A 50-70mm thick high-toughness 10crni3mocu steel plate and a production method thereof

Abstract

This invention discloses a 50-70mm thick high-strength and high-toughness 10CrNi3MoCu steel plate, comprising the following chemical composition by mass percentage (wt%): C: 0.08-0.10, Si: 0.17-0.25, Mn: 0.50-0.60, P < 0.010, S ≤ 0.002, Ni: 2.3-2.4, Cr: 1.4-1.5, Mo: 0.23-0.25, Cu: 0.9-1.0, and (10*C+Cu+Mn): Ni = 0.9-1.1, Si+Mn ≤ 0.8. 0, P+S≤0.010, the rest is Fe and residual elements. After quenching and tempering, its microstructure is lower bainite + tempered sorbite + a small amount of retained austenite. Its yield strength is 580-630MPa, tensile strength is 650-700MPa, elongation at break ≥18%, reduction of area ≥50%, impact energy at -20℃ ≥300J, shear area ratio 100%, impact energy at -84℃ ≥200J, shear area ratio ≥80%, no cracks in the b=7a bending test, and the fracture surface after the fracture test is fibrous, without white spots, bright lines or penetrating cracks. It has good comprehensive performance and fully meets the quality requirements of 10CrNi3MoCu steel plate with high strength, high toughness and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of medium and heavy plate production, specifically to a 50-70mm thick high-strength and high-toughness 10CrNi3MoCu steel plate and its production method. Background Technology

[0002] 10CrNi3MoCu steel is used for high-pressure resistant shells, which are load-bearing components. Operating in deep-sea environments, the steel plate is required to have high strength, excellent low-temperature impact toughness, and corrosion resistance, while ensuring a 100% fiber cross-section at -20℃ impact fracture. These stringent requirements and high technical difficulty exist, and there are no readily available precedents to follow.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] One objective of this invention is to provide a 50-70mm thick high-strength and high-toughness 10CrNi3MoCu steel plate; another objective of this invention is to provide a method for producing a 50-70mm thick high-strength and high-toughness 10CrNi3MoCu steel plate.

[0005] To achieve the above objectives, the present invention is implemented as follows: a 50-70mm thick high-strength and high-toughness 10CrNi3MoCu steel plate, wherein the steel plate contains the following chemical composition (unit, wt%) by mass percentage: C: 0.08-0.10, Si: 0.17-0.25, Mn: 0.50-0.60, P < 0.010, S ≤ 0.002, Ni: 2.3-2.4, Cr: 1.4-1.5, Mo: 0.23-0.25, Cu: 0.9-1.0, and (10*C+Cu+Mn): Ni = 0.9-1.1, Si+Mn ≤ 0.80, P+S ≤ 0.010, and the remainder being Fe and residual elements.

[0006] Regarding the composition design, it should be noted that Cu can significantly improve the strength of steel plates and also significantly improve the corrosion resistance of steel. However, adding a large amount of Cu to steel can cause Cu to segregate at the grain boundaries, resulting in Cu embrittlement and cracking. Therefore, a large amount of Ni is added to transform the copper-rich layer on the steel surface into a copper-rich layer with a melting point exceeding 1200℃, producing copper-nickel compounds with higher melting points. These compounds are distributed in the intergranular region and will not melt at high temperatures, thus avoiding copper embrittlement defects. Moreover, as a non-carbide-forming element, Ni can significantly improve the toughness and plasticity of steel. Therefore, in this invention, the content of Ni and Cu is controlled at Ni:Cu ≥ 2.

[0007] Carbon (C) can improve the strength and hardenability of steel plates, but excessive C content can affect the low-temperature impact toughness, especially when the carbon content exceeds 0.10%, as this increases the number of small-angle grain boundaries, which is detrimental to improving impact toughness. Mn (Mn) produces a solid solution strengthening effect, improving hardenability, lowering the martensite transformation point, and increasing the amount of retained austenite after quenching. However, excessive Mn content increases the J coefficient of the steel plate, causing temper brittleness and increasing segregation. Cu (Cu) can significantly improve the hardenability and corrosion resistance of steel plates, but it easily causes hot brittleness. Ni (Ni) can expand the austenite range, stabilize austenite elements, and lower the critical transformation temperature of steel, significantly improving the low-temperature impact toughness and increasing the number of large-angle grain boundaries. To achieve a balance between strength and toughness, the proportion of elements that improve strength and toughness is controlled in this invention: (10*C+Cu+Mn):Ni = 0.9~1.1.

[0008] Si and Mn can increase the strength and hardenability of steel plates, which is beneficial for refining grains during rolling and cooling after normalizing, thereby improving the strength and toughness of steel plates. However, excessive content will lead to an increase in the J coefficient of steel plates and cause temper brittleness. Therefore, in this invention, Si+Mn≤0.80 is controlled.

[0009] Furthermore, the steel plate is in a quenched and tempered state, and its microstructure consists of lower bainite + tempered sorbite + a small amount of retained austenite; its yield strength is 580-630MPa, tensile strength is 650-700MPa, elongation at break is ≥18%, reduction of area is ≥50%, impact energy at -20℃ is ≥300J, shear area ratio is 100%, impact energy at -84℃ is ≥200J, shear area ratio is ≥80%, no cracks are found in the b=7a bending test, and the fracture surface after the fracture test is fibrous, without white spots, bright lines or penetrating cracks.

[0010] In addition to the above-mentioned component design, the present invention includes the following production method:

[0011] a. First critical quenching: The temperature is increased in three stages: 700℃, 750℃, and 800℃. The heating time for each stage is 20-30 min, and the total heating time is 80-90 min. The holding temperature is 830-840℃, and the holding time is 1.0 min / mm. After taking it out of the furnace, it is quenched to room temperature. The quenching water temperature is 15-22℃, and the quenching roller speed is 3.0 m / min.

[0012] b. Second critical quenching: The temperature is increased in three stages: 700℃, 750℃, and 800℃. The heating time for each stage is 20-30 min, and the total heating time is 80-90 min. The holding temperature is 820-830℃, and the holding time is 1.0 min / mm. After taking it out of the furnace, it is quenched to room temperature. The quenching water temperature is 15-22℃, and the quenching roller speed is 3.0 m / min.

[0013] c. High-temperature tempering: rapidly heat to 670-680℃, set the holding temperature to 630-650℃, and the total tempering time is 170-250min.

[0014] It should be noted that after critical quenching and sub-temperature quenching, the number of austenite nucleation sites in the steel increases significantly, the grain refinement effect is obvious, and after tempering, the lower bainite + tempered sorbite with the best strength and toughness matching effect is obtained, and a small amount of retained austenite exists. The retained austenite will produce the TRIP effect during mechanical property testing, stress-induced martensitic phase transformation, thereby improving the strength and toughness of the steel plate.

[0015] Preferably, when the C content is <0.09%, the tempering and heat preservation temperature is set to 630-640℃; when the C content is ≥0.09%, the tempering and heat preservation temperature is set to 640-650℃.

[0016] Preferably, when the quenching water temperature is 15-19℃, the tempering holding time is 210-250 min; when the quenching water temperature is 20-22℃, the tempering holding time is 170-210 min.

[0017] Preferably, when the C content is <0.09%, the quenching water temperature is 15-19℃, the tempering holding temperature is set to 630-640℃, and the holding time is 210-250min; when the C content is <0.09%, the quenching water temperature is 20-22℃, the tempering holding temperature is set to 630-640℃, and the holding time is 170-210min; when the C content is ≥0.09%, the quenching water temperature is 15-19℃, the tempering holding temperature is set to 640-650℃, and the tempering time is 210-250min; when the C content is ≥0.09%, the quenching water temperature is 20-22℃, the tempering holding temperature is set to 640-650℃, and the holding time is 170-210min.

[0018] This invention also includes the following production method:

[0019] g. Smelting: The converter uses high-alloy steel scrap as waste steel with Cr content ≥1.5%, Mo content ≥0.5%, and Ni content ≥1.0%. Top and bottom combined oxygen blowing smelting is used, and the C content of the converter tapped steel is ≤0.05%. The process route of VD decarburization + LF refining + VD vacuum degassing is adopted. After VD decarburization, the C content is ≤0.02%. During the LF refining process, white slag is generated to adsorb inclusions, and Ca is added to modify the inclusions. After VD vacuum degassing, the H content in the molten steel is ≤1.0 ppm, the O content is ≤20 ppm, and the N content is ≤30 ppm.

[0020] h. Ingot casting: Water-cooled ingot molds with a thickness of ≥700mm are used for casting, ensuring a compression ratio of ≥10. The casting superheat is controlled at 30-40℃. The casting time for the main body is 15-18min, the casting time for the riser is 5-7min, and the mold is removed 10-12h after casting.

[0021] i. Cleaning: ① After the steel ingot is demolded and slowly cooled for 24 hours, cleaning begins when the surface temperature drops to 350-400℃. The cleaning temperature is ≥350℃, and the furnace loading temperature after cleaning is ≥300℃. The 300mm area at 1 / 2 width of the steel ingot is cleaned, but the edge of the width is not cleaned; ② After the steel ingot is rolled into an intermediate billet, the surface of the intermediate billet is fully cleaned at a cleaning temperature ≥200℃. After cleaning, the surface of the intermediate billet is coated with a high-temperature anti-oxidation coating.

[0022] j. Heating: The steel ingot is simmered at 400-500℃ for 24 hours with a heating rate of ≤60℃ / h, and then held at 1180-1200℃ for 12 hours. After holding at 1180-1200℃ for 6 hours, the steel is turned over. The intermediate billet is heated at 1180-1200℃ for 5-6 hours.

[0023] k. Rolling: The steel ingot is rolled into a 300mm thick intermediate billet using hot rolling process. After heating, the intermediate billet is first rolled to a thickness of 140-160mm and then cooled in ACC controlled cooling. When it turns red to 840-860℃, the second stage rolling begins, with a final rolling temperature of 820-840℃.

[0024] f. Post-rolling cooling: After rolling, the rolls are cooled again by ACC, with 4-6 cooling cycles and a final cooling temperature of ≤400℃.

[0025] The beneficial effects of this invention are as follows: Through the rational design of the steel plate composition, the control of the steel plate production process, and the precise control of the heat treatment process, the obtained steel plate has a microstructure of lower bainite + tempered sorbite + a small amount of retained austenite; its yield strength is 580-630MPa, tensile strength is 650-700MPa, elongation at break is ≥18%, reduction of area is ≥50%, impact energy at -20℃ is ≥300J, shear area ratio is 100%, impact energy at -84℃ is ≥200J, shear area ratio is ≥80%, no cracks are found in the b=7a bending test, and the fracture surface after the fracture test is fibrous, without white spots, bright lines, or penetrating cracks. Attached Figure Description

[0026] Figure 1 This is a process curve diagram of the first critical quenching of the steel plate described in this invention.

[0027] Figure 2 This is a process curve diagram of the second critical quenching of the steel plate described in this invention.

[0028] Figure 3 The high-temperature tempering process curve of the steel plate described in this invention. Detailed Implementation

[0029] To better understand the present invention, the following embodiments further illustrate the content of the invention, but the scope of protection of the present invention is not limited to the following embodiments. Numerous specific details are set forth in the following description to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the present invention can be practiced without one or more of these details.

[0030] Example 1:

[0031] a. Smelting composition: C: 0.08, Si: 0.18, Mn: 0.53, P: 0.006, S: 0.001, Ni: 2.4, Cr: 1.46, Mo: 0.24, Cu: 0.92, the rest are Fe and residual elements; Ni:Cu = 2.6, (10*C+Cu+Mn):Ni = 0.94, Si+Mn = 0.71, P+S≤0.007.

[0032] b. The converter uses high-alloy steel scrap as waste steel, with Cr: 2.0%, Mo: 0.95%, Ni: 1.3%, and top and bottom oxygen blowing smelting. The C content of the converter tapped steel is 0.04%. The process route is VD decarburization + LF refining + VD vacuum degassing. After VD decarburization, the C content is 0.02%. During the LF refining process, white slag is generated to adsorb inclusions, and Ca is added to modify the inclusions. After VD vacuum degassing, the H content in the molten steel is 0.87 ppm, O is 18 ppm, and N is 27 ppm.

[0033] c. Use a water-cooled ingot mold with a thickness of 780mm for casting, with a compression ratio of 11.1-15.6, a casting superheat of 36℃, a casting time of 16min for the main body, a casting time of 6min for the riser, and demolding 11h after casting.

[0034] d. Demold the steel ingot and allow it to cool slowly for 24 hours. Clean the ingot at a temperature of 380℃. Charge the steel ingot into the furnace at a temperature of 320℃. Clean the 300mm area at half the width of the steel ingot, but do not clean the edge of the width. After the steel ingot is rolled into an intermediate billet, clean the surface of the intermediate billet completely at a temperature of 230℃. After cleaning, apply a high-temperature anti-oxidation coating to the surface of the intermediate billet.

[0035] e. The steel ingot is simmered at 460℃ for 24 hours with a heating rate of 50.2℃ / h, held at 1180-1200℃ for 12 hours, and then turned over after holding for 6 hours; the intermediate billet is heated at 1180-1200℃ for 5.3 hours.

[0036] f. The steel ingot is rolled into a 300mm thick intermediate billet using hot rolling process. After heating, the intermediate billet is rolled to a thickness of 160mm in the first stage. After rolling, it enters ACC controlled cooling. When it is reddened to 840-860℃, the second stage rolling to the finished plate begins. The final rolling temperature is 820-840℃.

[0037] g. After rolling, the material is cooled again by ACC, with 4-6 cooling cycles and a final cooling temperature of 360-393℃.

[0038] h. A two-stage quenching + high-temperature tempering process is adopted, wherein: ① During the first critical quenching: the temperature is raised in three stages: 700℃, 750℃, and 800℃. The first two stages of heating time are each 30min, and the total heating time is 85min. The holding temperature is 835℃, and the holding time is 65min. After being taken out of the furnace, the furnace is quenched to room temperature in a quenching machine with a quenching water temperature of 21℃ and a quenching roller speed of 3.0m / min; ② During the second critical quenching: the temperature is raised in three stages: 700℃, 750℃, and 800℃. The first two stages of heating time are each 30min, and the total heating time is 85min. The holding temperature is 825℃, and the holding time is 60min. After being taken out of the furnace, the furnace is quenched to room temperature in a quenching machine with a quenching water temperature of 21℃ and a quenching roller speed of 3.0m / min; ③ During tempering, the temperature of the heating stage is set at 680℃ for rapid heating, and the temperature of the holding stage is set at 635℃. The total tempering time is 190min.

[0039] Its mechanical properties are shown in Table 1:

[0040] Table 1 Mechanical Properties

[0041]

[0042] Example 2:

[0043] a. Smelting composition:

[0044] C: 0.10, Si: 0.20, Mn: 0.55, P: 0.007, S: 0.001, Ni: 2.36, Cr: 1.45, Mo: 0.24, Cu: 0.94, the others are Fe and residual elements; Ni:Cu = 2.5, (10*C+Cu+Mn):Ni = 1.06, Si+Mn = 0.75, P+S≤0.008.

[0045] b. The converter uses high-alloy steel scrap as waste steel, with Cr: 1.94%, Mo: 0.92%, Ni: 0.95%, and top and bottom oxygen blowing smelting. The C content of the steel tapped from the converter is 0.04%. The process route is VD decarburization + LF refining + VD vacuum degassing. After VD decarburization, the C content is 0.02%. During the LF refining process, white slag is generated to adsorb inclusions, and Ca is added to modify the inclusions. After VD vacuum degassing, the H content in the molten steel is 0.9 ppm, O is 20 ppm, and N is 26 ppm.

[0046] c. Use a water-cooled ingot mold with a thickness of 840mm for casting, with a compression ratio of 12-16.8, a casting superheat of 34℃, a casting time of 18min for the main body, a casting time of 7min for the riser, and demolding 12h after casting.

[0047] d. Demold the steel ingot and allow it to cool slowly for 24 hours. Clean the ingot at a temperature of 373℃. Charge the steel ingot into the furnace at a temperature of 315℃. Clean the 300mm area at half the width of the steel ingot, but do not clean the edge of the width. After the steel ingot is rolled into an intermediate billet, clean the surface of the intermediate billet completely at a temperature of 250℃. After cleaning, apply a high-temperature anti-oxidation coating to the surface of the intermediate billet.

[0048] e. The steel ingot is simmered at 450℃ for 24 hours with a heating rate of 53℃ / h, held at 1180-1200℃ for 12 hours, and then turned over after holding for 6 hours; the intermediate billet is heated at 1180-1200℃ for 5.5 hours.

[0049] f. The steel ingot is rolled into a 300mm thick intermediate billet using hot rolling process. After heating, the intermediate billet is rolled to a thickness of 160mm in the first stage. After rolling, it enters ACC controlled cooling. When it is reddened to 840-860℃, the second stage rolling to the finished plate begins. The final rolling temperature is 820-840℃.

[0050] g. After rolling, the material is cooled again by ACC, with 4-6 cooling cycles and a final cooling temperature of 350-382℃.

[0051] h. A quenching + high-temperature tempering process is adopted, wherein: ① During the first critical quenching: the temperature is raised in three stages: 700℃, 750℃, and 800℃. The first two stages of heating time are 30min each, and the total heating time is 88min. The holding temperature is 835℃, and the holding time is 65min. After being taken out of the furnace, the furnace is quenched to room temperature in a quenching machine with a quenching water temperature of 18℃ and a quenching roller speed of 3.0m / min; ② During the second critical quenching: the temperature is raised in three stages: 700℃, 750℃, and 800℃. The first two stages of heating time are 30min each, and the total heating time is 85min. The holding temperature is 825℃, and the holding time is 60min. After being taken out of the furnace, the furnace is quenched to room temperature in a quenching machine with a quenching water temperature of 18.5℃ and a quenching roller speed of 3.0m / min; ③ During tempering, the temperature of the heating stage is set at 670℃ for rapid heating, and the temperature of the holding stage is set at 645℃. The total tempering time is 230min.

[0052] Its mechanical properties are shown in Table 2:

[0053] Table 2 Mechanical Properties

[0054]

[0055] In summary, the production method of this invention is highly effective in producing 50-70mm thick 10CrNi3MoCu steel plates with high strength, high toughness, and corrosion resistance. The various steps work together synergistically to achieve excellent overall performance, resulting in 50-70mm thick steel plates with high strength, high toughness, and corrosion resistance.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for producing a 50-70mm thick high-strength and high-toughness 10CrNi3MoCu steel plate, characterized in that, The steel plate contains the following chemical composition by mass percentage (wt%): C: 0.08~0.10, Si: 0.17~0.25, Mn: 0.50~0.60, P<0.010, S≤0.002, Ni: 2.3~2.4, Cr: 1.4~1.5, Mo: 0.23~0.25, Cu: 0.9~1.0, and (10*C+Cu+Mn): Ni=0.9~1.1, Si+Mn≤0.80, P+S≤0.010, with the remainder being Fe. The steel plate is in a quenched and tempered state, and its microstructure consists of lower bainite + tempered sorbite + a small amount of retained austenite. Its yield strength is 580-630MPa, tensile strength is 650-700MPa, elongation at break is ≥18%, reduction of area is ≥50%, impact energy at -20℃ is ≥300J, shear area ratio is 100%, impact energy at -84℃ is ≥200J, shear area ratio is ≥80%, no cracks are found in the b=7a bending test, and the fracture surface is fibrous after the fracture test, without white spots, bright lines or penetrating cracks. The production methods for the aforementioned steel plates include smelting, ingot casting, cleaning, heating, rolling, and post-rolling cooling, as detailed below: a) Smelting: The converter uses high-alloy steel scrap as scrap steel with Cr content ≥1.5%, Mo content ≥0.5%, and Ni content ≥1.0%. Top and bottom oxygen blowing is used for smelting, and the C content of the steel tapped from the converter is ≤0.05%. The process route of VD decarburization + LF refining + VD vacuum degassing is adopted. After VD decarburization, the C content is ≤0.02%. During the LF refining process, white slag is generated to adsorb inclusions, and Ca is added to modify the inclusions. After VD vacuum degassing, the H content in the molten steel is ≤1.0 ppm, the O content is ≤20 ppm, and the N content is ≤30 ppm. b) Ingot casting: Water-cooled ingot molds with a thickness of ≥700mm are used for casting, ensuring a compression ratio of ≥10. The casting overheating is controlled at 30-40℃. The casting time for the main body is 15-18min, the casting time for the riser is 5-7min, and the mold is removed 10-12h after casting. c) Cleaning: ① After the steel ingot is demolded and cooled slowly for 24 hours, cleaning begins when the surface temperature drops to 350-400℃. The cleaning temperature is ≥350℃, and the furnace loading temperature after cleaning is ≥300℃. The 300mm area at 1 / 2 of the width of the steel ingot is cleaned, but the edge of the width is not cleaned; ② After the steel ingot is rolled into an intermediate billet, the surface of the intermediate billet is fully cleaned at a cleaning temperature ≥200℃. After cleaning, a high-temperature anti-oxidation coating is applied to the surface of the intermediate billet. d) Heating: The steel ingot is simmered at 400-500℃ for 24 hours with a heating rate of ≤60℃ / h, and then held at 1180-1200℃ for 12 hours. After holding at 1180-1200℃ for 6 hours, the steel is turned over. The intermediate billet is heated at 1180-1200℃ for 5-6 hours. e) Rolling: The steel ingot is rolled into a 300mm thick intermediate billet using hot rolling process. After heating, the intermediate billet is first rolled to a thickness of 140-160mm and then cooled in ACC controlled cooling. When it turns red to 840-860℃, the second stage rolling begins, with a final rolling temperature of 820-840℃. f) Post-rolling cooling: After rolling, the rolls are cooled again by ACC, with 4-6 cooling cycles and a final cooling temperature of ≤400℃. g) Two critical quenching processes and high-temperature tempering, as detailed below: a. First critical quenching: The temperature is increased in three stages: 700℃, 750℃, and 800℃. The heating time for each stage is 20-30 min, and the total heating time is 80-90 min. The holding temperature is 830-840℃, and the holding time is 1.0 min / mm. After taking it out of the furnace, it is quenched to room temperature. The quenching water temperature is 15-22℃, and the quenching roller speed is 3.0 m / min. b. Second critical quenching: The temperature is increased in three stages: 700℃, 750℃, and 800℃. The heating time for each stage is 20-30 min, and the total heating time is 80-90 min. The holding temperature is 820-830℃, and the holding time is 1.0 min / mm. After taking it out of the furnace, it is quenched to room temperature. The quenching water temperature is 15-22℃, and the quenching roller speed is 3.0 m / min. c. High-temperature tempering: rapidly heat to 670-680℃, set the holding temperature to 630-650℃, and the total tempering time is 170-250min.

2. The method for producing 50-70mm thick high-strength and high-toughness 10CrNi3MoCu steel plate according to claim 1, characterized in that: When the carbon content is <0.09%, the tempering and holding temperature is set to 630-640℃; when the carbon content is ≥0.09%, the tempering and holding temperature is set to 640-650℃.

3. The method for producing 50-70mm thick high-strength and high-toughness 10CrNi3MoCu steel plates according to claim 1, characterized in that: When the quenching water temperature is 15-19℃, the tempering holding time is 210-250 min; when the quenching water temperature is 20-22℃, the tempering holding time is 170-210 min.

4. The method for producing 50-70mm thick high-strength and high-toughness 10CrNi3MoCu steel plates according to claim 1, characterized in that: When the carbon content is <0.09%, the quenching water temperature is 15-19℃, and the tempering holding temperature is set to 630-640℃ for 210-250 min; when the carbon content is <0.09%, the quenching water temperature is 20-22℃, and the tempering holding temperature is set to 630-640℃ for 170-210 min; when the carbon content is ≥0.09%, the quenching water temperature is 15-19℃, and the tempering holding temperature is set to 640-650℃ for 210-250 min; when the carbon content is ≥0.09%, the quenching water temperature is 20-22℃, and the tempering holding temperature is set to 640-650℃ for 170-210 min.

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