JPS5920729B2 - Method for manufacturing steel materials with extremely excellent pickling properties - Google Patents

Description

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

Generally, steel materials are manufactured by charging steel materials to be heated, such as slabs, beam blanks, billets, plumes, etc., into a heating furnace.
It is heated at 0 to 1400°C for several hours and then hot rolled.

By heating in the above heating furnace, the normal material becomes 0.5 to 1.5%.
, 3 to 5% of scales occur in high-temperature heated materials,
The scale generated in these heating furnaces is generally called primary scale.

Most of this primary scale is removed when the steel passes through a scale breaker during hot rolling.

On the other hand, new scale is formed during and after rolling, and this is generally called secondary scale.

Most of the hot-rolled materials are then passed through a pickling line, where secondary scales are fermented and removed, and then cold-rolled and used as polishing materials or plated plates.

Generally, HCt solution is used for pickling, but in addition to the high cost of hydrochloric acid, the cost of waste 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 ratio is really high.

Many efforts have been made to omit or simplify the pickling process, but no satisfactory results have been obtained.

That is, for example, a hot coil is quenched by dipping in uncoiled water, or a Ca, Mg compound is applied during hot rolling to cause a small amount of Ca, Mg, etc. to exist in the scale.
→ suppress the transformation of αFe+Fe3O4, and the G of the quadratic scale
Considerations have been made to improve m speed, but
Although a partial effect is observed, it is not sufficient, and the amount of secondary scale remains unchanged, so the hydrochloric acid consumption rate is not reduced.

In view of the above-mentioned circumstances, the inventors of the present invention have conducted various studies and found that
This product succeeded in suppressing the amount of secondary scale to 175 or less and increasing the dissolution rate of the secondary scale by more than 10 times.

The present invention will be explained in detail below.

The gist of the present invention is that a pretreatment agent (secondary scale pickling property improver) is applied to the surface of the steel material to be heated, such as a slab, before being inserted into the heating furnace, and an antioxidant is applied thereon and then heated. be.

As a result of many studies, the present inventors mixed SiC powder and metal sulfide powder in a predetermined ratio, applied a predetermined amount to the slab surface, further applied an antioxidant on top of it, and heated it.
It has been found that the pickling properties of the secondary scale are greatly improved by rolling.

Hereinafter, the contents of the present invention will be explained in detail.

First, the relationship between the mixing ratio of SiC and metal sulfide powders, such as ZnS powder, secondary scale pickling property, and secondary scale production amount is shown in FIGS. 1 and 2, respectively.

The manufacturing conditions for the steel material are as follows.

Heating conditions: 1220°CX4. Ohr Rolling ratio: 98 Coiling temperature near 1O°C Antioxidant: 0.5 kg/rrt2SiC:Zn
5=l :l (weight ratio) Coating amount: 20,097 m2 As is clear from the figure, when SiC and ZnS are used in combination, the effect is improved compared to when each is used alone, and the effect is extremely excellent when the mixing ratio is . The rate of dissolution of secondary scale is 10 to 20 times lower than that without treatment, and the amount of secondary scale is less than a fraction of that without treatment.

Next, the influence of SiC particle size in the 5iC-ZnS mixture was investigated.

Figures 3 and 4 show SiC powder and ZnS powder yt:1(
This figure shows the influence of the particle size of SiC powder on the secondary scale pickling property and the influence on the amount of secondary scale produced when SiC powder is mixed at a ratio of 200 g/rrL2 (weight ratio) and applied at 200 g/rrL2.

The manufacturing conditions for the steel material are the same as in the case of FIG.

As is clear from the figure, the effect improves as the size of the SiC grains becomes smaller, and in particular, when the size of the SiC grains is 30 μm or less, extremely excellent pickling properties are exhibited.

Next, FIGS. 5 and 6 show the coating amount and secondary scale of a mixed powder of SiC and ZnS at a ratio of 1:1 (weight ratio).

This figure shows the relationship between pickling property and the amount of secondary scale produced.

The manufacturing conditions for the steel material are the same as in the case of FIG.

The effect gradually improves as the amount of application increases, and 1Of
l/rn2 or more, especially 209/m2 to 800. ! ? /m
In the case of 2, the dissolution rate of the secondary scale after rolling is 10 times or more compared to the case without treatment, and the amount of secondary scale is approximately 115 or less.

The above example shows the case of ZnS as the metal sulfide, but other examples such as F e S = A 453-8
bz Sa -K2S-Cd S -Au2Se C
r5-Co5. HgS, SuS, SrS, Sea, W
S2゜Ti S2. Cub, Na25t pbs, Ni
S.

Similar results can be obtained with vS etc.

When applying the above mixed powder to the slab surface, the mixed powder may be soaked with water and applied with a needle as required;
Inorganic binders such as water glass, polyphosphoric acid, colloidal silica alumina sol, or various water-soluble resins may be appropriately mixed and applied.

In this case, if only the above mixed powder is applied and heated without applying an antioxidant, a large amount of primary scale will be generated during heating because the layer of the mixed powder alone will not have antioxidant ability. When the mixed powder passes through a scale breaker, it is removed along with the primary scale, and its effect on improving the secondary scale pickling properties of the mixed powder is extremely diminished.

Therefore, by applying an antioxidant, primary scaling during heating can be prevented.

still. The antioxidant is removed upon passing through the scale breaker.

Any antioxidant may be used as long as it has excellent atmospheric barrier properties.

As explained above, according to the present invention, the secondary scale pickling property can be significantly improved, and the secondary scale dissolution rate is improved by 10 to 20 times, so that the pickling line can be passed through the pickling line at high speed, and a large amount of In addition, since the amount of secondary scale is reduced to 175 or less, the amount of acid (hydrochloric acid or sulfuric acid) used is also greatly reduced, and the acid consumption rate is greatly reduced, resulting in economical effects. It is a huge sculpture.

Examples will be described below.

Example 1 SiC powder with an average particle size of 15μ and FeSa were mixed at a ratio of 1:1 (weight ratio) on the surface of a slab for hot coil polishing solution, and mixed with a small amount of water-soluble resin, so that the coating amount of the mixed powder was 200. ,9
7 m2, and Cr203-chamotte-8in□-At-water glass antioxidant was applied on top of it.
5 kg/rn2 was applied, heated for 1225'CX6hr, and then rolled at 715°C to produce a wood and hot coil.

The amount of secondary scale was measured and found to be 15 g/rrL2.

Further, as a result of measuring the fermentation time of the secondary scale with HC7 solution at 90°C and 210%, the time required for all the scale to melt was approximately 4 seconds.

On the other hand, when untreated material (sample material) was heated and rolled in the same slab under the same conditions, the amount of secondary scale was approximately 86g/
It was rrL2.

Furthermore, as a result of pickling under the same conditions, it took approximately 51 seconds to completely dissolve the scale.

Example 2 SiC powder and ZnS powder with an average particle size of 3μ were mixed at a ratio of 4=1 (weight ratio) on the surface of a hot coil slab for plating,
Mixed with a small amount of water-soluble resin, the amount of mixed powder applied is 150g.
/m2, and on top of that, the same antioxidant 'r0.65ky/rrL2 as in Example 1 was applied, and 1180
After heating and rolling at 570°C for 4.5 hours, wood and hot coils were manufactured.

The amount of secondary scale was measured and found to be 8 g/rrL2.

Furthermore, as a result of measuring the dissolution time of the secondary scale with a 110% HCt solution at 90°C, it was found that the time required for all the scale to dissolve was approximately 2 seconds.

On the other hand, when untreated material (sample material) was heated and rolled under the same conditions using the same slab, the amount of secondary scale was approximately 41g/
It was rrL2.

Furthermore, as a result of pickling under the same conditions, it took approximately 25 seconds for all the scale to melt.

Example 3 SiC powder with an average particle size of 25μ was mixed on the surface of a wire billet at a ratio of 5=1 (weight ratio), and mixed with an appropriate amount of water-soluble resin, so that the amount of the mixed powder applied was 100g/rrL2Vc. On top of that, 0.4 kg/rn2 of the same antioxidant as in Example 1 was applied, and heated at 1050°C x 2.5
After heating for hours, the wire was rolled and wound at 550°C to produce a wire rod.

The amount of secondary scale was measured and found to be 7 g/rrL2.

Further, as a result of measuring the dissolution time of the secondary scale with a 10% HCt solution at 90°C, it was found that the time required for all the scale to complete fermentation was approximately 2 seconds.

On the other hand, when untreated material (sample material) was heated and rolled in the same slab under the same conditions, the amount of secondary scale was 44g/rr.
It was L2.

Furthermore, as a result of pickling under the same conditions, it took approximately 23 seconds to completely dissolve the scale.

[Brief explanation of the drawing]

FIGS. 1 and 2 are charts showing the relationship between the mixing ratio of SiC and ZnS, the secondary scale pickling time, and the amount of secondary scale produced. Figures 3 and 4 are graphs showing the relationship between SiC particle size and secondary scale pickling time, and the relationship between the amount of secondary scale produced, and Figures 5 and 6 are graphs showing the relationship between the amount of 5iC-ZnS mixture applied and secondary scale. It is a chart showing the relationship between pickling time and the amount of secondary scale produced.

Claims (1)

[Claims] I A steel material with extremely excellent pickling properties, which is characterized by making a mixture of SiC powder and metal sulfide exist on the surface of the steel material to be heated, and forming an antioxidant layer thereon, then heating and rolling it. Production method.