JPS58224148A - Chromium steel for member of exhaust system of automobile - Google Patents

Abstract

PURPOSE:To provide Cr steel which has resistance to high temp. oxidation equivalent to that of SUH 409 class steel, is highly resistance to corrosion by the condensate of the exhaust gas of an automobile and has excellent formability and weldability, by adding proper amts. of Si and Cu to Cr steel contg. Cr in a specific amt. and decreasing C, N, S as far as possible. CONSTITUTION:Titled Cr steel contains, by weight %, <=0.02 C, 1.5<Si<3.0, <=0.50 Mn, 5.0<Cr<10.0, 0.05-0.80 Cu, <0.003 S, <0.02 N, if necessary <=0.30 total of >=1 kinds among Ti, Nb, Zr and consists of the balance Fe. Here, C and N not only spoil formability and weldability but also deteriorate corrosion resistance by depositing carbide and nitride of Cr and are therefore contained in a lower rate preferably. If S is reduced as far as possible, the corrosion resistance against the condensate of the exhaust gas of an automobile is improved. Further, Ti, Nb, Zr improve the resistance to oxidation, the corrosion resistance against said condensate and formability additionally.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates primarily to chromium steel for use in automobile catalytic converters, mufflers and exhaust pipes, which has excellent corrosion resistance due to automobile exhaust gas condensate and high temperature oxidation resistance.

Automotive exhaust system equipment such as catalytic converters, mufflers, and exhaust pipes, which have been widely used as a measure to treat automobile exhaust gas in recent years, are required to have high-temperature oxidation resistance in the exhaust gas environment and corrosion resistance due to exhaust gas condensate.

Conventionally, ordinary steel or aluminized steel sheets have often been used for these purposes, but ordinary steel has insufficient oxidation resistance and corrosion resistance, and aluminized steel sheets cannot be processed for strength due to the nature of the equipment. Since welding is required, corrosion problems due to cracking and peeling of the aluminum layer in heavily machined parts,
Alternatively, corrosion problems often occur at the base metal spray part of the welding part.

On the other hand, stainless steel plates such as 8UH409 and 5US304 are sometimes used to overcome these drawbacks of aluminized steel plates, but they are not only excessive in quality but also expensive in terms of oxidation resistance and corrosion resistance due to exhaust gas condensate. It is.

Therefore, there is a desire to develop a material that is inexpensive and has a suitable quality that can withstand the environment in which it is used, but there is currently no material that can be produced on an industrial scale.

The present inventors have conducted various experiments with the aim of providing a chromium steel that is superior to aluminized and 'd4 plates and has high-temperature oxidation resistance and corrosion resistance due to automobile exhaust gas condensate that are equivalent to SU H409 class stainless steel. As a result, in chromium steel, which contains less Cr than stainless steel with a Cr content of more than 4% and less than 10%, by adding an appropriate amount of Sl and Cu, and at the same time reducing C, N, and S as much as possible, If desired, by adding T1, Nb and Zr, it exhibits high-temperature oxidation resistance equivalent to 5UH409 and corrosion resistance due to automobile exhaust condensate, and has excellent formability and weldability. home.

Next, the reasons for limiting the composition of the steel of the present invention will be described.

It is well known that addition of Sl alone can improve oxidation resistance at high temperatures, but its coexistence with Cu significantly improves corrosion resistance, especially against automobile exhaust gas condensate. However, if it is less than 15, the effect is insufficient, and if it is more than 5.04, it not only hardens the steel and reduces cold workability, but also impairs weldability.
It was set to be more than 1.5% and less than 5.0%.

Mn Fi is an element necessary for the deoxidation reaction in the steelmaking process, but if it exceeds 0.50%, the antioxidation property is impaired, so 050
Section below.

Or is an essential element for improving high-temperature oxidation resistance and corrosion resistance due to automobile exhaust gas condensate. To achieve this, it is necessary to add more than 5.0 Cr, but the improvement effect will not be saturated even if 10.0% or more is added, and the workability will also decrease, so 5.0 Cr should be added. exceeding and less than 10.0%
I did 1.

It has been found that although Cu alone improves the acid resistance of steel, its coexistence with Si significantly improves the corrosion resistance, especially against automobile exhaust gas condensate. That is, 0.054
When the above amount of Cu is added, the corrosion resistance is significantly improved due to the combined effect with Si, and even if it is added in excess of 0.80%, the improvement effect will not be saturated, but it will inhibit hot workability.

Furthermore, since addition of an appropriate amount of Cu also improves cold workability, the Cu content is set to 0.05 to 0.0, so J.

It has been confirmed that corrosion resistance due to automobile exhaust gas condensate can be improved by reducing S as much as possible in the normal steelmaking process or in combination with outside furnace refining.
o O was 3% or less.

C and N not only impair formability and weldability (,Cr
It is desirable that the content of C,
Both N should be 0.02% or less.

Furthermore, by adding one or more of Ti, Nb, and Zr as necessary, oxidation resistance, corrosion resistance due to automobile exhaust gas condensate, and moldability are further improved. However, if the total amount of addition exceeds 0.30 mm, not only will the effect of improving these properties be saturated, but also the weldability will deteriorate, so the upper limit of the total amount of addition is set at 0.60 mm.

Examples of the present invention are shown below.

Table 1 shows the chemical components of the invention steel and comparative steel. These steel plates 1 were melted, hot forged, cold rolled, annealed, and pickled using normal manufacturing processes to obtain cold rolled steel plates with a thickness of 1.2 m, and the required performance was compared. For comparison, the cold-rolled steel plates in Table 1 were processed into test pieces of 30 x 307 rIm, and then wet-polished with No. 600, and the corrosion resistance due to automobile exhaust gas condensate was evaluated under the test conditions shown in Table 2. Ta.

Table 3 shows the results by measuring the weight change after the test.

Table 3 (Test results) As is clear from the table above, the steel of the present invention is superior to comparative steel, ordinary steel,
It has better corrosion resistance from automobile exhaust gas condensate than aluminized steel, and has 8UH40? It can be seen that it exhibits properties equivalent to stainless steel.

Table 6 also shows that at a temperature level of 800°C, which is the assumed usage environment for the steel of the present invention, 200°C
The properties of the oxide generated on the surface of the test piece after holding for a certain period of time are shown. This result shows that the steel of the present invention has sufficient high-temperature oxidation resistance in an automobile exhaust environment.

As mentioned above, the steel of the present invention not only has excellent corrosion resistance and high-temperature oxidation resistance in an automobile exhaust environment, but also has good formability and weldability, so it can be used for various combustion equipment, including surrounding parts of automobile exhaust systems. Acid can be used in a wide range of applications, such as incinerator parts, as a material that is cheaper and has higher performance than stainless steel.

Claims (1)

[Claims] 1. In weight%, C: 0.02% or less, st: t
More than s chi and less than 5.04, Mn: α50% or less, Cr:
More than 5.0% and less than 10.0%, Cu: 0. ．． 05
~0.80%, 8: B, 003 or less, N: 0.0
Chromium steel for automobile exhaust system parts, characterized in that it contains less than 2% Fe, with the remainder consisting of Fe and unavoidable impurities. 2. In weight%, C: 0.02% or less, Si: more than TS but less than 5.0%, Mn: 0.50% or less, Cr: 5.
More than 0 and less than 10.04, Cu: 0.05 to 0.80
俤, S: 09, 03 or less, N: 0.02 or less, and further contains one or more of T1, Nb, and Zr in a total of 0.30% or less, and the balance is Fe and unavoidable elements. A chromium steel for automobile exhaust system parts that is characterized by its resistance to impurities.