JPS5811771A - Zinc-aluminum silicon alloy covered steel - Google Patents

Abstract

PURPOSE:To obtain Zn-Al-Si alloy covered steel which is excellent in a gloss holding property when heating, and heat resistance, by making a steel basis contain N in accordance with Zn content in a Zn-Al-Si alloy bath. CONSTITUTION:In case of steel covered with an alloy bath consisting of 30- 85wt% Al, 1.5-15% Si content against Al, and the remains of Zn and inevitable impurities, when carbon content of steel is regulated to <=0.20%, solid solution nitrogen quantity of steel against Zn in the alloy bath is regulated to y>=2.1X 10<-5>X+17.5X10<-4> (provided that (y) and (x) denote solid solution nitrogen quantity % and zinc content % in the covered layer, respectively), and also y<=0.02 is regulated, in case of heating the steel to a high temperature, it can be suppressed that the interfacial alloy layer grows up to the surface, the surface becomes discolored and loses its gloss, due to mutual diffusion with the steel.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on zinc oxide, which has excellent gloss retention properties and heat resistance when heated.
Regarding aluminum-silicon alloy coated steel.

Coated steel whose surface is coated with Za-AL-8 Todoroki alloy by hot-dip plating, sintering, etc. has excellent corrosion resistance and heat resistance, and has thus far been used for various purposes. Conventionally,
The steel used is one consisting of 17) coated Mli powder A/, 25-70'L 8i0.5- (for AtK), and residual Zn, but when heated at high temperature fK, the steel There was a drawback that an interfacial alloy layer grew to the surface Wi due to interdiffusion with the surface, resulting in discoloration of the surface and loss of gloss.

As a method to suppress such alloy layer growth.

In the case of U-drawn alloy coated steel, a method of incorporating nitrogen into the steel base is known.

Therefore, the present inventors applied this method to Zn-Al-81
Many studies have been conducted to apply this method to alloy-coated steel.

When the steel base was rimmed steel, an interfacial alloy layer sometimes grew at the surface Kt even though it was heated at the same temperature. Therefore, the inventors of the present invention further conducted various experiments in pursuit of the cause.

It has been found that the growth rate of the interfacial alloy layer is related to the zinc content in the alloy bath, and when heated at the same temperature, the higher the zinc content, the faster the growth rate.

The present invention aims to solve such problems.

F) The object of the present invention is to provide a Zn-AL-81 alloy coated steel that can be used in high-temperature applications even if the Zn content is increased compared to the conventional coating layer.

The present invention aims to solve the problems associated with conventional coated steel by incorporating nitrogen into the steel matrix in accordance with the Zn content in the alloy bath. That is, the present invention reduces the carbon content of the steel to 0 in a steel coated with an alloy bath consisting of 30 to 85% by weight of aluminum, a silicon content of 1.5 to 15-1 with respect to aluminum, residual zinc, and unavoidable impurities. .20 weight or less, and the amount of solid solution nitrogen in the steel relative to zinc in the alloy bath is y≧2. I XIQ-'x+17.5X
10-' (where y is the solid solution nitrogen content in the steel cable ground - 1X is the zinc content in the alloy bath), y≦0.02, and a zinc-aluminum-silicon alloy coated steel characterized by It is provided by.

The following is a detailed explanation of the present invention. 0 reduces the amount of effective solid solution nitrogen in the steel matrix and promotes the diffusion of U into the steel matrix.

Therefore, since the growth of the alloy layer becomes easier when the value of 0 is high, the amount needs to be 0.20% by weight or less.

Further, the amount of solid solution nitrogen in the steel cable soil, which is a feature of the present invention, needs to be increased in accordance with the zinc content in the plating bath, as shown in Table 1. Figure 1 plots the relationship between the amount of solid solution N in the steel cable underground and the amount of a in the alloy bath, which is effective at a heating temperature of 450°C. This indicates that we must increase the

Therefore, when we find the line related to these plots, we get y
=2.1xlo-'x+17.5xlo-' (however, y
etN amount, X is Z weight) is obtained. However, if the amount of N is increased by too much, the workability of the steel base will decrease, so 0.02
It is preferable to make it less than or equal to the weight.

It is known that Za 81 has the effect of suppressing the growth of the alloy layer during the production of aluminum coated steel.
A similar effect can be obtained with At-drawn alloy coated steel. However, if the content is less than ts1 of the U amount in the bath, there will be no effect of suppressing the alloy layer, and if it exceeds 915-, the workability of the alloy coating layer will deteriorate and the corrosion resistance will also deteriorate, which is not preferable.

Furthermore, when the amount of solid solute nitrogen in the steel base is increased according to the Zn content in the alloy bath, the growth of the alloy layer is suppressed depending on the type of alloy layer generated during plating and the respective heat. This is thought to be due to the difference in physical stability. That is, when the Zn content in the alloy bath is small, thermally stable A1.
-Fe-81 ternary alloy layer is formed, but as the 2m content increases, the formation ratio of Pa-Zn or Fe-Za-Ist alloy layer with low thermal stability becomes high. When the alloy layer easily grows to the surface of the plating layer by heating, it becomes K.

Table 1 Note 1) The coated steel is a 0.8x200x100mm steel plate (0:
0.004-0.018%, Mn: 0.20-0.
34'Ir, 81:Tr, P: 0.006-0
．． 012tlb, 8: 0.007-0.012
After degreasing and pickling the Zn-kt-81 alloy bath (Zn, 81: as shown in Table 1) at 660°C, Fe: 0.04-0.06%, a: Remaining) K
Dip for 7 seconds to plate, and adjust the plating thickness to 30μ.9.

$) Quantification of solid solution nitrogen in underground steel cables is JI8.0.1228
K said.

1) Heating tests were conducted on coated steel at 450℃, 500℃, and 550℃.
The bales were heated for 100 hours in a nine atmosphere atmosphere and their appearance was judged according to the following criteria.

There is no growth of an O interfacial alloy layer, and the surface has a silvery white luster.

△ The interfacial alloy layer has grown close to the surface, and the surface has yellowed.

X: The interfacial alloy layer has grown to the surface, and the surface has turned grayish-black.

As described above, the Zn-Al-81 alloy coated steel according to the present invention has less growth of interfacial alloy layer than the conventional rimmed steel coated with VCZn-At-81 alloy, so it has good gloss retention even when exposed to high temperatures. It has excellent corrosion resistance.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the amount of solid solution nitrogen in the steel base and the zinc content in the coating layer, when the coated steel of the present invention is heated at 450°C for 100 hours, and the surface of the coating layer maintains a silvery white luster. This shows that. 1st Figure 3 0 1021) ``3C) 'it) GO button 7Y
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Claims (1)

[Claims] In steel coated with an alloy bath consisting of aluminum 30 to 85 weight -, silicon content to aluminum 1.5 to 15 -1 residual zinc and unavoidable impurities, the carbon content of the steel is 0.20 weight or less, in the alloy bath The amount of solid solution nitrogen in steel with respect to zinc is y≧2.1×1O−1x+17.5X10
A zinc-aluminum-silicon alloy coated steel characterized in that -' (where y is the solid solution silicon content and X is the zinc content in the coating layer), and y≦0.02.