolled intermediate billet is 140 mm×140 mm.

[0032] Example 1

[0033] This embodiment provides a method for continuously forming a large square billet, comprising the following steps:

[0034] (1) Heating a large square billet with a grade of ML40Cr in a heating furnace;

[0035] (2) Descaling the surface of the billet with high-pressure water after it comes out of the furnace;

[0036] (3) The descaled billet is rolled by 9 consecutive passes with alternating vertical and horizontal rolling to obtain an intermediate billet;

[0037] In the 9 consecutive rolling passes of the blanking process with alternating vertical and horizontal positions, the rolling hole profiles are all box-shaped holes, which are, in order of rolling, the first rolling hole profile, the second rolling hole profile, the third rolling hole profile, the fourth rolling hole profile, the fifth rolling hole profile, the sixth rolling hole profile, the seventh rolling hole profile, the eighth rolling hole profile and the ninth rolling hole profile.

[0038] The specific slab rolling parameters are shown in Table 1, and the pass parameters are shown in Table 2.

[0039] Example 2

[0040] This embodiment provides a method for continuously forming a large square billet, comprising the following steps:

[0041] (1) Heating a large square billet with a grade of ML08Al in a heating furnace;

[0042] (2) Descaling the surface of the billet with high-pressure water after it comes out of the furnace;

[0043] (3) The descaled billet is rolled by 9 consecutive passes with alternating vertical and horizontal rolling to obtain an intermediate billet;

[0044] In the 9 consecutive rolling passes of the blanking process with alternating vertical and horizontal positions, the rolling hole profiles are all box-shaped holes, which are, in order of rolling, the first rolling hole profile, the second rolling hole profile, the third rolling hole profile, the fourth rolling hole profile, the fifth rolling hole profile, the sixth rolling hole profile, the seventh rolling hole profile, the eighth rolling hole profile and the ninth rolling hole profile.

[0045] The specific slab rolling parameters are shown in Table 1, and the pass parameters are shown in Table 2.

[0046] Example 3

[0047] This embodiment provides a method for continuously forming a large square billet, comprising the following steps:

[0048] (1) Heating a large square billet with a grade of LX82A in a heating furnace;

[0049] (2) Descaling the surface of the billet with high-pressure water after it comes out of the furnace;

[0050] (3) The descaled billet is rolled by 9 consecutive passes with alternating vertical and horizontal rolling to obtain an intermediate billet;

[0051] In the 9 consecutive rolling passes of the blanking process with alternating vertical and horizontal positions, the rolling hole profiles are all box-shaped holes, which are, in order of rolling, the first rolling hole profile, the second rolling hole profile, the third rolling hole profile, the fourth rolling hole profile, the fifth rolling hole profile, the sixth rolling hole profile, the seventh rolling hole profile, the eighth rolling hole profile and the ninth rolling hole profile.

[0052] The specific slab rolling parameters are shown in Table 1, and the pass parameters are shown in Table 2.

[0053] Comparative Examples 1-3

[0054] This comparative example provides a method for continuously opening a large square billet, comprising the following steps:

[0055] (1) Heating a large square billet of grade ML40Cr in a heating furnace;

[0056] (2) Descaling the surface of the billet with high-pressure water after it comes out of the furnace;

[0057] (3) The descaled billet is rolled by 9 consecutive passes with alternating vertical and horizontal rolling to obtain an intermediate billet;

[0058] In the 9 consecutive rolling passes of the blanking process with alternating vertical and horizontal positions, the rolling hole profiles are all box-shaped holes, which are, in order of rolling, the first rolling hole profile, the second rolling hole profile, the third rolling hole profile, the fourth rolling hole profile, the fifth rolling hole profile, the sixth rolling hole profile, the seventh rolling hole profile, the eighth rolling hole profile and the ninth rolling hole profile.

[0059] The specific slab rolling parameters are shown in Table 1, and the pass parameters are shown in Table 2.

[0060] Comparative Example 4

[0061] This comparative example provides a method for continuously opening a large square billet, comprising the following steps:

[0062] (1) Heating a large square billet with a grade of ML08Al in a heating furnace;

[0063] (2) Descaling the surface of the billet with high-pressure water after it comes out of the furnace;

[0064] (3) The descaled billet is rolled by 9 consecutive passes with alternating vertical and horizontal rolling to obtain an intermediate billet;

[0065] In the 9 consecutive rolling passes of the blanking process with alternating vertical and horizontal positions, the rolling hole profiles are all box-shaped holes, which are, in order of rolling, the first rolling hole profile, the second rolling hole profile, the third rolling hole profile, the fourth rolling hole profile, the fifth rolling hole profile, the sixth rolling hole profile, the seventh rolling hole profile, the eighth rolling hole profile and the ninth rolling hole profile.

[0066] The specific slab rolling parameters are shown in Table 1, and the pass parameters are shown in Table 2.

[0067] Comparative Example 5

[0068] This comparative example provides a method for continuously opening a large square billet, comprising the following steps:

[0069] (1) Heating a large square billet with a grade of ML08Al in a heating furnace;

[0070] (2) Descaling the surface of the billet with high-pressure water after it comes out of the furnace;

[0071] (3) The descaled billet is rolled by 7 consecutive passes with alternating vertical and horizontal rolling to obtain an intermediate billet;

[0072] In the 7-pass continuous rolling process of alternating vertical and horizontal rolling, the rolling holes are all box-shaped holes, which are the first rolling hole, the second rolling hole, the third rolling hole, the fourth rolling hole, the fifth rolling hole, the sixth rolling hole and the seventh rolling hole in the order of rolling.

[0073] The specific slab rolling parameters are shown in Table 1, and the pass parameters are shown in Table 2.

[0074] Comparative Example 6

[0075] This comparative example provides a method for continuously opening a large square billet, comprising the following steps:

[0076] (1) Heating a large square billet with a grade of LX82A in a heating furnace;

[0077] (2) Descaling the surface of the billet with high-pressure water after it comes out of the furnace;

[0078] (3) The descaled billet is rolled by 9 consecutive passes with alternating vertical and horizontal rolling to obtain an intermediate billet;

[0079] In the 9 consecutive rolling passes of the blanking process with alternating vertical and horizontal positions, the rolling hole profiles are all box-shaped holes, which are, in order of rolling, the first rolling hole profile, the second rolling hole profile, the third rolling hole profile, the fourth rolling hole profile, the fifth rolling hole profile, the sixth rolling hole profile, the seventh rolling hole profile, the eighth rolling hole profile and the ninth rolling hole profile.

[0080] In each comparative example, the pass parameters of Example 1 and Comparative Example 1 are the same, but the blanking rolling parameters are different; the blanking rolling parameters of Example 1 and Comparative Example 2 are the same, but the pass elongation coefficient is different; the blanking rolling and pass parameters of Example 1 and Comparative Example 3 are different. The blanking rolling parameters of Example 2 and Comparative Example 4 are the same, but the inner fillet of the pass is different; the blanking rolling parameters of Example 2 and Comparative Example 5 are the same, but the number of rolling pass is different. Example 6 and Comparative Example 6 have different blanking rolling and pass parameters.

[0081] Table 1 Billet rolling parameters

[0082] Brand Carbon content Heating temperature Descaling water pressure Final rolling speed Example 1 ML40Cr 0.40％ 1230℃ 18MPa 0.83m / s Comparative Example 1 ML40Cr 0.40％ 1180℃ 25MPa 0.73m / s Comparative Example 2 ML40Cr 0.40％ 1230℃ 18MPa 0.83m / s Comparative Example 3 ML40Cr 0.40％ 1180℃ 25MPa 0.73m / s Example 2 ML08Al 0.08％ 1200℃ 20MPa 0.82m / s Comparative Example 4 ML08Al 0.08％ 1200℃ 20MPa 0.82m / s Comparative Example 5 ML08Al 0.08％ 1200℃ 20MPa 0.82m / s Example 3 LX82A 0.82％ 1250℃ 20MPa 0.85m / s Comparative Example 6 LX82A 0.82％ 1190℃ 25MPa 0.75m / s

[0083] Table 2 Hole type parameters

[0084]

[0085]

[0086] Test example

[0087] The intermediate blanks obtained from the embodiments and comparative examples were shot peened and then subjected to magnetic particle inspection. The crack ratio and grinding ratio of the intermediate blank corners were counted. The results are shown in Table 3.

[0088] Table 3 Statistical results of intermediate billet rolling crack ratio and grinding ratio

[0089]

[0090]

[0091] It can be seen from the above table that by limiting the parameters of the blanking rolling and the pass parameters, the intermediate blank obtained by the blanking method provided by the present invention has effectively controlled rolling cracks compared with the comparative example, and the rolling crack ratio is reduced from 8-85% to less than 3%. Among them, from the comparison of the effects of comparative examples 1-3 and embodiment 1, it can be seen that whether it is changing the pass elongation coefficient or the blanking rolling parameter crack, it will have a great impact on the rolling crack; from the comparison of the effects of comparative examples 4, 5 and embodiment 2, it can be seen that comparative example 4 changes the pass inner fillet radius parameter, and the intermediate blank rolling crack ratio is significantly improved; comparative example 5 changes the number of rolling pass types, which ultimately leads to a sharp increase in the rolling crack ratio.

[0092] In each embodiment of the present application, the grinding ratio of Embodiments 1-2 is significantly reduced; for Embodiment 3, the obtained intermediate blank can be free of grinding.

[0093] The above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for continuously opening large square billets, characterized in that: The steps include: S1: heating the large square billet; S2: Descaling the surface of the heated blank using high pressure water; S3: The descaled billet is subjected to 9-pass continuous rolling in alternating vertical and horizontal positions to obtain an intermediate billet; In the 9-pass continuous rolling process of alternately setting the vertical and horizontal positions, the rolling pass types are all box-shaped holes, and the rolling sequence is the first rolling pass type, the second rolling pass type, the third rolling pass type, the fourth rolling pass type, the fifth rolling pass type, the sixth rolling pass type, the seventh rolling pass type, the eighth rolling pass type and the ninth rolling pass type; Among them, the elongation coefficients of the first to ninth rolling pass profiles are 1.05±0.01, 1.26±0.01, 1.23±0.01, 1.21±0.01, 1.21±0.01, 1.27±0.01, 1.20±0.01, 1.29±0.01, and 1.19±0.01, respectively; The inner fillet radii of the first to ninth rolling hole types are 30±2mm, 30±2mm, 34±2mm, 30±2mm, 28±2mm, 26±2mm, 23±2mm, 20±2mm, and 20±2mm respectively.

2. The processing method according to claim 1, characterized in that: The bite angles of the first to ninth rolling pass types are 18±1°, 28±1°, 32±1°, 25±1°, 30±1°, 27±1°, 27±1°, 25±1°, and 23±1°, respectively.

3. The processing method according to claim 1 or 2, characterized in that: The filling degrees of the rolling holes are 92±1%, 94±1%, 89±1%, 90±1%, 88±1%, 93±1%, 90±1%, 86±1% and 89±1% respectively.

4. The processing method according to claim 1, characterized in that: In step S1, the bloom is heated to a temperature of 1200-1250°C.

5. The processing method according to claim 1, characterized in that: In step S2, the pressure of the high-pressure water used for descaling is 15-20 MPa.

6. The processing method according to claim 1, characterized in that: In step S3, the final rolling speed is 0.80-0.85 m / s.

7. The processing method according to claim 1, characterized in that: The cross-sectional dimensions of the large square billet before processing are (300-320 mm)×(380-400 mm), the corner radius is 20±3 mm, and the carbon content is 0.05-0.92 wt%; The cross-sectional dimensions of the intermediate billet obtained are (140-160 mm)×(140-160 mm).

8. An intermediate blank, characterized in that: The intermediate billet is obtained by subjecting a large square billet to the continuous billeting processing method described in any one of claims 1 to 7.

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