Ultrahigh-strength fire-resistant keel angle steel for ships and method for manufacturing the same

Abstract

The application discloses a kind of super-high-strength marine fire-resistant keel angle steel and preparation method thereof;Belong to high-strength structural steel manufacturing field;Its chemical composition is as follows: C, Si, Mn, P, S, Ni, Mo, Ti, Al, Ca;The rest is Fe and impurities;Its operation steps are as follows: converter, electric furnace smelting, continuous casting;Rolling, cooling after rolling and heat treatment and other processes.The application provides a kind of room temperature yield strength greater than 880MPa, -60 ℃ V type notch impact energy ≥88J, yield strength ≥580MPa at 600 ℃ high temperature high-quality steel, the super-large ocean-going ship built is safer, can resist the impact of external load in harsh environment.And it has good fire resistance, still has higher strength in high temperature environment, is used to build large ocean-going ship keel, reinforcing rib and other structural members, better safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-strength structural steel manufacturing, and discloses an ultra-high-strength fire-resistant keel angle steel for ships and a preparation method thereof. BACKGROUND

[0002] In order to improve the transportation efficiency, ocean-going transport ships are developing towards large-scale and super-large-scale year by year. The length of some super-large ships even exceeds 400 meters, and it is necessary to use high-quality ultra-high-strength steel to build key components such as keels of ships. On the other hand, according to data, hundreds of ships catch fire every year due to various factors, not only causing personnel and property losses of the ships themselves, but also causing serious ecological damage to the oceans and other waters. The commonly used steel materials such as A, B, AH32, DH32, AH36, DH36 cannot meet the construction of super-large ships due to low strength, low fracture toughness, and poor quality. Moreover, when encountering a hurricane, a harsh ocean, or a reef, other ship collision, or other external load impact, the ships built with these ordinary steel materials are prone to extrusion deformation or even fracture, and some may even catch fire. Therefore, the mechanical properties and quality of the steel materials for building super-large ocean-going ships are increasingly required to have ultra-high strength such as yield strength ≥ 880 MPa, V-type notch impact energy ≥ 88 J at-60℃, and fire resistance such as yield strength ≥ 580 MPa at 600℃, and the quality of the steel materials for building is also required to have low inclusion C class ≤ 1.0 level, so as to ensure the safe operation of large ocean-going ships. The present application aims to provide a kind of ultra-high-strength steel material for building super-large ocean-going ships, which has a yield strength of more than 880 MPa at room temperature, a V-type notch impact energy of more than 88 J at-60℃, and a yield strength of more than 580 MPa at 600℃, so as to make the built super-large ocean-going ships more safe and resistant to external load impact in harsh environments.

[0003] A large-size high-strength and tough symmetrical flat-bulb steel and a production method thereof are disclosed in Chinese patent application (application number 201911023030.3). The chemical composition of the large-size flat-bulb steel is as follows in terms of weight percentage: C 0.12% to 0.18%, Si 0.20% to 0.40%, Mn 1.05% to 1.55%, V 0.040% to 0.080%, Ti 0.007% to 0.020%, N 0.0080% to 0.0120%, Als 0.015% to 0.030%, P ≤ 0.015%, S ≤ 0.005%, and the balance of Fe and inevitable impurities. The production method includes smelting, continuous casting, heating, rolling, and cooling processes. The produced symmetrical flat-bulb steel has excellent mechanical properties: yield strength is above 400 MPa, impact absorption energy at-60℃ is above 100 J, and after 5% strain and 250℃ aging treatment for 1h, the impact absorption energy at-60℃ is above 70 J. The maximum size can reach 40#.

[0004] Chinese invention patent application (application number 201611096842.7) discloses "a high-strength flat-bulb steel with uniform cross-section performance and its production process", the chemical composition of the flat-bulb steel is as follows: C 0.07-0.12%, Si 0.30-0.50, Mn 1.00-1.50%, P≤0.015, S≤0.010, Ni 0.50-1.00%, V 0.05-0.12%, Ti 0.005-0.012%, N 0.014-0.024%, wherein C / N≤5.5, Ti / V≤0.15, Mn / Ni≤2.0, the balance being Fe and unavoidable impurities. The production process includes electric furnace smelting, secondary refining, continuous casting, blooming, rolling and heat treatment process. The yield strength of the product is not less than 440 MPa, the low temperature impact energy at-40℃ is not less than 49 J, and the cross-section performance uniformity is good.

[0005] Chinese patent with application number 201110417082.6 discloses "a flat-bulb steel with yield strength of 590 MPa and its production method", the chemical composition of the flat-bulb steel is as follows: C 0.06-0.11%, Si 0.17-0.37%, Mn 0.30-0.60%, S≤0.010%, P≤0.015%, Ni 2.60-3.00%, Cr 0.90-1.20%, Mo 0.20-0.27%, V 0.04-0.10%, the balance being Fe and unavoidable impurities. The production method mainly includes converter smelting, secondary refining, bloom continuous casting, billet heating, rolling, heat treatment, the steel pouring temperature in the continuous casting tundish is ≤1540℃, the billet heating adopts medium frequency induction heating method, the heating temperature is between 1150-1250℃, the starting rolling temperature is between 1150-1250℃, the final rolling temperature is between 800-850℃, and the billet is air-cooled after the final rolling. The heat treatment process adopts quenching + high temperature tempering, the quenching is medium frequency induction quenching, the quenching temperature is between 820-920℃, and the water cooling is adopted; the tempering temperature is 600-680℃, the furnace time is 30-60 min, and the air cooling is adopted.

[0006] Therefore, 1. The existing ship steel and its technical production angle steel are not suitable for building key steel structure parts such as keel of large ocean transport ships due to its low strength, which is easy to cause extrusion deformation (plastic yield) or even fracture in severe marine environment such as hurricane, storm, external load collision, etc., causing serious personnel, property and marine ecological loss. In addition, the existing conventional ship steel has low fire resistance, and when a fire occurs, the steel structure part will rapidly collapse in a short time due to the sharp decrease of the strength under heating, which is difficult to support for a certain period of time to obtain rescue, causing serious loss; 2. The ship keel steel provided by the existing patent technology does not involve fire resistance, and the strength decreases sharply under the environment with temperature higher than 600℃, which is insufficient to cope with fire. SUMMARY

[0007] The application aims to provide a super-high-strength marine fire-resistant keel angle steel and a preparation method thereof.

[0008] The super-high-strength marine fire-resistant keel angle steel contains the following chemical elements and their weight percentages: C: 0.19-0.26%, Si: 0.11-0.16%, Mn: 0.7-0.9%, P≤0.004%, S≤0.002%, Ni: 1.8-2.5%, Mo: 0.28-0.42%, Ti: 0.15-0.25%, Al: 0.15-0.25%, and Ca: 0.0008-0.0015%, with the balance being Fe and inevitable impurities.

[0009] Further, the weight percentage of C is preferably 0.19-0.21%.

[0010] Further, the weight percentage of Si is preferably 0.12-0.14%.

[0011] Further, the weight percentage of Ni is preferably 0.18-0.22%.

[0012] Further, the weight percentage of Mo is preferably 0.29-0.35%.

[0013] Further, the weight percentage of Ti is preferably 0.15-0.20%.

[0014] Further, the weight percentage of Al is preferably 0.16-0.20%.

[0015] Further, the preparation method of the super-high-strength marine fire-resistant keel angle steel comprises the following steps:

[0016] 1) Converter, electric furnace smelting, continuous casting;

[0017] The converter or electric furnace is charged with CaO, blast furnace molten iron with a C content of about 4.4%, scrap steel, MnFe, SiFe, NiFe, MoFe, TiFe, and other alloy materials and auxiliary materials, and is melted, P is removed by FeO, decarburization is performed by blowing oxygen, the alloy element content is analyzed and the target value is adjusted, LF is used to remove S, Al blocks are used for further deoxidization, vacuum degassing is used, SiCa wire is fed, argon is blown for stirring, harmful inclusions in the steel are removed, and finally a 260mm*260mm square billet is obtained by continuous casting;

[0018] 2) Rolling;

[0019] The billet heating temperature is 1210-1280 DEG C, the holding time is greater than or equal to 4.5 hours, the billet is rolled immediately after being discharged, the rolling starting temperature is greater than or equal to 1050 DEG C, and the final rolling temperature is less than or equal to 870 DEG C;

[0020] 3) post-rolling cooling;

[0021] Post-rolling air cooling.

[0022] 4) heat treatment;

[0023] Induction quenching: the rolled keel angle steel is quenched at a temperature of 916-938 DEG C by using a medium-frequency induction quenching device, so that a supersaturated martensite structure of solute atoms is obtained;

[0024] The purpose of using induction quenching is that: since the induction quenching has a very fast heating rate, the workpiece can be heated to the set temperature in 3-8 seconds, and then rapidly water-cooled to room temperature; the process is designed to improve the nucleation rate of martensite and inhibit the growth rate of martensite, so that a super-fine lath martensite structure is obtained, and excellent comprehensive mechanical properties are obtained;

[0025] Ageing treatment: the quenched keel angle steel is aged at a temperature of 416-618 DEG C, the holding time is 166-218 minutes, the discharge air cooling is performed to room temperature, and nanoscale dispersed precipitated phases such as MoSi2, Ni3(TiAl) and Ti(CN) are obtained.

[0026] The principle of the main controlled alloying elements in the application is explained as follows:

[0027] C (carbon): a certain content of the cheap alloying element C is added in the steel, which can significantly improve the strength of the steel; the carbon atoms added in the steel are located in the interstitial position in the iron matrix structure, which produces microstructure distortion, causes the dislocation to be difficult to migrate under the action of external load, and thus enhances the strength of the steel; on the other hand, the alloying element Mo is treated by the heat treatment method of the application, and a high-temperature stable nanoscale and dispersedly distributed precipitated phase MoC is obtained, which can not only improve the room temperature strength of the steel, but also improve the high temperature strength of the steel by precipitate strengthening; if the C content is too low, such as less than 0.19%, the yield strength of the steel is difficult to reach 880 MPa, and if the C content exceeds 0.26%, the impact toughness of the steel is obviously reduced, so the alloying element C component range is set to 0.19-0.26%.

[0028] Si (Silicon): Adding appropriate amount of alloying element Si in structural steel, on one hand, forming substitutional solid solution strengthening effect to improve the yield strength of steel, on the other hand, combining with the added alloying element Mo, generating fine dispersed strengthening phase MoSi2, the precipitated phase has high temperature stability, which can significantly improve the high temperature strength of steel, i.e. enhancing the fire resistance of steel; but if the Si content is added excessively, such as higher than 0.16%, the low temperature toughness is reduced while the strength is improved, so the alloying element Si composition range is set to 0.11%~0.16%.

[0029] Mn (Manganese): The added alloying element Mn, on one hand, improves the room temperature strength of steel through substitutional solid solution strengthening, on the other hand, Mn can reduce the phase transition temperature and non-recrystallization temperature, through controlled rolling, rolling in the non-recrystallization temperature region can significantly refine the grain and improve the comprehensive mechanical properties, if too much Mn is added, MnS harmful inclusions are easily formed, which deteriorates the low temperature toughness and thickness direction performance, so the alloying element Mn composition range is set to 0.7~0.9%.

[0030] P (Phosphorus), S (Sulfur): P and S in structural steel are harmful elements, excessive P content is easy to segregate at the grain boundary, weakening the grain boundary and reducing the comprehensive mechanical properties of steel, S is easy to react with Mn to produce MnS inclusions which are easy to deform, deteriorating the layered tearing performance of steel and significantly reducing the toughness of steel, so P and S are controlled in a low content range: P≤0.004%, S≤0.002%.

[0031] Ni (Nickel): The added alloying element Ni replaces part of Fe atoms in the iron-based crystal lattice, reducing the friction resistance of dislocations in the crystal structure, effectively reducing the damage caused by external load impact on the steel structure, improving the impact toughness; on the other hand, using the preparation method of the present application, Ni atoms react with the added alloying elements Al, Ti, etc. to generate high-temperature stable nanoscale precipitated phase Ni3(AlTi) to form dispersion strengthening effect, improving the high temperature strength of steel, so the addition of alloying element Ni can improve the strength and toughness of steel, obtaining high-quality steel material with room temperature yield strength greater than 880 MPa, -60℃ V-type notch impact energy ≥88 J, and 600℃ high temperature yield strength ≥580 MPa, but Ni is a noble metal, excessive addition will increase the cost, so the alloying element Ni composition range is set to 1.8~2.5%.

[0032] Ti (Titanium): The added alloying element Ti can react with the added alloying element Ni to generate high-temperature stable phase Ni3Ti intermetallic compound, improving the high temperature strength of steel, and can solidify the residual harmful elements O, C, N, etc. in the steel to generate dispersed and fine precipitated phase Ti x O yTiC, Ti(CN) etc. can inhibit grain boundary migration to refine grains and improve toughness of the steel. Ti is a relatively inexpensive alloying element, so the range of the alloying element Ti is set to 0.15-0.25%.

[0033] Al (aluminum) : adding a certain content of the alloying element Al, on the one hand, Al is a high-efficiency deoxidizing element, which can remove most of the harmful element O in the steel, on the other hand, the added Al reacts with the alloying element Ni to form a high-temperature stable precipitated phase Ni3Al intermetallic compound, which improves the high-temperature strength of the steel, and ensures that the yield strength of the steel structure is ≥580 MPa at 600℃. Al is a relatively inexpensive alloying element, but too high Al content causes difficulty in continuous casting, so the range of Al content is set to 0.15-0.25%.

[0034] Ca (calcium) : in the late smelting process, the molten steel is treated by feeding SiCa wire, and the Ca content is controlled in the range of 0.0008-0.0015%, which can remove large particles of harmful inclusions such as MnS, AlN, Al2O3, SiO2 etc. in the molten steel, purify the molten steel, and improve the comprehensive mechanical properties of the steel, and significantly improve the casting performance.

[0035] Advantages: compared with the prior art, the characteristics of the present application are: 1. The ultra-high strength marine fire-resistant keel angle steel provided by the present application can be used for building reinforced bars, keels and other structural members of large ocean-going ships, has good high-temperature strength, and still has sufficient strength to support the steel structure when the ambient temperature is higher than 600℃, ensuring sufficient safety of the crew, the ship and the transported goods; 2. The ultra-high strength angle steel provided by the present application can also be applied to the construction of offshore oil and gas drilling platform steel structures, which can ensure the safety of the platform in harsh sea waves, hurricanes and other marine environments, and still has sufficient strength in high-temperature danger such as fire, so as to gain valuable rescue time. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a microstructure diagram of the steel treated by induction quenching + aging in the embodiment of the present application: ultra-fine lath martensite + nanoscale precipitated phase diagram. DETAILED DESCRIPTION

[0037] The present application will be further described below in conjunction with the drawings and embodiments.

[0038] The ultra-high strength marine fire-resistant keel angle steel contains the following chemical element components and their weight percentages: C: 0.19-0.26%, Si: 0.11-0.16%, Mn: 0.7-0.9%, P≤0.004%, S≤0.002%, Ni: 1.8-2.5%, Mo: 0.28-0.42%, Ti: 0.15-0.25%, Al: 0.15-0.25%, Ca: 0.0008-0.0015%, and the balance is Fe and inevitable impurities.

[0039] Further, the weight percentage of C is preferably 0.19-0.21%.

[0040] Further, the weight percentage of Si is preferably 0.12-0.14%.

[0041] Further, the weight percentage of Ni is preferably 0.18-0.22%.

[0042] Further, the weight percentage of Mo is preferably 0.29-0.35%.

[0043] Further, the weight percentage of Ti is preferably 0.15-0.20%.

[0044] Further, the weight percentage of Al is preferably 0.16-0.20%.

[0045] Further, a preparation method of the ultra-high strength marine fire-resistant keel angle steel comprises the following steps:

[0046] 1) converter, electric furnace smelting, continuous casting;

[0047] The converter or electric furnace is charged with CaO, blast furnace molten iron with a C content of about 4.4%, scrap steel, MnFe, SiFe, NiFe, MoFe, TiFe and other alloy materials, auxiliary materials are melted, FeO is added to remove P, oxygen is blown to remove C, the alloy element content is sampled and analyzed and the target value is adjusted, LF is used to remove S, Al blocks are further added for deoxidization, vacuum degassing is used, SiCa wire is fed, argon is blown for stirring, harmful inclusions in the steel are removed, and finally 260mm*260mm square billets are continuously cast;

[0048] 2) rolling;

[0049] The casting billet heating temperature is 1210-1280℃, the holding time is ≥4.5 hours, the casting billet is immediately rolled after being discharged, the opening rolling temperature is ≥1050℃, and the final rolling temperature is ≤870℃;

[0050] 3) post-rolling cooling;

[0051] Post-rolling air cooling.

[0052] 4) heat treatment;

[0053] induction quenching: the rolled keel angle steel is quenched at a temperature of 916-938 ℃ by using a medium-frequency induction quenching device, so that a martensite structure with supersaturated solute atoms is obtained;

[0054] The purpose of using induction quenching is that, since the induction quenching has a very fast heating rate, the workpiece can be heated to the set temperature in 3-8 seconds of power-on time, and then rapidly cooled to room temperature by water pouring, the process design improves the nucleation rate of martensite and suppresses the growth rate of martensite, so that a super-fine lath martensite structure is obtained, and excellent comprehensive mechanical properties are further obtained.

[0055] aging treatment: the quenched keel angle steel is aged at a temperature of 416-618 ℃, and is kept for 166-218 min, and is discharged to air cooling to room temperature, so that nanoscale dispersed precipitated phases such as MoSi2, Ni3(TiAl) and Ti(CN) are obtained.

[0056] According to the chemical element composition, mass percentage and production method requirements of the application, five examples, namely example 1, example 2, example 3, example 4 and example 5, are prepared. In order to verify the influence of the chemical components and mass percentage content and the casting blank heating temperature, the finish rolling temperature in the rolling process and the heat treatment parameters on the performance parameters, three comparative examples, namely comparative example 1, comparative example 2 and comparative example 3, are prepared, that is, eight batches of steel materials are smelted and rolled. Among them, the mass percentage content of the chemical components of comparative example 1 is not within the range of the application, while the process parameters in the preparation process are within the range of the application, the mass percentage content of the chemical components of comparative example 2 is within the range of the application, while the process parameters in the preparation process are not within the range of the application, and the mass percentage content of the chemical components of comparative example 3 and the process parameters in the preparation process are both not within the range of the application. The weight percentage of the chemical element composition of the five examples and the three comparative examples is shown in Table 1, wherein the balance is Fe and unavoidable impurities. The production process control parameters and the performance quality of the keel angle steel are shown in Table 2.

[0057] Table 1 Comparison of chemical composition of examples and comparative examples of the application (wt%)

[0058]

[0059]

[0060] Table 2 Steel performance of production process control of examples and comparative examples of the application

[0061]

[0062] As can be seen from Table 1 and Table 2, the chemical composition and mass percentage of the keel angle steel produced by the embodiments 1-5 of the present application and the parameters of the production process control have the yield strength at room temperature higher than 880 MPa, the yield strength at 600 DEG C higher than 580 MPa, while the steel produced by the comparative example 1, the comparative example 2 and the comparative example 3 has the yield strength at room temperature lower than 596 MPa, the yield strength at 600 DEG C lower than 298 MPa, and the impact energy at-60 DEG C lower than 37 J, wherein the yield strength at room temperature of the keel angle steel prepared by the embodiment 2 of the present application is 889 MPa, the yield strength at 600 DEG C is 621 MPa, the impact energy at-60 DEG C reaches 166 J, the comprehensive mechanical properties are excellent, the manufacture of the keel structure of the large ocean-going ship is safe and reliable, and the yield strength at high temperature is excellent, the capacity of supporting load at 600 DEG C environment is sufficient, and the embodiment 2 is the best embodiment.

[0063] The ocean-going ship gradually develops towards large scale to improve the transportation efficiency, the super large ocean-going ship needs to use the super high strength steel to resist the impact of the severe ocean hurricane and sea wave, the ocean-going transportation safety is paid more and more attention, the ship structure design selects the steel to consider not only the strength and low temperature fracture toughness, but also needs to use the steel with good fire resistance to improve the overall safety of the ship. The present application aims to provide a kind of super high strength angle steel with good fire resistance, which is used to build the keel of the large ocean-going ship, and the ship has higher safety, high added value and higher efficiency than ordinary steel.

[0064] The present application provides a kind of high-quality steel material with the yield strength at room temperature greater than 880 MPa, the impact energy of V-shaped notch at-60 DEG C ≥88J, the yield strength at 600 DEG C high temperature ≥580 MPa, the super large ocean-going ship built by the steel material is more safe, can resist the impact of external load in severe environment. And has good fire resistance, still has high strength in high temperature environment, is used to build the keel of the large ocean-going ship, reinforcing rib and other structural parts, and has better safety.

Claims

1. A type of ultra-high strength marine fire-resistant keel angle steel, characterized in that, Its chemical composition and mass percentage are as follows: C: 0.19~0.26%, Si: 0.11~0.16%, Mn: 0.7~0.9%, P≤0.004%, S≤0.002%, Ni: 0.18~0.25%, Mo: 0.28~0.42%, Ti: 0.15~0.25%, Al: 0.15~0.25%, Ca: 0.0008~0.0015%; the balance is Fe and unavoidable impurities. The preparation steps are as follows: (1) Converter, electric furnace smelting, and continuous casting; the specific process is as follows: CaO, blast furnace iron with a C content of 4.4%, scrap steel, MnFe, SiFe, NiFe, MoFe, TiFe alloy materials and auxiliary materials are charged into the converter or electric furnace and melted. FeO is added to remove P, oxygen is blown to remove carbon, the content of alloy elements is sampled and analyzed and the target value is adjusted. The LF treatment in the ladle furnace is used to remove S, Al blocks are added to remove oxygen, vacuum degassing is used, SiCa wire is fed, argon gas is blown to stir, harmful inclusions in the steel are removed, and finally continuous casting is made into a 260mm×260mm square billet; (2) Rolling; the specific process is as follows: billet heating temperature: 1210~1280℃, holding time ≥4.5 hours, billet is rolled after exiting the furnace, initial rolling temperature ≥1050℃, final rolling temperature ≤870℃; (3) Post-rolling cooling; that is, air cooling after rolling; (4) Heat treatment; The specific process includes induction hardening and aging treatment; The induction hardening process involves using a medium-frequency induction hardening facility to quench the rolled keel angle steel at a temperature range of 916~938℃ to obtain a martensitic structure with supersaturated solute atoms. The aging treatment process is as follows: the quenched keel angle steel is subjected to a temperature range of 416~618℃ for 166~218min, and then air-cooled to room temperature to obtain nanoscale dispersed precipitates MoSi2, Ni3(TiAl) and Ti(CN).

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