Die-welding-resistant SA516Gr70 pressure vessel steel plate for end socket and production method of die-welding-resistant SA516Gr70 pressure vessel steel plate

Abstract

The invention discloses a die welding resistant SA516Gr70 pressure vessel steel plate for an end socket and a production method of the die welding resistant SA516Gr70 pressure vessel steel plate. The steel plate comprises the following chemical components: 0.17-0.20% of C, 0.15-0.30% of Si, 1.05-1.20% of Mn, 0.015-0.020% of Nb, 0.15-0.30% of Ni, 0.04-0.12% of Mo, 0.1-0.2% of Cu, 0.1-0.25% of Cr, 0.02-0.05% of Alt, less than or equal to 0.012% of P, less than or equal to 0.003% of S, less than or equal to 0.45% of carbon equivalent CE, and the balance of Fe and inevitable impurities. The production method comprises the steps of blank heating, controlled rolling and normalizing heat treatment. By accurately controlling the chemical components of the steel plate and optimizing the process parameters, the high-performance steel plate is efficiently and stably produced, and the steel plate has the characteristics of stable strength, excellent impact toughness, excellent performance after welding and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a die-welding-resistant SA516Gr70 pressure vessel steel plate for heads and a production method thereof. Background Art

[0002] In pressure vessel manufacturing, the head is a core component, and its quality directly determines the overall performance, safety, and reliability of the pressure vessel. Restoring the performance of pressure vessel steel plates used for head ends after hot forming is a critical step in ensuring head quality. Previously, simulated normalizing water cooling followed by tempering was a common method for restoring thick steel plates. However, in recent years, simulated normalizing air cooling has become increasingly popular for restoring the performance of thick head plates due to its many advantages. It simplifies the process flow, significantly shortens production cycle time, significantly improves production efficiency, and effectively reduces processing costs. At the microstructural level, simulated normalizing air cooling promotes the formation of a uniform and fine ferrite and pearlite structure in the steel plate, achieving grain refinement, significantly improving the toughness and ductility of the steel plate while enhancing strength. Furthermore, compared to simulated normalizing water cooling, simulated normalizing air cooling achieves a more moderate cooling rate, significantly reducing the internal stress generated during cooling, effectively minimizing deformation and creating favorable conditions for subsequent processing and assembly.

[0003] However, achieving good die-weldability for steel plates after simulated normalizing and air-cooling presents significant challenges. Especially for steel plates destined for export, users demand extremely high consistency between the production methods for the steel plate body and the performance recovery process for the hot-formed heads. They find it difficult to accept normalizing the steel plate body, followed by a simulated normalizing and tempering process after hot-forming the heads to restore performance and ensure performance after subsequent die-welding and multiple repairs. Furthermore, if the steel plate body is delivered as normalized and tempered, this approach would increase production costs and extend delivery times, making this a difficult choice for users.

[0004] From a welding perspective, to reduce welding difficulty, improve welding quality, and ensure long-term die-weldability, the alloy composition, microalloying element additions, and carbon equivalent limits of ordered steel plates are strictly controlled. Currently, users also place strict restrictions on the chemical composition and carbon equivalent (CEV) of steel plates. Common restrictions include: C ≤ 0.20, Mn: 0.8-1.2, Nb, V, Ti ≤ 0.02, Nb + V ≤ 0.02 (or 0.03), CEV ≤ 0.45, etc. These stringent requirements are particularly prevalent for steel plates intended for export. Furthermore, to prevent equipment problems during processing or use requiring repair, the steel plates are often required to maintain long-term die-weldability.

[0005] A search of existing literature and patents revealed a relative lack of inventions and research related to ensuring simulated normalizing air cooling and long-time die welding for thick head plates after hot forming. Existing research mostly focuses on thin-gauge head plates, or on the requirements for long-time or high-temperature die welding of cylinder plates. These studies struggle to meet the stringent requirements for long-time die welding performance of thick head plates after simulated normalizing air cooling. Some studies can meet the performance requirements of thick plate heads after long-time die welding, but their high CEV design is not conducive to subsequent welding performance. This makes it extremely necessary to develop a steel plate and its production method suitable for thick head plates that can guarantee long-time die welding performance after simulated normalizing air cooling, while meeting stringent chemical composition and carbon equivalent requirements. Summary of the Invention

[0006] This invention aims to provide a die-weld-resistant SA516Gr70 pressure vessel steel plate for head ends. This plate, after simulated normalizing and air cooling, ensures long-term die-weldability, effectively reduces welding defects, and exhibits excellent overall mechanical properties, meeting the stringent requirements for head ends in pressure vessels. The invention also provides a production method that achieves efficient and stable production of this high-performance steel plate by precisely controlling the steel plate's chemical composition and optimizing process parameters.

[0007] To achieve the above-mentioned object of the invention, the present invention adopts the following technical solution: a mold-resistant welding SA516Gr70 pressure vessel steel plate for head, the chemical composition and mass percentage of the steel plate are as follows: C: 0.17~0.20%, Si: 0.15~0.30%, Mn: 1.05~1.20%, Nb: 0.015~0.020%, Ni: 0.15~0.30%, Mo: 0.04~0.12%, Cu: 0.1~0.2%, Cr: 0.1~0.25%, Alt: 0.02~0.05%, P≤0.012%, S≤0.003%, and the rest are Fe and unavoidable impurities, and the carbon equivalent CEV of the steel plate is ≤0.45% (carbon equivalent CEV=C+ Mn / 6+ (Cr+Mo+V) / 5+ (Ni+Cu)15).

[0008] The thickness of the steel plate of the present invention is 50 to 100 mm.

[0009] The surface hardness of the steel plate of the present invention is ≤190HB, and the metallographic structure is composed of ferrite+pearlite.

[0010] The steel plate of the present invention has the following properties as delivered and after hot forming air cooling + simulated normalizing air cooling + die welding: yield strength R P0.2 ≥290MPa, tensile strength Rm ≥485MPa, elongation ≥25%, average transverse impact energy AKV ≥100J at -20℃ at 1 / 4 thickness position.

[0011] The steel plate described in the present invention needs to be subjected to head hot forming air cooling + simulated normalizing air cooling before die welding; the die welding system: temperature 620-635°C, insulation time 12-14h, furnace temperature above 300°C, heating and cooling speed 40-100°C / h; hot forming + simulated normalizing air cooling system: simulated hot forming 900-930°C insulation 1.0-2.0min / mm air cooling + simulated normalizing 900±10°C insulation 2min / mm air cooling.

[0012] Another object of the present invention is to provide a production method for the above-mentioned SA516Gr70 pressure vessel steel plate for head sealing, the production method including billet heating, controlled rolling, and normalizing heat treatment processes; in the billet heating process, the maximum furnace temperature in the heating section does not exceed 1280°C, the furnace temperature in the soaking section is 1210~1250°C, the total heating coefficient is ≥9min / cm, the time in the furnace = billet thickness * heating coefficient, and a 300mm thick billet is used.

[0013] In the controlled rolling process of the present invention, the steel plate adopts type II controlled rolling, the rough rolling in stage I ensures that the reduction amount of two or more passes is 30-35 mm, the finishing rolling temperature in stage II is ≤820°C, and ACC rapid cooling is performed after rolling, and the red-return temperature is 650-700°C.

[0014] The normalizing heat treatment process of the present invention is as follows: normalizing temperature 890-920° C., heating coefficient 1.7-2.2 min / mm, furnace time = steel plate thickness * heating coefficient, air cooling or weak water cooling after leaving the furnace.

[0015] The beneficial effects produced by the above technical solution are: 1. The present invention effectively improves the long-time die welding performance and comprehensive mechanical properties of the steel plate after simulated normalizing and air cooling by precisely controlling the chemical composition, adding appropriate amounts of alloying elements such as Nb, Ni, Mo, and Cu, and strictly limiting the content of impurities such as P and S. Among them, the Nb element enhances the strength and resistance to welding cracks of the steel plate by refining the grains and strengthening by precipitation, ensuring the stability of the steel plate structure during long-time die welding; the Ni and Mo elements improve the strength and toughness of the steel plate, ensuring that the performance after die welding meets the use requirements; the Cu element helps to improve the corrosion resistance of the steel plate and enhance the reliability of the steel plate under complex working conditions. Strictly controlling the carbon equivalent CEV≤0.45% greatly reduces the difficulty of welding, improves the welding quality, and provides a strong guarantee for long-time die welding. 2. The production method of the present invention achieves precise regulation of the microstructure and properties of the steel plate by precisely controlling the process parameters of each process such as billet heating, controlled rolling, and normalizing heat treatment. Appropriate furnace temperatures and heating coefficients during the billet heating process ensure uniform billet heating; controlled rolling and ACC rapid cooling during the rolling process ensure the ideal grain size and microstructure of the steel plate. Appropriate water cooling after normalizing the steel plate body also ensures grain size coarsening, laying the foundation for long-term die-welding performance after simulated normalizing and air-cooling. 3. The present invention achieves a specific thickness range, low surface hardness, and a ferrite + pearlite metallographic structure, giving the steel plate excellent processability while maintaining stable and excellent mechanical properties. Both as-delivered and after die-welding, it meets high strength and toughness performance indicators, effectively handling the various demanding operating conditions encountered during pressure vessel manufacturing and long-term die-welding use of the head. 4. Through a rational head hot forming combined with simulated normalizing and air-cooling, the present invention ensures the stability and uniformity of the steel plate's microstructure during processing, and the stability of the steel plate's performance during long-term die-welding. This results in the efficient and stable production of SA516Gr70 pressure vessel steel plate with long-term die-welding performance after simulated normalizing and air-cooling. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below with reference to specific embodiments. Example 1

[0017] The mold-resistant SA516Gr70 pressure vessel steel plate for the head in this embodiment has a thickness of 12 mm and its chemical composition and mass percentage are as follows: C: 0.17%, Si: 0.17%, Mn: 1.17%, Nb: 0.015%, Ni: 0.18%, Mo: 0.05%, Cu: 0.15%, Cr: 0.13%, P: 0.012%, S: 0.002%, Alt: 0.038%, and the balance is Fe and unavoidable impurities; carbon equivalent CEV: 0.423; and its production method includes billet heating, controlled rolling, stacking slow cooling, and normalizing heat treatment steps, as follows: (1) Billet heating: The highest heating temperature of the continuous casting billet is 1260℃, the temperature of the soaking section is 1232℃, the actual time in the furnace is 305min, the total heating coefficient is 10.5min / cm, and the heating is sufficient.

[0018] (2) Controlled rolling: The steel plate adopts type II controlled rolling. In the stage I rough rolling, there are three passes with a reduction of more than 30 mm, namely 32.1 mm, 30.3 mm, and 31 mm. The final rolling temperature in the stage II is 820 °C. After rolling, the ACC is rapidly cooled and returns to 671-682 °C.

[0019] (3) Normalizing heat treatment: Normalizing temperature 890-910℃, heating coefficient 2.2min / mm, furnace time 110min, air cooling after leaving the furnace.

[0020] The die welding heat treatment process in this example is as follows: 620°C for 12 hours, a furnace exit temperature of 400°C, and a heating and cooling rate of 40-50°C / hour. The head sealing process before die welding heat treatment involves hot forming at 930°C for 1 minute / mm with air cooling, followed by simulated normalizing at 900°C for 2 minutes / mm with air cooling. The measured mechanical properties of the steel plates in the as-delivered and die-welded state are shown in Table 1. The metallographic structure is ferrite + pearlite. Example 2

[0021] The mold-resistant SA516Gr70 pressure vessel steel plate for the head in this embodiment has a thickness of 62 mm and its chemical composition and mass percentage are as follows: C: 0.18%, Si: 0.24%, Mn: 1.19%, Nb: 0.017%, Ni: 0.22%, Mo: 0.04%, Cu: 0.16%, Cr: 0.12%, P: 0.010%, S: 0.0013%, Alt: 0.041%, and the balance is Fe and unavoidable impurities; carbon equivalent CEV: 0.436; and its production method includes billet heating, controlled rolling, stacking slow cooling, and normalizing heat treatment steps, as follows: (1) Billet heating: The highest heating temperature of the continuous casting billet is 1266℃, the temperature of the soaking section is 1230℃, the actual time in the furnace is 290min, the total heating coefficient is 9.67min / cm, and it is fully heated.

[0022] (2) Controlled rolling: The steel plate adopts type II controlled rolling. In the stage I rough rolling, there are two single-pass reductions of more than 30 mm, which are 31.4 mm and 30.5 mm respectively; the final rolling temperature in the stage II is 810 °C, and the ACC is rapidly cooled after rolling, and the red-return temperature is 653-661 °C.

[0023] (3) Normalizing heat treatment: Normalizing temperature 900-920℃, furnace time 120min, heating coefficient 1.93min / mm, water cooling after leaving the furnace.

[0024] The die welding heat treatment process in this example is as follows: 625°C for 750 minutes (12.5 hours), a furnace exit temperature of 300°C, and a heating and cooling rate of 40-55°C / hour. The head sealing process before die welding heat treatment involves hot forming at 910°C for 2 minutes / mm with air cooling, followed by simulated normalizing at 910°C for 2 minutes / mm with air cooling. The measured mechanical properties of the steel plates in the as-delivered and die-welded state are shown in Table 1. The metallographic structure is ferrite + pearlite. Example 3

[0025] The mold-resistant SA516Gr70 pressure vessel steel plate for the head in this embodiment has a thickness of 75 mm and its chemical composition and mass percentage are as follows: C: 0.18%, Si: 0.30%, Mn: 1.1%, Nb: 0.017%, Ni: 0.25%, Mo: 0.07%, Cu: 0.11%, Cr: 0.21%, P: 0.010%, S: 0.001%, Alt: 0.045%, and the balance is Fe and unavoidable impurities; carbon equivalent CEV: 0.443; its production method includes billet heating, controlled rolling, stacking slow cooling, and normalizing heat treatment steps, as follows: (1) Billet heating: The highest heating temperature of the continuous casting billet is 1256℃, the temperature of the soaking section is 1236℃, the actual time in the furnace is 296min, the total heating coefficient is 9.86min / cm, and it is fully heated.

[0026] (2) Controlled rolling: The steel plate adopts type II controlled rolling. In the stage I rough rolling, there are two single-pass reductions of more than 30 mm, which are 31.5 mm and 30.1 mm respectively; the final rolling temperature in the stage II is 808 ° C, and the ACC is rapidly cooled after rolling, and the red-return temperature is 660-675 ° C.

[0027] (3) Normalizing heat treatment: Normalizing temperature 900-920℃, furnace time 140min, heating coefficient 1.86min / mm, weak water cooling after furnace.

[0028] The die welding heat treatment process in this example is as follows: 635°C for 750 minutes (12.5 hours), a furnace exit temperature of 300°C, and a heating and cooling rate of 40-55°C / hour. The head sealing process before die welding heat treatment involves hot forming at 900°C with a 2-minute / mm hold and air cooling, followed by simulated normalizing at 910°C with a 2-minute / mm hold and air cooling. The measured mechanical properties of the steel plates in the as-delivered and die-welded state are shown in Table 1. The metallographic structure is ferrite + pearlite. Example 4

[0029] The mold-resistant SA516Gr70 pressure vessel steel plate for the head in this embodiment has a thickness of 86 mm and its chemical composition and mass percentage are as follows: C: 0.20%, Si: 0.28%, Mn: 1.06%, Nb: 0.017%, Ni: 0.2%, Mo: 0.1%, Cu: 0.1%, Cr: 0.15%, P: 0.011%, S: 0.0009%, Alt: 0.033%, and the balance is Fe and unavoidable impurities; carbon equivalent CEV: 0.447; its production method includes billet heating, controlled rolling, stacking slow cooling, and normalizing heat treatment steps, as follows: (1) Billet heating: The highest heating temperature of the continuous casting billet is 1259℃, the temperature of the soaking section is 1238℃, the actual time in the furnace is 311min, the total heating coefficient is 10.37min / cm, and it is fully heated.

[0030] (2) Controlled rolling: The steel plate adopts type II controlled rolling. In the stage I rough rolling, there are two single-pass reductions of more than 30 mm, which are 32.6 mm and 31.9 mm respectively; the final rolling temperature in the stage II is 811 °C, and the ACC is rapidly cooled after rolling, and the red-return temperature is 656-668 °C.

[0031] (3) Normalizing heat treatment: Normalizing temperature 900-910℃, furnace time 180min, heating coefficient 2.09min / mm, weak water cooling after furnace.

[0032] The die welding heat treatment process in this example is as follows: 625°C for 840 minutes (14 hours), a furnace exit temperature of 300°C, and a heating and cooling rate of 40-55°C / hour. The head sealing process before die welding heat treatment involves hot forming at 920°C with a holding time of 1.5 minutes / mm and air cooling, followed by simulated normalizing at 900°C with a holding time of 2 minutes / mm and air cooling. The measured mechanical properties of the steel plates in the as-delivered and die-welded state are shown in Table 1. The metallographic structure is ferrite + pearlite. Example 5

[0033] The mold-resistant SA516Gr70 pressure vessel steel plate for the head in this embodiment has a thickness of 100 mm and its chemical composition and mass percentage are as follows: C: 0.19%, Si: 0.19%, Mn: 1.05%, Nb: 0.016%, Ni: 0.23%, Mo: 0.09%, Cu: 0.12%, Cr: 0.18%, P: 0.008%, S: 0.0013%, Alt: 0.022%, and the balance is Fe and unavoidable impurities; carbon equivalent CEV: 0.4429; and its production method includes billet heating, controlled rolling, stacking slow cooling, and normalizing heat treatment steps, as follows: (1) Billet heating: The highest heating temperature of the continuous casting billet is 1271℃, the temperature of the soaking section is 1233℃, the actual time in the furnace is 320min, the total heating coefficient is 10.6min / cm, and it is fully heated.

[0034] (2) Controlled rolling: The steel plate adopts type II controlled rolling. In the stage I rough rolling, there are two single-pass reductions of more than 30 mm, which are 33.6 mm and 31.2 mm respectively; the final rolling temperature in the stage II is 815 °C, and the ACC is rapidly cooled after rolling, and the red-return temperature is 662-686 °C.

[0035] (3) Normalizing heat treatment: Normalizing temperature 900-910℃, furnace time 200min, heating coefficient 2.0min / mm, weak water cooling after furnace.

[0036] The die welding heat treatment process in this example is as follows: 625°C for 12 hours, a furnace exit temperature of 300°C, and a heating and cooling rate of 90-100°C / hour. The head sealing process before die welding heat treatment includes hot forming at 910°C for 1.5 minutes / mm with air cooling, followed by simulated normalizing at 900°C for 2 minutes / mm with air cooling. The measured mechanical properties of the steel plates in the as-delivered and die-welded state are shown in Table 1. The metallographic structure is ferrite + pearlite.

[0037] Table 1 Mechanical properties of the head plates of Examples 1 to 3 in the delivery and mold-welded states

[0038] Note: The actual setting value of the heating and cooling rate during the die welding heat treatment is the middle average rate.

[0039] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A die-welded SA516Gr70 pressure vessel steel plate for head, characterized in that: The chemical composition and mass percentage of the steel plate are as follows: C: 0.17-0.20%, Si: 0.15-0.30%, Mn: 1.05-1.20%, Nb: 0.015-0.020%, Ni: 0.15-0.30%, Mo: 0.04-0.12%, Cu: 0.1-0.2%, Cr: 0.1-0.25%, Alt: 0.02-0.05%, P≤0.012%, S≤0.003%, and the rest are Fe and unavoidable impurities. The carbon equivalent CEV of the steel plate is ≤0.45%.

2. The die-weld-resistant SA516Gr70 pressure vessel steel plate for head according to claim 1, characterized in that: The thickness of the steel plate is 50 to 100 mm.

3. The die-weld-resistant SA516Gr70 pressure vessel steel plate for head according to claim 1, characterized in that: The surface hardness of the steel plate is ≤190HB, and the metallographic structure is ferrite+pearlite.

4. The die-weld-resistant SA516Gr70 pressure vessel steel plate for head according to any one of claims 1 to 3, characterized in that: The performance of the steel plate as delivered and after hot forming air cooling + simulated normalizing air cooling + die welding all meet the following requirements: yield strength R P0.2 ≥290MPa, tensile strength Rm ≥485MPa, elongation ≥25%, average transverse impact energy AKV ≥100J at -20℃ at 1 / 4 thickness position.

5. The die-weld-resistant SA516Gr70 pressure vessel steel plate for head according to claims 1-3, characterized in that: The steel plate needs to be subjected to head hot forming and air cooling + simulated normalizing air cooling before die welding; the die welding system: temperature 620-635°C, insulation time 12-14h, furnace temperature above 300°C, heating and cooling speed 40-100°C / h; hot forming + simulated normalizing air cooling system: simulated hot forming 900-930°C insulation 1.0-2.0min / mm air cooling + simulated normalizing 910±10°C insulation 2min / mm air cooling.

6. A method for producing a die-welded SA516Gr70 pressure vessel steel plate for head according to any one of claims 1 to 5, characterized in that: The production method includes billet heating, controlled rolling, and normalizing heat treatment processes; in the billet heating process, the maximum furnace temperature in the heating section does not exceed 1280°C, the furnace temperature in the soaking section is 1210-1250°C, and the total heating coefficient is ≥9min / cm.

7. The method for producing the die-weld-resistant SA516Gr70 pressure vessel steel plate for head sealing according to claim 6, characterized in that: In the controlled rolling process, the steel plate adopts type II controlled rolling, the rough rolling in stage I ensures that there are two or more passes with a reduction of 30-35 mm, the finishing rolling temperature in stage II is ≤820°C, and ACC rapid cooling is performed after rolling, with the red-return temperature being 650-700°C.

8. The method for producing the die-weld-resistant SA516Gr70 pressure vessel steel plate for head according to claim 6, characterized in that: The normalizing heat treatment process is as follows: normalizing temperature 890-920° C., heating coefficient 1.8-2.5 min / mm, air cooling or weak water cooling after leaving the furnace.

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