JPH0441664A - Multilayer plated steel sheet and its manufacture - Google Patents

Abstract

PURPOSE:To easily manufacture a multilayer plated steel sheet excellent in corrosion resistance, heat resistance and workability by carrying out Ti vacuum vapor deposition on the surface of a steel sheet in specified conditions for the ion current intensity ratio of H2O to gaseous H2 and the sheet temp., and then carrying out Al (alloy) vacuum vapor deposition. CONSTITUTION:First, Ti is vapor-deposited in vacuum on the surface of a steel sheet at >400 deg.C sheet temp. while the ion currents of H2O and gaseous H2 in the residual gas in the vapor deposition chamber are monitored with a gas analyzer so that the intensity ratio of ion currents is controlled to <=5. Thus, a Ti-plating layer having the crystal orientation (0002) of Ti grains parallel to the base steel sheet is formed to >=0.1mum thickness. Then, an Al (alloy)- plating layer is formed to >=1mum thickness as a second layer by the vapor deposition of Al (alloy) in vacuum. In the process of vapor deposition of Al (alloy), it is preferable to carry out in <=1X10<-2>Torr vacuum at >200 deg.C sheet temp.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a multi-layer plated steel sheet with excellent corrosion resistance, heat resistance and workability, and a method for manufacturing the same.

(Prior art) Al-plated steel plates and ^1 alloy-plated steel plates have been used in large quantities in the past, but in this type of boat fishing, the steel plates are directly coated.
This is a single-layer plated steel sheet plated with 1 or ^1 alloy using a hot-dip plating method.

This ^1 or Al alloy single-layer plated steel sheet has excellent corrosion resistance and heat resistance if the thickness of the plating layer is normal, so it has been used for automobile exhaust gas system parts, combustion equipment parts, and household equipment. Widely used for parts, etc. However, recently, depending on the application, in order to reduce the manufacturing cost of parts, thinner materials are required, and expansion of use to applications that are affected by seawater is being considered.

(Problem to be solved by the invention, α) However, when a thin Al or Al alloy plated steel sheet is exposed to the atmosphere or a humid environment in which the plated layer cannot exhibit much sacrificial corrosion protection, it becomes fish-like in a relatively short period of time. Red rust [Fe(OH)al] is generated.

In addition, when used in an environment where halogen ions are present, such as in applications that are affected by seawater, the corrosion-resistant oxide film on the surface is dissolved, resulting in white rust mainly composed of ^1(OH)3. Pitting corrosion may occur on the surface or reach the steel base. When pitting corrosion occurs on 4I, it is pure^1
Since it progresses by about 1 μm per 20 hours on a plated steel plate, it reaches the steel base in a short time and causes red rust.

Therefore, when used in applications that are affected by seawater, the plating thickness is increased to approximately 40 μm to prevent pitting corrosion from occurring in a short period of time, but increasing the plating thickness in this way increases the cost. There was a problem.

In addition, in the case of Al or Al alloy plated steel sheets, chemical conversion treatments such as chromate treatment are applied as post-treatment.
This effect is temporary and does not essentially improve corrosion resistance.

＾1 When producing coated steel sheets by hot-dip plating, workability is reduced at the interface between the base steel sheet and the plating layer ＾1-
Since Fe alloy is produced, workability cannot be said to be good.

In particular, in the case of a thinned product, the majority of the product is a ^1-Fe alloy layer, so the workability is noticeably lowered. Furthermore, since the plating layer is close to pure^1, its heat resistance is also low.

Therefore, when workability and heat resistance are important, Al-5I alloy plating with 8 to 12% of Sl added is applied. However, this alloy-plated steel sheet cannot withstand severe processing because ^l-Fe alloy is generated at the interface between the base steel sheet and the plating layer. In addition, in the case of this alloy plated steel sheet,
When low-carbon rimmed steel or Al-killed steel is used as the plated base plate, when heated above 600°C, the interface between the plating layer and the base steel sheet is preferentially oxidized, and when heated above 700°C,
Since the plating layer becomes alloyed and peels off, heat resistance is not necessarily sufficient. This heat resistance problem can be improved by using special killed steel such as low-carbon Ti-added steel or ultra-low carbon-0°2Ti-added steel for the plated base plate.
Although the plating layer does not peel off even if repeatedly heated to 0°C or higher, using such special killed steel makes the product considerably more expensive than ^1 killed steel, which is not desirable.

Al-plated steel sheets that do not generate a ^1-Fe alloy layer at the interface between the base steel sheet and the plating scraps can be manufactured by electroplating using non-aqueous solutions or vacuum evaporation; When heated to high temperatures, the plating layer ^1
diffuses into the base steel plate and oxidizes the base steel plate, resulting in poor heat resistance. In addition, since there are pinholes in the plating layer that reach the base steel plate, there are two problems with corrosion resistance in a severe corrosive environment.

As mentioned above, the conventional Al or ^1 alloy plated steel sheets had problems, α, and the present invention solves these problems by producing a multilayer plated steel sheet having a surface layer of Al or Al alloy, and its production. The present invention provides a method (means for solving problems) in which a plated steel plate is coated with T as a first layer on the surface of the steel plate.
Crystal orientation of crystal grains (form a T1 plating layer with a thickness of 0.1 μm or more with the 00021 plane parallel to the base steel plate, and add an Al or Al alloy plating layer as a second layer on top of the A multi-layer plated steel plate with a thickness of 1 μm or more was used.

In addition, during the production of multi-layered steel sheets with such a structure, the ionic currents of H2O and H2 gas contained in the residual gas in the deposition chamber are monitored using a gas analyzer, and the ionic current intensity ratio is 5 or less. At the same time, the steel plate temperature is set to 400°C or higher, and T1 is vacuum-deposited on the steel plate surface to form a T1 plating layer with a thickness of 0.1 μm or more in which the crystal orientation (0002) plane of the Ti crystal grains is parallel to the base steel plate. After that, ^1 or Al
The alloy was vacuum deposited to form a ^1 or Al alloy plating layer.

(effect) be.

The present inventors investigated the cause of pitting corrosion in Al or Al alloy plated steel sheets and found that the cause was pinholes present in the plating layer.

That is, if a pinhole exists in the plating layer that reaches the steel base, a local battery is formed between the steel base and the plating layer, a galvanic current flows between them, and the plating layer becomes base in potential and melts. This lupanic current increases when the water that enters the pinhole has high conductivity, such as seawater, and the plating layer dissolves rapidly, causing local corrosion in the pinhole area. Pitting corrosion occurs.

However, if a Ti-plated outer layer is formed as the first layer on the surface of the steel sheet and an Al or Al alloy plated layer is formed as a second layer on top of it, the first Ti-plated outer layer will suffer pitting corrosion. When pitting corrosion starts at a pinhole in the second Al or Al alloy plating layer, corrosion products such as Al(OH) generated by the pitting immediately seal the pinhole. In addition, when corrosion products occur in the pinhole, the first T1 plating layer is covered with the corrosion products, so the Ti plating layer and Al
Also, since the Lupanic current between the Al alloy plating layers becomes extremely small, pitting corrosion of the base steel sheet is prevented for a long period of time.

However, this effect of the Ti plating layer is based on the assumption that there are no pinholes in the Ti plating layer, and Ti plating plated by normal electroplating or vacuum evaporation has many pinholes. If present and heated to high temperatures,
It was found that heat resistance and corrosion resistance were not exhibited because ^1 rapidly diffused into the base steel plate through pinholes, and in an environment where CI- existed, corrosion products no longer contained the pinholes.

Therefore, the present inventors investigated the cause of pinholes occurring in Ti plating when plating is performed using ordinary electroplating or vacuum evaporation methods, and found that T plated using these methods
The crystal orientation of the i-plated layer is relatively random, and (011
There are crystal grains that have grown so that the 0) plane or (1120) plane is parallel to the steel sheet surface. If such crystal grains exist, the continuity of the plating layer will be lost and pinholes will occur in the vicinity. It turns out that it does. On the other hand, in the case of T1 crystal grains grown so that the (0002) plane is parallel to the steel sheet surface,
It was found that the plating layer becomes a continuous, uniform film, and the stronger the preferential orientation, the fewer the number of pinholes. Therefore, in the present invention, the crystal grains of the T1 outer layer are (0002
) plane was grown so that it was parallel to the surface of the steel plate.

The thickness of the 1st/1l Ti plating layer in the present invention is 0.1μ
m or more. This means that it is less than about 0.1 μm.
This is because the suppression of the formation of the 1-Fe alloy layer is insufficient, and the effects of improving corrosion resistance, heat resistance, and workability are insufficient. However, if the thickness is 0.5 μI or more, the flexibility decreases and cracks or peeling are likely to occur. Therefore, for applications where workability is important, it is preferable to set the gloss to 0.5 μI or less. In addition, the thickness of the second layer ^1 or the alloy plating layer is 1 μm.
Above, it is preferably set to 30 μI or less. 1μ
If the thickness is less than the opening, the mating layer is too thin, so the surface protection effect is not effectively exhibited, resulting in insufficient corrosion resistance and heat resistance. The plating thickness of this second layer can be set to 10 μm or more depending on the application.

To form a $1 layer of Ti plating on the surface of a steel plate, first place a mass filter in the vacuum chamber, evacuate the vacuum chamber until it reaches a high vacuum region, and then remove the residual gas in the vacuum chamber with the mass filter. Monitor.

After preliminarily melting the Ti in the crucible to achieve the desired T evaporation rate, the H2
Ionic current intensity ratio of O and H2ys (IHzO/182
) is 5 or less, and if confirmed, heat the base steel plate and start plating when it reaches 400'CL''J]2.

Here, the ion current intensity ratio (IH
,o/I,, ) is monitored in the deposition chamber.
When exposed to the atmosphere, the material of the evaporation chamber and the evaporation substances deposited inside the chamber absorb gases such as -1, 0, and 02 from the atmosphere, and release them during exhaust. These gases cannot be completely evacuated even under high vacuum conditions, and remain as residual gases in the deposition chamber, affecting the properties of the plating layer.

However, H20 gas, which accounts for most of the residual gas, decomposes into H2f gas and 027y gas in a high vacuum, and its influence on the plating layer is reduced. Therefore, the degree of decrease in H,0 gas is managed by the ionic current intensity ratio of H20 gas and H2 gas.

In addition, setting the ion current intensity ratio (I, U./IH) of H20 and H2ff to 5 or less suppresses the adsorption of H2C, f on the evaporation surface during the growth process of the plating layer, and , T
I atoms are sufficiently diffused on the steel plate surface to make the plating layer dense and prevent pinholes from occurring.
It suppresses adsorption of gas to the base steel sheet and its inclusion in the plating layer, improving plating adhesion and workability, and also provides good plating adhesion even at a low heating temperature of the base steel sheet. Furthermore, in parallel with these, Ti
This is to preferentially orient the (0002) plane of the plating layer. Note that this ion current intensity ratio (1,,4./1..
12) In order to reduce the value to 5 or less, there are methods such as charging an active metal such as T1 into the vapor deposition chamber and allowing it to be adsorbed to the metal, or continuing to exhaust the air and waiting for it to naturally decrease. It's fine.

Furthermore, heating the base steel plate to 400°C or higher during vapor deposition activates the surface diffusion of Ti atoms incident on the vapor deposition surface, making the plating layer denser and improving plating adhesion. This is to preferentially orient the 0002) plane.

A currently commonly used quadrupole mass spectrometer may be used as a mass filter for monitoring the ion current intensity ratio of H20 and H2 gas. This analyzer is designed to measure the components in the ionized gas under reduced pressure into masses and measure the ion current of each component, but it is not possible to monitor the residual gas ion current in the deposition chamber. After connecting the mass filter to the vapor deposition chamber and bringing the pressure inside the mass filter to the same degree of vacuum as the vapor deposition chamber or slightly reduced pressure, open the connected pulp to introduce the residual gas into the mass filter and measure it.

When gas is introduced into the mass filter, the gas is ionized at the quadrupole electrode section and separated into mass classes, and the separated ions are detected at the detection section with an ion collector or secondary electron multiplier. , it is now possible to measure the ion current of masses.

Therefore, by comparing the intensities of the ion currents, the relative values of each gas component can be confirmed. After measurement, close the connecting pulp.

Al or Al alloy plating on the T1 plating layer is performed by vacuum evaporation in order to allow thinning.

The plating metal may be evaporated by any of electron beam evaporation, resistance heating evaporation, and high frequency heating evaporation. When plating an Al alloy, a binary or multiple simultaneous vapor deposition method may be used.

The vacuum degree of the vacuum chamber is 1. It is preferable to heat the steel plate to 200° C. or more at a temperature of 10 −2 Torr or less. If the degree of vacuum is greater than I x 10" Torr, pinholes will occur more often, and the steel plate temperature may be lowered to 20" Torr.
If the temperature is lower than 0°C, the adhesion with the first Ti plating layer tends to decrease.6 The composition of the Al alloy plating layer is not particularly limited, but includes, for example, Mg, Si, Ti, ■, Cr, Hn, Fe
, Co, Ni.

Cu, Zn, Y, Zr, Nb, No, Sn, Ta
1 to 50% of the total amount of one or more of 2#t1 or more
It may contain.

(Example) After degreasing an Al-killed steel plate and placing it in a vacuum chamber,
Ion current intensity ratio of 420 and H2tt (■Hyu./I
The temperature of the steel plate was controlled as shown in Table 1, and the steel plate was subjected to vacuum evaporation T1 plating to improve the crystal orientation of Ti crystal grains.
The number of pinholes was investigated.

In addition, vacuum evaporated Ti plating is applied to water-cooled copper nozzle according to JIS standard.
Ti equivalent to type 1 is put in, and a steel plate is placed above the vacuum chamber to achieve a vacuum degree of lXl0-5 to Ix10.
After setting the temperature to 100 Torr, Ti was melted and evaporated using an electron beam, and 11 was deposited on the steel plate at a deposition rate of 10 μm/min. Further, the steel plate was heated with an electron beam, the temperature was measured with an infrared radiation thermometer, and the ionic current intensity ratio of H2C and H2 gas was monitored with a quadrupole mass spectrometer.

Next, after T1 plating, a hearth containing Al or ^1 alloy was placed in the vacuum chamber, and the 11 vapor deposition plated steel sheet was heated as shown in Table 1 while the degree of vacuum was 1 x 10''□4. , ^1
Plating or various ^1 alloy platings were applied.

Corrosion resistance, heat resistance, and workability were investigated for the contact plated steel sheet manufactured as described above.

In addition, the investigation of the Ti plating layer and the investigation of the multilayer plated steel sheet were conducted as follows.

(1) Crystal grain orientation of Ti-plated outer layer It was determined by XIIA diffraction that the crystal orientation was random if the diffraction peak was close to that of standard Ti powder.

(2) Number of pinholes 7 The number of pinholes occurring per IC transfer 2 was counted by the Eloxyl test.

(3) Corrosion resistance Salt spray test (SST) according to JIS Z 2371
The time required for red rust to appear was measured. The test piece contains
A piece with dimensions of 70 x 150 was used, and the end and back surfaces were sealed.

(4) 11 After carrying out a cycle test three times in which one cycle is a heating and cooling test of heating at 600 °C for 5 hours and air cooling for 19 hours in a thermal atmosphere, the ^l Fe alloy layer before and after the cycle test was The state of production was compared by microscopic observation and evaluated based on the following criteria.

◎ ＾1- Great effect in suppressing the formation and growth of Fe alloy layer ○
^L-Fe alloy layer formation and growth suppression effect Δ ^1
- Slightly inferior effect on suppressing the formation and growth of Fe alloy layer × ^l Great effect suppressing the formation and growth of Fe alloy layer (5) Workability After bending closely at 180° with the plated side facing outward, apply sellotape to the folded part. The adhesion of the plating layer was classified into the following four levels based on the amount of plating metal that adhered to the tape.

◎ Excellent plating adhesion ○ Good plating adhesion Δ Slightly poor plating adhesion × Poor plating adhesion Table 1 shows the crystal grain orientation and number of pinholes in the Ti plating layer.
Table 2 shows the corrosion resistance, heat resistance, and workability of the multilayer plated steel sheets.

(Effects of the Invention) As described above, the multilayer plated steel sheet of the present invention has T
The i-plated layer has no pinholes and is dense, so it has excellent corrosion resistance. Furthermore, since there is no ^1-Fe alloy layer, it has excellent heat resistance and workability.

Further, the multilayer plated steel sheet of the present invention is easy to manufacture because it is sufficient to control the ion current intensity ratio of H2O and 82ys and the steel sheet temperature during Ti vapor deposition plating.

Claims (3)

[Claims] (1) Form a Ti plating layer with a thickness of 0.1 μm or more in which the crystal orientation (0002) plane of the Ti crystal grains is parallel to the base steel sheet as a first layer on the surface of the steel sheet, and on top of that as a second layer,
A multilayer plated steel sheet characterized by forming an Al or Al alloy plating layer with a thickness of 1 μm or more. (2) Monitor the ion current of H_2O and H_2 gas contained in the residual gas in the deposition chamber with a gas analyzer,
The ionic current intensity ratio is set to 5 or less, the steel plate temperature is set to 400°C or higher, and Ti is vacuum-deposited on the steel plate surface to form a Ti plating layer in which the crystal orientation (0002) plane of the Ti crystal grains is parallel to the base steel plate. After applying A to a thickness of 0.1 μm or more,
1. A method for producing a multilayer plated steel sheet, which comprises vacuum-depositing Al or an Al alloy to form an Al or Al alloy plating layer with a thickness of 1 μm or more. (3) When vacuum depositing Al or Al alloy, the degree of vacuum is 1.
2. The method for producing a multilayer plated steel sheet according to claim 2, wherein the vapor deposition is carried out at a temperature of 10^-^2 Torr or less and a steel plate temperature of 200C or more.