Example 1
Change in Properties Depending on Content of Trivalent Chromium Compound
A surface treatment solution composition containing trivalent chromium including: a trivalent chromium compound produced by adding chromium phosphate and chromium nitrate to distilled water, reacting them at 80° C. for 1 hour, and cooling them to room temperature; vanadium acetyl acetonate as a vanadium-based rust-inhibiting and corrosion-resisting agent; cobalt (III) nitrate as a cobalt-based rust-inhibiting and corrosion-resisting agent; a mixture of tetraethyl orthosilicate and 3-glycidoxypropyl trimethoxysilane in a weight ratio of 1:1 as a silane coupling agent; and water, and mixed in the amounts illustrated in Table 2 below (based on the solids content of the composition), was prepared.
In the following examples, cases in which the surface treatment solution composition according to the present disclosure satisfies the specified content range illustrated in Table 1 below were described as Inventive Examples, and cases in which one or more components do not satisfy the specified content range illustrated in Table 1 were described as Comparative Examples.
A hot-dip galvanized steel sheet was cut to have a size of 7 cm×15 cm (width×length), and oil was removed therefrom. Then, the prepared surface treatment solution composition was bar-coated on the hot-dip galvanized steel sheet in a dry film layer thickness of 0.4 μm. Subsequently, the steel sheet coated with the surface treatment solution composition was completely dried using a hot-air drying furnace under conditions of PMT 60° C., to prepare a specimen having a trivalent chromate inorganic film, as illustrated in
Flat sheet corrosion resistance, processed part corrosion resistance, and blackening resistance of the prepared specimens were evaluated. The evaluation results are presented in Table 2 below. The evaluation methods for flat sheet corrosion resistance, processed part corrosion resistance, and blackening resistance were as follows.
<Flat Sheet Corrosion Resistance>
Based on the method specified in ASTM B117, the rate of occurrence of white rust in the steel sheet was measured over time after the specimens were treated. The evaluation criteria are as follows:
⊚: 144 hours or more of white rust occurrence time
∘: 96 hours or more and less than 144 hours of white rust occurrence time
Δ: 55 hours or more and less than 96 hours of white rust occurrence time
×: Less than 55 hours of white rust occurrence time
<Processed Part Corrosion Resistance>
The specimens were pushed up to a height of 6 mm using an Erichsen tester, and a frequency of occurrence of white rust was measured after 24 hours. The evaluation criteria are as follows:
⊚: Less than 5% frequency of occurrence of white rust after 48 hours
Δ: 5% or more and less than 7% frequency of occurrence of white rust after 48 hours
×: Greater than 7% frequency of occurrence of white rust after 48 hours
<Blackening Resistance>
The color change (color difference: ΔE) of the specimens before and after the test was observed by allowing the specimens in an air-conditioning equipment maintaining at 50° C. and a relative humidity of 95% for 120 hours. The evaluation criteria are as follows:
⊚: ΔE≤2
∘: 2<ΔE≤3
Δ: 3<ΔE≤4
×: ΔE>4
As illustrated in Table 2 above, when the content of the trivalent chromium compound satisfied the content proposed by the present disclosure (Inventive Examples 1 to 4), all of the properties exhibited good or higher results.
Meanwhile, when the trivalent chromium compound was added in a relatively small amount (Comparative Example 1), flat sheet corrosion resistance, processed part corrosion resistance, and blackening resistance exhibited poor results. When the trivalent chromium compound was added in a relatively larger amount (Comparative Example 2), all of the properties, except for blackening resistance, exhibited poor results.
Example 2
Changes in Properties Depending on Ratios of Chromium Phosphate (III) and Chromium Nitrate (III)
The trivalent chromium surface treatment solution composition according to Inventive Example 3 was used in the same manner as in Example 1 to prepare hot-dip galvanized steel sheet specimens in which a trivalent chromate inorganic film was formed, except that a ratio of chromium phosphate (III) and chromium nitrate (III) was controlled to be the ratio of chromium phosphate and chromium nitrate illustrated in Table 3 below.
Flat sheet corrosion resistance and blackening resistance of the prepared specimens were evaluated in the same manner as in Example 1, and the evaluation results are illustrated in Table 3.
As illustrated in Table 3 above, corrosion resistance may be improved as a ratio of chromium phosphate is increased, while blackening resistance may be improved as a ratio of chromium nitrate is increased. When the ratio of chromium phosphate to chromium nitrate is less than or more than the ratio of chromium phosphate and chromium nitrate illustrated in the present disclosure, the corrosion resistance or blackening resistance tends to be poor.
Example 3
Changes in Properties Depending on Content and Type of Silane Compound
Hot-dip galvanized steel sheet specimens on which a trivalent chromate inorganic film layer is formed was prepared in the same manner as in Example 1, except that chromium nitrate and chromium phosphate as a trivalent chromium compound; vanadium acetyl acetonate as a vanadium-based rust-inhibiting and corrosion-resisting agent; cobalt (III) nitrate as a cobalt-based rust-inhibiting and corrosion-resisting agent; and a silane mixture of tetraethyl orthosilicate and 3-glycidoxypropyl trimethoxysilane in a weight ratio of 1:1 as a silane coupling agent, were mixed in the amounts illustrated in Table 4 below (based on the solids content of the composition).
Flat sheet corrosion resistance, processed part corrosion resistance, and blackening resistance of the prepared specimens were evaluated in the same manner as in Example 1, and further, alkali resistance, fuel resistance and fingerprint resistance were evaluated as follows, and the evaluation results may be illustrated in Table 4.
<Alkali Resistance>
The specimens were immersed in an alkaline degreasing solution at 60° C. for 2 minutes, washed with water, air dried, and then measured with regard to a difference in color (ΔE) before and after the operations. The alkali degreasing solution was Finecleaner L 4460 A: 20 g/2.4 L+L 4460 B 12 g/2.4 L (pH=12) manufactured by Parkerizing Co., Ltd. The evaluation criteria are as follows:
⊚: ΔE≤2
∘: 2<ΔE≤3
Δ: 3<ΔE≤4
×: ΔE>4
<Weldability>
Weldability was evaluated by using a pneumatic AC Spot welding machine, and maintaining pressing force of 250 kg, welding time of 15 cycles, and electric current carrying electric current of 7.5 kA without spatter and constant strength. The evaluation criteria are as follows:
◯: Weldable
Δ: Poor welding quality
×: Not Weldable
<Fuel Resistance>
Evaluation of fuel resistance was to evaluate high temperature fuel resistance with regard to degraded gasoline and biodiesel. The following degraded gasoline and biodiesel were used for fuel resistance evaluation.
Degraded gasoline: 78.58% by volume of gasoline+20% by volume of ethanol+1.42% by volume of pure water+100 ppm of formic acid+100 ppm of acetic acid
Biodiesel: 81% by volume of diesel+9% by volume of BIO diesel+5% by volume of pure water+5% by volume of methanol+20 ppm of formic acid+0.3% by weight of peroxide
After the obtained specimen was processed to have a cup shape, each of the fuels was filled, a surface thereof was covered with a glass plate, and the specimen and the glass plate were sealed using an O-ring. Thereafter, after standing at 85° C. for 3 months, corrosion resistance of the steel plate was observed to evaluate fuel resistance. The evaluation criteria are as follows.
⊚: 0% of Corrosion Area
◯: more than 0% and 5% or less of Corrosion Area
□: more than 5% and 30% or less of Corrosion Area
Δ: greater than 30% and 50% or less of Corrosion Area
×: greater than 50% of Corrosion Area
As illustrated in Table 4 above, when the content of the silane compound satisfied the content range proposed by the present disclosure (Inventive Examples 8 to 11), all of the properties exhibited good or higher results.
Meanwhile, when the silane compound was added in a relatively small amount (Comparative Example 7), alkali resistance and fuel resistance exhibited poor results. When the silane compound was added in a relatively larger amount (Comparative Example 8), the film may become too dry to form an excessively hard film. Therefore, processed part corrosion resistance was deteriorated, blackening resistance was poor, and welding quality was poor.
Example 4
The trivalent chromium surface treatment solution composition according to Inventive Example 10 was used in the same manner as in Example 1 to obtain hot-dip galvanized steel sheet specimens on which a trivalent chromate inorganic film is formed, except that the silane compound illustrated in Table 5 was used.
Each of the specimens were evaluated for flat sheet corrosion resistance in the same manner as in Example 1, and the results are illustrated in Table 5.
As illustrated in Table 5 above, Inventive Examples 12 to 45 exhibited good or excellent flat sheet corrosion resistance. In particular, in the case of the test specimen treated with the trivalent chromium surface treatment solution composition prepared according to the composition of Inventive Example 41, white rust did not occur even after more than 144 hours, which exhibited the most excellent.
Example 5
Changes in Properties Depending on Content of Vanadium-Based Rust-Inhibiting and Corrosion-Resisting Agent
Hot-dip galvanized steel sheet specimens on which a trivalent chromate inorganic film layer is formed was prepared in the same manner as in Example 1, except that chromium nitrate and chromium phosphate as a trivalent chromium compound; vanadium acetyl acetonate as a vanadium-based rust-inhibiting and corrosion-resisting agent; cobalt (III) nitrate as a cobalt-based rust-inhibiting and corrosion-resisting agent; and a silane mixture of tetraethyl orthosilicate and 3-glycidoxypropyl trimethoxysilane in a weight ratio of 1:1 as a silane coupling agent, were mixed in the amounts illustrated in Table 6 below (based on the solids content of the composition).
Flat sheet corrosion resistance, processed part corrosion resistance, blackening resistance, and alkali resistance of the prepared specimens were evaluated in the same manner as in Examples 1 and 3, and the evaluation results may be illustrated in Table 6.
As illustrated in Table 6 above, when the content of the rust-inhibiting and corrosion-resisting agent satisfied the content proposed by the present disclosure (Inventive Examples 46 to 48), all of the properties exhibited good or higher results.
Meanwhile, when the rust-inhibiting and corrosion-resisting agent was added in a relatively small amount (Comparative Example 9), all of the properties, except for blackening resistance and alkali resistance, exhibited poor results. When the rust-inhibiting and corrosion-resisting agent was added in a relatively larger amount (Comparative Examples 10 and 11), all of the properties, except for corrosion resistance, exhibited poor results.
Example 6
Changes in Properties Depending on Content of Cobalt-Based Rust-Inhibiting and Corrosion-Resisting Agent
Hot-dip galvanized steel sheet specimens on which a trivalent chromate inorganic film layer is formed was prepared in the same manner as in Example 1, except that chromium nitrate and chromium phosphate as a trivalent chromium compound; vanadium acetyl acetonate as a vanadium-based rust-inhibiting and corrosion-resisting agent; cobalt (III) nitrate as a cobalt-based rust-inhibiting and corrosion-resisting agent; and a silane mixture of tetraethyl orthosilicate and 3-glycidoxypropyl trimethoxysilane in a weight ratio of 1:1 as a silane coupling agent, were mixed in the amounts illustrated in Table 7 below (based on the solids content of the composition).
Flat sheet corrosion resistance, processed part corrosion resistance, and blackening resistance of the prepared specimens were evaluated in the same manner as in Examples 1 and 3, and the evaluation results are illustrated in Table 7.
As illustrated in Table 7 above, when the content of the rust-inhibiting and corrosion-resisting agent satisfied the content proposed by the present disclosure (Inventive Examples 49 to 51), all of the properties exhibited good or higher results.
Meanwhile, when the rust-inhibiting and corrosion-resisting agent was added in a relatively small amount (Comparative Example 12), blackening resistance exhibited poor results. When the rust-inhibiting and corrosion-resisting agent was added in a relatively larger amount (Comparative Examples 13 and 14), corrosion resistance exhibited poor results.
Example 7
Change in Properties Depending on Thickness of Film Layer and Drying Temperature
Hot-dip galvanized steel sheet specimens on which a trivalent chromate inorganic film layer is formed was prepared in the same manner as in Example 1, except that a thickness of the inorganic film, after drying, and a PMT temperature in the drying process are as illustrated in Table 8 below.
Alkali resistance, fuel resistance, weldability, flat sheet corrosion resistance, corrosion resistance, and blackening resistance of the prepared specimens were evaluated in the same manner as in Examples 1 and 3, and the evaluation results are illustrated in Table 8.
As illustrated in Table 8 above, when the inorganic film layer was formed at 0.3 μm to 0.5 μm (Inventive Examples 52 to 57), all of the properties exhibited good or higher results. Meanwhile, when the inorganic film was formed to be relatively thin (Comparative Example 15), all of the properties, except for weldability, exhibited moderate results (Δ). Meanwhile, when the inorganic film was formed to be relatively thick (Comparative Example 16), all of the properties, except for weldability, exhibited good or higher results, but weldability exhibited poor. In this regard, a thicker film exceeding 0.5 μm is not preferable and required in view of economy.
In addition, as illustrated in Table 8 above, when the inorganic film layer was formed by setting a drying temperature of the inorganic film to 50 to 60° C. (Inventive Examples 52 to 54 and 56), all of the properties exhibited good or higher results.
When the drying temperature was relatively low (Inventive Example 55), sufficient drying was not carried out, and alkali resistance and fuel resistance exhibited moderate results (Δ). Meanwhile, when the drying temperature was relatively high (Inventive Example 57), the steel sheet was not sufficiently cooled during the cooling process (air cooling) in air, and, consequently, blackening resistance exhibited moderate results (Δ) due to the condensation phenomenon by a packaging operation.
While example embodiments have been illustrated and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present disclosure as defined by the appended claims.
