JPS61139659A - Production of steel sheet plated with zn-al alloy with less blister - Google Patents

Abstract

PURPOSE:To obtain a steel sheet plated with a Zn-Al alloy with less hydrogen blister by cold rolling a steel slab contg. specified amounts of C and O so that the product of the amount of oxygen in the steel and the cold rolling reduction rate is regulated to a specified value or above and by plating the cold rolled steel sheet with a Zn-Al alloy by hot dipping. CONSTITUTION:The steel slab consisting of <0.003wt% C, 0.03-0.08wt% O and the balance Fe is produced by a continuous casting. The slab is hot rolled, pickled, and cold rolled so that the product of the amount (wt%) of oxygen in the steel and the cold rolling reduction rate (%) is regulated to >=2.4. The resulting steel strip is annealed and plated with a Zn-Al alloy consisting of 3-10wt% Al, 5ppm-1wt% rare earth element and the balance Zn on a continuous hot plating line.

Description

[Detailed description of the invention]

<Field of Application of Industry-L> The present invention relates to a method for manufacturing a Zn-Al alloy coated steel plate with fewer surface defects, particularly hydrogen blisters, on the hot-dip zinc-aluminum alloy coated steel plate. <Prior art and its problems> One of the methods for improving the corrosion resistance of steel sheets is hot-dip galvanizing, and the product, hot-dip galvanized steel sheets, can be used as building materials,
It is widely used in various applications such as automobiles and home appliances. In recent years, many attempts have been made to improve quality, mainly corrosion resistance, in these fields, and some of these have already been commercialized. Here, most of the methods adopted for quality improvement-H are methods of adding metal elements, mainly aluminum, to zinc, and the quality of the product depends on the size of the added part. It's quite different. Among them, zinc-aluminum alloy coated steel sheets with an aluminum content of less than 10% have the same sacrificial corrosion protection as hot-dip galvanized steel sheets and are excellent in corrosion resistance, so they have been studied in detail in recent years. No. 46528, Publication No. 7-500475, and other publications disclose industrial methods for producing the same. However, in such galvanized steel sheets, blistering of the plating layer may occur immediately after hot-dip plating or after a few seconds, and as a result of investigation, it has been found that hydrogen absorbed in the steel sheet during the original annealing process of the hot-dip galvanizing line is released after plating. It was assumed that this was to prevent This phenomenon is also observed in the case of hot-dip galvanized steel sheets, and it is said that the degree of blistering varies depending on the type of steel sheet. Since hot-dip zinc-aluminum alloy coated steel sheets have slightly more blisters than hot-dip galvanized steel sheets, we investigated ways to prevent such blisters, and completed the present invention by obtaining a steel sheet for hot-dip galvanized steel sheets with less blisters. <Object of the invention> The present invention provides Z with few plating surface defects, that is, hydrogen blisters.
To provide a method for manufacturing n-Al alloy plated steel sheet [
] target. <Structure of the Invention> The present invention provides C: 0.003 wt% or less, O: 0.003 wt% or less.
0.03 wt% or more, 0.06 wt% or less, the balance is substantially Fe
When manufacturing a steel slab by a continuous casting method and cold rolling it after hot rolling pickling, the product of the amount (%) in the steel and the cold rolling reduction (%) is at least 2.4 or more. Cold rolled to form a steel strip, then annealed on a continuous hot-dip plating line, Al: 3wt% or more, 10wt% or less, rare earth elements: 5 ppffl or less - 11% or less, the balance essentially consisting of Zn. The present invention provides a method for manufacturing a Zn-Al alloy plated steel sheet with less blistering, which is characterized by applying plating. The present invention will be explained in more detail below. In order to prevent hydrogen stored in steel at high temperatures from being released as the temperature drops, it is effective to disperse second phases such as oxides, carbides, nitrides, and sulfides in steel. This is a well-known method for preventing foot jumps in steel plates for crawlers. Particularly in the case of cold-rolled steel sheets, it is effective to disperse oxides. This is thought to be because, during cold rolling, voids are formed around the oxide due to the difference in deformability between the steel base and the oxide, and hydrogen is stored in the voids. Therefore, as a steel plate for crawling, oxygen in steel T14
Capped steel with high resistance is used. However, since capped steel is made into a slab through an ingot making and blooming process,
Not only is the cost high, but it also takes a relatively long time to solidify the molten steel, so coarse oxides are present in the surface layer. Such coarse oxides are not preferable as plating materials because they cause surface defects such as pinholes when performing hot-dip metal plating that is thinner than wax. Therefore, it is necessary to produce steel with a high oxygen star content by a continuous casting method that allows the steel to be cooled and solidified relatively quickly, and to refine the oxide. However, when continuously casting steel with high oxygen content,
When C exists in steel, CO gas is generated, and its bubbles remain near the surface of the slab, causing surface defects after hot rolling and cold rolling. In order to prevent the generation of such CO gas bubbles, the carbon content in the steel should be 0.003% or less. If the C impact is 0.003% or less, the O amount in the steel is 0.06
%, surface defects due to CO bubbles do not appear. Further, if the amount of O in the steel is less than 0.03%, no effect of preventing hydrogen blisters can be expected. The steel whose composition has been adjusted as described above is hot-rolled and cold-rolled by conventional methods and used as a plating base plate. By setting an appropriate cold-rolling reduction ratio, the occurrence of hydrogen blistering can be effectively prevented. City can. In other words, in high-butyric continuously cast steel, the oxides are finer than in capped steel, so unless the reduction rate is sufficiently high, the formation of voids is insufficient, and hydrogen blistering prevention is 1.
is not effective. The necessary rolling reduction for this purpose is such that the product of the cold rolling reduction (%) and the amount of O (wt%) in the steel is 2.4 or more. When applying Zn-Al alloy plating to the steel sheet manufactured by this method, it is performed using continuous plating equipment that continuously performs annealing and plating. The annealing temperature can be adjusted as required, as long as it is higher than the plating bath temperature.
Although plating is possible at any temperature, especially when obtaining a processed steel plate, it is preferable to set the temperature to be above the recrystallization temperature and below the Arβ transformation point. Plating can be applied to any Zn-based plating in the same way as ordinary cold-rolled steel sheets, but it is especially applicable to Zn-Al alloy plating containing 3 to 10% AI, which is prone to hydrogen blistering. Then, the effect is especially by N3. Furthermore, in order to improve the coverage of plating and prevent the occurrence of pinhole defects, 5ppmNtwt% was added to the plating bath.
Rare EarthMetal
), a good plating surface can be obtained. Representative examples of REM include La and Ce. If it is less than 5 ppm, the effect of improving the throwing power cannot be obtained, and if it exceeds 1 wt%, the effect of improving the throwing power is saturated, which not only increases the cost, but also reduces the fluidity of the bath, and the surface This may cause defects. EXAMPLES The present invention will be specifically described below with reference to Examples. (Example ■) In order to confirm the effect of adding REM to the plating bath, the following experiment was conducted. REM in 5% A1-Zn
Olo, 0005.0.001.0.005 respectively
The annealed cold-rolled steel sheet was immersed in a molten metal bath containing 0.01.0.1% by weight for 5 seconds, and the degree of unplating was visually determined. The cold-rolled steel sheet used contained 0.0025% C and 0
A continuously cast slab containing 0.042% of
It is of mm. Annealing prior to plating is 20%) +2
- After annealing at 750°C 12ml in N2 atmosphere 4
It was cooled to 70°C and immersed in a plating bath maintained at 440°C or 470°C. Table 1 shows the plating throwing power. At a bath temperature of 440°C, the amount of REM added is 0.
If it is less than 0.0005%, non-plating will occur. Furthermore, at a bath temperature of 470°C, the amount of REM added is 0.0005% or more.
In step 2, a sound plating surface was obtained. That is, it was found that by adding REM to the plating bath, a stable and good plated surface could be obtained. Table 1 0: No plating ×: No plating (Example 2) C-Iil- was set to 0.003% or less, and 0@ was 0
．． 025.0.031, 0.038, 0.043,
After tapping O, Q52 t% steel and forming it into a slab by continuous casting, it is hot-rolled to a thickness of 3.
A 2 11 m hot rolled sheet was obtained. Next, the plate thickness is 0.4, 0.6, 0.8, 1.0, 1.2, 1.4 by cold rolling.
mm cold-rolled steel plate, annealed in continuous hot-dipping equipment,
5% Al-Zn plating is applied using the melting method, and the reduction rate is 0.5%.
The product was made into a product by temper rolling. The annealing before immersion in the plating bath was performed by soaking at 750° C. for 120 seconds, and the atmosphere was a 20% H2-N2 mixed gas. The temperature of the plating bath was 440'0, the temperature of the plate immediately before immersion in the plating bath was 470°C, and the plating thickness was 20 lm. Samples cut from each product were left in a constant temperature bath at 100'O for one week, and then tested for the presence of hydrogen blisters. Figure 1 shows a plate thickness of 0.4 mm (reduction rate of 87.5%).
and 0 in steel at 1.0 mm (reduction rate 68.8%).
The relationship between the content and the hydrogen blistering situation is shown. The 0.4 mm one with a high reduction rate (87.5%) has an O content of 0.03% or less and does not generate hydrogen blisters. For 1 mm with a low rolling reduction rate (88.8%), in order to prevent hydrogen blisters, an O of 0.035% or more is required.
is necessary. That is, the hydrogen blistering prevention] 1- is more effective as the O amount in the steel and the cold rolling reduction rate are higher. The amount of O in the steel is 0.
If it is less than 0.3%, in order to prevent hydrogen blisters, ・90
% or more is required, which reduces the efficiency of cold rolling and makes it industrially meaningless. Therefore, after setting the O-hiro in the steel to 0.03% or more,
It is necessary to select a cold rolling rolling car appropriately. Figure 2 shows the relationship between cold rolling reduction and O content in steel. Downstream rate [%] ×

It can be seen that hydrogen blistering does not occur in the range of [0] [w7%]≧2.4. (Example 3) Al
Al-Zn alloy plating with different speeds was applied by a melting method, and the effect of the amount of Al in the plating on hydrogen blistering was investigated. The annealing conditions were the same as in Example 2, and All in the bath was 0.
02.3.5.10 and 10%, R,E
Mitshu metal (a mixture of La and Ce) was used as M, which was 0.005wt in all baths.
It was set as a constant %. The bath temperature is 30° below the melting point of each alloy.
℃, and the plate temperature when entering the bath is 20°C higher than the bath temperature.
°C increased. Figure 3 shows the tendency of hydrogen blistering after heat treatment at 100°C for one week. When the AI concentration in the plating tank is 0.5%, hydrogen blisters are most likely to occur, and the hydrogen blisters in the steel (0) (wt%) x [reduction rate] (%
) is 2.4 or more, hydrogen blisters can be prevented by 1L, but it can be seen that hydrogen blisters are less likely to occur even if the AI concentration in the plating is higher or lower than this. Therefore, the present invention is particularly suitable for application to plated steel sheets containing Zn in a range of 3 to 10% of AI. <Effects of the Invention> As is clear from the above explanation, according to the present invention, C is 0.003% or less - 10 is 0.03 to 0.06
A slab containing % of AI is rolled so that the product of the amount of oxygen in the steel (t%) and the cold rolling reduction (%) is 2.4 or more H, and this cold rolled steel sheet H is coated with 3 to 10 wt% of AI. If Zn-Al alloy plating containing the following is applied, a Zn-Al alloy plated steel sheet with less hydrogen blistering can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the influence of O content on the tendency of hydrogen blistering. FIG. 2 is a graph showing cold rolling reduction and O content in relation to hydrogen blistering tendency. FIG. 3 is a graph showing the amount of Al in the plating layer and the tendency of hydrogen blistering. ;"゛), 7':,, 1 13 -33・6-FIG, 1 08 abundance (wt 'mu) ○Nenjutsu 7 creases △100'C, Iweek J&+=4"! × Meichi 7
! Occurs after the dispatch FIG, 2 Mutaku Kushigekushi ('/,) FIG, 3

Claims (1)

[Claims] C: 0.003wt% or less, O: 0.03wt% or more,
When manufacturing a steel slab consisting of 0.06 wt% or less with the remainder substantially Fe by a continuous casting method, and cold rolling it after hot rolling pickling, the amount of oxygen in the steel (wt%) and the cold rolling reduction are determined. rate(%
) is cold rolled to form a steel strip so that the product is at least 2.4, and then annealed by a continuous hot-dip plating line and Al: 3 wt% or more, 10 wt% or less, rare earth elements 5 ppm or more, 1%. Hereinafter, Z with less blistering is characterized by being plated with the remainder essentially consisting of Zn.
A method for manufacturing an n-Al alloy plated steel sheet.