Method for detecting thickness of nodulation layer on inner wall of submersed nozzle for smelting rare earth steel

Abstract

The invention discloses a method for detecting the thickness of a nodulation layer on the inner wall of a submersed nozzle for smelting rare earth steel, and belongs to the technical field of ferrous metallurgy. The method comprises the following steps: (1) a process route: blast furnace molten iron, molten iron pretreatment, converter top and bottom combined blowing smelting, LF (ladle furnace) external refining, VD (vacuum degassing) vacuum treatment, beam blank continuous casting and slow cooling; (2) in order to guarantee the yield of rare earth elements, rare earth alloy is added after VD vacuum breaking, LF dislocation S is smaller than or equal to 0.008%, and [O] is strictly controlled to be smaller than or equal to 20 ppm; (3) the liquidus temperature TL is 1514 DEG C; (4) the slow cooling time is larger than or equal to 24 h after the casting blank is offline; (5) the finish rolling temperature is controlled at 880-930 DEG C; (6) sampling and processing the water gap of the casting machine for smelting the heat; and 7) detecting the water inlet sample by using a scanning electron microscope. Detection and analysis are carried out through field production sampling, the thickness of the nodulation layer is obtained, and a reference is provided for smelting rare earth steel to produce nozzle inner wall nodulation.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a method for detecting the thickness of a nodule layer on the inner wall of an immersion nozzle for smelting rare earth steel. Background Art

[0002] With the development of society and the economy, market competition in the steel industry has become increasingly fierce, and people have increasingly diverse requirements for the performance of steel materials. Steel research and development has promoted the rapid development of China's steel industry and the continuous advancement of steelmaking technology. Rare earth steel is a new process technology that incorporates rare earth elements into steel to enhance its overall performance. Rare earth elements can improve steel's strength, toughness, corrosion resistance, and weldability. Therefore, the development and application of rare earth steel is of great significance. However, the addition of rare earth elements during the steelmaking process can cause nodules to form on the inner wall of the nozzle, leading to instability in the casting process of the casting machine. In more serious cases, the nozzle can become blocked, causing the casting machine to stop casting, disrupting normal production and causing considerable financial losses. Therefore, studying the nodules formed on the inner wall of the rare earth steel is of vital importance.

[0003] Chinese patent application number 201910205858.4 discloses a method for applying like charges to suppress nodules on the inner wall of an immersion nozzle. By applying like charges to suppress nodules on the inner wall of an immersion nozzle, a stable forward current is applied to the inner wall of the immersion nozzle, which limits the sintering and adhesion of inclusions on the inner wall of the immersion nozzle, thereby suppressing nodules. The method provided by the present invention for applying like charges to suppress nodules on the inner wall of an immersion nozzle can effectively suppress nodules on the inner wall of the nozzle through the repulsive force of like charges.

[0004] Chinese patent application number 201510589544.0 discloses a method for reducing the speed of nodulation on the inner wall of an aluminum-carbon immersion nozzle. The method comprises: a conductive element is provided in the middle and upper part of the aluminum-carbon immersion nozzle, the conductive element on the aluminum-carbon immersion nozzle is connected to the positive electrode of a pulse power supply via a wire, the negative electrode of the pulse power supply is connected to a stopper rod or a long nozzle via a wire, and a low-density pulse current is applied to the molten steel in the aluminum-carbon immersion nozzle by the pulse power supply. The method of the present invention has a low pulse current density and low energy consumption, avoids accidental harm to operators caused by high voltage and high current, significantly reduces the speed of nodulation on the aluminum-carbon immersion nozzle, has low implementation cost, and is easy to operate.

[0005] The document "Analysis of Causes and Control Measures for Nodule Formation and Blockage in Continuous Casting Immersed Nozzles" discusses the structure and approximate chemical composition of nodules and blockages in immersed nozzles, introduces the various causes of nodules and blockages on the inner wall of nozzles, and summarizes measures to inhibit nodules from four aspects: improving nozzle material and structure, reducing inclusions or modifying inclusions, optimizing local molten steel flow conditions, and applying external fields. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for detecting the thickness of the nodule layer on the inner wall of an immersed nozzle for smelting rare earth steel. When smelting rare earth steel, nodules or blockages often occur on the inner wall of the immersed nozzle. In order to better understand the thickness of the nodule layer on the inner wall of the nozzle when smelting rare earth steel, on-site production sampling is used for detection and analysis to obtain the thickness of the nodule layer, providing a reference for the nodule on the inner wall of the nozzle in the production of rare earth steel.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for detecting the thickness of a nodule layer on the inner wall of an immersion nozzle for smelting rare earth steel, comprising the following steps:

[0009] 1). Process route: blast furnace molten iron - molten iron pretreatment - converter top and bottom blowing smelting - LF refining - VD vacuum treatment - beam blank continuous casting - slow cooling;

[0010] 2) To ensure the recovery rate of rare earth elements, rare earth alloy is added after VD is broken, LF off-site S≤0.008%, and [O] is strictly controlled ≤20ppm;

[0011] 3). Liquidus temperature TL = 1514°C;

[0012] 4). The slow cooling time after the billet comes off the production line is greater than or equal to 24 hours;

[0013] 5). The final rolling temperature is controlled at 880℃-930℃;

[0014] 6). Take samples from the nozzle of the casting machine used to smelt this heat;

[0015] 7). Use a scanning electron microscope to test the water outlet samples.

[0016] Furthermore, after VD is broken, a CeFe alloy with a rare earth content of 30% by mass is added.

[0017] Furthermore, the addition amount of rare earth alloy is 25-35kg / 100t.

[0018] Furthermore, the addition amount of the rare earth alloy is 25 kg / 100 t.

[0019] Furthermore, the addition amount of the rare earth alloy is 30 kg / 100 t.

[0020] Furthermore, the addition amount of the rare earth alloy is 35 kg / 100 t.

[0021] Furthermore, the method is used to understand the thickness of the nodule layer on the inner wall of the nozzle during the smelting of rare earth steel through on-site production sampling and detection analysis, providing a reference for the nodule layer on the inner wall of the nozzle during the smelting of rare earth steel.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] When smelting rare earth steel, adding the rare earth element Ce will cause nozzle nodules, leading to nozzle blockage and affecting smooth casting. The present invention uses sampling, testing and analysis to clarify how thick the nodule layer on the inner wall of the nozzle will be when a certain amount of rare earth element is added when smelting steel containing rare earth elements. This provides a reference for multi-furnace continuous casting and is expected to have good economic and social effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the accompanying drawings.

[0025] Figure 1 This is a picture of the nodule layer on the inner wall of the nozzle without adding rare earth Ce;

[0026] Figure 2 This is a picture of the nodule layer on the inner wall of the nozzle with rare earth Ce added. DETAILED DESCRIPTION

[0027] The steel grade selected in the present invention is Q355D, and the technical solution adopted is:

[0028] 1. Process route: blast furnace molten iron - molten iron pretreatment - converter top and bottom blowing smelting - LF refining - VD vacuum treatment - beam blank continuous casting - slow cooling;

[0029] 2. To ensure the recovery rate of rare earth elements, 30% CeFe alloy (30kg / 100t) is added after VD is broken, LF off-site S≤0.008%, and [O] is strictly controlled to ≤20ppm.

[0030] 3.Liquidus temperature TL = 1514°C.

[0031] 4. The slow cooling time after the ingot comes off the production line is greater than or equal to 24 hours.

[0032] 5. The final rolling temperature is controlled at 880℃-930℃.

[0033] 6. Samples are taken from the casting machine nozzles of the smelting furnaces with added rare earth and blank furnaces respectively.

[0034] 7. Use a scanning electron microscope to test the water outlet samples.

[0035] At the same time, a blank group was set up without adding rare earth elements.

[0036] Scanning electron microscope analysis was performed on two groups of nozzle samples:

[0037] like Figure 1 As shown, there is no nodule layer on the inner wall of the blank nozzle sample from the heat without adding rare earth. EDS scanning shows its composition, which is composed of Al, Mg, Ca, Mn, C, O and other elements.

[0038] like Figure 2 As shown, there is an obvious nodule layer on the inner wall of the nozzle sample of the rare earth addition furnace, and the thickness of the nodule layer is 223um-366um. EDS scanning shows its composition, which is composed of elements such as Al, Mg, Ca, Fe, C, Ce, and O.

[0039] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for detecting the thickness of a nodule layer on the inner wall of an immersion nozzle for smelting rare earth steel, characterized by: The steps include: 1). Process route: blast furnace molten iron - molten iron pretreatment - converter top and bottom blowing smelting - LF refining - VD vacuum treatment - beam blank continuous casting - slow cooling; 2) To ensure the recovery rate of rare earth elements, rare earth alloy is added after VD is broken, LF off-site S≤0.008%, and [O] is strictly controlled ≤20ppm; 3). Liquidus temperature TL = 1514°C; 4). The slow cooling time after the billet comes off the production line is greater than or equal to 24 hours; 5). The final rolling temperature is controlled at 880℃-930℃; 6). Take samples from the nozzle of the casting machine used to smelt this heat; 7). Use a scanning electron microscope to test the water outlet samples.

2. The method for detecting the thickness of the nodule layer on the inner wall of an immersion nozzle for smelting rare earth steel according to claim 1, characterized in that: After VD is broken, CeFe alloy with a rare earth content of 30% by mass is added.

3. The method for detecting the thickness of the nodule layer on the inner wall of an immersion nozzle for smelting rare earth steel according to claim 1, characterized in that: The addition amount of rare earth alloy is 25-35kg / 100t.

4. The method for detecting the thickness of the nodule layer on the inner wall of an immersion nozzle for smelting rare earth steel according to claim 3, characterized in that: The addition amount of rare earth alloy is 25kg / 100t.

5. The method for detecting the thickness of the nodule layer on the inner wall of an immersion nozzle for smelting rare earth steel according to claim 3, characterized in that: The addition amount of rare earth alloy is 30kg / 100t.

6. The method for detecting the thickness of the nodule layer on the inner wall of an immersion nozzle for smelting rare earth steel according to claim 3, characterized in that: The addition amount of rare earth alloy is 35kg / 100t.

7. The method for detecting the thickness of the nodule layer on the inner wall of an immersion nozzle for smelting rare earth steel according to claim 3, characterized in that: This method is used to understand the thickness of the nodule layer on the inner wall of the nozzle during the smelting of rare earth steel through on-site production sampling and analysis, providing a reference for the nodule layer on the inner wall of the nozzle during the smelting of rare earth steel.

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