Low cost smelting method of low carbon molybdenum containing steel

Abstract

The present application belongs to the field of steelmaking, and particularly relates to a low-cost smelting method of low-carbon molybdenum-containing steel. The method comprises controlling a higher end-point C content in the converter tapping process to avoid over-oxidation of the molten steel and thus reduce iron loss; using a lower-cost high-carbon alloy to replace a high-cost low-carbon alloy in the converter tapping process; heating the molten steel and adjusting the composition of the molten steel to a certain range in the LF refining process; and adding molybdenum oxide balls containing ferrous oxide in the RH process under vacuum conditions to decarburize under vacuum and reduce the molybdenum oxide. According to the method of the present application, the converter tapping process does not need low-carbon tapping, and the oxidizability of the molten steel can be reduced to reduce iron loss. Meanwhile, the present application uses a low-cost high-carbon alloy and molybdenum oxide to replace a high-cost low-carbon alloy and molybdenum-iron alloy, respectively, and eliminates the high-energy-consumption and high-pollution molybdenum-iron smelting process, thereby greatly reducing the smelting cost of low-carbon molybdenum-containing steel.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of steelmaking, and particularly relates to a low-cost smelting method of low-carbon molybdenum-containing steel. BACKGROUND

[0002] Molybdenum element can improve the strength, hardness and corrosion resistance of steel materials in cooperation with other alloy elements, and is therefore a commonly used alloy element in alloy steel. The alloying raw materials commonly used in the production of current low-carbon molybdenum-containing steel are molybdenum iron, low-carbon chromium iron, low-carbon manganese iron and other low-carbon alloys, and the smelting process is generally low-carbon tapping at the end point of the converter or electric furnace, and molybdenum iron alloy, low-carbon alloy and the like are added during tapping for alloying while controlling the alloy carbon increment.

[0003] The conventional production process needs to control low-carbon tapping, which can easily cause the increase of FeO content in slag and the increase of steel material consumption. In addition, the molybdenum iron alloy and low-carbon alloy used in the conventional process are relatively expensive. Therefore, the cost of producing low-carbon molybdenum-containing steel by the conventional process is relatively high.

[0004] In order to reduce the cost of molybdenum alloying, some domestic manufacturers or scholars have researched a process of using molybdenum oxide to replace molybdenum iron for direct alloying. The use of molybdenum oxide to replace molybdenum iron for direct alloying is generally used in initial smelting furnaces such as converters and electric furnaces. Since molybdenum oxide has serious volatility at 597-1151℃, it is necessary to add lime, limestone or magnesium oxide and the like to inhibit the volatilization of molybdenum oxide, and it is also necessary to additionally add carbon powder, silicon iron powder, silicon carbide, calcium carbide, aluminum or directly use C, Si, Al and other elements in the molten steel as reducing agents.

[0005] For example, patent CN107557516A discloses a process of pressing molybdenum oxide powder and volatilization inhibitor powder into molybdenum raw material particles and then adding them into the molten iron in the converter, and directly reducing and alloying molybdenum in the converter. In the technical solution of the patent, the molybdenum raw material particles are added during the smelting process in the converter, the iron and carbon in the molten steel are used as reducing agents to reduce the molybdenum in the molybdenum trioxide into molybdenum single element and enter the molten steel, and CaZrO3 and CaAl4O7 powders are used as volatilization inhibitors to inhibit the sublimation of molybdenum trioxide and improve the molybdenum yield. The scheme cannot solve the problem of carbon increase caused by the use of low-price high-carbon alloy in the tapping process and the refining process, and the prepared molybdenum raw material particles are not suitable for the RH vacuum degassing process, which can easily cause the loss of Si and Mn in the molten steel in the RH process and make it difficult to decarburize. In addition, CaZrO3 is not a commonly used metallurgical auxiliary material, and it is difficult to obtain. SUMMARY

[0006] The application aims to provide a low-cost smelting method of low-carbon molybdenum-containing steel. The method can control a higher converter end-point C content in the production of low-carbon molybdenum-containing steel, avoid over-oxidation of molten steel, and reduce iron loss; low-cost high-carbon alloy and molybdenum oxide are used to replace high-cost low-carbon alloy and molybdenum-iron alloy, thereby greatly reducing the production cost of low-carbon molybdenum-containing steel.

[0007] The application discloses a low-cost smelting method of low-carbon molybdenum-containing steel, which adopts a smelting process of "converter smelting-LF refining-RH vacuum treatment-continuous casting", and specifically comprises the following steps.

[0008] (1) the converter end-point C content is controlled to be 0.10%-0.50%, and a high-carbon alloy is added during tapping according to the composition requirements of the steel grade;

[0009] (2) the composition of the molten steel is adjusted and the temperature is raised in the LF refining process, and the composition of the molten steel at the LF end point is controlled to be C: 0.55%-0.65%, Si: 0.12%-0.42%, Mn: 0.40%-0.60%, Cr: 1.95%-2.50%, P≤0.015%, S≤0.015%, and the end-point temperature is 1670°C-1700°C;

[0010] (3) the molybdenum balls are added under the RH vacuum condition, wherein the molybdenum balls are formed by mixing molybdenum oxide and ferrous oxide powder;

[0011] (4) the molten steel is poured on the continuous casting platform after soft blowing.

[0012] Further, the composition of the molybdenum balls is MoO3: 55%-70%, FeO: 18%-23%, P≤0.06%, Cu≤0.50%, and the rest is impurities. The diameter of the molybdenum balls is 10mm-30mm.

[0013] Further, the high-carbon alloy includes but is not limited to high-carbon ferromanganese and high-carbon ferrochrome. In order to further reduce the cost, no low-carbon alloy is used in the smelting process.

[0014] Further, the RH vacuum degree in the step (3) is controlled to be 5000Pa-8000Pa, and the vacuum treatment time is 8-12min.

[0015] In the application, argon is used as the lifting gas in the RH, and the flow rate of the lifting gas is 60-100Nm 3 / h.

[0016] The composition of the low-carbon molybdenum-containing steel is C: 0.06%-0.13%, Si: 0.10%-0.40%, Mn: 0.35%-0.60%, Cr: 1.90%-2.50%, Mo: 0.90%-1.10%, P≤0.015%, S≤0.015%, O≤0.003%, and H≤0.0002%.

[0017] The present application mixes molybdenum oxide with ferrous oxide powder to make molybdenum balls. The ferrous oxide can combine with the molybdenum oxide to form iron molybdate, thereby inhibiting the volatilization of the molybdenum oxide, and can also act as an oxygen source together with the molybdenum oxide to remove excess carbon from the molten steel during the RH vacuum treatment process, so that the carbon content of the molten steel meets the requirements of the steel grade. If the content of the ferrous oxide is too low, the effect of inhibiting the volatilization of the molybdenum oxide is not ideal; if the content of the ferrous oxide is too high, the carbon content at the end of the RH process will be too low, and even the yield of Si and Mn will be affected. After the RH is broken, carbon powder or even alloy needs to be added, resulting in an increase in the process time and production cost.

[0018] The high-carbon alloy is added during the converter tapping process and the refining process, and the molybdenum balls are added under the RH vacuum condition. If the high-carbon alloy and the molybdenum balls are all added during the converter tapping process or the refining process, the molten steel is only naturally decarburized, the equilibrium carbon-oxygen product is relatively high, the carbon content of the molten steel cannot be removed to the range required by the steel grade, and the composition of the molten steel will be out of standard, resulting in rejection, in addition, the oxygen content of the molten steel will be too high, and the cleanliness is poor.

[0019] Compared with the prior art, the present application has the following advantages:

[0020] The present application does not need low-carbon tapping during the converter tapping process, which can reduce the oxidizability of the molten steel and thus reduce the iron loss. In addition, the present application uses the principle of vacuum decarburization in the RH vacuum treatment process, and uses low-cost high-carbon alloy and molybdenum oxide to replace high-cost low-carbon alloy and molybdenum-iron alloy, thereby achieving the purpose of reducing the production cost. Compared with the conventional process, the present application has a significant cost advantage. DETAILED DESCRIPTION

[0021] The following specifically describes a low-cost smelting method of a low-carbon molybdenum steel according to the present application. The process methods not specifically described in the examples are conventional methods in the art.

[0022] Example 1

[0023] (1) The C content of the molten steel at the end of the converter is 0.12%. 1000 kg of silicon-manganese alloy, 4900 kg of high-carbon chromium iron, and 150 kg of carbon additive are added during the converter tapping process.

[0024] (2) The molten steel is heated and the composition of the molten steel is adjusted in the LF refining process. A total of 100 kg of silicon-manganese alloy, 30 kg of silicon-iron alloy, 50 kg of high-carbon chromium iron, and 70 kg of carbon additive are added during the LF refining process. The temperature of the molten steel at the end of the refining process is 1683℃, and the composition of the molten steel is C: 0.57%, Si: 0.13%, Mn: 0.55%, Cr: 1.95%, Mo: 0.02%, P: 0.012%, and S: 0.009%.

[0025] (3) Argon is used as the lifting gas in the RH, and the flow rate of the lifting gas is 80 Nm 3(1) The C content of the molten steel at the converter end point was detected to be 0.12%. During the tapping process of the converter, 300 kg of ferrosilicon, 900 kg of high-carbon ferromanganese, and 4900 kg of high-carbon ferrochrome were added.

[0026] It was calculated that the cost of alloy (including carbon additive) used from the converter tapping to the RH treatment in Example 1 was 3503.87 yuan / t of steel, as shown in Table 1.

[0027] Example 2

[0028] (1) The C content of the molten steel at the converter end point was detected to be 0.12%. During the tapping process of the converter, 300 kg of ferrosilicon, 900 kg of high-carbon ferromanganese, and 4900 kg of high-carbon ferrochrome were added.

[0029] (2) The LF refining was used to raise the temperature and adjust the composition of the molten steel. A total of 50 kg of high-carbon ferromanganese, 50 kg of high-carbon ferrochrome, and 140 kg of carbon additive were added during the LF refining process. The molten steel temperature at the end of the refining was 1695°C, and the composition of the molten steel was C: 0.55%, Si: 0.14%, Mn: 0.54%, Cr: 1.96%, Mo: 0.01%, P: 0.011%, and S: 0.007%.

[0030] (3) The RH used argon as the lifting gas, and the lifting gas flow rate was 80 Nm 3 / h, the vacuum degree was 5000 Pa, 3100 kg of molybdenum balls were added from the bin under the RH vacuum condition, and after the molybdenum balls were added, the vacuum treatment was performed for 10 min. After the RH was broken, the molten steel sample was taken, and the composition of the molten steel was C: 0.08%, Si: 0.11%, Mn: 0.51%, Cr: 1.94%, Mo: 0.92%, P: 0.010%, and S: 0.006%, which met the composition requirements of the steel grade. After soft blowing, the ladle was lifted to the continuous casting platform for casting.

[0031] It was calculated that the cost of alloy (including carbon additive) used from the converter tapping to the RH treatment in Example 2 was 3511.89 yuan / t of steel, as shown in Table 1.

[0032] Comparative Example 1

[0033] Compared with Example 1, Comparative Example 1 used a conventional tapping process with low-carbon alloy and molybdenum iron. The converter required low-carbon tapping, the molten steel was highly oxidizing, the iron loss was high, and the cost of low-carbon alloy and molybdenum iron was high.

[0034] (1) The carbon content of the molten steel at the end of the converter was found to be 0.05%. During the tapping process of the converter, 1000 kg of silicon-manganese alloy, 4600 kg of low-carbon ferrochrome, and 2100 kg of ferromolybdenum were added.

[0035] (2) LF refining: heating and adjusting the steel composition. During the LF refining process, 100 kg of ferrosilicon alloy, 50 kg of ferrosilicon alloy, 50 kg of low-carbon ferrochrome, and 50 kg of ferromolybdenum were added. The final steel temperature was 1620℃, and the steel composition was: C: 0.09%, Si: 0.12%, Mn: 0.54%, Cr: 1.95%, Mo: 0.93%, P: 0.012%, S: 0.013%.

[0036] (3) RH uses argon as the booster gas, with a booster gas flow rate of 80 Nm³. 3 / h, vacuum degree ≤100Pa, vacuum treatment for 12min. After RH voiding, take a sample of molten steel. The composition of the molten steel is C: 0.09%, Si: 0.12%, Mn: 0.54%, Cr: 1.95%, Mo: 0.93%, P: 0.012%, S: 0.013%, which meets the steel grade composition requirements. After soft blowing, lift the ladle onto the continuous casting platform for casting.

[0037] According to calculations, the cost of the alloy (including carburizer) used in Comparative Example 1 from converter tapping to RH treatment is 4154.76 yuan / t, which is more than 640 yuan / t higher than the alloy cost of Example 1, as shown in Table 1.

[0038] Comparative Example 2

[0039] Compared with Example 1, the molybdenum balls used in Comparative Example 2 did not contain FeO, resulting in a lower Mo yield. This required the addition of ferromolybdenum, leading to a higher total alloy cost and increased RH process time.

[0040] (1) The carbon content of the molten steel at the end of the converter was found to be 0.13%. During the tapping process of the converter, 1000 kg of silicon-manganese alloy, 4900 kg of high-carbon ferrochrome and 150 kg of carbon raiser were added.

[0041] (2) LF refining: Heating and steel composition adjustment. During the LF refining process, 100 kg of ferrosilicon alloy, 30 kg of ferrosilicon alloy, 50 kg of high-carbon ferrochrome, and 70 kg of carbon raiser were added. The final steel temperature was 1675℃, and the steel composition was: C: 0.56%, Si: 0.12%, Mn: 0.54%, Cr: 1.96%, Mo: 0.02%, P: 0.011%, S: 0.008%.

[0042] (3) RH uses argon as the booster gas, with a booster gas flow rate of 80 Nm³. 3(1) The C content of the molten steel at the converter endpoint was detected to be 0.11%. During the tapping process of the converter, 1000 kg of silicon-manganese alloy, 4900 kg of high-carbon chromium iron, and 100 kg of carbon additive were added.

[0043] It was calculated that the alloy (including carbon additive) cost per ton of steel used by Comparative Example 2 from tapping of the converter to RH treatment was 3924.24 yuan / t, which was higher than the alloy cost of the embodiment by more than 410 yuan / t, as shown in Table 1. The RH process time was increased by about 8 min.

[0044] Comparative Example 3

[0045] Compared with Example 1, the C content at the LF endpoint in Comparative Example 3 was low, the C content at the RH breakage was low, and carbon powder needed to be added, which increased the process time.

[0046] (1) The C content of the molten steel at the converter endpoint was detected to be 0.11%. During the tapping process of the converter, 1000 kg of silicon-manganese alloy, 4900 kg of high-carbon chromium iron, and 100 kg of carbon additive were added.

[0047] (2) The LF refining was used to raise the temperature and adjust the composition of the molten steel. During the LF refining process, a total of 100 kg of silicon-manganese alloy, 30 kg of silicon-iron alloy, 50 kg of high-carbon chromium iron, and 70 kg of carbon additive were added. The temperature of the molten steel at the endpoint of the refining was 1685°C, and the composition of the molten steel was C: 0.43%, Si: 0.12%, Mn: 0.54%, Cr: 1.96%, Mo: 0.02%, P: 0.010%, and S: 0.006%.

[0048] (3) The RH used argon as the lifting gas, and the lifting gas flow rate was 80 Nm 3 / h, the vacuum degree was 8000 Pa, and under the RH vacuum condition, 3100 kg of molybdenum balls were added from the bin. After the molybdenum balls were added, the vacuum treatment was performed for 12 min. After the RH breakage, the composition of the molten steel was C: 0.004%, Si: 0.11%, Mn: 0.47%, Cr: 1.91%, Mo: 0.91%, P: 0.011%, and S: 0.009%. The C content was lower than the composition requirement of the steel grade, and 110 kg of carbon additive was added. After soft blowing, the composition of the molten steel was detected to be C: 0.08%, which met the composition requirement of the steel grade, and the ladle was lifted to the continuous casting platform for casting.

[0049] The alloy (including carbon additive) cost of Example 3 from the converter tapping to the RH treatment is 3507.07 yuan / t, as shown in Table 1, and the RH process time is increased by 6 minutes.

[0050] Comparative Example 4

[0051] Compared with Example 1, CaO is added as a volatilization inhibitor in the molybdenum ball used in Comparative Example 4, and a large amount of Si in the molten steel is oxidized, and the decarburization is insufficient, so additional oxygen blowing decarburization is required, and the total cost of the alloy is high.

[0052] (1) The C content of the molten steel at the end of the converter is 0.13%. 1000 kg of silicon-manganese alloy, 4900 kg of high-carbon chromium iron, and 150 kg of carbon additive are added during the tapping process of the converter.

[0053] (2) The LF refining temperature is increased, and the composition of the molten steel is adjusted. A total of 100 kg of silicon-manganese alloy, 30 kg of silicon-iron alloy, 50 kg of high-carbon chromium iron, and 80 kg of carbon additive are added during the LF refining process. The final molten steel temperature in the refining process is 1688°C, and the composition of the molten steel is C: 0.56%, Si: 0.14%, Mn: 0.56%, Cr: 1.96%, Mo: 0.01%, P: 0.010%, and S: 0.008%.

[0054] (3) The RH adopts argon as the lifting gas, and the lifting gas flow rate is 80 Nm 3 / h, and the vacuum degree is 8000 Pa. Under the RH vacuum condition, 3100 kg of molybdenum ball is added from the bin, and CaO is used to replace FeO in the molybdenum ball. After the addition of the molybdenum ball, the vacuum treatment is carried out for 12 minutes, and the composition of the molten steel is C: 0.31%, Si: 0.02%, Mn: 0.53%, Cr: 1.94%, Mo: 0.93%, P: 0.009%, and S: 0.007%. The C content exceeds the steel grade composition requirement, and the Si content is lower than the steel grade composition requirement. Oxygen blowing is carried out for 12 minutes for decarburization, and then 260 kg of silicon-iron is added. After soft blowing, the molten steel sample is taken for detection, and the C content is 0.11% and the Si content is 0.15%, which meets the steel grade composition requirement, and the ladle is lifted to the continuous casting platform for casting.

[0055] The alloy (including carbon additive) cost of Example 3 from the converter tapping to the RH treatment is 3507.07 yuan / t, as shown in Table 1, and the RH process time is increased by 6 minutes.

[0056] The qualified steel grades prepared in the examples and comparative examples have no big difference in performance, and meet the user requirements.

[0057] Table 1 Alloy addition amount and cost

[0058]

Claims

1. A low cost smelting method of low carbon molybdenum containing steel, characterized in that, The smelting process is "converter smelting-LF refining-RH vacuum treatment-continuous casting", which comprises the following steps: (1) Controlling the C content of converter end point to be 0.10%-0.50%, and adding high-carbon alloy during tapping according to the composition requirements of the steel grade; (2) Adjusting the composition of the molten steel and increasing the temperature in the LF refining, and controlling the composition of the molten steel at the end point of the LF refining: C: 0.55%-0.65%, Si: 0.12%-0.42%, Mn: 0.40%-0.60%, Cr: 1.95%-2.50%, P≤0.015%, S≤0.015%, and the end point temperature is 1670°C-1700°C; (3) Adding molybdenum balls under the RH vacuum condition; (4) Soft blowing and continuous casting; The molybdenum balls are a mixture of molybdenum oxide and ferrous oxide powder, and the composition of the molybdenum balls is MoO3: 55%-70%, FeO: 18%-23%, P≤0.06%, Cu≤0.50%, and the rest is impurities; the diameter of the molybdenum balls is 10mm-30mm.

2. The low cost smelting method of low carbon molybdenum containing steel as claimed in claim 1, wherein, No low-carbon alloy is used in the smelting process.

3. The low cost smelting method of low carbon molybdenum containing steel as claimed in claim 1, wherein, The high-carbon alloy includes high-carbon ferromanganese and high-carbon ferrochrome.

4. The low cost smelting method of low carbon molybdenum containing steel as claimed in claim 1, wherein, The RH vacuum degree is controlled to be 5000Pa-8000Pa in step (3), and the vacuum treatment time is 8-12min.

5. The low cost smelting method of low carbon molybdenum containing steel as claimed in claim 4 wherein, The RH vacuum degree is controlled, argon is used as the lifting gas, and the lifting gas flow is 60-100 Nm 3 / h.

6. The low cost smelting method of low carbon molybdenum containing steel as claimed in claim 1, wherein, The composition of the low-carbon molybdenum steel is: C: 0.06%-0.13%, Si: 0.10%-0.40%, Mn: 0.35%-0.60%, Cr: 1.90%-2.50%, Mo: 0.90%-1.10%, P≤0.015%, S≤0.015%, O≤0.003%, and H≤0.0002%.

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