JPS60204875A - Manufacture of alumin hot dip aluminum coated steel sheet - Google Patents

Abstract

PURPOSE:To manufacture a hot dip aluminum coated steel sheet having superior suitability to plating by hot-dipping a pretreated steel sheet in an Al bath contg. specified amounts of Si and one or more among La, Ce, Nd, Pr and Y. CONSTITUTION:A steel sheet is pretreated and dipped in an Al bath contg. 0- 11wt% Si and 0.01-1.0wt% one or more among La, Ce, Nd, Pr and Y to manufacture a hot dip aluminum coated steel sheet. Since those rare earth metals are expensive, it is preferable that inexpensive misch metal such as lanthanum or cerium misch metal is used in manufacture on an industrial scale.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a hot-dip aluminized steel sheet with excellent mating properties.

Traditionally, υfIi aluminized steel sheets have been widely used in fields that require heat resistance and corrosion resistance, but when used in these fields, they are usually divided into different types. Generally bath melted aluminum 9mm mating steel plate 9Aj-St
Steel plate 1-1 in alloy bath! ! There are two types of aluminized steel: Type 1 aluminized steel, which is plated by crushing, and Type 2 aluminized steel, which is plated by immersing the steel plate in a pure A1 bath. It is suppressed from 1c in the bath, does not grow to 3-5 μm, and has good processability and heat resistance, so it is used in fields where processability and heat resistance are required, and the latter is 20 elemental alloy layer on brittle Fe-A
Because it grows to a thickness of about μrn and has poor workability, it is used in fields that require light processing and corrosion resistance.

Conventionally, these hot-dip aluminized steel sheets (hereinafter referred to as hot-dip A
Industrially, hot-dip galvanized steel sheets (referred to as 1-galvanized steel sheets) are manufactured on a sensimer type continuous hot-dip galvanizing line, similar to hot-dip galvanized steel sheets. Gas (Hz approx. 11%) J
-30 to -40 for hot-dip galvanized steel sheet
Unless the temperature is lowered to J-9, pinhole-like plating with a diameter of 1III or less will be repelled, and spot-like non-plating will occur.

Table 1 shows the relationship between the occurrence of dotted plating and the snout atmospheric gas point.
Unless the temperature is lowered by 0°C or more, the occurrence of dotted plating cannot be completely prevented.

Table 1 8 Table 1 shows the occurrence of dotted plating v4 on the same original plate (C
O,04,S40.01. MnO,28,Po,0
13, So, 011, sol AJ O, 015, remaining F
e (more than % by weight) of aluminum-killed copper steel plate] using gold,
This was reduced annealed for 30 seconds in a HNX gas atmosphere at t-750°C, and then put into the same atmosphere with a bath temperature of 680°C.
5% S1 bath Temperature 460℃ (1) Zn -0,18
%AI bath for 3 seconds for plating. The amount of plating layer is 60 f/fit2 on both sides, and the number of 5 dots is 50 x 1001111 Dots are generated on both sides of the sample? 8 as counted visually.

If dotted spots occur on the appearance, the number of spots is 5 M.
If it is less than Vdm2, the appearance is good and Mero, but 5 pieces/dx”
If the temperature exceeds t-℃, the appearance gradually deteriorates. For this reason, conventional dot plating is used! The dew point of the atmospheric gas in the snout portion was controlled to be below -50'C in order to keep it below 5[k 511 I/dm2.

However, the dew point of the snout should be lower than r-50℃.
is the dew point t-60 of the atmospheric gas supplied to the pretreatment reduction zone
℃ or less, and in terms of equipment, the sealing of joints in annealing furnaces, cooling furnaces, etc. had to be strictly sealed, making management extremely difficult and rare.

In view of this situation, the present invention provides a method for manufacturing a hot-dip Al-plated steel sheet that does not cause dot plating even if the dew point of the atmospheric gas at the snout portion is lowered to the other end.

As mentioned above (dot-like plating on hot-melt steel sheets can be prevented by setting the atmospheric gas dew point of the pretreatment reduction zone to 16 -50°C or less at the snout part,
It is known that lowering the dew point prevents the occurrence of dotted plating because the oxide film present on the surface of the plating bath in the sunwat decreases. In other words, AI
Zn is more easily oxidized and has a higher melting point than Zn, so if the dew point of the snout is the same, an oxide film will be formed on the surface of the plating bath. Therefore, the dew point of the snout will be -30
When the temperature is -40°C, an oxide film is not significantly formed on the surface in a zinc bath, but it is significantly formed in an aluminum bath. The following occurs. Therefore, the dew point of the snout? If it is low, there will be less oxide film formed on the surface of the plated yukata, and it will not occur on the dotted plating.

However, since the above-mentioned problem occurs when the dew point of the snout part is below t''-50°C -50°C, the present inventors have developed a method that allows the dew point of the snout part to be extremely low in terms of bath composition. Upon investigation, we found that 0.0l-LO of rare earth elements was added to the plating bath.
Should I add NE amount%? I found it. When we investigated the effects of various rare earth elements, we found that La, Ce%Nd%Pr:F+5 and Y are preferable.
It has also been found that even if 22 or more of these rare earth elements are added, the same effect can be obtained as long as the total amount is the same as when one type is added. <L"C In the present invention, the steel plate is pretreated L (La, Ce, Nd, Pr, Yo)
In an aluminum bath to which one or more of
& Crush "C Hot-dip plating tI# Signal melt M!I
A method for manufacturing an AI-plated steel sheet is provided.

The rare earth element added to the plating bath for unexploded EJHC% may be a single rare earth element, but since a single rare earth element is expensive and slow, industrially inexpensive Mitsushimetal (a mixture of natural composition '!E) is used. It is advantageous to use rare earth metals. Typical compositions of lanthanum metal and seri metal are as follows.

1) Cerium Mitsushmetal Ce: 45-60, +0) Other rare earths 35-5
0゜The remainder is Fe, Mg, AI, 5i181
．． Is it impure? C1u upper lit%) 2) Lanthanum Mitsushmetal La: 60-90, Ce: 8.5, Nd: 6.
5, Pr: 2, Fe: 0.2. Mg: 0.
0 3, AI: o, ts, S: 0.43, and the remainder is impurities (more than % by weight), and the occurrence of spot rate plating is 11. The amount of painting for 7 increases and 8 decreases. The attached drawing shows an investigation of the amount of rare earth elements added and the number of dot-like platings, and the more the rare earth element content increases, the less dot-like plating occurs. Is the above-mentioned aluminium-killed steel sheet used in this investigation? Dew point -40℃, composition 50%H, -N! Gas (H
After reduction annealing at 750°C for 30 seconds in a mixed gas of NX gas and AX gas - Al-2 at 680°C under atmosphere
, immersed in a 5% St bath for 3 seconds to coat the plate.Amount of adhesion on one side: 8097 m2 (1) Hot-dip A1 plated steel sheet 5
0 yaa x 100 III O) Sample? How many dot-like platings occurred on both sides of the sample? It is counted visually. Furthermore, the cerium metal has the above-mentioned composition. However, as is clear from the accompanying drawings, when the amount of rare earth element added is less than 0.01% by weight, the number of dot-like platings increases rapidly. - If the amount of rare earth elements added exceeds L01%, the production cost will increase significantly in industrial production, weight segregation will occur in the bath, and the addition of rare earth elements will not be effective. Addition is 0.O
It is preferable to set it to 1 to LO heavy basin%. The solubility of rare earth elements in an aluminum bath is at a bath temperature of 650 to 700°C.
If you add 1ON value%, the intermetallic figurines of AI and rare earth elements will float in the bath, and the addition of 7 will be metallurgically meaningless, giving it a rough appearance. You only get the product.

Furthermore, the effect of adding rare earth elements is clearly demonstrated by the investigation of the amount of rare earth elements added and the number of unplated pieces (plating bath KS).
It can be obtained even if r is added. In general, when producing hot-dipped Al-plated steel sheets, even if 1 csi2 is added to the plating bath, the plating performance is l
Since it does not have any effect on l'c and only completely suppresses the growth of the alloy layer, the effect of rare earth element addition is independent of the presence or absence of Si addition.However, the 5r(1) f/A addition is
1C plate-like St crystallizes as primary crystals in the mitotsugi layer that exceeds a single layer, and the extension of the plating layer itself is extremely reduced, making it unfavorable for processing.
Therefore, even if we forget to invent it, if we add rare earth elements like Si addition 41 Arashi or above, the dew point will be high and the temperature and the temperature will decrease. There is currently no clear button. However, rare earth elements are relatively slow to oxidize, so the oxidation rate of aluminum on the bath surface can be suppressed, and the oxidized skin of aluminum with high viscosity Mk
When the steel plate enters the plating bath, the oxidation of aluminum B1. Membrane involvement? It is presumed that it suppresses

Next, let's get practical. Full explanation of the J-tree invention.

Practical l Aluminum killed steel plate warehouse with plate thickness 0.6 tm Dew point -46
℃.

Composition 50%H, -N! 750°C, 30°C in an atmospheric gas of
Second reduction mjll! After washing, 1 c ruru bath under the same atmosphere @720
A 1l AI bath was prepared at ℃, and La and Y were added as rare earth elements.
Hot MA1 plated steel sheet of A- by immersion in VC bath containing S and Nd2, coating amount on one side 60 //, A-
1-a was built.

A sample of 5Qw x 100sw was taken from the obtained steel plate, and the number of dot-shaped platings that occurred on both sides of +: was counted. Table 2 shows the number of occurrences of this dot-like plating, 1rLa,
From Table 2, the amount of rare earth elements added is 0. When O1 weight it% is exceeded, a remarkable decrease in the number of dotted unplated spots is observed. In addition, in conventional baths in which all rare earth elements are added, a healthy plated surface cannot be obtained unless the atmospheric dew point near the bath surface is below 152°C. It can be seen that when it is added, a substantially sound abutment surface can be obtained even at an atmospheric dew point of 146°C.

However, if the amount added exceeds 10%, dross will form on the surface of the plate, the surface appearance will be significantly impaired, and the product cannot be used as a plated product.

Practical 2 The same steel plate as in Example 1 was heated at 750°C by changing the 4ikjllI point in an atmospheric gas with a composition of 50% H2-N.
Reduction annealing for 30 seconds and Vc in the same atmosphere as L wave (670°C o)
Three A1-8.5% Si baths were immersed in a bath to which 0.1% by weight of Ce1rsn lanthanum metal was added to produce a hot-dip A1 plated steel plate with a plating thickness of 80 i/m on one side. In the same manner as in Example 1, the total number of dotted unplated spots was counted and summarized in Table 3.The S-lanthanum metal having the above-mentioned composition was used.

Table 3 shows that when Ce or lanthanum metal is added, spot-like unplating occurs even if the dew point near the bath surface is at the same temperature! ? Even if the dew point is increased by about 5°C compared to the case without additives, the same product value can be obtained.

As described in detail above, the rare earth element kO,
If 0l-LO dust amount% is added, the atmospheric gas dew point in the pretreatment reduction zone will be higher than the conventional one by 5℃ or more.

Moreover, if the addition amount is close to kLO storm amount %, it can be brought close to the dew point in the case of manufacturing hot-dip galvanized steel sheets.
Manufacturing management becomes easier.

[Brief explanation of drawings]

The attached drawing shows a dew point of -40°C, a composition of 50% H, -N, and a picture area f.
An aluminum-killed steel plate was reduced annealed at 750°C for 30 seconds in i-gas, and then immersed in an AI-2,5% S1 bath (bath @ 680°C for 3 seconds) to coat the hot-dipped steel plate. This figure shows the relationship between the number of point-like unplated spots formed in the bath and the amount of y, zLa, and Ceg-treated cerium metal added to the bath.

Claims (1)

[Claims] (IJ steel plate pre-treated L r4, then La, Ce,
Nd', Pr, Y)')%0) 1 M or more k O
,01~LO weight t%g and Si t-0~11 weight%
A method for producing a hot-dip aluminum-plated steel sheet, characterized by hot-dip plating by immersing it in added aluminum. (27) The method for producing a hot-dip aluminized steel sheet according to claim 1gi, characterized in that the method is carried out using Mitsushi metal with additions of La, Ce, Nd, Pr, and Y.