SA-516Gr70 acid-resistant pressure vessel steel plate subjected to high-temperature PWHT heat treatment and manufacturing method of SA-516Gr70 acid-resistant pressure vessel steel plate

Abstract

The invention discloses a high-temperature PWHT heat treatment acid-resistant pressure vessel steel plate and a manufacturing method, and relates to the technical field of steel production, and the steel plate comprises the following chemical components in percentage by mass: 0.14%-0.18% of C, 0.20%-0.40% of Si, 0.95%-1.20% of Mn, less than or equal to 0.008% of P, less than or equal to 0.0015% of S, 0.20%-0.38% of Ni, 0.025%-0.055% of Alt, less than or equal to 0.020% of Nb, less than or equal to 0.030% of V, less than or equal to 0.020% of Ti, 0.0008%-0.0035% of Ca and the balance of Fe and residual elements. The steel plate structure is tempered sorbite and a small amount of ferrite, the thickness of the steel plate is 12-50 mm, the manufacturing method of the steel plate comprises the procedures of steelmaking, heating, rolling, cooling and heat treatment, and the problems that in the prior art, after high-temperature PWHT, the performance is unstable, the low-temperature toughness of the core of a thick plate is insufficient, and the anti-HIC risk is high are solved; excellent comprehensive mechanical properties, full-thickness uniform toughness and acid corrosion resistance are still realized.

Description

Technical Field

[0001] This invention relates to the field of steel production technology, and in particular to a high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate and its manufacturing method. Background Technology

[0002] SA-516Gr70 is a carbon steel plate for pressure vessels according to ASME standards, mainly used in critical parts of equipment in industries such as petroleum, chemical, machinery, power plants, and pipelines. Ordinary SA-516Gr70 steel plates are susceptible to corrosion failure when exposed to water-containing or H2S-corrosive media, therefore, SA-516Gr70 steel plates are required to have good acid resistance and low-temperature impact resistance. However, with the increasing quality requirements of the market for steel plates in recent years, more and more container manufacturers and customers are placing higher demands on steel plates. For SA-516Gr70 steel, it is required to undergo high-temperature PWHT heat treatment to ensure that the steel plate has lower hardness, especially in the low-temperature impact and HIC resistance at half the plate thickness, to meet more complex and variable working conditions.

[0003] Patent CN 120210664A discloses a normalized high-strength medium-carbon acid-resistant container steel and its preparation method. It mainly involves continuous casting, slab heating, controlled rolling, and normalizing heat treatment to finally obtain a steel plate with a thickness of 15-50mm. However, its Mn content is 1.20-1.35%, Nb content is 0.025-0.035%, and V content is 0.030-0.040%. The smelting method and microstructure of the steel are not disclosed, and PWHT heat treatment and impact performance at 1 / 2 thickness are not mentioned.

[0004] Patent CN 114807751B discloses an A516Gr.70(HIC) acid-resistant pipe fitting steel with excellent mold welding and low-temperature performance, and its manufacturing method. According to the disclosed method, steel plates with a thickness of 6-50mm can be produced. However, the heat treatment method used is TMCP + tempering. At the same time, its C content is 0.08-0.11%, Mn content is 0.9-1.10%, and V content is 0.005-0.009%. The impact performance at 1 / 2 thickness and the PWHT heat treatment temperature are not disclosed.

[0005] Patent CN 105603304B discloses a thick steel plate for Q370R pressure vessels with good resistance to HIC and SSCC, and its manufacturing method. The steel plate thickness is 10-60mm. It is produced using a process of smelting, continuous casting, rolling, normalizing, and water cooling. Its alloy composition, such as Mn, Cu, and Mo, is relatively high, and the PWHT heat treatment temperature is relatively low, with an impact temperature of only -20℃. At the same time, the steel plate is not tempered after water cooling, resulting in high internal stress in the steel plate structure and a risk of HIC cracking.

[0006] Therefore, existing acid-resistant pressure vessel steel plates mostly employ different heat treatment processes such as "normalizing," "TMCP + tempering," or "normalizing + water cooling," with few using a normalizing + accelerated cooling + tempering heat treatment process. Furthermore, there is little attention paid to the -45℃ impact resistance at half the thickness and the high-temperature PWHT heat treatment. Some have addressed PWHT heat treatment, but the steel plates were not tempered after water cooling, and the relatively low PWHT temperature still poses a risk of HIC cracking. Summary of the Invention

[0007] To address the aforementioned technical problems and overcome the shortcomings of existing technologies, this invention provides a high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate and its manufacturing method.

[0008] To solve the above technical problems, the technical solution of the present invention is as follows: A high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate, characterized in that its chemical composition and mass percentage are as follows: C: 0.14%~0.18%, Si: 0.20%~0.40%, Mn: 0.95%~1.20%, P≤0.008%, S≤0.0015%, Ni: 0.20%~0.38%, Alt: 0.025~0.055%, Nb: ≤0.020%, V: ≤0.030%, Ti: ≤0.020%, Ca: 0.0008%~0.0035%, with the remainder being Fe and residual elements.

[0009] The technical solution further defined in this invention is: Preferably, its chemical composition and mass percentage are as follows: C: 0.15-0.17%, Si: 0.25%-0.35%, Mn: 1.05%-1.15%, P≤0.008%, S≤0.0015%, Ni: 0.25%-0.35%, Alt: 0.040-0.055%, Nb: ≤0.015%, V: ≤0.020%, Ti: ≤0.015%, Ca: 0.0008%-0.0025%, with the remainder being Fe and residual elements.

[0010] Preferably, its chemical composition and mass percentage are as follows: C: 0.16-0.18%, Si: 0.20%-0.30%, Mn: 0.95%-1.05%, P≤0.008%, S≤0.0015%, Ni: 0.28%-0.38%, Alt: 0.035-0.050%, Nb: ≤0.020%, V: ≤0.020%, Ti: ≤0.015%, Ca: 0.0015%-0.0030%, with the remainder being Fe and residual elements.

[0011] Preferably, its chemical composition and mass percentage are as follows: C: 0.14-0.16%, Si: 0.30%-0.40%, Mn: 1.10%-1.20%, P≤0.008%, S≤0.0015%, Ni: 0.20%-0.30%, Alt: 0.025-0.040%, Nb: ≤0.020%, V: ≤0.030%, Ti: ≤0.020%, Ca: 0.0020%-0.0035%, with the remainder being Fe and residual elements.

[0012] Preferably, the microstructure of the steel plate is tempered sorbite with a small amount of ferrite, and the thickness of the steel plate is 12-50 mm.

[0013] This invention provides a method for manufacturing a high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate, characterized by the following specific steps: Steelmaking process: hot metal pretreatment desulfurization, converter deep dephosphorization, LF deep desulfurization, ultra-low residual element control of As, Sb, Sn, Pb, Bi, and B; using dynamic light pressure reduction and electromagnetic stirring technology to obtain SA-516Gr70 continuous casting billets with center segregation C1.0 grade and below. Heating process: The continuously cast steel billet is loaded into a walking beam furnace for heating at a temperature of 1170℃~1210℃ and a heating coefficient of 9.0~13.0min / cm to ensure the uniformity of heating of the continuously cast steel billet; Rolling process: 260-370mm cross-section continuous casting billet is used, and a two-stage controlled rolling process is adopted. The rolling temperature of the first stage is controlled between 1030℃ and 1150℃, and the rolling temperature of the second stage is controlled between 850℃ and 910℃. Cooling process: The rolled steel plate is cooled by a water cooling device. The temperature of the steel plate after cooling is controlled at 650℃~700℃. Then the steel plate is cooled in the air. Heat treatment process: The steel plate is first subjected to normalizing heat treatment, with a normalizing heating temperature of 880~920℃ and a normalizing heating and holding time of 1.8~2.5min / mm + 10~20min. After normalizing heat treatment, the steel plate is put into a water cooling device for accelerated cooling, and then subjected to tempering heat treatment, with a tempering heating temperature of 650℃~680℃ and a tempering heating and holding time of 2.0~3.5min / mm + 20~40min.

[0014] The steel plates prepared by the above method have a yield strength ≥310MPa, tensile strength 485~585MPa, elongation after fracture ≥23%, impact absorption energy at -45℃ at 1 / 4 thickness ≥80J, impact absorption energy at -45℃ at 1 / 2 thickness ≥60J, and HIC test results satisfy CLR≤10%, CTR≤3%, and CSR≤1%.

[0015] The beneficial effects of this invention are: (1) The present invention adopts a lower alloy composition design with less Mn and Ni content, without relying on high-content precious alloys. While ensuring performance, it reduces raw material and smelting costs. At the same time, the present invention strictly controls the upper limit of harmful elements such as P and S, i.e. P≤0.008% and S≤0.0015%, and combines Ca element micro-alloying and ultra-low residual element control to significantly improve the steel plate's resistance to hydrogen-induced cracking and meet CLR≤10% and CTR≤3%; (2) The present invention uses a 260mm-370mm cross-section continuous casting billet to improve the density of the core structure of the steel plate with a larger compression ratio, thereby improving the HIC resistance of the material. The HIC results meet the following requirements: CLR≤10%, CTR≤3%, CSR≤1%. The present invention adopts the "two-stage rolling + post-rolling water cooling + air cooling" technology. Through the two-stage controlled rolling process and wide temperature range regulation (first stage 1030℃~1150℃, second stage open rolling 850~910℃), combined with the cooling control of the red-hot temperature of 650℃~700℃, it can not only ensure the density of the core structure of the steel plate, but also achieve stable production in a wide thickness range of 12~50mm. The compression ratio is reasonable and the performance in the thickness direction is uniform, ensuring the uniformity of the microstructure performance in the thickness direction of the steel plate. (3) The present invention can retain a small amount of ferrite structure obtained before normalizing, so as to improve the core impact performance. After tempering heat treatment, the impact absorption energy of 1 / 2 thickness of steel plate is basically the same as that of 1 / 4 thickness. The impact absorption energy at -45℃ at 1 / 4 thickness is ≥80J, and the impact absorption energy at -45℃ at 1 / 2 thickness is ≥60J. Attached Figure Description

[0016] Figure 1 The microstructure is located at 1 / 4 of the steel plate thickness. Figure 2 The microstructure is located at 1 / 2 the thickness of the steel plate. Detailed Implementation Example 1

[0017] This embodiment provides a high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate with a thickness of 12mm. Its chemical composition and mass percentage are as follows: C 0.173%, Si: 0.26%, Mn: 0.97%, P: 0.0059%, S: 0.0006%, Ni: 0.33%, Al: 0.047%, Nb: 0.005%, V: 0.004%, Ti: 0.0032%, Ca 0.0018%, with the remainder being Fe and residual elements.

[0018] The manufacturing method includes the following steps: Steelmaking process: After desulfurization in hot metal pretreatment, S is 0.008%; after deep desulfurization in the converter, P is 0.005%; after deep desulfurization in the LF furnace, S is 0.0006%; ultra-low residual elements such as As, Sb, Sn, Pb, Bi, and B are controlled; qualified hot metal is used as raw material for smelting; alloys are added during the steelmaking process to avoid the increase of residual elements; after RH treatment, the temperature of the molten steel is 1550℃, and the superheat of the molten steel is controlled at 14~19℃ in the continuous casting tundish; the continuous casting adopts dynamic light pressure and electromagnetic stirring technology; the center segregation of the 260mm thick billet is C1.0 grade. Heating process: The continuously cast steel billet is loaded into a walking beam furnace for heating. The heating coefficient is ≥9.0 min / cm, the heating temperature is 1210℃, and the soaking zone is held for 45 minutes to ensure the heating uniformity of the continuously cast steel billet. Rolling process: A two-stage controlled rolling process is adopted. The first stage rolling end temperature is 1030℃, and the reduction of the last two passes in this stage is 32mm and 30mm respectively. The second stage starting rolling temperature is 910℃, and the finishing rolling temperature is 812℃. Cooling process: The rolled steel plate is cooled by a water cooling device until the steel plate reaches a red-hot temperature of 700℃, and then air-cooled. Heat treatment process: The steel plate undergoes normalizing + accelerated cooling + tempering heat treatment. The normalizing heating temperature is 920℃, and the normalizing heating and holding time is 40min; the tempering heating temperature is 680℃, and the tempering heating and holding time is 62min.

[0019] The properties of the above-mentioned steel plates are shown in the table below: Example 2

[0020] This embodiment provides a high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate with a thickness of 32mm. Its chemical composition and mass percentage are as follows: C 0.154%, Si: 0.33%, Mn: 1.16%, P: 0.0067%, S: 0.0006%, Ni: 0.21%, Al: 0.034%, Nb: 0.008%, V: 0.005%, Ti: 0.003%, Ca 0.0026%, with the remainder being Fe and residual elements.

[0021] The manufacturing method includes the following steps: Steelmaking process: After desulfurization in hot metal pretreatment, S is 0.009%; after deep desulfurization in the converter, P is 0.006%; after deep desulfurization in the LF furnace, S is 0.0005%; ultra-low residual elements such as As, Sb, Sn, Pb, Bi, and B are controlled; qualified hot metal is used as raw material for smelting; alloys are added during the steelmaking process to avoid the increase of residual elements; after RH treatment, the temperature of the molten steel is 1547℃, and the superheat of the molten steel is controlled at 15~21℃ in the continuous casting tundish; dynamic light pressure and electromagnetic stirring technology are used in continuous casting; the center segregation of C in the 320mm thick billet is grade C0.5. Heating process: The continuously cast steel billet is loaded into a walking beam furnace for heating. The heating coefficient is ≥11.0 min / cm, the heating temperature is 1194℃, and the soaking zone is held for 52 minutes to ensure the heating uniformity of the continuously cast steel billet. Rolling process: A two-stage controlled rolling process is adopted. The rolling end temperature of the first stage is 1045℃, and the reduction of the last two passes in this stage is 35mm and 32mm. The rolling start temperature of the second stage is 880℃, and the rolling end temperature is 809℃. Cooling process: The rolled steel plate is cooled by a water cooling device until the steel plate reaches a red-hot temperature of 682℃, and then air-cooled. Heat treatment process: The steel plate undergoes normalizing + accelerated cooling + tempering heat treatment. The normalizing heating temperature is 907℃ and the normalizing heating and holding time is 71min; the tempering heating temperature is 662℃ and the tempering heating and holding time is 120min.

[0022] The properties of the above-mentioned steel plates are shown in the table below: Example 3

[0023] This embodiment provides a high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate with a thickness of 50mm. Its chemical composition and mass percentage are as follows: C: 0.168%, Si: 0.30%, Mn: 1.12%, P: 0.0065%, S: 0.0008%, Ni: 0.29%, Al: 0.054%, Nb: 0.007%, V: 0.006%, Ti: 0.004%, Ca: 0.0017%, with the remainder being Fe and residual elements.

[0024] The preparation method includes the following steps: Steelmaking process: After desulfurization in hot metal pretreatment, S is 0.007%; after deep desulfurization in converter, P is 0.005%; after deep desulfurization in LF, S is 0.0006%; ultra-low residual elements such as As, Sb, Sn, Pb, Bi, and B are controlled; qualified hot metal is used as raw material for smelting; alloys are added during the steelmaking process to avoid the increase of residual elements; after RH treatment, the temperature of the molten steel is 1543℃, and the superheat of the molten steel is controlled at 13-18℃ in the continuous casting tundish; dynamic light pressure and electromagnetic stirring technology are used in continuous casting; the center segregation of the 370mm thick billet is C1.0 grade. Heating process: The continuously cast steel billet is loaded into a walking beam furnace for heating. The heating coefficient is ≥9.0 min / cm, the heating temperature is 1173℃, and the soaking zone is held for 66 minutes to ensure the heating uniformity of the continuously cast steel billet. Rolling process: A two-stage controlled rolling process is adopted. The rolling end temperature of the first stage is 1067℃, and the reduction of the last two passes in this stage is 38mm and 35mm. The rolling start temperature of the second stage is 850℃, and the rolling end temperature is 814℃. Cooling process: The rolled steel plate is cooled by a water cooling device until the steel plate reaches a red-hot temperature of 650℃, and then air-cooled. Heat treatment process: The steel plate undergoes normalizing + accelerated cooling + tempering heat treatment. The normalizing heating temperature is 887℃, and the normalizing heating and holding time is 113min. The tempering heating temperature is 653℃, and the tempering heating and holding time is 154min.

[0025] The properties of the above-mentioned steel plates are shown in the table below:

[0026] This invention, through a lower alloy composition design and controlled rolling technology, followed by water cooling and air cooling after rolling, ensures the uniformity of microstructure and properties along the thickness direction of the steel plate. By selecting a suitable normalizing + accelerated cooling + tempering heat treatment process, a steel plate with a microstructure of tempered sorbite and a small amount of ferrite is obtained. Figure 1 , 2 As shown. The impact absorption energy at 1 / 2 thickness of the steel plate is basically equivalent to that at 1 / 4 thickness. The impact absorption energy at -45℃ at 1 / 4 thickness is ≥80J, and the impact absorption energy at -45℃ at 1 / 2 thickness is ≥60J. The HIC results satisfy CLR≤10%, CTR≤3%, and CSR≤1%.

[0027] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.14%~0.18%, Si: 0.20%~0.40%, Mn: 0.95%~1.20%, P≤0.008%, S≤0.0015%, Ni: 0.20%~0.38%, Alt: 0.025~0.055%, Nb: ≤0.020%, V: ≤0.030%, Ti: ≤0.020%, Ca: 0.0008%~0.0035%, with the remainder being Fe and residual elements.

2. The high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate according to claim 1, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.15-0.17%, Si: 0.25-0.35%, Mn: 1.05-1.15%, P≤0.008%, S≤0.0015%, Ni: 0.25-0.35%, Alt: 0.040-0.055%, Nb: ≤0.015%, V: ≤0.020%, Ti: ≤0.015%, Ca: 0.0008%-0.0025%, with the remainder being Fe and residual elements.

3. The high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate according to claim 1, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.16~0.18%, Si: 0.20%~0.30%, Mn: 0.95%~1.05%, P≤0.008%, S≤0.0015%, Ni: 0.28%~0.38%, Alt: 0.035~0.050%, Nb: ≤0.020%, V: ≤0.020%, Ti: ≤0.015%, Ca: 0.0015%~0.0030%, with the remainder being Fe and residual elements.

4. The high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate according to claim 1, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.14~0.16%, Si: 0.30%~0.40%, Mn: 1.10%~1.20%, P≤0.008%, S≤0.0015%, Ni: 0.20%~0.30%, Alt: 0.025~0.040%, Nb: ≤0.020%, V: ≤0.030%, Ti: ≤0.020%, Ca: 0.0020%~0.0035%, with the remainder being Fe and residual elements.

5. A high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate according to any one of claims 1-4, characterized in that: The microstructure of the steel plate is tempered sorbite with a small amount of ferrite, and the thickness of the steel plate is 12-50mm.

6. A method for manufacturing a high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate according to any one of claims 1-4, characterized in that: Specifically, the following procedures are included: Steelmaking process: hot metal pretreatment desulfurization, converter deep dephosphorization, LF deep desulfurization, ultra-low residual element control of As, Sb, Sn, Pb, Bi, and B; using dynamic light pressure reduction and electromagnetic stirring technology to obtain SA-516Gr70 continuous casting billets with center segregation C1.0 grade and below. Heating process: The continuously cast steel billet is loaded into a walking beam furnace for heating at a temperature of 1170℃~1210℃ and a heating coefficient of 9.0~13.0min / cm to ensure the uniformity of heating of the continuously cast steel billet; Rolling process: 260-370mm cross-section continuous casting billet is used, and a two-stage controlled rolling process is adopted. The rolling temperature of the first stage is controlled between 1030℃ and 1150℃, and the rolling temperature of the second stage is controlled between 850℃ and 910℃. Cooling process: The rolled steel plate is cooled by a water cooling device. The temperature of the steel plate after cooling is controlled at 650℃~700℃. Then the steel plate is cooled in the air. Heat treatment process: The steel plate is first subjected to normalizing heat treatment, with a normalizing heating temperature of 880~920℃ and a normalizing heating and holding time of 1.8~2.5min / mm + 10~20min. After normalizing heat treatment, the steel plate is put into a water cooling device for accelerated cooling, and then subjected to tempering heat treatment, with a tempering heating temperature of 650℃~680℃ and a tempering heating and holding time of 2.0~3.5min / mm + 20~40min.

7. The method for manufacturing the high-temperature PWHT heat-treated SA-516Gr70 acid-resistant pressure vessel steel plate according to claim 6, characterized in that: The resulting steel plate has a yield strength ≥310MPa, tensile strength 485~585MPa, elongation after fracture ≥23%, impact absorption energy at -45℃ at 1 / 4 thickness ≥80J, impact absorption energy at -45℃ at 1 / 2 thickness ≥60J, and HIC test results satisfy CLR≤10%, CTR≤3%, and CSR≤1%.

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