JPS59177381A - Production of galvanized steel sheet having resistance to blackening - Google Patents

Abstract

PURPOSE:To produce a plated steel sheet having excellent resistance to blackening by treating a hot dip galvanized steel sheet which is performed by Zn-alloy hot dipping on the surface, by Ni ion and Co ion solns. CONSTITUTION:A hot dip galvanized steel sheet subjected to hot dipping of zinc or zinc alloy on the surface is treated with an Ni ion or Co ion soln. or a soln. in which both ions are mixed. The soln. contg. the Ni ion or Co ion may be a acidic bath of sulfate, hydrochloride or the like or an alkaline bath contg. a complexing agent such as ammonia. The treatment is accomplished at about 1-20g/l concn. of metallic ions in terms of Ni or Co, about 30-60 deg.C treatment temp. and about 1-4 or about 11-13.5pH. The steel sheet is treated by short- term dipping or spraying and the amt. of the Ni or Co to be adheared thereon is preferably about 0.3-1.5mg/m<2> and if necessary, the steel steet is further subjected to chromate treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a zinc-based or zinc-based alloy bath sub-Hilj lead-based plated plate/η plate having excellent blackening resistance.

Today, as demand for hot-dip galvanized steel sheets increases and their uses diversify, further improvements in performance are required in terms of appearance, workability, chemical conversion treatment properties (painting pretreatment properties), and edibility. In order to improve workability and chemical conversion treatment properties, the so-called zero spangle treatment, in which atomized water droplets are sprayed onto the surface of the plated layer to make the zinc crystals thinner, is becoming popular before the zinc layer solidifies after plating.

After the zero spangle treatment, skin pass rolling (normal rolling ratio ~3φ) is performed to further improve the appearance and surface shape.
) is being carried out.

However, after skin pass rolling, if chromic acid treatment is applied to improve the eating quality and coating adhesion, the plated surface will change from blue to brown to gray during storage and transportation for a relatively short time after production. Problems such as discoloration C (hereinafter referred to as black discoloration) often occur.

On the other hand, to improve corrosion resistance, AC1M2 was added to the zinc bath.
Methods of alloying by adding other metals, such as metals, have been researched both domestically and internationally, and some have already been put into practical use.

However, if these zinc-based alloy hot-dip coated steel sheets are treated with chromic acid after plating, they will not be treated with the above-mentioned zero spangle treatment i.
Similar to 1j lead steel sheet (skin pass material), the phenomenon of black spots on the plating surface is observed during inventory or transportation.

In addition, when a zinc-based alloy hot-dip plated steel sheet is subjected to skin pass rolling (rolling rate 91 to 3), blackening is more likely to occur in a short period of time. This black discoloration is sometimes observed where black discoloration occurs in the spotted pattern due to spangles when stored for a long period of time, even if the galvanized iron plate is not skin-passed.
The above-mentioned zero spangle treated skin pass phase and alloy plated steel sheet are characterized in that they occur in a very short period of time. Black discoloration is more likely to occur when zero-spangled skin pass materials or alloy-plated steel sheets are left exposed indoors, but when they are cut and left in piles or packed in coils. As for the environment, it tends to occur easily in hot and humid atmospheres.

11. According to the research results of Akesha et al., the plating surface that has blackened has a thicker layer of 111+ hydroxide, a mixed layer of lead and zinc carbonate (thickness ranges from several 100 to several 100X) compared to the plating surface before blackening. ) is detected. From the results of the above investigation, the mechanism of blackening 4L is estimated as follows. AC and N42 added as alloys exist in the form of metals or oxides on the surface of alloyed steel sheets, and these
A local battery is formed between +' and p1, which naturally contains water and is interposed with a chromate film layer that easily absorbs water.Electrochemical corrosion (reaction of water or chromic acid with zinc metal) in a eclipse environment. This is thought to be because the process progresses abnormally quickly. It is presumed that the reason why the plated surface appears black is that fine irregularities are formed due to corrosion of the Zn layer, and the existence of a thin film layer of zinc hydroxide or zinc carbonate on top of this causes the appearance of black due to optical interference.

The reason why black discoloration is more likely to occur when skin pass rolling is applied is thought to be that the skin pass creates intermediate or fresh Zn surfaces in the plating layer, which creates chemically more active local batteries and accelerates g-erosion. It will be done. In order to prevent this blackening of the plated surface, post-treatment methods using non-chromic acid systems and methods of MTA electrolytic galvanizing have been considered. For example, it has been proposed to apply a non-chromic acid type Tl1l / J÷ (d water fZ, sex (・) i fat), but as can be inferred from the mechanism of blackening described in -4 = thin 4ff
, l The IIW coating layer is unable to cut off the penetrating moisture, resulting in blackening.

Electricity! A proposed method for preventing blackening by 111 lead plating involves removing the impurity concentration layer on the surface with an alkaline solution and then applying a thin electric bending plating, but this requires expensive equipment: (
Not only does it require +iii throw Ct, but the processing method is outside of 4.

Therefore, the inventors developed a simple method that did not require expensive equipment.
As a result of extensive research into a treatment method that is both effective and effective in preventing blackening, we have found that
We discovered a method of processing with a solution containing ions.

That is, according to the present invention, zinc or a small amount of A+! .

A steel sheet coated with hot-dip Zn-based plating of a zinc-based alloy containing IJ12 etc. is dipped in a solution containing 1141 ions, Co ions, or a mixture of the two for a period of time, followed by d-spray treatment. 7. If necessary. Furthermore, they found that an excellent blackening prevention effect can be obtained by adding /Ali to the usual chromic acid treatment.

VCr'e, Mn, 'Sn, other than the method of the present invention
Treatment with a solution containing Cu ions was also performed at autopsy, but Fe,
A slight blackening prevention effect was observed in the Mn ion solution) 1, but 8n.

(j1) On the contrary, those treated with Imen solution became more likely to turn black.Also, the qJ1' characteristic of this treatment method was due to the immersion treatment Jgl
Since i-Kada is a spray treatment, simple equipment is required.

The cost is low because processing of the processing liquid is easy and the adhesion of Go and N1 is very small.

Regarding the Φ matter of this processing method, it is N1 or G.

Solutions containing ions include sulfates of nickel and cobalt.

An acidic bath containing dissolved chloride salts, nitrates, acetates, citrates, etc., may be used, as well as ammonia.

Alkaline baths containing complexing agents such as organic acids may also be used. The metal ion concentration and temperature +pr+ in the treatment solution are not particularly limited and have a wide appropriate range.

Regarding metal ion concentration, Nj i or CO is 1~
If the IjJ of 20 f/l is well surrounded and less than 1/1, the processing time will be longer, and if the I/l is less than 20, the amount of metal ions (14) removed by drag-out will increase. It is uneconomical.The temperature of the processing liquid is 300 yen.
A range of ~60°C is suitable, and the temperature is below 30°C.
, 1-year-olds require longer treatment time.On the other hand, when the temperature exceeds 60°C, the energy required for addition and 1~ increases.

Regarding pH, the appropriate range is PH1 to PH4 for an acidic bath, and PH11 to PH13,5 for an alkaline bath.If the pH is outside this range, there will be too much water attached to the plating surface with Ni or Co. Or, conversely, a phenomenon that is difficult to attach occurs. According to the inventors' detailed experimental results, the Ni-Mada Go adhesion to the plating surface, which is necessary to prevent blackening, is 0.
．． A range of 3~], , 5 rrq/m is appropriate.

Metal (If the J load is less than O, J my/++', there is a risk of black discoloration during a hot and humid summer.) If this happens, the outer fins will become yellow to light brown and not only will they not move out of the original metal surface quickly, but will also increase the aging of the bath, which is economically disadvantageous. (
I'1 month ■:, Karetaka tH1, ゛-+-q-+ According to experiments by the inventors, it is 0.3 to 1.
It is possible to adopt a processing time of sweat within a wide range of 0 seconds.

The blackening prevention mechanism by this treatment method is zero spangle galvanized steel sheet (skin pass advantage) where blackening occurs -1:
When a bamboo alloy galvanized steel sheet is immersed in a solution containing Go and Ni, Ni or Co precipitates on the active surface of the plating surface (electrochemically on the anode surface) in the form of metal particles or oxides. It is presumed that this suppresses the activity and, as a result, prevents the progress of corrosion based on local batteries.

The present invention will be explained in detail below with reference to Examples.

Example 1 A zero-spangle treated galvanized steel sheet produced on a known continuous hot-dip galvanizing line was subjected to skin pass rolling and then subjected to the treatment of the present invention, and the occurrence of blackening was investigated by an accelerated test.

The processing conditions and evaluation of blackening resistance were as follows.

(1) Sample material size 0.5X 10100X200 (
Non-chromate treatment) i1i lead metal key; 1V79:A
'150 ri2/m2 skin pass river hi
E rate Section 1 (11) Previous ll shi Ili + (Inventor J't) 8) None + 1) Old line Jllll! NiSO4・6H2o
50g//-, PH temperature 5o℃.

Immersion time 2 seconds Oil immersion time 2 seconds p) N l + Co 11 process N
j, S04 '6820 25S'/l, CjoS
O4-7H,,02!3 W/l-, PH2, temperature fj'
,'-50℃.

Soaking for 70 hours and 1 second (++i) (A: and (+ Rinsing with tap water (1
v) RiOm fop processing C:r0330'f/L,
50°C, immersion time 5 seconds (v) In I"1lj-blackening test (a) Trial size 100X], OOmrn,
Score 5 sheets each and take one nail.

Packaging introduction, packaging (b) Atmosphere and leaving time ■ 49℃, (N8 Section RH, 7 days ■ 70℃, (18th Section T (H, 3 days) (c) Judgment criteria Judgment Black deformed deafness ◎ No blackening （−）　　　Turn very lightly to gray △　Black discoloration less than 30 × Black discoloration 30% or more The test results are shown in Table 1.

It has been shown that those treated according to the present invention have excellent blackening resistance. In fact, even after being stored in a warehouse for one year in coil form, no blackening occurred.

Table 1 Accelerated silent sitting test results (Example 1) Zn -4
', -0, 'jy % M7 alloy plating was carried out, and then the treatment of the present invention was carried out, and the occurrence of blackening was investigated by an accelerated test.

Place f11! Condition 1? and blackening resistance evaluation were as follows: (1) Test prick size O,,5X loOX200mm (non-chromate treatment) Zinc deposition amount 120V/;n' skin pass None failure, light pretreatment method; The chromic acid treatment and surface 1 black discoloration evaluation test were the same as in Example 1.

The test results are shown in Table 2.

All specimens treated according to the present invention exhibit excellent side heat denaturation.

In fact, no blackening occurred even when the coil was stored in a warehouse for one year.

Claims (2)

[Claims] (1) A zinc-plated steel sheet whose surface has been subjected to lead-repellent or zinc alloy hot-dip plating is coated with Ni ion or co
A method for producing a lead-based plated steel sheet with excellent blackening properties during melting, characterized by treatment with a solution containing ions or a mixture of both. (2) Zinc-plated steel sheet whose surface is hot-dipped with illλ lead or zinc alloy + Ni ion or F, T
, a surface treatment with excellent black discoloration characterized by treatment with CO ions or a solution containing both, followed by chromate treatment! l! 1dli box type plated steel plate H1 manufacturing method