JPH01309943A - Al-containing ferritic stainless steel strip and steel plate having excellent red heat characteristics - Google Patents

Abstract

PURPOSE:To manufacture the subject steel strip by specifying the plate thickness of a steel contg. specific ratios of C, Si, Mn, Cr, S, Al, P and O. CONSTITUTION:The plate thickness (t) (mm) of a steel contg., by weight, <=0.03% C, <=1.5% Si, <=0.5% Mn, 12-30% Cr, <=0.005% S, 2-6% Al, <=0.03% P, <=0.005% O and the balance Fe with inevitable impurities is regulated in such a manner that (t)=-0.013X[Al]+(ta)+0.02 is satisfied. Furthermore, in the Formula, [Al] denotes the Al content (wt.%) and (ta) denotes the set plate thickness (mm) in the design of a stove. By this method, the Al-contg. ferritic stainless steel strip (or steel plate) having improved red heat characteristics and suitable as a material for a combustion tube of a stove can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to improvement of the glow property of Al-containing ferritic stainless steel strips and steel plates used as materials for combustion tubes of stoves and the like.

(Prior Art and its Problems) Conventionally, Fe-Cr-Al ferritic stainless steel has been frequently used for stove combustion tubes. When this steel type is held at high temperatures, an oxide of AI is formed on the surface, which forms a protective film and exhibits excellent oxidation resistance.

In recent years, energy conservation has become a social issue, and along with this, there has been a need to improve the combustion efficiency of stoves. In addition, recent stoves make direct use of the radiant heat, and the majority of stoves are designed so that the combustion tube can be seen directly from the outside to give a sense of warmth. As a result, the temperature of the combustion tube is much higher than before, and as a result, abnormal oxidation occurs in the stove combustion tube.
Oxidation conditions are becoming stricter.

On the other hand, the oxidation resistance of Fe-Cr-Al ferritic stainless steel has been improved by increasing the A1 content and thickening the A1 oxide film.

On the other hand, the temperature of the combustion tube rises as heat generated by the combustion of kerosene is transferred to the combustion tube, but the thicker the oxide film, the larger the heat capacity of the combustion tube, and the oxide film is difficult for heat to transfer. The temperature of the combustion tube becomes difficult to rise, and as a result, the red-hot property decreases.

As mentioned above, there is a need to improve the combustion efficiency of stoves, and in response to the fact that the temperature of the combustion tube is higher than before,
When the amount of A1 added to Fe-Cr-Al ferritic stainless steel is increased, A] the oxide film becomes thicker and the heat radiation property decreases. Therefore, in addition to high-temperature oxidation resistance, abnormal oxidation resistance, and scale peeling resistance, excellent thermal radiation properties are strongly desired for stove combustion tube steel strips and steel plates.

(Knowledge related to problem solving) The present invention is based on Fe-C used as a combustion tube material for stoves.
The objective was to improve the thermal radiation properties of r-Al ferritic stainless steel strips and steel plates.To solve the first problem, by limiting the alloying elements of the steel and by slightly reducing the thickness of the combustion tube, the combustion tube could be significantly improved. It was found that the higher the temperature, the better the red-hot property.

(Structure of the invention) The above purpose is 1) C: 0.03% or less, Si: 1.5% or less, Mn: 0.5% or less.

Cr: 12-30%.

Contains S: 0.005 or less, A1: 2 to 6%, P: 0.03% or less, O: 0.005% or less, with the remainder consisting of Fe and unavoidable impurities, and satisfies the following formula: An Al-containing ferritic stainless steel strip and steel plate having excellent red-hot properties, characterized by having the following plate thickness:

t=-0,013X(Al]+ta+0.02t: plate thickness (am).

(Al): Al content (wt%), ta: Set plate thickness in stove design (mm) 2) ■), Ti,
A1-containing ferritic stainless steel strip or steel sheet containing 0.01 to 0.5% of one or more of V, Zr, Nb, and Ta; 3) one rare earth element and one rare earth element in the composition of 1); An Al-containing ferritic stainless steel strip or steel plate containing 0.005% or more and 0.3% or less of two or more kinds of Ca and Y and one or two kinds of Ca and Y.

4) In the composition of 1), Ti, V, Zr, Nb,
0.01 to 0.5% of one or more of Ta;
This is achieved by an Al-containing ferritic stainless steel strip or steel plate containing one or more rare earth elements and one or two types of Ca and Y in an amount of 0.005% or more and 0.3% or less.

Next, the reasons for limiting the steel composition in the present invention will be explained below.

C: Since C has an adverse effect on oxidation resistance and deteriorates the toughness of the steel sheet, a lower content is desirable.

However, reducing the content to an extreme level will increase manufacturing costs, so the upper limit is set to 0.03% or less.

Si: Similar to Cr and A1, Si is effective in improving high-temperature oxidation resistance, but when the content increases, the toughness of the hot rolled sheet decreases and manufacturability deteriorates. In addition, 1.5% or more of Si
The upper limit is set at 1.5% because if it contains, the cold-rolled annealed plate becomes hard and the ductility deteriorates, and the workability of combustion tube processing etc. is deteriorated.

Mn: Mn is an effective element for improving hot workability, but it deteriorates oxidation resistance, so the upper limit is set to 0.5%.

Cr: A basic element that maintains oxidation resistance, but 12
If it is less than 30%, the properties cannot be obtained, and if it is added in excess of 30%, the toughness will deteriorate, so the upper limit is set at 30%.

Since SOS has a negative effect on oxidation, such as promoting abnormal oxidation, it is desirable that it be low, and should be 0.005% or less.

Al: Al is an important element that maintains the oxidation resistance of this steel. In order to exhibit this characteristic in the use of the present invention, it is necessary to contain 2% or more. On the other hand, if it is contained in a large amount, processability will deteriorate, so the maximum content is 6%.

P: Since P has a negative effect on oxidation resistance, it is preferable to keep it as low as 0.03% or less.

O: O tends to cause inclusions and has a negative effect on oxidation, so the content should be 0.005% or less.

Ti, V, Zr, Nb, Ta: These elements are effective for oxidation resistance and scale peeling resistance. It is also effective in improving workability. In order to exhibit this effect, it is necessary to add at least 0.01% or more.

On the other hand, if added in excess, the toughness will deteriorate, so the maximum is 0.5.
up to %.

Rare earth elements, Ca, and Y: In order to prepare for severe oxidation conditions such as those used in the present invention, it is effective to add one or more of REM, Ca, and Y in combination. These are effective in improving the peeling resistance of scale and suppressing the occurrence of abnormal oxidation. To achieve this effect, 0
．． Requires addition of 0.05% or more. However, if added in excess, it may cause blisters due to so-called inclusions.
Since this results in a large defect, the upper limit is set at 0.3%.

The reason why the conditional expression regarding plate thickness was derived will be explained in detail later.

(Specific Disclosure of the Invention) Steel having the composition shown in Table 1 was made into a plate with a thickness of 0.4 mm by a conventional method, and after conducting a continuous oxidation test for 1 hour at 850°C, the results were calculated based on the amount of Cr. As shown in Fig. 1.2, the case where the oxide film was thin and healthy without abnormal oxidation or other phenomena that caused an abnormality is shown in Figure 1.2, and the case where an abnormality occurred is shown as a black circle. From this result, the oxidation properties are largely dependent on Cr and A1, and in cases where it is necessary to maintain oxidation resistance over a long period of time, such as in stove combustion tubes.

It can be seen that A1 of 2% or more is required. However, as shown in FIG. 2, as the amount of A1 added increases, the oxide film tends to become thicker, although it is within a very thin range.

Figures 3 and 4 show the results of a combustion experiment conducted using an actual stove on a combustion tube with a plate thickness of 0.40 mm made of six steel types whose compositions are shown in the figures. Figure 3 shows the amount of kerosene consumed, and Figure 4 shows the change in combustion cylinder temperature over time. 1st
, As in Figure 2, the cases where the oxide film is thin and healthy without any abnormality such as abnormal oxidation occurring are shown by white circles, and the cases where abnormalities occur are shown by black circles. From FIGS. 3 and 4, although the amount of kerosene consumed is almost constant, the combustion tube temperature varies depending on the composition of the combustion tube material.

1.4% A1 steel undergoes abnormal oxidation in a relatively short period of time, causing a rapid drop in temperature. 1.8% AltR undergoes abnormal oxidation in 350 hours and the temperature drops. However, up to 350 hours, the 1.8% A1 steel had the highest temperature, and the higher the Al content, the lower the combustion tube temperature. Like this A
When the 1 content is high, abnormal oxidation is less likely to occur and combustion can be endured for a long time. However, as the A1 content increased, the combustion tube temperature decreased, resulting in poor red heat properties.

Therefore, as a result of detailed studies on the conditions for maintaining oxidation resistance and red-hot property, we found that just by making the thickness of the combustion tube slightly thinner, the temperature of the combustion tube becomes significantly higher, and the red-hot property is improved. I got the knowledge that Based on this knowledge, we have adjusted the plate thickness of the combustion tube so that even with steel with a high Al content and improved oxidation resistance, we can obtain incandescent properties equivalent to or higher than the 1.8% AI-containing steel before abnormal oxidation. The relationship between Al content and temperature was investigated. In other words, combustion tubes were created by changing the plate thickness and the amount of Al in steel based on 18Cr, and a combustion experiment was conducted using an actual stove with a plate thickness of 0.4 mm according to the stove design, and after 500 hours, the temperature of the combustion tube was is 760℃, 7
70℃.

Plots were made for those that reached 780°C. The results are shown in FIG. From this figure, it was found that the following formula holds true between the Al amount and plate thickness at each combustion cylinder temperature. t=-0,013X(Al)+0.4+K ---
(1) t: Thickness of the combustion tube (mm).

(Al): Al content (wt%) of the combustion tube material, where the combustion tube temperature is 760℃ K: 0.042770℃
In the case of K=0.023, in the case of 780°C, K=0.006.

Here, the relationship between combustion cylinder temperature and K is shown in FIG.

From this figure, the following equation holds.

K = -1,71X10-3XT+1.34 ---
(2) T: Combustion cylinder temperature Substituting equation (2) into equation (1) = -0,013X (Al) +0.4-1.71
X 1O-3
Assuming that A1-containing steel does not undergo abnormal oxidation,
Even with other A1-containing steels, the thickness of the combustion tube that would provide a combustion tube temperature higher than that in this case is determined as follows. 1
．． 8%A], ff, and a combustion tube is designed with a plate thickness ta, and by substituting t=ta, (At)=1.8 into (3), ta=-0,013X(AI)+0. 4-1.71xl
O-'xT+1.34 Substitute this into equation (3) and get 1', t=-0,013X(Al)+ta+0.0
2 ---- (5) If the A1 content value of the material used for the combustion tube and the stove design plate thickness are entered into equation (5), and the combustion tube is created with a plate thickness that is less than the determined value of t, then In addition to improving oxidation resistance by increasing the AI content, a combustion tube temperature equal to or higher than that of 1.8% Al-containing steel is obtained, and the red heat property is good.

Table 2 shows the thickness of the combustion tube after processing and the actual stove.
It shows the temperature of the combustion tube when it is burned for a certain period of time. The results show that the combustion cylinder having the composition and plate thickness of the present invention had a higher temperature and better glow property than the comparative example. The design thickness of the combustion tube of the stove used in this experiment was 0.4.
It is m1m1.

Table 2 (Effects of the Invention) The A1-containing ferritic stainless steel strip or steel plate for stove combustion tubes, which has limited alloying elements according to the present invention and satisfies the requirements of a constant plate thickness, has excellent glow resistance. Therefore, the red-hot property, which was a problem in the prior art, has been improved, and a suitable bath 1--
A1-containing ferritic stainless steel strip or steel plate for combustion can be provided.

[Brief explanation of the drawing]

Figure 1 shows 850'CX in the atmosphere depending on the amount of ^1 and the amount of Cr.
Figure 2 shows the presence or absence of abnormal oxidation after a 500-hour continuous oxidation test. Figure 2 shows ferritic stainless steels based on 18Cr and with different amounts of A1 added at 850°C in the atmosphere.
. Fig. 3 shows the thickness of the oxide film after the continuous oxidation test. Ferritic stainless steels based on 1111Cr with different amounts of A1 added were processed into combustion tubes with a thickness of 0.40 mm.
Figure 4 shows the change in kerosene consumption over time after a combustion experiment was conducted using an actual stove. A combustion experiment was conducted using an actual machine, and the graph showing the change in combustion tube temperature over time. Figure 5 shows the combustion tube made of a steel plate with added plate thickness and Al addition amount, and after 500 hours, the combustion tube temperature was 760°770.
, and a diagram showing the relationship between Alt and plate thickness for those that reach 780°C. FIG. 6 is a diagram showing the relationship between the value of K in equation (I) and the combustion cylinder temperature.

Claims (1)

[Claims] 1. C: 0.03% or less, Si: 1.5% or less, Mn: 0.5% or less, Cr: 12 to 30%, S: 0.005% or less, Al: 2 ~6%, P: 0.03% or less, O: 0.005% or less, and the balance is Fe and unavoidable impurities; the plate thickness must be as follows, satisfying the following formula: Al-containing ferritic stainless steel strip and steel plate with excellent red heat properties, t = -0.013 x [Al] + ta + 0.02 t: plate thickness (mm), [Al]: Al content (wt%) ),
ta: Set plate thickness in stove design (mm) 2, C: 0.03% or less, Si: 1.5% or less, Mn: 0.5% or less, Cr: 12-30%, S: 0.005 % or less, Al: 2 to 6%, P: 0.03% or less, O: 0.005% or less, one or more of Ti, V, Zr, Nb, and Ta in an amount of 0.01 to 0. Contains 5%,
An aluminum-containing ferritic stainless steel strip or steel plate with excellent red-hot properties, which is a steel with the balance consisting of Fe and unavoidable impurities, and which satisfies the following formula and has the following plate thickness: t=-0 .013×[Al]+ta+0.02 t: plate thickness (mm), [Al]: Al content (weight%),
Ta: Set plate thickness in stove design (mm) 3, C: 0.03% or less, Si: 1.5% or less, Mn: 0.5% or less, Cr: 12-30%, S: 0.005 Below, Mn: 0.5% or less, P: 0.03% or less, O: 0.005% or less, one or more rare earth elements, and one or two types of Ca, Y, 0.005%. Al-containing ferritic stainless steel with excellent red heat property, characterized by having a thickness of t or less that satisfies the following formula; Steel strip or steel plate, t = -0.013 x [Al] + ta + 0.02 t: plate thickness (mm), [Al]: Al content (wt%),
ta: Set plate thickness in stove design (mm) 4, C: 0.03% or less, Si: 1.5% or less, Mn: 0.5% or less, Cr: 12-30%, S: 0.005 % or less, Al: 2 to 6%, P: 0.03% or less, O: 0.005% or less, 0.01 to 0.0% of one or more of Ti, V, Zr, Nb, and Ta. A steel containing 0.005% or more and 0.3% or less of one or more rare earth elements and one or two kinds of Ca and Y, with the balance consisting of Fe and unavoidable impurities; Al-containing ferritic stainless steel strips and steel plates with excellent red heat properties, characterized by having a thickness of t or less that satisfies the following formula: t = -0.013 x [Al] + ta + 0.02 t: plate thickness ( mm), [Al]: Al content (wt%),
ta: Set plate thickness in stove design (mm)