JPS6013407B2 - Method for manufacturing steel materials with excellent pickling properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing steel materials with excellent pickling properties.

In general, steel products are produced by charging steel materials to be heated, such as slabs, beam blanks, billets, and blooms, into a heating furnace.
It is manufactured by heating at 0 to 140,000 for several hours and then rolling.

By heating in the above heating furnace, the normal material becomes 0.5 to 1.5%.
, scale occurs by about 3 to 5% in high-temperature heating materials,
The scale generated in these heating furnaces is called primary scale, and most of this primary scale is removed when the sheet passes through a scale breaker during hot rolling. On the other hand, new scale is formed during and after subsequent rolling, and this is generally called secondary scale. Most of the hot-rolled materials are then passed through a pickling line to dissolve and remove secondary scale, and are then cold-rolled and used as polishing materials or plated plates. Generally, HCI liquid is used for pickling, but in addition to the high cost of hydrochloric acid, the cost of sulfuric acid treatment is also large from the perspective of pollution prevention, and the total treatment cost is extremely large, which adds up to the steel manufacturing cost. The proportion is really large.

Therefore, it would be extremely beneficial to omit or simplify the pickling step, but despite past efforts, satisfactory results have not been achieved. That is, for example, after winding a hot coil, it is dipped in water to rapidly cool it, or during hot rolling, a mixture of Ca and M milk is applied to form a C in the scale.
a, Mg, etc. are mixed, Fe0→QFe+Fe
Studies have been carried out on suppressing the transformation of 304 and improving the dissolution rate of secondary scale, but although some improvement has been recognized, it is not sufficient, and the amount of secondary scale is still low. Therefore, the basic unit of hydrochloric acid will not be reduced.

In view of the above circumstances, the present inventors conducted various studies and succeeded in suppressing the amount of secondary scale to less than 1'a and increasing the dissolution rate of secondary scale by more than 5 times. . The present invention will be explained in detail below.

The gist of the present invention is to apply a pretreatment agent (secondary scale pickling property improver) to the surface of the steel material to be heated, for example, a slab, before inserting it into a heating furnace, and to apply an antioxidant thereon, followed by heating and rolling. It is in.

As a result of many studies, the inventors of the present invention found that by mixing SIC powder and fine powder of AI203, applying a specific amount to the surface of the slab, and then applying an antioxidant and heating and rolling, secondary scale acid We created this product because we thought it would greatly improve washability.

Figures 1 and 2 show the SIC of steel materials obtained under the following conditions.
2 shows the mixing ratio of the powders in the piles 203 and 203, and the effects on the pickling properties of secondary scales and the effects on the amount of secondary scales produced. As is clear from Figures 1 and 2, the mixing ratio of SIC and Yama 203 is 2 spicy such as SIC.

The effect is remarkable when 3×・oo=20 to 80 (%), and the amount of secondary scale is 1/2 lower than the amount of secondary scale generated of 80 evenings/day or more in the case of no treatment, and Even compared to the case of SIC alone, there is a large to medium reduction in secondary scale.

On the other hand, the scale melting rate is more than 5 times that of 5-machi sand or more without treatment, and even compared to the case of SIC alone, it is recognized that the effect is significantly improved. Figures 3, 4, 5, and 6 show the SIC powder used and AI203.
This study investigated the influence of powder particle size.

Heating conditions: rolling ratio; winding temperature: conditions for antioxidant are the same as in the case of FIG. First, Figures 3 and 4 are S
When IC powder and N203 (particle size 2 French) powder are mixed at a ratio of 1:1 (weight ratio) and the mixed powder is coated with a coating amount of 200 ta', the secondary scale pickling property of the particle size of SIC powder and 2 The effect on the amount of next scale production is shown.
As is clear from FIGS. 3 and 4, the grain size of the SIC is 7. It can be seen that when the temperature is below 100 mL, excellent pickling properties and the effect of reducing the amount of secondary scale formation are exhibited. Next, in Figures 5 and 6, 1:1 of AI203 powder is added to SIC fine powder with an average weight of 2:
The influence of the particle size of AI203 powder on the secondary scale pickling property and the amount of secondary scale produced is shown in the case where the powders were mixed at a ratio of 1 (weight ratio) and applied 200 times/day.
As is clear from FIGS. 5 and 6, excellent effects are exhibited when the grain size of the peaks 203 is 5 mm or less. Next, we investigated the influence of the amount of powder mixed with SIC and M203 on the secondary scale pickling property and the amount of secondary scale formed.
As shown in FIG. Application amount is 20 evenings/me or more and 600 evenings/
Approximately below is most effective. The heating conditions for the steel material; rolling ratio, coiling temperature, and antioxidant conditions are the same as in the case of FIG. 1. SIC: Mountain 2031:1 (weight ratio) SIC,
AI203=2 sides. When applying the above mixed powder to the slab surface, the mixed powder may be diluted with water and applied in the required amount, or water glass, polyphosphoric acid, tetrapolyphosphoric acid, sodium tetrapolyphosphate, colloidal silica, alumina sol, etc. Appropriate amounts of inorganic binders or organic substances such as various water-soluble resins, film-forming agents, and thickeners may be mixed and applied.

Further, in the present invention, the above-mentioned mixed powder is applied to the surface of the slab, and an antioxidant is further applied thereon and heated.

If only the above mixed powder is applied and heated without applying an antioxidant, the layer of the mixed powder alone does not have antioxidant ability, so a large amount of primary scale is generated during heating, and when it passes through the scale breaker, Since both the primary scale and the primary scale are removed, the effect on improving the secondary scale pickling properties of the mixed powder is diminished. Therefore, by applying an antioxidant, it is possible to
This is to prevent the next scale.

Note that the antioxidant is removed when passing through the scale breaker. Any antioxidant may be used as long as it has excellent atmospheric barrier properties. As explained above, the present invention significantly improves the secondary scale pickling performance, and the dissolution rate of secondary scale is improved by more than 5 times, so it is possible to pass through the pickling line at high speed. In addition, since the amount of secondary scale is reduced to less than 1/2, the amount of acid (hydrochloric acid or sulfuric acid) used is less than 1'2, so the acid consumption rate remains 1' less. , its economic effects are extremely large. Example 1 SIC powder with an average particle size of 5〆 and average particle size 1 Butsunoyama 203 powder were mixed in a 1:1 (weight ratio) on the surface of a slab for polishing plate hot coil, and mixed with a small amount of water-soluble resin. SIC powder and N
Apply the mixture of 203 powder so that the coating amount is 200 ta', then apply 0.6k9/ of antioxidant on top of it, and
215oo x 5. After heating and rolling, it was rolled at 710°C to produce a hot coil.

The amount of secondary scale was measured and the result was 19 evenings/day.

Further, as a result of measuring the dissolution time of the secondary scale with a 10% HCI solution at 90:00, it was found that the time required for all the scale to thorn off was approximately 8 seconds. In contrast, when untreated material (bare material) was heated and rolled under the same conditions in the same slab,
The secondary scale amount was approximately 86 evenings/day. Furthermore, as a result of pickling under the same conditions, it took approximately 51 seconds for all the scale to be removed. Example 2 SIC powder with an average particle size of 4 peaks and an average particle size of 1.
Mix the autumn AI203 powder at a ratio of 1:3 (weight ratio), mix it with a certain amount of water-soluble resin, and apply it so that the amount of the mixture of SIC powder and AI203 is 100 tons, and then apply oxidation on top. Apply inhibitor at 0.7 x 9', 1200oo x 5. After heating the plate: It was rolled and rolled at 560 qo to produce a hot coil.

As a result of measuring the amount of secondary scale, it was 7.5 evenings/day.

Further, as a result of measuring the dissolution time of the secondary scale with a 90qC, 10% HCI solution, the time required for all the scale to completely dissolve was approximately 4 seconds. On the other hand, when untreated material (Namura) was heated and rolled under the same conditions using the same slab,
The amount of secondary scale was approximately 4M/m. In addition, as a result of pickling under the same conditions, it took about 2 hours to remove all the scales.
It took 4 seconds.

[Brief explanation of the drawing]

FIGS. 1 and 2 are charts showing the relationship between the mixing ratio of SIC powder and AI203 powder, secondary scale pickling time, and secondary scale production amount. Figures 3, 4, 5, and 6 are for SIC powder, AI2
A chart showing the relationship between the particle size of Q powder, secondary scale pickling time, and secondary scale production amount. FIGS. 7 and 8 are charts showing the relationship between the amount of the mixture of SIC powder and AI203 powder applied, the secondary scale pickling time, and the amount of secondary scale produced.
Many drawings 2 drawings Kaya drawing filial drawings 3 drawings 6 drawings 7 drawings 8th figure

Claims (1)

[Claims] 1 SiC powder of 7μ or less and Al_2O_ of 5μ or less
3. Mix the powder according to the formula below and apply it to the surface of the heated steel material.
600 (g/m^2) and forming a layer of antioxidant thereon, followed by heating and rolling. (Al_2O_3)/(SiC+Al_2O_3)×1
00=20~80(%)