Electroslag remelting process for TP347H austenitic stainless steel of hydrogen pipeline in coal chemical industry

Abstract

The invention relates to an electroslag remelting process for TP347H austenitic stainless steel of a hydrogen pipeline in the coal chemical industry, the formula of a slag system is uniquely designed, and the TP347H austenitic stainless steel comprises the following chemical components in percentage by weight: 60%-65% of CaF2, 20%-25% of Al2O3, 10%-15% of CaO and 1%-2% of MgO. The slag system with the ratio is matched with the melting point of a steel grade, so that the condition that an electroslag ingot does not have surface defects such as double skins and shunting holes can be ensured, and the quality of the steel grade is improved. And in addition, the slag deoxidizing capacity is effectively improved, and impurities and non-metallic inclusions in molten steel are more sufficiently removed. In the aspect of process parameters, by controlling the current voltage, the melting rate, the swing proportion parameter and other key process parameters, the remelting process is stably carried out, the component segregation and solidification defects are effectively reduced, and the electroslag remelting quality and performance of the TP347H stainless steel of the hydrogen pipeline in the coal chemical industry can be effectively improved; and the long-term stable service requirement of the coal chemical industry hydrogen-containing pipeline in a high-temperature, high-pressure and hydrogen-containing complex environment can be well met.

Description

Technical Field

[0001] This invention belongs to the field of electroslag metallurgical technology for hydrogen-containing pipeline materials in coal chemical industry, specifically an electroslag remelting process for TP347H austenitic stainless steel in hydrogen-containing pipelines for coal chemical industry. Background Technology

[0002] In the application of hydrogen-bearing pipelines in coal chemical industry, TP347H austenitic stainless steel has become a key material choice due to its excellent resistance to intergranular corrosion, high-temperature strength, and oxidation resistance. Electroslag remelting, as an advanced metal purification and refining technology, can significantly improve the purity of TP347H steel and enhance its microstructure and mechanical properties.

[0003] However, existing electroslag remelting technology for TP347H stainless steel still has some problems in practical applications. In terms of slag system selection, traditional electroslag systems have limited ability to remove impurities and inclusions. In addition, the melting points of commonly used binary and ternary slag systems are poorly matched with the melting point of this steel, which easily leads to slag skin cracking during the electroslag remelting process, resulting in a heavy skin on the surface of the electroslag ingot.

[0004] The setting of process parameters in the electroslag remelting process is also crucial. In the existing technology, the unreasonable control of parameters such as current, voltage, swing amplitude, and melting rate makes it impossible to achieve a constant and shallow state of the molten metal pool, which leads to the segregation of certain alloying elements and metal solidification defects.

[0005] Faced with increasingly stringent quality and performance requirements for TP347H stainless steel materials in coal chemical hydrogen pipelines, the limitations of traditional electroslag remelting processes have become increasingly apparent, urgently requiring a new electroslag remelting process to meet the needs of actual production. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an electroslag remelting process for TP347H austenitic stainless steel in coal chemical hydrogen pipelines, so as to solve the problems mentioned in the background.

[0007] To solve the above problems, the technical solution of the present invention is implemented as follows: An electroslag remelting process for TP347H austenitic stainless steel in coal chemical hydrogen-containment pipelines includes the following steps: Step 1) Select TP347H continuous casting billets or ingot casting billets with the correct specifications and composition as consumable electrodes. After welding the dummy electrodes, use shot blasting equipment to remove the oxide scale, dust, cutting slag impurities on the surface, and bake at 400℃ or above for ≥4 hours. At the same time, prepare electroslag remelting pre-melted slag material. The chemical composition and weight percentage of the slag system are: CaF2 60%~65%, Al2O3 20%~25%, CaO 10%~15%, MgO 1%~2%. Before use, bake and keep warm in a baking furnace to remove moisture from the slag to avoid porosity defects in the lower part of the electroslag ingot. Step 2) Before powering on, blow argon gas downwards into the crystallizer for 10-15 minutes to purge the air from the crystallizer. Continue blowing argon gas downwards throughout the remelting process at a flow rate of 30-50 Nm³. 3 / h. The arc-initiating agent is a cut block of consumable electrode body. The consumable electrode is used to directly supply electricity, and the preheated slag is added into the crystallizer at a rate of 20kg / min to 30kg / min. Initially, the slag should be added at the lowest rate to prevent the arc from being extinguished by adding the slag too quickly and violently. The slag addition time is generally controlled at 30-50 minutes. During the formation of the slag pool, the voltage and current need to be gradually increased according to the fluctuation of the current curve. The voltage increase rate is generally 0.1V / min, and the current increase rate is generally 100A / min. This ensures that the slag can be melted and cleared quickly, while also allowing the consumable electrode to be immersed in the slag pool to a certain depth. Step 3) After the slag is cleaned, the electrodes are gradually melted by controlling the voltage and current; the melting rate is monitored in real time to ensure the stability of the remelting process. The process setting is melting rate v = (0.012~0.015) × D, where the melting rate unit is kg / min and the crystallizer diameter D unit is mm. At the same time, during the entire normal melting process, the deviation fluctuation between the actual current and the set current is monitored. The ratio of (actual current - set current) / set current is controlled within the fluctuation range of -10% to +10% by setting the swing ratio parameter. The swing ratio parameter setting range is 0.001~0.005. Step 4) When the melting weight of the consumable electrode reaches 92%~96% of the total weight, start to gradually reduce the voltage and current to reduce the electrode melting rate and the depth of the molten metal pool to achieve the purpose of riser feeding. The frequency and amplitude of voltage reduction should be lower than the frequency and amplitude of current reduction. The current reduction rate is generally controlled at 200~300A / min. Step 5) After remelting, the electroslag ingot is cooled in the mold of the crystallizer for a period of time, then removed from the mold and allowed to cool naturally to room temperature indoors. The surface is inspected, and areas with slag grooves or slag marks are ground with a grinding wheel until they pass inspection before proceeding to the next processing step.

[0008] The positive effects of the technical solution of the present invention are as follows: The electroslag remelting process for TP347H austenitic stainless steel in coal chemical hydrogen-contaminated pipelines described herein features a slag melting point that closely matches the steel grade, ensuring that the electroslag ingot does not exhibit surface defects such as scale or flow dividers. Furthermore, by rationally adjusting the composition ratio, the deoxidizing capacity of the slag is effectively improved, enabling more thorough removal of impurities and non-metallic inclusions from the molten steel.

[0009] The electroslag remelting process for TP347H austenitic stainless steel in coal chemical hydrogen-contaminated pipelines achieves stable electroslag remelting through control of key process parameters such as current, voltage, melting rate, and swing amplitude ratio. The constant molten pool state effectively reduces component segregation and solidification defects, resulting in a denser microstructure and superior overall performance in the product.

[0010] The electroslag remelting process for TP347H austenitic stainless steel in a coal chemical hydrogen pipeline, as described in this invention, results in TP347H stainless steel with lower oxygen content, more uniform composition distribution, and a denser microstructure, thus exhibiting superior performance in terms of intergranular corrosion resistance, high-temperature strength, and oxidation resistance. Detailed Implementation

[0011] Example 1: An electroslag remelting process for TP347H austenitic stainless steel in a coal chemical hydrogen-containing pipeline, with ingot specifications of 28 tons, crystallizer of Φ1300 / 1350mm, and consumable electrode specifications of Φ800mm die-cast billet. The specific smelting steps are as follows: Step 1) After welding the Φ500mm×1600mm dummy electrode, use shot blasting equipment to remove surface oxide scale, dust, cutting slag and other impurities, and bake at 450℃ for 4 hours; prepare 1200kg of pre-melted slag material according to the mass percentage of CaF2:65%, Al2O3:23%, CaO:10%, MgO:2%, and bake the slag material at 600℃ in a baking furnace for 6 hours to remove moisture from the slag. Step 2) Arrange the arc-initiating agent made from the consumable electrode body in a triangular pattern on the ingot retainer plate. After setting up the crystallizer, apply 30 Nm 3 Argon gas is blown down into the crystallizer at a flow rate of / h for 15 minutes to purge the air from the crystallizer. At the same time, after checking that all systems of electroslag remelting are normal, the consumable electrode is lowered to contact the arc-starting agent and energize it. The preheated slag is added into the crystallizer at a rate of about 20~30 kg / min, and the slag adding time is controlled to 45 minutes. During the formation of the slag pool, the voltage and current are gradually increased to quickly melt and clear the slag. Step 3) After the slag is cleaned, the melting rate of the consumable electrode is maintained at 17 kg / min by controlling the voltage and current. During the normal melting process, the swing amplitude ratio parameter is adjusted to control the ratio of (actual current - set current) / set current within the fluctuation range of -10% to +10%. Step 4) When the melting weight of the consumable electrode reaches 26.5t, the depth of the molten metal pool is gradually reduced to achieve the purpose of riser feeding. The current reduction rate is generally controlled at 200~300A / min. Step 5) After remelting, the electroslag ingot is cooled in the mold of the crystallizer for 200 minutes. After the mold is removed, it is naturally cooled to room temperature indoors. The surface of the electroslag ingot is inspected. Areas with slag grooves or slag marks are ground with a grinding wheel until they pass the inspection and are transferred to the next processing step.

[0012] Visual inspection of the electroslag ingots after molding revealed good tail-end forming. Compared to TP347H electroslag ingots produced using traditional processes, the surface was smooth, free of slag grooves and slag scars, effectively reducing the finishing workload and improving production efficiency. Sampling and testing of the electroslag ingots after forging showed an oxygen content below 12 ppm, and all indicators of composition, inclusions, and performance met the standard requirements for TP347H stainless steel for hydrogen-bearing pipelines in coal chemical industries.

[0013] As can be seen from the above embodiments, the process of the present invention can effectively improve the electroslag remelting quality and performance of TP347H stainless steel in coal chemical hydrogen pipelines, and can well meet the long-term stable service requirements of coal chemical hydrogen pipelines in complex environments of high temperature, high pressure and hydrogen.

Claims

1. A process for electroslag remelting of TP347H austenitic stainless steel in a coal chemical hydrogen-containment pipeline, characterized in that, Includes the following steps: Step 1) Select TP347H continuous casting billet or ingot casting billet with the correct specifications and composition as consumable electrode. After welding the dummy electrode, use shot blasting equipment to remove the oxide scale, dust, cutting slag impurities on the surface, and bake at 400℃ or above for ≥4h. At the same time, prepare electroslag remelting pre-melted slag material. The chemical composition and weight percentage of the slag system are: CaF2 60%~65%, Al2O3 20%~25%, CaO 10%~15%, MgO 1%~2%. Before use, bake and keep warm in the baking furnace to remove moisture from the slag to avoid porosity defects in the lower part of the electroslag ingot. Step 2) Before powering on, blow argon gas downwards into the crystallizer for 10-15 minutes to purge the air from the crystallizer. Continue blowing argon gas downwards throughout the remelting process at a flow rate of 30-50 Nm³. 3 / h, the arc-starting agent is a self-consumable electrode body cut into a block sample, and the self-consumable electrode is directly used to supply electricity. At the same time, the preheated slag is added into the crystallizer at a slag addition rate of 20kg / min~30kg / min. When adding slag in the initial stage, it is necessary to add it at the lowest speed to prevent the slag from being added too quickly and violently and extinguishing the arc. The slag addition time is generally controlled at 30-50min. During the formation of the slag pool, the voltage and current need to be gradually increased according to the fluctuation of the current curve. The voltage increase rate is generally 0.1V / min, and the current increase rate is generally 100A / min. This ensures that the slag can be melted and cleared quickly, and that the self-consumable electrode is immersed into the slag pool to a certain depth. Step 3) After the slag is cleaned, the electrodes are gradually melted by controlling the voltage and current. During the melting process, the melting rate is monitored in real time to ensure the stability of the remelting process. The process setting is melting rate v = (0.012~0.015) × D, where the melting rate unit is kg / min and the crystallizer diameter D unit is mm. At the same time, during the entire normal melting process, the deviation fluctuation between the actual current and the set current is monitored. This is controlled by setting the swing ratio parameter: the ratio of (actual current - set current) / set current is within the fluctuation range of -10% to +10%, and the swing ratio parameter setting range is 0.001~0.

005. Step 4) When the melting weight of the consumable electrode reaches 92%~96% of the total weight, start to gradually reduce the voltage and current to reduce the electrode melting rate and the depth of the molten metal pool to achieve the purpose of riser feeding. The frequency and amplitude of voltage reduction should be lower than the frequency and amplitude of current reduction, and the current reduction rate should be controlled at 200~300A / min. Step 5) After remelting, the electroslag ingot is cooled in the mold inside the crystallizer. After the mold is removed, it is naturally cooled to room temperature indoors. The surface is inspected. Areas with slag grooves or slag marks are ground with a grinding wheel until they pass the inspection and then transferred to the next processing step.