JPS61106793A - Steel material for fuel exhaust pipe system having superior corrosion and heat resistances - Google Patents

Abstract

PURPOSE:To improve the corrosion and heat resistances of a Cr steel material for a fuel exhaust pipe system by forming a diffusion coated layer of Ni, Co or an Ni-Co alloy and a plated layer of Ni, Co or an Ni-Co alloy on the steel material contg. optionally Ti, Nb, Zr or V. CONSTITUTION:The diffusion coated layer of Ni, Co or an Ni-Co alloy and a plated layer of Ni, Co or an Ni-Co alloy are formed on a Cr stainless steel material consisting of, by weight, <=0.02% C, 3-20% Cr, 0.005-0.10% acid-sol. Al and the balance Fe with inevitable impurities or further contg. 0.03-0.5% one or more among Ti, Nb, Zr and V. The plated layer may further contain one or more among P, Mo and Cr. By this surface treatment, corrosion from the defective part of the plated layer is reduced, and the corrosion and heat resistances of the steel material are improved.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to steel materials used in exhaust systems after fuel combustion in automobiles, motorcycles, etc. The invention relates to a steel material that has excellent corrosion resistance and heat resistance.

Ru.

(Prior art) Cr-containing stainless steel (aluminum plated In recent years, there have been changes in the fuels used (for example, the use of alcohol or alcohol-containing fuels instead of gasoline), the use of catalytic converters due to exhaust gas regulations, etc. Due to qualitative changes in exhaust gas or exhaust gas condensate, it has become increasingly difficult to ensure a sufficient corrosion-resistant life with the above-mentioned materials. Corrosion from the outside of the exhaust system due to corrosion (this is a situation in which it is desirable to have all the same corrosion resistance).

(Object of the invention) The present invention has been made in response to these circumstances.
This was done for the purpose of improving the corrosion resistance and thermal properties of Cr-based stainless steel materials, reducing the occurrence of red rust in the exhaust system 1 (after fuel combustion of automobiles or motorcycles, etc.), and extending the corrosion-resistant life. It was made for the purpose of being a friend.

(Structure of the Invention) Therefore, the gist of the present invention is as follows: (1) C by weight: 0.02% or less Cr: 3 to 20% Acid-soluble Az: o, oos to 0.10% Steel material with the remainder being unavoidable impurities and iron.
One or more of Ti, Nb, Zr, and V Total 0
．． 03~0.5% addition steel material f, Ni, Co
, Ni-Co alloy plated coating layer or this
, Mo.

A steel material for fuel exhaust pipe systems that has corrosion resistance and heat resistance and is coated with a plating layer of an alloy containing one or more types of Cr.

(2) C: 0.02% by weight or less Cr: 3-20% acid soluble, 'u: Q, Q Q 5-0.10% remaining unavoidable impurities and iron-free steel or steel material Ti
, Nb, Zr, V01 or 2 or more)0
．． Steel materials with 0.03 to 0.5% addition [in contrast, Ni, Co
, a diffusion coating layer of Ni-Co alloy, and a plating coating layer of NiHCo, Ni-Co alloy on the surface of the diffusion coating layer, or an alloy containing one or more of P, Mo, and Cr. This is a steel cable material for fuel exhaust pipe systems that has a plating coating layer and has excellent corrosion resistance and heat resistance.

The present invention will be explained in detail below.

Steel sheets containing 13% or more of Cr and 5% or more of special E are free from ammonium, ammonium nitrate, ammonium sulfate, or aldehydes (for example, formaldehyde, etc.) contained in fuel exhaust gas or their condensates. It exhibits relatively good corrosion resistance, and also has relatively good resistance to oxidation when heated to high temperatures, that is, heat resistance.

However, these exhaust gases or the condensate of the exhaust gas contain Ct"" ions in the form of ammonium chloride, etc., but since the content of these Ct- ions is large, they condense at high concentrations. Coexistence with moisture and water vapor can cause red rust to occur, especially in the dark spots. Mari, °
The parts to which these Ct~ ions condense and adhere tend to undergo total oxidation even when heated.

These areas where red rust has formed and adhered are due to crevice corrosion due to the formation of oxygen concentration batteries with areas where red rust has not formed.
The underside with red rust is particularly susceptible to perforation corrosion in the presence of Ct- ions, which significantly reduces the corrosion resistance life of the fuel exhaust pipe system.

In addition, in a corrosive environment where there is salt sprayed to prevent roads from freezing (during this winter), there is concern that the corrosion resistance life will be shortened due to perforation corrosion from the outside of the fuel exhaust pipe system.

The tendency of these above-mentioned corrosion problems is particularly significant when the Cr content is less than 3%.

Increasing the Cr content alleviates the above tendency, but it is not necessarily sufficient, and when the Cr content exceeds 20%, workability and weldability deteriorate, making it difficult to weld when manufacturing an exhaust pipe. In addition, when installing an exhaust pipe, the workability of the steel pipe (%f, pipe expandability and bending workability), and the installation of a partition plate inside the exhaust pipe may pose problems such as spot welding. f Rub.

Therefore, in the present invention, the Cr content is in the range of 3 to 20%, preferably 5 to 15%, judging from both the amount of red rust produced when the above Ct- ions are concentrated and condensed, workability, and weldability. A Cr-containing steel plate is used.

As mentioned above, from the point of view of corrosion resistance, Cr has the greatest effect, but from the perspective of targeting materials for automobiles and other fuel exhaust pipe systems, the steel composition of C and acid-soluble M ( Even if the content is limited, increasing the content of O C precipitates chromium carbide and completely deteriorates the mechanical properties and corrosion resistance of the steel. Therefore, the C content is preferably 0.02% or less. is preferably 0.005 inch or less.

At, acid-soluble AA (sol, Al
) If the amount is less than 0.005%, the oxygen gas f
It is difficult to prevent the generation of bubbles, which significantly increases the incidence of surface defects in steel and becomes the starting point for deterioration of the corrosion resistance of steel materials. In addition, excess acid-soluble At exceeding 0.10% is
At-based oxide't-Steel surface (spotted here to improve corrosion resistance [(
At the starting point of deterioration or on the surface of the diffusion treatment layer or plated coating layer applied to the steel sheet, non-plating, pinholes, etc. occur, impairing the integrity of the diffusion coating layer or plated coating layer surface.

Steel with the above composition has excellent corrosion resistance. The present invention is based on the above-mentioned steel composition (T of 0.03 to 0.50
By containing one or more of i, Nb, Zr, and V f to combine with C in the steel, the Cr contained in the steel can be made effective by a total of 9, and furthermore excellent formability and corrosion resistance can be completely improved. It is.

If the content of steel components such as Ti and Nb is less than 0.03%, the effect of preventing the precipitation of chromium carbide and improving formability and corrosion resistance a is small;
．． If it exceeds 50%, the effect becomes saturated) and becomes uneconomical, and the precipitation of these components tends to harden the material and deteriorate moldability. Especially, preferably the content of these elements is 0.075 to 0.2
The range is 0%.

In the present invention, since such a steel plate is used as it is as a steel material for a fuel exhaust pipe system, it is insufficient in terms of corrosion resistance. Therefore, these steel plates contain Ni, 'Co,
Ni-Co alloy plated coating layer or P
, Mo, Cr, or Ni, Co, Ni-C
o alloy diffusion coating layer and the surface of the coating layer include Ni, Co,
Ni-Co alloy plating coating layer or P on these
A plating coating layer of an alloy containing one or more of Mo, Cr, Mo, and Cr is provided.

In other words, due to the influence of moisture, Ct- ions, etc. contained in the fuel exhaust gas or condensate when the steel sheet is used)
Corrosion resistance is not necessarily sufficient, and it is naturally necessary to provide excellent corrosion resistance with a long corrosion resistance life even against external corrosion of the fuel exhaust pipe system.

Therefore, from these viewpoints, the present invention has excellent corrosion resistance against ammonium, ammonium nitrate, ammonium sulfate, aldehydes, C6- ions, moisture (steam), etc., and has excellent corrosion resistance against E when heated to high temperatures. Also, a plated coating layer or a diffusion coating layer of a metal or alloy that has a small amount of oxide generation and excellent heat resistance and a plated coating layer FCR-containing steel sheet (this provides excellent heat resistance)
It is important to ensure corrosion resistance and heat resistance. (1) The metal or alloy having the above-mentioned corrosion resistance and heat resistance includes Ni, Co, Ni-Co alloy, or P.

The plating coating layer selected from alloys containing one or more of Mo and Cr ensures corrosion resistance and heat resistance, and prevents defects in the coating layer (such as pinholes or during molding). The steel substrate has relatively excellent, although not necessarily sufficient, corrosion resistance against corrosion from the eaves, etc. that rub against the base steel, and oxidation during high temperature heating.

By utilizing heat resistance, it is possible to ensure excellent corrosion resistance and 1Fit heat resistance.

Furthermore, in the present invention, the above-mentioned corrosion resistance, heat resistance, and the above-mentioned effects are further improved. Ni, Co that easily generates a diffusion layer
, after the full diffusion coating layer of Ni-Co alloy is applied, Ni
, Co, Ni-Co alloy or these (P, Mo
.

A plated coating layer of an alloy containing one or more types of Cr is provided.

That is, by providing this diffusion coating layer G on the surface of the FCR-containing steel plate, the corrosion resistance of the Cr-containing steel plate surface can be improved.

As the heat resistance is the same as above, the potential difference in the corrosive environment f between the outermost plating layer and the diffusion coating layer becomes closer (thus, defects (pinholes, etc.) in the plating layer) Even if scratches that reach the diffusion coating layer are formed during molding, etc., corrosion from the defective parts of the plating layer in ships with corrosive environments will be significantly reduced. Similarly, high temperature oxidation (this is greatly reduced by the diffusion layer).

Therefore, these treatments improve the corrosion resistance and heat resistance of the fuel exhaust pipe system, and can be expected to extend its corrosion-resistant life.

Therefore, the coating method or coating conditions of the plating coating layer or the diffusion coating layer provided in the present invention are not particularly specified, but the surface of the Cr-containing steel plate may be cleaned by degreasing, pickling, etc. After the activation process 1, for example, the activation process is carried out under the following conditions.

(1) Ni plating; Current density: 1 to 150 A/dR (2) Co plating; Current density: 1 to 150 A/dR (3) Ni-Co alloy plating (e.g. Ni-50%
In the case of CO composition] Current density: 1 to 150 A/d- (4) Ni-P alloy plating; Current density: 5 to 75 A/d7r? (5) Ni-Cr alloy plating; (nickel sulfate 260 g/current density = 5 to 60 A/d) (6) Co-Mo alloy plating; current density = 5 to 100 k/(1,1 (7) Ni -Co-P alloy plating; Current density: 5 to 80 A/d.
- Applied to a thickness of 1 to 10μ, particularly preferably 0.5 to 5μ
μ thickness is desirable. This is because if the thickness is less than 0.1μ, the uniform coverage of the ore coating layer is extremely insufficient, and a large amount of pinholes are generated, and the effect of improving corrosion resistance or heat resistance cannot be obtained by applying a coating layer. This is because there are cases where it cannot be obtained. Furthermore, if the thickness of the coating layer exceeds 10 μm, the effect of improving corrosion resistance will be saturated (and the adhesion and moldability of the coating layer will tend to deteriorate), so it is better to avoid this as much as possible.

Regarding the alloy composition of the coating layer, the Ni-Co alloy composition when combined with Ni and Cot has almost the same excellent corrosion resistance and heat resistance as each metal.
Alloy compositions over a full range of compositions may be used.

On the other hand, in the case of alloying one or more of P, Mo, and Cr containing Ni, Co, and Ni--Co alloys, preferred amounts of each alloy are selected for the following reasons. That is, when P and Mo are alloyed in an amount exceeding 40%, or when they are alloyed with Cr in an amount exceeding 40%, the coating layer becomes hard, and the adhesion and moldability of the coating layer decrease. It also tends to deteriorate the electrolytic efficiency in electroplating operations. Therefore, P, Mo
, P, M when an alloyed coating layer of Cr is provided.
It is preferable that the content of Cr is used in an amount of 40% or less, preferably 20% or less, and Cr is used in a content of 15% or less, preferably 15% or less. Further, when two or more of these are alloyed, it is preferable that the total amount of the alloying elements to be combined be selected within the maximum allowable amount of the alloying elements used. That is, p + Mo: 40%
Below, P + Cr: 30% or less, Mo + Cr: 3
When alloyed within the range of 0% or less, P + Mo + Cr: 3Q% or less, the corrosion resistance of the coating layer improves,
Corrosion resistance life is extended.

In addition, in the present invention, a Crf-containing steel plate is coated with a plating layer by electroplating as described above (a method of providing the same corrosion resistance and heat resistance). A diffusion coating layer is easily generated between the coating layer and the steel plate by heating diffusion treatment, N”・°°・ゝ”
−°°0°″″″′″′. ”“Rn6nh.

□ This is the corrosion resistance of the Cr-containing steel plate surface as described above.

In addition to improving heat resistance, the potential difference in the corrosive environment f between the outermost plated coating layer and the diffusion coating layer becomes closer, resulting in defects (pinholes, etc.) in the plated coating layer,
Even if flaws are generated on the diffusion coating layer R during molding, corrosion from the defective parts of the plating layer in a corrosive environment is significantly reduced, and high-temperature oxidation from the defective parts can be significantly reduced. Similarly, E and F are significantly reduced by the diffusion layer, thereby further improving the corrosion resistance and heat resistance of the fuel exhaust pipe system and extending its corrosion-resistant life. The method of providing this diffusion coating layer, the diffusion treatment conditions, etc. are not particularly specified, and may be, for example, Ni, Co, etc. as described above.

The diffusion treatment may be performed after providing an electroplated layer of Ni--Co or the like, or applying an aqueous solution containing Ni and Co ions by the following method. For example, (1) io
o gyt nickel chloride - 0.5 g/l surfactant aqueous solution (2) 75 g/l cobalt chloride - 1 g/l surfactant + *rim''
(3) 60 g/z nickel citrate
After immersing the steel plate in a surfactant-based water bath solution of 2 g/l (copal saccharide), the coating may be adjusted by a high-pressure gas wiping method, and then a diffusion treatment may be performed after drying. .

Thus, Ni and Co are subjected to these diffusion treatments.

The thickness of the Ni-Co alloy is preferably 0.01 μm or more, preferably 0.1 μm or more. This 1-1f,,0.01
If the thickness is less than μ, the uniform coverage of these coating layers will not be sufficient, and an extremely large amount of pinholes will be generated, and the pinholes will remain as they are even after the 'j'c diffusion process. The thickness of the diffusion layer is also insufficient, and the potential proximity effect, corrosion resistance improvement effect, etc. that are the objectives of the present invention tend not to be obtained. At the same time, the above metal diffusion treatment is carried out in a reducing or non-oxidizing atmosphere;
Cr-containing steel sheets are relatively easily oxidized due to the influence of moisture, oxygen, etc. that are contained in small amounts, and Cr
If oxides of
The thickness is preferably 0.01 μm or more.

Next, the first diffusion treatment is carried out using a continuous annealing furnace or a batch type box-type annealing furnace in a reducing atmosphere or non-oxidizing atmosphere, and the temperature is 600 to 1000°C, preferably 650°C.
It is carried out at a temperature of ~950°C. At temperatures below 600°C, the diffusion treatment is sufficiently carried out; however, it takes a long time and is not suitable for industrial production, and at temperatures above 1000°C, the resulting product cannot be molded. This is not preferable because roughness (so-called ridging phenomenon) occurs due to the coarsening of crystal grains.

Depending on the heating method and control method used to ensure the soaking temperature of the annealing furnace used, the diffusion treatment time may vary from several tens of seconds to several hundred seconds for continuous annealing, and from several hours to several hours for batch annealing. The C
Using an r-containing steel plate, a continuous annealing furnace is used to perform the diffusion treatment for both the annealing and diffusion treatment of the steel plate. By heating the diffusion coating for ~180 seconds, a diffusion coating layer is obtained which achieves the object of the present invention.

Then, after the diffusion treatment and cooling in the above atmosphere, in the present invention, the member remains in the surface condition E. Therefore, after specific activation treatment using an acid solution such as HCl, H, 80, etc., the Ni , Co, Ni-Co alloy plating coating layer, or an alloy plating coating layer containing one or more of P, Mo, and Cr.

First, a chromate-based treatment may be applied to the surface of the coating layer of the product of the present invention, targeting the outer surface of the materials of these exhaust pipe systems, for the same purposes as corrosion resistance and coating performance.

As this chromate-based treatment, Cry.

Water bath solution or Cr0J anion-added Cry, -
80, -", Cry, -PO,-", Cr
This is carried out by z-immersion treatment, electrolytic treatment, etc. using a y3-F-based bath. In this case, the product of the present invention has excellent corrosion resistance and is composed of a coating layer with stable chemical reactivity on the surface, so Cr03f anions are contained.
y3- So, , Cathode electrolytic treatment using Cry3-F-based bath 10 to 150 mg of Cr deposited from F
/lr? (Single-sided application)] It is preferable that the applied product has an excellent friend effect (improved corrosion resistance and paintability).

As described above, the method of the present invention can be used as a material for exhaust pipe systems after fuel combustion for automobiles, motorcycles, etc.
The synergistic effect of the steel composition of the present invention and the coating layer makes it possible to provide a product with excellent corrosion resistance and heat resistance.

In addition, although the steel components of the present invention are defined as described above, there are impurities in these steels from converters, etc.
Even if Ni, Mo, etc. are contained in amounts of 1% or less and 0.3% or less, respectively, the effect on performance 2 is small.

Examples of the present invention will be described below.

Table 1 Using a steel sheet with a steel composition in which the Cr content was mainly changed, the present invention In addition, Table 2 shows the results of the performance evaluation of the products of the present invention, which are coated with a plated coating layer or a plated coating layer after diffusion treatment. We conducted a comparative evaluation test targeting system corrosion.

■Evaluation targeting the inside of the exhaust system The product of the present invention was tested to prevent corrosion inside the exhaust pipe.
Each piece was bent to a length of 5.4 m, and the following evaluation tests were conducted on each piece, and the corrosion resistance of the relative f was evaluated based on the measurement results such as the occurrence of red rust, corrosion loss, and plate thickness reduction at the rusted part.

(A) (Ammonium sulfate 1.5g/ammonium mononitrate 1.5g/
5g/z - ammonium chloride 1.5g/l) water bath solution 90
Heat the product at ℃G and immerse it in these solutions for 60 days (CB) Place the product in the gas phase of the above solution, heat the solution (90℃) for 24 hours, and leave it at room temperature for 24 hours.
- 200 cycles of corrosion test (,C) as one cycle
After heating the bent product at 750°C in the air for 240 hours, the test (A) was carried out (D).The same test was carried out after heating at 750°C in the air for 240 hours (B).
(E) in Table 2 for test materials that were subjected to the same bending process as in ■ for corrosion of the external surface of the exhaust pipe.

The heating and salt spray tests shown in CF) were conducted, and the relative corrosion resistance was evaluated based on the occurrence of red rust, the decrease in plate thickness at the lower part of the rust-adhered area, etc.

■Paint adhesion evaluation test After coating with a heat-resistant paint consisting of Zn powder, At powder pigment, and water glass vehicle, and heating at 650°C for 150 hours, a base material test was conducted and the paint film was peeled off. Based on the situation, the paint adhesion was evaluated as 7'C (F in Table 2).

■Workability After the product of the present invention was made into a steel pipe using high-frequency induction electric welding, its elongation, expansion ratio, and flattening ratio were measured, and these were comprehensively evaluated to evaluate its workability (Table 2). q).

Claims (2)

[Claims] (1) C in weight%: 0.02% or less Cr: 3-20% Acid-soluble Al: 0.005-0.10% The balance is unavoidable impurities and steel made of iron or T
i, Nb, Zr, V or more from 0.03 to 0
．． It is characterized by applying a plating coating layer of Ni, Co, or Ni-Co alloy, or a plating coating layer of an alloy containing one or more of P, Mo, and Cr to the steel material containing 5% additive. A steel material for fuel exhaust pipe systems with excellent corrosion resistance and heat resistance. (2) C in weight%: 0.02% or less Cr: 3-20% Acid-soluble Al: 0.005-0.10% The balance is unavoidable impurities and steel made of iron or T
i, Nb, Zr, V or more from 0.03 to 0
．． Ni, Co, Ni-Co alloy diffusion coating layer and Ni, Co, Ni on the surface of the diffusion coating layer for steel material with 5% addition.
-Co alloy plated coating layer or P, Mo,
A steel material for a fuel exhaust pipe system having excellent corrosion resistance and heat resistance, characterized by being coated with a plating layer of an alloy containing one or more types of Cr.