Ultrasonic-assisted technology for reducing segregation of microalloy elements in smelting process of Mn-V series non-quenched and tempered steel

Abstract

The invention discloses an ultrasonic-assisted technology for reducing segregation of microalloy elements in the smelting process of Mn-V series non-quenched and tempered steel, which comprises the following steps: feeding a vanadium-iron alloy wire into molten steel, and simultaneously applying ultrasonic waves to the molten steel so as to reduce the segregation of the microalloy elements in the smelting process of the Mn-V series non-quenched and tempered steel. According to the method, rapid melting of the vanadium-iron alloy wire is promoted through high temperature, meanwhile, local enrichment of the vanadium element is prevented through the synergistic effect of argon stirring and ultrasonic sound stream, then segregation of microalloy elements in the Mn-V series non-quenched and tempered steel smelting process is reduced, the yield strength of a Mn-V series non-quenched and tempered steel casting blank can be stabilized to be 550 MPa or above through the technology, and the yield strength of the Mn-V series non-quenched and tempered steel casting blank can be improved. And meanwhile, the magnetic mark defect rate is reduced to 0.3% or below, and a reliable solution is provided for steel for high-end engineering machinery.

Description

Technical Field

[0001] The present invention relates to the field of metallurgical technology, and more particularly, to an ultrasonic-assisted technology for reducing microalloy element segregation during the smelting process of Mn-V series non-quenched and tempered steel. Background Art

[0002] Non-quenched and tempered steel, due to its non-requirement of quenching and tempering treatment, has the characteristics of simple processing procedures, low energy consumption, and uniform properties, and is widely used in the production of automotive parts, such as crankshafts, connecting rods, etc. Typical non-quenched and tempered steels are classified according to their compositions, including Mn-V series, Mn-V-S series, Mn-S series, etc. The main difference lies in the different requirements for mechanical properties or cutting properties of the final parts. Mn-V series non-quenched and tempered steel with relatively high C, Mn, and V elements has good fatigue and impact properties and is generally used in the preparation of heavy truck crankshafts.

[0003] At present, it is difficult to control the magnetic marks of non-quenched and tempered crankshafts, and there is no direct and effective method to reduce magnetic marks during the smelting process. Summary of the Invention

[0004] The purpose of the present invention is to provide an ultrasonic-assisted technology for reducing microalloy element segregation during the smelting process of Mn-V series non-quenched and tempered steel to overcome the above-mentioned defects existing in the prior art.

[0005] The present invention solves its technical problems by adopting the following technical solutions.

[0006] An embodiment of the present invention provides an ultrasonic-assisted technology for reducing microalloy element segregation during the smelting process of Mn-V series non-quenched and tempered steel, which includes: feeding ferrovanadium alloy wire into the molten steel, and simultaneously applying ultrasonic waves to the molten steel to reduce microalloy element segregation during the smelting process of Mn-V series non-quenched and tempered steel.

[0007] The present invention has the following beneficial effects:

[0008] The present invention provides an ultrasonic-assisted technology for reducing microalloy element segregation during the smelting process of Mn-V series non-quenched and tempered steel. The ultrasonic-assisted technology for reducing microalloy element segregation during the smelting process of Mn-V series non-quenched and tempered steel provided by the present invention promotes the rapid melting of ferrovanadium alloy wire through high temperature, and simultaneously uses the synergistic effect of argon stirring and ultrasonic streaming to prevent local enrichment of vanadium element, thereby reducing microalloy element segregation during the smelting process of Mn-V series non-quenched and tempered steel. Detailed Embodiments

[0009] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0010] The ultrasonic-assisted technology for reducing microalloy element segregation in the smelting process of Mn-V series non-quenched and tempered steel provided by the embodiments of the present invention will be specifically described below.

[0011] The embodiments of the present invention provide an ultrasonic-assisted technology for reducing microalloy element segregation in the smelting process of Mn-V series non-quenched and tempered steel, which includes: feeding ferrovanadium alloy wire into the molten steel, and simultaneously applying ultrasonic waves to the molten steel to reduce microalloy element segregation in the smelting process of Mn-V series non-quenched and tempered steel.

[0012] In some optional embodiments, it includes the following steps: when the temperature of the molten steel is stable, start the wire feeding machine; synchronously turn on the ultrasonic wave, and the vibration direction of the vibration wave is along the movement path of the alloy wire; open the bottom blowing argon of the ladle to assist the molten pool circulation.

[0013] The ultrasonic-assisted technology for reducing microalloy element segregation in the smelting process of Mn-V series non-quenched and tempered steel provided by the embodiments of the present invention can promote the rapid melting of FeV80 at high temperature; the argon stirring and ultrasonic streaming cooperate to prevent local enrichment of vanadium elements, and greatly reduce microalloy element segregation in the smelting process of Mn-V series non-quenched and tempered steel.

[0014] In some optional embodiments, when the temperature of the molten steel is stable, start the wire feeding machine; the method of synchronously turning on the ultrasonic wave includes: installing an ultrasonic transducer 30 cm below the outlet of the wire feeding machine, the immersion depth of the ultrasonic horn into the molten steel is 50 - 80 mm, and the angle with the wire feeding path is 45°. The 45° angle can simultaneously generate longitudinal vibration (promote alloy dissolution) and transverse acoustic streaming (enhance stirring); the immersion depth ensures that the ultrasonic action area covers the molten area of the alloy wire.

[0015] In some optional embodiments, the ultrasonic parameters of the ultrasonic transducer are set as follows: the frequency is 20 kHz; the power is 2 kW; the amplitude is 50 μm. The 20 kHz ultrasonic wave can generate dense cavitation bubbles (diameter ~100 μm) in the molten steel; the 2 kW power ensures that an instantaneous high pressure >100 MPa is generated when the bubbles collapse, breaking the primary VC particles.

[0016] In some optional embodiments, the stable temperature range of the molten steel is 1550 - 1600 °C, preferably 1580 ± 10 °C.

[0017] In some optional embodiments, the wire feeding speed of the wire feeding machine is 0 - 10 m / min, the accuracy is ±0.1 m / min, and the preferred wire feeding speed is 5 m / min.

[0018] In some optional embodiments, the flow rate of the bottom blowing argon of the ladle is controlled at 0.5 - 2.0 NL / min, preferably 1.2 NL / min.

[0019] In some optional embodiments, before adding the ferrovanadium alloy wire, the following pretreatment is carried out: cutting the FeV80 alloy wire with a diameter of φ3mm into 1.5m lengths, and subjecting it to surface sandblasting treatment to make Ra = 6.3μm. The short-segment cutting of the FeV80 alloy wire facilitates the transmission of ultrasonic vibration; the rough surface increases the contact area with the molten steel and accelerates dissolution.

[0020] In some optional embodiments, it further includes: when feeding the ferrovanadium alloy wire into the molten steel, if the melting time of the ferrovanadium alloy wire > 40 seconds, increasing the ultrasonic power to 2.5kW or reducing the wire feeding speed to 4m / min; if violent tumbling appears on the molten steel surface, reducing the argon gas flow rate to 0.8NL / min.

[0021] In some optional embodiments, the yield strength of the Mn-V series non-quenched and tempered steel billet obtained is stably above 550MPa, and at the same time, the magnetic flaw defect rate is reduced to below 0.3%.

[0022] The present invention will be further described below in conjunction with the embodiments.

[0023] An ultrasonic-assisted technique for reducing microalloy element segregation in the smelting process of 48MnV:

[0024] The core equipment is configured as follows

[0025]

[0026]

[0027] Example 1

[0028] Step 1. Pretreatment of the ferrovanadium alloy wire

[0029] Cut the FeV80 alloy wire (diameter φ3mm) into 1.5m lengths and perform surface sandblasting treatment (Ra = 6.3μm).

[0030] Step 2. Installation of the ultrasonic transducer

[0031] Install an ultrasonic horn 30cm below the outlet of the wire feeder, with the immersion depth in the molten steel being 50 - 80mm and the angle with the wire feeding path being 45°.

[0032] Step 3. Setting of ultrasonic parameters

[0033] Frequency: 20kHz (optimal range for cavitation effect);

[0034] Power: 2kW (energy density ≥ 15W / cm 2 )

[0035] Amplitude: 50μm (above the cavitation threshold);

[0036] Step 4: Coordinated operation of wire feeding and ultrasonic wave:

[0037] 1. When the molten steel temperature is stabilized at 1580 ± 10 °C, start the wire feeder with a wire feeding speed of 5 m / min.

[0038] 2. Simultaneously turn on the ultrasonic wave with the vibration direction along the movement path of the alloy wire.

[0039] 3. Set the bottom blowing flow rate of argon gas to 1.2 NL / min to assist the molten pool circulation.

[0040] 4. If the melting time > 40 seconds, increase the ultrasonic power to 2.5 kW or decrease the wire feeding speed to 4 m / min; if there is violent churning on the molten steel surface, reduce the argon gas flow rate to 0.8 NL / min.

[0041] Example 2

[0042] Similar to the steps of Example 1, the difference is only that: when the molten steel temperature is stabilized at 1600 °C, start the wire feeder with a wire feeding speed of 7 m / min.

[0043] Example 3

[0044] Similar to the steps of Example 1, the difference is only that: when the molten steel temperature is stabilized at 1580 ± 10 °C, start the wire feeder with a wire feeding speed of 5 m / min.

[0045] Comparative Example 1

[0046] The traditional process uses a conventional smelting method, mainly including the following steps:

[0047] 1. Addition of ferrovanadium alloy wire: Directly feed the unpretreated FeV80 alloy wire (diameter φ3 mm) into the molten steel with a wire feeding speed of 5 m / min.

[0048] 2. Without ultrasonic assistance: Do not apply ultrasonic vibration and rely only on natural melting and diffusion.

[0049] 3. Argon gas stirring: The bottom blowing argon gas flow rate in the ladle is 1.2 NL / min, but it does not cooperate with the ultrasonic wave.

[0050] 4. Molten steel temperature: Stabilized at 1580 ± 10 °C, consistent with the traditional process.

[0051] Comparative Example 2

[0052] Similar to the steps of Example 1, the difference is only that: the ultrasonic frequency is reduced to 15 kHz.

[0053] Comparative Example 3

[0054] Similar to the steps of Example 1, the difference is only that: the ultrasonic power is increased to 3 kW.

[0055] Comparative Example 4

[0056] Similar to the steps of Example 1, except that: the wire feeding speed was increased to 12 m / min.

[0057] Comparative Example 5

[0058] Similar to the steps of Example 1, except that: the argon flow rate was reduced to 0.3 NL / min.

[0059] Comparative Example 6

[0060] Similar to the steps of Example 1, except that: the molten steel temperature was increased to 1620 °C.

[0061] Comparative Example 7

[0062] Similar to the steps of Example 1, except that: the FeV80 alloy wire was not cut.

[0063] Comparative Example 8

[0064] Similar to the steps of Example 1, except that: the amplitude of the ultrasonic transducer was reduced to 30 μm.

[0065] The test results of the traditional process (Comparative Example 1) and the ultrasonic-assisted process used in Examples 1-3 of the present invention were statistically analyzed, and the statistical results are shown in Table 1 below.

[0066] Table 1

[0067]

[0068]

[0069] The test results of Comparative Examples 2-8 were compared with those of Example 1, and the results are shown in Table 2 below:

[0070] Table 2

[0071]

[0072]

[0073] It can be seen from the experimental results in Table 1 and Table 2 that in Comparative Example 1, smelting was carried out using the traditional process, the VC refinement effect was poor, the VC size was large, the segregation index of vanadium element was high, the equiaxed crystal ratio was low, the consumption of ferrotitanium per ton of steel was high, and the magnetic flaw defect rate was high. In Comparative Example 2, due to the too low frequency, the cavitation effect was insufficient and the VC refinement effect was weakened. In Comparative Example 3, due to the too high power, the molten steel was disturbed, destroying the stability of the molten pool. In Comparative Example 4, due to the too fast speed, the alloy wire was not fully melted, increasing the consumption. In Comparative Example 5, due to the insufficient flow rate, the stirring efficiency was reduced, affecting the uniform distribution of elements. In Comparative Example 6, due to the too high temperature, the grain coarsening occurred and the mechanical properties decreased. In Comparative Example 7, the uncut alloy wire hindered the ultrasonic energy transmission, reducing the uniformity. In Comparative Example 8, due to the insufficient amplitude, the cavitation threshold could not be reached and the VC refinement effect decreased significantly.

[0074] However, for the non-quenched and tempered steel for 48MnV crankshaft prepared by the solution provided in the embodiment of the present invention, the VC size is refined, the segregation index of vanadium element is reduced, the uniformity is improved, the equiaxed crystal ratio is increased, and the consumption of ferrotitanium per ton of steel and the magnetic flaw defect rate both decrease significantly. A large number of practices have proved that this technology can stably maintain the yield strength of the 48MnV billet above 550 MPa, and at the same time reduce the magnetic flaw defect rate to less than 0.3%. While ensuring the mechanical properties, the defect rate is significantly reduced, providing an efficient and stable industrial solution for high-end engineering machinery steel.

[0075] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An ultrasonic-assisted technique for reducing the segregation of microalloying elements during the smelting process of Mn-V series non-quenched and tempered steel, characterized in that, It includes: Fe-V ferroalloy wire is fed into the molten steel, and at the same time, ultrasonic waves are applied to the molten steel to reduce the segregation of microalloying elements during the smelting process of Mn-V non-quenched and tempered steel.

2. The ultrasonic-assisted technique according to claim 1, wherein It includes the following steps: When the temperature of the molten steel is stable, start the wire feeder; synchronously turn on the ultrasonic wave, and the vibration direction of the vibration wave is along the movement path of the alloy wire; open the bottom blowing argon of the ladle to assist the molten pool circulation.

3. The ultrasonic assistance technique according to claim 2, characterized in that, When the temperature of the molten steel is stable, start the wire feeder; the method of synchronously turning on the ultrasonic wave includes: installing an ultrasonic transducer 30 cm below the outlet of the wire feeder, immersing the ultrasonic horn into the molten steel to a depth of 50-80 mm, and making an angle of 45° with the wire feeding path.

4. The ultrasonic-assisted technique according to claim 3, characterized in that, The ultrasonic parameters of the ultrasonic transducer are set as follows: the frequency is 20 kHz; the power is 2 kW; the amplitude is 50 μm.

5. The ultrasonic-assisted technique according to claim 2, wherein The stable temperature range of the molten steel is 1550-1600 °C, preferably 1580±10 °C.

6. The ultrasonic-assisted technique according to claim 2, wherein The wire feeding speed of the wire feeder is 0-10 m / min, the accuracy is ±0.1 m / min, and the preferred wire feeding speed is 5 m / min.

7. The ultrasonic assistance technique according to claim 2, wherein The flow rate of the bottom blowing argon of the ladle is controlled at 0.5-2.0 NL / min, preferably 1.2 NL / min.

8. The ultrasonic assistance technique according to claim 2, characterized in that, Before adding the Fe-V ferroalloy wire, the following pretreatment is carried out: cutting the FeV80 alloy wire with a diameter of φ3 mm into a length of 1.5 m, and subjecting it to surface sandblasting treatment to make Ra = 6.3 μm.

9. The ultrasonic-assisted technique according to claim 2, characterized in that, It also includes: When feeding the Fe-V ferroalloy wire into the molten steel, if the melting time of the Fe-V ferroalloy wire > 40 seconds, increase the ultrasonic power to 2.5 kW or reduce the wire feeding speed to 4 m / min; if the molten steel surface shows violent tumbling, reduce the argon flow rate to 0.8 NL / min.

10. The ultrasonic-assisted technique according to any one of claims 2-9, characterized in that The yield strength of the Mn-V non-quenched and tempered steel slab obtained is stably above 550 MPa, and at the same time, the magnetic flaw defect rate is reduced to less than 0.3%.

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