CN104226949B - A kind of method reducing strand C element segregation degree - Google Patents

Abstract

The present invention discloses a kind of method reducing strand C element segregation degree, its feature is the electromagnetic agitation method using and changing frequency, by changing electromagnetic agitation frequency, change electromagnetic field length of penetration in strand, change size and the distribution of electromagnetic force simultaneously, thus improve solidification end MOLTEN STEEL FLOW state and process of setting, reduce the purpose of C element segregation degree；Meanwhile, using optimal stirring frequency can also suitably reduce coil input current, reach energy-conservation purpose, hence it is evident that improve the internal soundness of strand, the method can also suitably reduce the size of coil input current, reduces energy consumption.

Description

A kind of method reducing strand C element segregation degree

Technical field

The invention belongs to continuous casting and material electromagnetic processing forming field, coagulate particularly to casting process Gu end electromagnetism flow control technology, a kind of method reducing strand C element segregation degree.

Background technology

In casting process, the kinestate of casting blank solidification end molten steel is to affect Inner Quality of Billet A key factor.Owing to dendrite bridging can cause the feeding of solidification end position insufficient, produce Raw Shrinkage cavity defect.Simultaneously as the different solubility that element is in liquid-solid two-phase, can make Become element segregation.Electromagnetic agitation is controlling and is improving solid-liquid interface forward position molten steel flow, expansion The aspects such as isometry crystalline region, crystal grain thinning, raising casting billet surface and internal soundness all play can not The effect substituted.This be embodied in numerous patent (such as Publication No. CN1266759A, The patent of invention etc. of CN1638893A with CN101185957), academic journal exchanges with meeting In file.The mechanism that rotary electromagnetic field reduces solidification end element segregation grade is: electromagnetic force is drawn The momentum convection risen adds the heat of melt, matter transmitting procedure, makes melt temperature distribution the most equal Even, thermograde reduces, and the solid rate making heart portion melt is more aligned, and increases in short-term Feature fraction solid, the freezing rate of solidification melt in latter stage increases, and makes heart portion melt in the short time Solidify the most simultaneously, slow down the composition skewness that solute element reallocation causes.But, electricity Magnetic stirring is too strong can promote that solidification front solute exchanges, and causes segregation serious, it is now recognized that the brightest Producing of band causes mainly due to electromagnetic agitation is too strong.Scholar is had to be sent out by experimental study Existing, in only having C, Si content at white band and carrying, outside band, differ bigger, it is believed that white band Mainly due to caused by C, Si element negative segregation.In order to obtain optimal mixing effect, reduce Element segregation grade, it is necessary to select suitable mixing position, the simultaneously electric current, frequently of electromagnetic agitation Rate, alr mode (being alternately rotated or single direction rotation) etc. all can produce impact to continuous casting billet structure, Need to be studied by experiment and simulation.

In casting process, along with conditions such as pouring molten steel temperature, intensity of cooling, casting speeds Difference, the wick-containing size at solidification end is the most different.The now solidified shell magnetic to electromagnetic agitation Field has certain shielding action, in order to make the molten steel of solidification end obtain big electromagnetic agitation Power, currently mainly take is the coil current size improving agitator.Ordinary circumstance coil is Big current value is determined by the safe current of equipment, the limited space that can improve.

Summary of the invention

The present invention discloses a kind of method reducing strand C element segregation degree, according to electromagnetic field Principle, from electromagnetic hydroimechanics, optimize electromagnetic force distribution in strand.Employing changes The electromagnetic agitation method of Frequency, by changing electromagnetic agitation frequency, changes electromagnetic field at strand In length of penetration, change size and the distribution of electromagnetic force simultaneously, thus improve solidification end steel Water flow regime and process of setting, and then reduce C element segregation degree, hence it is evident that improve strand Internal soundness, the method can also suitably reduce the size of coil input current, reduces energy consumption.

The method that the present invention is mainly combined with verification experimental verification by sunykatuib analysis realizes, specifically Step is as follows:

1. utilize finite element software to set up electromagnetic agitation analogue model, calculate different electromagnetic agitation electricity The size of electromagnetic stirring force and distribution at wick-containing when stream and frequency, different shell thickness； Utilize vector potential A and scalar potential φ to solve electromagnetic field, establish below equation:

$B=\▿\×A---\left(1\right)$

$E=-\▿\mathrm{\φ}---\left(2\right)$

B and E is magnetic induction and electric field intensity respectively, according to Maxwell equation, The partial differential of magnetic field and electric field can be obtained, according to partial differential equation, can be in the hope of electricity The accounting equation of magnetic force F is as follows:

$F=J\×B=\frac{1}{\mathrm{\μ}}(B\·\▿)B-\frac{1}{2\mathrm{\μ}}\▿B^2---\left(3\right)$

The magnetic induction density B of various location in molten steel_zCan calculate with formula (4).

$B_z=B_0{e}^{-x\sqrt{\mathrm{\π}f\mathrm{\μ}\mathrm{\σ}}}---\left(4\right)$

Wherein, B₀For molten steel surface induction intensity, σ is molten steel electrical conductivity, and f is electric current Frequency. formula (4) is brought in formula (3), can obtain between electromagnetic force and frequency Relation.

2. the distribution of the electromagnetic force obtained according to step 1 calculates the velocity flow profile of wick-containing, and contrast is not Obtain the condition of Peak Flow Rate during same parameter condition, determine optimal stirring frequency；

Flow field continuity equation is as follows:

$\frac{\∂\mathrm{\ρ}}{\∂t}+\frac{\∂}{\∂x_i}\left({\mathrm{\ρu}}_i\right)=0---\left(5\right)$

In inertial coodinate system, the momentum conservation equation in i direction is:

$\frac{\∂}{\∂t}\left({\mathrm{\ρu}}_i\right)+\frac{\∂}{\∂x_j}\left({\mathrm{\ρu}}_i{u}_j\right)=-\frac{\∂p}{\∂x_i}+\frac{\∂{\mathrm{\τ}}_{ij}}{\∂x_j}+{\mathrm{\ρg}}_i+F_i---\left(6\right)$

Wherein p is static pressure, g_iFor gravity, F_iFor the electromagnetic induction power in i direction, τ_ijFor stress tensor.

3., by the experimental analysis strand C element regularity of distribution, optimal electromagnetic agitation frequency is verified in amendment Rate, uses magnetic stirrer that molten steel is applied electromagnetic agitation.

The present invention changes the size of wick-containing position electromagnetic force by regulating frequency, and then improves solidifying Gu end MOLTEN STEEL FLOW state and process of setting, reduce the purpose of C element segregation degree； Meanwhile, use optimal stirring frequency can also suitably reduce coil input current, reach energy-conservation Purpose, hence it is evident that improve the internal soundness of strand, the method can also suitably reduce coil input electricity The size of stream, reduces energy consumption.

Accompanying drawing explanation

Fig. 1 is electromagnetic agitation structural representation of the present invention.

Fig. 2 is the relation between wick-containing position maximum electromagnetic stirring force and frequency.

The velocity field vector distribution of wick-containing position when Fig. 3 is 4Hz stirring frequency.

The velocity field vector distribution of wick-containing position when Fig. 4 is 7Hz stirring frequency.

1: wick-containing；2: solidified shell；3: air；4: iron core；5: coil

Detailed description of the invention

Below in conjunction with the accompanying drawings the detailed description of the invention of the present invention is elaborated:

As it is shown in figure 1, the magnetic induction at wick-containing 1 is relevant with the thickness of solidified shell 2, When different continuous-casting conditions, the thickness of solidified shell is the most different, thus penetrates into strand wick-containing 1 The magnetic induction of position is the most different.The size of magnetic induction determines the big of electromagnetic force Little.

The present invention is that the method combined with verification experimental verification by sunykatuib analysis is realized, specifically Step is as follows:

1. utilize finite element software to set up electromagnetic agitation analogue model, calculate different electromagnetic agitation electricity The size of electromagnetic stirring force and distribution at wick-containing when stream and frequency, different shell thickness；Profit Solve electromagnetic field with vector potential A and scalar potential φ, establish below equation:

$B=\▿\×A---\left(1\right)$

$E=-\▿\mathrm{\φ}---\left(2\right)$

B and E is magnetic induction and electric field intensity respectively, according to Maxwell equation, The partial differential of magnetic field and electric field can be obtained, according to partial differential equation, can be in the hope of electricity The accounting equation of magnetic force F is as follows:

$F=J\×B=\frac{1}{\mathrm{\μ}}(B\·\▿)B-\frac{1}{2\mathrm{\μ}}\▿B^2---\left(3\right)$

The magnetic induction density B of various location in molten steel_zCan calculate with formula (4),

$B_z=B_0{e}^{-x\sqrt{\mathrm{\π}f\mathrm{\μ}\mathrm{\σ}}}---\left(4\right)$

Wherein, B₀For molten steel surface induction intensity, σ is molten steel electrical conductivity, and f is electric current Frequency, is brought into formula (4) in formula (3), can obtain between electromagnetic force and frequency Relation；

2. the distribution of the electromagnetic force obtained according to step 1 calculates the velocity flow profile of wick-containing, contrast Obtain the condition of Peak Flow Rate during different parameters condition, determine optimal stirring frequency；

3. flow field continuity equation is as follows:

$\frac{\∂\mathrm{\ρ}}{\∂t}+\frac{\∂}{\∂x_i}\left({\mathrm{\ρu}}_i\right)=0---\left(5\right)$

In inertial coodinate system, the momentum conservation equation in i direction is:

$\frac{\∂}{\∂t}\left({\mathrm{\ρu}}_i\right)+\frac{\∂}{\∂x_j}\left({\mathrm{\ρu}}_i{u}_j\right)=-\frac{\∂p}{\∂x_i}+\frac{\∂{\mathrm{\τ}}_{ij}}{\∂x_j}+{\mathrm{\ρg}}_i+F_i---\left(6\right)$

Wherein p is static pressure, g_iFor gravity, F_iFor the electromagnetic induction power in i direction, τ_ijFor stress tensor.

4., by the experimental analysis strand C element regularity of distribution, amendment verifies that optimal electromagnetism stirs Mix frequency, use magnetic stirrer that molten steel is applied electromagnetic agitation.

By computing formula (3) and (4), draw the relation between electromagnetic stirring force and frequency, Simulate calculated 280 × 380mm bloom wick-containing position maximum electromagnetic stirring force and frequency Between relation as in figure 2 it is shown, from figure 2 it can be seen that start time along with the increase of frequency, Electromagnetic stirring force is gradually increased, and when frequency reaches 17Hz, electromagnetic stirring force reaches maximum. Along with the continuation of frequency raises, maximum electromagnetic stirring force is gradually lowered.Therefore when agitator coil When inputting identical electric current, stirring frequency selects can obtain the electromagnetic agitation of maximum at 17Hz Power.If stirring intensity is too strong, then coil input current can be reduced, so can not only protect Card mixing effect, can reduce equipment operating cost with saves energy simultaneously.

Fig. 3 shows strand 280 × 380mm, and wick-containing is 90 × 160mm difference stirring frequency The velocity field vector distribution of wick-containing position during rate.When stirring frequency is 4Hz, at wick-containing Big flow velocity is 2.9cm/s, and as shown in Figure 4, when frequency brings up to 7Hz, Peak Flow Rate carries High to 3.6cm/s, higher by 24% than the former.Along with the raising of flow velocity, the heat transfer of strand and biography Mass-energy is enough enhanced, and advantageously reduces the thermograde of molten steel at wick-containing, promotes that wick-containing is coagulated simultaneously Gu, thus C element segregation can be eased.

Owing to LX80 level cord steel is to field trash requirement, continuous casting center segregation and organizational controls etc. Requirement very strict, prior art is difficult to solve this variety steel asking at continuous casting center segregation Topic, now uses the inventive method, stirs LX80 level cord steel continuous casting center segregation different Experimental study, result has been carried out for LX80 steel solidification end electromagnetic agitation effect when mixing frequency As shown in table 1: as it can be seen from table 1 when without electromagnetic agitation, Continuous Casting Square maximum upwards C segregation index is 1.19, is 1.15 to the maximum, relatively applies the highest of electromagnetic agitation on cross section A lot.When applying 4Hz electromagnetic agitation magnetic field, maximum C segregation index is 1.09, works as stirring When field frequency is 7Hz, throwing direction maximum C segregation index is reduced to 1.08, and strand is horizontal On cross section, maximum C segregation index is only 1.05.The above results illustrates, applies electromagnetic agitation energy Enough effectively reduction strand C segregation indexes, meanwhile, the optimization of frequency contributes to wick-containing flow field Optimize and the improvement of process of setting, and then improve C element distribution.

The C segregation index of table 1 strand

Changed the size of wick-containing position electromagnetic force by regulating frequency, and then improve solidification end MOLTEN STEEL FLOW state and process of setting, reduce the purpose of C element segregation degree；Meanwhile, Use optimal stirring frequency can also suitably reduce coil input current, reach energy-conservation purpose.

Claims (1)

1. the method reducing strand C element segregation degree, it is characterised in that use and change The electromagnetic agitation method of Frequency, by changing electromagnetic agitation frequency, changes electromagnetic field at strand In length of penetration, change size and the distribution of electromagnetic force simultaneously, thus improve solidification end steel Water flow regime and process of setting, specifically comprise the following steps that

1) utilize finite element software to set up electromagnetic agitation analogue model, calculate different electromagnetic agitation electricity The size of electromagnetic stirring force and distribution at wick-containing when stream and frequency, different shell thickness；Profit Solve electromagnetic field with vector potential A and scalar potential φ, establish below equation:

$B=\▿\×A---\left(1\right)$

$E=-\▿\mathrm{\φ}---\left(2\right)$

B and E is magnetic induction and electric field intensity respectively, according to Maxwell equation, Obtain the partial differential of magnetic field and electric field, according to partial differential equation, try to achieve electromagnetic force F Accounting equation is as follows:

$F=J\×B=\frac{1}{\mathrm{\μ}}(B\·\▿)B-\frac{1}{2\mathrm{\μ}}\▿B^2---\left(3\right)$

The magnetic induction density B of various location in molten steel_zCalculate with formula (4),

$B_z=B_0{e}^{-x\sqrt{\mathrm{\π}f\mathrm{\μ}\mathrm{\σ}}}---\left(4\right)$

Wherein, B₀For molten steel surface induction intensity, σ is molten steel electrical conductivity, and f is electric current Frequency, is brought into formula (4) in formula (3), obtains the pass between electromagnetic force and frequency System；

2) according to step 1) distribution of the electromagnetic force that obtains calculates the velocity flow profile of wick-containing, right Than different parameters condition time obtain Peak Flow Rate condition, determine most preferably stir frequency Rate；

Flow field continuity equation is as follows:

$\frac{\∂\mathrm{\ρ}}{\∂t}+\frac{\∂}{\∂x_i}\left({\mathrm{\ρu}}_i\right)=0---\left(5\right)$

In inertial coodinate system, the momentum conservation equation in i direction is:

$\frac{\∂}{\∂t}\left({\mathrm{\ρu}}_i\right)+\frac{\∂}{\∂x_j}\left({\mathrm{\ρu}}_i{u}_j\right)=-\frac{\∂p}{\∂x_i}+\frac{\∂{\mathrm{\τ}}_{ij}}{\∂x_j}+{\mathrm{\ρg}}_i+F_i---\left(6\right)$

Wherein p is static pressure, g_iFor gravity, F_iFor the electromagnetic induction power in i direction, τ_ijFor stress tensor；

3) by the experimental analysis strand C element regularity of distribution, amendment verifies that optimal electromagnetism stirs Mix frequency, use magnetic stirrer that molten steel is applied electromagnetic agitation.