Composite coating steel sheets having good corrosion resistance paintability and corrosion resistance after paint coating

A composite coating steel sheet is disclosed which has good corrosion resistance, paintability and corrosion resistance after paint coating. The steel sheet comprises a plated base steel sheet, such as a galvanized, zinc alloy plated or aluminum plated steel sheet, and a chromate film formed on the plated base steel sheet. A composite silicate resin film is formed on the chromate film. The composite silicate film is composed of a reaction product of a colloidal silica, an organic resin and a silane compound.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a composite coating steel sheet and particularly 
to a plated base steel sheet provided thereon with multiple coatings to 
improve corrosion resistance, paintability and corrosion resistance after 
paint coating. 
2. Description of the Prior Art 
Chromate treatment has been commonly employed as rust preventive treatment 
of galvanized steel sheets, zinc alloy plated steel sheets and aluminum 
plated steel sheets. In most cases, such treatment is intended merely for 
a temporary rust preventive measure and the corrosion reistance thereby 
obtained is at a low level such that white rust appears in 24 to 48 hours 
when the treated steel sheets are subjected to a salt spray test. 
Accordingly, in a case where the products are intended for use under a 
severe corrosive environment for a long period of time, there has been no 
practical way other than applying a thick paint coating at a level of more 
than 10.mu. to prevent corrosion. However, in recent years the costs of 
paints have been rapidly raised reflecting the increase in price of 
petroleum products, and it is strongly desired to develop steel sheet 
products having good corrosion resistance, which can be produced simply by 
surface treatments without using paints. 
Under the circumstances, there has been a certain development in the art of 
chromate treatment. A typical one is a coating type chromate treatment in 
which various binders are added to the chromate treatment solution, 
whereby products having improved corrosion resistance are actually 
produced. Even in this case, however, the corrosion resistance thereby 
obtainable is at best at a level of 200 hours against formation of white 
rust when subjected to a salt spray test. 
Even when paint coating is required to provide an aesthetic outer 
appearance, it is usual to attempt to cut down the costs for the paint by 
choosing a low grade paint or by minimizing the thickness of the paint 
coating. In such a case, the steel sheets are required to have not only 
high corrosion resistance but also good paintability and corrosion 
resistance after paint coating. It is necessary that these properties are 
well balanced. 
However, there has been no chromate treated products which fully satisfy 
these requirements. Some products which satisfy the requirement for high 
corrosion resistance, tend to fail in providing adequate paintability or 
corrosion resistance after paint coating. Whereas those having good 
paintability tend to fail in the requirement for high corrosion 
resistance. 
For example, so-called unichrome treatment is known whereby it is intended 
to provide high corrosion resistance without paint coating by means of a 
reactive chromate. According to this method, a plated steel sheet is 
dipped in a treatment solution composed of chromic acid and a mineral acid 
for a long period of time to form a chromate film coating having a 
thickness of from about 500 to about 700 mg/m.sup.2 as calculated as the 
amount of metal chromium. However, such a treatment has drawbacks that the 
dipping process requires a long period of time and the degradation or 
ageing of the treatment solution is rapid, and it is totally 
unsatisfactory as a strip coating technique. Further, as the chromate film 
is rather thick, it is susceptible to cracking and its paintability is not 
good. If the thickness of the chromate film is decreased to a level of 100 
mg/m.sup.2, the film cracking may be avoided, but the corrosion resistance 
is reduced to a level of 100 hours, thus loosing the high corrosion 
resistant characteristics. 
On the other hand, in coating type chromate treatment, a binder is used to 
fix or trap a substantial amount of chromium therein and to prevent the 
film cracking by the binder. However, it has a drawback that the treatment 
solution is susceptible to gelation, and even when it is not susceptible 
to gelation, it tends to form a thick film which requires a special 
treatment for drying. 
In recent years, it has been proposed, for the purpose of avoiding the 
above mentioned difficulties, to form a double layer coating by duplex 
plating treatment. Namely, a thin chromate film is formed as the first 
layer in a short period of time, and then an inorganic or organic 
substance is coated thereon to form a film as the second layer which 
protects the first layer of the chromate film. Use of inorganic materials 
is disclosed in Japanese Laid-Open Patent Application No. 9545/75 and 
Japanese Patent Publication No. 19981/78 in which a chromate film is 
electrolytically formed as the first layer and a treatment solution 
comprising a chromic acid and silica sol is applied and then dried to form 
a film as the second layer. High corrosion resistance is obtainable by 
forming the second layer sufficiently thick. However, the film thereby 
obtained is apt to be peeled off because of the thick silica layer and 
thus lacks in durability after processing. Further, as the silica sol has 
poor affinity to a paint, the treated surface is not satisfactory as a 
substrate for paint coating. 
A typical example in which an organic material is used for the second 
layer, is Japanese Patent Publication No. 35620/77, in which a chromimum 
hydrated oxide layer is formed as the first layer and then a water soluble 
organic resin layer is formed as the second layer. However, adequate 
effectiveness cannot be expected from the organic resin layer disclosed 
therein, since the functional groups present in the organic resin of the 
second layer tend to attract water and therefore it is impossible to 
obtain a high level of corrosion resistance. Even if the thickness of the 
second layer is increased as much as 1.mu., a high level of corrosion 
resistance will not be obtainable, and in such a case, it will be 
difficult to completely dry the film by hot air only and a special 
apparatus for drying will be required. 
Further, in Japanese Patent Publications No. 36100/74, No. 18445/75, No. 
4611/74 and No. 1986/74, it is proposed to form a chromate film as the 
first layer and an organic film as the second layer. However, in each of 
these cases, the functional groups in the organic resins in the second 
layer tend to attract water and it is impossible to obtain a high level of 
corrosion resistance. These products are presumably effective rather as a 
substrate for paint coating taking the advantage of the functional groups. 
As mentioned above, the products having a second layer formed with an 
inorganic or organic material are effective either for the corrosion 
resistance without paint coating or for the paintability, but they can not 
satisfy both of the required properties at the same time. It is 
conceivable to form the second layer with use of a mixture of an organic 
material and an inorganic material. However, a mere mixture does not 
provide better results, and to the contrary, it is likely in many cases 
that desirable properties of the individual components are imparied. 
Thus, it has been difficult to produce a chromate treated steel sheets 
which are substrates for paint coating and which at the same time have 
superior corrosion resistance. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to overcome the above 
mentioned difficulties in the conventional surface treated steel sheets, 
and to provide steel sheets having good corrosion resistance, paintability 
and corrosion resistance after paint coating. 
It has now been found that superior corrosion resistance, paintability and 
corrosion resistance after paint coating are obtainable by forming, on a 
plated base steel sheet such as a galvanized steel sheet, a zinc alloy 
plated steel sheet or an aluminum steel sheet, a first layer of a chromate 
film by chromate treatment of either reaction type or coating type and 
then forming, on such a first layer, a second layer of a composite 
silicate resin film composed of silica sol and an organic resin. If either 
one of the first and second layers is omitted, the desired level and 
balance of the properties are not obtainable. 
Thus, the present invention provides a composite coating steel sheet which 
comprises a plated base steel sheet, a chromate film formed on the surface 
of the plated steel sheet and a composite silicate resin film formed on 
the chromate film and comprising a colloidal silica, an organic resin and 
a silane compound.

DETAILED DESCRIPTION OF THE INVENTION 
Plated Base Steel Sheet 
As the plated base steel sheet there may be used a galvanized steel sheet, 
a zinc-iron alloy plated steel sheet, a zinc-nickel alloy plated steel 
sheet, a zinc-manganese alloy plated steel sheet, or an aluminum plated 
steel sheet. It may further be a multi-layer plated steel sheet which has 
become popular in recent years, and which has two or more such plated 
layers. In the case of the zinc-iron alloy plated steel sheet, the iron 
content in the plated layer is from 5 to 50% by weight, preferably from 10 
to 30% by weight. If the iron content is outside this range, the corrosion 
resistance and paintability become poor. In the case where the zinc-nickel 
plated steel sheet is employed, the nickel content in the plated layer is 
from 5 to 20% by weight, preferably from 12 to 13% by weight. If the 
nickel content is less than 5%, the corrosion resistance becomes poor. On 
the other hand, if the nickel content is more than 20%, it simply adds to 
the cost and such is not economically practical. 
Chromate Film 
A chromate film is formed on the above mentioned plated base steel sheet as 
the first layer. 
The chromate treatment to form this first layer of the chromate film may be 
conducted in accordance with chromate treatment known per se in the art. 
The amount of chromium deposited on the base steel sheet must be from 10 
to 150 mg/m.sup.2, preferably from 40 to 100 mg/m.sup.2. If the amount is 
less than 10 mg/m.sup.2, the film tends to be uneven. On the other hand, 
an excessive amount over 150 mg/m.sup.2 is not desirable as it facilitates 
degradation of the treatment solution and adds to the costs. As a typical 
example, a reaction type chromate treatment solution comprises from 1 to 
100 g/l, as calculated as metal chromium, of a water soluble chromium 
compound, and from 0.2 to 20 g/l of sulfuric acid, as major component, in 
which the trivalent chromium content in the total chromium is not more 
than 50% by weight, preferably from 20 to 35% by weight. Proper amounts of 
heavy metal ions such as Zn.sup.2+, Co.sup. 2+, or Fe.sup.3+, or other 
mineral acids such as phosphoric acid or hydrofluoric acid, may further be 
added. 
With respect to the chromium compound among the major components, if the 
amount, as calculated as metal chromium, is less than 1 g/l, it is 
difficult to obtain the desired chromate film in a short period of time. 
On the other hand, if the amount exceeds 100 g/l, the stability of the 
treatment bath will be impaired to a considerable extent. 
With respect to sulfuric acid, if the amount is less than 0.2 g/l the 
desired chromate film cannot easily be obtained in a short period of time, 
and uniformity in treatment becomes poor. On the other hand, if the amount 
exceeds 20 g/l, the etching rate of zinc tends to be too fast to be 
desirable. 
If the proportion of Cr.sup.3+ in the total chromium exceeds 50%, the 
stability of the bath will be disturbed, whereupon the bath tends to 
undergo gelation, and the corrosion resistance of the steel sheet before 
paint coating will be poor so that even when the coating amount of the 
chromate film is at the predetermined level, the desired high level of 
corrosion resistance is not obtainable. 
The function of the addition of heavy metal ions such as Zn.sup.2+ besides 
the above mentioned major components, is to improve the treating 
efficiency of the treatment solution, and their amounts may suitably be 
determined depending upon the proportions of the major components. 
As a typical example of a coating type chromate treatment solution, there 
may be mentioned a treatment solution prepared by adding to the above 
mentioned reaction type chromate treatment solution, an organic polymer 
resin containing in its molecule a substantial number of carboxyl groups 
and which is water soluble and compatible with the above mentioned 
reaction-type chromate treatment solution and adjusting the pH to from 2.0 
to 3.5. As the organic polymer, it should preferably have an average 
molecular weight of from 1,000 to 500,000. The amount of the organic 
polymer is selected within a range of from 0.02 to 30 g/l as calculated at 
the resin. If the amount is less than 0.02 g/l, it is not possible to 
completely trap chromium in the film when the film is formed. On the other 
hand, if the amount exceeds 30 g/l, the stability of the bath tends to be 
poor. If the pH is less than 2.0, the bath tends to have characteristics 
similar to the reaction-type chromate treatment solution, and if the pH 
exceeds 3.5, the stability of the bath tends to be impairred. 
In any case, the chromium amount in the first layer of the chromate film 
should be within a range of from 10 to 150 mg/m.sup.2. It is important 
that when the treatment solution for the second layer is applied, there 
should not be elution of chromium from the first layer. If an eluted 
component from the first layer enters the composite silicate resin 
treatment solution during the treatment of the second layer, the balance 
of the resin treatment solution will be disturbed, and in an extreme case, 
gelation of the treatment solution will occur. Accordingly, it is 
necessary to conduct forcible drying and washing with water after the 
treatment of the first layer so as to prevent elution of the components 
from the first layer. 
Composite Silicate Resin Film 
The composite silicate resin film is formed on the above mentioned first 
layer of the chromate film. 
The composite silicate resin is composed of a resin or a mixture of resins, 
which are prepared by reacting a water dispersible silica with a water 
soluble or water dispersible organic polymer resin having in its molecule 
a hydroxyl group (such as polyvinyl alcohol, hydroxyethyl cellulose, 
starch, polyester, alkyd, epoxy ester or acrylic copolymer) in the 
presence of a silane compound. As the silica, so-called colloidal silica 
having a particle size of 7 to 100.mu., preferably from 10 to 50.mu., is 
used. As the resin to be used may be any resin so long as it can react and 
bond with the silica. Further, ultraviolet or electon beam curing type 
functional groups may be introduced to the structure of the resin. 
The role of the silane compound is to act as a catalyst during the 
composite forming reaction of the silica with the organic resin and to 
perform an important function as a cross linking agent for the reactants 
and as a cross linking agent to establish a firm bond between the second 
layer and the first layer. As such a silane compound, a commercially 
available product may be used. 
The ratio of the water dispersible silica to the water soluble or water 
dispersible organic resin in the composite silicate resin composition, 
must be from 5:95 to 95:5, based on the weight ratio of the solid content. 
If the ratio is less than the lower limit, a high level of corrosion 
resistance is not obtainable even when applied to the first layer of the 
chromate film. On the other hand, if the ratio exceeds the upper limit, 
good paintability is not obtainable. The amount of the silane compound is 
from 0.5 to 15% by weight, preferably from 1 to 10% by weight, based on 
the weight of the total solid content of the silica and organic resin. If 
the amount is less than 0.5% by weight, adequate cross linking with the 
chromate film cannot be expected. On the other hand, if the amount exceeds 
15% by weight, no further improvement of the effectiveness is observed. 
Further, by an addition of an alkoxide chelate compound to the above 
mentioned composite silicate resin treatment solution, the corrosion 
resistance can be improved. The alkoxide chelate compound has a structure 
of R.sub.2 MR.sub.2 ', RM.sub.3 ', MR.sub.4 ' or R.sub.3 MR', where R is 
an allyl group or an aryl group, which may have an amino group or a 
mercapto group on its side chain, M is titanium, zirconium or aluminum, 
and R' is a radical composed of an alkoxy group having from 1 to 8 carbon 
atoms or an alkoxyalkoxy group having from 2 to 10 carbon atoms, which is 
condensed with a dicarboxylic acid, a hydroxycarboxylic acid, a diketone, 
an ester or an alkanolamine, as the ligand. 
The alkoxide chelate compound is added to the composite silicate resin in a 
solid content weight ratio of the resin: the alkoxide chelate compound 
being from 97:3 to 80:20. If the amount of the alkoxide chelate compound 
is less than the lower limit, free hydroxyl groups left in the cured film 
become substantial and it is impossible to improve the corrosion 
resistance or water repelling property to an adequate degree. On the other 
hand, if the amount is in excess of the upper limit, the condensation of 
the alkoxide chelate compound itself occurs preferentially, and it becomes 
difficult to form a uniform film. Further, the alkoxide chelate compound 
tends to undergo self-polymerization and become viscous at time passes 
thus leading to thickening of of the composite silicate resin treatment 
solution whereby the treatment solution becomes hardly applicable after 
several days from its preparation. In order to avoid, such a difficulty, 
at least one of the additives selected from the group consisting of oxy 
acids of molybdenum, tungsten, vanadium, tin, boron, and silicon and salts 
of such oxy acids may be added to the composite silicate resin treatment 
solution in place of the alkoxide chelate compound. 
The amount of such additives should be not more than 10% by weight, 
preferably from 0.3 to 5% by weight, based on the solid content weight of 
the composite silicate resin treatment solution. If the amount exceeds 10% 
by weight, there is an undesirable possibility of deterioration of the 
stability of the treatment solution. 
Further, one or more such additives may be added together with the above 
mentioned alkoxide chelate compound. In such a case, the total amount of 
such additives and the alkoxide chelate compound should be not more than 
10% by weight, preferably from 0.3 to 5% by weight, based on the solid 
content weight of the composite silicate resin, and the ratio of the 
alkoxide chelate compound: such additives should be from 95:5 to 5:95, 
preferably from 80:20 to 20:80. Effectiveness is obtainable within the 
above ranges, and if the total amount of addition exceeds the upper limit, 
there is a possibility that the stability of the treatment solution is 
disturbed. 
In the case where the composite silicate resin is composed of a reaction 
product of polyvinyl alcohol and the silica sol, it is possible to improve 
the drying characteristic of the film by incorporating, together with the 
alkoxide chelate compound, one or more additives selected from the group 
consisting of water soluble salts of copper, zinc, aluminum, zirconium, 
chromium, cobalt, and nickel (for instance, zinc chloride), and 
coodination compounds of such elements (for instance, ethylenediamine 
tetraacetic acid zinc complex salt). The amount of such additives is 
preferably from 0.3 to 5% by weight, based on the solid content weight of 
the composite silicate resin. If the amount exceeds this upper limit, 
there is a possibility that the stability of the composition is disturbed. 
Further, the ratio of the composite silicate resin plus such additives to 
the alkoxide chelate compound is from 97:3 to 80:20, based on the solid 
content weight. 
Further, in the case where an ultraviolet or electron beam curing type 
resin is employed, it is possible to facilitate the curing of the 
composite silicate resin film by incorporating a photosensitizer such as 
zinc oxide, titanium oxide (anatase type) or titanic acid, and an oxy acid 
of molybdenum, tungsten or vanadium (for instance, vanadium trioxide) or 
its salt (for instance, lithium orthovanadate). This is attributable to 
the fact that an oxidation reduction reaction occurs among the three 
components, whereby the functional groups in the resin and a cation 
compound formed by the reaction form a salt bond or a coordination bond. 
The amount of the oxy acid or its salt is from 0.1 to 6% by weight, based 
on the solid content weight of the composite silicate resin, and the 
amount of the photosensitizer is from 30 to 200% by weight, based on the 
amount of the oxy acid or its salt. 
Relation Between the Thickness of the Chromate Film and the Thickness of 
the Composite Silicate Resin Film 
Now, the relation between the first layer of the chromate film and the 
second layer of the composite silicate resin film will be described. An 
interrelation exists, as shown in FIG. 1, between the coating amount of 
chrominum for the first layer and the film thickness of the second layer. 
For the coating amount of chromium for the first layer being from 10 to 
150 mg/m.sup.2, the film thickness of the second layer must be from 0.01 
to .mu.4. Therefore, in order to obtain a predetermined level of corrosion 
resistance, it is necessary to select the coating amount of chromium for 
the first layer and the film thickness of the second layer based on this 
relationship. For instance, in order to obtain corrosion resistance of 500 
hours, if the coating amount of chromium in the first layer is 40 
mg/m.sup.2, the film thickness of the second layer must be at least 
1.5.mu., and if the coating amount of chromium is 150 mg/m.sup.2, the film 
thickness of the second layer must be at least 0.4.mu. . 
Generally, for the purpose of practical application, it is desirable that 
for the coating amount of chromium being from 10 to 150 mg/m.sup.2, the 
fiom thickness of the second layer is set to be from 0.4 to 4.mu.. The 
above ranges are desirable from the standpoint of the manufacture of the 
products, and as is apparent from the graph of FIG. 1, if the film 
thickness of the second layer is set to be less than 0.4.mu., it is 
necessary to increase the coating amount of chromium, which tends to lead 
to degradation of the chromate treatment solution. On the other hand, if 
the film thickness of the second layer is set to be greater than 4.mu., 
the costs will increase to an uneconomical level and the products become 
hardly weldable under commonly employed welding conditions, although the 
degradation of the chromate treatment solution will be reduced. 
However, in a case where such a high level of corrosion resistance is not 
required, the film thickness of the second layer may be less than 0.4.mu. 
and at least 0.01.mu. for the coating amount of chromium in the first 
layer being from 10 to 150 mg/m.sup.2. In this case, the conditions for 
both layers to provide the desired corrosin resistnace may be presented in 
a more obvious manner by modifying the graph as shown in FIG. 2, in which 
the vertical axis is for the film thickness of the second layer and the 
horizontal axis is for the coating amount of chromium of the first layer, 
and the corrosion resistance represented by the spraying time of a salt 
spray test is presented as a parameter. From FIG. 2, it will be understood 
that in order to obtain corrosion resistance of 200 hours, for instance, 
the film thickness of the second layer may be set to be 0.1.mu. when the 
coating amount of chromium of the first layer is 80 mg/m.sup.2, and 
0.02.mu. when the coating amount of chromium is 120 mg/m.sup.2. 
Having thus described the relationship between the coating amount of the 
first layer and the film thickness of the second layer, it should be added 
that it is essential to provide a double layer structure composed of the 
chromate film and the composite silicate resin film. Without this double 
layer structure, a high level of corrosion resistance is not obtainable. 
Now, the invention will be described with reference to the Examples. 
EXAMPLES 
Tests for white rust formation, paintability and corrosion resistance after 
paint coating were conducted with respect to the steel sheets No. 1 to No. 
37 of the present invention which had various coating amounts of chromium 
in the respective first layers and various film thicknesses of the 
respective second layers, as indicated in the Table below. The results 
thereby obtained are shown in comparison with comparative steel sheets No. 
38 to No. 53. As the chromate treatment solution for the first layer, the 
following three compositions were used as representatives: 
A: (CrO.sup.3, H.sub.2 SO.sub.4, H.sub.3 PO.sub.4)=(10 g/l, 2 g/l, 2 g/l) 
B: (CrO.sub.3, H.sub.2 SO.sub.4, Cr.sup.3+, Zn.sup.2+)=(10 g/l, 2 g/l, 2 
g/l, 3 g/l) 
C: To the composition B, 2 g/l of a polyacrylic acid having a molecular 
weight of about 100,000 was added, and then the pH was adjusted to 3 with 
aqueous ammonia. 
Further, as the composite silicate resin treatment solution, the following 
three compositions were used as representatives: 
(a): As the organic resin, an acrylic copolymer and an epoxy resin were 
mixed in a solid content ratio of 70:30, and the mixture was reacted and 
bonded with silica sol in a solid content ratio of 60:40. 
(b): To the treatment solution (a), trifunctional dibutyl titanate prepared 
by reacting butyl titanate with triethanol amine was added as the alkoxide 
chelate compound in a solid content weight ratio of 90:10. 
(c): To the treatment solution (a), ammonium metavanadate was added in a 
solid content weight ratio of 100:1. 
However, it should be understood that the treatment solutions are not 
limited to those mentioned above. 
As the plated base steel sheets, there were used, an electro-galvanized 
steel sheet, an zinc-nickel alloy plated steel sheet, and an 
electrolytically formed zinc-iron alloy plated steel sheet. As the plated 
base sheet, other zinc alloy plated steel sheets or aluminum plated steel 
sheets may also be used. 
The steps of the treatments were as follows: 
EQU Weak alkaline degreasing.fwdarw.washing with 
water.fwdarw.drawing.fwdarw.reaction type chromate treatment (A, 
B).fwdarw.drawing.fwdarw.washing with 
water.fwdarw.drying.fwdarw.application of the composite silicate 
resin.fwdarw.drying. 
EQU Weak alkaline degreasing.fwdarw.washing with 
water.fwdarw.drawing.fwdarw.coating type chromate treatment 
(C).fwdarw.forcible drying.fwdarw.application of the composite silicate 
resin.fwdarw.drying. 
It will be seen from the Table below, that the steel sheets No. 1 to No. 37 
of the present invention have distinctly superior corrosion resistance to 
the conventional comparative steel sheets No. 38 to 53. It will also be 
seen that they are superior to the conventional phosphate treated steel 
sheet (comparative steel sheet No. 44) in the paintability. 
The comparative steel sheet No. 45 is a steel sheet on which the composite 
silicate resin film was formed without the chromate treatment. The 
comparative steel sheet No. 46 is a steel sheet on which the composite 
silicate resin film was formed after phosphate treatment. The comparative 
steel sheet No. 45 had good paintability comparable to the steel sheets of 
the present invention, but it is inferior in the corrosion resistance and 
corrosion resistance after paint coating. The comparative steel sheet No. 
46 does not have adequate corrosion resistance and paintability and it is 
inferior in the corrosion resistance after paint coating. 
______________________________________ 
N 
No. H I J K L M O P Q R 
______________________________________ 
1 S A 20 a 1 200 .circleincircle. 
.circleincircle. 
.circleincircle. 
1 
2 " " " " 4 650 " " " 0.5 
3 " B " " 1 200 " " " 1 
4 " " " " 4 650 " " " 0.5 
5 " " " b 1 750 " " " 1 
6 " " " " 4 800 " " " 0.5 
7 " A 70 a 0.4 330 " " " 1 
8 " " " " 1 500 " " " 0.5 
9 " " " C 1 600 " " " 0.5 
10 " " " " 1.5 700 " " " " 
11 " " " b 0.4 400 " " " 0.7 
12 " " " " 1 600 " " " 0.5 
13 " " " " 1.5 900 " " " " 
14 " B " a 0.4 330 " " " 1 
15 " " " b " 400 " " " 0.7 
16 S C 70 b 0.4 400 .circleincircle. 
.circleincircle. 
.circleincircle. 
0.6 
17 " A 150 a " 500 " " " 1 
18 T Ni 12% A 70 a 0.5 800 " " " 0.8 
19 " " " " a 1 1000 " " " 0.5 
20 " " A " b 0.5 900 " " " 0.5 
21 " " " " " 1 1200 " " " 0.5 
22 " " " " c 0.5 1000 " " " 0.5 
23 " " " " " 1 1300 " " " 0.2 
24 " 5 " " " " 800 " " " 1.0 
25 " 20 " " " " 700 " " " 1.0 
26 " 12 B " " " 1300 " " " 0.2 
27 " " C " " " 1300 " " " 0.2 
28 U Fe 10% A 70 a 0.5 400 " " " 0.5 
29 " " " " " 1 600 " " " 0.3 
30 " " " 70 b 1 720 " " " 0.5 
31 " " " " c 0.5 500 " " " 0.5 
32 " " " " " 1 800 " " " 0.2 
33 U Fe 10% B 70 c 1 800 .circleincircle. 
.circleincircle. 
.circleincircle. 
0.2 
34 " " C " " " 800 " " " 0.2 
35 " 5 A " " " 400 " " " 1.0 
36 " 30 A " " " 400 " " " 1.0 
37 " 50 A " " " 400 " " " 1.5 
38 V " 20 -- -- &lt;24 x x x 5 
39 " " 70 -- -- 80 x x x 5 
40 " B 20 -- -- &lt;24 x x x 5 
41 " B 70 -- -- 80 x x x 5 
42 " C 20 -- -- &lt;24 .DELTA. 
x .DELTA. 
4 
43 " " 70 -- -- 80 .DELTA. 
x .DELTA. 
4 
44 " W -- -- -- &lt;72 .circleincircle. 
.circle. 
.circle. 
3 
45 " -- -- a 1 &lt;24 .circleincircle. 
.circleincircle. 
.circleincircle. 
5 
46 " X -- a 1 &lt;20 .circleincircle. 
.circle. 
.circle. 
3 
47 T Ni: 5% A 70 -- -- 130 .DELTA. 
x .DELTA. 
2.5 
48 " Ni: 12% " " -- -- 150 .DELTA. 
x .DELTA. 
2.0 
49 " Ni: 20% " " -- -- 130 .DELTA. 
x .DELTA. 
3.0 
50 Y Fe: 5% A 70 -- -- 60 .circle. 
.DELTA. 
.DELTA. 
1.0 
51 " Fe: 10% " " -- -- 100 .circleincircle. 
.circle. 
.circle. 
1.0 
52 " Fe: 30% " " -- -- 60 .circle. 
.DELTA. 
.DELTA. 
1.0 
53 " Fe: 50% " " -- -- 60 .circle. 
.DELTA. 
.DELTA. 
1.5 
______________________________________ 
No. 1 to No. 37: Inventive steels; 
No. 38 to No. 53: Comparative steels 
H: Mother sheets 
I: Chromate treatment solution 
J: Cr plating amount (mg/m.sup.2) 
K: Compound organic silicate treatment solution 
L: Secondary film thickness (.mu.) 
M: Time (hr) till appearance of white rust 
N: Coating adhesion Refer to NOTE 1. 
O: Lattice cut test Refer to NOTE 2. 
P: Lattice cut Erichsen test Refer to NOTE 3. 
Q: Dupon shock Refer to NOTE 4. 
R: Corrosion resistance after plating Refer to NOTE 
S: Galvanized steel sheets 
T: Zn--Ni alloy steel sheet 
U: Zn--Fe alloy steel sheet by galvanization 
V: Galvanized steel sheet 
W: Phosphate treatment solution 
X: Phosphate treatment solution 
Y: Zinc--Fe alloy steel sheet by galvanization 
*.sup.o Peeled length on one side 
NOTE 1: Melamine alkyd paint (paint film thickness: 30) 
NOTE 2: Squares of 1 m/m were arranged in the vertical and horizontal 
direction; 10 squares in each direction 
NOTE 3: Pressed by 5 m/m after forming the squares of NOTE 2 
NOTE 4: Weight of 1 kg was dropped from height of 50 cm with use of 
1/2.phi. punch. 
NOTE 5: The paint of NOTE 1 was used; the paint film formed was crosscut, 
subjected to a salt spray test for 360 hours and peeled with a scotch 
tape. The evaluation standards for paintability: .circleincircle. . . . N 
peeling of the applied paint film with scotch tape was observed .circle. 
. . Peeling off of the applied paint with a scotch tape was slight .DELTA 
. . . About 40% of the applied paint film was peeled off x . . . More tha 
40% of the applied paint film was peeled off.