Q345R steel plate with excellent hydrogen-induced cracking resistance and manufacturing method thereof

Abstract

This invention discloses a Q345R steel plate with excellent resistance to hydrogen-induced cracking and its manufacturing method, belonging to the field of steel material preparation technology. The chemical composition and mass percentage of the Q345R steel plate of this invention are as follows: C: 0.08~0.20; Si: 0.10~0.35; Mn: 0.80~1.20; P: ≤0.008; S≤0.002; Cu: 0.15~0.30; Cr: 0.10~0.20; Nb+V≤0.020; T i: 0.005~0.015; Alt: 0.01~0.03; O≤0.001; N≤0.004, Ca: 0.0015-0.0050, balance is Fe and unavoidable impurities, Ceq≤0.43. This solves the problem of the difficulty in matching and harmonizing the strength, plasticity, low-temperature impact performance and hydrogen-induced cracking resistance of Q345R steel plate. The produced steel plate has a yield strength ≥345MPa in the delivery state and after 620℃*12h simulated welding heat treatment state, tensile strength 500~630MPa, elongation at section ≥21, Z-direction reduction of area ≥35, Charpy impact energy at 1 / 2 thickness position at -30℃ ≥120J, and hydrogen-induced cracking resistance CLR≤5, CTR≤1.5, CSR≤0.5.

Description

Technical Field

[0001] This invention belongs to the field of steel material preparation technology, specifically relating to a Q345R steel plate with excellent resistance to hydrogen-induced cracking and its manufacturing method. Background Technology

[0002] Q345R steel plates are widely used in pressure vessels and storage equipment in industries such as petroleum, chemical, and nuclear power. These fields typically involve hydrogen-containing environments, such as hydrogenation units in oil refineries and liquefied gas storage tanks in petroleum gas processing plants. In these environments, hydrogen comes into contact with the steel. Hydrogen atoms, with their extremely small atomic radii, can easily diffuse into the steel matrix through grain boundaries and defects. Hydrogen reduces the atomic bonding force between grains, decreasing the steel's toughness and even inducing brittle fracture under stress. This hydrogen-induced cracking is both delayed and sudden, potentially occurring unexpectedly during equipment operation, seriously threatening equipment and the safety of personnel and property. To meet the requirements of complex operating environments, there is an urgent need to develop high-strength marine engineering steels with excellent resistance to hydrogen-induced cracking.

[0003] Patent CN111492083B, entitled "High-strength steel with excellent resistance to hydrogen-induced cracking and low-temperature impact toughness and its manufacturing method," provides a high-strength steel with excellent resistance to hydrogen-induced cracking and low-temperature impact toughness and its manufacturing method, employing a TMCP + normalizing production process. However, its yield strength cannot be guaranteed to reach 355 MPa, failing to meet the high-strength requirements. Patent CN106521332A, entitled "A steel plate resistant to stress-directed hydrogen-induced cracking and its manufacturing method," proposes a steel plate resistant to stress-directed hydrogen-induced cracking, characterized by high purity, excellent low-temperature impact toughness at -20℃, excellent resistance to lamellar tearing, and excellent resistance to stress-directed hydrogen-induced cracking. However, it cannot guarantee impact toughness at even lower temperatures. Summary of the Invention

[0004] To address the aforementioned deficiencies, the present invention aims to provide a Q345R steel plate with excellent resistance to hydrogen-induced cracking. By optimizing the alloy content design and adopting a smelting-controlled rolling and cooling-normalizing heat treatment process, a Q345R steel plate with excellent resistance to hydrogen-induced cracking and a thickness of up to 90 mm was finally obtained.

[0005] Another object of the present invention is to provide a method for manufacturing Q345R steel plate with excellent resistance to hydrogen-induced cracking.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a Q345R steel plate with excellent resistance to hydrogen-induced cracking, comprising the following percentage components: C: 0.08~0.20; Si: 0.10~0.35; Mn: 0.8~1.20; P: ≤0.008; S≤0.002; Cu: 0.15~0.30; Cr: 0.10~0.20; Nb+V≤0.02; Ti: 0.005~0.015; Alt: 0.01~0.03; O≤0.001; N≤0.004; Ca: 0.0015-0.0050, with the balance being Fe and unavoidable impurities, Ceq≤0.43, wherein, Ceq=C+Mn / 6+(Cu+Ni) / 15+(Cr+Mo+V) / 5.

[0007] The mechanism of action of the above alloy components in this invention is as follows: C is an essential element to ensure strength and hardenability. It has a significant effect on improving the strength of steel through solid solution strengthening and precipitation strengthening. However, the increase in carbon content seriously affects the weldability and low-temperature toughness of steel. From the perspective of product performance, it is preferable to control the C content at 0.08 to 0.20.

[0008] Si is a solid solution strengthening element and also the main deoxidizing component in the steelmaking process. In order to obtain a sufficient deoxidation effect, it must contain more than 0.10. However, if the content is too high, it will seriously damage the low-temperature toughness, elongation and weldability of ultra-high strength steel plates. Considering the economy and operability of steelmaking, the preferred Si content is 0.10 to 0.35.

[0009] In addition to improving the strength of steel plates, Mn, as the most important alloying element, also plays a role in expanding the austenite phase region, lowering the Ar3 point temperature, and refining ferrite grains to improve the low-temperature toughness of steel plates. However, when the Mn content is too high, Mn segregation and strip-shaped MnS are easily formed, resulting in poor low-temperature toughness and resistance to hydrogen-induced cracking in the core of thick plates, and a decrease in the performance of the weld heat-affected zone. Therefore, the preferred Mn content range is 0.80 to 1.20%.

[0010] P is an element that has an adverse effect on impact value. It can segregate in the center of the slab and accumulate at grain boundaries, which can impair low-temperature toughness. The material of this invention is controlled to be no higher than 0.008.

[0011] S is an element that has an adverse effect on impact value and can form sulfide inclusions, which can become crack sources. The material of this invention is controlled to be no higher than 0.002.

[0012] Cu: ε-Cu precipitation strengthening can significantly improve the strength of steel. Appropriate amounts of Cu can increase strength without compromising impact toughness. Cu precipitates can increase the density of effective hydrogen traps, resulting in smaller hydrogen-induced cracks. However, excessive Cu content can cause hot brittleness, which is detrimental to the toughness of the base material and the heat-affected zone. Therefore, the Cu content in this invention ranges from 0.15 to 0.30%.

[0013] Cr can improve the hardenability and strength of steel plates. Cr can also inhibit the transformation of proeutectoid ferrite and pearlite, which is beneficial for obtaining acicular ferrite structure. Cr has a similar solid solution strengthening effect to Mn and is less prone to segregation. However, excessive Cr content increases the tendency for temper brittleness and increases welding difficulty, while excessively low content cannot effectively exert its strengthening effect. In this invention, the Cr content is controlled at 0.10-0.20%.

[0014] The addition of Nb and V promotes grain refinement of the steel's rolled microstructure, simultaneously improving strength and toughness. Niobium effectively refines the microstructure during controlled rolling by inhibiting austenite recrystallization and strengthens the matrix through precipitation. Simultaneously, the presence of Nb precipitates increases the density of effective hydrogen traps, resulting in smaller hydrogen-induced cracks. Adding V to steel refines the grain structure, improves strength and toughness, and enhances the steel's resistance to tempering softening during tempering. Insufficient addition yields little effect; excessive V content reduces the steel's toughness and weldability. With an appropriate N content, V can fully precipitate, significantly reducing particle size and spacing, resulting in precipitation strengthening and increased strength. Therefore, this invention controls the Nb+V content to below 0.03%.

[0015] Ti, when present in trace amounts, forms nitrides, carbides, or carbonitrides, which can refine grains and improve the toughness of the base material. However, when the Ti content is too high, excess Ti easily precipitates as TiC at the grain boundaries, severely degrading the low-temperature toughness of the steel plate. Therefore, in this invention, the Ti content is controlled between 0.005 and 0.015%.

[0016] Alt (Al): A deoxidizing and grain-refining element. At high temperatures, Al forms fine AlN precipitates, which inhibit austenite grain growth during the austenitization process of slabs / steel plates, thus refining the austenite grains and improving the toughness of the steel at low temperatures. Excessive Al content leads to the formation of larger Al oxides, reducing the low-temperature impact resistance of the steel plate. Additionally, it makes the slab prone to edge and corner cracks during continuous casting. The preferred Alt content is controlled between 0.01 and 0.03%.

[0017] O is an element that has an adverse effect on impact toughness. It combines with other elements in steel to form non-metallic inclusions, which become crack initiation sites. In this invention, the O content is controlled to be no higher than 0.001.

[0018] Nitrogen (N) will react with Al to form coarse AlN crystals that precipitate along the original austenite grain boundaries, affecting the hardenability and low-temperature impact toughness of the steel. In this invention, the N content is controlled to be no higher than 0.003%. Ca reacts with oxides in molten steel, transforming brittle inclusions into liquid or near-spherical inclusions. These inclusions are more likely to float in molten steel. Furthermore, calcium has a strong affinity for sulfur, which can generate stable CaS inclusions and reduce slender MnS inclusions, thereby improving the steel plate's resistance to hydrogen-induced cracking. Therefore, the Ca content is controlled at 0.0015-0.0040%.

[0019] Furthermore, the Q345R steel plate, in both the delivery state and the state after simulated welding heat treatment at 620℃*12h, has a yield strength ≥345MPa, a tensile strength of 500~630MPa, an elongation at break ≥21%, a reduction of area in the Z direction ≥35%, a Charpy impact energy ≥120J at 1 / 2 position of steel plate thickness at -30℃, and resistance to hydrogen-induced cracking properties CLR≤5, CTR≤1.5, and CSR≤0.5.

[0020] The manufacturing method of the Q345R steel plate with excellent resistance to hydrogen-induced cracking includes the following steps: smelting → continuous casting → slow cooling of the billet → rolling → plate stacking cooling → heat treatment, specifically: 1) Deep desulfurization of molten iron before smelting, and the addition of calcium wire in batches during refining to improve the morphology of inclusions and increase the purity of molten steel. The superheat of molten steel in the tundish is 5-15℃, and the casting is carried out under full protection. The thickness of the continuous casting billet is 210-300mm. After the continuous casting billet is removed from the line, it is stacked and slowly cooled for 24 hours. 2) The continuously cast billet adopts a 4-stage heating process: preheating stage, heating stage 1, heating stage 2, and soaking stage. The heating temperature of the preheating stage is 800-850℃, the heating temperature of heating stage 1 is 950-1080℃, the heating temperature of heating stage 2 is 1130-1180℃, and the heating temperature of the soaking stage is 1050-1110℃. The heating time of the preheating stage is 0.1-0.2 min / mm, the heating time of heating stage 1 is 0.2-0.4 min / mm, the heating time of heating stage 2 is 0.1-0.3 min / mm, and the heating time of the soaking stage is 0.3-0.5 min / mm. The process employs a two-stage rolling process. The first stage begins at a rolling temperature of 950-1000℃ with a single-pass reduction of not less than 15%. The intermediate billet thickness is ≥2 times the finished product thickness. The intermediate billet is water-cooled with a cooling rate ≥2℃ / s. The second stage begins at a rolling temperature of 780-820℃ with a single-pass reduction of not less than 12. The final rolling temperature is 740-790℃. The steel plate after final rolling directly enters the rapid cooling process with a reddening temperature of 560-620℃. 3) The heat treatment adopts the normalizing and rapid cooling process, with a heating temperature of 920℃ and a holding time of T=2.0min / mm.

[0021] The beneficial effects of this invention are as follows: Through alloy composition design, smelting, continuous casting-controlled cooling-normalizing rapid cooling process design, the problem of difficulty in matching and harmonizing the strength, plasticity, low-temperature impact performance and hydrogen-induced cracking resistance of Q345R steel plates is solved. The produced steel plates have a yield strength ≥345MPa, tensile strength 490~630MPa, elongation at break ≥21, Z-direction reduction of area ≥35, Charpy impact energy at 1 / 2 thickness position at -30℃ ≥120J, and hydrogen-induced cracking resistance CSR≤0.5, CLR≤5, CTR≤1.5.

[0022] This invention fully leverages the technical advantages of thick plate rolling mills and heat treatment equipment, and combines 210-300mm thick continuous casting slabs to develop steel plates with excellent performance and resistance to hydrogen-induced cracking with a maximum thickness of 90mm; (3) The microstructure of the steel plate is a mixed structure of ferrite + pearlite + a small amount of bainite. Detailed Implementation

[0023] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0024] This embodiment provides a method for preparing Q345R steel plate with excellent resistance to hydrogen-induced cracking. The chemical composition and weight percentage of the steel plate in this embodiment are shown in Table 1: Table 1 Chemical composition and weight percentage (wt) of Q345R steel plate in this embodiment.

[0025] Table 1 shows the chemical composition and weight percentage (wt%) of the Q345R steel plate in the examples.

[0026] The method for preparing the Q345R steel plate with excellent resistance to hydrogen-induced cracking in the examples includes the following steps: 1) Smelting, continuous casting, and slow cooling of billets: Production is carried out using deep desulfurization of molten iron, converter smelting, ladle refining, vacuum treatment, and continuous casting processes. The entire casting process is protected, with electromagnetic stirring activated. After continuous casting, continuously cast billets are obtained, with a thickness of 210–300 mm. The billets are then stacked for slow cooling after being removed from the production line. 2) Rolling process: The continuously cast billet is heated in 4 stages, namely the preheating stage, heating stage 1, heating stage 2, and soaking stage. The heating temperatures and times for the preheating stage, heating stage 1, heating stage 2, and soaking stage are shown in the table below. Two-stage rolling is adopted. The initial rolling temperature of the first stage is 950-1000℃, and the single-pass reduction rate is not less than 15%. The thickness of the intermediate billet is ≥2 times the thickness of the finished product. The intermediate billet is water-cooled with a cooling rate ≥2℃ / s. The initial rolling temperature of the second stage is 780-820℃, and the single-pass reduction rate is not less than 12%. The final rolling temperature is 740-790℃. The steel plate after final rolling directly enters the rapid cooling process, and the reheating temperature is 560-620℃.

[0027]

[0028] Note: The solution used is A, which is 5NaCl + 0.5CH3COOH + saturated H2S aqueous solution, and is continuously soaked for 96 hours according to GB / T8650 standard.

Claims

1. A Q345R steel plate with excellent resistance to hydrogen-induced cracking, characterized in that... The composition contains the following percentages: C: 0.08–0.20; Si: 0.10–0.35; Mn: 0.8–1.20; P: ≤0.008; S≤0.002; Cu: 0.15–0.30; Cr: 0.10–0.20; Nb+V≤0.02; Ti: 0.005~0.015; Alt: 0.01~0.03; O≤0.001; N≤0.004, Ca: 0.0015-0.0050, balance is Fe and unavoidable impurities, Ceq≤0.43, where Ceq=C+Mn / 6+(Cu+ Ni) / 15+(Cr+Mo+V) / 5.

2. The Q345R steel plate with excellent resistance to hydrogen-induced cracking according to claim 1, characterized in that, The Q345R steel plate, in its delivery state and after simulated welding heat treatment at 620℃*12h, has a yield strength ≥345MPa, tensile strength 500~630MPa, elongation at break ≥21%, Z-direction reduction of area ≥35%, Charpy impact energy at 1 / 2 thickness position at -30℃ ≥120J, and resistance to hydrogen-induced cracking CLR≤5, CTR≤1.5, and CSR≤0.

5.

3. The method for manufacturing the Q345R steel plate with excellent resistance to hydrogen-induced cracking as described in claim 1 or 2, characterized in that... The process includes the following steps: smelting → continuous casting → slow cooling of the billet → rolling → plate cooling → heat treatment, specifically: 1) Deep desulfurization of molten iron before smelting, and the addition of calcium wire in batches during refining to improve the morphology of inclusions and increase the purity of molten steel. The superheat of molten steel in the tundish is 5-15℃, and the casting is carried out under full protection. The thickness of the continuous casting billet is 210-300mm. After the continuous casting billet is removed from the line, it is stacked and slowly cooled for 24 hours. 2) The continuously cast billet adopts a 4-stage heating process: preheating stage, heating stage 1, heating stage 2, and soaking stage. The heating temperature of the preheating stage is 800-850℃, the heating temperature of heating stage 1 is 950-1080℃, the heating temperature of heating stage 2 is 1130-1180℃, and the heating temperature of the soaking stage is 1050-1110℃. The heating time of the preheating stage is 0.1-0.2 min / mm, the heating time of heating stage 1 is 0.2-0.4 min / mm, the heating time of heating stage 2 is 0.1-0.3 min / mm, and the heating time of the soaking stage is 0.3-0.5 min / mm. The process employs a two-stage rolling process. The first stage begins at a rolling temperature of 950-1000℃ with a single-pass reduction of not less than 15%. The intermediate billet thickness is ≥2 times the finished product thickness. The intermediate billet is water-cooled with a cooling rate ≥2℃ / s. The second stage begins at a rolling temperature of 780-820℃ with a single-pass reduction of not less than 12. The final rolling temperature is 740-790℃. The steel plate after final rolling directly enters the rapid cooling process with a reddening temperature of 560-620℃. 3) The heat treatment adopts the normalizing and rapid cooling process, with a heating temperature of 920℃ and a holding time of T=2.0min / mm.

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