Raw material pure iron steel coil for powder metallurgy and production method thereof

Abstract

The invention discloses a raw material pure iron steel coil for powder metallurgy and a production method of the raw material pure iron steel coil. The raw material pure iron steel coil comprises the following chemical components in percentage by weight: less than or equal to 0.0015% of C; si < = 0.005%; less than or equal to 0.020% of Mn; p < = 0.008%; als is less than or equal to 0.015%; s < = 0.005%; less than or equal to 0.010% of Cr; less than or equal to 0.010% of Ni; cu < = 0.008%; ti < = 0.005%; [O] < = 0.004%; n < = 0.005%; the balance is Fe and inevitable inclusions; the raw material pure iron steel coil is produced in a steelmaking + continuous casting + hot continuous rolling + transverse cutting mode, and the pure iron steel coil has extremely low strength, high ductility and high purity and can be used in powder metallurgy. The production method has the advantages of high production efficiency, high material yield and short delivery cycle, and can greatly reduce the cost of the production process and improve the material yield of a user.

Description

Technical Field

[0001] The invention belongs to the technical field of steel, and in particular relates to a raw material pure iron steel coil for powder metallurgy and a production method thereof. Background Art

[0002] Pure iron is an iron alloy with very low carbon content. It is widely used as an iron-based raw material for smelting high-temperature alloys, heat-resistant alloys, precision alloys, maraging steel and other alloy steels due to its excellent properties such as low coercivity, good thermal conductivity and electromagnetic properties, soft texture and high toughness. It is mainly divided into three categories according to its use: raw material pure iron, electromagnetic pure iron and military pure iron. At present, the pure iron produced by steel enterprises is mainly raw material pure iron.

[0003] Raw pure iron is mainly used in powder metallurgy, permanent magnet materials, lithium batteries, amorphous strips, soft magnetism and other industries. At present, there are two main types of raw pure iron for steel enterprises. One is to use converter smelting and continuous casting to produce slabs, and then cut into small square billets or small square billets are further processed into bars; the other is to use medium frequency furnace or electric furnace smelting to directly produce small square billets or wire rod production line to roll into bars. Due to production process costs and material recovery rate and other reasons, a small number of pure irons are also produced by medium plate single sheet rolling.

[0004] Regarding the existing technology of using converter smelting and continuous casting to produce raw material pure iron slabs, such as Chinese patent CN105986053A, which discloses a method for producing industrial pure iron. The converter smelting uses all iron without scrap steel, which is costly, and does not explain the converter three-stage smelting control parameters and the steelmaking method of obtaining ultra-low [Mn] content through refining outside the furnace. LF dephosphorization and slag removal are required, the process is complicated and the cost is high. Chinese patent CN113774277A discloses an ultra-low carbon and ultra-low manganese industrial pure iron and preparation method. Through the pretreatment of molten iron KR desulfurization, low-sulfur molten iron is obtained and then added to the converter. The converter smelting is carried out through a series of technical measures such as one-time slag pouring, controlling the amount of flux added, molten steel temperature, oxygen gun position, and free oxygen content in molten steel, so that the molten steel can obtain high-purity molten steel with a carbon content of ≤0.002% and a manganese content of ≤0.035%, but it is impossible to obtain molten steel with extremely low residual content of Cr, Ni, and Cu.

[0005] Regarding the existing technology of using medium frequency furnace or electric furnace to smelt raw material pure iron slabs, such as Chinese patent CN102352421A discloses a "process for smelting industrial pure iron using converter waste slag granular iron", which has limitations because the raw material is converter waste slag granular iron and the equipment uses medium frequency induction furnace or vacuum induction furnace for smelting. For example, Chinese patent CN105603312A discloses "a method for manufacturing ultra-pure industrial pure iron", which uses EBT electric furnace smelting and adds lanthanum-cerium alloy for deoxidation and desulfurization, which is relatively costly.

[0006] Regarding the existing technology of producing raw pure iron by single sheet rolling of medium plate, such as Chinese patent CN114959488A which discloses "an industrial pure iron medium and thick plate and its production method", the production process route adopted is molten iron pretreatment - converter smelting + RH vacuum refining - continuous casting - cutting medium slab - billet heating - high-pressure water dephosphorization - rolling - air cooling finishing - inspection and delivery to warehouse, and the production efficiency is relatively low. Summary of the invention

[0007] In order to reduce production costs and improve production efficiency and material yield, the present invention provides a raw material pure iron steel coil for powder metallurgy and a production method thereof, which adopts steelmaking + continuous casting + hot rolling + cross-cutting to produce raw material pure iron steel coil. This steel coil has extremely low strength, high elongation, and high purity, and can be used in powder metallurgy. The production method has high production efficiency, high material yield, and short delivery cycle, which can greatly reduce production process costs and improve user material yield.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] The present invention provides a raw material pure iron steel coil for powder metallurgy, comprising the following chemical components in weight percentage: C≤0.0015%; Si≤0.005%; Mn≤0.020%; P≤0.008%; Als≤0.015%; S≤0.005%; Cr≤0.010%; Ni≤0.010%; Cu≤0.008%; Ti≤0.005%; [O]≤0.004%; N≤0.005%; the rest is Fe and unavoidable inclusions; the metallographic structure of the raw material pure iron steel coil for powder metallurgy is ferrite.

[0010] The raw material pure iron steel coil for powder metallurgy has a yield strength of ≤180MPa, a tensile strength of ≤280MPa, an elongation A50≥70%, a yield strength ratio of ≤0.60, a cold bending performance of 180°, and no cracks at D=0a.

[0011] The production method of the raw material pure iron steel coil for powder metallurgy provided by the present invention comprises the following steps: molten iron pretreatment → converter smelting → alloy fine-tuning station → RH refining → continuous casting → hot rolling → cross-cutting;

[0012] When pre-treating molten iron, use scrap steel with Cr, Ni, and Cu content ≤ 80ppm. Do not use slag steel, palm iron, or cast iron.

[0013] During converter smelting, the double slag method is adopted, the converter basicity is 1.5-2.0 before slag pouring, and the converter basicity is 3.5-4.0 after slag pouring, and the free O content in the molten steel at the converter end point is controlled to be above 0.0800%;

[0014] During continuous casting, ultra-low carbon steel protective slag with a C content of ≤4.5% is used for protective casting, and the billet head is ≥4.6m and the tail is ≥4.6m;

[0015] During hot rolling, the descaling inlet and outlet nozzles are all opened; the R2DT longitudinal temperature difference is ≤40℃; the finishing rolling temperature is ≥900℃.

[0016] Furthermore, in the molten iron pretreatment step, a group of ultra-low carbon steel grades are arranged for furnace and trough washing before production to determine whether the manganese alloy has been weighed in the previous furnace of the converter. If the manganese alloy has been weighed, the hopper is vibrated empty or the belt is idle for 1-2 minutes. The target [S] after molten iron desulfurization is ≤0.0010%, and the total time for adding scrap steel and iron is ≤16 minutes.

[0017] In the converter smelting step, the converter auxiliary blowing and post-stirring adopt weak stirring mode ≤0.05Nm 3 / t.min; endpoint temperature is controlled at 1650±5℃, and endpoint oxygen is controlled at ≥800ppm.

[0018] In the RH refining step, the vacuum degree is ≤2.6 mbar, the decarburization time is ≥10 min and the CO concentration in the exhaust gas is <1.0%.

[0019] In the RH refining step, it is strictly forbidden to add cold materials to cool down. When the temperature is high, add carbon powder in the early and middle stages of decarburization or appropriately extend the processing time to cool down.

[0020] During the continuous casting step, the stopper rod argon blowing flow rate is ≥6NI / min.

[0021] In the hot rolling step, the slab furnace temperature is 1180-1250°C; the convexity during finish rolling is controlled to be 60±20μm, the wedge is controlled to be 0±30μm, and the straightness is controlled to be ±150I;

[0022] After hot rolling, the front-stage centralized cooling process is adopted, the head non-cooling section is eliminated, the coiling temperature is controlled at 650±20℃, the coiler tower type is controlled at ±50mm, the overflow edge is <20mm, and it is air-cooled to room temperature after coiling.

[0023] In the cross-cutting step, the cross-cutting production speed is 20-40m / s, the centering error range of the steel coil width is controlled within ±20mm, the longitudinal inclination of the straightening roller is controlled within ±2.0mm, and the lateral inclination is controlled within ±1.0mm.

[0024] In the steelmaking process design, the present invention does not use scrap steel with high nickel, copper and chromium content, prohibits the use of slag steel, palm iron and cast blocks, and reduces the content of impurity elements such as nickel, copper and chromium in steel; adopts a double slag method to reduce the amount of slag in steel as much as possible, thereby reducing the return of residual elements from the slag to molten steel in subsequent processes, thereby improving the purity of molten steel; the converter basicity before slag pouring is 1.5-2.0, and a low basicity is used to facilitate the pouring of slag; the basicity after slag pouring is controlled to 3.5-4.0, and a higher basicity can effectively reduce the residual elements in molten steel; the free O content in the molten steel at the converter end point is controlled to be above 0.0800%, and a high end point oxygen value is used. Promoting the oxidation of Mn into the slag is beneficial to reducing the manganese content in the molten steel at the end of the converter, with a manganese removal rate of ≥80% and a dephosphorization rate of ≥90%; using ultra-low carbon steel protection slag to reduce the C in the protection slag from entering the molten steel to produce carbon increase; cutting the head of the ingot to ≥4.6m, cutting the tail to ≥4.6m, reducing the residual element content of the head and tail ingots, avoiding downgrading of the head and tail ingots, and improving the yield rate.

[0025] In the rolling process design of the present invention, in order to maintain the surface quality of the raw pure iron plate, the inlet and outlet water nozzles of the descaling are all opened at one time, and the pressure of all descaling water is ≥180Bar; the longitudinal temperature difference of R2DT is ≤40℃, reducing the instability of rolling force caused by temperature fluctuations, and controlling the final rolling temperature of finishing rolling to be ≥900℃ to reduce the rolling force fluctuation caused by organizational changes during the rolling process, and ensure the rolling stability of the subsequent finishing rolling unit; the convexity is controlled at 60±20μm, the wedge is controlled at 0±30μm, and the straightness is controlled at ±150I to ensure a good rolling plate shape; in addition, the cooling adopts the front-stage centralized cooling process and cancels the head non-cooling section. The raw pure iron has a low strength and does not need to be assisted by adding the head non-cooling section to coil, which can effectively reduce costs and improve benefits. In the cross-cutting process design, the cross-cutting production speed is selected as 20-40m / s, the centering error range of the steel coil width is controlled within ±20mm, the longitudinal inclination of the straightening roller is controlled at: ±2.0mm, and the lateral inclination is controlled at: ±1.0mm, which can effectively improve the plate shape and improve the yield rate.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The invention is suitable for large-scale production of raw material pure iron, with low production cost and high efficiency. The hot-rolled raw material pure iron steel plate produced by the invention has a purity of more than 99.94%, wherein the center looseness, center crack, corner crack, triangular area crack, Al2O3 inclusion and honeycomb bubble are all at level 0, and the center segregation is ≤B0.5 level; the microstructure is a coarse ferrite structure, wherein the ferrite volume fraction is ≥99%, the yield strength of the product is ≤180MPa, the tensile strength is ≤280MPa, the elongation A50 is ≥70%, the yield strength ratio is ≤0.60, the cold bending performance is 180°, D=0a has no cracks, has extremely low strength, high elongation and high purity, and under the condition of extremely low strength, the shearing processing efficiency is higher than that of high-strength steel coil, and the power energy consumption cost of the equipment required by the customer can be significantly reduced.

[0028] The production method of raw material pure iron steel coil provided by the present invention improves production efficiency by more than 3 times compared with the medium plate production method; compared with the continuous casting billet flame cutting method, the utilization rate is increased by 5 percentage points, the cost is reduced by 200 yuan / ton, and the delivery cycle is increased by 1 time, which can greatly reduce the production process cost and improve the user's material recovery rate, achieving a win-win situation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the pickling macrostructure diagram of the hot-rolled steel plate produced in Example 1. It can be seen that the central segregation of the pickling macrostructure is ≤B0.5, and the central looseness, central cracks, corner cracks, triangular area cracks, Al2O3 inclusions, and honeycomb bubbles are all at level 0, and there is no white bright band. DETAILED DESCRIPTION

[0030] The present invention provides a raw material pure iron steel coil for powder metallurgy, comprising the following chemical components in weight percentage: C≤0.0015%; Si≤0.005%; Mn≤0.020%; P≤0.008%; Als≤0.015%; S≤0.005%; Cr≤0.010%; Ni≤0.010%; Cu≤0.008%; Ti≤0.005%; [O]≤0.004%; N≤0.005%; the rest is Fe and unavoidable inclusions; the metallographic structure of the raw material pure iron steel coil for powder metallurgy is ferrite.

[0031] The production process of the pure iron steel coil as raw material for powder metallurgy includes molten iron pretreatment, converter smelting, alloy fine-tuning station, RH, continuous casting, heating, rolling, cooling and cross-cutting processes. Specifically:

[0032] 1) Pretreatment of molten iron: Arrange a group of ultra-low carbon steel grades to wash the furnace and tank before production, determine whether the manganese alloy has been weighed in the previous furnace of the converter, and vibrate the hopper or idle the belt for 1-2 minutes if necessary. The target [S] after molten iron desulfurization is ≤0.0010%. Use scrap steel with Cr, Ni, and Cu contents of ≤80ppm. It is prohibited to use slag steel, palm iron, and cast blocks. The total time for adding scrap steel and mixing iron is ≤16min.

[0033] 2) Converter smelting: double slag method is adopted, converter basicity before slag pouring: 1.5-2.0, basicity control after slag pouring: 3.5-4.0; converter auxiliary blowing and post-stirring adopt weak stirring mode ≤0.05Nm 3 / t.min; endpoint temperature is controlled at 1650±5℃, and endpoint oxygen is controlled at ≥800ppm.

[0034] 3) RH refining: vacuum degree ≤ 2.6mbar, decarburization time ≥ 10min and CO concentration in exhaust gas < 1.0%. It is strictly forbidden to add cold material to cool down. When the temperature is high, add carbon powder in the early and middle stages of decarburization or appropriately extend the processing time to cool down.

[0035] 4) Continuous casting: the argon blowing flow rate of the stopper rod is ≥6NI / min, ultra-low carbon steel protective slag is used, the head of the ingot is ≥4.6m, and the tail is ≥4.6m.

[0036] 5) Hot rolling: slab furnace temperature: 1180-1250℃, in order to maintain the surface quality, the inlet and outlet nozzles of the descaling are all opened, all descaling water pressures are ≥180Bar, R2DT longitudinal temperature difference is ≤40℃; finishing rolling temperature is ≥900℃, convexity is controlled at 60±20μm, wedge is controlled at 0±30μm, and straightness is controlled at ±150I. The front-end centralized cooling process is adopted, the head non-cooling section is cancelled, the coiling temperature is controlled at: 650±20℃, the coiler tower type is controlled at ±50mm, the overflow edge is <20mm, and air cooling is performed to room temperature after coiling.

[0037] 6) Cross-cutting: The cross-cutting production speed is 20-40m / s, the centering error range of the steel coil width is controlled within ±20mm, the longitudinal inclination of the straightening roller is controlled within ±2.0mm, and the lateral inclination is controlled within ±1.0mm.

[0038] The present invention is described in detail below with reference to the embodiments.

[0039] The chemical composition of the raw pure iron steel coil in the embodiment and the comparative example is shown in Table 1, and the balance is iron and unavoidable inclusions. The steelmaking process parameters of the raw pure iron steel coil in the embodiment and the comparative example are shown in Table 2. The rolling process and mechanical properties of the raw pure iron steel coil in the embodiment and the comparative example are shown in Table 3.

[0040] Table 1 Measured chemical composition of the examples (mass percentage, wt%)

[0041] serial number C Si Mn P S Als Cr Ni Cu Ti O N Example 1 0.0008 0.0011 0.0193 0.0057 0.0032 0.0081 0.0050 0.0047 0.0067 0.0001 0.0035 0.0025 Example 2 0.0008 0.001 0.0197 0.0062 0.0025 0.0085 0.0051 0.0049 0.0071 0.0001 0.0030 0.0019 Example 3 0.0007 0.0011 0.0145 0.0044 0.0026 0.0065 0.0044 0.0049 0.0078 0.0001 0.0038 0.0015 Example 4 0.0009 0.0015 0.0185 0.0057 0.0022 0.0088 0.0045 0.0046 0.0072 0.0002 0.0027 0.0021 Comparative Example 1 0.0023 0.003 0.0501 0.0185 0.0071 0.0152 0.0223 0.0121 0.0131 0.0010 0.0086 0.0042 Comparative Example 2 0.0022 0.004 0.0562 0.0203 0.0082 0.0162 0.0231 0.0102 0.0125 0.0020 0.0080 0.0045

[0042] Table 2 Main parameters of steelmaking in various embodiments and comparative examples

[0043]

[0044] Table 3 Main rolling process parameters and mechanical properties of the embodiment

[0045]

[0046]

[0047] From the above content, it can be seen that the raw material pure iron steel coil produced by the production method of raw material pure iron steel coil for powder metallurgy provided by the present invention has a loose center, a central crack, a corner crack, a triangular area crack, an Al2O3 inclusion, and a honeycomb bubble, all of which are level 0, and a central segregation ≤ level B0.5; its yield strength ≤180MPa, tensile strength ≤280MPa, elongation A50 ≥70%, yield strength ratio ≤0.60, cold bending performance 180°, D=0a without cracks, extremely low strength, high elongation and high purity, its performance is close to the limit minimum value of steel, the shearing processing efficiency is high, and the power energy consumption cost of the equipment required for customer use is significantly reduced.

[0048] The above-mentioned reference embodiments provide a detailed description of a pure iron steel coil as a raw material for powder metallurgy and a production method thereof, which is illustrative rather than restrictive. Several embodiments may be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A pure iron steel coil as raw material for powder metallurgy, characterized in that: The chemical composition includes the following weight percentages: C≤0.0015%; Si≤0.005%; Mn≤0.020%; P≤0.008%; Als≤0.015%; S≤0.005％； Cr≤0.010%; Ni≤0.010%; Cu≤0.008%; Ti≤0.005%; [O]≤0.004%; N≤0.005%; The rest is Fe and inevitable inclusions; the metallographic structure of the pure iron steel coil as raw material for powder metallurgy is ferrite.

2. The raw material pure iron steel coil for powder metallurgy according to claim 1, characterized in that: The raw material pure iron steel coil for powder metallurgy has a yield strength of ≤180MPa, a tensile strength of ≤280MPa, an elongation A50≥70%, a yield strength ratio of ≤0.60, a cold bending performance of 180°, and no cracks at D=0a.

3. The method for producing a pure iron steel coil as raw material for powder metallurgy according to claim 1 or 2, characterized in that: The production method comprises the following steps: molten iron pretreatment → converter smelting → alloy fine-tuning station → RH refining → continuous casting → hot rolling → cross-cutting; When pre-treating molten iron, use scrap steel with Cr, Ni, and Cu content ≤ 80ppm. Do not use slag steel, palm iron, or cast iron. During converter smelting, the double slag method is adopted, the converter basicity is 1.5-2.0 before slag pouring, and the converter basicity is 3.5-4.0 after slag pouring, and the free O content in the molten steel at the converter end point is controlled to be above 0.0800%; During continuous casting, ultra-low carbon steel protective slag with a C content of ≤4.5% is used for protective casting, and the billet head is ≥4.6m and the tail is ≥4.6m; During hot rolling, the descaling inlet and outlet nozzles are all opened; the R2DT longitudinal temperature difference is ≤40℃; the finishing rolling temperature is ≥900℃.

4. The method for producing a pure iron steel coil as raw material for powder metallurgy according to claim 3, characterized in that: In the molten iron pretreatment step, the target [S] after molten iron desulfurization is ≤0.0010%, and the total time for adding scrap steel and adding iron is ≤16min.

5. The method for producing a pure iron steel coil as raw material for powder metallurgy according to claim 3, characterized in that: In the converter smelting step, the converter auxiliary blowing and post-stirring adopt weak stirring mode ≤0.05Nm 3 / t.min; endpoint temperature is controlled at 1650±5℃, and endpoint oxygen is controlled at ≥800ppm.

6. The method for producing a pure iron steel coil as raw material for powder metallurgy according to claim 3, characterized in that: In the RH refining step, the vacuum degree is ≤2.6 mbar, the decarburization time is ≥10 min and the CO concentration in the exhaust gas is <1.0%.

7. The method for producing a pure iron steel coil as raw material for powder metallurgy according to claim 3, characterized in that: During the continuous casting step, the stopper rod argon blowing flow rate is ≥6NI / min.

8. The method for producing a pure iron steel coil as raw material for powder metallurgy according to claim 3, characterized in that: In the hot rolling step, the slab furnace temperature is: 1180~1250℃; the convexity during finish rolling is controlled to be 60±20μm, the wedge is controlled to be 0±30μm, and the straightness is controlled to be ±150I.

9. The method for producing a pure iron steel coil as raw material for powder metallurgy according to claim 3, characterized in that: After hot rolling, the front-stage centralized cooling process is adopted, the head non-cooling section is eliminated, the coiling temperature is controlled at 650±20℃, the coiler tower type is controlled at ±50mm, the overflow edge is <20mm, and it is air-cooled to room temperature after coiling.

10. The method for producing a pure iron steel coil as raw material for powder metallurgy according to claim 3, characterized in that: In the cross-cutting step, the cross-cutting production speed is 20-40m / s, the centering error range of the steel coil width is controlled within ±20mm, the longitudinal inclination of the straightening roller is controlled within ±2.0mm, and the lateral inclination is controlled within ±1.0mm.

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