JPS6365062A - Hot dip galvanized steel sheet - Google Patents

Abstract

PURPOSE:To improve the adhesion of a Zn layer to a steel sheet when a hot dip galvanized steel sheet is produced, by incorporating specified amounts of Ti and Al into the Zn layer. CONSTITUTION:When the surface of a steel sheet such as a capped or killed steel sheet is hot dip galvanized to form a Zn layer, a compsn. consisting of 0.0002-0.1wt% Ti, 0.05-0.8wt% Al and the balance Zn is provided to the Zn layer. A hot dip galvanized steel sheet having superior adhesion and aging stability is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to hot-dip galvanized steel sheets, and more specifically,
This invention relates to hot-dip galvanizing jI4 temporary which has excellent plating adhesion even immediately after plating and after a long period of time has passed after plating.

[Prior art] One method of continuously applying hot-dip galvanizing to the strip is after-in-line annealing, in which the oxide film on the surface of the steel strip is reduced and the strip is annealed at the same time in an annealing furnace with a reducing atmosphere. ,
The steel strip whose surface has been activated in a reduction furnace is cooled to a predetermined temperature and immersed in a hot-dip galvanizing bath to produce a galvanized steel sheet.

Hot-dip galvanized steel sheets include spangle products and zero-spangle products, and spangle products are obtained by plating in a plating bath containing usually 0.1 to 0.2 wt% of Pb and then slowly cooling. Additionally, zero spangle products can basically be manufactured by plating with a plating bath that does not contain Pb, but in order to manufacture both products in one line, it is necessary to use a plating bath that contains Pb and a plating bath that does not contain Pb. This requires two plating baths, one for plating baths that does not require plating, and additional equipment costs and operating costs are incurred for switching between these two plating baths. Therefore, after both products are plated in a plating bath containing Pb, spangled products are manufactured by slow cooling, and zero-spangled products are manufactured by rapid cooling.

However, hot-dip galvanized steel sheets manufactured using plating baths that do not contain Pb suffer from deterioration in plating adhesion over time, such as peeling of the plating when processed after a long period of time after manufacture. For this deterioration of plating adhesion over time, P
There is a countermeasure to include sb in the plating bath instead of h, but this poses a new problem of increased cost.

In addition to rimmed steel and capped steel, the scraps plated by in-line annealing include A.
Various killed steels such as I and Si are also coming into use.

However, these killed steel sheets tend to form a strong, dense and stable oxide film on the surface, making it difficult to sufficiently clean and activate the steel sheet to be plated by in-line annealing, resulting in poor plating adhesion. causes deterioration.

One way to improve the plating adhesion of these steel sheets is to increase the AI content in the plating bath, but this reduces the reactivity of the plating bath to the insufficiently activated steel sheet surface. The purpose is to increase However, there is a problem that the amount of dross generated increases.

Also, as a countermeasure for ponds, increase the temperature of the reduction furnace, H! It is conceivable to increase the gas concentration, but this would require complicated operations and increase costs.

[Problems to be Solved by the Invention] In view of the various problems in conventional hot-dip galvanizing described above, the present inventor has conducted extensive research, and as a result, the present invention aims to prevent the deterioration of the plating's hardness over time. At the same time, we developed a hot-dip galvanized steel sheet that has good plating adhesion not only to capped steel but also to various types of killed steel sheets where the surface of the steel sheet is not sufficiently activated.

[Means for solving the problems] The tentative characteristics of hot-dip galvanizing J171 according to the present invention are as follows: Ti 0.0002-0.1vt%, AI 0.05-0.
0.8 wt%, with the remainder being Zn and unavoidable impurities.

Hot-dip galvanizing preparation according to the present invention will be explained in detail below.

That is, the hot-dip galvanized steel sheet according to the present invention can be manufactured by subjecting the steel strip to hot-dip galvanizing after passing through an annealing furnace having a reducing atmosphere.

1st Back Regarding the hot-dip galvanized conditioned plate according to the present invention, the steel plates shown in Table 1, which will be specifically explained below, were heated to 80% in a non-oxidizing furnace (air-fuel ratio 0.92).
Heat to a temperature of 0°C and place in a reduction furnace (H!:N, = 1 = 2)
After being exposed to light for 30 seconds, the steel plate was cooled to a temperature of 460°C and placed in a hot dip galvanizing bath (AIG,
2ht%, Pb 0.18wt%, TiO~0.2w
t%, balance Zn and inevitable impurities. ) and then pulled out. After that, N! The relationship between Ti content in the coating layer and coating adhesion of a hot-dip galvanized steel sheet obtained by controlling the coating weight to 80 g/m' on one side by gas wiping was investigated. The Ti content in the plating layer was determined by dissolving the plating layer with hydrochloric acid, and then analyzing the solution by atomic absorption spectrometry.

Plating adhesion was investigated by conducting an impact test and observing the state of cracks and peeling of the plating layer in the processed area. The evaluation criteria is (good adhesion) l → 2-3-4
(poor adhesion).

Figure 1 shows the results. Capped, IFi, (1st
Indicated by O in the figure. ), the plating adhesion is good even if the plating layer does not contain Ti, and the killed steel sheet (indicated by ・ in Figure 1) has good plating adhesion even if the plating layer does not contain Ti. Although poor adhesion is exhibited, the effect of improving plating adhesion is observed when the Ti content in the plating layer is 0.0002 wt% or more.

Next, the relationship between the Ti content in the plating layer of the hot-dip galvanized steel sheet produced under the above conditions and the plating adhesion over time was investigated.

The plating adhesion over time was evaluated by performing an impact test after being immersed in hot water at a temperature of 95° C. for 50 hours to simulate the effect of aging after plating. The evaluation criteria are the same as in Figure 1.

Figure 2 shows the results. If Ti is not contained in the plating layer, the killed steel sheet (indicated in Figure 2) will have poor plating adhesion from the time of plating, and the capped steel sheet (indicated by O in Figure 2) will have poor plating adhesion after plating. Poor adhesion is observed. However, the Ti content in the plating layer is 0.0002v
At t% or more, the effect of improving plating adhesion is observed for both the killed steel sheet and the capped steel sheet.

In this case, the reason why the plating adhesion improvement effect is obtained with the Ti-containing plating layer is that the bonding state of the plating layer/base condition plate boundary is strengthened by the Ti content, and the plating adhesion is improved. The Ti content is preferably 0.1 wt%. Then, Ti was added from 0.0002 to 0.000. ivt
The plating layer containing Ti is 0.0001 to 0.1%.
It is obtained by plating in a plating bath containing wt%.

The Al content in the plating layer is desirably 0.05 wt% or more in order to suppress the growth of the Zn-Fe alloy layer that adversely affects plating adhesion.
If the 1 content is increased, dross is likely to be generated in the plating bath, so it is desirable that the Al content is 0.8 wt% or less.

Furthermore, regarding the inclusion of Pb in the plating layer,
In particular, although there are no restrictions, it is necessary to contain Pb in the plating layer for the production of spangle products, and the spangle size will reach saturation even if the content exceeds a certain dietary intake amount. The content of I is preferably 0.5 wt% or less.

[Example] The present invention describes an embodiment of a hot-dip galvanized steel sheet.

Example killed steel plate (AI 0.051wt%, Si 0.02
wt%, C0.060wt%, Mn 0.27vt%,
P 0.016wt%, S0.016wt%, balance Fe
and unavoidable impurities. ) in a non-oxidizing furnace (air-fuel ratio 0.93)
Heated to 740°C in a reduction furnace (Ht:Nt=1:
3) for 20 seconds, the conditioning plate was cooled to 460°C and placed in a Ti-containing plating bath (AI 0.22wt) at 460°C.
%, Pb 0.19wL%, Ti 0.004vt%,
The remainder is Zn and inevitable impurities. ) and Ti-free plating bath (AI 0.21wt%, Pb 0.19w
t%, balance Zn and inevitable impurities. ) and then pulled out. Thereafter, a product was manufactured by controlling the coating weight to 90 g/m'' on one side by air wiping.

Ti in the plating layer of products plated with a Ti-containing plating bath
The content is 0. It was OO'ht%.

Table 2 shows the test results of plating adhesion and aging plating adhesion of these products.

Table 2 From Table 2, it can be seen that both the plating adhesion and the aging plating adhesion are improved by containing Ti in the plating layer.

[Effects of the Invention] As explained above, since the hot-dip galvanized steel sheet according to the present invention has the above-mentioned configuration, it is a hot-dip galvanized steel sheet with excellent plating adhesion and aged plating adhesion, and is also free from spangles and zero. This has the effect that it can be used as a spangled product.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing the relationship between the Ti content in the fitting layer and the impact rank.

Claims (1)

[Claims] Ti0.0002-0.1wt%, Al0.05-0.
A hot-dip galvanized steel sheet characterized by having a plating layer containing 8 wt% Zn and the remainder consisting of Zn and unavoidable impurities.