Preparation process of low-turning-amount high-strength steel 300M electrode blank

Abstract

The invention discloses a preparation technology of a low-turning-amount high-strength steel 300M electrode blank. The preparation technology comprises the following steps that S1, a steel ingot of a 300M steel grade is smelted through an electric furnace, an AOD furnace, an LF furnace and a VD furnace in sequence, and molten steel is obtained; s2, the molten steel is poured to obtain an electrode blank, specifically, the molten steel is poured into an electrode mold with the controlled temperature and argon blowing in the mold, the electrode mold is provided with a riser, and low-carbon casting powder is hung away from the mold bottom before pouring, so that it is guaranteed that light leakage does not occur in the pouring process; an efficient heat generating agent is added when pouring is conducted to the 1 / 2 position of a dead head, and carbonized rice husks playing a role in heat preservation are added after pouring is completed. According to the method, the surface quality of the high-strength steel 300M electrode blank can be improved and the generation of surface pores can be avoided by adopting the measures of low-carbon casting powder, electrode mold temperature control, argon blowing in the mold and the like, so that the turning scrap amount is reduced by more than 50%, the production efficiency is improved, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of 300M steel electrode blank preparation, and in particular to a preparation process of a 300M steel electrode blank with low turning amount and high strength. Background Art

[0002] 300M steel is a high-strength, high-toughness martensitic age-hardening steel widely used in aerospace, nuclear industry and other fields. However, in the process of preparing electrode blanks, the surface porosity of 300M steel is quite serious, such as Figure 1 As shown, this not only affects the quality of the electrode blank, but also increases the turning amount, reduces production efficiency and increases production costs. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a preparation process of a 300M high-strength steel electrode billet with low turning amount, which can solve the serious problem of pores on the surface of the 300M steel electrode billet, reduce the amount of turning chips, thereby improving production efficiency and reducing production costs.

[0004] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0005] A preparation process of a low-turning high-strength steel 300M electrode blank comprises the following steps:

[0006] S1. The 300M steel ingot is sequentially smelted by an electric furnace + AOD furnace + LF furnace + VD furnace to obtain molten steel;

[0007] S2. pouring molten steel to obtain electrode blanks: pouring molten steel into an electrode mold with a controlled temperature and argon gas blown into the mold, the electrode mold is provided with a riser, and before pouring, low-carbon protective slag is hung from the bottom of the mold to ensure that there is no leakage during the pouring process; adding a high-efficiency heating agent when pouring to 1 / 2 of the riser, and adding carbonized rice husks for heat preservation after pouring.

[0008] Preferably, the steel ingot in step S1 is 6 tons; the electrode mold in step S2 has a diameter of Ф570 mm and a quantity of 3; the low-carbon protective slag is hung 150-200 mm from the bottom of the mold at 2.0-3.0 kg / t; the high-efficiency heating agent is a siliceous heating agent that delays the solidification of the steel, and 1.0-2.0 kg / t is added; the carbonized rice husk does not contact the molten steel, is added on top of the high-efficiency heating agent, and 1.5-3.0 kg / t is added.

[0009] Preferably, in step S2, 2.5 kg / t of low-carbon protective slag is hung at a distance of 150-200 mm from the mold bottom, and 1.2 kg / t of high-efficiency heating agent is added.

[0010] Preferably, in step S2, the electrode mold is kept warm in an annealing furnace, and the temperature is measured with a temperature gun before use. When the measured temperature reaches 200°C, the electrode mold is taken out of the furnace, placed in the mold, and the temperature reaches 80-100°C before pouring. There is a cooling process from taking out of the furnace to before pouring, and the time is controlled within 2 hours.

[0011] Preferably, the pressure of the argon gas blown in step S2 is 0.1 MPa.

[0012] Preferably, in step S2, MS-45 low-carbon protective slag is used, and its specific components include: carbon, calcium fluoride, calcium oxide, silicon oxide and aluminum oxide. The slag system ratio is: 20% calcium fluoride, 20% calcium oxide, 40% silicon oxide and 10% aluminum oxide, and the carbon content of the slag system is controlled below 1%.

[0013] Preferably, the specific method for ensuring that there is no flash leakage during the pouring process in step S2 is: during the pouring process, observe the rise of the molten steel in the electrode mold, and add low-carbon protective slag in time when the center of the low-carbon protective slag is found to be red to prevent flash leakage.

[0014] Due to the adoption of the above technical scheme, the technical progress achieved by the present invention is as follows.

[0015] The present invention can improve the surface quality of high-strength steel 300M electrode blanks and solve the problem of surface pores by adopting low-carbon protective slag, controlling the temperature of the electrode mold, blowing argon gas in the mold, etc., thereby reducing the amount of turning chips by more than 50%, improving production efficiency and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the finished product picture of 300M electrode blank prepared by the existing process;

[0017] Figure 2 This is a finished picture of a 300M electrode blank prepared by the process of the present invention. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] A preparation process of a low-turning high-strength steel 300M electrode blank comprises the following steps:

[0020] S1. The 300M steel ingot is smelted in sequence by an electric furnace + an AOD furnace + a LF furnace + a VD furnace to obtain molten steel.

[0021] This step specifically includes the following steps:

[0022] S11. Electric furnace smelting.

[0023] The full melting temperature of the charge is ≥1550℃. Take samples for analysis of all elements, pay attention to harmful and residual elements, and provide a reference for the initial adjustment of AOD composition. The reference tapping temperature is: T≥1650℃, C≥1.5% (if the tapping C does not meet the requirements, increase the C in the ladle by 1.5%, and the recarburizer shall be recovered at a rate of 60%).

[0024] S12.AOD furnace smelting.

[0025] S121. Blow Ar throughout the process.

[0026] S122. AOD furnace temperature before steel mixing ≥ 800℃. Gas supply parameters should meet P 氧 ≥1.7MPa, P 氩 ≥1.7MPa, P 氮 ≥1.7MPa.

[0027] S123. Before adding steel, Ar=500~700Nm 3 / h, cooling air flow 130~350Nm 3 / h.

[0028] S124. After the molten steel is added into the AOD furnace, the oxidized slag is made to remove P to P≤0.001%, and all the oxidized slag is removed. The temperature is measured and the full analysis sample is taken.

[0029] S125. Add 200kg of lime and metal Si to raise the temperature, T≥1670℃, and then remove the slag after heating.

[0030] S126. After slagging, add 100-300kg lime, 50-250kg 98 fluorite (the amount of lime and 98 fluorite can be adjusted according to the slag condition), deoxidized calcium silicon block or metal silicon 3-5kg / t, the reduction time is ≥7min, and the steel is tapped after reduction. During the steel tapping process, Ar gas protects the steel liquid level, and the ladle is filled with argon for ≥3min before steel tapping. When tapping, add calcium silicon block or metal silicon 30-60kg with the steel flow. The steel tapping control target is P≤0.001%, Si: 0.90-1.60%, C: 0.35-0.39%.

[0031] S13.LF furnace smelting.

[0032] After S131.LF is in place, connect the argon gas, and stir with large argon gas to break the slag shell. After the ladle car arrives at the heating station, take component samples and gas samples, adjust the argon flow rate, and send electricity to heat up; considering the Al in the steel, feed the aluminum wire at 0.025%; when the slag is black, you can choose to slag, and then use lime and 98 fluorite to re-slag; use C powder, calcium silicon powder (lumps) or metal silicon for diffusion deoxidation in batches throughout the process; the dosage is 1.5~3kg / t.

[0033] S132. During the power transmission and temperature raising process, lime and 98 fluorite are added according to the slag conditions to adjust the fluidity of the slag. After the slag becomes white, component samples and gas samples are taken.

[0034] S133. After sampling, adjust the alloy composition and add C powder and calcium silicon powder for diffusion deoxidation; the oxygen control target is ≤20ppm, and the deoxidation system can be adjusted according to the on-site deoxidation situation.

[0035] S134. White slag retention time ≥ 25min.

[0036] S135. When the power is on and the temperature rises to >1690℃, take samples for analysis and if S≤0.0008%, put them into the tank.

[0037] S14.VD furnace smelting.

[0038] S141. Before putting the slag into the tank, take component samples and gas samples to ensure good degassing.

[0039] S142. After sitting on the bag, adjust the argon gas flow rate to 15-50L / min, and close the tank cover after confirming that the argon gas is normal.

[0040] S143. After closing the cover, evacuate to below 67Pa and maintain for ≥15min. This is a critical process. During the evacuation process, pay attention to the rise of slag in the furnace to avoid slag leakage.

[0041] S144. After breaking the air, measure the temperature, take component samples and gas sticks, and start soft blowing of argon when the composition is suitable. The soft blowing time should be ≥10min.

[0042] S145. The reference temperature of the hanging bag is 1540~1560℃ (target 1545℃).

[0043] S2. pouring molten steel to obtain electrode blanks: pouring molten steel into an electrode mold with a controlled temperature and argon gas blown into the mold, the electrode mold is provided with a riser, and before pouring, low-carbon protective slag is hung from the bottom of the mold to ensure that there is no leakage during the pouring process; adding a high-efficiency heating agent when pouring to 1 / 2 of the riser, and adding carbonized rice husks for heat preservation after pouring.

[0044] In this step, before pouring, the electrode mold is kept warm in the annealing furnace, and the temperature is measured with a temperature gun before use. When the measured temperature reaches 200°C, it is taken out of the furnace, placed in the mold, and used when the temperature reaches 80-100°C before pouring. There is a cooling process from taking out of the furnace to before pouring, and the time is controlled within 2 hours.

[0045] During the pouring process, the flow rate pressure of argon gas was 0.1 MPa.

[0046] MS-45 low-carbon protective slag is used, and the specific ingredients include: carbon, calcium fluoride, calcium oxide, silicon oxide, aluminum oxide, etc. The slag system ratio is: calcium fluoride 20%, calcium oxide 20%, silicon oxide 40% and aluminum oxide 10%. And the carbon content of the slag system is controlled below 1%. The low-carbon protective slag is hung 150-200mm from the bottom of the mold. The low-carbon protective slag will melt during the pouring process, and the melted slag liquid will fill the gap between the molten steel and the mold wall. Because this is a process product, not a final product, it will not affect the strength of the electrode blank.

[0047] The specific method to ensure that there is no leakage during the pouring process is: observe the rise of molten steel in the electrode mold during the pouring process, and add low-carbon protective slag in time when the center of the low-carbon protective slag turns red, so as to prevent leakage. If leakage occurs, the molten steel will absorb air and affect the quality of the electrode blank.

[0048] like Figure 2 As shown, the present invention can improve the surface quality of high-strength steel 300M electrode blanks and solve the generation of surface pores by adopting low-carbon protective slag, controlling the temperature of the electrode mold, blowing argon gas in the mold, etc., thereby reducing the amount of turning chips by more than 50%, improving production efficiency, and reducing production costs. The specific principle of solving the generation of surface pores is as follows: the use of protective slag can ensure that the gas is discharged from the rising steel liquid surface, the control of the electrode mold temperature ensures that the electrode mold does not absorb moisture in the air, and prevents moisture from entering the steel liquid. The filling of argon gas in the mold can remove oxygen in the air and prevent oxygen from reacting with carbon in the steel to generate carbon monoxide.

[0049] Embodiment 1

[0050] S1. 6 tons of 300M steel ingots are smelted in sequence using an electric furnace + AOD furnace + LF furnace + VD furnace to obtain molten steel.

[0051] S2. pouring the molten steel to obtain the electrode blank: pouring the molten steel into 3 electrode molds with a diameter of Ф570mm. The electrode molds are controlled to have a temperature of 80-100°C and argon is blown into the molds at 0.1MPa. The electrode molds are provided with risers, and before pouring, low-carbon protective slag is hung 150mm from the bottom of the mold at a concentration of 2.0-3.0kg / t to ensure that there is no leakage during the pouring process; when pouring to 1 / 2 of the riser, 1.0-2.0kg / t of high-efficiency heating agent is added, and after pouring, 1.5-3.0kg / t of carbonized rice husk is added.

[0052] In this step, the slag system of the low-carbon protective slag is 20% calcium fluoride, 20% calcium oxide, 40% silicon oxide and 10% aluminum oxide, and the slag system is controlled to be C=1%.

[0053] The low-turning-amount high-strength steel 300M electrode blank prepared in the first embodiment has no pores on the surface, and the amount of turning chips is reduced by 50% or more.

[0054] Embodiment 2

[0055] S1. 6 tons of 300M steel ingots are smelted in sequence using an electric furnace + AOD furnace + LF furnace + VD furnace to obtain molten steel.

[0056] S2. Pouring molten steel to obtain electrode blanks: pouring molten steel into 3 electrode molds with a diameter of Ф570mm. The electrode molds are controlled to have a temperature of 80°C and argon is blown into the molds at 0.1MPa. The electrode molds are provided with risers, and before pouring, 2.0kg / t of low-carbon protective slag is hung 150mm from the bottom of the mold to ensure that there is no leakage during the pouring process; 1.0kg / t of high-efficiency heating agent is added when pouring to 1 / 2 of the riser, and 1.5kg / t of carbonized rice husk is added after pouring.

[0057] In this step, the slag system of the low-carbon protective slag is 20% calcium fluoride, 20% calcium oxide, 40% silicon oxide and 10% aluminum oxide, and the slag system is controlled to be C=1%.

[0058] The low-turning-amount high-strength steel 300M electrode blank prepared in Example 1 has no pores on the surface and the amount of turning chips is reduced by 50%.

[0059] Embodiment 3

[0060] S1. 6 tons of 300M steel ingots are smelted in sequence using an electric furnace + AOD furnace + LF furnace + VD furnace to obtain molten steel.

[0061] S2. Pouring the molten steel to obtain the electrode blank: pouring the molten steel into 3 electrode molds with a diameter of 570 mm. The temperature of the electrode molds is controlled to be 100°C and argon is blown into the molds at 0.1 MPa. The electrode molds are provided with risers, and before pouring, 3.0 kg / t of low-carbon protective slag is hung 200 mm from the bottom of the mold to ensure that there is no leakage during the pouring process; 2.0 kg / t of high-efficiency heating agent is added when pouring to 1 / 2 of the riser, and 3.0 kg / t of carbonized rice husk is added after pouring.

[0062] In this step, the slag system of the low-carbon protective slag is 25% calcium fluoride, 15% calcium oxide, 40% silicon oxide and 10% aluminum oxide, and the slag system is controlled to have C=0.75%.

[0063] The low-turning-amount high-strength steel 300M electrode blank prepared in Example 1 has no pores on the surface and the amount of turning chips is reduced by 55%.

[0064] Embodiment 4

[0065] S1. 6 tons of 300M steel ingots are smelted in sequence using an electric furnace + AOD furnace + LF furnace + VD furnace to obtain molten steel.

[0066] S2. Pouring molten steel to obtain electrode blanks: pouring molten steel into 3 electrode molds with a diameter of Ф570mm. The electrode molds are controlled to have a temperature of 90°C and argon is blown into the molds at 0.1MPa. The electrode molds are provided with risers, and before pouring, low-carbon protective slag is hung 175mm from the bottom of the mold at a concentration of 2.5kg / t to ensure that there is no leakage during the pouring process; when pouring to 1 / 2 of the riser, 1.2kg / t of high-efficiency heating agent is added, and after pouring, 2.0kg / t of carbonized rice husk is added.

[0067] In this step, the slag system of the low-carbon protective slag is 22% calcium fluoride, 18% calcium oxide, 40% silicon oxide and 10% aluminum oxide, and the slag system is controlled to have C=0.5%.

[0068] The low-turning-amount high-strength steel 300M electrode blank prepared in Example 1 has no pores on the surface and the amount of turning chips is reduced by 60%.

Claims

1. A process for preparing a low turning amount high strength steel 300M electrode blank, characterized in that: The following steps are involved: S1. The 300M steel ingot is sequentially smelted by an electric furnace + AOD furnace + LF furnace + VD furnace to obtain molten steel; S2. pouring molten steel to obtain electrode blanks: pouring molten steel into an electrode mold with a controlled temperature and argon gas blown into the mold, the electrode mold is provided with a riser, and before pouring, low-carbon protective slag is hung from the bottom of the mold to ensure that there is no leakage during the pouring process; adding a high-efficiency heating agent when pouring to 1 / 2 of the riser, and adding carbonized rice husks for heat preservation after pouring.

2. The process for preparing a low-turning high-strength steel 300M electrode blank according to claim 1, characterized in that: The steel ingot in step S1 is 6 tons; the electrode mold in step S2 has a diameter of Ф570mm and a quantity of 3; the low-carbon protective slag is hung 150-200mm from the bottom of the mold at 2.0-3.0kg / t; the high-efficiency heating agent is a siliceous heating agent that delays the solidification of the steel, and 1.0-2.0kg / t is added; the carbonized rice husk does not contact the molten steel, is added on the high-efficiency heating agent, and 1.5-3.0kg / t is added.

3. The process for preparing a low-turning high-strength steel 300M electrode blank according to claim 2, characterized in that: In the step S2, 2.5 kg / t of low carbon protective slag is hung 150-200 mm from the mold bottom, and 1.2 kg / t of high efficiency heating agent is added.

4. The process for preparing a low-turning high-strength steel 300M electrode blank according to claim 1, characterized in that: In step S2, the electrode mold is kept warm in the annealing furnace, and the temperature is measured with a temperature gun before use. When the measured temperature reaches 200°C, the electrode mold is taken out of the furnace, placed in the mold, and the temperature reaches 80-100°C before pouring. The cooling process from taking out of the furnace to before pouring is controlled within 2 hours.

5. The process for preparing a low-turning high-strength steel 300M electrode blank according to claim 1, characterized in that: The pressure of the argon gas blown in step S2 is 0.1 MPa.

6. The process for preparing a low-turning high-strength steel 300M electrode blank according to claim 1, characterized in that: In the step S2, MS-45 low-carbon protective slag is used, and its specific components include: carbon, calcium fluoride, calcium oxide, silicon oxide and aluminum oxide. The slag system ratio is: 20% calcium fluoride, 20% calcium oxide, 40% silicon oxide and 10% aluminum oxide, and the carbon content of the slag system is controlled below 1%.

7. The process for preparing a low-turning high-strength steel 300M electrode blank according to claim 1, characterized in that: The specific method for ensuring that there is no leakage during the pouring process in step S2 is: during the pouring process, observe the rise of the molten steel in the electrode mold, and add low-carbon protective slag in time when the center of the low-carbon protective slag turns red to prevent leakage.

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