CN101658911B - Continuous-casting dynamic soft-reduction pressing quantity on-line control method of large square blank - Google Patents

Abstract

The invention relates to a continuous-casting dynamic soft-reduction pressing quantity on-line control method of a large square blank, in particular to a continuous-casting dynamic soft-reduction process of the large square blank in iron and steel production; the method is as follows: casting blank surface pressing quantity of all pressing points is calculated in an on-line way according to basic principles that center segregation and porosity can be eliminated by solidifying contraction of a soft-reduction pressing quantity compensating liquid core, so as to determine the roll gap setting value of racks of all tension levelers; the roll gap setting value is transmitted to a one-level basic automation control system, so as to adjust the roll gap of the tension leveler remotely and realize soft reduction. After adopting the invention, the special indexes for improving the quality of a casting piece are that: the center segregation of the casting blank is less than or equal to 1.0 grade, center carbon segregation index of the casting blank is 0.95-1.10, and the average is 1.05; center porosity and center line shrinkage of the steel casting blank of a bearing can be obviously improved, the center porosity of the casting blank is less than or equal to 1.0 grade, the proportion thereof can reach more than 90 percent, and the center line shrinkage is less than or equal to 0.5 grade; by adopting the invention, the disadvantages of center segregation, center porosity and center line shrinkage of the large square blank can be remarkably alleviated.

Description

A kind of continuous-casting dynamic soft-reduction pressing quantity on-line control method of large square blank

Technical field

The bloom continuous casting that the present invention relates in a kind of iron and steel production is gently depressed technology, particularly relates to a kind of continuous-casting dynamic soft-reduction pressing quantity on-line control method of large square blank.

Background technology

In the continuous casting production process, strand is under extraneous cooling effect, constantly solidify from outside to inside, the free molten steel that the solidification shrinkage amount that produces can be flowed by the center replenishes into, but solidifying latter stage, because the increase of molten steel flow resistance in the two-phase section of similar porous media, the solidification shrinkage amount can't in time be compensated, the pressure drop that forms will cause near the strand center interdendritic enrichment segregation element molten steel to center flow, compile and finally solidify, thereby form the center gross segregation, the solidification shrinkage amount that can not get simultaneously compensating will finally form center porosity.

Internal soundness problems such as continuous casting billet center segregation, loose and shrinkage cavity become the key factor that influence cord usefulness steel quality.They can reduce comprehensive properties of rolled steel, shorten the service life of steel; Reduce steel toughness, for high-carbon steel, center segregation reduces its wire drawing limit and ductility, especially can obviously reduce its toughness, influence drawing property, the tangible wire rod of center segregation when carrying out drawing, because of segregation place carbon content higher, intensity and plasticity and matrix differ bigger, can't be out of shape with the matrix synchronous coordination, crackle at first produces in the steel wire center and expansion during drawing, as formation of crack, cause the fracture of " V " shape nib shape very soon, make the drawing broken string; Cause the steel hydrogen embrittlement, reduce decay resistance; Reduce the steel fatigue behaviour, cause fracture of wire or the like easily.

In disclosed paper document, bloom is gently depressed the methods that adopt field trial of determining of drafts more, because the bloom continuous casting machine equipment has nothing in common with each other, the factor that influences experimental result is more, it does not possess versatility, waste time and energy, as " special steel " magazine (the 30th the 1st phase the 44th of volume in February, 2009,45 pages, passive light is depressed the application of technology in GCr15 bearing steel continuous casting is produced, Liu Wei etc.) having put down in writing northern full special steel adopts passive light to depress technology to improve GCr15 bearing steel 240mm * 240mm bloom segregation, the center porosity rank of GCr15 bearing steel bloom is reduced to 1.0～1.5 grades by 2.0～2.5 grades, strand center carbon segregation index is reduced to 1.07～1.13 by 1.17～1.26, and along the cast direction, strand center carbon content is tending towards even; " technology " magazine (the 1st～4 page of the 2nd phase in February, 2008, gently depress the application practice of technology in the bearing steel continuous casting, Wu Wei, Liu Wei etc.) reported that the northeast special steel adopts end gently to depress technology and improves GCr15 bearing steel 240mm * 240mm bloom slab quality, putting enforcement simultaneously in one, two, three straightening seats in the plane gently depresses, drafts is 7～8mm, the distribution ratio of three frames was respectively 3: 3: 2,3: 2: 2.After implementing gently to depress, the horizontal segregation index of strand reduces to 1.00～1.18 by 1.06～1.28, and the vertical segregation index of strand reduces to 0.95～1.18 by 1.07～1.5; " steel-making " magazine (the 21st the 3rd phase 5～8 of volume in June, 2005, the improvement of SWRH82B continuous casting billet center segregation, the He Jinping work) reported that Wuhan Iron ﹠ Steel's first steel mill adopts passive light to depress technology and reduces SWRH82B high-carbon steel 200mm * 200mm bloom segregation; " Heilungkiang metallurgy " magazine (the 9th～12 page of the 4th phase in April, 2003, the discussion of bearing steel continuous casting process technology, Song Liucheng, Zhang Wenming) reported when French SOLLAC company bloom continuous casting pulling rate is 0.7～1.10m/min that drafts is regulated strand center carbon segregation index and dropped to 1.1～12 by 1.15～1.30 between 0～12mm in the long zone of 4m.

At present disclosed relevant continuous casting is gently depressed the patent documentation of technology, as CN200710048924.9, CN200810304476.9 number patent documentation discloses a kind of realization continuous casting and has gently depressed the drafts control method, and its method is gently depressed drafts for calculating according to strand center solid rate; The CNO1122537.8 patent discloses a kind of continuous casting soft reduction method and has implemented the device of this method, and it has mainly proposed a kind of device of gently depressing enforcement.These methods all are to configure in advance gently to depress drafts, are difficult to improve effectively quality problems such as continuous casting billet center segregation, loose and shrinkage cavity.

Summary of the invention

There is shortcoming at prior art, the invention provides a kind of continuous-casting dynamic soft-reduction pressing quantity on-line control method of large square blank that can significantly alleviate center segregation, center porosity, central pipe.

Technical scheme of the present invention is as follows: comprise the steps:

Step 1: determine the two adjacent some liquid core solidification shrinkage amounts of interior strand of depressing, formula is as follows:

${\mathrm{\ΔV}}_b=\frac{{\∫}_0^{L_{a-b}}(\frac{{\mathrm{dM}}_b}{\mathrm{dz}}-\frac{{\mathrm{dM}}_a}{\mathrm{dz}})\mathrm{dz}}{{\mathrm{\ρ}}_s}---\left(1\right)$

In the formula, M _bBe the quality of B point along z direction unit length, Ma is the quality of A point along z direction unit length, ρ _sBe solid phase density, L _A-bBe strand length between A～B;

Step 2: utilize the liquid core solidification shrinkage amount in the step 1, determine liquid core drafts, formula is as follows:

$R_{\mathrm{center}}^b=\frac{{\mathrm{\ΔV}}_b}{X_b\·L_{a-b}}---\left(2\right)$

In the formula, X _bStrand width for B point place;

Step 3: determine to depress efficient, formula is as follows:

${\mathrm{\η}}_i=\frac{\mathrm{\Δ}{A}_i}{{\mathrm{\ΔA}}_H}---\left(3\right)$

In the formula, Δ A _iReduction, Δ A for strand cross section liquid core area before and after depressing _HReduction for the strand cross section gross area before and after depressing;

Step 4: utilize the efficient of depressing in liquid core drafts in the step 2 and the step 3, determine the casting billet surface drafts, formula is as follows:

$R_a^{i\′}=\frac{{\∫}_0^{Y_i}{\∫}_0^{X_i}{\stackrel{\‾}{\mathrm{\ρ}}|}_{z=Z_i}\mathrm{dxdy}-{\∫}_0^{Y_{i-1}}{\∫}_0^{X_{i-1}}{\stackrel{\‾}{\mathrm{\ρ}}|}_{z=Z_{i-1}\mathrm{dxdy}}}{{\mathrm{\ρ}}_s\·X_i}\·\frac{1}{{\mathrm{\η}}_i}---\left(4\right)$

Step 5: utilize the casting billet surface drafts and the slab thickness of step 4, determine respectively to draw the fixed value of roller slit of sedan-chair machine frame, formula is as follows:

In the formula, i 〉=2; Gap _HFor entering the slab thickness of air cooling zone, mm;

Be the correction factor of i frame drafts, relevant with the casting machine structure;

Be the drafts of i frame depress roller, mm;

Step 6: fixed value of roller slit is issued to one-level basic automatization control system, and remote adjustment is drawn sedan-chair machine roll gap, finishes the on-line implement of gently depressing technology.

Described strand is meant middle and high carbon alloy steel continuous casting blooms, and its steel grades distributes by mass percentage: C content is that 0.2-1.7%, Cr content are 0.5～1.65%, Si content is that 0.15-0.35%, Mn content are 0.25-0.65%.

Described strand, its cross dimensions is greater than 220mm * 220mm.

The described remote adjustment of step 6 is drawn sedan-chair machine roll gap, and its regulating cycle is generally 2-10 second.

The invention has the beneficial effects as follows, the inventive method is applied in the continuous casting of bloom and can alleviates defectives such as center segregation, center porosity, central pipe significantly, stabilize and increase continuous casting blooms slab quality and performance.Using the specific targets of improving slab quality behind the present invention is: strand center segregation≤1.0 grade, strand center carbon segregation index 0.95-1.10, average 1.05; Can obviously improve bearing steel strand center porosity and central pipe, strand center porosity≤1.0 grade, ratio reaches more than 90%, central pipe≤0.5 grade.

Description of drawings

Fig. 1, be the distribution schematic diagram of strand thickness of solidified slab shell in secondary and depress roller on the embodiment of the invention bloom continuous casting streamline;

Fig. 2, depress the strand schematic cross-section of starting point, the A point in the corresponding diagram 1 for the embodiment of the invention;

Fig. 3, be the 1st strand schematic cross-section of depressing under the frame in the embodiment of the invention pressure range;

Fig. 4, be i in the embodiment of the invention pressure range the strand cross sectional representation of depressing under the frame;

Fig. 5, be the online calculation flow chart of embodiment of the invention bloom continuous-casting dynamic gentle pressure amount.

Fig. 6, be embodiment of the invention large square bland continuous-casting machine schematic diagram.

The specific embodiment

The invention will be further described in conjunction with the accompanying drawings: Fig. 1 is the distribution schematic diagram of strand thickness of solidified slab shell in secondary and depress roller on the bloom continuous casting streamline, wherein starting point is depressed in the expression of A point, the B point is depressed a little for first, and the i point is that i depresses a little, and depresses a little and all be in the two-phase section.Fig. 2 depresses the strand schematic cross-section of starting point, the A point in the corresponding diagram 1 for the embodiment of the invention; Fig. 3 is the 1st strand schematic cross-section of depressing under the frame in the embodiment of the invention pressure range; Fig. 4 is i in the embodiment of the invention pressure range the strand cross sectional representation of depressing under the frame; Fig. 5 dynamically gently depresses online calculation flow chart for bloom continuous casting, specifies as follows in conjunction with Fig. 1, Fig. 2, Fig. 3 and Fig. 4 to bloom continuous-casting dynamic gentle pressure amount computational process:

Wide for x, thick for y, long for the bloom continuous casting base slab quality M of z be:

$M={\∫}_0^X{\∫}_0^Y{\∫}_0^Z\stackrel{\‾}{\mathrm{\ρ}}(x,y,z)\mathrm{dxdydz}---\left(1\right)$

In the formula, X-strand width; The Y-slab thickness; Z-strand length; The width of x-strand; The thickness direction of y-strand; The throwing direction of z-strand; ρ (x, y, z)-the strand density function.

The solid rate f at strand density function and strand diverse location place _sRelevant, formula is as follows:

ρ＝ρ _l(1-f _s)+ρ _sf _s (2)

In the formula, ρ _l-density of liquid phase; ρ _s-solid phase density; f _s-solid rate.

Wherein, f _sFormula as follows:

$f_s\left(T\right)=\frac{T_l-T+\frac{2}{\mathrm{\π}}(T_s-T_l)\{1-\cos \left(\frac{\mathrm{\π}(T-T_l)}{2(T_s-T_l)}\right)\}}{(T_l-T_s)(1-\frac{2}{\mathrm{\π}})}---\left(3\right)$

In the formula, T is the strand central temperature, T _lAnd T _sBe respectively liquidus temperature and solid-state temperature.

In like manner, B point and i point place strand can be expressed as along the quality of Z direction unit length:

$\frac{{\mathrm{dM}}_b}{\mathrm{dz}}={\∫}_0^{Y_b}{\∫}_0^{X_b}{\stackrel{\‾}{\mathrm{\ρ}}(x,y)|}_{z=Z_b}\mathrm{dxdy}---\left(4\right)$

$\frac{{\mathrm{dM}}_i}{\mathrm{dz}}={\∫}_0^{Y_i}{\∫}_0^{X_i}{\stackrel{\‾}{\mathrm{\ρ}}(x,y)|}_{z=Z_i}\mathrm{dxdy}---\left(5\right)$

In the formula, X _b-Di-individual depressing a little is the width of B point place strand; Y _b-first is depressed a little is the thickness of B point place strand; X _i-be i to depress a width of locating strand; Y _i-be i to depress a thickness of locating strand.

When not implementing dynamically gently to depress, because the supporting role of solidified shell, the width of diverse location strand and thickness difference are very little only to be the changing value of base shell thermal contraction.

Under the perfect condition, when the molten steel that the liquid core of continuous solidification shrinkage is poured in replenished, strand did not produce center porosity and segregation, and slab quality increases.In the real process, do not have the filling of feeding molten steel, form inner loose and hole.Utilize the slab quality incremental difference between 2, oppositely derive and obtain the volume shrinkage mass Δ V that solidification shrinkage causes between A, the B at 2 _b

$\mathrm{\Δ}{V}_b=\frac{{\∫}_0^{L_{a-b}}(\frac{{\mathrm{dM}}_b}{\mathrm{dz}}-\frac{{\mathrm{dM}}_a}{\mathrm{dz}})\mathrm{dz}}{{\mathrm{\ρ}}_s}---\left(6\right)$

In the formula, L _A-bStrand length between-A～B.

Bu Chang solidification shrinkage volume delta V as required _b, determine to be applied to the drafts on the liquid core.

Suppose the drafts of casting billet surface can full remuneration the dilatation Δ V of the inner loose and shrinkage cavity of strand in the compensation A-B section _b, and ignore the distortion of strand width, the drafts that applies at the B point

For:

$R_{\mathrm{center}}^b=\frac{{\mathrm{\ΔV}}_b}{X_b\·L_{a-b}}---\left(7\right)$

Simultaneous formula (1-7) derivation can get B point place and should be applied on the liquid core

Drafts is:

$R_{\mathrm{center}}^b=\frac{{\∫}_0^{X_b}{\∫}_0^{Y_b}{\stackrel{\‾}{\mathrm{\ρ}}|}_{z=Z_b}\mathrm{dxdy}-{\∫}_0^{X_a}{\∫}_0^{Y_a}{\stackrel{\‾}{\mathrm{\ρ}}|}_{z=Z_a}\mathrm{dxdy}}{{\mathrm{\ρ}}_s\·X_b}---\left(8\right)$

Therefore, the i bloom of ordering is dynamically gently depressed liquid core drafts Computing formula be:

$R_{\mathrm{center}}^i=\frac{{\∫}_0^{X_i}{\∫}_0^{Y_i}{\stackrel{\‾}{\mathrm{\ρ}}|}_{z=Z_i}\mathrm{dxdy}-{\∫}_0^{X_{i-1}}{\∫}_0^{Y_{i-1}}{\stackrel{\‾}{\mathrm{\ρ}}|}_{z=Z_{i-1}}\mathrm{dxdy}}{{\mathrm{\ρ}}_s\·X_i}---\left(9\right)$

Aforementioned calculation goes out

Only be to shrink the required drafts that is applied on the liquid core for solidification of molten steel in the compensation liquid core two-phase section, actual gently depresses in the process implementing process, most drafts consumption is in the broadening and extensional of casting blank shell, and promptly the drafts that applies of casting billet surface can not be delivered on the liquid core fully.For addressing this problem, introduce and depress efficiency parameters:

${\mathrm{\η}}_i=\frac{\mathrm{\Δ}{A}_i}{{\mathrm{\ΔA}}_H}---\left(10\right)$

In the formula, Δ A _i-reduction, the Δ A of strand cross section liquid core area before and after depressing _H-the reduction of the strand cross section gross area before and after depressing.

According to the above-mentioned liquid core drafts of asking for and depress efficiency parameters, can further obtain surperficial drafts.

$R_a^{i\′}=\frac{{\∫}_0^{Y_i}{\∫}_0^{X_i}{\stackrel{\‾}{\mathrm{\ρ}}|}_{z=Z_i}\mathrm{dxdy}-{\∫}_0^{Y_{i-1}}{\∫}_0^{X_{i-1}}{\stackrel{\‾}{\mathrm{\ρ}}|}_{z=Z_{i-1}\mathrm{dxdy}}}{{\mathrm{\ρ}}_s\·X_i}\·\frac{1}{{\mathrm{\η}}_i}---\left(11\right)$

As shown in Figure 6, bloom is dynamically gently depressed most dependence air cooling zone straightening machine top roll and is depressed realization, and first straightening machine top roll is that measuring roll is 1#, and responsible detection enters the slab thickness of air cooling zone.In the process implementing process, according to trying to achieve i the setting value Gap that the frame depress roller is final after the slab thickness that enters air cooling zone and i frame depress roller drafts overlap-add procedure ⁱ

In the formula, i 〉=2; Gap _HFor entering the slab thickness of air cooling zone, mm;

Be the correction factor of i frame drafts, relevant with the casting machine structure;

Be the drafts of i frame depress roller, mm.

Embodiment:

On certain large square bland continuous-casting machine, adopt the present invention to produce the medium high carbon steel alloy.Concrete device parameter is: the cold base cross dimensions of large square bland continuous-casting machine 280mm * 325mm, metallurgical length 33.149m.As shown in Figure 6,7 straightening machine frame 1#～7# are arranged in its air cooling zone, dynamic light pressing control method is by each frame inner arc roll-in base position of remote adjustment, make strand be subjected to the roller pressure contraction distortion, finish and dynamically gently depress implementation process, producing steel grade is bearing steel GCr15, cord steel 72A, hard wire steel 82B.

Produce slab quality as shown in Table 1 and Table 2.

Strand low power testing result before and after table 1 comes into operation

Strand carbon segregation before and after table 2 comes into operation

By table 1 as seen, each steel grade strand low power testing result was all obviously improved after system came into operation, all 0 ~ 1.5 grade of ratio of steel grade center porosity defective grading improves 38.14%, 0 ~ 1.5 grade of ratio of central pipe defective grading improves 27.74%, strand crack defect, general shrink defects all be improved significantly.

As shown in Table 2, each steel grade strand carbon segregation index all has tangible reduction, and wherein GCr15 steel center carbon segregation is controlled at 0.924-1.06, and 72A steel center carbon segregation is controlled at 0.868-1.129,82B steel center carbon segregation is controlled at 0.918-1.069, and the center carbon segregation all is no more than 1.13.

Claims (4)

1. a continuous-casting dynamic soft-reduction pressing quantity on-line control method of large square blank is characterized in that: comprise the steps:

Step 1: determine the two adjacent some liquid core solidification shrinkage amounts of interior strand of depressing, formula is as follows:

In the formula, M _bBe the quality of B point along z direction unit length, Ma is the quality of A point along z direction unit length, ρ _sBe solid phase density, L _A-bBe strand length between A～B;

Step 2: utilize the liquid core solidification shrinkage amount in the step 1, determine liquid core drafts, formula is as follows:

In the formula, X _bStrand width for B point place;

Step 3: determine to depress efficient, formula is as follows:

In the formula, Δ A _iReduction, Δ A for strand cross section liquid core area before and after depressing _HReduction for the strand cross section gross area before and after depressing;

Step 4: utilize the efficient of depressing in liquid core drafts in the step 2 and the step 3, determine the casting billet surface drafts, formula is as follows:

Step 5: utilize the casting billet surface drafts and the slab thickness of step 4, determine respectively to draw the fixed value of roller slit of sedan-chair machine frame, formula is as follows:

In the formula, i 〉=2; Gap _HFor entering the slab thickness of air cooling zone, mm; Be the correction factor of i frame drafts, relevant with the casting machine structure;

Be the drafts of i frame depress roller, mm;

Step 6: fixed value of roller slit is issued to one-level basic automatization control system, and remote adjustment is drawn sedan-chair machine roll gap, realizes onlinely gently depressing.

2. a kind of continuous-casting dynamic soft-reduction pressing quantity on-line control method of large square blank according to claim 1, it is characterized in that: described strand, be meant middle and high carbon alloy steel continuous casting blooms, its steel grades distributes by mass percentage: C content is that 0.2-1.7%, Cr content are that 0.5-1.65%, Si content are that 0.15-0.35%, Mn content are 0.25-0.65%.

3. a kind of continuous-casting dynamic soft-reduction pressing quantity on-line control method of large square blank according to claim 1 is characterized in that: described strand, its cross dimensions is greater than 220mm * 220mm.

4. a kind of continuous-casting dynamic soft-reduction pressing quantity on-line control method of large square blank according to claim 1 is characterized in that: the described remote adjustment of step 6 is drawn sedan-chair machine roll gap, and its regulating cycle is 2-10 second.

Images