Electroslag process for improving surface defects of tail end of zynm7 electroslag ingot

Abstract

The application relates to an electroslag process for improving the tail end surface defects of ZYNM7 electroslag ingots, and the chemical components and weight percentages of the electroslag slag system are as follows: CaF 2 70%~75%, Al2O3 10%~14%, CaO 10%~14%, SiO2 1%~3%, MgO 1%~2%, the arc starting agent adopts a consumable electrode body cutting block sample, the slag melting adopts a graphite electrode arc starting, the slag adding speed is controlled to be 6kg / min~10kg / min, after the slag adding is finished, the slag material is refined by using low voltage and low current, the refining period time is controlled to be 20min~30min, during the period, the voltage and current values are 0.6 times~0.8 times of the maximum voltage and current of the normal smelting period, after the slag material is melted and cleaned, SiO2 is added, then power is turned off alternately, after the consumable electrode is alternated, the power is entered into a power boosting period, the maximum voltage is kept unchanged during the whole process, and the current is changed in four stages.

Description

Technical Field

[0001] This invention belongs to the field of electroslag metallurgy technology, and specifically relates to an electroslag process for improving the surface defects at the tail end of ZYNM7 electroslag ingots. Background Technology

[0002] Electroslag remelting, as a secondary refining technology, is a remelting and recasting process carried out in a copper water-cooled crystallizer, involving slag in chemical and physical reactions. Compared with ordinary ingots, products produced by electroslag remelting have the characteristics of high purity, good density, uniform composition, and smooth surface. ZYNM7 steel is a high-nitrogen, chromium-manganese austenitic steel, a non-magnetic product. This material has a high content of Cr, Ni, and Mn elements, and significantly increases the content of N element, which is beneficial to mechanical properties and pitting corrosion resistance. The melting point of the steel is only about 1390℃. This steel conforms to the Q-ZTG45-2021 standard, and its chemical composition is: C ≤0.05%, Si≤1.00%, Mn 16.00%~22.00%, Cr 16.50~20.00%, Ni ≤4.00%, Mo ≤2.20%, N≥0.45%, S≤0.015%, P≤0.035%.

[0003] In the initial stage of electroslag remelting, due to factors such as the cooling intensity of the bottom water tank and the circulating water in the crystallizer, the electroslag filling ratio, and the physicochemical properties of the slag system, surface quality defects such as "toad-eye" marks and slag scars often occur in the 0mm to 400mm range from the tail end of the electroslag ingot. These defects can easily lead to folding and cracking of the forging surface during subsequent forging processes. Therefore, the electroslag ingot must be finished and ground or peeled before being transferred to the next stage. This increases labor intensity and production costs, reduces production efficiency, and affects delivery cycle. Sometimes, even serious defects such as deep slag grooves and slag encapsulation occur. These defects cannot be eliminated by grinding or peeling, directly causing short-length scrap or complete scrapping. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing process technology and provide an electroslag process for improving the surface defects at the tail end of ZYNM7 electroslag ingots.

[0005] To solve the above problems, the technical solution of the present invention is implemented as follows:

[0006] An electroslag process for improving surface defects at the tail end of ZYNM7 electroslag ingots is characterized by the following: the chemical composition of the steel is: C≤0.05%, Si≤1.00%, Mn 16.00%~22.00%, Cr 16.50~20.00%, Ni≤4.00%, Mo≤2.20%, N≥0.45%, S≤0.015%, P≤0.035%; the chemical composition and weight percentage of the electroslag system are: CaF2 70%~75%, Al2O3 10%~14%, CaO 10%~14%, SiO2 1%~3%, MgO 1%~2%, and the slag is baked and kept warm in a baking furnace before use to reduce the moisture content; the specific process is as follows:

[0007] Step 1) The arc-starting agent is a block sample cut from the consumable electrode body, and the slag is started with a graphite electrode. The slag addition rate is controlled at 6 kg / min to 10 kg / min depending on the crystallizer specifications. When adding slag, CaF2 is added first, and after CaF2 is added, Al2O3, CaO and MgO are added alternately and slowly.

[0008] Step 2) After the slag is added, the slag is refined using low voltage and low current. The refining period is controlled at 20-30 minutes, and the voltage and current values ​​during this period are 0.6-0.8 times the maximum voltage and current during the normal smelting period.

[0009] Step 3) After the slag has been cleared, add SiO2 and continue refining for 2 to 5 minutes, then switch off the power and repeat.

[0010] Step 4) After the self-consuming electrode alternates, the power boost period begins. During this period, the maximum voltage remains constant throughout the process, while the current is adjusted in four stages. The specific operation is as follows:

[0011] In the first stage, set the current A1 to 40%~50% of the maximum current and maintain it for 5min~8min; in the second stage...

[0012] In the first stage, the current A2 is set to 80%~90% of the maximum current and held for 5min~8min; in the second stage, the current A3 is set to 60%~70% of the maximum current, and gradually increased from A3 to the maximum current A4 at a rate of 100A / min; in the third stage, the current is held at the maximum current A4 until the actual melting rate reaches the process-set melting rate, after which the normal smelting period begins; the process-set melting rate v = (0.0125~0.015) × D, where the melting rate is in kg / min and the crystallizer diameter D is in mm.

[0013] The positive effects of the technical solution of the present invention are as follows:

[0014] The electroslag process described above for improving the surface defects at the tail end of ZYNM7 electroslag ingots has a slag melting point that is well matched with the melting point of ZYNM7 steel, and takes into account the control of chemical composition, gas and non-metallic inclusions during the electroslag process.

[0015] The electroslag process for improving the surface defects at the tail end of ZYNM7 electroslag ingots involves setting the current A1 to 40%~50% of the maximum current during the first stage of the power enhancement period and maintaining it for 5min~8min. This process increases the slag temperature on the slag layer surface while preheating the end of the consumable electrode, ensuring that the consumable electrode does not melt or melts minimally.

[0016] The electroslag process described above for improving the surface defects at the tail end of ZYNM7 electroslag ingots involves setting the current A2 to 80%~90% of the maximum current during the second stage of the power boosting period and maintaining it for 5min~8min. During this period, the self-consumable electrode is inserted into the slag pool to a certain depth, which can effectively raise the temperature of the lower slag layer. At the same time, the current of 80%~90% will not allow the electrode to be inserted into the slag pool too deeply.

[0017] The electroslag process described above for improving the surface defects at the tail end of ZYNM7 electroslag ingot involves reducing the current to A3 in the third stage of the power enhancement period, and then gradually increasing it to the maximum current A4. Before this, the slag pool temperature has been raised. By giving a current of 60% to 70% and gradually increasing it from a low power, it is possible to avoid excessive power in the initial stage of remelting, which would lead to a large instantaneous melting rate and prevent insufficient heat supply from the slag resistance, which would cause difficulties in forming the ingot tail.

[0018] The electroslag process described above for improving the surface defects at the tail end of ZYNM7 electroslag ingots maintains a constant voltage and fluctuates current throughout the power increase period, keeping a single variable during operation. This facilitates operation and allows for better control of the electrode insertion depth into the slag pool. Detailed Implementation

[0019] Example 1: An electroslag process for improving surface defects at the tail end of ZYNM7 electroslag ingots. Ingot specifications: 2.8 tons, crystallizer: Φ580 / 620mm, slag quantity: 120kg, consumable electrode specification: Φ400mm continuous casting billet. The chemical composition of the steel is: C ≤0.05%, Si≤1.00%, Mn 16.00%~22.00%, Cr16.50~20.00%, Ni ≤4.00%, Mo ≤2.20%, N≥0.45%, S≤0.015%, P≤0.035%. The chemical composition and weight percentage of the electroslag system are: CaF2 70%, Al2O3 13%, CaO 13%, SiO2 2%, MgO 2%. It is baked and kept warm in a baking furnace before use.

[0020] The specific smelting steps are as follows:

[0021] Step 1) The arc-initiating agent is a block of self-consumable electrode body, and the slag is initiated by a graphite electrode. The slag addition rate is controlled at about 8 kg / min. When adding slag, CaF2 is added first, and after CaF2 is added, Al2O3, CaO and MgO are added alternately and slowly.

[0022] Step 2) After the slag is added, the slag is refined using low voltage and low current. The refining time is controlled at 20-30 minutes, and the voltage and current values ​​during this period are 0.8 times the maximum voltage and current during the normal smelting period.

[0023] Step 3) After the slag has been cleared, add SiO2 and continue refining for 3 minutes, then switch off the power and repeat.

[0024] Step 4) After the self-consuming electrode alternates, the power boost period begins. Throughout the process, the maximum voltage remains constant, and the current varies in four stages. The specific operation is as follows:

[0025] In the first stage, the current A1 is set to 50% of the maximum current and held for 5 minutes;

[0026] In the second stage, the current A2 is set to 85% of the maximum current and held for 5 minutes;

[0027] In the third stage, the current A3 is set to 65% of the maximum current, and then gradually increased to the maximum current A4.

[0028] The current-increasing rate is 100A / min;

[0029] In the fourth stage, the current is maintained at the maximum current A4 until the actual melting rate reaches the process-set melting rate, after which the normal smelting period begins. The process-set melting rate during the normal smelting period is v = 7.5 kg / min.

[0030] The process described in this invention is used to produce ZYNM7 electroslag ingots. After the ingots are removed from the mold, they are visually inspected and the tail end of the ingots is well formed. Compared with the traditional process for producing ZYNM7 electroslag ingots, the surface is smooth and there are no defects such as slag grooves or slag scars. This effectively reduces the amount of finishing work for the electroslag ingots, improves production efficiency, and ensures the delivery cycle.

Claims

1. An electroslag process for improving surface defects at the tail end of a ZYNM7 electroslag ingot, characterized by: The chemical composition of the steel is: C≤0.05%, Si≤1.00%, Mn 16.00%-22.00%, Cr 16.50-20.00%, Ni≤4.00%, Mo≤2.20%, N≥0.45%, S≤0.015%, P≤0.035%, the chemical composition of the electroslag slag system and its weight percentage are: CaF2 70%-75%, Al2O3 10%-14%, CaO 10%-14%, SiO2 1%-3%, MgO 1%-2%, and the slag is baked in an oven before use to reduce the moisture in the slag; the specific process is as follows: Step 1), the arc starting agent adopts a consumable electrode body cutting block sample, the slag melting adopts a graphite electrode arc starting, and the slag adding speed is controlled to be 6 kg / min-10 kg / min according to the different specifications of the crystallizer; when the slag is added, CaF2 is first added, and after the addition of CaF2 is completed, Al2O3, CaO and MgO are alternately and slowly added; Step 2), after the addition of the slag is completed, the slag is refined by using a low voltage and a low current, the refining period time is controlled to be 20 min-30 min, during which the voltage value is 0.6 times-0.8 times of the maximum voltage in the normal smelting period, and the current value is 0.6 times-0.8 times of the maximum current in the normal smelting period; Step 3), after the slag is melted and cleared, SiO2 is added, and the refining is continued for 2 min-5 min, and then the power is turned off alternately; Step 4), after the graphite electrode is replaced by the consumable electrode, the power boosting period is entered, the power boosting period is the whole process of keeping the maximum voltage unchanged, and the current is changed and adjusted in four stages, and the specific operation is as follows: In the first stage, the current A1 is set to 40%-50% of the maximum current, and is kept for 5 min-8 min; in the second stage, the current A2 is set to 80%-90% of the maximum current, and is kept for 5 min-8 min; in the third stage, the current A3 is set to 60%-70% of the maximum current, and gradually increases from A3 to the maximum current A4, and the current increasing rate is 100 A / min; in the fourth stage, the current is kept at the maximum current A4 until the actual melting rate reaches the process setting melting rate, and then enters the normal smelting period; the process setting melting rate v=(0.0125-0.015)×D, the unit of the melting rate is kg / min, and the unit of the crystallizer diameter D is mm.