JPS6013027A - Production of aluminum plated steel sheet having excellent high-temperature strength and heat resistance - Google Patents

Abstract

PURPOSE:To improve the heat resistance and high-temp. strength of an Al plated steel sheet obtd. in the stage of producing said steel sheet by incorporating a specific amt. of Ti and Nb into the steel sheet and coiling the steel sheet within a specific temp. range in a continuous hot rolling stage. CONSTITUTION:A steel having the compsn. contg. 0.005-0.020% C, 0.05-0.40% Mn, <0.010% N, 0.10-0.50% Ti where the ratio of Ti/(C+N) is made to >=10, 0.05-0.30% Nb and 0.01-0.10% Al is used for a steel sheet in the stage of producing an Al plated steel sheet by subjecting a cold rolled steel sheet to Al hot dipping. The coiling in the continuous hot rolling stage for the steel sheet is accomplished in a temp. range of 550-650 deg.C. The (Ti, Nb) carbonitride is uniformly and finely dispersed by the combination of the improved resistance to oxidation at a high temp. by Ti, Nb and the temp. conditions for coiling of the steel sheet in the stage of hot rolling, by which the high-temp. strength after Al plating is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention a relates to an aluminum-plated steel sheet with excellent heat resistance, and more specifically relates to fixing of C-work N in steel by T1-work Nb, and Ti′:g? The present invention relates to a method for producing a hot-dip aluminized steel sheet that has improved high-temperature oxidation resistance and high-temperature strength, as well as control of the precipitation of Nb carbonate and arsenic substances.

Conventional general-purpose hot-dip aluminized steel plate, pure A1 or HAl-sj on the surface of mild steel or high-strength steel (~10 inches)
It is coated with alloy gold plating and is widely used as a low-grade heat-resistant forest material. The withstand temperature of these conventional hot-dip aluminized steel sheets was at most 600 C [excessive force].

1TrI thermal properties of this kind of molten aluminum plated steel sheet,
Furthermore, in order to improve the high-temperature strength, a proposal has been made to improve the high-temperature strength. For example, CIl'i Kosho 5
No. 3-15454, (2) Special Publication No. 51-35532,
(3) JP-A-56-102556, (4) JP-A-56-102556
-102523, (5) those described in JP-A-57-140868, and the like. Among these, (2)
The proposals in (5) to (5) are related to the same applicant as the present application.

Although these proposals have improved the high-temperature strength of aluminum-plated steel sheets to some extent, they are still insufficient for use under harsh conditions, such as for use in automobile exhaust gas treatment equipment. It is suitable for applications such as parts that require cold-open formability at room temperature as well as oxidation resistance and strength properties at 500 to 800 C. Stainless steels traditionally used for various purposes, such as A-S-409
When aluminum-plated steel sheets are used instead of heat-resistant steel, it is necessary to further improve heat resistance and high-temperature strength.

It is the object of the present invention to meet this requirement.

To this end, the invention provides c ; o, oos ~ 0
．． 020, Mn; 0.05-0.40%, N;
o, o1o%1o, T1; o,1o ~o,so%
Ti/(C+NI ratio is 1o or more, Nl); o
, os ~0.30%, Al; 0.01~0.1
%, the balance being Fe and unavoidable impurities as a base material, and aluminum plating is applied to this to obtain an aluminum plated steel sheet. Take temperature to 550'
The present invention provides a method for producing an aluminum-plated steel sheet with excellent heat resistance, which is controlled to a range of C to 650C.

The base steel of the hot-dip aluminized steel plate used in the method of the present invention is similar to the Nb-containing steel described in part in the above-mentioned (5)% Patent Publication No. 140868/1983, but this method of the present invention does not contain Nb. By appropriately controlling the manufacturing aspects of the steel, particularly the winding temperature in the hot rolling process, the high-temperature strength is further improved compared to the aluminum-plated steel sheet described in the publication. In addition, the aluminum-plated steel sheet obtained by the method of the present invention maintains good high-temperature strength even after being exposed to high temperatures of around 800C for a long time, which was achieved in JP-A-57-140868. I/-
One that can demonstrate high-temperature strength and sustainability of high-temperature strength for one millisecond, and effectively achieves the stated purpose of improving high-temperature strength without losing high-temperature oxidation resistance at temperatures exceeding 600C. It is.

The effect of the chemical components of the base steel in the present invention and the reason for limiting the content will be briefly described below.

CV's, a component harmful to the high-temperature oxidation resistance of aluminium-plated steel sheets at temperatures above 600C.

The first harmful effect of C is that it significantly reduces the diffusion ability of A1 in the base steel, significantly inhibiting the diffusion of A1 in the plating layer into the base steel, and causing the base steel to deteriorate during high temperature heating. The problem is that a large amount of pores and voids are generated at the interface of the fastening layer. These pores and voids in the A1 plated coating layer and the A into the base steel.
This is thought to occur because the diffusion rate of Fe from the base steel into the plating coating layer is higher than the diffusion rate of No. 1. The second harmful effect of C is that O (oxygen) that reaches the surface of the base steel through defects and grain boundaries in the plating coating layer combines with C in the base steel to form Co-1-Co. □, and this Co-4-Co2 accumulates in the pores and voids generated at the interface between the base steel and the plating coating layer, increasing the internal pressure 2 of the pores and voids, and increasing the bond between the base steel and the plating coating layer. The point is that the interfacial strength of the material is significantly reduced. The above harmful effects of C can be completely removed by adding Ti1i5 to the base steel and fixing all C as Tie precipitates. In the present invention, T1
By adding Nbr and Nbr in combination, all of the Ci (Ti, N
b) The high-temperature strength of aluminium-plated steel sheets is improved by fixing carbonitrides and finely dispersing carbonitrides (Ti, Nb) by appropriately controlling the winding temperature of hot rolling. improve. Therefore, C is an element that contributes to the improvement of high temperature strength, which is the main objective of the present invention, as (Ti, Nbl carbonitride).The high temperature strength improvement effect of C is due to precipitation dispersion strengthening, and the C content However, if the C content exceeds 0.L120%, the high-temperature strength will further increase, but the required amount of T1 will increase, resulting in a decrease in surface quality and weldability, and furthermore, it will become more economical. Therefore, the upper limit was set at 0.020%.In addition, if C is less than 0.005%, (Ti, NbI carbonitride V
Since the strengthening effect of C is extremely small, its lower limit is 1.
o, oos% closed.

Mnrr, the amount added when a normal steel manufacturing method is adopted is taken as the allowable amount, and the lower limit is 05% and the upper limit is 0.40%.

T1 is one of the basic elements that contributes to improving high-temperature oxidation resistance and high-temperature strength, which are the main objectives of the present invention. The reason why Ti has improved high temperature oxidation resistance is thought to be due to the following reasons. In other words, the carbon steel in the base steel is N1Ti (
C, N) By fixing the precipitates, diffusion of A1 from the plating layer into the base steel becomes extremely easy, and pores and voids at the interface between the base steel and the plating layer are reduced. The amount produced is drastically reduced. Due to ineffectiveness, the outermost layer (outermost layer of the plated steel plate) of Al, 20.?
A thermally and chemically stable and dense oxide layer (covered with α-Fe layer containing a high concentration of A1, which is the main component, is formed and exhibits excellent high-temperature oxidation resistance. ,ru.Tj,
i, Eq. vC ((, 1 - When present in an amount of 10 times or more of the amount of NJ in the form of solid solution Tj in the base steel, the high temperature oxidation resistance is further improved. During high-temperature heating, the above-mentioned outermost layer has an oxide layer with a main component of 1', -?0%, and a high concentration of AJ immediately below it, and 1.3) an α-Fo layer (Al diffusion By selectively oxidizing the interface rTi with the layer), the interface VrcTi is concentrated and becomes a stable and dense layer of the oxide layer mainly composed of 81,03. Don't think about it.'-1
As mentioned earlier, (Ti, Nb
) Contributes to improvement of high temperature strength by finely precipitating and dispersing as carbonitrides. Don't try the above, the effect of Tj,
Even if a large amount of vC115 is added beyond the Ti content H7>: o, s, it will not increase, and will only cause deterioration of the surface quality of the base steel. And so. If the T1-containing elbow is not #i, the solid solution T in the base steel may be 70% to fix C and N in the base steel.
] - amount decreases and becomes insufficient to make the above-mentioned A11203-based oxide layer more stable and dense, so its lower limit 1o,i.

I closed it.

Nb slag is one of the basic elements contributing to the improvement of high temperature strength, which is the main objective of the present invention. Nbf''r, in combination with the hot rolling winding temperature conditions, contributes to the improvement of high temperature strength by being uniformly and finely present in the base steel as Nb1 carbonitride. As a result of extensive research into the effect of Nb on improving high-temperature strength, wood inventors found that when the winding temperature of hot-rolled steel is set in the range of 550C to 650C, (Ti
, Nb) Carbonitrides are uniformly and finely precipitated in the base steel, resulting in a precipitation dispersion strengthening effect? In addition, as shown in the examples below, even if the high temperature of about 850 C or less can be maintained for a long time during the subsequent manufacturing process and when using aluminum plated steel, (Ti, Nb) carbonitrides It was found that because the agglomeration and hypertrophic growth are slow, the fractional strengthening effect of (Ti, Nb) carbonitrides is not maintained, and secondary recrystallization of the ferrite phase, which is the matrix phase, is suppressed. The effects of Nb as described above will not increase even if added in large amounts exceeding 0.30% of the total amount, and will only unnecessarily reduce the economic efficiency of coated steel sheets. Therefore, set the upper limit to 06
0% binding. If the Nb content is less than 0.50, the effect of improving high-temperature strength is extremely small, so the lower limit is set as skin o5 and candy (~).

Al slag is used for the purpose of deoxidizing molten steel, but in the steel of the present invention, 1
Yield of 77i and Nb! 7 It is important as a preliminary deoxidizing element that is often added, and from this point of view the lower limit of total 0.01%
Toshi 1 child. Furthermore, even if A1 is added in excess of 0.1 ratio, the deoxidizing effect will not be significantly improved, so the upper limit is set at 0.10 ratio and 1
child.

In the case of the T11-oriented Oka as in the present invention, almost the entire amount forms vcT i N precipitates during melting and solidification, and does not decompose or agglomerate in any subsequent steps. Therefore, in order to effectively utilize T1,
Although it is preferable to keep the N content as low as possible, it is impossible to completely remove Ni with current steel manufacturing methods, so the N content is set to 0.010% or less.

Containing large amounts of P and S impairs processability, so it is preferable to keep them as small as possible, but it is unavoidable that P and S should be contained in amounts of p: 0.04 or less, s: 0.04 or less. If so, there is no problem 17r in terms of the present invention.

The present invention is characterized by strictly controlling the hot-rolling temperature of the base steel. In order to obtain the precipitation and dispersion state of the above-mentioned (Ti, Nb) carbonitrides in the base steel, which contributes to the improvement of the high-temperature strength of aluminum-plated steel sheets, which is the main objective of the present invention, it is necessary to control the hot-rolling winding temperature. This is an extremely important force. When the winding temperature exceeds 650C, (Ti, Nb)
Carbonitrides tend to precipitate coarsely, making it impossible to obtain a sufficient strengthening effect. Winding temperature i 550 C-65Or+7)
Toss within range (Ti.

Nb) is uniformly precipitated in carbonitrides and a sufficient strengthening effect can be obtained. Furthermore, in this case, even if it is kept at high temperature for a long time during the process after hot rolling and during use, (Ti, N
Since the agglomeration and hypertrophic growth of bI carbonitrides is extremely slow, even after the subsequent annealing process or high temperature use of aluminum plated steel sheet products, the strength properties of plated steel sheets at room and high temperatures will deteriorate. Has a small advantage. Winding temperature 1
If the temperature is lower than sso c, (Ti, Nb) carbonitrides will become finer and the strength properties of the base steel will further increase. (Ti, Nb)
Carbonitride agglomeration-hypertrophic growth occurs rapidly and the strength properties at room and high temperatures are significantly reduced.

For the above reasons, the winding temperature in hot rolling is 550C.
In carrying out the present invention, it is particularly limited to the method of aluminum plating. Although it is not practical, it is convenient to use the fused aluminium/mumetsu method, which has been established as a mass production method. In this case, as mentioned above, there is little decrease in high temperature strength even when subjected to in-line annealing.

Next, the present invention will be specifically explained with reference to Examples.

Example 1 Steel with the composition shown in Table 1? f: After being melted in a 10 kli + vacuum melting furnace, cast, and forged, it was rolled in a continuous hot rolling process in a through hole, and rolled at various rolling temperatures shown in Table 1 to a thickness of 4.0 mm. It is made into a hot-rolled steel strip and subjected to the usual pickling and cold rolling processes.1. Tensile properties at room temperature, high temperature strength (600C), and oxidation test results of a sample of a cold-rolled sheet with a thickness of 0.0 mm and aluminum plating with a basis weight of 8ay7.1 using a NOF type hot-dip aluminum plating machine. Also listed. In the oxidation test, the oxidation weight increase on the plated surface was measured after holding the sample at 800 C in the atmosphere for 20 hours and then cooling it at room temperature 1 10 times.

The following is clearly the result from table 1.

Samples A, B, Q do not contain Nb, T1 processed Ti/(
Although the c+1 ratio is different, the high-temperature strength at 600 p is uniformly low in these six Nb-free samples. 1. Comparing the oxidation weight gain of samples A, B, and C, T1
The oxidation weight gain of sample C, whose content of processed Ti/(CJNJ ratio is within the range of the present invention), is the lowest, and the effect of T1 can be seen.In addition, sample Ci, the base steel, is made from Japanese Patent Publication No. 51-35532.
□ High resistance @ excellent oxidation VC,
Characteristic of superior ductility at room temperature? However, it has sufficient high temperature strength and does not sag.

Although the sample contains Nb (z) but does not have Ti mirror, and has excellent high temperature strength at 6ooc,
Poor high temperature oxidation resistance.

Samples E, F, GSH, and I have different base steel compositions within the scope of the present invention, but the seven hot-rolling temperatures are different. Among these, sample E1F (tl winding temperature is higher than the temperature range of the present invention, the high temperature strength at 600C is substantially the same as sample C, is sufficient and does not sag,
This sample B is the Nb-containing steel disclosed in Fi″r Japanese Unexamined Patent Publication No. 57-140868 (the rolling temperature was 7.
40C is shown). Samples G, H, and Ii have a winding temperature within the range of the present invention, but when comparing samples JF, C) and H1■, it is found that the winding temperature is at room temperature and at a high temperature (600tZ'). The lower the winding temperature of hot rolling, the higher the strength at
It is clear that the effect is great when the temperature is 650C or less. It is clear that if the ratio of Ti/(C-4-NJ) falls within the range of the present invention, high resistance to oxidation is achieved.

Example 2 The composition of molten steel produced using an 80 t LD converter was adjusted using a vacuum degassing apparatus to obtain steel having the composition shown in Table 2. These steels were continuously cast into slabs, rolled in a normal continuous hot rolling process, and rolled at various rolling temperatures shown in Table 2 to form hot rolled steel strips with a thickness of 4.0 mm. A cold-rolled sheet with a thickness of 1.0 through normal pickling and cold-rolling processes was coated with an NOF-type hot-dip aluminum plating machine with a basis weight of 807.
/d aluminum plating? provided. Mechanical properties at room temperature and high temperature strength of each plated steel sheet sample (600CJ, and mechanical properties at room temperature of the sample after being annealed by holding at 800C for 20 hours and cooling in a furnace at room @ 1) Results of measuring properties and high temperature strength (600C)
It is shown in Table 3.

-19. From the results in Table 3, we can conclude the following. It is the same as the test volume 1 published in Japanese Patent Publication No. 51-35532, and its high-temperature strength is poor. A slab having the same composition as Sample 1 was used for Sample 2, and the winding temperature during hot rolling was within the range of the present invention. Although the mechanical properties at room temperature, high temperature strength level, and bottom edge of the sample 2 were improved with aluminum plating, after annealing at 800C, a
Mechanical properties at room temperature and high temperature strength are significantly reduced.

For this reason, annealing treatment of 800[r]
This is thought to be due to agglomeration and enlargement of TiC precipitates and coarsening of ferrite crystal grains.

6.4 samples were prepared according to the method of the present invention, and 800
It is clear that after the annealing treatment of C, there was almost no decrease in the strength properties at room temperature and at high temperatures.

Sample 5a Base material composition a Although within the composition range of the present invention,
The winding temperature of hot rolling is within the range of the present invention. Although the strength properties at room temperature and high temperature after plating treatment are extremely high, the strength properties at room temperature and high temperature after being annealed at 800C are significantly lower.

The chemical composition value of the base steel for sample B is based on the above-mentioned JP-A-57-140.
It corresponds to the one described in the No. 868 publication, but at a winding temperature of 11!2, which is close to the winding temperature of 740C indicated in the publication, #
This is what I left behind. In this case, the high temperature strength at 600C is improved compared to Comparative Sample 1, but the strength after being heated to a high temperature for a long time (800C x 20 hr) is significantly lower.

Applicant: Nisshin Steel Co., Ltd.

Claims (1)

[Claims] C' 0.005-0.020%, Mn; 0.0
5-0.40%, N; 0.010% or less, Ti
0.10 to 0.50 and Ti/(c+Nl ratio of 10 or more, Nb; o, os to 0.60, Al;
The base material is a cold-rolled steel sheet with 0.01 to 0.1%, the balance being F'e and unavoidable impurities, and this is aluminum plated. An aluminum-plated steel sheet with excellent high-temperature strength and heat resistance, characterized in that the rolling temperature is controlled in the range of 550C to 650C in the continuous hot rolling process in the manufacturing process of the base material. manufacturing method.