Smelting method of steel for non-quenched and tempered crankshaft

Abstract

The invention provides a smelting method of steel for a non-quenched and tempered crankshaft, the steel for the non-quenched and tempered crankshaft comprises the following chemical components in percentage by weight: 0.25%-0.50% of C, 0.20%-0.80% of Si, 0.80%-1.80% of Mn, 0.020%-0.060% of S, 0.015%-0.060% of Al, 50-200ppm of N, less than or equal to 0.020% of P and the balance of Fe, inevitable impurities and one or more of V, Ti and Nb, and the total content of V, Ti and Nb is less than or equal to 0.20%. The smelting method comprises the steps of converter smelting, LF refining, RH vacuum degassing and continuous casting. Wherein 1-3 kg / t of silicon ball deoxidizer, 2-4 kg / t of lime and 4-8 kg / t of wollastonite are added during converter smelting and tapping; in the LF refining process, a siliceous deoxidizer with the total amount of 0.5-1.5 kg / t steel is added in batches for diffusion deoxidation during heating, and meanwhile, lime with the total amount of 2-6 kg / t steel and wollastonite with the total amount of 4-9 kg / t steel are added; and in the later stage of LF refining, sulfur-iron alloy is added, Al alloying is conducted in the RH vacuum degassing process, and calcium wires are fed after vacuum breaking. The casting continuity of the steel for the non-quenched and tempered crankshaft can be improved, and the content of inclusions can be controlled.

Description

Technical Field

[0001] This invention relates to the field of smelting technology for non-quenched and tempered crankshaft steel, and particularly to a smelting method for non-quenched and tempered crankshaft steel. Background Technology

[0002] Non-quenched and tempered crankshaft steel is an energy-saving and environmentally friendly steel that, through micro-alloying design and controlled rolling and cooling processes, omits the traditional quenching and tempering heat treatment (quenching + tempering) steps, while still ensuring excellent comprehensive performance. It is a key material for automotive lightweighting and sustainable manufacturing, and is especially suitable for mass-produced passenger car crankshafts. With the upgrading of micro-alloying technology, its application scope is gradually expanding to key components such as connecting rods and camshafts.

[0003] In terms of composition design, the following approach is adopted for non-quenched and tempered crankshaft steel: 1) C content of 0.25%~0.5% to ensure appropriate strength; 2) Conventional alloying elements such as Si, Mn, and Al to improve solid solution strengthening and hardenability; 3) Main addition of microalloying elements such as V, Ti, and Nb to refine grains and precipitation strengthening, inhibit austenite grain growth and improve toughness; 4) S content of 0.020%~0.060% to improve machinability.

[0004] The process of smelting non-quenched and tempered crankshaft steel is generally carried out by electric furnace (converter) - LF refining - RH vacuum degassing - continuous casting. The main problems to be solved in the smelting process are composition adjustment, casting continuity and inclusion control. At present, the number of continuous casting heats of non-quenched and tempered crankshaft steel in China is usually less than 5 heats, and the casting stability control is relatively difficult. The main reason is that the contradiction between the Al alloying deoxidation process and the S alloying oxidation process has not been effectively resolved. Nodules are prone to occur during the casting process, which has a great impact on the stability of production and quality, and at the same time greatly increases the manufacturing cost.

[0005] Therefore, it is necessary to develop a smelting method for non-quenched and tempered crankshaft steel to improve the casting continuity of non-quenched and tempered crankshaft steel and control the content of inclusions. Summary of the Invention

[0006] The purpose of this invention is to provide a smelting method for non-quenched and tempered crankshaft steel, so as to solve the problems of poor casting continuity and high inclusion content of existing non-quenched and tempered crankshaft steel, while effectively reducing production costs.

[0007] To solve the above-mentioned technical problems, the present invention provides a smelting method for non-quenched and tempered crankshaft steel. The chemical composition of the non-quenched and tempered crankshaft steel, by weight percentage, is as follows: C: 0.25%~0.50%, Si: 0.20%~0.80%, Mn: 0.80%~1.80%, S: 0.020%~0.060%, Al: 0.015%~0.060%, N: 50~200ppm, P≤0.020%, with the remainder being Fe, unavoidable impurities, and one or more of V, Ti, and Nb, and the total content of V, Ti, and Nb ≤0. 20%; the smelting method includes: converter smelting, LF refining, RH vacuum degassing and continuous casting; wherein, when the steel is tapped from the converter, 1~3 kg / t of silicon ball deoxidizer, 2~4 kg / t of lime and 4~8 kg / t of wollastonite are added; during the LF refining process, during the heating period, a total of 0.5~1.5 kg / t of silicon deoxidizer is added in batches for diffusion deoxidation, and at the same time, 2~6 kg / t of lime and 4~9 kg / t of wollastonite are added; in the later stage of LF refining, ferrosulfide alloy is added; during the RH vacuum degassing process, Al alloying is carried out, and after breaking the void, calcium wire is fed.

[0008] Optionally, the interval between adding the ferrosulfide alloy and feeding the calcium wire after breaking the void is greater than 30 minutes.

[0009] Optionally, during converter smelting and tapping, when the tapping quality reaches 1 / 4 to 1 / 3, silicon ball deoxidizer is added to the ladle according to the final carbon content or oxygen level; when the tapping quality reaches 4 / 5, 2 to 4 kg / t of lime and 4 to 8 kg / t of wollastonite are added.

[0010] Optionally, after the white slag is formed by LF refining, silicon, calcium, and barium are added in batches during subsequent heating and holding periods, while large-scale argon stirring is not allowed during the holding period of the white slag.

[0011] Optionally, during the LF refining process, the binary basicity of the top slag is 1.0~1.5, wherein CaO: 35~55%, SiO2: 35~50%, TFe+MnO≤3.5%, and Al2O3≤10%.

[0012] Optionally, when adding ferrous sulfate alloy, a 0.003% to 0.005% attenuation margin can be reserved.

[0013] Optionally, during the RH vacuum degassing process, nitrogen is used as the boosting gas, and in the later stage of vacuum treatment, the vacuum pump is gradually shut off and the test hole is opened to adjust the vacuum level to 100-300 mbar in order to control the N content of the molten steel.

[0014] Optionally, during the RH vacuum degassing process, the Al content of the molten steel can be adjusted by adding aluminum particles in the later stage of vacuum treatment.

[0015] Optionally, the Al content of the molten steel can be adjusted by adding aluminum particles according to the finished product Al composition requirement +0.008%.

[0016] Optionally, during the RH vacuum degassing process, a weak stirring time of more than 2 minutes should be ensured before feeding calcium wire. The amount of calcium wire used for the first furnace of each casting is 0.6~1.0 m / t steel, and the amount of calcium wire used for consecutive furnaces is 0.4~0.7 m / t steel. The target requirement for the Ca content of the molten steel is 8~13 ppm.

[0017] The present invention provides a smelting method for non-quenched and tempered crankshaft steel, which has the following beneficial effects: By adding 1-3 kg / t of silicon ball deoxidizer, 2-4 kg / t of lime, and 4-8 kg / t of wollastonite during converter smelting and tapping, and during the LF refining process, adding a total of 0.5-1.5 kg / t of silicon deoxidizer in batches during heating for diffusion deoxidation, while simultaneously adding 2-6 kg / t of lime and 4-9 kg / t of wollastonite, a low-basicity (1.0-1.5) slag system and a suitable slag quantity is generated, thereby ensuring deoxidation and sulfur control effects. Furthermore, by adding ferrosulfur alloy in the later stages of LF refining and performing Al alloying during RH vacuum degassing, followed by calcium wire feeding after void breaking, the time interval between S alloying and calcium treatment is increased to avoid CaS affecting casting. Ultimately, this improves casting stability and inclusion control, thereby increasing the number of consecutive castings and achieving low-cost smelting. Attached Figure Description

[0018] Figure 1 It is the casting curve of molten steel produced by the smelting method of non-quenched and tempered crankshaft steel in the comparative example during continuous casting. Figure 2 This is the casting curve of molten steel produced by the smelting method for non-quenched and tempered crankshaft steel in this embodiment of the invention during continuous casting. Detailed Implementation

[0019] This embodiment provides a smelting method for non-quenched and tempered crankshaft steel. The chemical composition of the non-quenched and tempered crankshaft steel, by weight percentage, is: C: 0.25%~0.50%, Si: 0.20%~0.80%, Mn: 0.80%~1.80%, S: 0.020%~0.060%, Al: 0.015%~0.060%, N: 50~200ppm, P≤0.020%, with the remainder being Fe, unavoidable impurities, and one or more of V, Ti, and Nb, and the total content of V, Ti, and Nb ≤0.20%. The smelting methods include: converter smelting, LF refining, RH vacuum degassing, and continuous casting; Among them, 1~3 kg / t of silicon ball deoxidizer, 2~4 kg / t of lime and 4~8 kg / t of wollastonite are added when the steel is produced by converter smelting; During the LF refining process, a total of 0.5~1.5 kg / t steel of siliceous deoxidizer is added in batches during heating for diffusion deoxidation, while 2~6 kg / t steel of lime and 4~9 kg / t steel of wollastonite are added at the same time. In the later stages of LF refining, a ferrous sulfate alloy is added: Al alloying is carried out during RH vacuum degassing, and calcium wire is fed after the vacuum is broken.

[0020] In this embodiment, by adding 1-3 kg / t of silicon ball deoxidizer, 2-4 kg / t of lime, and 4-8 kg / t of wollastonite during converter smelting and tapping, and during the LF refining process, adding a total of 0.5-1.5 kg / t of silicon deoxidizer in batches during heating for diffusion deoxidation, while simultaneously adding 2-6 kg / t of lime and 4-9 kg / t of wollastonite, a low-alkalinity (1.0-1.5) slag system and a suitable slag quantity is generated, thereby ensuring deoxidation and sulfur control effects. By adding ferrosulfur alloy in the later stage of LF refining and performing Al alloying during RH vacuum degassing, followed by calcium wire feeding after void breaking, the time interval between S alloying and calcium treatment is increased to avoid CaS affecting casting. Ultimately, this achieves improved casting stability and inclusion control.

[0021] Preferably, the interval between adding the ferrosulfide alloy and feeding the calcium wire after breaking the void is greater than 30 minutes. This can effectively avoid CaS affecting the casting, resulting in better casting stability and a lower level of inclusions in the molten steel.

[0022] Preferably, during the converter smelting process, when the steel quality reaches 1 / 4 to 1 / 3, silicon ball deoxidizer is added to the ladle according to the final carbon content or oxygen level; when the steel quality reaches 4 / 5, 2 to 4 kg / t of lime and 4 to 8 kg / t of wollastonite are added.

[0023] Preferably, during the converter smelting process, when the steel quality reaches 1 / 2, ferrosilicon, ferrosilicon, ferromanganese, and a carbon raiser are added to stabilize the yield of Si and Mn elements.

[0024] Preferably, when the steel is tapped from the converter and the tapping quality reaches 4 / 5, 2-4 kg / t of lime and 4-8 kg / t of wollastonite are added to the molten steel, and the steel is strongly stirred to fully slag and shorten the slag formation time in refining.

[0025] Preferably, after the white slag is formed by LF refining, silicon, calcium, and barium are added in batches during subsequent heating and holding periods to maintain the reducibility of the top slag. At the same time, large-scale argon gas stirring is not allowed during the white slag holding period to avoid affecting the reducibility of the top slag.

[0026] Preferably, the total amount of silicon, calcium, and barium added is 0.5-1 kg / t of steel, and it needs to be added in batches (10-20 kg per batch).

[0027] Preferably, when adding the ferrosulfide alloy in the later stage of LF refining, the molten steel is in a state of weak stirring.

[0028] Preferably, during the LF refining process, the binary basicity of the top slag is 1.0~1.5, wherein CaO: 35~55%, SiO2: 35~50%, TFe+MnO≤3.5%, and Al2O3≤10%.

[0029] When adding ferrosulfide alloy, a 0.003% to 0.005% attenuation margin is reserved to avoid the impact of subsequent Al alloying and calcium treatment on S.

[0030] Preferably, nitrogen is used as the boosting gas during the RH vacuum degassing process, and in the later stage of vacuum treatment, the vacuum pump is turned off in stages and the test hole is opened to adjust the vacuum degree to 100~300mbar in order to control the N content of the molten steel.

[0031] Preferably, during the RH vacuum degassing process, the Al content of the molten steel is adjusted by adding aluminum particles in the later stage of vacuum treatment.

[0032] Preferably, aluminum particles are added to adjust the Al content of the molten steel according to the Al composition requirement of the finished product +0.008%.

[0033] Preferably, during the RH vacuum degassing process, a weak stirring time of more than 2 minutes should be ensured before feeding calcium wire. The amount of calcium wire used in the first furnace of each casting is 0.6~1.0 m / t steel, and the amount of calcium wire used in consecutive furnaces is 0.4~0.7 m / t steel. The target requirement for the Ca content of molten steel is 8~13 ppm.

[0034] Preferably, continuous casting uses acidic and alkaline covering agents to maintain the reducing properties of molten steel while effectively keeping it warm.

[0035] Preferably, during continuous casting, the covering agent is superheated to 25~50°C to maintain a constant casting speed.

[0036] Examples 1 to 5 were conducted using a silicon deoxidation process for converter steelmaking and LF refining, with the LF refining producing low-basicity white slag controlled at 1.0-1.5, fine-tuning of the sulfur content in the molten steel at the end of the LF process, Al alloying in the later stage of RH vacuum, calcium treatment after RH vacuum breaking, and casting. Comparative Examples 1 to 4 were also conducted using an aluminum deoxidation process for converter steelmaking and LF refining, with the LF refining producing high-basicity white slag controlled at 4-7, Al alloying in the LF process, S alloying in the later stage of RH vacuum, calcium treatment after RH vacuum breaking, and casting.

[0037] Table 1. Auxiliary material consumption during electric arc furnace steelmaking process (kg / t steel) Table 2. Auxiliary material consumption in the LF refining process (kg / t steel) The composition control of the refining slag obtained in LF refining in Examples 1 to 5 and Comparative Examples 1 to 4 is shown in Table 3.

[0038] Table 3. Composition control of refining slag from LF refining furnace The composition of the steel after casting in Examples 1 to 5 and Comparative Examples 1 to 4 is shown in Table 4.

[0039] Table 4 Final composition control after casting Table 5 shows the inclusion control of the steel after casting in Examples 1 to 5 and Comparative Examples 1 to 4.

[0040] Table 5. Inclusion Control Status refer to Figure 1 and Figure 2 , Figure 1 This is the casting curve of molten steel produced by the non-quenched and tempered crankshaft steel smelting method in the comparative example during continuous casting. Figure 2 This is the casting curve of molten steel produced by the smelting method for non-quenched and tempered crankshaft steel in this embodiment of the invention during continuous casting. The green line represents the casting curve, the horizontal axis is time, the vertical axis is liquid level, and the black line is the curve showing the relationship between the stopper rod position (height) and time. Figure 1 and Figure 2It can be seen that the molten steel produced by the non-quenched and tempered crankshaft steel smelting method of the present invention has a stable liquid level height during continuous casting, good casting stability, stable stopper rod position (height), and good casting stability and castability.

[0041] The main advantages of Examples 1 to 5 compared to Comparative Examples 1 to 4 are as follows: Significantly improved casting stability of molten steel during continuous casting: Although Comparative Examples 1 to 4 met the requirements in terms of chemical composition, O, N, etc., the position of the stopper rod fluctuated greatly during the casting process, and a relatively obvious nodule phenomenon occurred. In Comparative Examples 1 to 4, four heats of steel were divided into two castings due to nodule formation. In contrast, Examples 1 to 5 of this application were cast in one casting for five heats, and the stopper rod control was more stable.

[0042] The inclusion control level is more stable: because the time span of S alloying and calcium treatment is extended in the process of this application, the amount of sulfur-iron alloy used is smaller, and the casting stability is increased. After adopting the same rolling process, the inclusion control level of the process of this invention is more stable. The average grade of A fine inclusions is 1.8, which is better than the grade of 2.5 in the comparative example, and the grade of B inclusions does not exceed 0.5.

[0043] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A method for smelting non-quenched and tempered crankshaft steel, characterized in that, The chemical composition of the non-quenched and tempered crankshaft steel, by weight percentage, is: C: 0.25%~0.50%, Si: 0.20%~0.80%, Mn: 0.80%~1.80%, S: 0.020%~0.060%, Al: 0.015%~0.060%, N: 50~200ppm, P≤0.020%, with the remainder being Fe, unavoidable impurities, and one or more of V, Ti, and Nb, and the total content of V, Ti, and Nb ≤0.20%. The smelting methods include: converter smelting, LF refining, RH vacuum degassing, and continuous casting; Among them, 1~3 kg / t of silicon ball deoxidizer, 2~4 kg / t of lime and 4~8 kg / t of wollastonite are added when the steel is produced by converter smelting; During the LF refining process, a total of 0.5~1.5 kg / t steel of siliceous deoxidizer is added in batches during heating for diffusion deoxidation, while 2~6 kg / t steel of lime and 4~9 kg / t steel of wollastonite are added at the same time. In the later stages of LF refining, a ferrous sulfate alloy is added: Al alloying is carried out during RH vacuum degassing, and calcium wire is fed after the vacuum is broken.

2. The smelting method for non-quenched and tempered crankshaft steel as described in claim 1, characterized in that, The interval between adding the sulfur-iron alloy and feeding the calcium wire after breaking the void should be greater than 30 minutes.

3. The smelting method for non-quenched and tempered crankshaft steel as described in claim 1, characterized in that, When steel is tapped from a converter, when the tapped steel reaches 1 / 4 to 1 / 3 of its weight, silicon ball deoxidizer is added to the ladle according to the final carbon content or oxygen content; when the tapped steel reaches 4 / 5 of its weight, 2 to 4 kg / t of lime and 4 to 8 kg / t of wollastonite are added.

4. The smelting method for non-quenched and tempered crankshaft steel as described in claim 1, characterized in that, After the white slag is formed by LF refining, silicon, calcium and barium are added in batches during the subsequent heating and holding period. At the same time, large-scale argon stirring is not allowed during the holding period of the white slag.

5. The smelting method for non-quenched and tempered crankshaft steel as described in claim 1, characterized in that, During the LF refining process, the binary basicity of the top slag is 1.0~1.5, with CaO: 35~55%, SiO2: 35~50%, TFe+MnO≤3.5%, and Al2O3≤10%.

6. The smelting method for non-quenched and tempered crankshaft steel as described in claim 1, characterized in that, When adding ferrous sulfate alloy, a tolerance of 0.003% to 0.005% should be reserved for attenuation.

7. The smelting method for non-quenched and tempered crankshaft steel as described in claim 1, characterized in that, During the RH vacuum degassing process, nitrogen is used as the boosting gas. In the later stage of vacuum treatment, the vacuum pump is turned off in stages and the test hole is opened to adjust the vacuum degree to 100~300mbar in order to control the N content of the molten steel.

8. The smelting method for non-quenched and tempered crankshaft steel as described in claim 1, characterized in that, During the RH vacuum degassing process, the Al content of the molten steel is adjusted by adding aluminum particles in the later stage of vacuum treatment.

9. The smelting method for non-quenched and tempered crankshaft steel as described in claim 8, characterized in that, The Al content of the molten steel is adjusted by adding aluminum granules to meet the Al composition requirements of the finished product plus a target of 0.008%.

10. The smelting method for non-quenched and tempered crankshaft steel as described in claim 1, characterized in that, During the RH vacuum degassing process, a weak stirring time of more than 2 minutes must be ensured before feeding calcium wire. The amount of calcium wire used for the first furnace of each casting is 0.6~1.0 m / t steel, and the amount of calcium wire used for consecutive furnaces is 0.4~0.7 m / t steel. The target requirement for the Ca content of molten steel is 8-13 ppm.

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