Method for improving removal rate of inclusions in LF refining process of GCr15 bearing steel

Abstract

The invention discloses a method for improving the removal rate of inclusions in the LF refining process of GCr15 bearing steel, and the method specifically comprises the following steps: S1, after tapping of a GCr15 bearing steel electric furnace, adding alloy and aluminum balls to carry out deoxidation alloying, and adding lime and refining slag to carry out argon blowing operation at the same time; s2, then entering an LF station, supplying power to the LF furnace for heating, continuing slagging, adding refining slag, then carrying out SiC surface deoxidation, and adopting ladle bottom argon blowing stirring in the whole LF refining process; s3, after LF refining is completed, the steel ladle is hoisted to a VD station, soft blowing treatment is conducted after vacuum breaking, and operation is completed. The inclusion removal effect and removal rate of the steel ladle can be improved, so that the cleanliness of molten steel is improved.

Description

Technical Field

[0001] The invention relates to a method for improving the inclusion removal rate in the LF refining process of GCr15 bearing steel, and belongs to the field of metallurgy. Background Art

[0002] Bearing steel is a very important material for manufacturing basic parts of mechanical equipment, and is widely used in military, aerospace, transportation and other fields. With the rapid development of the manufacturing industry, the quality and service life of mechanical equipment have increased significantly, and higher requirements have been put forward for the fatigue life and quality stability of bearing steel. At the end of the 20th century, the development of clean steel smelting technology promoted the improvement of bearing steel quality. The total oxygen content of bearing steel was reduced from 30ppm to 5ppm, and the fatigue life increased by 100 times; with the improvement of metallurgical technology and equipment capabilities, the total oxygen content of bearing steel has been continuously reduced. At present, advanced domestic and foreign companies can stably control it below 5ppm; it is generally believed internationally that when the total oxygen content in bearing steel is less than 5ppm, the sulfur content is less than 20ppm, and the titanium content is less than 10ppm, it reaches the ultra-high purity level.

[0003] Bearing steel is aluminum-deoxidized steel. Common inclusions in the finished steel are alumina, magnesium-aluminum spinel, calcium-magnesium-aluminum composite inclusions, alumina and manganese sulfide composite inclusions, magnesium-aluminum spinel and manganese sulfide composite inclusions, calcium-magnesium-aluminum and manganese sulfide composite inclusions, manganese sulfide, titanium nitride, etc. When the sulfur content in the molten steel is high, a large amount of manganese sulfide inclusions will be formed. A large amount of manganese sulfide inclusions will precipitate out of the molten steel during the cooling process. These inclusions will compound with the inclusions formed at the steelmaking temperature to form new inclusions. These inclusions will deteriorate the cleanliness of the molten steel. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the inclusion removal rate in the LF refining process of GCr15 bearing steel in view of the shortcomings of the above prior art, which can improve the inclusion removal effect and removal rate, thereby improving the cleanliness of molten steel.

[0005] The technical solution of the present invention to solve the above technical problems is: a method for improving the inclusion removal rate in the LF refining process of GCr15 bearing steel, which specifically comprises the following steps: S1: After tapping the electric furnace, GCr15 bearing steel is deoxidized and alloyed by adding alloy and aluminum balls, and at the same time lime and refined slag are added for argon blowing; S2: Then enter the LF station, the LF furnace is powered on to increase temperature and continue slagging and adding refined slag, and then the SiC surface is deoxidized. During the LF refining process, argon blowing and stirring are used at the bottom of the ladle; S3: After LF refining is completed, the ladle is hoisted to the VD station, and soft blowing is performed after breaking the air to complete the operation.

[0006] The present invention further defines the technical solution: Preferably, the GCr15 bearing steel in s1 comprises the following components by mass percentage: C: 0.95-1.05; Si: 0.15-0.35; Mn: 0.25-0.45; P≦0.020; S≦0.012; Cr1.40-1.60; Alt≦0.050, and the balance is Fe and unavoidable impurities.

[0007] Preferably, the amount of lime added in S1 is 300kg-400kg, and the CaO content in the lime exceeds 90%.

[0008] Preferably, the refined slag in S1 is pre-melted slag, the addition amount of which is 700kg-900kg, and the composition ratio is CaO: 45-55%, Al2O3: 40-50%, and other components are <5%.

[0009] Preferably, during the LF refining process in the S3, SiO2 originates from the deoxidation of SiC in the refining process and is transferred to the slag by the steel slag reaction, and MgO originates from the erosion of refractory materials out of the slag line. The composition of the refined slag is adjusted and the alloy is added to fine-tune the composition of the molten steel. The adjusted composition range is: CaO: 40-55%, SiO2: 7-14%, Al2O3: 28-38%, MgO: 1-8%.

[0010] Preferably, the duration of argon blowing and stirring at the bottom of the ladle in S3 is 60 min-70 min.

[0011] The beneficial effects of the present invention are as follows: the present invention adjusts the refining slag component ratio and inclusion removal rate to 35%-65% during the LF refining process, and the number of inclusions is ≯0.4-28 pieces / mm2, thereby effectively improving the purity of molten steel, reducing the influence of inclusions such as calcium aluminate and spinel on the fatigue life of GCr15 bearing steel, and providing a guarantee for avoiding failure of aluminum deoxidized bearing steel during service. DETAILED DESCRIPTION Example

[0012] This embodiment provides a method for improving the inclusion removal rate in the LF refining process of GCr15 bearing steel, which specifically includes the following steps: S1: After GCr15 bearing steel is tapped from an electric furnace, alloy and aluminum balls are added for deoxidation and alloying. At the same time, lime and refined slag are added for argon blowing. The amount of lime added is 300kg-400kg, and the CaO content in the lime exceeds 90%. The refined slag is pre-melted slag, and the amount added is 700kg-900kg. The composition ratio is CaO: 45-55%, Al2O3: 40-50%, and other components are <5%. The above GCr15 bearing steel includes the following components by mass percentage: C: 0.95-1.05; Si: 0.15-0.35; Mn: 0.25-0.45; P≦0.020; S≦0.012; Cr1.40-1.60; Alt≦0.050, and the balance is Fe and unavoidable impurities; S2: Then enter the LF station, the LF furnace is powered on to increase temperature and continue slag making, the slag system ratio and SiC addition amount are adjusted according to calculation, and then the SiC surface is deoxidized. During the LF refining process, argon blowing and stirring are adopted at the bottom of the ladle, and the duration of argon blowing and stirring at the bottom of the ladle is 60min-70min; S3: During LF refining, SiO2 originates from the deoxidation of SiC in the refining process and is transferred to the slag by the steel slag reaction. MgO originates from the erosion of the refractory material at the slag line. The composition of the refined slag is adjusted and the composition of the molten steel is fine-tuned by adding alloys. The adjusted composition range is: CaO: 40-55%, SiO2: 7-14%, Al2O3: 28-38%, MgO: 1-8%. After LF refining is completed, the ladle is hoisted to the VD station, and soft blowing is carried out after breaking the air to complete the operation.

[0013] Case 1: A 100-ton LF refining furnace in a certain factory adopts the present invention, and conducts GCr15 bearing steel tests. The molten steel is sampled for inclusion scanning and composition detection. The results are characterized by the number, size, composition, type, etc. of inclusions. Taking 40mm2 scanning area as the standard, the inclusions contain nearly circular pure Al2O3, circular CaO-MgO-Al2O3, irregular MgO-Al2O3, Al2O3-MnS composite inclusions, CaO-MgO-Al2O3-MnS composite inclusions, MgO-Al2O3-MnS composite inclusions, etc. The number density of inclusions is about 0.4-40 pieces / mm2. When LF is switched, the total oxygen content is about 10-40ppm, the S content is about 10-40ppm, and the inclusion removal rate before and after LF refining is about 40%.

[0014] Case 2: A 100-ton LF refining furnace of a certain factory adopts the present invention, and carries out GCr15 bearing steel test, samples the molten steel for inclusion scanning and composition detection, and characterizes the results by the number, size, composition, type, etc. of inclusions. Taking 40mm2 scanning area as the standard, the inclusions contain nearly circular pure Al2O3, circular CaO-MgO-Al2O3, irregular MgO-Al2O3, Al2O3-MnS composite inclusions, CaO-MgO-Al2O3-MnS composite inclusions, MgO-Al2O3-MnS composite inclusions, etc. The number density of inclusions is about 0.4-28 pieces / mm2. When LF is switched, the total oxygen content is about 10-20ppm, and the S content is about 5-25ppm. The inclusion removal rate before and after LF refining is greatly improved to 62%.

[0015] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A method for improving the inclusion removal rate in the LF refining process of GCr15 bearing steel, characterized in that: The specific steps include: S1: After tapping the electric furnace, GCr15 bearing steel is deoxidized and alloyed by adding alloy and aluminum balls, and at the same time lime and refined slag are added for argon blowing; S2: Then enter the LF station, the LF furnace is powered on to increase temperature and continue slagging and adding refined slag, and then the SiC surface is deoxidized. During the LF refining process, argon blowing and stirring are used at the bottom of the ladle; S3: After LF refining is completed, the ladle is hoisted to the VD station, and soft blowing is performed after breaking the air to complete the operation.

2. The method for improving the inclusion removal rate in the LF refining process of GCr15 bearing steel according to claim 1, characterized in that: The GCr15 bearing steel in s1 includes the following components by mass percentage: C：0.95-1.05； Si: 0.15-0.35; Mn: 0.25-0.45; P≦0.020; S≦0.012; Cr1.40-1.60; Alt≦0.050, the balance is Fe and inevitable impurities.

3. The method for improving the inclusion removal rate in the LF refining process of GCr15 bearing steel according to claim 1, characterized in that: The amount of lime added in S1 is 300kg-400kg, and the CaO content in the lime exceeds 90%.

4. The method for improving the inclusion removal rate in the LF refining process of GCr15 bearing steel according to claim 1, characterized in that: The refined slag in S1 is pre-melted slag, the addition amount of which is 700kg-900kg, and the composition ratio is CaO: 45-55%, Al2O3: 40-50%, and other components are <5%.

5. The method for improving the inclusion removal rate in the LF refining process of GCr15 bearing steel according to claim 1, characterized in that: During the LF refining process in the S3, SiO2 originates from the deoxidation of SiC in the refining process and is transferred to the slag by the steel slag reaction. MgO originates from the erosion of the refractory material out of the slag line. The composition of the refined slag is adjusted and the alloy is added to fine-tune the composition of the molten steel. The adjusted composition range is: CaO: 40-55%, SiO2: 7-14%, Al2O3: 28-38%, MgO: 1-8%.

6. A method for improving the inclusion removal rate in the LF refining process of GCr15 bearing steel according to claim 1, characterized in that: The duration of blowing argon and stirring the bottom of the ladle in S3 is 60 min-70 min.