KR860001772B1 - Method prevention of graphite deposition of cold steel sheet - Google Patents

Abstract

The graphite deposition of low carbon-cold steel sheet is prevented by coating the steel sheet surface. Electrolyte is 3% Na4SiO4. The steel sheet coating material is mixed in this electrolyte. The steel sheet coating material is Na2S2O3.5H2O of 0.01-0.0001 mol/l or ZnO of 0.01-0.0001 mol/l. The electrolyte represses resolution-reactionof CO before and during annealing. The steel sheet is coated by the electrolyte of the deposition tank. Na4SiO4 is resolved into 4Na+, 2OH- and H2SiO42- in water. H4SiO4 of silicagel form increases the adhesion force of the coating material.

Description

Prevention method of graphite precipitation during annealing of low carbon cold rolled steel sheet

1 (a), 1 (b) and 1 (c) are photographs showing the surface properties of the steel sheet when Na 2 S 2 O 2.5 H 2 O is used as the graphitization inhibitor of the present invention.

Fig. 2 (a), Fig. 2 (b) and Fig. 3 (c) are photographs showing the steel sheet surface properties when ZnO is used as the graphitization inhibitor of the present invention.

3 is a photograph showing the surface properties of the steel sheet of Comparative Example 1;

The present invention relates to a method of preventing graphite precipitation during annealing of low carbon cold rolled steel sheet, in particular, graphite precipitation during annealing of low carbon cold rolled steel sheet which is widely used in various surface treatment steel sheets such as automotive steel sheets, galvanized steel sheets, and plated steel plates. It relates to a method for preventing surface contamination by.

O₂=CO로 되어 일산화탄소가 생성된 후 2CO=CO₂+C (흑연)으로 분해되어 강판표면에 흑연이 석출되기 때문이다.It is already known that low carbon cold rolled steel has problems such as black contamination on the surface of the steel sheet when it is annealed, thereby deteriorating the surface properties, lowering the product value, and degrading paintability and plating properties. The reason is that carbon present in the refined rolling oil or annealing atmosphere gas adhered to the steel plate surface is concentrated on the steel plate surface by carburizing during annealing, or the carbon produced by the decomposition of cementite is diffused from the steel to the surface. C + reacts with traces of oxygen on the steel surface

This is because carbon monoxide is formed by O ₂ = CO, and the carbon monoxide is decomposed into 2CO = CO ₂ + C (graphite) to precipitate graphite on the surface of the steel sheet.

Therefore, conventionally, a method of adjusting the annealing atmosphere, adding trace elements, or treating the surface of the steel sheet before annealing has been devised as a method for preventing black contamination of the surface caused by graphite precipitation. Among them, the annealing atmosphere adjustment method is a method of suppressing the decomposition of carbon monoxide into graphite by adding 0.5-50 ppm of hydrogen sulfide in the atmosphere gas, which is effective when the coil surface is in contact with the atmosphere gas, but is similar to that of a tight coil. Likewise, it is less effective when the coil surface cannot be in sufficient contact with the atmosphere gas. In addition, the method of adding trace elements suppresses graphite precipitation by adding chromium or manganese, which is a cementite stabilizing element, to the steel to reduce carbides from spreading to the surface, but has the drawback of changing the mechanical properties of the product. The next method for surface treatment of steel sheet before annealing is to add chemicals to the rolling oil or to apply chemicals to the surface of steel sheet before annealing.However, when adding chemicals to rolling oil, there are disadvantages that adversely affect the rolling lubrication. Although the surface is inactivated to suppress the graphite precipitation reaction, a sufficient effect cannot be expected since the coating agent is evaporated during annealing.

The present invention is a method for solving the above-mentioned drawbacks, and is a method of preventing graphite deposition by applying a chemical to inhibit the decomposition reaction of CO before annealing and a compound which is continuously maintained during annealing on the surface of the steel sheet. ) when Oda 3% all sogyu oxygen in solution (using Na ₄ SiO _4), and characterized in that the dilution of a compound of _{Na 2 S 2 O 3 .5H 2} O or ZnO in the jeoncheong solution and above this, as follows.

In order to suppress the decomposition reaction of CO, Na ₂ S ₂ O _3. 5H ₂ O or ZnO is used as a coating agent, and the method of applying this to the surface of the steel sheet is to dilute the coating agent in the electrolytic solution during the electrolytic cleaning process before annealing. The coating is applied to the surface of the steel sheet by passing through it, and no special auxiliary equipment is required.

The concentration of the coating agent is preferably Na ₂ S ₂ O _3. 5H ₂ O is 0.01-0.0001mo | / 1, and ZnO is 0.01-0.001 mol / 1. For the concentration of the coating agent is less than the above lower limit, no effect of suppressing the precipitation of graphite in the steel sheet surface, and when it exceeds the upper limit, if the _{Na 2 S 2 O 3 .5H 2} O is the surface oxidation of the steel sheet surface quality is lowered In the case of ZnO, a large amount of sediment is generated to contaminate the electrolytic solution.

The reason why the precipitation of graphite can be prevented by the present invention is that the material coated on the surface of the steel sheet acts to suppress the graphite reaction of the carbon deposited during annealing.

In addition, in order to continuously maintain the coating agent on the surface of the steel sheet and to reinforce the effect of inhibiting graphite precipitation, sodium osilicate (Na ₄ SiO ₄ ) is used in the present invention. All sogyu oxygen Oda is dissolved in water, _{Na 2 SiO 4 + 2H 2 O} = 4Na + + 2OH-H 2 SiO 4 and ionizing 2 ^_ This, in turn, ^{_{H 2 SiO 4 2 - + H}} + = H 3 SiO 4 -, ^{_{H 3 SiO 4 - + H +}} = H is a ₄ SiO ₄ are present in the state of the most H ₄ SiO _4.

The molecular state of H ₄ SiO ₄ remains in the form of silica gel on the surface of the steel sheet to enhance the adhesion of the coating agent to increase the effect of the coating agent during annealing, as well as H ₂ O lost during annealing is CO + H ₂ Graphite precipitation is suppressed by causing the reaction of O = CO ₂ + H ₂ to reduce CO in the atmosphere. In addition to this effect, Osososilicate also acts as a degreasing agent during the pretreatment process.If the concentration of the pretreatment solution is less than 3%, incomplete degreasing of the steel sheet leaves rolling oil on the surface of the steel sheet. Since the concentration increase beyond that point is uneconomical, a concentration of 3% of the pretreatment solution is suitable.

EXAMPLE

C: 0.07 Si: 0.006%, Mn: 0.37%, P: 0.014%, S: 0.019% The cold rolled steel was degreased and annealed in a gas atmosphere at 680 ° C for 10 hours. At this time, the liquid condition of the degreasing bath during the degreasing treatment was carried out divided into eight as shown in the first table a-h and a-g is an embodiment of the present invention, h is a comparative example.

[Table 1]

The first and second and also in each case with a _{Na 2 S 2 O 3 .5H 2} O and ZnO as a coating material according to the embodiment of the present invention turns 2, the third turn is the case of the comparison of the first table h.

As compared with FIGS. 1 to 3 of Table 1, it can be seen that black pollution of the steel sheet due to the precipitation of graphite is prevented by the method of the present invention.

Claims (1)

When annealing low carbon cold rolled steel, the surface of the steel sheet is coated with a coating agent to prevent the precipitation of graphite. In the electrolytic cleaning process before annealing, 3% oligosulfite (Na ₄ SiO ₄ ) is used as the electrolytic cleaning solution. A method for preventing precipitation of graphite, comprising adding a steel sheet coating agent of 0.01-0.0001 mol / 1 of Na ₂ S ₂ O _3. 5H ₂ O or 0.01-0.0001 mol / 1 of ZnO.

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