CN117230388A - Medium-chromium high-strength steel with excellent anti-oil corrosion and hydrogen induced cracking resistance, and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of metal materials, and particularly relates to medium-chromium high-strength steel with excellent anti-oil corrosion and hydrogen-induced cracking resistance, and a preparation method and application thereof. The medium chromium high-strength steel comprises the following chemical components in percentage by mass: 0.011< C <0.069%,0.11< Si <0.29%,0.011< Mo+Cu <0.49%,1.51< Cr <1.99%,0.041< Ti <0.059%,0.005< RE <0.019%, S < 0.0010%, and the balance Fe and unavoidable impurities, while the above chemical composition must also satisfy the formula: cu/mo=1-2. The steel plate adopts the low-carbon, low-silicon and medium-chromium cheap chemical composition design, does not contain noble corrosion-resistant metal elements such as Ni and the like, and greatly reduces the material cost; the invention adopts Si deoxidation instead of the traditional Al deoxidation technology, and is assisted with Ti-RE composite deoxidation to form fine, dispersed and uniform composite oxysulfide, thereby greatly reducing the density of corrosive active inclusion and obviously improving the corrosion resistance of crude oil.

Description

A medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking and its manufacture Preparation methods and applications

Technical field

The invention belongs to the technical field of metal materials, and specifically relates to a medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking and its preparation method and application.

Background technique

Oil tankers are one of the main means of ocean transportation of crude oil. In recent years, oil tanker failure accidents due to corrosion of cargo oil tanks have occurred frequently. It not only causes huge economic losses and safety accidents, but also causes serious harm to marine environment mirrors. Therefore, the anti-corrosion issue of oil tanker cargo tanks has attracted more and more attention.

Crude oil, especially high-sulfur and high-acid crude oil, has a serious impact on corrosion of steel-structured cargo tanks, threatening the safety of oil tanker operations. Moreover, there is also the problem of corrosion on the upper deck of the cargo tank. A large number of studies have found that the uniform corrosion of the upper deck of cargo oil tanks has the following characteristics: (1) high concentration of H ₂ S gas on the tank top; (2) the impedance effect of the oil film; (3) the destructive effect of retained water and tank washing on the oil film; (4) High acidity in pitting pits; (5) Isometric nature of pitting pits.

There are many factors that lead to HIC in steel. Generally, as the pH value in the environment decreases, the HIC sensitivity of steel increases. Therefore, an increase in acidic gas _CO2 will also increase HIC sensitivity. In addition, if the solution contains Cl ^-, it will also reduce the HIC resistance of the steel. In addition, temperature also has a significant impact on the HIC properties of steel.

In addition to the great influence of the environment on the occurrence of HIC in steel, the chemical composition, microstructure, segregation and non-metallic inclusions of the steel itself also have a great influence on its HIC performance. The increase in C, Mn, S, and P content in steel reduces its anti-HIC sensitivity, while Cu and Mo increase its anti-HIC sensitivity. Jin et al. [Jin T Y, Liu Z Y, Cheng Y F. Effect of non-metallic inclusions on hydrogen-induced cracking of API5L X100 steel [J]. International Journal of Hydrogen Energy 2010,35:8014-8021] found that Al-rich, Non-metallic inclusions of Si can easily cause HIC in X100 pipeline steel, and HIC extends along the non-metallic inclusions; Huang Feng et al. trapping efficiency of HIC sensitivity; Zhou Qi et al [Zhou Qi, Ji Genshun, Zhang Jianbin, et al. Sulfide inclusions and hydrogen-induced cracking in pipeline steel [J]. Materials Engineering 2002, 9:37-39.] It was found that long strips of MnS can significantly reduce the HIC resistance of pipeline steel.

Corrosion-resistant steel for oil tanker cargo tanks is an important new steel variety that has been researched and developed internationally in recent years. The main protective measures taken against corrosion in oil tankers' cargo tanks include adding corrosion inhibitors, using anti-corrosion coatings and using corrosion-resistant steel plates. Among them, the process of adding corrosion inhibitors is complicated and the long-term investment is high; and there are serious local corrosion risks during the use of the coating. The oil tanker must be maintained and recoated every 2.5 years, which requires high costs. Extending the construction period, closing the cargo tank space, and harsh construction environment will also affect the construction quality to a certain extent.

Due to the high concentration of H ₂ S gas in the tank top of the oil tanker, the water retained at the bottom contains chloride ions. The essence of the corrosion is mainly chloride ion corrosion and hydrogen-induced cracking. Chloride ion corrosion is mainly related to corrosion-active inclusions in materials. Hydrogen-induced cracking is mainly related to the microstructure type of the material, and acicular ferrite is considered to be an ideal microstructure resistant to hydrogen-induced cracking [Huang Feng, Liu Jing, Deng Zhao Jun, et al. Effect of microstructure and inclusions on hydrogen induced cracking susceptibility and hydrogen trappingefficiency of X120 pipeline steel[J].Materials Science and Engineering A2010,527:6997-7001.]. Therefore, the present invention will mainly use the density of corrosion-active inclusions and the saturation current density at the electrostatic potential (Е = -300mV) to evaluate the local corrosion resistance, and use the number of acicular ferrite to evaluate the resistance to hydrogen-induced cracking. performance.

Contents of the invention

In order to solve the deficiencies of the existing technology, the present invention provides a medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking and its preparation method and application. The invention can solve the problem of insufficient anti-oil corrosion and hydrogen-induced cracking resistance of traditional high-strength steel, as well as the high alloy cost caused by alloying with Ni, Mo, and Cu.

The technical solutions provided by the invention are as follows:

A medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking. Its chemical composition in mass percentage is: 0.011<C<0.069%, 0.11<Si<0.29%, 0.011<Mo+Cu<0.49%, 1.51<Cr<1.99%, 0.041<Ti<0.059%, 0.005<RE<0.019%, S≤0.0010%, the rest is Fe and inevitable impurities. At the same time, the above chemical composition also satisfies the formula: in terms of mass percentage, Cu /Mo=1-2.

The medium-chromium high-strength steel provided by the above technical solution with excellent resistance to oil corrosion and hydrogen-induced cracking can form fine, dispersed and uniform complex oxysulfides, and has the ability to greatly reduce the density of corrosion-active inclusions and has significantly improved resistance to corrosion. Crude oil corrosion properties.

At the same time, the medium-chromium high-strength steel provided by the above technical solution, which has excellent resistance to oil corrosion and hydrogen-induced cracking, can significantly improve its resistance to hydrogen-induced cracking (HIC) due to the use of specific contents of Cr and RE.

At the same time, the medium-chromium high-strength steel provided by the above technical solution has excellent resistance to oil corrosion and hydrogen-induced cracking and has high strength.

The roles of each element in medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking are as follows:

C element: C element is one of the most basic elements added to steel. Its solid solution strengthening and precipitation strengthening can significantly affect the mechanical properties of steel. However, C will significantly reduce the local corrosion performance of steel. At the same time, C is not conducive to the welding performance of steel. Under normal circumstances, steel with excellent welding performance is required, and the carbon content must be strictly controlled. The C content in low-alloy high-strength steel is generally required to be less than 0.20%. Therefore, the carbon content in the steel of the present invention is 0.011-0.069%.

Si element: Si can inhibit the production of acid in the rust layer and prevent the intrusion ^{of Cl-} . In the inner rust layer, Si mainly exists in the form of divalent oxides in the spinel oxide. Higher Si is conducive to refining α-FeOOOH in the rust layer, making the inner rust layer dense and preventing the intrusion of Cl ^- . At the same time, Si element solid solution in ferrite and austenite plays a strengthening role and improves the mechanical properties of steel. However, if the Si element in the matrix exceeds a certain range, it will promote the nucleation of imitation grain boundary ferrite, inhibit the formation of acicular ferrite, and increase the percentage of MA components in the steel. Excessive Si is not conducive to the plasticity and toughness of the steel. , and also reduce the welding performance of steel. Therefore, the silicon content in the steel of the present invention is 0.11-0.29%.

Cr element: As the Cr content in steel increases, α-FeOOH can be effectively refined. When the Cr content in α-FeOOH exceeds 5%, it can prevent the entry of corrosive anions, such as Cl ^- , thereby improving the anti-oil properties of the steel. Corrosion and hydrogen-induced cracking resistance. At the same time, the enrichment of Cr element in the rust layer increases the electrode potential of the substrate. The chromium content in the steel of the invention is therefore 1.51-1.99%.

Cu element: Cu element is one of the alloying elements commonly added in corrosion-resistant steel. The general addition range in steel is 0.3%-0.5%. Adding Cu element to seawater corrosion-resistant steel can not only slow down the local corrosion caused by S-containing inclusions, improve the corrosion resistance of the steel, but also improve the flow performance of molten steel. The role of Cu element in corrosion resistance in steel is due to the accumulation of Cu ²⁺ in the inner rust layer, which reduces the critical current density of the activation peak, thereby reducing the active dissolution rate of the steel matrix. Therefore, the copper content in the steel of the present invention is 0.011-0.49%.

Mo element: Mo is an important alloy element in steel and is widely used in alloy structural steel, stainless steel, tool and die steel, heat-resistant steel and other fields. Mo can significantly improve the pitting corrosion resistance of stainless steel and corrosion-resistant steel. In addition, it also has the following main functions in steel: improving the strength and toughness of steel (especially high temperature performance), improving the corrosion resistance of steel in acid and alkali solutions and marine environments, increasing the hardness and wear resistance of steel, improving the It can improve the hardenability and hardenability of parts, purify grain boundaries and improve delayed fracture resistance, etc. Therefore, the molybdenum content in the steel of the present invention is 0.011-0.49%.

Ti element: Ti has low dissolution in steel and mainly precipitates in the form of C and N compounds. The Ti element is generally added to carbon steel for microalloying, and the content addition range generally does not exceed 0.05%. At higher temperatures, Ti, C, and N form carbonitrides that are insoluble in austenite, effectively inhibiting the growth of austenite grains during the heating process, pinning grain boundaries, and refining austenite grains; at higher temperatures, At low temperatures, fine dispersed nanoscale precipitates are formed, pinning dislocations, and precipitation strengthening. Excessive Ti content increases the precipitation temperature of TiC and TiN, and the particles grow and coarsen rapidly, reducing the ability of grain boundaries and dislocation pinning, and reducing the strength and toughness of steel. Therefore, the titanium content in the steel of the present invention is 0.041-0.059%.

RE element: The main functions of RE element in the steel matrix are as follows: purification of molten steel, metamorphic inclusion and micro-alloying. Purify molten steel: Rare earths have extremely strong chemical reactivity, so they can easily combine with sulfur elements and oxygen elements in molten steel to form high-melting point compounds, which precipitate from the molten steel and purify the molten steel. In addition, rare earths also have strong deoxidizing ability. Its deoxidizing ability is stronger than Mg, Al and Ti elements, and is the same as Ca element. Its desulfurization ability is also very strong, second only to Ca element. Metamorphic inclusions: Adding rare earth elements to steel can change the shape, size and distribution of inclusions formed in the steel, and at the same time react with the inclusions to change the type of inclusions. It replaces harmful inclusions in steel to improve the mechanical properties of the steel matrix and effectively improves the corrosion resistance of the steel. Rare earth elements are highly metallic and preferentially combine with sulfur elements to eliminate the formed MnS inclusions and spheroidize and disperse the inclusions, effectively controlling the type, shape and distribution of inclusions. Microalloying: Adding rare earth elements to steel can play a role in solid solution strengthening. In addition, rare earths refine the structure by inhibiting the recrystallization and growth of deformed austenite grains. The combination of rare earth elements and hydrogen elements reduces the susceptibility to hydrogen-induced cracking and interacts with elements such as C, N, and V to change the phase transformation point of steel structure formation. Therefore, the rare earth content in the steel of the present invention is 0.005<RE<0.019%, and lanthanum or cerium, or a mixture of lanthanum and cerium rare earths can be specifically selected.

S element: S is a harmful element in steel. It easily forms lamellar segregation of sulfides, greatly reducing the strength and plasticity in the plate thickness direction (Z direction), often causing lamellar tearing. S also easily generates FeS with a low melting point, causing hot brittle cracks in steel during hot rolling and welding. Therefore, an effective desulfurization process must be adopted during smelting to ensure that the S content is controlled in a low range, so that the steel can have excellent toughness and welding performance. Therefore, the sulfur content in the steel of the present invention is S≤0.0010%.

Specifically, the structure type of medium-chromium high-strength steel is a composite structure type of acicular ferrite and polygonal grain boundary ferrite, in which the area proportion of acicular ferrite is ≥85%.

Specifically, the density of corrosion-active inclusions in medium-chromium high-strength steel is ≤2/mm ² .

Specifically, the saturation current density of medium-chromium high-strength steel at electrostatic potential E=-300mV is ≤5.0mA.

The invention also provides a method for preparing medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking, which includes the following steps:

1) The molten steel is smelted, refined and vacuum treated in sequence, and then continuously cast into billets;

2) Perform conventional heating and soaking of the cast slab;

3) Continuously roll the cast slab into product steel plates, and control the final rolling temperature to 750-850°C. After rolling, water and cool to 410-550°C;

4) Cool the steel plate to room temperature naturally to obtain.

The smelting of step 1) specifically includes the following steps: use a converter or electric arc furnace to make molten iron, scrap steel, or molten iron and scrap steel together, adjust the temperature and composition of the molten steel, adjust the tapping temperature to 1585-1675°C, and adjust the temperature and composition of the molten steel. The oxygen content is 150-390ppm; after the molten steel enters the ladle, stir it with micro-bubbles for 4-8 minutes, and then use Fe-Si alloy or Fe-Si-Mn alloy in the ladle to pre-deoxidize, and adjust the free oxygen content in the molten steel to 50-90ppm, stir with micro-bubbles for 4-6 minutes, and then use Ti-RE composite alloy for final deoxidation to obtain molten steel that meets the chemical composition; Ti-RE composite alloy is added in the form of block alloy or cored wire. In molten steel, the particle size of Ti-RE composite alloy is 8-16mm; the addition amount of Ti-RE composite alloy is 1.2-4.8kg per ton of molten steel.

Specifically, the refining method is LF refining followed by VD refining or RH refining, and the refined molten steel is continuously cast according to conventional processes.

The invention also provides the application of medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking, as crude oil tanker cargo tank materials, inferior crude oil refining pipeline materials, tobacco processing container materials, tobacco processing pipeline materials, hydrogen transportation Transportation pipeline materials or hydrogen transportation container materials.

The medium-chromium high-strength steel provided by the present invention can be widely used in the above scenarios because it is resistant to oil corrosion, hydrogen-induced cracking and high strength.

Description of drawings

Figure 1 Optical micrograph of corrosion-active inclusions;

Figure 2 Sample potentiodynamic polarization curve;

Figure 3 is the electrochemical impedance test chart of the sample, which shows the impedance diagram part, the bode diagram part and the phase angle diagram part in sequence;

Figure 4 Equivalent circuit of sample electrochemical impedance spectrum.

Detailed ways

The principles and features of the present invention are described below. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

Example 1

A medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking. Its chemical composition in mass percentage is: C 0.035%, Si 0.15%, Mo 0.15%, Cu 0.29%, Cr 1.71%, Ti0.045 %, RE 0.012%, S0.009%, the rest is Fe and inevitable impurities.

The smelting and refining method is: use a converter to make the molten iron and then adjust the temperature and composition of the molten steel. Adjust the tapping temperature to 1635°C and the free oxygen content in the molten steel to 271ppm; use micro-bubble stirring after the molten steel enters the ladle. 6 minutes, then use Fe-Si alloy for pre-deoxidation in the ladle, adjust the free oxygen content in the molten steel to 70ppm, stir with micro-bubbles for 5 minutes, and then use Ti-RE alloy for final deoxidation; Ti-RE alloy is used as a block The molten steel is added in the form of a solid alloy, the particle size of the Ti-RE alloy is 12mm; the adding amount of the Ti-RE composite alloy is 2.9kg per ton of molten steel, and then the molten steel is subjected to LF refining and RH refining.

LF Refining:

Controlling the viscosity of the refining slag between 1.55 and 1.95 Pa·s can improve the ability of the slag to absorb inclusions, thereby improving the cleanliness of the molten steel. Controlling the alkalinity of the refining furnace white slag to 5.3≤R≤7.5 is beneficial to improving the desulfurization rate and is beneficial to Improve the cleanliness of molten steel and reduce oxide inclusions in molten steel; control the MI slag index (=CaO/SiO ₂ : Al ₂ O ₃ ratio) MI > 0.153, and the sulfur distribution coefficient will increase greatly, thereby controlling the refining slag to a certain alkali Appropriate fluidity under the temperature; the white slag retention time is 14.5min, the refining cycle is 39.5min, and the soft blowing time is guaranteed to be 4.5min, thereby controlling the outbound [O] content.

RH vacuum treatment:

The vacuum chamber pressure is pumped below 66.7kPa for 13.45 minutes, and the bottom blow argon gas flow is 14.95m ³ /h to achieve 4 cycles of molten steel. It is strictly required to control the type and weight of the alloy added, and use higher-grade low-carbon ferromanganese, Metal manganese, low carbon ferrosilicon, ferrotitanium and other alloys ensure that the composition of the molten steel is fully qualified, and ensure that the vacuum is maintained for more than 5.1 minutes after the alloy is added to obtain purer molten steel; at the same time, the appropriate molten steel temperature is provided for continuous casting to ensure that the tundish is passed through The heat is 20.05°C above the liquidus line.

The refined molten steel is then continuously cast according to conventional processes: the temperature of the continuous casting tundish is 1541°C, and the casting speed is 1.15 m/s.

The rolling process is: heating and soaking the cast slab at 1190°C, and the residence time in the furnace is 3.5 hours; continuously rolling into product steel plates, and controlling the final rolling temperature to 790°C, and watering and cooling to 480°C after rolling ; Cool to room temperature naturally and set aside.

The structure type of the steel plate obtained according to the above method is acicular ferrite + polygonal grain boundary ferrite, and the acicular ferrite is 87%; the density of corrosion-active inclusions in the steel plate is 1.2/mm ² ; the steel plate is The saturation current density at electrostatic potential (E=-300mV) is 2.4mA.

The yield strength of the steel plate is 375MPa, the tensile strength is 530MPa, and the elongation is 35%. Chloride ion corrosion is mainly related to corrosion-active inclusions in the material, and hydrogen-induced cracking is mainly related to the microstructure type of the material. Acicular ferrite is considered to be an ideal microstructure resistant to hydrogen-induced cracking. Since the microstructure is a uniform structure dominated by acicular ferrite (87%), the resistance to hydrogen-induced cracking is also excellent.

Example 2

A medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking. Its chemical composition in mass percentage is: C 0.063%, Si 0.27%, Mo 0.13%, Cu 0.28%, Cr 1.95%, Ti0.057 %, RE 0.017%, S0.009%, the rest is Fe and inevitable impurities.

The smelting and refining method is: use a converter to make the molten iron and then adjust the temperature and composition of the molten steel. Adjust the tapping temperature to 1670°C and the free oxygen content in the molten steel to 385ppm; use micro-bubble stirring after the molten steel enters the ladle. 7 minutes, then use Fe-Si alloy for pre-deoxidation in the ladle, adjust the free oxygen content in the molten steel to 85ppm, stir with micro-bubbles for 6 minutes, and then use Ti-RE alloy for final deoxidation; Ti-RE alloy is used as a block The molten steel is added in the form of an alloy, the particle size of the Ti-RE alloy is 15mm; the adding amount of the Ti-RE alloy is 4.5kg per ton of molten steel, and then the molten steel is subjected to LF refining and RH refining.

LF Refining:

Control the viscosity of the refining slag at 1.51~1.91Pa·s to improve the ability of the slag to absorb inclusions, thereby improving the cleanliness of the molten steel; controlling the alkalinity of the refining furnace white slag to 5.1≤R≤7.3 is conducive to improving the desulfurization rate and is beneficial to Improve the cleanliness of molten steel and reduce oxide inclusions in molten steel; control the MI slag index (=CaO/SiO ₂ : Al ₂ O ₃ ratio) MI > 0.155, and the sulfur distribution coefficient will increase greatly, thereby controlling the refining slag to a certain alkali Appropriate fluidity under the temperature; the white slag retention time is 14.3min, the refining cycle is 39.3min, and the soft blowing time is guaranteed to be 4.6min, thereby controlling the outbound [O] content.

RH vacuum treatment:

The vacuum chamber pressure is pumped to below 66.6kPa for 13.4 minutes, and the bottom blowing argon gas flow is 14.9m ³ /h to achieve 5 cycles of molten steel. It is strictly required to control the type and weight of the alloy added, and use higher-grade low-carbon ferromanganese, Metal manganese, low-carbon ferrosilicon, ferro-titanium and other alloys ensure that the composition of the molten steel is fully qualified, and ensure that the vacuum is maintained for more than 5.3 minutes after the alloy is added to obtain purer molten steel; at the same time, the appropriate molten steel temperature is provided for continuous casting to ensure that the tundish is passed through The heat is 19.8°C above the liquidus line.

The refined molten steel is then continuously cast according to conventional processes: the temperature of the continuous casting tundish is 1543°C, and the casting speed is 1.11 meters/second.

The rolling process is: heating and soaking the billet at 1210°C, and the residence time in the furnace is 3.3 hours; continuously rolling into product steel plates, and controlling the final rolling temperature to 835°C, and watering and cooling to 537°C after rolling ; Cool to room temperature naturally and set aside.

The structure type of the steel plate obtained according to the above method is acicular ferrite + polygonal grain boundary ferrite, and the acicular ferrite is 86%; the density of corrosion-active inclusions in the steel plate is 1.59/mm ² ; the steel plate is The saturation current density at electrostatic potential (E=-300mV) is 2.87mA.

The yield strength of the steel plate is 380MPa, the tensile strength is 535MPa, and the elongation is 34%. Chloride ion corrosion is mainly related to corrosion-active inclusions in the material, and hydrogen-induced cracking is mainly related to the microstructure type of the material. Acicular ferrite is considered to be an ideal microstructure resistant to hydrogen-induced cracking. Since the microstructure is a uniform microstructure dominated by acicular ferrite (86%), the resistance to hydrogen-induced cracking is also excellent.

Example 3

A medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking. Its chemical composition in mass percentage is: C 0.018%, Si 0.25%, Mo 0.15%, Cu 0.32%, Cr 1.95%, Ti0.043 %, RE 0.009%, S0.008%, the rest is Fe and inevitable impurities.

The smelting and refining method is: use an electric arc furnace to make the scrap steel and then adjust the temperature and composition of the molten steel. Adjust the tapping temperature to 1610°C and the free oxygen content in the molten steel to 185ppm; use micro-bubbles after the molten steel enters the ladle. Stir for 4 minutes, then use Fe-Si-Mn alloy in the ladle for pre-deoxidation, adjust the free oxygen content in the molten steel to 57ppm, stir with micro-bubbles for 4 minutes, and then use Ti-RE alloy for final deoxidation; Ti-RE The composite alloy is added to the molten steel in the form of cored wire. The particle size of the Ti-RE alloy is 9mm. The addition amount of the Ti-RE composite alloy is 1.4kg per ton of molten steel. The molten steel is then subjected to LF refining and VD refining.

LF Refining:

Control the viscosity of the refining slag at 1.53~1.93Pa·s to improve the ability of the slag to absorb inclusions, thereby improving the cleanliness of the molten steel; controlling the alkalinity of the refining furnace white slag to 5.2 ≤ R ≤ 7.5 is beneficial to improving the desulfurization rate and is beneficial to Improve the cleanliness of molten steel and reduce oxide inclusions in molten steel; control the MI slag index (=CaO/SiO ₂ : Al ₂ O ₃ ratio) MI > 0.157, and the sulfur distribution coefficient will increase greatly, thereby controlling the refining slag to a certain alkali Appropriate fluidity under the temperature; the white slag retention time is 14.4min, the refining cycle is 39.5min, and the soft blowing time is guaranteed to be 4.7min, thereby controlling the outbound [O] content.

RH vacuum treatment:

The vacuum chamber pressure is pumped to below 66.5kPa for 13.2 minutes, and the bottom blowing argon gas flow is 14.9m ³ /h to achieve 6 cycles of molten steel. It is strictly required to control the type and weight of the alloy added, and use higher-grade low-carbon ferromanganese, Metal manganese, low carbon ferrosilicon, ferrotitanium and other alloys ensure that the composition of the molten steel is fully qualified, and ensure that the vacuum is maintained for more than 5.2 minutes after the alloy is added to obtain purer molten steel; at the same time, it provides a suitable molten steel temperature for continuous casting to ensure that the tundish is passed through. The heat is 19.9°C above the liquidus line.

The refined molten steel is then continuously cast according to conventional processes: the temperature of the continuous casting tundish is 1539°C, and the casting speed is 1.21 m/s.

The rolling process is: heating and soaking the billet at 1215°C, and the residence time in the furnace is 3.4 hours; continuously rolling into product steel plates, and controlling the final rolling temperature to 788°C, and watering and cooling to 486°C after rolling ; Cool to room temperature naturally and set aside.

The structure type of the steel plate obtained according to the above method is acicular ferrite + polygonal grain boundary ferrite, and the acicular ferrite is 89%; the density of corrosion-active inclusions in the steel plate is 1.37/mm ² ; the steel plate is The saturation current density at electrostatic potential (E=-300mV) is 1.93mA.

The yield strength of the steel plate is 390MPa, the tensile strength is 550MPa, and the elongation is 33%. Chloride ion corrosion is mainly related to corrosion-active inclusions in the material, and hydrogen-induced cracking is mainly related to the microstructure type of the material. Acicular ferrite is considered to be an ideal microstructure resistant to hydrogen-induced cracking. Since the microstructure is a uniform structure dominated by acicular ferrite (89%), the resistance to hydrogen-induced cracking is also excellent.

Comparative example 1

A medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking. Its chemical composition in mass percentage is: C 0.035%, Si 0.15%, Mo 0.15%, Cu 0.29%, Cr 1.49%, Ni 0.58% , Al 0.035, S0.009%, the rest is Fe and inevitable impurities.

The smelting and refining method is: use a converter to make the molten iron and then adjust the temperature and composition of the molten steel. Adjust the tapping temperature to 1631°C and the free oxygen content in the molten steel to 301ppm; use micro-bubble stirring after the molten steel enters the ladle. 6 minutes, then use pure aluminum blocks in the ladle for pre-deoxidation and final deoxidation, adjust the free oxygen content in the molten steel to 4ppm, and then perform LF refining and RH refining of the molten steel.

LF Refining:

Control the viscosity of the refining slag at 1.53~1.94Pa·s to improve the ability of the slag to absorb inclusions, thereby improving the cleanliness of the molten steel; controlling the alkalinity of the refining furnace white slag to 5.15≤R≤7.42 is beneficial to improving the desulfurization rate and is beneficial to Improve the cleanliness of molten steel and reduce oxide inclusions in molten steel; control the MI slag index (=CaO/SiO ₂ : Al ₂ O ₃ ratio) MI > 0.153, and the sulfur distribution coefficient will increase greatly, thereby controlling the refining slag to a certain alkali Appropriate fluidity under the temperature; the white slag retention time is 14.5min, the refining cycle is 39.5min, and the soft blowing time is guaranteed to be 4.55min, thereby controlling the outbound [O] content.

RH vacuum treatment:

The vacuum chamber pressure is pumped below 66.67kPa for 13.4 minutes, and the bottom blowing argon gas flow rate is 14.8m ³ /h to achieve 4 cycles of molten steel. It is strictly required to control the type and weight of the alloy added, and use higher-grade low-carbon ferromanganese, Metal manganese, low-carbon ferrosilicon, ferro-titanium and other alloys ensure that the composition of the molten steel is fully qualified, and ensure that the vacuum is maintained for more than 5.35 minutes after the alloy is added to obtain purer molten steel; at the same time, the appropriate molten steel temperature is provided for continuous casting to ensure that the tundish is passed through The heat is 19.7°C above the liquidus line.

The refined molten steel is then continuously cast according to conventional processes: the temperature of the continuous casting tundish is 1542°C, and the casting speed is 1.18 meters/second.

The rolling process is: heating and soaking the cast slab at 1190°C, and the residence time in the furnace is 3.3 hours; continuously rolling into product steel plates, and controlling the final rolling temperature to 791°C, and watering after rolling to cool to 483°C ; Cool to room temperature naturally and set aside.

The structure type of the steel plate obtained according to the above method is acicular ferrite + polygonal grain boundary ferrite, and the acicular ferrite is 86%; the density of corrosion-active inclusions in the steel plate is 11/mm ² ; the steel plate is The saturation current density at electrostatic potential (E=-300mV) is 6.4mA. The yield strength of the steel plate is 365MPa, the tensile strength is 515MPa, and the elongation is 32%.

Comparative example 2

A medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking. Its chemical composition in mass percentage is: C 0.0358%, Si 0.17%, Mo 0.13%, Cu 0.27%, Cr 1.63%, Ti 0.041% , RE0.013%, S 0.008%, the rest is Fe and inevitable impurities.

The smelting and refining method is: use a converter to make the molten iron and then adjust the temperature and composition of the molten steel. Adjust the tapping temperature to 1633°C and the free oxygen content in the molten steel to 289ppm; use micro-bubble stirring after the molten steel enters the ladle. 5 minutes, then use pure aluminum blocks in the ladle for pre-deoxidation and final deoxidation, adjust the free oxygen content in the molten steel to 5ppm, and then perform LF and RH refining of the molten steel.

LF Refining:

Controlling the viscosity of the refining slag between 1.59 and 1.98 Pa·s can improve the ability of the slag to absorb inclusions, thereby improving the cleanliness of the molten steel. Controlling the alkalinity of the refining furnace white slag to 5.31≤R≤7.42 is beneficial to improving the desulfurization rate and is beneficial to Improve the cleanliness of molten steel and reduce oxide inclusions in molten steel; control the MI slag index (=CaO/SiO ₂ : Al ₂ O ₃ ratio) MI > 0.151, and the sulfur distribution coefficient will increase greatly, thereby controlling the refining slag to a certain alkali Appropriate fluidity under the temperature; the white slag retention time is 14.18min, the refining cycle is 39.47min, and the soft blowing time is guaranteed to be 4.68min, thereby controlling the outbound [O] content.

RH vacuum treatment:

The vacuum chamber pressure is pumped below 66.57kPa for 13.4 minutes, and the bottom blowing argon gas flow is 14.79m ³ /h to achieve 5 cycles of molten steel. It is strictly required to control the type and weight of the alloy added, and use higher-grade low-carbon ferromanganese, Metal manganese, low-carbon ferrosilicon, ferro-titanium and other alloys ensure that the composition of the molten steel is fully qualified, and ensure that the vacuum is maintained for more than 5.27 minutes after the alloy is added to obtain purer molten steel; at the same time, the appropriate molten steel temperature is provided for continuous casting to ensure that the tundish is passed through The heat is 19.78°C above the liquidus line.

The refined molten steel is then continuously cast according to conventional processes: the temperature of the continuous casting tundish is 1541°C, and the casting speed is 1.17 m/s.

The rolling process is: heating and soaking the cast slab at 1180°C, and the residence time in the furnace is 3.6 hours; continuously rolling into product steel plates, and controlling the final rolling temperature to 785°C, and watering and cooling to 485°C after rolling ; Cool to room temperature naturally and set aside.

The structure type of the steel plate obtained according to the above method is acicular ferrite + polygonal grain boundary ferrite, and the acicular ferrite is 85%; the density of corrosion-active inclusions in the steel plate is 16/mm ² ; the steel plate is The saturation current density at electrostatic potential (E=-300mV) is 7.4mA. The yield strength of the steel plate is 370MPa, the tensile strength is 520MPa, and the elongation is 31%.

The following is an analysis and test of the corrosion resistance of the medium-chromium high-strength steel prepared in Example 1 with excellent resistance to oil corrosion and hydrogen-induced cracking. The results are as follows:

1. Test method

The method for measuring the density of corrosion-active inclusions is as follows: corrode the polished sample with a corrosive solution. The proportion of the corrosive solution is 100ml ethanol solution containing: 5.0ml concentrated hydrochloric acid, 0.012gCuCl ₂ , 0.06gSnCl ₂ , 3.0gFeCl ₃ , and the treatment time is 7s, blow dry, and then use an optical microscope to count the number of pitting pits at 100x.

The electrochemical corrosion experimental environment is room temperature, and the corrosion liquid is 3.5% NaCl solution to simulate the corrosion environment. The electrode adopts a classic three-electrode system. The sample is the working electrode, the platinum electrode is the auxiliary electrode, and the saturated calomel electrode is the reference electrode (SCE). The electrochemical equipment is a ZAHNER electrochemical workstation. Parameters are set using Thales electrochemical software, and the workstation is connected to a computer for data display.

The electrochemical corrosion experiment was conducted at room temperature, and the potentiodynamic polarization curve (Tafel) and electrochemical impedance (EIS) of the small sample were tested. Before the test, the sample was soaked in the corrosive solution for 40 minutes. After the open circuit potential (OCP) stabilized, the electrochemical impedance and potentiodynamic polarization tests were performed. The transition signal of the sine wave applied by the electrochemical impedance is 10mV, and the test scanning range is 10mHz~10kHz. The scanning rate of the potentiodynamic polarization curve is 0.5mV/s, and the scanning range is -600mV～1.2V. The potentiodynamic polarization curve and electrochemical impedance curve were fitted using origin and Zsimpwin software respectively.

The AC impedance method perturbs the electrode system with small-amplitude sine waves of different frequencies. The equivalent circuit of the electrode is inferred through the relationship between the electrode system response and the disturbance signal. The parameters of each component in the equivalent circuit are fitted to obtain the material. The corrosion kinetic parameters can intuitively and quantitatively analyze the factors affecting the corrosion resistance of the material, and further understand the corrosion behavior of the material.

Corrosion electrochemical experiments were all conducted in a classic three-electrode system. The electrochemical sample to be tested was used as the working electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the platinum sheet was used as the counter electrode. The test temperature was normal temperature 25°C. When the base metal is welded at room temperature, the sample is first immersed in the corrosive liquid to test the open circuit potential (OCP) for 40 minutes. After the open circuit potential stabilizes, the electrochemical impedance test is started. The amplitude of the sine wave applied by the electrochemical AC impedance is 10mV, the scanning frequency range is 10mHz~10kHz, and the scanning time is 40 minutes.

2. Test results and analysis

Figure 1 is an optical micrograph of corrosion-active inclusions in the invention steel. It can be seen from the photo that there are very few corrosion-active inclusions in the invention steel. After measurement, the density of corrosion-active inclusions in the invented steel was 1.2/mm ² .

As shown in Figure 2, there is no obvious passivation area in the anode area of the polarization curve, indicating that the sample shows that no obvious passivation film is formed, and the electrode activity is only controlled by activation.

Table 1 Sample potentiodynamic polarization curve fitting results

Figure 3 shows the sample AC impedance test results. From the Nyquist diagram in Figure 3, it can be seen that the impedance arc in high and medium frequencies is composed of a single capacitive reactance arc, which reflects the capacitive characteristics. There is no obvious inductive reactance arc in the low frequency band. As can be seen from the bode diagram and phase angle diagram in Figure 3, there is only one peak. Combined with the Nyquist diagram, it can be seen that there is only one time constant, indicating that there is only one relaxation process that affects the state variable in the electrode system. Therefore, the simple equivalent circuit diagram in Figure 4 can be used to simulate the corrosion process at different temperatures. In the circuit diagram, Rs represents the resistance of the corrosion solution, and Q represents the constant phase angle element related to the electric double layer capacitance. Considering the "diffusion effect" caused by the microscopic unevenness of the working electrode surface, the error of using the constant phase angle element instead of the pure capacitance is smaller. Rct represents charge transfer resistance. Use Zsimpwin software to fit the AC impedance universal equivalent circuit diagram in Figure 4. The fitting results are shown in Table 2. The constant phase angle index n in the table reflects the degree of deviation between the actual capacitance and the ideal capacitance. The larger the value of n, the greater the difference between the ideal capacitance and the actual capacitance. The smaller the deviation of the capacitance, the n value of the electric double layer capacitance of the corrosion electrode is generally between 0.5-1. It can be seen from Table 2 that ions are difficult to erode the surface of the substrate. The absence of inductive arc generation in the low-frequency stage in the Nyquist diagram confirms this, indicating that no pitting corrosion was induced in the sample. The AC impedance spectrum fitting results are consistent with the trend and fitting results of the potentiodynamic polarization curve mentioned above.

Table 2 Sample electrochemical AC impedance fitting results

According to the above test results, it can be seen that: the results of the potentiodynamic polarization curve of the sample show that under the experimental corrosion conditions, the sample shows that no obvious passivation film is formed, and the electrode activity is only controlled by activation; the electrochemical impedance fitting results show that under the experimental corrosion conditions, The specimen did not induce pitting corrosion, which is consistent with the results of the potentiodynamic polarization curve. The test results show that the sample has excellent pitting corrosion resistance.

To sum up, the steel plate of the present invention is designed with low-carbon, low-silicon, and medium-chromium cheap chemical components, and does not contain precious corrosion-resistant metal elements such as Ni at all, greatly reducing material costs; the present invention does not use traditional Al deoxidation technology. Instead, Si deoxidation and composite deoxidation supplemented by Ti-RE form fine, dispersed and uniform composite oxysulfides, which greatly reduce the density of corrosion-active inclusions and significantly improve the resistance to crude oil corrosion. This kind of high-strength steel is especially suitable for use in hydrogen-rich and polychloride ion environments such as crude oil tankers, low-quality crude oil refining pipelines, tobacco processing containers and pipelines, hydrogen transportation pipelines and containers, etc. It is resistant to hydrogen embrittlement, acidity, and Chloride ions have superior properties.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (9)

1. A medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking, characterized in that its chemical composition in mass percentage is: 0.011<C<0.069%, 0.11<Si<0.29%, 0.011<Mo +Cu<0.49%, 1.51<Cr<1.99%, 0.041<Ti<0.059%, 0.005<RE<0.019%, S≤0.0010%, the rest is Fe and inevitable impurities. At the same time, the above chemical composition also satisfies the formula: In terms of mass percentage, Cu/Mo=1-2. 2. The medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking according to claim 1, characterized in that: RE is lanthanum, cerium or a mixture of lanthanum and cerium. 3. The medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking according to claim 1, characterized in that: the structure type of the medium-chromium high-strength steel is acicular ferrite and polygonal grain boundary ferrite. Composite structure type, in which the area proportion of acicular ferrite is ≥85%. 4. The medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking according to claim 1, characterized in that: the density of corrosion-active inclusions in the medium-chromium high-strength steel is ≤ 2/mm ² . 5. The medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking according to claim 1, characterized in that: the saturation current density of the medium-chromium high-strength steel at the electrostatic potential E=-300mV is ≤5.0mA. 6. A method for preparing medium-chromium high-strength steel with excellent resistance to oil corrosion and hydrogen-induced cracking according to any one of claims 1 to 5, characterized in that it includes the following steps: 1) The molten steel is smelted, refined and vacuum treated in sequence, and then continuously cast into billets; 2) Perform conventional heating and soaking of the cast slab; 3) Continuously roll the cast billet into product steel plates, and control the final rolling temperature to 750-850°C. After rolling, water and cool to 410-550°C; 4) Cool the steel plate to room temperature naturally to obtain. 7. The preparation method according to claim 6, characterized in that the smelting of step 1) specifically includes the following steps: using a converter or an electric arc furnace to make molten iron, scrap steel, or molten iron and scrap steel together and then adjusting the temperature and composition of the molten steel. , adjust the tapping temperature to 1585-1675℃, and the free oxygen content in the molten steel is 150-390ppm; after the molten steel enters the ladle, use micro-bubbles to stir for 4-8 minutes, and then use Fe-Si alloy or Fe-Si in the ladle -Mn alloy is pre-deoxidized, the free oxygen content in the molten steel is adjusted to 50-90ppm, stirred with micro-bubbles for 4-6 minutes, and then the Ti-RE composite alloy is used for final deoxidation to obtain molten steel that meets the chemical composition; Ti -RE composite alloy is added to molten steel in the form of block alloy or cored wire. The particle size of Ti-RE composite alloy is 8-16mm; the adding amount of Ti-RE composite alloy is 1.2-4.8kg per ton of molten steel. 8. The preparation method according to claim 6 or 7, characterized in that: the refining method is VD refining or RH refining after LF refining, and the refined molten steel is continuously cast according to conventional processes. 9. An application of medium-chromium high-strength steel with excellent anti-oil corrosion and hydrogen-induced cracking properties according to any one of claims 1 to 5, characterized in that: as a material for crude oil tank cargo tanks and inferior crude oil refining pipelines Materials, tobacco processing container materials, tobacco processing pipeline materials, hydrogen transport pipeline materials or hydrogen transport container materials.