A production process for controlling the oxygen and nitrogen content of 15B36Cr

Abstract

The application discloses a production process for controlling the oxygen and nitrogen content of 15B36Cr, and belongs to the technical field of steel preparation. The application controls the S content of molten iron in a furnace to be less than or equal to 0.02%, controls the terminal point of an electric furnace, protects casting in the whole continuous casting process and the like, and controls the whole process, so that the [O] in the molten steel is less than or equal to 15 ppm, the N is less than or equal to 60 ppm, the B content yield is improved, the inclusion actual level can reach B class less than or equal to 1 level, C class 0 level, D class less than or equal to 1 level, the maximum inclusion size DS is less than or equal to 1 level, the service performance of the steel is improved, and the technical problems of unstable oxygen and nitrogen content control and easy overproof in the prior production process are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel production, and particularly relates to a production process for controlling oxygen and nitrogen contents of 15B36Cr. BACKGROUND

[0002] 15B36Cr can be used to produce various engineering machines such as track plates, connecting pieces and link shafts of Volvo excavators and bulldozers due to its good toughness, hardenability and certain wear resistance. From the perspective of use, high oxygen content may lead to large size and large number of inclusions, thus causing fatigue failure. Therefore, oxygen content and inclusion control are very important for the steel used for excavator parts. When the oxygen content in the steel is high, the non-metallic inclusions in the steel are more. In addition, since 15B36Cr steel needs to ensure its hardenability, boron needs to be added. High oxygen and nitrogen contents will react with B to form B2O3 and BN, etc. The nitrogen content needs to be controlled during smelting to reduce the production of BN inclusions. In addition, too much nitrogen will combine with aluminum and titanium elements in the molten steel to form brittle inclusions with certain edges, thus reducing the toughness and plasticity of the material. Therefore, it is of great significance to control the oxygen and nitrogen contents in the steel.

[0003] At present, there are relatively few methods for simultaneously controlling oxygen and nitrogen in the prior art. The methods mainly focus on oxygen and nitrogen control processes in the converter smelting process, and rarely involve the whole process. If control is only performed from a certain production link, the gas content in the molten steel will increase. Therefore, it is an urgent problem to be solved to develop a production process for effectively controlling the oxygen and nitrogen contents in multiple production links to reduce the oxygen and nitrogen contents of 15B36Cr and improve the performance of the product. SUMMARY

[0004] In view of this, the purpose of the present application is to provide a production process for controlling the oxygen and nitrogen contents of 15B36Cr. The present application controls the [O] and N contents in the molten steel to be ≤15ppm and ≤60ppm respectively by controlling the S content of the molten iron charged into the furnace, the end-point carbon control of the electric furnace, the slag basicity control of the LF, the RH Ca treatment prohibition, the whole-process protection casting of continuous casting and other measures without increasing new processes and equipment. The B content yield is improved, the inclusion physical level can reach B class ≤1 level, C class 0 level and D class ≤1 level, the maximum inclusion size DS is ≤1 level, the performance of the steel is improved, and the technical problems such as unstable oxygen and nitrogen content control and easy over-standard of the existing production process are solved.

[0005] In order to achieve the above-mentioned purposes, the present application provides the following technical scheme:

[0006] The present application provides a production process for controlling the oxygen and nitrogen contents of 15B36Cr, mainly including the following steps:

[0007] (1) Smelting: Oxygen oxidation, foam slag, pre-deoxidation, alloying, end point carbon content 0.05wt% to 0.15wt%, tapping conditions: P ≤ 0.013%, tapping temperature 1610-1630℃, tapping time controlled at 3-5min;

[0008] (2) LF furnace refining: LF refining process produces white slag, white slag time ≥ 20 min, argon blowing and stirring at the bottom of the ladle, argon pressure 0.2 MPa ~ 0.4 MPa, static argon blowing time ≥ 15 min, LF furnace off-station temperature 1630 ° C ~ 1635 ° C, steelmaking slag basicity: quaternary slag basicity CaO + MgO / (SiO2 + Al2O3) ≥ 4, LF refining time 70 ~ 90 min;

[0009] (3) RH refining: RH temperature is 1620-1630℃, vacuum degree is below 67Pa, holding time is ≥15min, "soft argon blowing" stirring time is ≥20min, soft blowing should be done with slight movement of slag surface and no exposure of molten steel to prevent secondary oxidation, chemical composition should meet target requirements, and ladle temperature should be controlled at 1565-1575℃;

[0010] (4) Continuous casting: The temperature of the first furnace of the ladle platform is 1565-1575℃, the temperature of the tundish is 1515-1520℃, the casting speed is 0.8-1.2m / min, and the water flow rate of the crystallizer is 120-160M 3 / h, full-process protective casting, high-carbon steel protective slag is used for the crystallizer protection slag; the superheat of the molten steel is controlled at 15-25℃, the argon flow rate for the long shroud protection casting is 20-40L / min, and the liquid level in the tundish moves slightly and the molten steel surface is not exposed; the remaining steel volume in the tundish is ≥3.5 tons; the remaining steel volume in the tail furnace is ≥10 tons;

[0011] (5) Heating: adopt three-stage heating, preheating temperature <600℃, 85-87min, 2nd stage heating temperature 850-870℃, 158-161min, 1st stage heating temperature 1210-1240℃, 169-172min, soaking temperature 1210-1230℃, 116-119min, furnace discharge temperature 1180-1210℃;

[0012] (6) Rolling: starting rolling temperature 1100℃~1200℃, finishing rolling temperature 850℃~1100℃.

[0013] Based on the above technical solution, further, the smelting process in step (1) is carried out in an ECOARC ecological electric furnace, using scrap steel and molten iron as furnace charge, with the scrap steel ratio being 0-60% and the molten iron ratio being ≥40%.

[0014] Based on the above technical solution, further, in step (1), the oxygen flow rate is 1000~5000Nm 3 / h.

[0015] Based on the above technical scheme, further, in step (1), the graphite pressure ball 10-30 kg / t is added after sending electricity, and 20-40 kg / t of lime, 10-30 kg / t of dolomite and 1-10 kg / t of ladle ash are added after the graphite pressure ball is added.

[0016] Based on the above technical scheme, further, in step (1), the pre-deoxidizer aluminum iron 2.0-3.0 kg / t is added during pre-deoxidation; the C-increasing agent and the alloy are sequentially added when 1 / 5-1 / 3 of the steel is tapped, and the alloy includes 15-20 kg / t of high-carbon ferromanganese and 1-3 kg / t of high-carbon ferrochrome.

[0017] Based on the above technical scheme, further, in step (2), 3-7 kg / t of lime, 1-2 kg / t of alumina ball, 1-2 kg / t of SiC, 0.3-0.7 kg / t of ferrosilicon, 2-4 kg / t of high-carbon ferromanganese and 0.5-1.5 kg / t of high-carbon ferrochrome are added during the white slag making process.

[0018] Based on the above technical scheme, further, in step (2), the feeding of silicon-calcium wire is strictly prohibited during the LF refining process to prevent the generation of large particle inclusions.

[0019] Based on the above technical scheme, further, in step (3), the hydrogen is determined after vacuum, and the hydrogen content is not more than 1.2 ppm.

[0020] Based on the above technical scheme, further, in step (3), no alloy and carbon-increasing agent is added during the RH process, and the feeding of calcium wire is strictly prohibited during the RH process.

[0021] Based on the above technical scheme, further, in step (4), the electromagnetic stirring current of the crystallizer is 300-360 A, the frequency is 1-3 Hz, the end electromagnetic stirring current is 380-420 A, the frequency is 5-9 Hz, and the stirring mode is 10s-3s-10s alternation.

[0022] Based on the above technical scheme, further, in step (5), the billet is descaled by high-pressure water after leaving the heating furnace, and the descaling pressure is 20-30 MPa.

[0023] The present application has the following beneficial effects compared with the prior art:

[0024] The present invention adopts a production process of electric furnace smelting, LF refining, and billet continuous casting. By controlling the S content of molten iron entering the furnace, controlling the electric furnace endpoint (increasing the endpoint carbon content and reducing the hazard of excessively high oxygen content in low-carbon steel electric furnace tapping during later treatment), improving the basicity of quaternary slag in LF and increasing the LF tapping temperature, it is ensured that favorable deoxidation is achieved in this stage. At the same time, part of the high-basicity slag is melted to reduce nitrogen increase. RH is strictly prohibited from calcium wire feeding to prevent nitrogen increase. Continuous casting is protected throughout the casting process to prevent secondary oxidation of the ladle flow and the tundish flow. Through the above series of measures, the entire process is controlled, the oxygen and nitrogen contents in the molten steel are reduced, the B content yield is increased, the size and quantity of steel inclusions are reduced, the service performance of the steel is improved, and the technical problems of unstable control of oxygen and nitrogen content and easy exceeding of the standard in the existing production process are solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0026] Figure 1 This is a micrograph of 15B36Cr prepared in Example 1.

[0027] Figure 2 This is the inclusion map of 15B36Cr prepared in Example 1. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative work all fall within the scope of protection of the present invention.

[0029] Example 1

[0030] This embodiment provides a production process for controlling the oxygen and nitrogen content of 15B36Cr. The chemical composition and mass percentage of 15B36Cr are shown in Table 1.

[0031] Table 1. Chemical composition and mass percentage of 15B36Cr

[0032]

[0033] The specific process is as follows:

[0034] (1) ECOARC ecological electric furnace smelting: scrap steel and molten iron are used as furnace charge, with scrap steel ratio of 60%, molten iron ratio of 40%, and S content in molten iron ≤0.02%. In the electric furnace smelting process, three-phase electrodes are used for heating. 18.18 kg / t of graphite pellets are added in the second minute of power supply (after the fifth car of material is loaded into this furnace). After the graphite pellets are added, 34 kg / t of lime, 24 kg / t of dolomite, and 5.45 kg / t of ladle ash are added; the oxygen lance is started to enter the furnace door, with a flow rate of 4000 Nm 3 / h, oxygen oxidation, to create foamy slag, and adding 2.83kg / t of pre-deoxidizer (aluminum iron) during pre-deoxidation; during the alloying process, a carbon-enhancing agent (1kg / t, with a carbon content of more than 98.5%) and alloying materials (16.6kg / t of high-carbon ferromanganese with a manganese content of 65% and 1.92kg / t of high-carbon ferrochrome with a chromium content of 50%) are added in sequence when 1 / 4 of the steel is tapped. The final carbon content of the electric furnace is 0.10wt%, and the tapping temperature is 1610°C. The final carbon content and temperature are guaranteed to be hit in one go. The tapping conditions are: P ≤ 0.013%, residual elements meet the requirements, and the tapping time is controlled within 3 minutes.

[0035] (2) LF furnace: adopts submerged arc heating, arc light does not leak out, shortens electrode heating time, adds 3.63kg / t lime, 1.36kg / t alumina balls, 1.18kg / t SiC, and adds 0.5kg / t ferrosilicon, 2.63kg / t high carbon ferromanganese and 0.8kg / t high carbon ferrochrome, produces white slag refining, white slag time ≥ 20min, argon blowing and stirring at the bottom of the ladle, argon pressure 0.2MPa~0.4MPa. Finely adjust the molten steel composition and temperature to the target requirements, the temperature fine adjustment target value is 1640℃; static argon blowing time is greater than 15min, LF furnace off-station temperature is 1630℃~1635℃, steelmaking slag basicity: quaternary slag basicity CaO+MgO / (SiO2+Al2O3) ≥ 4, LF refining time is 70~90min;

[0036] (3) RH refining: RH entry temperature is 1625°C, vacuum is maintained below 67 Pa for 20 minutes; hydrogen is determined after vacuuming, and the hydrogen content is set at 1.1ppm. The "soft argon blowing" stirring time is 30 minutes. Soft blowing is preferably performed with slight movement of the slag surface and no exposure of the molten steel to prevent secondary oxidation. The chemical composition meets the target requirements; the ladle temperature is controlled at 1570°C. No alloy or recarburizer is added during the RH process. Feeding calcium wire is strictly prohibited during the RH process.

[0037] (4) Continuous casting: The temperature of the first furnace of the ladle platform is 1565℃, the temperature of the tundish is 1515℃, the casting speed is 1m / min, and the water flow rate of the crystallizer is 140M 3 / h, mold electromagnetic stirring current 350A, frequency 2Hz, end-stage electromagnetic stirring current 400A, frequency 7Hz. Stirring method: alternating (10s-3s-10s); strictly implement protective casting throughout the entire process, using high-carbon steel mold slag. Molten steel superheat is controlled at 20°C, and the argon flow rate for protective casting in the long shroud of the large ladle is 20-40L / min, with the tundish liquid level moving slightly but not revealing the molten steel surface. Steel remaining in the large ladle: 3.5 tons. Steel remaining in the tundish: 10 tons in the tail furnace.

[0038] (5) Heating: adopt three-stage heating, preheating temperature <600℃, 85-87min, 2nd stage heating temperature 850-870℃, 158-161min, 1st stage heating temperature 1210-1240℃, 169-172min, soaking temperature 1210-1230℃, 116-119min, furnace discharge temperature 1180-1210℃;

[0039] (6) Rolling process: After the steel billet leaves the heating furnace, it must be descaled with high-pressure water before rolling. The descaling pressure is 25 MPa, the starting rolling temperature is 1100℃~1200℃, and the final rolling temperature is 850℃~1000℃.

[0040] (7) Finished product inspection

[0041] Table 2. Inclusion ratings in billets

[0042] Gauge A (coarse) A (fine) B (coarse) B (fine) C (coarse) C (fine) D (coarse) D (fine) (DS) 210 mm x 210 mm 0.5 0 0 0 0 0 0 0 0 210 mm x 210 mm 1.0 0.5 0.5 0.5 0 0 0 0 0

[0043] Table 3. Inclusion ratings of 15B36Cr steel after rolling

[0044]

[0045] Table 4. Macrostructure of 15B36Cr after rolling

[0046] Grade General porosity Central porosity Sizing segregation 15B36Cr 0.5 1 0.5

[0047] Table 5. End hardenability of 15B36Cr after rolling

[0048] Grade J1.5 / HRC J20 / HRC 15B36Cr 53～59 46～52

[0049] Table 6. Macro-rating of 15B36Cr after rolling

[0050] Grade Equiaxed crystal ratio Central porosity Central segregation Corner crack Subcutaneous crack Shrinkage hole 15B36Cr 33.95 Class 0 Class 0 Class 0 Class 0 Class 0

[0051] Example 2

[0052] This embodiment provides a production process for controlling the oxygen and nitrogen content of 15B36Cr. The chemical composition and mass percentage of 15B36Cr are shown in Table 1. The specific process is as follows:

[0053] (1) ECOARC ecological electric furnace smelting: scrap steel and molten iron are used as furnace charge, with scrap steel ratio of 50%, molten iron ratio of 50%, and S content in molten iron of ≤0.02%. In the electric furnace smelting process, three-phase electrodes are used for heating. 25.20 kg / t of graphite pellets are added in the second minute of power supply (after the fifth car of material is loaded into this furnace). After the graphite pellets are added, 38 kg / t of lime, 30 kg / t of dolomite, and 6.30 kg / t of ladle ash are added; the oxygen lance is started to enter the furnace door with a flow rate of 4000 Nm 3 / h, oxygen oxidation, to create foamy slag, and adding 2.95kg / t of pre-deoxidizer (aluminum iron) during pre-deoxidation. During the alloying process, a carbon-enhancing agent (1.2kg / t, with a carbon content of more than 98.5%) and alloying materials (18.9kg / t of high-carbon ferromanganese with a manganese content of 65% and 2.30kg / t of high-carbon ferrochrome with a chromium content of 50%) were added in sequence when 1 / 3 of the steel was tapped. The final carbon content of the electric furnace was 0.12wt%, and the tapping temperature was 1630°C. The final carbon content and temperature were guaranteed to be hit in one go. The tapping conditions were: P ≤ 0.013%, residual elements met the requirements, and the tapping time was controlled within 4 minutes.

[0054] (2) LF furnace: adopts submerged arc heating, arc light does not leak out, shortens electrode heating time, adds 4.80kg / t lime, 1.85kg / t alumina balls, 1.90kg / t SiC, and adds 0.6kg / t ferrosilicon, 2.98kg / t high carbon ferromanganese and 1.0kg / t high carbon ferrochrome, produces white slag refining, white slag time ≥ 20min, argon blowing and stirring at the bottom of the ladle, argon pressure 0.2MPa~0.4MPa. Finely adjust the molten steel composition and temperature to the target requirements, the temperature fine adjustment target value is 1640℃; static argon blowing time is greater than 15min, LF furnace leaving station temperature is 1630℃~1635℃, steelmaking slag basicity: quaternary slag basicity CaO+MgO / (SiO2+Al2O3) ≥ 4, LF refining time is 70~90min;

[0055] (3) RH refining: RH entry temperature is 1630°C, vacuum is maintained below 67 Pa for 20 minutes; hydrogen is determined after vacuuming to a hydrogen content of 1.0 ppm, and the "soft argon blowing" stirring time is 30 minutes. Soft blowing is preferably performed with slight movement of the slag surface and no exposure of the molten steel to prevent secondary oxidation, and the chemical composition meets the target requirements; the ladle temperature is controlled at 1575°C, and no alloy or recarburizer is added during the RH process. Calcium wire feeding is strictly prohibited during the RH process.

[0056] (4) Continuous casting: The temperature of the first furnace on the ladle platform is 1565℃, the temperature of the tundish is 1520℃, the casting speed is 1m / min, and the water flow rate of the crystallizer is 130M 3 / h, crystallizer electromagnetic stirring current 350 A, frequency 2 Hz, end electromagnetic stirring current 400 A, frequency 7 Hz. Stirring mode: alternating (10 s-3 s-10 s); strictly implement the whole process protection casting, crystallizer protective slag uses high carbon steel protective slag. The liquid steel superheat is controlled at 25℃, the ladle long nozzle protection casting argon flow is 20-40 L / min, the ladle liquid surface is slightly moved, and the liquid surface is not exposed. The ladle residual steel amount is 3.5 tons. The tundish residual steel amount is 10 tons.

[0057] (5) Heating: three-stage heating is adopted, preheating temperature < 600℃, 85-87 min, 2-stage heating temperature 850-870℃, 158-161 min, 1-stage heating temperature 1210-1240℃, 169-172 min, soaking temperature 1210-1230℃, 116-119 min, and discharge temperature 1180-1210℃;

[0058] (6) Rolling process: the billet must be rolled after high-pressure water descaling, descaling pressure 25 MPa, opening rolling temperature 1100-1200℃, and finishing rolling temperature 850-1000℃.

[0059] (7) Finished product inspection

[0060] Table 7. Inclusion rating of middle billet

[0061] Gauge A (coarse) A (fine) B (coarse) B (fine) C (coarse) C (fine) D (coarse) D (fine) (DS) 390 mm x 480 mm 0.0 0.5 0 0.5 0 0 0 0 0

[0062] Table 8. Inclusion rating of 15B36Cr steel after rolling

[0063]

[0064] Table 9. End quenching property of 15B36Cr after rolling

[0065] Grade J1.5 / HRC J20 / HRC 15B36Cr 49～55 41～46

[0066] Table 10. Macroscopic rating of 15B36Cr after rolling

[0067] Grade Equiaxed crystal ratio Central porosity Central segregation Corner crack Subcutaneous crack Shrinkage hole 15B36Cr 31.75 Class 0 Class 0 Class 0 Class 0 Class 0

[0068] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A production process for controlling the oxygen and nitrogen content of 15B36Cr, characterized in that: The following steps are involved: (1) Smelting: Oxygen oxidation, foam slag, pre-deoxidation, alloying, end point carbon content 0.05wt%~0.15wt%, tapping conditions: P≤0.013%, tapping temperature 1610-1630℃, tapping time controlled at 3~5min; (2) LF furnace refining: LF refining process produces white slag, white slag time ≥ 20min, argon blowing and stirring at the bottom of the ladle, argon pressure 0.2MPa~0.4MPa, static argon blowing time ≥ 15min, LF furnace off-station temperature 1630℃~1635℃, steelmaking slag basicity: quaternary slag basicity CaO+MgO / (SiO2+Al2O3) ≥ 4, LF refining time 70~90min; (3) RH refining: RH temperature is 1620~1630℃, vacuum degree is below 67Pa, holding time is ≥15min, "soft argon blowing" stirring time is ≥20min, soft blowing should be done with slight movement of slag surface and no exposure of molten steel, hanging ladle temperature is controlled at 1565~1575℃, and calcium wire feeding is strictly prohibited during RH process; (4) Continuous casting: The temperature of the first furnace on the ladle platform is 1565~1575℃, the temperature of the tundish is 1515~1520℃, the casting speed is 0.8~1.2m / min, and the water flow rate of the crystallizer is 120~160m 3 / h, full process protection casting, molten steel superheat is controlled at 15~25℃, the argon flow rate for large ladle long nozzle protection casting is based on the tundish liquid level moving slightly and not exposing the molten steel surface; (5) Heating: adopt three-stage heating, preheating temperature <600℃, 80~90 min, 2nd stage heating temperature 850~870℃, 150~170 min, 1st stage heating temperature 1210~1240℃, 160~180 min, soaking temperature 1210~1230℃, 110~130 min, furnace discharge temperature 1180~1210℃; (6) Rolling: starting rolling temperature 1100℃~1200℃, finishing rolling temperature 850℃~1100℃; In step (1), a three-phase electrode is used to heat the battery. After power is supplied, 10-30 kg / t of graphite pellets are added. After the graphite pellets are added, 20-40 kg / t of lime, 10-30 kg / t of dolomite, and 1-10 kg / t of ladle ash are added. In step (1), 2.0-3.0 kg / t of pre-deoxidizing agent aluminum iron is added during pre-deoxidation; when 1 / 5-1 / 3 of the steel is tapped, a C-increasing agent and alloy material are added in sequence, wherein the alloy material includes 15-20 kg / t of high carbon ferromanganese and 1-3 kg / t of high carbon ferrochromium; In step (2), it is strictly forbidden to feed calcium silicon wire during the LF refining process to prevent the generation of large particle inclusions; In step (4), the crystallizer electromagnetic stirring current is 300~360A, the frequency is 1~3Hz, the end electromagnetic stirring current is 380~420A, the frequency is 5~9Hz, and the stirring mode is: 10s-3s-10s alternating; In step (1), the smelting process is carried out in an ECOARC ecological electric furnace, using scrap steel and molten iron as furnace charge, with the scrap steel ratio being 0-60%, the molten iron ratio being ≥40%, and the sulfur content in the molten iron being ≤0.02%.

2. The production process according to claim 1, characterized in that The oxygen flow rate in step (1) is 1000~5000Nm 3 / h.

3. The production process according to claim 1, characterized in that During the white slag production process in step (2), 3-7 kg / t lime, 1-2 kg / t alumina balls, 1-2 kg / t SiC, 0.3-0.7 kg / t ferrosilicon, 2-4 kg / t high carbon ferromanganese and 0.5-1.5 kg / t high carbon ferrochrome are added.

4. The production process according to claim 1, characterized in that In step (3), the hydrogen content is determined after vacuum, and the determined hydrogen content does not exceed 1.2 ppm.

5. The production process according to claim 1, characterized in that: In step (5), the steel billet is descaled by high-pressure water after leaving the heating furnace, and the descaling pressure is 20~30MPa.

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