JPS6376850A - Fe-cr-al-nd alloy having superior resistance to peeling of oxide scale - Google Patents

Abstract

PURPOSE:To obtain the titled low-cost alloy having superior hot rollability, cold rollability, oxidation resistance and resistance to peeling of oxide scale without adding Ce by providing a compsn. consisting of prescribed amounts of C, Si, Cr, Al and Nd and the balance Fe with inevitable impurities. CONSTITUTION:The titled Fe-Cr-Al-Nd alloy consists of, by weight, <=0.02% C, <=1.5% Si, 13-27% Cr, >3.5-<8% Al, 0.03-0.20% Nd and the balance Fe with inevitable impurities. The alloy is suitable for use as a material for a catalytic converter for cleaning exhaust gas from an automobile. The converter undergoes severe repeated oxidation in a hot oxidizing atmosphere. The alloy is also useful as a material for parts of a heater and the apparatus of an exhaust system for combustion gas.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is directed to Fe-Cr which has excellent peeling resistance of oxide scale.
- Regarding Al-Nd alloys, it is suitable for automotive exhaust gas purification m catalytic converters that undergo intense repeated oxidation in high-temperature oxidizing atmospheres, as well as combustion gas exhaust system equipment, devices,
It is also useful for Ia11 parts.

[Conventional technology]

Conventionally, cordierite (2M g O, 2A, 203-5SiO2) has been used in catalytic converters for automobile exhaust gas purification.
) extruded fired honeycomb coated with γ-alumina fine particles as a catalyst carrier and then coated with a catalyst such as PT is used.

As shown in Japanese Patent Application Laid-open No. 56-96726,
If this cordierite honeycomb is made into a metal honeycomb made by assembling oxidation-resistant stainless steel foil, there are various advantages such as miniaturization of the converter and improvement of engine performance. In the cited publication, an Fe-Cr-Al alloy (C
r: 15-25% by weight, A exchange: 3-6mF1, Taro, Y
:0.3 to 1.0% by weight), but since Y is a rare metal, it is very expensive and there is also concern about the supply amount, making it uneconomical to use it in general automobiles. In contrast, in JP-A-58-177437, Cr
: 8-25% by weight, AJI: 3-8ffE amount%,
Total rare earth elements up to 0.06% by weight, 0.002-0
．． Alloy containing 0.5% Ce, La, Nd, etc. (
We propose the use of Fe-Cr-Al1-REM alloy (hereinafter referred to as Fe-Cr-Al1-REM alloy). This is a Fe-Cr-Al alloy that prevents scale exfoliation by adding rare earth elements.
It has been used since the beginning for heating wires, etc.

Fe-Cr-AJI-REM alloys such as Kono have sufficient oxidation scale peeling resistance for general purposes, but they are difficult to remove when starting, accelerating, and stopping, such as in catalytic converters for exploding automobile exhaust gas. When exposed to severe high temperature repeated oxidation and intense vibration, the oxide scale will peel off.

In addition, since it is a foil, it is thin, and the catalyst is coated on top of the foil.
If the oxide scale peels off, it will lead to a decrease in the exhaust gas exploding ability.

Fe-Cr with scale peeling prevented by REM addition
In the -Al-REM alloy, rare earth elements other than Y reduce hot workability, so addition of 0.05 fi amount % or more is considered to be ineffective.

(Problems to be solved by Nos. 9 and 11) In view of the above-mentioned circumstances, the present invention provides new findings as a result of research into materials that are subjected to high temperature repeated oxidation and have extremely high peeling resistance of oxide scale in an environment of severe vibration. Based on this knowledge, final IJ
The objective is to complete the invention and provide such materials. That is, according to the research of the present inventors,
The above-mentioned drawbacks due to the addition of rare earth elements are mainly caused by Ce, and when Nd alone is added in an amount of 0.03% by weight or more, rolling processing is possible without causing cracking during hot working, and #We have newly found that oxidation properties and peeling resistance of oxide scales are significantly improved.

However, in the above-mentioned Japanese Patent Application Laid-Open No. 58-177437, "at least O, OO, where the total of all rare earths is up to 0.06%"
2% and up to 0.05% cerium and lanthanum,
Additives from the group consisting of neodymium and praseodymium"
As such, Ce is required.

On the other hand, there is no distinction between La, Nd, etc., and there are no examples in which Nd is added alone.

[Means for solving problems]

The first aspect of the present invention is C: 0.02% by weight or less S [: 1.5% by weight or less Cr: 13% by weight or more 27m)j 1% or less Al: 3.5
More than 8% by weight Nd: 0.03 weight Cx or more 0
．． Contains 20% by weight or more of F, and does not contain Ce, with the remainder being F.
Fe-Cr-A with excellent AS resistance of oxide scale characterized by consisting of e and inevitable impurities! It is an L-Nd alloy.

The second invention of the present invention is obtained by adding Ti:C at least 5 times the weight % and 0.10 weight % or less to the first invention.

The third invention of the present invention is the first invention in which lanthanoids other than Ce and Nd are O,0O1fii% or more and o,tgH% or less,
The total amount of lanthanoids is 0.2 (lffi%).

Furthermore, the fourth invention of the present invention provides the third invention with T i : C
This is the sum of 5 times or more of the weight percent and less than or equal to the o-io weight percent.

[Effect]

The alloy of the present invention has the effect of extremely high oxidation resistance and oxidized scale removability depending on the content of each component, and the reasons for limiting each component will be described below.

■ Nd: If it is less than 0.03% by weight, oxidation resistance and peeling resistance of oxide scale cannot be ensured in a foil with a thickness of about 50 μm;
If it is less than 0% by weight, hot rolling becomes impossible, so 0.05
The content was set to be 0.620% by weight or more and less than 0.620% by weight.

■ Lanthanoids excluding Ce and Nd: Lanthanoids are La, Ce, Nd, and 15 other totally tropic elements with atomic numbers from 57 to 71. Lanthanoids other than Ce and Nd have almost the same effect as Nd in improving the oxidation property and peeling resistance of oxide scale, and when refining Nd from raw ore, other lanthanoids such as La are used rather than pure Nd. Since it may be easier to use a form of Nd containing lanthanoids,
．． 001 to 0.10% by weight. However, since the hot workability decreases, the total rank-made is 0.
．． The content shall be 20% by weight or less.

■ Cr: Oxidation resistance cannot be ensured if the content is less than 13-fold Cx.

27 weights! If it exceeds ^%, the toughness decreases and cold working becomes difficult, so it was set at 13 to 27fffit%.

■ Emperor A: Oxidation resistance cannot be ensured below 3.5% by weight, and 8% by weight
Since hot rolling becomes difficult if the content exceeds 3.5% by weight and less than 8% by weight.

(2) SL: Effective in improving oxidation resistance, but if it exceeds 1.5% by weight, processability decreases, so the content was set at 1.5% by weight or more.

■C: If it is excessive, it lowers toughness and worsens cold rollability and workability, so it is necessary to keep it at 0.02ffi% or less.

■ Ti: If Ti is added in addition to the above, Ti becomes carbide, fixes C, and improves toughness. Ti is C
The modified R effect will not appear unless it is added at least 5 times the concentration, but 0.1 ton? If it is added in excess of 10%, the oxidation resistance will be lowered, so it is expressed as 5X weight; (%C-0.10 tons).

〔Example〕

Table 1 shows the chemical composition of the alloy of the unexplored 151 examples,
Table 2 shows the chemical components of the alloys of comparative examples.

The examples and comparative examples were melted into 10 kg ingots and then hot rolled at 1200"C to a thickness of 3 mm. At this stage, the total concentration of Ce, La, and Nd (7) was 0.
．． 058 wt% B-3, Ce concentration 0.085 rr
Ci, 1% (7) B-6, NdejlCO, 24rB
r,,% of B-17, Nd and Lac7) B-19 with a sum of 0.23 tons and 111%, and B-25 with an Al content of 8.5% by weight, the steel ingot was rolled during hot rolling; , no further tests were conducted.

The above B-3, 6, 17° 19.2 of Examples and Comparative Examples
Comparative examples other than No. 5 were then annealed at 900° C. and then subjected to a Charpy test to examine their toughness. Some of the results are shown in Figure 1. C-1 has a low C concentration of 2% by weight of O, OO, and C-2 has a high C concentration of 0.09% by weight of Ti (0.09% by weight). had good toughness with a ductile-brittle transition temperature of 60 to 80°C, and was easy to cold-roll. On the other hand, B-21, which has a high C content of 0.028% by weight, has a transition temperature of 1
At 50°C, the toughness was poor and cold rolling was difficult, so warm rolling was required. Similarly, B- with 27.5% by weight of Cr
24 and B-23 with 1.7% by weight of Si also have a transition temperature of 10
The temperature exceeded 0°C, making cold rolling difficult.

After that, descaling, cold rolling, and annealing were repeated until the plate thickness was 50.
It was made into micrometer foil. From now on, the plate thickness will be 50 m1 and the width will be 20 m.
A test piece with a length of 30 mm was taken and an oxidation test was conducted at 1150° C. in the air.

Part of the results are shown in Figure 2. Ce is 0.035!
B-15 with IZ amount %, Nd is 0.031 weight %, but B-16 with Ce added 0.042 weight % is 10
It is completely oxidized within 0 to 120 hours and does not retain its original shape.
On the other hand, although the degree of Cr and Aie is high, Nd is 0.032% by weight C-1, Nd is 0.051% by weight,
C-8 with La of 0.02 weight and 61% is expensive Fe-Cr-
Like the AM-Y alloy B-1, the oxidation weight increase was 1.2 mg/am' even after 200 hours, showing very good oxidation resistance. In this way, Ce reduces oxidation resistance, but N
d, La, and Y greatly improve the oxidation resistance. Similarly, Ti is 0.31% by weight of B-22, Cr is 1% by weight.
1.8% by weight 17) B-26, B with 3.1% by weight of An
-27 also had insufficient oxidation resistance.

Finally, test pieces of the same shape were heated to 1150°C in the atmosphere for 3 days.
After oxidation was performed for 0 minutes and then quenched for 12 minutes, the oxidation was repeated 200 times, and then the oxide scale was examined using an electron microscope.

B-3, B-16 containing Ce, Nd concentration o, o i
B-18, which contains the same <0.024 wt% La but has a low Nd concentration of 0.013 wt%, B-26, B-27, which has a low Cr and An concentration of 0.013 wt%. About half of the oxide scale had peeled off in the sample, but no peeling was observed in B-1 containing Y among the examples and comparative examples.

The above results were integrated and evaluated in Tables 1 and 2, and Fe-Cr-An in Table 1 which is within the scope of the present invention.
It is clear that the -Nd (-Ti) alloy is superior both in terms of manufacturability and properties.

Nd and La do not significantly reduce hot workability and significantly improve oxidation resistance and peeling resistance, but Ce improves hot workability,
It is clear that the oxidation resistance is significantly reduced.

The evaluation categories in Tables 1 and 2 are as follows:
According to 8i standard.

Hot rolling properties: Q: After heating to 1200°C, it was possible to roll for fS.

X: After heating at 1200°C, hot rolling was impossible.

Toughness: O: The brittle-ductile transition temperature in hot rolled annealed plate is less than 100°C.

X: M The brittle-ductile transition temperature of the spread weight plate is 100°C or higher.

IfFt oxidation property: Weight increase after heating in air at 1150° C. for 144 hours with 0:50 pm thick foil is less than 1.5 mg/cm'.

X: Weight increase of 50 gm thick foil after heating in air at 1150°C for 144 hours is t, 5 mg/cm' or more.

Peeling resistance: No peeling of oxide scale after 200 repetitions of heating a 0:50 JLm thick foil in the air at 1150°C for 30 minutes and then rapidly cooling it for 12 minutes.

, X: 50 μm thick foil with peeling of oxide scale when repeated 200 times, each time consisting of heating at 1150° C. in air for 30 minutes and then quenching for 12 minutes.

In addition, in the above-mentioned Japanese Patent Application Laid-open No. 56-96726S+, an Al2O3 whisker with a length of I3tum was formed on the surface by a special heat treatment, and the steel of the present invention was also coated with a catalyst. When carried out, good Al2O3 whiskers are produced, so this method is also suitable for catalytic converters.

[Effect of Ill]

The steel of the present invention has excellent hot rolling properties, cold rolling properties, oxidation resistance, and peeling resistance of oxide scale, and is inexpensive.

Unexploded 1'' steel is suitable as stainless steel foil for automobile catalytic converters, and greatly contributes to automobile pollution control. Furthermore, the present invention is not limited to this, and can be used in other applications that are subject to severe oxidation.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the Charpy test results after annealing the hot rolled sheet, and FIG. 2 is a graph showing the oxidation resistance test results for 504m foil.

Claims (1)

[Claims] 1 C: 0.02% by weight or less Si: 1.5% by weight or less Cr: 13% by weight or more and 27% by weight or less Al: More than 3.5% by weight and less than 8% by weight Nd: 0. 03% by weight or more and 0.20% by weight or less,
Fe with excellent peeling resistance of oxide scale, characterized in that it does not contain Ce and the remainder consists of Fe and unavoidable impurities.
-Cr-Al-Nd alloy. 2 C: 0.02 wt% or less Si: 1.5 wt% or less Cr: 13 wt% or more and 27 wt% or less Al: More than 3.5 wt% but less than 8 wt% Nd: 0.03 wt% or more 0. 20% by weight or less Ti:C
Fe-Cr-Al- with excellent peeling resistance of oxide scale, characterized in that it contains 5 times or more of 0.10% by weight or less, does not contain Ce, and the remainder consists of Fe and unavoidable impurities. Nd-based alloy. 3 C: 0.02 wt% or less Si: 1.5 wt% or less Cr: 13 wt% or more and 27 wt% or less Al: More than 3.5 wt% but less than 8 wt% Nd: 0.03 wt% or more 0. Less than 20% by weight Ce, N
Lanthanoids excluding d: Contains a total of 0.001% by weight or more and 0.10% by weight or less, does not contain Ce, and has a total of 0.001% by weight or more and 0.10% by weight or less, and does not contain Ce.
An Fe-Cr-Al-Nd alloy having excellent peeling resistance of oxide scale, characterized in that the balance is 20% by weight or less of Fe and unavoidable impurities. 4 C: 0.02 wt% or less Si: 1.5 wt% or less Cr: 13 wt% or more and 27 wt% or less Al: More than 3.5 wt% but less than 8 wt% Nd: 0.03 wt% or more 0. Less than 20% by weight Ce, N
Lanthanoids excluding d: Contains 0.001% by weight or more in total Ti: 5 times or more of C weight% and 0.10% by weight or less, does not contain Ce, and has a total of 0.001% by weight or more of lanthanoids.
An Fe-Cr-Al-Nd alloy having excellent peeling resistance of oxide scale, characterized in that the remainder is Fe and unavoidable impurities at 20% by weight or less.