Preparation method of high-quality GCr15 bearing steel

Abstract

The invention discloses a preparation method of high-quality GCr15 bearing steel. The preparation method comprises the steps of molten iron pretreatment, converter smelting, LF refining, VD vacuum treatment, continuous casting and slow cooling in a slow cooling pit. Key performance indexes such as hardness, wear resistance and contact fatigue performance of the GCr15 bearing steel are further improved by means of optimizing component design, improving a heat treatment process and the like. According to the preparation method of the high-quality GCr15 bearing steel, the oxygen content of the bearing steel is lower than 10 ppm, the cleanliness of a product is further improved, and therefore the fatigue performance is improved.

Description

Technical Field

[0001] The invention belongs to the field of metallurgy and rolling technology, and in particular relates to a method for preparing high-quality GCr15 bearing steel. Background Art

[0002] GCR15 bearing steel, also known as GCr15 steel or high carbon chromium bearing steel, is a high carbon chromium bearing steel with less alloy content and the most widely used. GCr15 bearing steel is widely used in machinery manufacturing, automobile manufacturing, aerospace and other fields. For example, it is used to manufacture transmission parts such as bearings, gears, cams, and precision tools such as molds and measuring tools. In the field of automobile manufacturing, it is mainly used to manufacture bearings and gears for key components such as automobile engines and transmissions. In the field of aerospace, it is widely used to manufacture transmission parts and precision instruments for aircraft, rockets and other aircraft due to its excellent mechanical properties and stability. With the continuous advancement of science and technology and the rapid development of industry, the application field of GCr15 bearing steel will continue to expand. In the future, by optimizing composition design, improving heat treatment process and other means, the key performance indicators of GCr15 bearing steel such as hardness, wear resistance and contact fatigue performance can be further improved. At the same time, with the rapid development of emerging fields such as new energy vehicles and intelligent manufacturing, GCr15 bearing steel is expected to play a greater role in these fields. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing high-quality GCr15 bearing steel, so that the oxygen content of the bearing steel is lower than 10ppm, and the cleanliness of the product is further improved, thereby improving fatigue performance.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention discloses a method for preparing high-quality GCr15 bearing steel, comprising molten iron pretreatment → converter smelting → LF refining → VD vacuum treatment → continuous casting → slow cooling in a slow cooling pit; wherein:

[0006] Converter smelting:

[0007] The molten iron must be KR desulfurized, and double slag removal operation is adopted to ensure clean slag removal; clean scrap steel is used to avoid exceeding the requirements of trace elements, and iron-containing materials are added; the total loading amount of molten iron and scrap steel is 165±10 tons, and the scrap steel is adjusted according to the molten iron conditions or iron-steel ratio requirements, the molten iron temperature is ±10℃, the scrap steel addition amount is ±1 ton, the silicon content of molten iron is ±0.1%, and the scrap steel is ±2 tons; the gun position control adopts low-high-low or high-low-high-low control, and the oxygen flow rate is 17000-32000m 3 / h, gun position 1.3-2.0m; it is recommended to use double slag when the silicon content of molten iron is greater than 0.5%, and single slag when the silicon content of molten iron is less than 0.5%, and the end point basicity is controlled according to 2.7-3.5; the control target of the converter end point is: C ≥ 0.10%, T ≥ 1600℃; it is required to pull carbon once, and spot blowing is prohibited; 200-300kg of dolomite thick slag is added before tapping, and double sliding slag is used for tapping, and slag is prohibited; an aluminum deoxidation process is adopted, and 96 aluminum iron, ferrosilicon, silicon manganese, low titanium high carbon ferrochrome, and low nitrogen coke are used for deoxidation and alloying. The specific alloy addition type and addition amount are calculated according to the weight of the molten steel;

[0008] When tapping, strengthen the contact with the tank repairer and perform argon blowing according to regulations; Argon control requirements: large argon stirring in the early stage of tapping, when the tapping amount is greater than 2 / 3, adjust the argon flow rate to perform slag blocking operation to ensure that the alloy does not clump and the top slag material is well melted, and the end point adopts double sliding slag blocking with slide plates to prevent slag from falling, add 500kg synthetic slag during the tapping process, and add 500kg synthetic slag at the end of tapping; Temperature requirements (℃): Refining in-situ heating for 8-10min, the temperature of the molten steel is ≥1530℃; Refining in-situ clearance requirements: ≥600mm;

[0009] LF Refining:

[0010] Refining in-situ heating for 8-10 minutes, without adding any slag and deoxidizer, only slag melting and heating operation; further heating time is estimated according to the in-situ temperature and production sequence, and the heating efficiency is calculated at 4℃ / min; lime is added in batches during the heating process, and the amount of lime added is controlled to 800-1200kg according to the slag situation; according to the process composition and heating temperature, aluminum is added once, and the target Al before VD is controlled at 0.030%-0.040%; according to the in-situ molten steel composition and the target composition of the steel grade, the corresponding The amount of alloy added; the specific operation is to start adding alloy after the first sample comes back after refining and heating; fine-tune the composition according to the process sample; adding principle: silicon manganese + silicon iron is preferred for adding Si and Mn elements, and high carbon ferromanganese + silicon manganese is used with Mn when Si element is overloaded; low titanium high carbon ferrochrome is used with Cr; low nitrogen carburizer is used with C, and the carburization of high carbon ferromanganese and low titanium high carbon ferrochrome is considered before adding; refining off-site temperature is controlled ≥ L liquidus + 95-115℃, and the first furnace of pouring is 1600~1620℃;

[0011] VD Vacuum Treatment:

[0012] Primary steam temperature ≥260℃, pressure 37kg; secondary steam temperature ≥185℃, pressure 10kg; cooling water inlet and outlet flow difference ≤5m 3 / t; cooling water temperature ≤33℃; argon pressure ≥14kg; compressed air pressure ≥1.5kg; vacuum degree requirement ≤100Pa; argon flow requirement: 150-500NL / min, based on the actual argon blowing effect, to control the molten steel from overflowing; deep vacuum treatment time ≥15min; adjust the argon flow, based on the actual argon blowing effect, until the steel liquid surface creeps; soft blowing time ≥15min; the temperature of the first furnace of the pouring is controlled at 1525-1540℃, and the process furnace is controlled at 1500-1515℃;

[0013] Continuous Casting:

[0014] Baking time is 3-5h, baking temperature is >1200℃; before pouring, argon gas is used to replace the tundish; the long nozzle of the large ladle is poured with asbestos bowl and argon seal protection, and the argon flow rate is controlled to 1.0-3.0m 3 / h, preferably without exposing the molten steel surface; use special covering agent to prevent the molten steel surface in the tundish from being exposed; use automatic slag adding equipment to add protective slag, and use Stoberg special protective slag; the liquidus line of the steel grade is 1453℃, the superheat of the first furnace of the casting is ≤45℃, and the superheat of the second furnace and thereafter is ≤30℃; the starting speed is 0.25m / min, the normal speed range is 0.56-0.65m / min, and the target speed is 0.60m / min; the total water flow rate of the crystallizer is ≥1290m 3 / h, single flow rate 3250±100L / min, water inlet pressure ≥0.6MPa, crystallizer inlet and outlet water temperature difference 4-8℃, secondary cooling water volume 0.22L / kg, dynamic water distribution; current: 580±20A, frequency: 1.8±0.2Hz;

[0015] Depression: 180--200mm; Pressure: 110±10bar;

[0016] The ingot is slowly cooled for 72 hours and then sent to the rolling mill for rolling.

[0017] Furthermore, the composition requirements for LF in mass percentage are: C 0.94-0.0%, Si 0.1-0.25%, Mn 0.2-0.35%, Cr 1.35-1.5%, Al≥0.04, and the rest are iron and miscellaneous impurities.

[0018] Furthermore, the steel-making process uses 96% aluminum ingots for deoxidation, and calcium-containing deoxidizers are not allowed to be used for deoxidation.

[0019] Furthermore, the refining adopts the white slag making process, and aluminum particles are used to diffuse and deoxidize the top slag. The alloy is added in the middle and late stages. The amount of aluminum particles added is determined by the degree of top slag deoxidation. The amount added is 100-200kg / furnace, and the white slag time is ≥10min.

[0020] Furthermore, the target composition requirements of LF de-situ slag are: CaO: 55-60%, SiO2: 3-7%, Al2O3: 35-40%, MnO+FeO≤1.0%, and basicity R≥7.0.

[0021] Furthermore, it is strictly forbidden to add aluminum iron for deoxidation and calcium wire during the refining process.

[0022] Furthermore, in the VD vacuum treatment process: the target vacuum degree is ≤0.06kPa; it is strictly forbidden to add aluminum and iron from the VD in-place to the soft blow-off position; the target composition requirement of the VD molten steel is 0.030%≤Al≤0.050%.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are:

[0024] Originally, the oxygen content of bearing steel was controlled at ≥12ppm. Through a series of smelting operations, the oxygen content in the steel has been reduced. Currently, the oxygen content is controlled at ≤10ppm. Oxygen content is an important indicator for measuring the cleanliness of bearing steel. Low oxygen content can multiply the fatigue life of steel. DETAILED DESCRIPTION

[0025] A method for preparing high-quality GCr15 bearing steel, comprising:

[0026] Element content in molten iron: 0.5%≤Si≤0.7%, Pb≤0.002%, As≤0.010%, Sn≤0.010%, Sb≤0.005%, Ti≤0.06%. Molten iron must be desulfurized, the target for molten iron entering the furnace is [S]≤0.010%, and the temperature of molten iron entering the furnace is T≥1300℃. The materials and alloys used in the converter are required to be low-nitrogen carburizer, low-titanium high-carbon ferrochrome (Ti≤0.03%), and low-titanium ferrosilicon (Ti≤0.04%). Auxiliary materials are required to use lime produced within the past two days, and the ladle lime must ensure the particle size and activity. It is strictly forbidden to add expired, powdered, etc. lime.

[0027] Converter process:

[0028] The control target of converter endpoint: one-time carbon pulling, C≥0.10%, P≤0.015%, tapping temperature≥1630℃, final slag basicity R≥3.0; 96% aluminum ingots are used for deoxidation during tapping, and calcium-containing deoxidizers are not allowed to be used for deoxidation, and 500Kg of top slag lime and 500-1000kg of top slag modifier are added in combination; front and rear slag blocking is used for tapping, and slag is strictly controlled; the amount of aluminum ingot added for tapping corresponds to: slag blocking fails, 500kg of top slag lime + modifier, 50kg of aluminum particles, and 50kg of aluminum in steel. All parameters of converter production are normal, the desulfurization area controls the slag to the mirror surface, and double sliding is used to prevent slag at the end of the converter.

[0029] Table 1 Converter process

[0030]

[0031] Refining process:

[0032] Refining in situ adopts the method of gradually increasing the heating rate from low to high levels; slag making and desulfurization, composition adjustment and heating operations are carried out according to the composition and temperature of the molten steel in the converter; the refining adopts the white slag making process, and aluminum particles are used to diffuse and deoxidize the top slag. Supplementary alloys are added in the middle and late stages. The amount of aluminum particles added is determined by the degree of top slag deoxidation, the amount added is 100-200kg / furnace, and the white slag time is ≥10min; the target requirements for the composition of LF off-site slag are: CaO: 55-60%, SiO2: 3-7%, Al2O3: 35-40%, MnO+FeO≤1.0%, and basicity R≥7.0; it is strictly forbidden to add aluminum and iron for deoxidation and calcium wire during the refining process.

[0033] Table 2 Refining process

[0034]

[0035]

[0036] Table 3 Refined slag test results

[0037]

[0038] VD vacuum treatment process:

[0039] Vacuum degree ≤0.10kPa, target value ≤0.06kPa; deep vacuum time ≥15 minutes, soft blowing time ≥15 minutes; it is strictly forbidden to add aluminum and iron from VD in place to soft blowing out; the target requirement for molten steel composition after VD is out of place is 0.030%≤Al≤0.050%.

[0040] Table 4 Actual control of VD vacuum

[0041] Specific Examples Deep vacuum time (min) Vacuum degree(pa) Soft blowing time (min) Oxygen concentration (ppm) Specific Example 1 15 6 15 3 Specific Example 2 15 6 15 1.2

[0042] Continuous casting process:

[0043] Constant drawing speed control is adopted, and the drawing speed is 0.6±0.05m / min; electromagnetic stirring and light pressure reduction process are adopted for continuous casting; protective pouring is adopted, and online hydrogen determination is adopted for the tundish; molten steel superheat: ΔT≤30℃, and the liquidus temperature of this steel grade TL=1453℃; the continuous casting billet is quickly unloaded, and the billet is cooled in a slow cooling pit, and the slow cooling time is ≥72 hours.

[0044] Table 5 Actual composition of continuous casting slab

[0045]

[0046] Table 6 Actual casting speed and superheat of continuous casting billet

[0047] Specific Examples Pulling speed(m / min) Superheat(℃) Specific Example 1 0.58 23 Specific Example 2 0.58 20

[0048] Table 7 Actual gas control of continuous casting billet

[0049] Specific Examples Oxygen (ppm) Nitrogen (ppm) Specific Example 1 9 47 Specific Example 2 9 46

[0050] Through the implementation of this patent, the inclusions in the steel are significantly reduced, from the original non-metallic inclusion levels of A1.5, B2.0, C1.5, and D1.5 to the current A, B, C, and D levels of 0.5, and the cleanliness is significantly improved.

[0051] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing high-quality GCr15 bearing steel, characterized in that: Including molten iron pretreatment → converter smelting → LF refining → VD vacuum treatment → continuous casting → slow cooling in slow cooling pit; among which: Converter smelting: The molten iron must be KR desulfurized, and double slag removal operation is adopted to ensure clean slag removal; clean scrap steel is used to avoid exceeding the requirements of trace elements, and iron-containing materials are added; the total loading amount of molten iron and scrap steel is 165±10 tons, and the scrap steel is adjusted according to the molten iron conditions or iron-steel ratio requirements, the molten iron temperature is ±10℃, the scrap steel addition amount is ±1 ton, the silicon content of molten iron is ±0.1%, and the scrap steel is ±2 tons; the gun position control adopts low-high-low or high-low-high-low control, and the oxygen flow rate is 17000-32000m 3 / h, gun position 1.3-2.0m; it is recommended to use double slag when the silicon content of molten iron is greater than 0.5%, and single slag when the silicon content of molten iron is less than 0.5%, and the end point basicity is controlled according to 2.7-3.5; the control target of the converter end point is: C ≥ 0.10%, T ≥ 1600℃; it is required to pull carbon once, and spot blowing is prohibited; 200-300kg of dolomite thick slag is added before tapping, and double sliding slag is used for tapping, and slag is prohibited; an aluminum deoxidation process is adopted, and 96 aluminum iron, ferrosilicon, silicon manganese, low titanium high carbon ferrochrome, and low nitrogen coke are used for deoxidation and alloying. The specific alloy addition type and addition amount are calculated according to the weight of the molten steel; When tapping, strengthen the contact with the tank repairer and perform argon blowing according to regulations; Argon control requirements: large argon stirring in the early stage of tapping, when the tapping amount is greater than 2 / 3, adjust the argon flow rate to perform slag blocking operation to ensure that the alloy does not clump and the top slag material is well melted, and the end point adopts double sliding slag blocking with slide plates to prevent slag from falling, add 500kg synthetic slag during the tapping process, and add 500kg synthetic slag at the end of tapping; Temperature requirements (℃): Refining in-situ heating for 8-10min, the temperature of the molten steel is ≥1530℃; Refining in-situ clearance requirements: ≥600mm; LF Refining: Refining is heated in place for 8-10 minutes without adding any slag or deoxidizer, and only slag melting and heating operations are performed; further heating and heating time is estimated according to the in-place temperature and production sequence, and the heating efficiency is calculated at 4°C / min; lime is added in batches during the heating process, and the amount of lime added is controlled to be 800-1200kg according to the slag situation; according to the process composition and heating and heating, aluminum is added once, and the target Al is controlled at 0.030%-0.040% before VD; according to the in-place molten steel composition and the target composition of the steel grade, the relative The amount of alloy to be added; the specific operation is to start adding alloy after the first sample comes back after refining and heating; fine-tune the composition according to the process sample; adding principle: silicon manganese + silicon iron is preferred for adding Si and Mn elements, and high carbon ferromanganese + silicon manganese is used with Mn when Si element is overloaded; low titanium high carbon ferrochrome is used with Cr; low nitrogen coke is used with C, and the carbon increase of high carbon ferromanganese and low titanium high carbon ferrochrome is considered before adding; the refining off-site temperature is controlled ≥ L liquidus + 95-115℃, and the first furnace of the pouring is 1600~1620℃; VD Vacuum Treatment: Primary steam temperature ≥260℃, pressure 37kg; secondary steam temperature ≥185℃, pressure 10kg; cooling water inlet and outlet flow difference ≤5m 3 / t; cooling water temperature ≤33℃; argon pressure ≥14kg; compressed air pressure ≥1.5kg; vacuum degree requirement ≤100Pa; argon flow requirement: 150-500NL / min, based on the actual argon blowing effect, to control the molten steel from overflowing; deep vacuum treatment time ≥15min; adjust the argon flow, based on the actual argon blowing effect, until the steel liquid surface creeps; soft blowing time ≥15min; the temperature of the first furnace of the pouring is controlled at 1525-1540℃, and the process furnace is controlled at 1500-1515℃; Continuous Casting: Baking time is 3-5h, baking temperature is >1200℃; before pouring, argon gas is used to replace the tundish; the long nozzle of the large ladle is poured with asbestos bowl and argon seal protection, and the argon flow rate is controlled to 1.0-3.0m 3 / h, preferably without exposing the molten steel surface; use special covering agent to prevent the molten steel surface in the tundish from being exposed; use automatic slag adding equipment to add protective slag, and use Stoberg special protective slag; the liquidus line of the steel grade is 1453℃, the superheat of the first furnace of the casting is ≤45℃, and the superheat of the second furnace and thereafter is ≤30℃; the starting speed is 0.25m / min, the normal speed range is 0.56-0.65m / min, and the target speed is 0.60m / min; the total water flow rate of the crystallizer is ≥1290m 3 / h, single flow rate 3250±100L / min, water inlet pressure ≥0.6MPa, crystallizer inlet and outlet water temperature difference 4-8℃, secondary cooling water volume 0.22L / kg, dynamic water distribution; current: 580±20A, frequency: 1.8±0.2Hz; Depression: 180--200mm; Pressure: 110±10bar; The ingot is slowly cooled for 72 hours and then sent to the rolling mill for rolling.

2. The method for preparing high-quality GCr15 bearing steel according to claim 1, characterized in that: The composition requirements for LF in mass percentage are: C 0.94-0.0%, Si 0.1-0.25%, Mn 0.2-0.35%, Cr 1.35-1.5%, Al≥0.04, and the rest are iron and impurities.

3. The method for preparing high-quality GCr15 bearing steel according to claim 1, characterized in that: The steel-making process uses 96% aluminum ingots for deoxidation, and calcium-containing deoxidizers are not allowed to be used for deoxidation.

4. The method for preparing high-quality GCr15 bearing steel according to claim 1, characterized in that: The refining adopts the white slag making process, and aluminum particles are used to diffuse and deoxidize the top slag. The alloy is added in the middle and late stages. The amount of aluminum particles added is determined by the degree of top slag deoxidation. The amount added is 100-200kg / furnace, and the white slag time is ≥10min.

5. The method for preparing high-quality GCr15 bearing steel according to claim 1, characterized in that: The target composition requirements of LF off-site slag are: CaO: 55-60%, SiO2: 3-7%, Al2O3: 35-40%, MnO+FeO≤1.0%, and basicity R≥7.

0.

6. The method for preparing high-quality GCr15 bearing steel according to claim 1, characterized in that: It is strictly forbidden to add aluminum iron for deoxidation and calcium wire during the refining process.

7. The method for preparing high-quality GCr15 bearing steel according to claim 1, characterized in that: In the VD vacuum treatment process: the target vacuum degree is ≤0.06kPa; it is strictly forbidden to add aluminum and iron from VD in place to the soft blow-off position; the target composition requirement of molten steel after VD is removed is 0.030%≤Al≤0.050%.

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