CN115369323B - A kind of 800MPa grade hydrogen-induced cracking resistant container steel plate and its production method - Google Patents

Abstract

The invention relates to a 800 MPa-level hydrogen-induced crack resistant container steel plate and a production method thereof, wherein the steel plate comprises the chemical components of 0.2-0.25% of C, 0.15-0.35% of Si, 0.8-0.85% of Mn, less than or equal to 0.003% of P, less than or equal to 0.001% of S and less than or equal to Mo:0.03 to 0.05 percent, 0.2 to 0.3 percent of V, 0.0003 to 0.002 percent of Ca, 0.002 to 0.03 percent of Als and the balance of Fe and impurities. The steel plate tissue segregation is reduced by controlling the C, mn content in the steel, and the shape of inclusions in the steel is changed by adding Ca; the alloy element V, mo is added to refine grains, so that the steel plate has good toughness, and the steel plate is ensured to have good comprehensive performance after normalizing and simulated post-welding heat treatment through precipitation strengthening; the heat treatment mode of staged rolling and normalizing weak cooling/short-time normalizing is adopted, so that the finished steel plate is ensured to have uniform grain size and high strength in the whole thickness direction, and simultaneously has excellent hydrogen induced crack resistance.

Description

A kind of 800MPa level hydrogen-induced cracking resistant container steel plate and its production method

technical field

The invention relates to the technical field of steel plates for pressure vessels, in particular to a vessel steel plate with excellent resistance to hydrogen-induced cracking at 800 MPa level and a production method thereof.

Background technique

Hydrogen sulfide is one of the most corrosive and harmful media in oil and natural gas. In the process of natural gas transportation, hydrogen sulfide accounts for a large proportion of stress corrosion of pipelines. When used in a wet hydrogen sulfide environment, it can cause hydrogen bubbling (HB), hydrogen-induced cracking (HIC) and stress-oriented hydrogen-induced cracking (SOHIC) in carbon steel. In an acidic environment such as hydrogen sulfide, the cracks caused by the intrusion of hydrogen generated by corrosion into the steel are called hydrogen-induced cracking (HIC). In previous studies, it was found that the hydrogen-induced resistance of steel is closely related to the strength of steel. The higher the strength of the steel plate, the worse the hydrogen-induced resistance of the steel. At present, HIC-resistant steel plates are mainly used for pipeline steel and container steel. For container steel, not only the normalizing performance, but also the subsequent welding and repair need to be considered. Therefore, it is required that the performance of the steel plate after simulated post-weld heat treatment still meet the requirements.

With the increasing economic development and energy demand, oil and gas reserves as strategic materials have become one of the indicators to measure the sustainable economic development of various countries. my country is also building large-scale oil and liquefied natural gas storage tanks one after another. Therefore, it is urgent to develop a kind of steel with excellent comprehensive performance, whose strength and toughness are superior to conventional steel, and its welding performance and hydrogen sulfide stress corrosion resistance are similar to or even better than conventional steel, and its cost is lower than that of foreign materials with the same performance. Steel plates for liquefied petroleum balloon tanks.

The Chinese patent application with the application number CN201210055848.5 discloses "a hydrogen-induced cracking-resistant pressure vessel steel and its manufacturing method", which involves a low-carbon, high-strength, low-alloy thick steel plate with a tensile strength ≥ 620 MPa. The composition of the steel plate is as follows: The weight percentage is C: 0.15～0.25%, Si: 0.10～0.30%, Mn: 1.00～1.60%, P: ≤0.012%, S≤0.002%, Mo: 0.35～0.60%, V≤0.05%, Ni: 0.20 ～0.80%, Ca: 0.0013～0.0045% and Al: 0.002～0.050%, which adopts the heat treatment process of quenching and tempering, but this heat treatment process makes the production cost of the steel plate higher.

The Chinese patent application with the application number CN201310497333.5 discloses "a 450MPa class hydrogen-induced cracking resistant steel plate for pressure vessels and its production method, the steel plate includes C: 0.13-0.14%, Si: 0.20-0.30%, Mn: 0.90～0.95%, P≤0.008% and S≤0.001% of the chemical composition, through two-stage controlled rolling with 2.0 times the thickness, and controlled rolling and controlled cooling with accelerated cooling at a cooling rate of 10～12°C/S after rolling process, as well as off-line normalizing heat treatment process, finally make the tensile strength of the steel plate reach 450~464MPa. The strength level of the steel plate produced is relatively low, and there is no requirement for long-term simulation of post-weld heat treatment performance.

The Chinese patent application with the publication number CN105603304A discloses "a thick steel plate for Q370R pressure vessel with good HIC and SSCC properties and its manufacturing method". The composition is designed so that the steel plate has good anti-HIC and anti-SSCC properties. In order to improve the strength of the steel plate, high Mn (1.40-1.62%) composition design is adopted in the example. However, Mn elements are easy to form MnS inclusions with S elements, which become hydrogen traps and increase the risk of hydrogen-induced cracking; at the same time, the water-cooled heat treatment process after normalizing is adopted, and the difference in cooling rate will cause inhomogeneity in the thickness direction. Among the 6 examples, 3 examples have cracks in the hydrogen-induced cracking test results, and the stability of the HIC resistance performance of the steel plate is relatively poor. In the embodiment, the maximum thickness of the steel plate is only 60 mm, which cannot meet the use requirements of large pressure vessels in the petrochemical industry.

In view of the above situation, it is urgent to develop high-strength pressure vessel steel plates with good hydrogen-induced cracking resistance through new composition design and matching technology.

Contents of the invention

The invention provides an 800MPa grade hydrogen-induced crack resistant container steel plate and its production method. By controlling the content of C and Mn in the steel, the structure segregation of the steel plate can be reduced, and the shape of inclusions in the steel can be changed by adding Ca; crystallized grains to ensure good strength and toughness of the steel plate, and through precipitation strengthening to ensure that the steel plate has good comprehensive properties after normalizing and simulated post-weld heat treatment; the production process matched with the composition of the steel plate adopts staged rolling and weak normalizing The heat treatment method of cold/short time normalizing ensures that the finished steel plate has uniform grain size and high strength in the entire thickness direction, and also has excellent resistance to hydrogen-induced cracking.

In order to achieve the above object, the present invention adopts the following technical solutions to realize:

An 800MPa grade hydrogen-induced crack-resistant container steel plate, the chemical composition of the steel plate is C: 0.2%-0.25%, Si: 0.15%-0.35%, Mn: 0.8%-0.85%, P≤0.003%, S≤ 0.001%, Mo: 0.03%-0.05%, V: 0.2%-0.3%, Ca: 0.0003%-0.002%, Als: 0.002%-0.003%, and the rest are Fe and unavoidable impurities.

A kind of production method of 800MPa class hydrogen-induced cracking resistant container steel plate, the production process of steel plate comprises smelting-continuous casting-heating-rolling-heat treatment; Details are as follows:

1) Continuous casting process: the casting temperature of molten steel in the tundish is ≤1560°C, using electromagnetic stirring or continuous casting slab light reduction process, and the reduction rate is controlled at 6% to 9%;

2) Heating process: the heating temperature of the continuous casting slab is 1150-1200°C, and the soaking time is 1-3 hours;

3) Rolling process: a two-stage controlled rolling process is adopted; the final rolling temperature of the first stage is ≥1050°C, and the single-pass reduction rate is 8% to 11%; the second-stage rolling start temperature is ≥970°C, and the single-pass reduction rate is 5% to 8%;

4) Heat treatment process: the thickness of the finished steel plate is 40 ~ 100mm; different heat treatment processes are used for the rolled steel plate according to the thickness; among them, the steel plate with 40mm≤t<60mm adopts normalizing weak cold and heat treatment process, and the steel plate with 60mm≤t≤100mm adopts Short-time normalizing heat treatment process, t is the thickness of the steel plate.

Further, the smelting process adopts a smelting process of electric furnace smelting + VOD vacuum treatment.

Further, in the heat treatment process, the normalizing weak cold and heat treatment process is as follows: the heat treatment temperature is controlled at 880-890°C, the heating rate is 1.1-1.3.min/mm, and the net holding time is 0.5-0.6min/mm, to After warming, it is weakly cooled after being released from the furnace, and the cooling rate is 1.6-2.0°C/s; the temperature of turning red is 330-340°C.

Further, in the heat treatment process, the short-time normalizing heat treatment process is as follows: the heat treatment temperature is controlled at 860-880°C, the heating rate is 1.2-1.4min/mm, and the furnace is air-cooled after reaching the temperature, and the total time in the furnace is ≤2h.

Further, the microstructure of the finished steel plate is ferrite + pearlite + a small amount of bainite uniformly and dispersedly distributed.

Further, the properties of the finished steel plate are as follows: yield strength 444-453MPa, tensile strength 806-828MPa, elongation after fracture ≥ 24%; -20°C Charpy impact energy AV ₂ average of 3 samples ≥ 242J, b= 2a, 180° cold bending test d=3a is qualified; the hydrogen-induced cracking test is carried out according to GB/T 8650-2006, and the evaluation is qualified according to NACE TM0284 "Evaluation Method for Pipeline Steel and Pressure Vessel Steel Resistance to Hydrogen-induced Cracking".

Compared with prior art, the beneficial effect of the present invention is:

1) In terms of steel composition design: the composition design is simple and reasonable. In order to ensure the hydrogen-induced crack resistance of the steel plate, the segregation degree of the steel plate is guaranteed to be light by reasonably controlling the C and Mn content in the steel, and the shape of the inclusions in the steel is changed by adding Ca; In order to ensure that the steel plate has good strength and toughness, alloying elements V and Mo are added to the steel to refine the grains, and through precipitation strengthening to ensure that the steel plate has good comprehensive properties after normalizing and simulated post-weld heat treatment;

2) In terms of production technology: multi-pass rolling with small deformation is used, which is beneficial to refine the grain structure; the heat treatment method of staged rolling and normalizing weak cold/short-time normalizing is adopted to ensure that the finished steel plate is in the entire thickness direction It has uniform grain size and high strength, and also has excellent resistance to hydrogen-induced cracking.

Description of drawings

Fig. 1 is a photo of the metallographic structure of an 800MPa grade hydrogen-induced cracking resistant container steel plate according to the present invention.

Detailed ways

An 800MPa-grade hydrogen-induced crack-resistant container steel plate according to the present invention, the chemical composition of the steel plate is C: 0.2% to 0.25%, Si: 0.15% to 0.35%, Mn: 0.8% to 0.85%, and P≤0.003 %, S≤0.001%, Mo: 0.03%-0.05%, V: 0.2%-0.3%, Ca: 0.0003%-0.002%, Als: 0.002%-0.003%, and the rest are Fe and unavoidable impurities.

A kind of production method of 800MPa level hydrogen-induced cracking resistance container steel plate of the present invention, the production process of steel plate comprises smelting-continuous casting-heating-rolling-heat treatment; Specifically as follows:

1) Continuous casting process: the casting temperature of molten steel in the tundish is ≤1560°C, using electromagnetic stirring or continuous casting slab light reduction process, and the reduction rate is controlled at 6% to 9%;

2) Heating process: the heating temperature of the continuous casting slab is 1150-1200°C, and the soaking time is 1-3 hours;

3) Rolling process: a two-stage controlled rolling process is adopted; the final rolling temperature of the first stage is ≥1050°C, and the single-pass reduction rate is 8% to 11%; the second-stage rolling start temperature is ≥970°C, and the single-pass reduction rate is 5% to 8%;

4) Heat treatment process: the thickness of the finished steel plate is 40 ~ 100mm; different heat treatment processes are used for the rolled steel plate according to the thickness; among them, the steel plate with 40mm≤t<60mm adopts normalizing weak cold and heat treatment process, and the steel plate with 60mm≤t≤100mm adopts Short-time normalizing heat treatment process, t is the thickness of the steel plate.

Further, the smelting process adopts a smelting process of electric furnace smelting + VOD vacuum treatment.

Further, in the heat treatment process, the normalizing weak cold and heat treatment process is as follows: the heat treatment temperature is controlled at 880-890°C, the heating rate is 1.1-1.3.min/mm, and the net holding time is 0.5-0.6min/mm, to After warming, it is weakly cooled after being released from the furnace, and the cooling rate is 1.6-2.0°C/s; the temperature of turning red is 330-340°C.

Further, in the heat treatment process, the short-time normalizing heat treatment process is as follows: the heat treatment temperature is controlled at 860-880°C, the heating rate is 1.2-1.4min/mm, and the furnace is air-cooled after reaching the temperature, and the total time in the furnace is ≤2h.

Further, the microstructure of the finished steel plate is ferrite + pearlite + a small amount of bainite uniformly and dispersedly distributed.

Further, the properties of the finished steel plate are as follows: yield strength 444-453MPa, tensile strength 806-828MPa, elongation after fracture ≥ 24%; -20°C Charpy impact energy AV ₂ average of 3 samples ≥ 242J, b= 2a, 180° cold bending test d=3a is qualified; the hydrogen-induced cracking test is carried out according to GB/T 8650-2006, and the evaluation is qualified according to NACE TM0284 "Evaluation Method for Pipeline Steel and Pressure Vessel Steel Resistance to Hydrogen-induced Cracking".

The chemical composition design and action principle of a 800MPa grade hydrogen-induced cracking resistant container steel plate according to the present invention are as follows:

C often forms carbides with other alloying elements in steel, which strengthens the steel. From the perspective of ensuring the strength of the steel plate, it is hoped that the C content will be kept at a relatively high level, but a high C content will easily cause segregation in the steel, resulting in a significant decrease in the toughness and plasticity of the steel plate. The present invention solves this problem by using VC/N to refine grains. Therefore, under the premise of ensuring the strength of the steel plate, the C content is controlled at 0.2% to 0.25%.

Si has deoxidation and desulfurization effects in steel, and can improve the strength of steel plates through solid solution strengthening. Si is a cheap alloying element. Adding an appropriate amount of Si to steel can increase the hardness and strength of ferrite in steel. Si can increase the elastic limit, yield strength, yield ratio, and fatigue strength and fatigue ratio of steel, and can increase strength and improve local corrosion resistance to a certain extent. However, if the Si content is high, it will have a negative impact on the impact toughness of the heat-affected zone, so the present invention limits the Si content to 0.35%-0.50%.

Mn element is a commonly used desulfurizer in steel, and Mn is easy to form MnS inclusions with S; Mn segregation in steel produces high-strength and low-toughness hard phase martensite and bainite, which will increase the tendency of cracking after welding. The anti-hydrogen cracking performance is adversely affected, so the Mn content is not easy to be too high. Considering comprehensively the strength, toughness and hydrogen-induced cracking resistance of the steel plate, the present invention limits the Mn content to 0.8%-0.85%.

P and S are brittle elements in steel, and are also easily segregated elements, so the lower the content, the better. The two also have great damage to the low-temperature toughness of steel, but considering factors such as the operability of steelmaking, steelmaking cost and meeting the use requirements, the present invention controls the content of P and S below 0.003% and 0.001% respectively. %the following.

Mo: It is a weak solid solution strengthening element. Its main function in steel is to increase the supercooling ability of austenite, thereby refining the structure and obtaining a strengthening effect. It has a good impact on impact toughness and brittle transition temperature. In addition, Mo has a significant positive effect on the high temperature and long-term PWHT performance; but on the other hand, Mo will have an adverse effect on the weldability of the steel plate, and it is a precious metal with high cost. Therefore, the present invention controls the content of Mo at 0.03% to 0.05%.

V: As the main element in the steel of the present invention, it is a strong carbonitride-forming element. First of all, V is an element on the left side far away from iron in the periodic table of elements, and it is easy to form stable carbide (VC). The growth of bulk grains and the formation of ferrite are promoted at the same time. Therefore, the steel plate is not easy to overheat during heat treatment heating, which is beneficial to heat treatment operations. Secondly, V can fix the N element in steel. By reasonably controlling the content of Ti element, the content of V (C, N) in the alloy can be precisely controlled. During the rolling process, the steel plate rolled through the austenite region will produce a certain amount of deformation energy storage, and different degrees of deformation energy storage will have different kinetics of V (C, N) precipitation in austenite. degree of influence. In the experiment, by increasing the deformation energy storage to promote the precipitation of VC particles in the high temperature and low temperature stages of the austenite region, the recrystallization of austenite can be better inhibited and the growth of austenite grains can be prevented. At the same time, it can greatly reduce the critical nucleation size of VC in the austenite region, especially in the high-temperature region, and improve the precipitation strengthening effect of VC, thereby achieving the purpose of improving the strength of the steel plate while ensuring toughness. Stable VC plays the role of fixing C, reducing the reaction of free C and H in the steel, that is, reducing the generation of harmful substances such as methane, reducing the decarburization, bulging and cracking tendency of the steel plate, and making the steel plate excellent resistance to hydrogen-induced cracking be guaranteed. However, studies have shown that excessive V will cause abnormal grain growth, so the present invention controls the V content within the range of 0.2% to 0.3%.

Ca: plays a role in controlling the form of sulfide in steel, and has the effect of suppressing the formation of MnS by forming CaS. In order to obtain this effect, the Ca content needs to be 0.0003% or more. In addition, when the amount of Ca exceeds 0.005%, the size of CaS formed is too large, the brittleness also increases, and it is easy to become the starting point of the fracture crack source. Therefore, the present invention limits the Ca content to 0.0003%-0.002%.

Als: As a deoxidizing element in steel, AlN is formed in steel, which can effectively refine grains, and its content is controlled at 0.002% to 0.003% in the present invention.

The production method of a kind of 800MPa class hydrogen-induced cracking resistant container steel plate of the present invention, comprises the processes such as smelting-continuous casting-heating-rolling-heat treatment, specific design principle is as follows:

1. It is smelted by electric furnace smelting + VOD vacuum treatment process.

2. The continuous casting process is adopted, and the key point of the process is to control the casting temperature, that is, the casting temperature of molten steel in the tundish is ≤1560°C, and low-temperature casting can refine the original cast structure. In order to control segregation and porosity in the center of the continuous casting slab, electromagnetic stirring or continuous casting slab light reduction process is adopted, and the reduction rate is controlled at 6% to 9%.

3. The heating temperature of the continuous casting slab is 1150-1200°C, and the soaking time is 1-3 hours. When the heating temperature is lower than 1150°C, the coarse precipitates in the continuous casting slab cannot be dissolved, the austenitization of the steel plate is not complete, and the final rolling temperature in the first stage cannot be guaranteed; when the heating temperature is higher than 1200°C, it is easy to make the continuous casting The fine precipitates in the billet redissolve and cause excessive grain growth.

3. Continuous casting slab rolling adopts two-stage controlled rolling process. The final rolling temperature of the first stage is ≥1050°C. In this stage, large deformation is used for rapid rolling, and the single-pass reduction rate is 8% to 11%, ensuring complete dynamic recrystallization near the surface of the steel plate; the second-stage rolling temperature is ≥ 970°C. At this stage, small deformation is used for rapid rolling, and the single-pass reduction rate is 5% to 8%, so as to ensure that recrystallization does not occur near the surface of the steel plate.

4. The rolled steel plate adopts two processes of normalizing, weak cooling and short-time normalizing according to the thickness specification of the plate. Among them, the 40-60mm thick steel plate adopts normalizing and weak cooling, and the 60-100mm thick steel plate adopts short-time normalizing heat treatment process. The short-time normalizing heat treatment process is that the heat treatment temperature is 860-880°C, the heating rate is 1.2-1.4min/mm, and it is air-cooled after reaching the temperature, and the total time in the furnace is 1-1.2h. The normalizing weak cold and heat treatment process is that the heat treatment temperature is controlled at 880-890°C, the heating rate is 1.1-1.3.min/mm, and the net holding time is 0.5-0.6min/mm. 340°C.

The following examples are carried out on the premise of the technical solutions of the present invention, and detailed implementation methods and specific operation processes are provided, but the protection scope of the present invention is not limited to the following examples.

【Example】

Table 1 is the chemical composition of the steel plate, Table 2 is the continuous casting and rolling process parameters of the steel plate, Table 3 is the post-rolling heat treatment process parameters of the steel plate, Table 4 is the mechanical properties of the steel plate after simulated post-weld heat treatment, and Table 5 is the grain size and The test results of non-metallic inclusions, Table 6 shows the test results of hydrogen-induced cracking resistance of steel plates.

Table 1 steel plate chemical composition (wt%)

Example C Si mn P S Mo V Ca als 1 0.21 0.16 0.81 0.0028 0.0008 0.035 0.26 0.00036 0.0023 2 0.20 0.34 0.83 0.0015 0.0005 0.041 0.29 0.00042 0.0021 3 0.20 0.29 0.85 0.0019 0.0009 0.038 0.30 0.00036 0.0020 4 0.23 0.22 0.85 0.0010 0.0010 0.045 0.20 0.001 0.0026 5 0.25 0.32 0.82 0.0019 0.0007 0.039 0.28 0.0011 0.0024 6 0.24 0.35 0.83 0.0020 0.0008 0.048 0.25 0.0012 0.0023

Table 2 continuous casting and rolling process parameters of steel plate

Table 3 heat treatment process parameters of steel plate

Table 4 Mechanical properties of simulated post-weld heat treatment of steel plates

In Table 4, ReL is the yield strength, Rm is the tensile strength, and A is the elongation after fracture; in the cold bending test, b is the width of the sample, a is the nominal thickness, and d is the diameter of the bending center.

Table 5 Grain size and non-metallic inclusion test results

Table 6 Test results of hydrogen-induced cracking resistance of steel plates

Fig. 1 is a photograph of the metallographic structure of the finished steel plate produced in Example 1. The structure of the steel plate is ferrite + pearlite + a small amount of uniformly dispersed bainite, and the degree of segregation of the structure in the steel is relatively low.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (3)

1. A production method of an 800MPa grade hydrogen-induced cracking resistant container steel plate, characterized in that the chemical composition of the steel plate is C:0.2%～0.25%, Si:0.15%～0.35%, Mn:0.81%～0.85% by weight %, P≤0.003%, S≤0.001%, Mo: 0.03%～0.05%, V:0.25%～0.3%, Ca: 0.0003%～0.002%, Als: 0.002%～0.003%, the rest is Fe and unavoidable impurities; The production process of steel plate includes smelting-continuous casting-heating-rolling-heat treatment; details are as follows: 1) Continuous casting process: the casting temperature of molten steel in the tundish is ≤1560°C, using electromagnetic stirring or continuous casting slab light reduction process, and the reduction rate is controlled at 6% to 9%; 2) Heating process: the heating temperature of the continuous casting slab is 1150-1200°C, and the soaking time is 1-3 hours; 3) Rolling process: Two-stage controlled rolling process is adopted; the final rolling temperature of the first stage is ≥1050°C, and the single-pass reduction rate is 8% to 11%; the second-stage rolling temperature is ≥970°C, and the single-pass reduction rate is 5%~8%; 4) Heat treatment process: the thickness of the finished steel plate is 40 ~ 100mm; different heat treatment processes are used for the rolled steel plate according to the thickness; among them, the steel plate with 40mm≤t<60mm adopts normalizing weak cold and heat treatment process, and the steel plate with 60mm≤t≤100mm adopts Short-time normalizing heat treatment process, t is the thickness of the steel plate; The normalizing weak cold and heat treatment process is as follows: the heat treatment temperature is controlled at 882-890°C, the heating rate is 1.1-1.3min/mm, and the net holding time is 0.5-0.6min/mm. 1.6～2.0℃/s; the temperature of turning red is 330～340℃; The short-time normalizing heat treatment process is as follows: the heat treatment temperature is controlled at 860-880° C., the heating rate is 1.2-1.4 min/mm, and the furnace is air-cooled after reaching the temperature, and the total time in the furnace is ≤ 2 hours. 2. The production method of a 800MPa grade hydrogen-induced crack-resistant container steel plate according to claim 1, wherein the smelting process adopts a smelting process of electric furnace smelting+VOD vacuum treatment. 3. According to claim 1, a production method of 800MPa-grade hydrogen-induced cracking-resistant container steel plate is characterized in that the performance of the finished steel plate is as follows: yield strength 444-453MPa, tensile strength 806-828MPa, elongation after fracture ≥ 24 %; The average value of the -20°C Charpy impact energy kV ₂ of the 3 samples is ≥242J, b=2a, 180° cold bending test d=3a is qualified; the hydrogen-induced cracking test is carried out according to GB/T 8650-2006, according to NACE TM0284 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel" was qualified.