A method for producing high-strength hot-rolled coil for economical drill pipe equipment

Abstract

The invention discloses a production method of a high-strength hot-rolled coil for economical drill pipe equipment, wherein the mass percentage of the hot-rolled coil is C: 0.07-0.09%, Si: 0.10-0.20%, Mn: 1.30-1.50%, P: ≤0.010%, S≤0.005%, Nb: 0.030-0.050%, Ti: 0.060-0.080%, Alt: 0.020-0.050%; the preparation process route adopts molten iron pretreatment-converter-LF refining-RH-continuous casting-pile cooling-slab heating-high-pressure water dephosphorization-width setting-E1R1 rough rolling-E2R2 rough rolling-flying shear-finishing rolling high-pressure water descaling-F1-F7 finishing rolling-density laminar cooling-curling-tray transportation system-sampling inspection. The hot-rolled coil of the invention has the characteristics of low cost and excellent performance while meeting the mechanical properties and process performance technical requirements put forward by users.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgical plate production, and in particular to a production method of high-strength hot-rolled coil for economical drill pipe equipment. Background Art

[0002] At present, drill rods are used in engineering, construction, ports and other mechanical equipment with harsh working environments, such as boom structures, rotary drilling rigs, excavators, loaders, and hydraulic cylinders of dump trucks. The steel used in drill rod equipment is required to have high strength, high toughness, and good fatigue performance. With the revitalization of the equipment manufacturing industry and technological progress, especially the vigorous promotion of national infrastructure construction, the diameter of drill rod equipment is getting larger and larger. Seamless steel pipes can hardly meet the requirements of large diameters. Large-diameter straight seam welded pipes have emerged, and the demand for high-strength hot-rolled coils for straight seam welded pipes has increased significantly. It is urgent to develop a low-cost, high-performance hot-rolled coil for drill rod equipment, which has good market prospects. Summary of the invention

[0003] The purpose of the present invention is to provide a method for producing an economical high-strength hot-rolled coil for drill pipe equipment. The hot-rolled coil of the present invention has the characteristics of low cost and excellent performance while meeting the mechanical properties and process performance technical requirements put forward by users.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The invention discloses a production method of a high-strength hot-rolled coil for economical drill pipe equipment, wherein the mass percentage of the high-strength hot-rolled coil is C: 0.07-0.09%, Si: 0.10-0.20%, Mn: 1.30-1.50%, P: ≤0.010%, S≤0.005%, Nb: 0.030-0.050%, Ti: 0.060-0.080%, Alt: 0.020-0.050%, and the remainder is Fe and unavoidable inclusions; the preparation process route adopts molten iron pretreatment-converter-LF refining-RH-continuous casting-pile cooling-slab heating-high-pressure water dephosphorization-width setting-E1R1 rough rolling-E2R2 rough rolling-flying shear-finishing rolling high-pressure water descaling-F1-F7 finishing rolling-density laminar cooling-curling-tray transportation system-sampling inspection; wherein:

[0006] The smelting and continuous casting process ensures low sulfur and low phosphorus, and the chemical composition is controlled in a narrow range. The slab furnace temperature is ≥1200℃ to ensure that the slab structure is completely austenitized. The holding time is ≥30 minutes to ensure sufficient solid solution of the alloy elements. The rolling adopts controlled rolling and controlled cooling. The first stage of rough rolling is rolled in the recrystallization temperature area to fully refine the austenite grains. The final rolling temperature of rough rolling is greater than 1050℃. The second stage of finishing rolling is rolled in the non-recrystallization area. The final rolling temperature of finishing rolling is greater than 850℃. The slab structure is pressed or crushed to prepare for the subsequent cooling phase transformation. The coiling temperature is controlled at 600-630℃.

[0007] Furthermore, the specific preparation process includes the following steps:

[0008] Step 1: Pretreatment of molten iron. After desulfurization pretreatment, the S content of molten iron is ≤0.005%. Slag must be removed after desulfurization to ensure that the desulfurization slag removal area is greater than 90%;

[0009] The second step: converter smelting - LF refining - RH refining. The converter uses high-quality active lime and high-quality scrap steel to reduce the sulfur brought in by scrap steel. The converter bottom blowing gas adopts the full-process argon blowing mode. LF refining is further deoxidized, desulfurized, removed, and the composition and temperature are adjusted. The RH stage mainly degasses the molten steel and promotes the floating of inclusions. After vacuum treatment for 20 minutes, the vacuum is broken again to carry out calcium treatment. After the calcium treatment is completed, the soft blowing time must be guaranteed to be ≥8 minutes.

[0010] Step 3: Continuous casting, accurately control the superheat, and control the casting speed at 1.0-1.6m / min to ensure the quality of the ingot;

[0011] Step 4: Slab heating, strictly control the slab out-of-furnace temperature and soaking time, soaking time 40-60min, out-of-furnace temperature 1230±10℃;

[0012] Step 5: rolling, including rough rolling and finishing rolling. The rough rolling adopts 3+3 mode 2-stand rolling mill, and the reduction of each pass should be ≥10%, and the reduction rate of the 5th and 6th passes should be ≥25%; the finishing rolling adopts 7-stand continuous variable crown rolling mill, and the finishing rolling stage adopts constant speed rolling. The starting rolling temperature of the finishing rolling is ≤960℃, and the final rolling temperature of the finishing rolling is 860±10℃;

[0013] Step 6: The cooling adopts laminar cooling equipment, the cooling mode adopts the self-learning calculation result of the secondary system, and the coiling temperature is 610±10℃.

[0014] Furthermore, its mass percentage content is C: 0.08%, Si: 0.12%, Mn: 1.34%, P: 0.010%, S: 0.003%, Nb: 0.031%, Ti: 0.068%, Alt: 0.040%, and the rest is Fe and unavoidable inclusions.

[0015] Furthermore, its mass percentage content is C: 0.09%, Si: 0.16%, Mn: 1.31%, P: 0.008%, S: 0.002%, Nb: 0.035%, Ti: 0.075%, Alt: 0.038%, and the rest is Fe and unavoidable inclusions.

[0016] Furthermore, its mass percentage content is C: 0.08%, Si: 0.20%, Mn: 1.38%, P: 0.009%, S: 0.002%, Nb: 0.040%, Ti: 0.080%, Alt: 0.035%, and the rest is Fe and unavoidable inclusions.

[0017] Furthermore, its mass percentage content is C: 0.09%, Si: 0.15%, Mn: 1.35%, P: 0.008%, S: 0.003%, Nb: 0.038%, Ti: 0.070%, Alt: 0.032%, and the rest is Fe and unavoidable inclusions.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are:

[0019] The coil alloy has low cost and smooth controlled rolling and controlled cooling process. The metallographic structure is acicular ferrite, the grains are fine and uniform, and it has the characteristics of high strength, high toughness, high steel cleanliness, etc. It has excellent fatigue resistance, cold bending performance and welding performance. The mechanical properties and process performance meet the technical requirements of users and have excellent application effects. At the same time, the preparation method of the present invention is simple and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] Figure 1 Metallographic structure diagram of Example 1. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to specific examples. The examples are merely descriptions of the best mode for carrying out the present invention and do not limit the scope of the present invention in any way.

[0023] A method for producing an economical high-strength hot-rolled coil for drill pipe equipment comprises the following steps:

[0024] Step 1: Pretreatment of molten iron. After desulfurization pretreatment, the S content of molten iron is ≤0.005%. Slag must be removed after desulfurization to ensure that the desulfurization slag removal area is greater than 90%;

[0025] The second step: converter smelting - LF refining - RH refining. The converter uses high-quality active lime and self-produced high-quality scrap steel to reduce the sulfur brought in by scrap steel. The converter bottom blowing gas adopts the full-process argon blowing mode. LF refining is further deoxidized, desulfurized, removed, and the composition and temperature are adjusted. The RH stage mainly degassing the molten steel and promoting the floating of inclusions. After 20 minutes of vacuum treatment, the vacuum is broken again for calcium treatment. After the calcium treatment is completed, the soft blowing time must be guaranteed to be ≥8min;

[0026] Step 3: Continuous casting, accurately control the superheat, and control the casting speed at 1.0-1.6m / min to ensure the quality of the ingot;

[0027] Step 4: Slab heating, strictly control the slab out-of-furnace temperature and soaking time, soaking time 40-60min, out-of-furnace temperature 1230±10℃;

[0028] Step 5: rolling, including rough rolling and finishing rolling. The rough rolling adopts 3+3 mode 2-stand rolling mill, and the reduction of each pass should be ≥10%, and the reduction rate of the 5th and 6th passes should be ≥25%. The finishing rolling adopts 7-stand continuous variable crown (CVC) rolling mill, and the finishing rolling stage adopts constant speed rolling. The starting rolling temperature of the finishing rolling is ≤960℃, and the final rolling temperature of the finishing rolling is 860±10℃;

[0029] Step 6: The cooling adopts laminar cooling equipment, the cooling mode adopts the self-learning calculation result of the secondary system, and the coiling temperature is 610±10℃.

[0030] The chemical composition contents of the comparative examples and embodiments 1 to 4 of the present invention are shown in Table 1. Compared with the comparative examples, embodiments 1 to 4 do not contain expensive metals such as chromium, molybdenum and nickel, and reduce the niobium content and increase the titanium content (titanium is cheaper than niobium), with obvious cost advantages. The slab heating and rolling process parameters are shown in Table 2. Compared with the comparative examples, the coiling temperature (about 610°C) of embodiments 1 to 4 is easier to achieve precise control, while the medium-temperature coiling (about 420°C) of the comparative examples is more difficult to control (especially for mass production).

[0031] Table 1 Chemical composition (wt%) of comparative examples and embodiments 1 to 4 of the present invention

[0032] element C Si Mn P S Alt Nb Ti Cr Mo Ni Comparative Example 0.06 0.16 1.61 0.012 0.005 0.040 0.065 0.021 0.19 0.17 0.13 Example 1 0.08 0.12 1.34 0.010 0.003 0.040 0.031 0.068 / / / Example 2 0.09 0.16 1.31 0.008 0.002 0.038 0.035 0.075 / / / Example 3 0.08 0.20 1.38 0.009 0.002 0.035 0.040 0.080 / / / Example 4 0.09 0.15 1.35 0.008 0.003 0.032 0.038 0.070 / / /

[0033] Table 2 Slab heating and rolling process parameters of the comparative examples and embodiments 1 to 4 of the present invention

[0034]

[0035] The test results of the mechanical properties and process properties of the steel plate are shown in Table 3. It can be seen that the tensile strength and -20°C impact work of the comparative example have a large margin, which is much higher than the user's technical requirements; all indicators of Examples 1 to 4 meet the user's technical requirements, and the margin is moderate.

[0036] Table 3 Mechanical properties of the comparative examples and embodiments 1 to 4 of the present invention

[0037]

[0038] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing high-strength hot-rolled coil for economical drill pipe equipment, characterized in that: Its mass percentage is C: 0.07~0.09%, Si: 0.10~0.20%, Mn: 1.30~1.50%, P: ≤0.010%, S≤0.005%, Nb: 0.030~0.050%, Ti: 0.060~0.080%, Alt: 0.020~0.050%, and the rest is Fe and unavoidable inclusions; its preparation process route adopts molten iron pretreatment-converter-LF refining-RH-continuous casting-pile cooling-slab heating-high-pressure water dephosphorization-width setting-E1R1 rough rolling-E2R2 rough rolling-flying shear-finishing rolling high-pressure water descaling-F1~F7 finishing rolling-density laminar cooling-curling-pallet transportation system-sampling inspection; among which: The smelting and continuous casting process ensures low sulfur and low phosphorus, and the chemical composition is controlled in a narrow range. The slab furnace temperature is ≥1200℃ to ensure that the slab structure is completely austenitized. The holding time is ≥30 minutes to ensure sufficient solid solution of the alloy elements. The rolling adopts controlled rolling and controlled cooling. The first stage of rough rolling is rolled in the recrystallization temperature area to fully refine the austenite grains. The rough rolling and final rolling temperature are greater than 1050℃. The second stage of finishing rolling is rolled in the non-recrystallization area. The start rolling temperature of finishing rolling is ≤960℃, and the final rolling temperature of finishing rolling is greater than 850℃. The slab structure is pressed or crushed to prepare for the subsequent cooling phase transformation. The coiling temperature is controlled at 600~630℃.

2. The method for producing economical high-strength hot-rolled coil for drill pipe equipment according to claim 1, characterized in that: The specific preparation process includes the following steps: Step 1: Pretreatment of molten iron. After desulfurization pretreatment, the S content of molten iron is ≤0.005%. Slag must be removed after desulfurization to ensure that the desulfurization slag removal area is greater than 90%; The second step: converter smelting - LF refining - RH refining. The converter uses high-quality active lime and high-quality scrap steel to reduce the sulfur brought in by scrap steel. The converter bottom blowing gas adopts the full-process argon blowing mode. LF refining is further deoxidized, desulfurized, removed, and the composition and temperature are adjusted. The RH stage mainly degasses the molten steel and promotes the floating of inclusions. After vacuum treatment for 20 minutes, the vacuum is broken again for calcium treatment. After the calcium treatment is completed, the soft blowing time must be guaranteed to be ≥8 minutes. Step 3: Continuous casting, accurately control the superheat, and control the casting speed at 1.0~1.6m / min to ensure the quality of the ingot; Step 4: Slab heating, strictly control the slab out-of-furnace temperature and soaking time, soaking time 40~60min, out-of-furnace temperature 1230±10℃; Step 5: rolling, including rough rolling and finish rolling. The rough rolling adopts 3+3 mode 2-stand rolling mill, and the reduction of each pass should be ≥10%, and the reduction rate of the 5th and 6th passes should be ≥25%; the finish rolling adopts 7-stand continuous variable crown rolling mill, and the finish rolling stage adopts constant speed rolling. The final rolling temperature of the finish rolling is 860±10℃; Step 6: The cooling adopts laminar cooling equipment, the cooling mode adopts the self-learning calculation result of the secondary system, and the coiling temperature is 610±10℃.

3. The method for producing economical high-strength hot-rolled coil for drill pipe equipment according to claim 1, characterized in that: Its mass percentage is C: 0.08%, Si: 0.12%, Mn: 1.34%, P: 0.010%, S: 0.003%, Nb: 0.031%, Ti: 0.068%, Alt: 0.040%, and the rest is Fe and unavoidable inclusions.

4. The method for producing economical high-strength hot-rolled coil for drill pipe equipment according to claim 1, characterized in that: Its mass percentage is C: 0.09%, Si: 0.16%, Mn: 1.31%, P: 0.008%, S: 0.002%, Nb: 0.035%, Ti: 0.075%, Alt: 0.038%, and the rest is Fe and unavoidable inclusions.

5. The method for producing economical high-strength hot-rolled coil for drill pipe equipment according to claim 1, characterized in that: Its mass percentage is C: 0.08%, Si: 0.20%, Mn: 1.38%, P: 0.009%, S: 0.002%, Nb: 0.040%, Ti: 0.080%, Alt: 0.035%, and the rest is Fe and unavoidable inclusions.

6. The method for producing economical high-strength hot-rolled coil for drill pipe equipment according to claim 1, characterized in that: Its mass percentage is C: 0.09%, Si: 0.15%, Mn: 1.35%, P: 0.008%, S: 0.003%, Nb: 0.038%, Ti: 0.070%, Alt: 0.032%, and the rest is Fe and unavoidable inclusions.

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