Production method of high-surface-quality extra-thick plate

Abstract

The invention discloses a production method of a high-surface-quality extra-thick plate. The steel comprises the following chemical components in percentage by mass: 0.09 to 0.15 percent of C, 0.10 to 0.50 percent of Si, 1.0 to 1.50 percent of Mn, 0.2 to 1.50 percent of Cr, 0.4 to 0.7 percent of Mo, 0.3 to 2.5 percent of Ni, less than or equal to 0.020 percent of Nb, less than or equal to 0.070 percent of V, less than or equal to 0.020 percent of Ti, less than or equal to 0.010 percent of P, less than or equal to 0.012 percent of S, 0.015 to 0.050 percent of Als and the balance of Fe and inevitable impurities. A dynamic matching system of a blank state and process parameters is constructed, the optimal casting blank thickness and a differential pretreatment process are flexibly matched according to different finished product thicknesses of 80-150 mm, and an optimized heating model and a rolling descaling linkage mechanism are matched. The long-standing industrial bottlenecks of large grinding amount, low yield and high energy consumption in the production of the extra-thick plate are effectively solved, and grinding-free or low-grinding-rate and high-surface-quality production of the steel plate is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal material processing and relates to a production method of high-alloy super-thick plates, in particular, a steel plate with a thickness of 80-150 mm based on precise control of a blank state. BACKGROUND

[0002] In recent years, the demand for ship and offshore engineering steel in the field of offshore engineering continues to upgrade to 80 mm and above super-thick specifications, and the steel plates for offshore platforms with a thickness of less than 80 mm cannot meet the market demand; and the classification society clearly stipulates that the compression ratio of the billet (ingot) and the finished steel plate should be greater than or equal to 3, which directly forces the production end to match thicker specifications of the casting billet, further increasing the production threshold. More importantly, the production of thick casting billets with large compression ratios has multiple adverse effects: such steel contains high-alloy elements such as Ni, Cr and Mo, and a dense primary iron oxide scale is easily generated on the surface of the casting billet, which has strong adhesion and is difficult to remove by conventional means; at the same time, in order to ensure the core burn-through and uniform structure of the super-thick plate, long-time high-temperature heating is required, which further aggravates the oxidation of the casting billet surface, and the subsequent rolling passes and descaling passes are much less than those of medium and thin plates, making it difficult to remove the iron oxide scale, which is pressed into the matrix to form defects. These problems directly cause large grinding amount, low yield of finished steel plates, and further delay the delivery period due to grinding and rework, further increasing the production cost, which has become a common bottleneck for medium and heavy plate plants to produce super-thick plates with high surface quality. SUMMARY

[0003] In view of the deficiencies of the prior art, the application aims to provide a production method of high-alloy super-thick plates with high surface quality based on precise control of the blank state, which effectively solves the problem of iron oxide scale pressed into the super-thick plate and realizes high surface quality with no grinding or low grinding rate.

[0004] To achieve the above-mentioned purpose, the application adopts the following technical solution: A production method of super-thick plates with high surface quality, the process steps are blank pretreatment, heating, initial descaling, rolling, cooling, hot straightening, online surface quality detection, shot blasting, tempering and performance testing. The chemical composition of the steel is as follows: C=0.09-0.15, Si=0.10-0.50, Mn=1.0-1.50, Cr=0.2-1.50, Mo=0.4-0.7, Ni=0.3-2.5, Nb≤0.020, V≤0.070, Ti≤0.020, P≤0.010, S≤0.012, Als=0.015-0.050, and the balance is Fe and inevitable impurities; the thickness of the finished product is 80-150 mm; and the method comprises the following key steps: a) blank pre-treatment: select blank according to finished product thickness, when finished product thickness is 80-100 mm, adopt blank thickness of 300-350 mm, spray high-temperature anti-oxidation coating on blank surface; when finished product thickness is >100-150 mm, adopt blank thickness of >350 mm, first remove upper and lower surface oxide scale, then spray high-temperature anti-oxidation coating.

[0005] b) heating: send prepared blank into heating furnace, for blank thickness of >350-450 mm, total furnace time = (1.2-1.5) min / mm x blank thickness mm, among which soaking time is >60 min; for blank thickness of >350-450 mm, total furnace time = (1.4-1.6) min / mm x blank thickness mm, among which soaking time is >90 min; control soaking temperature at 1220-1250℃, furnace temperature is ≤1280℃.

[0006] c) initial descaling: adopt high-pressure water descaling treatment before rough rolling, set initial descaling box height at blank thickness mm + 130-150 mm.

[0007] d) rolling: adopt double-stand reversible rolling mill, adopt transverse and longitudinal alternating rolling mode in rough rolling stage to break up oxide scale; specifically, perform the sequence of 1st pass transverse rolling → 2nd pass emptying → 3rd pass longitudinal rolling → 4th pass emptying → 5th pass transverse rolling → 6th pass emptying → subsequent longitudinal rolling, roll to intermediate blank thickness of finished product thickness + 40-60 mm, and perform high-pressure water descaling at rolling mill inlet in specific pass; perform specific position descaling at first pass and last pass in finish rolling stage.

[0008] e) online surface quality detection: the produced super-thick plate has high surface quality with free grinding or grinding area less than 2%.

[0009] Further, a) blank pre-treatment: coat high-temperature anti-oxidation coating on upper and lower surface of blank, coating thickness is 1-2 mm, high-temperature anti-oxidation coating is Mg-Fe-Si component system.

[0010] Further, a) blank pre-treatment: for blank thickness of 300-350 mm, need to blow away loose surface oxide scale before coating; for blank thickness of >350-450 mm, remove surface oxide scale to expose clean metal matrix, and blank surface is fish scale-shaped.

[0011] Further, step d) rolling: in rough rolling stage, perform descaling at rolling mill inlet in 1st, 3rd, 5th, 7th and last pass; in finish rolling stage, perform descaling at rolling mill inlet and outlet in 1st pass, and perform descaling at rolling mill outlet in last pass.

[0012] Further, in the descaling of step d), the descaling water pressure is 190-212 Bar, and the rolling speed of the descaling pass is 1-2 m / s.

[0013] Further, in the descaling of step d), a middle blank swing cooling step is further included between rough rolling and finish rolling, the swing time is 40-60 s, and the roller way speed is 1-2 m / s.

[0014] The present application has the following beneficial effects: the present application realizes the flexibility and accurate control of the production of the heavy plate by constructing a "blank state-process parameter" dynamic matching system. The optimal casting blank thickness and pretreatment process are matched for different finished product thicknesses (80-150 mm), and the additional energy consumption and cost caused by blindly using an excessively thick casting blank are avoided. For example, for the finished product thickness of 80-100 mm, a medium-thickness blank of 300-350 mm is selected and a high-temperature antioxidant coating is used for protection, which not only meets the compression ratio requirement, but also avoids the lengthening of the heating time, the increase of the energy consumption and the increase of the grinding cost caused by the skinning treatment. The flexible strategy significantly reduces the risk of iron oxide scale pressing, reduces the grinding rework amount, improves the yield and delivery efficiency, and simultaneously realizes the synchronous improvement of the energy consumption control and the production efficiency through the optimization of the heating model and the descaling mechanism, so that the overall production cost is significantly reduced, and a replicable and generalizable heavy plate production technology scheme with high surface quality is provided for the industry. DETAILED DESCRIPTION

[0015] The present application will be further described below in combination with examples. Example 1

[0016] A production method of a heavy plate, the steel plate finished product thickness is 90 mm, and the chemical composition of the steel is C=0.15, Si=0.32, Mn=1.13, Cr=0.43, Mo=0.5, Ni=0.57, Ti=0.15, P=0.010, S=0.010, Als=0.029, and the balance is Fe and inevitable impurities. The key process steps of the steel plate are: a) Blank pretreatment: the blank thickness is selected as 302 mm according to the finished product thickness, the loose surface oxide scale is first blown clean, and the high-temperature antioxidant coating (Mg-Fe-Si component system) is coated on the upper and lower surfaces of the blank, and the coating thickness is 1-2 mm.

[0017] b) Heating: the blank is sent into the heating furnace, the total furnace time is 437 min, the soaking time is 65 min, the soaking temperature is controlled at 1220-1250℃, and the hearth temperature is ≤1280℃.

[0018] c) Initial descaling: high-pressure water descaling treatment is used before rough rolling, and the initial descaling box height is set to the blank thickness+145 mm.

[0019] d) Rolling: A double-stand reversing mill is used, and the rough rolling stage adopts a transverse and longitudinal alternating rolling mode to break the oxide scale. The rolling is performed in the order of 1st pass (transverse rolling)→2nd pass (emptying)→3rd pass (longitudinal rolling)→4th pass (emptying)→5th pass (transverse rolling)→6th pass (emptying)→subsequent longitudinal rolling, and the rolling is performed to an intermediate blank thickness of 140 mm, and high-pressure water descaling is performed at the mill inlet of a specific pass; the finishing rolling stage performs specific position descaling at the first pass and the last pass, and the specific rolling parameters are shown in Table 1. The intermediate blank swing time is 46 s, and the roller way speed is 2 m / s.

[0020] e) On-line surface quality detection: the produced super-thick plate has high surface quality without repair grinding. Example 2

[0021] A super-thick plate production method based on precise control of the blank state, the thickness of the steel plate finished product is 142 mm, and the mass percentage of the chemical composition of the steel is C=0.13, Si=0.14, Mn=1.12, Cr=0.82, Mo=0.46, Ni=1.8, V=0.053, P=0.007, S=0.001, Als=0.048, and the balance is Fe and unavoidable impurities. The key process steps of the steel plate are: a) Blank pretreatment: the blank thickness is selected as 435 mm according to the finished product thickness, the upper and lower surface oxide scale is first removed, the clean metal matrix is exposed by removing the surface oxide scale, the blank surface is fish scale-shaped, then the upper and lower surfaces of the blank are sprayed with high-temperature antioxidant coating (Mg-Fe-Si component system), and the coating thickness is 1-2 mm.

[0022] b) Heating: the blank is sent into the heating furnace, the total furnace time is 665 min, the soaking time is 102 min, the soaking temperature is controlled at 1220-1250℃, and the hearth temperature is ≤1280℃.

[0023] c) Initial descaling: high-pressure water descaling treatment is used before rough rolling, and the initial descaling box height is set to the blank thickness+150 mm.

[0024] d) Rolling: A double-stand reversing mill is used, and the rough rolling stage adopts a transverse and longitudinal alternating rolling mode to break the oxide scale. The rolling is performed in the order of 1st pass (transverse rolling)→2nd pass (emptying)→3rd pass (longitudinal rolling)→4th pass (emptying)→5th pass (transverse rolling)→6th pass (emptying)→subsequent longitudinal rolling, and the rolling is performed to an intermediate blank thickness of 140 mm, and high-pressure water descaling is performed at the mill inlet of a specific pass; the finishing rolling stage performs specific position descaling at the first pass and the last pass, and the specific rolling parameters are shown in Table 1. The intermediate blank swing time is 46 s, and the roller way speed is 2 m / s.

[0025] e) On-line surface quality inspection: the produced super-thick plate has a high surface quality with a dressing area less than 2%.

[0026] Table 1 Rolling process parameters of the steel plate of Example 1 .

[0027] Table 2 Rolling process parameters of the steel plate of Example 2 .

Claims

1. A method for producing a high surface quality extra-thick plate, comprising the following steps: billet pretreatment, heating, initial descaling, rolling, cooling, hot straightening, online surface quality inspection, shot blasting, tempering, and performance testing, characterized in that... The chemical composition of the steel (by mass percentage) is: C=0.09~0.15, Si=0.10~0.50, Mn=1.0~1.50, Cr=0.2~1.50, Mo=0.4~0.7, Ni=0.3~2.5, Nb≤0.020, V≤0.070, Ti≤0.020, P≤0.010, S≤0.012, Als=0.015~0.050, with the balance being Fe and unavoidable impurities; the finished product thickness is 80~150mm. This includes the following key steps: a) Billet pretreatment: Select billet according to the thickness of the finished product. When the finished product thickness is 80-100mm, use a billet with a thickness of 300-350mm and spray the surface of the billet with high-temperature anti-oxidation coating. When the finished product thickness is >100mm-150mm, use a billet with a thickness of >350mm. First, remove the iron oxide scale on the upper and lower surfaces, and then spray the high-temperature anti-oxidation coating. b) Heating: The prepared billet is sent into the heating furnace. For billets with a thickness of >350~450mm, the total time in the furnace is (1.2~1.5) min / mm × billet thickness in mm, of which the soaking time is ≥60min; for billets with a thickness of >350~450mm, the total time in the furnace is (1.4~1.6) min / mm × billet thickness in mm, of which the soaking time is ≥90min; the soaking temperature is controlled at 1220~1250℃, and the furnace temperature is ≤1280℃. c) Initial descaling: High-pressure water descaling is used before rough rolling. The height of the initial descaling box is set to the billet thickness in mm + 130~150 mm. d) Rolling: A two-stand reversible rolling mill is used. In the roughing stage, an alternating transverse and longitudinal rolling mode is adopted to break up the iron oxide scale. Specifically, the sequence is: 1st pass transverse rolling → 2nd pass empty rolling → 3rd pass longitudinal rolling → 4th pass empty rolling → 5th pass transverse rolling → 6th pass empty rolling → subsequent longitudinal rolling. The intermediate billet thickness is 40-60mm of the finished product thickness, and high-pressure water descaling is performed at the mill inlet of a specific pass. In the finishing stage, descaling is performed at specific locations in the first and last passes. e) Online surface quality inspection: The produced extra-thick plates have high surface quality with no need for grinding or less than 2% grinding area.

2. The method for producing a high surface quality extra-thick plate according to claim 1, characterized in that, In step a), the upper and lower surfaces of the blank are coated with a high-temperature anti-oxidation coating with a coating thickness of 1-2 mm. The high-temperature anti-oxidation coating is a Mg-Fe-Si composition system.

3. The method for producing a high surface quality extra-thick plate according to claim 1, characterized in that, In step a), for blanks with a thickness of 300-350mm, the loose surface iron oxide scale must be blown away before coating; for blanks with a thickness of >350-450mm, the surface iron oxide scale is removed to expose a clean metal substrate, and the surface of the blank has a fish scale pattern.

4. A method for producing a high surface quality extra-thick plate according to claim 1, characterized in that... Step d) Rolling: Descaling is performed at the mill inlet in the first, third, fifth, seventh and last passes of the roughing stage; descaling is performed at the mill inlet and outlet in the first pass of the finishing stage, and at the mill outlet in the last pass.

5. The method for producing a high surface quality extra-thick plate according to claim 1, characterized in that, In step d), the descaling water pressure is 190–212 Bar, and the rolling speed of the descaling pass is 1–2 m / s.

6. The method for producing a high surface quality extra-thick plate according to claim 1, characterized in that, Step d) includes an intermediate billet oscillation cooling step between roughing and finishing rolling, with an oscillation time of 40-60 s and a roller speed of 1-2 m / s.