A thick-gauge Q890E steel plate with good core toughness and corrosion resistance and its manufacturing method

Abstract

The present invention discloses a thick-gauge Q890E steel plate with good core toughness and corrosion resistance and a manufacturing method thereof. The steel plate comprises the following components: C: 0.14-0.17%, Si: 0.25-0.40%, Mn: 1.20-1.35%, P ≤ 0.010%, S ≤ 0.003%, Al: 0.020-0.040%, Nb: 0.020-0.035%, Ti: 0.010-0.020%, Cr: 0.50-0.60%, Mo: 0.40-0.50%, Ni: 0.25-0.35%, Cu: 0.28-0.38%, B: 0.0015-0.0025%, with the balance being Fe and unavoidable impurities. The steel plate has a carbon equivalent of ≤ 0.66% and an atmospheric corrosion resistance index of ≥ 6.2. The steel plate is 60-80mm thick and has good comprehensive performance, excellent core low-temperature toughness and corrosion resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of medium and thick steel plates, and in particular relates to a thick-gauge Q890E steel plate with good core toughness and corrosion resistance and a manufacturing method thereof. Background Art

[0002] With the rapid development of coal mining, hydraulic supports for coal mining machinery have become core equipment. High-strength steel plates account for approximately 80% of the weight of hydraulic supports. With the demand for lightweight assembly and stronger load-bearing capacity, high-strength steel Q890 is gradually replacing Q550 and Q690 grades. Because hydraulic supports must withstand complex and variable cyclic loads, the steel plates must not only have high strength but also good weldability and low-temperature toughness. Especially for extra-thick steel plates with a thickness of 60mm or more, although relevant manufacturing cases exist, they are subject to severe central segregation and porosity defects in continuous casting billets; insufficient rolling reduction ratios, resulting in non-penetration of core rolling deformation; and insufficient quenching and cooling, resulting in a mixed microstructure. These factors result in poor performance through the thickness of the steel plates, with low core impact energy and Z-direction shrinkage, and are in urgent need of solutions.

[0003] Furthermore, due to the complex underground operating environment and the extremely high humidity within the tunnels, which are often weakly alkaline, hydraulic supports are susceptible to pitting, roughening, and other corrosion issues when exposed to these conditions for extended periods. Years of service in these environments can lead to corrosion aging and degradation of component mechanical properties. While traditional surface treatment methods such as painting can be used, they are expensive and pose environmental risks. Therefore, the most fundamental way to extend the service life of Q890 steel plates is to improve their inherent corrosion resistance, but relatively little research and steel plate manufacturing methods are available.

[0004] Prior art 1: Patent "A method for producing Q890D ultra-high strength steel medium and thick plates by online quenching" (publication number: CN114990305A), using "C: 0.14-0.17%, Si: 0.20-0.50%, Mn: 1.00-1.50%, P≤0.015%, S≤0.003%, Cr: 0.30-0.40%, Mo: 0.40-0.70%, Ni: 0.30-0.60%, Nb: 0.015-0.040%, V: 0.03-0.06%, B: 0.001-0.002%, Ti: 0.005-0.025%, Alt: 0.02-0.0 5%, "composition design, slab thickness 300mm, through the first rough rolling start temperature 1050-1150℃, the second rough rolling start temperature 880-900℃, the intermediate billet thickness ≥110mm, the second rough rolling finish temperature 840-870℃, the initial temperature of online cooling 810℃~830℃, the red return temperature ≤200℃, the cooling rate 15-30℃ / s, the tempering temperature 600-620℃, the produced steel plate thickness 60-70mm, the yield strength 937-945MPa, the tensile strength 978-986MPa, the elongation 14.5-15%, the -20℃ impact energy 87-167J, the microstructure is lath martensite + granular bainite. This patented steel plate has an overall compression ratio of 4-5, a minimum intermediate billet thickness of 110mm, and a second-stage deformation rate of only 36.4-45.5%. Furthermore, the overall cooling rate is relatively low, which inevitably affects the cooling rate in the core, resulting in uneven microstructure. The -20°C impact energy averages 132J, with a maximum variation of 80J, failing to meet the requirements for good low-temperature toughness. Consequently, it is speculated that the core impact performance and Z-axis properties are also poor. Furthermore, this steel plate lacks corrosion resistance.

[0005] Existing technology 2, patent "A method for producing quenched and tempered high-strength Q890E extra-thick steel plate" (publication number: CN103555911A), uses "C≤0.16%, Si: 0.20-0.40%, Mn: 1.30-1.40%, P≤0.015%, S≤0.003%, Cr: 0.30-0.50%, Mo: 0.40-0.70%, Cu+Ni≤1.0%, Nb+V+Ti≤0.10%, B≤0.0025 %, Als: 0.03-0.05%." This patented steel plate utilizes a high-temperature heating + high-temperature gradient reduction + online quenching + offline quenching + tempering process to produce 100-120mm thick steel plates. These plates exhibit a yield strength of 882MPa, a tensile strength of 936-948MPa, an elongation of 17.8-18.2%, and a -40°C impact energy of 78.4-88.3J, 36.9-39.4J in the core, and 32.5-36.7% in the Z-direction. While this patented steel plate meets the -40°C impact energy requirements and the Z25 through-thickness shrinkage in the core, the overall margin is relatively low, partly due to the incompatibility with the selected 300mm ingot thickness. The total reduction ratio is only 2.5-3. The slab undergoes 13 consecutive air cooling passes using high-pressure water from the rolling mill in the first stage, and 7 air cooling passes in the second stage. This method is inefficient and complex for continuous industrial production, making it difficult to adapt. Another method is to use online quenching + offline quenching, which significantly increases the production process and cost. Similarly, this steel plate does not have corrosion resistance.

[0006] Existing technology 3, patent "A kind of ultra-high strength engineering machinery steel Q890D and its production method" (publication number: CN111945077A), adopts "C: 0.07-0.09%, Mn: 1.10-1.30%, Mo: 0.50-0.60%, Cr: 0.30-0.40%, Nb: 0.015-0.035%, Ti: 0.015-0.025%, B: 0.0008-0.0015%, Als ≥ 0.015%" composition design, through the first rough rolling start temperature 1080-1100℃, first-stage finishing rolling temperature ≥980℃, second-stage rolling temperature ≤950℃, finishing rolling temperature 840-880℃, relaxation 60-100s, cooling temperature 670-700℃, red-returning temperature ≤250℃, cooling rate ≥10℃ / s, tempering temperature 650℃, the produced steel plate thickness is 20mm, yield strength 907-1005MPa, tensile strength 987-1098MPa, elongation 13.8-16.3%, -20℃ impact energy 86-186J, and the microstructure is low carbon bainite. The composition design of Example 1, calculated using an empirical formula, yields a Tnr (recrystallization end temperature) of approximately 916°C. However, the actual second-stage rolling start temperature, 950°C, is approximately 34°C higher than Tnr, which inevitably produces a mixed-grain structure and severely impacts subsequent low-temperature toughness. This is consistent with the uneven impact energy results of 97 / 86 / 140J at -20°C. This patent utilizes a low-carbon composition design system to produce steel plates with a thickness of 20mm, raising significant uncertainty about its applicability to the production of extra-thick steel plates ≥ 60mm. Furthermore, the steel plates lack corrosion resistance. Summary of the Invention

[0007] The purpose of the present invention is to provide a thick-gauge Q890E steel plate with good core toughness and corrosion resistance and a manufacturing method thereof. The invention aims to adopt a reasonable and concise composition design, couple the clean steel smelting and continuous casting process technology, and use a large compression ratio to perform two-stage controlled rolling and online quenching + tempering technology to manufacture a 60-80mm thick steel plate with good low-temperature toughness in the core and corrosion resistance, so as to solve a series of problems of existing ultra-high strength steel such as poor low-temperature toughness, complex and long production process, corrosion resistance, and short service life.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A thick-gauge Q890E steel plate with good core toughness and corrosion resistance, the chemical composition and mass percentage of the steel plate are: C: 0.14-0.17%, Si: 0.25-0.40%, Mn: 1.20-1.35%, P≤0.010%, S≤0.003%, Al: 0.020-0.040%, Nb: 0.020-0.035%, Ti: 0.010-0.020%, Cr: 0.50-0.60%, Mo: 0.40-0.50%, Ni: 0.25-0.35%, Cu: 0.28-0.38%, B: 0.0015 -0.0025%, N≤30ppm, H≤2ppm, O≤20ppm, the balance is Fe and unavoidable impurities; carbon equivalent CEV≤0.66%, where CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15.

[0010] Preferably, the thickness of the steel plate is 60-80 mm, the yield strength of the steel plate is ≥980 MPa, the tensile strength is ≥1030 MPa, the elongation is ≥14%, the longitudinal impact energy of the steel plate at -40°C at 1 / 4 of the thickness is ≥120 J, the longitudinal impact energy at -40°C at 1 / 2 of the thickness is ≥100 J, and the cross-sectional shrinkage rate of the steel plate in the thickness direction (i.e., the cross-sectional shrinkage rate in the Z direction) is ≥50%.

[0011] Preferably, the corrosion resistance rate of the steel plate is 0.232-0.239 mm / year.

[0012] Preferably, the atmospheric corrosion resistance index of the steel plate is ≥6.2, I=26.01Cu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29CuNi-9.10NiP-33.39Cu 2 .

[0013] The present invention also provides a method for manufacturing the above-mentioned thick-gauge Q890E steel plate with good core toughness and corrosion resistance, comprising the following steps:

[0014] 1. Smelting: Hot metal pretreatment → Converter smelting → LF furnace refining → RH vacuum treatment → continuous casting. The bright surface of hot metal after desulfurization and slag stripping is ≥95%; converter double slag method smelting, slag blocking steelmaking, slag thickness ≤40mm; LF refining white ash is added at a consumption of 8kg per ton of steel, white slag is kept for ≥12 minutes after the first power supply, and the end point slag sample is controlled to have Al2O3>24%, and the CaO / Al2O3 content ratio is 1.7-1.9. Before leaving the station, ensure that ferroboron is added 5 minutes after the addition of ferrotitanium; RH high vacuum time is ≥20 minutes, and feeding after breaking the air The casting shall be 200-300 meters long in the pure calcium line, with the soft argon blowing time ≥10 minutes and the molten steel calming time before lifting ≥5 minutes; the casting shall maintain a constant pulling speed of 0.5-0.7m / min, the liquid level fluctuation shall be controlled to ±2mm, the superheat shall be 20-25℃, the casting shall be protected throughout and electromagnetic stirring and heavy pressure shall be applied, and the reduction under heavy pressure at the end of solidification shall be 15-25mm; the thickness of the ingot shall be ≥400mm, the internal center segregation of the slab shall be ≤C class 0.5 level, and there shall be no other defects.

[0015] 2. Heating: Use a walking beam heating furnace, the soaking section temperature is 1230-1250℃, and the soaking time is controlled at 0.3-0.4min / mm.

[0016] 3. Rolling: Two-stage segmented rolling is adopted, and the total reduction ratio is ≥5. In the rough rolling stage, high-pressure water descaling and cooling are turned on before each rolling. The starting rolling temperature is ≥1060℃, and the ending temperature is ≥980℃. The single-pass reduction of the last three passes is guaranteed to be ≥40mm. The thickness of the intermediate billet t0 is ≥2.0 times the thickness of the finished steel plate. In the finishing rolling stage, high-pressure water descaling and cooling are turned on every other pass. The starting rolling temperature is not higher than Tnr-0.15×t0℃, (t0 is the thickness of the intermediate billet, in mm). The cumulative reduction rate in the finishing rolling stage is ≥50%. After rolling, pre-straightening is carried out and rapid water cooling is performed. Among them, Tnr=887+464×C+890×Ti+363×Al-357×Si+6445×Nb-644×Nb 1 / 2 +732×V-230×V 1 / 2 .

[0017] 4. Online quenching: Steel plate cooling temperature ≥850℃, red-return temperature ≤100℃, cooling rate ≥25℃ / s. Use DQ+ACC cooling mode, with two-stage water pressure ≥0.5MPa and ≥0.2MPa respectively. The DQ frame uses 4 groups of slit nozzles, with the first group's upper spray flow rate of 140-160m 3 / h, the 2nd to 4th group of upward spray flow rate is 260-280m 3 / h, gap water ratio 2.1-2.3. ACC frame uses 26 groups of high-density nozzles, each group of upper and middle cavity flow 220-240m 3 / h, with a high-density water ratio of 2.45-2.6. The upper header of the DQ frame is 200-300mm from the upper surface of the steel plate, and the upper header of the ACC frame is 300-400mm from the upper surface of the steel plate. The roller speed is 0.20-0.30m / s. The steel plate moves to the ACC frame area and undergoes reciprocating swing cooling for 5-10 minutes.

[0018] 5. Offline tempering: The tempering and holding temperature of the steel plate is controlled at 580-620℃, the holding time is (1.0-1.3) min / mm × plate thickness mm, and air cooling is used.

[0019] The advantages of the present invention are:

[0020] (1) The present invention adopts a simple and low-cost "medium C + low Mn + microalloying" boron-containing composition design system, which regulates the content of each element from the source, with a carbon equivalent CEV ≤ 0.66%, ensuring both strength and toughness matching while also guaranteeing welding performance. The present invention rationally adds 0.28-0.38% copper, and the atmospheric corrosion index I ≥ 6.2, which can improve both the hardenability of the steel plate and the corrosion resistance.

[0021] (2) The present invention adopts clean steel smelting and continuous casting technology. First, it focuses on controlling the CaO / Al2O3 of the refined slag sample to 1.7-1.9, greatly improving the slag system's ability to absorb inclusions, and controlling the ferroboron to be added 5 minutes after ferrotitanium, fully deoxidizing and fixing nitrogen to obtain the maximum effective boron; secondly, it optimizes the matching of calcification and soft blowing processes, heavy pressure at the end of solidification, etc., to comprehensively intervene in defects such as inclusions, segregation, cracks, shrinkage cavities, etc. inside the billet, and finally obtains high-quality ingots, laying the foundation for the subsequent core performance of extra-thick plates.

[0022] (3) The present invention does not adopt complex processes such as "differential temperature rolling". Instead, it simply and reasonably matches thick slabs for rolling with a large compression ratio of ≥5. The austenite grains are greatly crushed by the last three passes of rough rolling ≥40mm, so that the deformation penetrates the core and refines the core grains. The thickness of the intermediate slab t0 is not less than 2 times the thickness of the finished product, so that the cumulative deformation rate of the two stages is ≥50%, further refining the austenite grains and increasing the dislocation density. After rough rolling, the temperature difference between the surface and the core of the intermediate slab is about 0.15×t0℃. Therefore, the start temperature of the finishing rolling is controlled to be no higher than Tnr-0.15×t0℃, so that the full thickness does not recrystallize for a long time after deformation, and the microstructure is uniform.

[0023] (4) The present invention adopts 5kg+2kg strong DQ water cooling mode, matching the strategy of "high opening cooling (≥850℃) + low return to red (≤100℃) + large cooling rate (≥25℃ / s)", and at the same time controls the flow rate of the first group of gaps to be lower than that of the second to fourth groups by 120m 3 / h. This prevents excessive water flow in the first set of gaps, which could cause a large amount of water to accumulate and form a water film, preventing the second to fourth sets of gaps from effectively impacting the steel plate. It also creates a water wall, preventing accumulated water from backflowing and pre-cooling the steel plate, which could affect the through-hardening effect. The steel plate is controlled to oscillate back and forth within the ACC frame for 5-10 minutes for deep cooling, allowing the supercooled austenite to bypass the high- and medium-temperature phase transformation zones and undergo a direct low-temperature transformation, resulting in an exceptionally thick 60-80mm steel plate with a primarily martensitic structure throughout its thickness. This also replaces offline quenching, shortening the process and saving costs.

[0024] (5) After tempering at 580-620°C, the steel plate has high strength and good plasticity and toughness. In particular, the longitudinal impact energy of the core at -40°C can reach over 100J. The Z-axis tensile section shrinkage is over 50%, which suppresses lamellar tearing during steel plate welding. The corrosion rate is 0.232-0.239mm / year, which is 35% lower than that of ordinary steels of the same grade. This steel plate has good application prospects in the production of high-performance, corrosion-resistant, and ultra-high-strength steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Austenite grain structure at 1 / 2 thickness of 80mm steel plate in Example

[0026] Figure 2 Austenite grain structure at 1 / 2 thickness of 80mm steel plate in comparative example

[0027] Figure 3 The microstructure of the quenched state at 1 / 2 thickness of the 80mm steel plate in Example

[0028] Figure 4 The tempered microstructure of the 80mm steel plate at 1 / 2 of the thickness in Example DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to specific examples. It should be understood that these examples are only used to describe specific implementations of the present invention and are not intended to limit the scope of protection of the present invention. Example 1:

[0030] A thick-gauge Q890E steel plate with good core toughness and corrosion resistance has a thickness of 60 mm. The chemical composition and weight percentage of the steel plate are as follows: C: 0.15%, Si: 0.26%, Mn: 1.22%, P: 0.008%, S: 0.002%, Al: 0.034%, Nb: 0.024%, Ti: 0.016%, Cr: 0.54%, Mo: 0.43%, Ni: 0.28%, Cu: 0.32%, B: 0.0022%, N: 28 ppm, H: 1.2 ppm, O: 12 ppm, the balance being Fe and unavoidable impurities; carbon equivalent CEV: 0.59%, and atmospheric corrosion resistance index I: 6.6.

[0031] The manufacturing steps and process parameters of the steel plate are

[0032] 1. Smelting: The bright surface of the molten iron after desulfurization and slag stripping was 98%; the converter double slag method was used for smelting, slag blocking was used for tapping, and the slag thickness was 30mm; 908kg of LF refined lime was added, and the white slag was kept for 13 minutes after the first power supply. The final slag sample had an Al2O3:31.4% and a CaO / Al2O3 ratio of 1.76. Ferroboron was added 5 minutes after ferrotitanium before leaving the station; RH high vacuum time was 25 minutes, and 250 meters of pure calcium wire was fed after breaking the vacuum. Soft argon blowing time was 12 minutes, and the molten steel was allowed to calm down before being hoisted away for 5 minutes; casting maintained a constant casting speed of 0.55m / min, superheat of 22℃, protected pouring and electromagnetic stirring, and the reduction under heavy pressure at the end of solidification was 18mm; the ingot thickness was 400mm, the central segregation inside the slab was Class C 0.5, and there were no other defects.

[0033] 2. Heating: Use walking beam heating furnace, soaking section temperature 1235℃, soaking time 0.38min / mm.

[0034] 3. Rolling: Total reduction ratio 6.7. High-pressure water descaling and cooling were used before each rough rolling pass. The starting rolling temperature was 1089°C and the ending temperature was 1022°C. The reductions for the last three passes were 44 / 44 / 44mm. The intermediate bar thickness was 137mm. High-pressure water descaling and cooling were used after every other pass in finishing rolling. Tnr-0.15×t0=917°C. The starting rolling temperature was 908°C. The cumulative finishing reduction was 56.2%. After rolling, pre-straightening was performed and the steel was rapidly cooled in water.

[0035] 4. Online quenching: Steel plate cooling temperature 867℃, red-return temperature 44℃, cooling rate 31.4℃ / s. DQ water pressure 0.5MPa, ACC water pressure 0.2MPa, among which the DQ frame gap nozzle first group upward spray flow rate is 140m 3 / h, the 2nd to 4th group of upward spray flow rate is 260m 3 / h, gap water ratio 2.15. ACC frame high-density nozzle 26 groups, each group of upper and middle cavity flow 220m 3 / h, high-density water ratio 2.50. The upper header of the DQ frame is 300mm from the upper surface of the steel plate, and the upper header of the ACC frame is 350mm from the upper surface of the steel plate. The roller speed is 0.28m / s. The reciprocating swing time of the steel plate in the high-density nozzle area is 5 minutes.

[0036] 5. Offline tempering: The steel plate tempering holding temperature is 620℃, the holding time is 69min, and air cooling is used. Example 2:

[0037] A thick-gauge Q890E steel plate with good core toughness and corrosion resistance has a thickness of 70 mm. The chemical composition and weight percentage of the steel plate are as follows: C: 0.16%, Si: 0.31%, Mn: 1.28%, P: 0.008%, S: 0.001%, Al: 0.033%, Nb: 0.027%, Ti: 0.018%, Cr: 0.55%, Mo: 0.43%, Ni: 0.27%, Cu: 0.31%, B: 0.0023%, N: 25 ppm, H: 1.0 ppm, O: 14 ppm, the balance being Fe and unavoidable impurities; carbon equivalent CEV: 0.61%, and atmospheric corrosion resistance index I: 6.6.

[0038] The manufacturing steps and process parameters of the steel plate are

[0039] 1. Smelting: The bright surface of the molten iron after desulfurization and slag stripping was 98%; the converter double slag method was used for slag blocking and steelmaking, with a slag thickness of 32mm; 914kg of LF refined lime was added, and the white slag was maintained for 14 minutes after the first power supply. The final slag sample had an Al2O3 ratio of 33.6% and a CaO / Al2O3 ratio of 1.79. Ferroboron was added 5 minutes after ferrotitanium before leaving the station; RH high vacuum was maintained for 25 minutes, and 280 meters of pure calcium wire was fed after breaking the vacuum. Soft argon blowing was performed for 14 minutes, and the molten steel was allowed to cool down before being hoisted away for 6 minutes. Casting was maintained at a constant casting speed of 0.55m / min, with a superheat of 24°C, protected pouring and electromagnetic stirring. The reduction under heavy pressure at the end of solidification was 20mm. The ingot thickness was 400mm, and the central segregation inside the slab was Class C 0.5, with no other defects.

[0040] 2. Heating: Use walking beam heating furnace, soaking section temperature 1240℃, soaking time 0.38min / mm.

[0041] 3. Rolling: Total reduction ratio 5.7. High-pressure water descaling and cooling were used before each rough rolling pass. The starting rolling temperature was 1078°C and the ending temperature was 1014°C. The reductions for the last three passes were 44 / 42 / 43mm. The intermediate bar thickness was 156mm. High-pressure water descaling and cooling were used after every other pass in finishing rolling. Tnr - 0.15 × t0 = 916°C. The starting rolling temperature was 901°C. The cumulative reduction for finishing rolling was 55.0%. After rolling, pre-straightening was performed and the bar was rapidly cooled in water.

[0042] 4. Online quenching: Steel plate cooling temperature 862℃, red-return temperature 48℃, cooling rate 29.7℃ / s. DQ water pressure 0.5MPa, ACC water pressure 0.2MPa, among which the DQ frame gap nozzle first group upward spray flow rate is 150m 3 / h, the 2nd to 4th group of upward spray flow rate is 270m 3 / h, gap water ratio 2.18. ACC frame high-density nozzle 26 groups, each group of upper and middle cavity flow 230m 3 / h, high-density water ratio 2.53. The upper header of the DQ frame is 280mm from the upper surface of the steel plate, and the upper header of the ACC frame is 330mm from the upper surface of the steel plate. The roller speed is 0.25m / s. The reciprocating swing time of the steel plate in the high-density nozzle area is 7 minutes.

[0043] 5. Offline tempering: The steel plate is tempered at a holding temperature of 610°C for 84 minutes and air-cooled. Example 3:

[0044] A thick-gauge Q890E steel plate with good core toughness and corrosion resistance is 80 mm thick. The chemical composition and weight percentage of the steel plate are: C: 0.165%, Si: 0.33%, Mn: 1.29%, P: 0.007%, S: 0.001%, Al: 0.028%, Nb: 0.026%, Ti: 0.017%, Cr: 0.54%, Mo: 0.44%, Ni: 0.30%, Cu: 0.32%, B: 0.0020%, N: 27 ppm, H: 1.5 ppm, O: 14 ppm, the balance being Fe and unavoidable impurities; carbon equivalent CEV: 0.61%, and atmospheric corrosion resistance index I: 6.7.

[0045] The manufacturing steps and process parameters of the steel plate are

[0046] 1. Smelting: The bright surface of the molten iron after desulfurization and slag stripping was 99%; the converter double slag method was used for slag blocking and tapping, with a slag thickness of 31mm; 904kg of LF refined lime was added, and the white slag was maintained for 14 minutes after the first power supply. The final slag sample had an Al2O3 ratio of 32.4% and a CaO / Al2O3 ratio of 1.82. Ferroboron was added 5 minutes after ferrotitanium before leaving the station; the RH high vacuum time was 28 minutes, and 300 meters of pure calcium wire was fed after breaking the vacuum. The soft argon blowing time was 15 minutes, and the molten steel was allowed to cool down before being hoisted away for 7 minutes. The casting was maintained at a constant casting speed of 0.60m / min, the superheat was 23℃, and electromagnetic stirring was used for protection pouring. The reduction under heavy pressure at the end of solidification was 21mm. The ingot thickness was 400mm, and the central segregation inside the slab was Class C 0.5, with no other defects.

[0047] 2. Heating: Use walking beam heating furnace, soaking section temperature 1250℃, soaking time 0.40min / mm.

[0048] 3. Rolling: Total reduction ratio 5.0. High-pressure water descaling and cooling were used before each rough rolling pass. The starting rolling temperature was 1083°C and the ending temperature was 1022°C. The reductions for the last three passes were 44 / 44 / 43mm. The intermediate bar thickness was 163mm. High-pressure water descaling and cooling were used after every other pass in finishing rolling. Tnr - 0.15 × t0 = 906°C. The starting rolling temperature was 895°C. The cumulative finishing reduction was 51.0%. After rolling, pre-straightening was performed and the steel was rapidly cooled in water.

[0049] 4. Online quenching: Steel plate cooling temperature 871℃, red-return temperature 51℃, cooling rate 29.1℃ / s. DQ water pressure 0.5MPa, ACC water pressure 0.2MPa, among which the DQ frame gap nozzle first group upward spray flow rate is 160m 3 / h, the 2nd to 4th group of upward spray flow rate is 280m 3 / h, gap water ratio 2.23. ACC frame high-density nozzle 26 groups, each group of upper and middle cavity flow 240m 3 / h, high-density water ratio 2.60. The upper header of the DQ frame is 260mm from the upper surface of the steel plate, and the upper header of the ACC frame is 300mm from the upper surface of the steel plate. The roller speed is 0.20m / s. The reciprocating swing time of the steel plate in the high-density nozzle area is 8 minutes.

[0050] 5. Offline tempering: The steel plate is tempered at a holding temperature of 580°C for 104 minutes and air-cooled.

[0051] Comparative Example 1:

[0052] A thick specification Q890E steel plate with a thickness of 80 mm, the chemical composition and mass percentage of the steel plate are: C: 0.15%, Si: 0.30%, Mn: 1.52%, P: 0.015%, S: 0.003%, Al: 0.033%, Nb: 0.025%, Ti: 0.014%, Cr: 0.43%, Mo: 0.43%, Ni: 0.30%, V: 0.035%, B: 0.0019%, N: 45ppm, H: 1.5ppm, O: 42ppm, the balance is Fe and unavoidable impurities; carbon equivalent CEV: 0.60%, atmospheric corrosion resistance index I: 2.3.

[0053] 1. Smelting: The bright surface of the molten iron after desulfurization and slag stripping was 96%. The converter was smelted using the double-slag method, with slag blocking and tapping, and the slag thickness was 45mm. 864kg of LF refined lime was added, and the white slag was maintained for 8 minutes after the first power supply. The final slag sample had an Al2O3 ratio of 28.9% and a CaO / Al2O3 ratio of 2.3. Ferroboron was added after ferrotitanium before leaving the station. The RH high vacuum was maintained for 15 minutes, and 200 meters of pure calcium wire was fed after breaking the vacuum. The soft argon blowing time was 8 minutes. The casting was maintained at a constant casting speed of 0.65m / min, the superheat was 26℃, and electromagnetic stirring was used for protection pouring. The soft reduction at the end of solidification was 8mm. The slab thickness was 325mm, the internal center segregation of the slab was Class C 1.5, and the center porosity was 0.5.

[0054] 2. Heating: Use walking beam heating furnace, soaking section temperature 1200℃, soaking time 0.30min / mm.

[0055] 3. Rolling: Total reduction ratio 3.75, rough rolling with three passes of high-pressure water descaling and cooling, start temperature 1085°C, end temperature 1014°C, and reductions of 36 / 36 / 34mm per pass in the last three passes. Intermediate bar thickness 154mm. Finishing rolling with two passes of high-pressure water descaling and cooling, Tnr-0.15×t0=886°C, start temperature 897°C, cumulative finishing reduction 48.1%, and air cooling after rolling.

[0056] 4. Use offline quenching + tempering method, the quenching holding temperature is 920℃, the holding time is 72min; the tempering holding temperature is controlled at 570℃, the holding time is 80min, and air cooling is used.

[0057] Corrosion test:

[0058] The corrosion experiment was carried out by suspension and immersion in the solution. The sample was suspended with a nylon rope and immersed in the solution. The water bath temperature was maintained at 35 ° C. A Na2SO4 solution with a concentration of 0.1 mol / L was placed in a beaker. The pH was adjusted to 8.5 with NaOH. The beaker mouth was sealed with plastic wrap. The immersion time was 72 hours, and the solution was replaced every 24 hours.

[0059] The corrosion specimen was processed into a 6mm×25mm×55mm cuboid. A small hole with a diameter of Φ3.0mm was drilled in the middle of the upper part of the specimen for hanging. The six sides of the specimen were polished step by step to 800# with sandpaper. After cleaning with acetone and anhydrous ethanol and drying, the mass of the specimen was weighed as the initial mass, and the length, width and height of the specimen were measured to calculate the surface area of ​​the specimen. The corrosion experiment used the weight loss method to determine the average corrosion rate of the specimen. After the experiment, the residual corrosion liquid and corrosion products on the surface were removed with cleaning fluid, the weight of the corroded specimen was weighed, and the corrosion rate was calculated:

[0060] CR(mm / y)= 365(d)*24(h)*W*10 / [S*72(h)*D];

[0061] W: weight loss (g); S: surface area (cm 2 ); D: density (g / cm 3 ).

[0062] The mechanical properties and corrosion test data of the above Examples 1-3 and Comparative Example 1 are shown in Table 1.

[0063] In summary, the 60-80mm thick Q890E steel plates produced in Examples 1-3 of the present invention have good comprehensive properties, especially the excellent low-temperature impact toughness of the core of the steel plate, which can reach more than 100J at -40°C; the thickness Z-axis shrinkage is more than 50%, indicating high purity of the steel, which inhibits lamellar tearing during steel plate welding; at the same time, compared with Comparative Example 1 produced by conventional methods, the corrosion rate is reduced by an average of 0.13mm / year, showing good corrosion resistance. Figure 1-2 It can be seen that after the sample preparation and interception method rating according to GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals" by reheating and quenching, the austenite grain size of the embodiment at 80mm thickness 1 / 2 can reach level 10.5, with uniform and fine grains, while the grain size of the comparative example is level 8.5, with relatively coarse and uneven grains, indicating that the rolling strategy of the present invention can achieve a strong deformation penetration effect. Figure 3 It can be seen that the quenched state of 1 / 2 of the 80mm thickness of the embodiment is mainly martensite, and the lath structure is narrow and slender. It also highlights that the water cooling strategy of the present invention can achieve a strong quenching and hardening effect, breaking the shackles of the limited quenching ability of the core of the ultra-thick steel plate during online quenching. Figure 4 After tempering, a uniform tempered bainite structure is finally formed, which optimizes the comprehensive mechanical properties of the steel plate. Thus, the present invention adopts a simple and efficient production method, coupled with key process control, to achieve the production of low-cost, high-efficiency, high-toughness, corrosion-resistant, and extra-thick 60-80mm Q890E steel plates, with significant economic benefits and application value.

Claims

1. A method for manufacturing thick-gauge Q890E steel plate with good core toughness and corrosion resistance, characterized by: The steel plate includes the following components in percentage by mass: C: 0.14-0.17%, Si: 0.25-0.40%, Mn: 1.20-1.35%, P≤0.010%, S≤0.003%, Al: 0.020-0.040%, Nb: 0.020-0.035%, Ti: 0.010-0.020%, Cr: 0.50-0.60%, Mo: 0.40-0.50%, Ni: 0.25-0.35%, Cu: 0.28-0.38%, B: 0.0015-0.0025%, N≤30ppm, H≤2ppm, O≤20ppm, the balance being Fe and unavoidable impurities; carbon equivalent CEV≤0.66%, where CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; The manufacturing method comprises the following steps: Smelting: Hot metal pretreatment → Converter smelting → LF furnace refining → RH vacuum treatment → continuous casting; bright surface ≥95% after molten iron desulfurization and slag stripping; converter double slag method smelting, slag blocking for tapping, slag thickness ≤40mm; LF refining lime is added at a rate of 8kg per ton of steel. After the first power supply, the white slag is maintained for ≥12 minutes, and the endpoint slag sample is controlled to have Al2O3 >24%, with a CaO / Al2O3 ratio of 1.7-1.9; RH high vacuum time ≥20 minutes, after breaking the vacuum, pure calcium wire is fed for 200-300 meters, soft argon blowing time ≥10 minutes, and molten steel is allowed to calm down before being hoisted away for ≥5 minutes; casting maintains a constant casting speed of 0.5-0.7m / min, liquid level fluctuation is controlled to ±2mm, superheat is 20-25℃, casting is protected throughout the process, and electromagnetic stirring and heavy pressure are used; slab thickness ≥400mm, internal center segregation ≤C Class 0.5, and no other defects are present; Heating: Using a walking beam heating furnace, the soaking section temperature is 1230-1250℃, and the soaking time is controlled at 0.3-0.4min / mm; Rolling: Two-stage segmented rolling is adopted. In the rough rolling stage, high-pressure water descaling and cooling are started before each rolling. The starting rolling temperature is ≥1060℃ and the ending temperature is ≥980℃. The single-pass reduction of the last three passes is guaranteed to be ≥40mm; the intermediate billet thickness t0 is ≥2.0 times the finished steel plate thickness; in the finishing rolling stage, high-pressure water descaling and cooling are started every other pass, and the starting rolling temperature is not higher than Tnr-0.15×[t0]℃, where [t0] is the intermediate billet thickness in mm; the cumulative reduction rate in the finishing rolling stage is ≥50%, and after rolling, the steel is pre-straightened once and quickly cooled in water, where Tnr=887+464×C+890×Ti+363×Al-357×Si+6445×Nb-644×Nb 1 / 2 +732×V-230×V 1 / 2 ; Online quenching: steel plate cooling temperature ≥ 850℃, red-return temperature ≤ 100℃, cooling rate ≥ 25℃ / s; adopt DQ+ACC cooling mode, the water pressure of DQ section and ACC section are ≥ 0.5MPa and ≥ 0.2MPa respectively, among which the DQ frame adopts 4 groups of slit nozzles, and the upper spray flow rate of the first group is 140-160m 3 / h, the 2nd to 4th group of upward spray flow rate is 260-280m 3 / h, gap water ratio 2.1-2.3; ACC frame uses 26 groups of high-density nozzles, each group of upper and middle cavity flow 220-240m 3 / h, high density water ratio 2.45-2.6; the distance between the upper header of the DQ frame and the upper surface of the steel plate is 200-300mm, the distance between the upper header of the ACC frame and the upper surface of the steel plate is 300-400mm, and the roller speed is 0.20-0.30m / s; Offline tempering: The tempering and holding temperature of the steel plate is controlled at 580-620℃, the holding time is (1.0-1.3) min / mm×plate thickness mm, and air cooling is used.

2. The method for manufacturing thick-gauge Q890E steel plate with good core toughness and corrosion resistance according to claim 1, characterized in that: The thickness of the steel plate is 60-80 mm, the yield strength of the steel plate is ≥980 MPa, the tensile strength is ≥1030 MPa, the elongation is ≥14%, the longitudinal impact energy of the steel plate at -40°C at 1 / 4 of the thickness is ≥120 J, the longitudinal impact energy of the steel plate at -40°C at 1 / 2 of the thickness is ≥100 J, and the Z-direction section shrinkage rate of the steel plate is ≥50%.

3. The method for manufacturing thick-gauge Q890E steel plate with good core toughness and corrosion resistance according to claim 1, characterized in that: The corrosion resistance rate of the steel plate is 0.232-0.239 mm / year.

4. The method for manufacturing thick-gauge Q890E steel plate with good core toughness and corrosion resistance according to claim 1, characterized in that: The atmospheric corrosion resistance index of the steel plate is ≥6.2, where I=26.01Cu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29CuNi-9.10NiP-33.39Cu 2 .

5. The method for manufacturing thick-gauge Q890E steel plate with good core toughness and corrosion resistance according to claim 1, characterized in that: Before LF refining leaves the station, ensure that ferroboron is added 5 minutes after the addition of ferrotitanium; during the casting process, the reduction under heavy pressure at the end of solidification is 15-25mm; the total compression ratio in the rolling stage is ≥5; during online quenching, the steel plate moves to the ACC frame area for reciprocating swing cooling, and the swing time is 5-10 minutes.

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