JPH06330226A - Multiple-layered steel excellent in high temperature corrosion resistance and its production - Google Patents

Abstract

PURPOSE:To obtain a multiple-layered steel tube excellent in high temp. corrosion resistance by forming a coating layer of austenitic stainless steel having a specified compsn. contg., high Ni on the internal tube of a steel tube for a boiler through a metal diffusing layer having a specified thickness. CONSTITUTION:On a steel tube for a boiler as an internal layer, a coating layer of austenitic stainless steel is formed as an external layer to obtain the multiple-layered steel tube. At this time, the coating layer is obtd. by subjecting the powder of steel contg., by weight, <=0.08% C, 0.3 to 2.0% Mn, 18 to 27% Cr, 17 to 50% Ni, 0.5 to 3.0% Mo, 0.03 to 0.3% Ti, 0.05 to 0.6% Nb, 0.001 to 0.01% B, <=0.04% P <=0.005% S and 0.02 to 0.3% N and furthermore contg. one or more kinds of 0.5 to 9.0% Al and 0.7 to 7.0% Si and one or more kinds among 0.0005 to 0.05% Ca, 0.001 to 0.1% Y, 0.001 to 0.2% La and 0.001 to 0.2% Ce to HIP treatment and hot working, and the space of the external layer and internal layer is provided with an intermediate layer constituted of a metal diffusing layer of >=5mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has excellent high temperature corrosion resistance to chlorides and hydrogen chloride (HCl) gas in waste combustion environment, etc. and has good hot workability during manufacturing. The present invention relates to a multi-layer steel pipe and a method for manufacturing the same.

[0002]

2. Description of the Related Art Among general wastes and industrial wastes, an incinerator having excellent high temperature corrosion characteristics against high concentration chloride and HCl gas generated by combustion of waste plastics and automobile shredder dust. And there was no existing steel material for combustion boiler. Therefore, the wastes have a high calorific value, but they are sorted and collected as non-combustible / non-combustible substances and are mainly landfilled. In addition, when it is mixed with general waste and burned in the boiler without being separated and collected, the steam conditions of the boiler are pressure 294.2 N / cm ² and temperature 350 ° C or less due to severe corrosive environmental conditions. It is not used as a low-pollution, efficient and low-pollution fuel source.

On the other hand, the present applicant has filed Japanese Patent Application No. 3-16
No. 5946 and Japanese Patent Application No. 5-39040, A
1; 0.5 to 6.0%, Si; 0.7 to 3.0%, and Ni; 17 to 50%, and austenitic stainless steel excellent in high temperature corrosion resistance. Is proposed. However, if the contents of Al and Si exceed 6.0% and 3.0%, respectively, with the aim of further improving the high-temperature corrosion resistance, there arises a problem that hot work cracking occurs during manufacturing. . Furthermore, when the Al content and the Si content in the melting method exceed 6.0% and 3.0%, respectively, component segregation occurs during solidification, and a specimen is taken from a minor crack after hot working. When the high-temperature corrosion resistance was evaluated, there was a problem that the high-temperature corrosion resistance deteriorated as compared with a material having Al of 6.0% or less and Si of 3.0% or less. From the above points, the upper limits of the Al amount and the Si amount have to be limited to 6.0% and 3.0%, respectively.

On the other hand, regarding the method for producing a multi-layer material or its hot working material by the HIP method, the applicant of the present invention has disclosed in Japanese Unexamined Patent Publication No. 64-202 and Japanese Patent Application No. 3-95136 for hot working. It is proposed that at least one of the multilayer materials is manufactured by the powder-HIP method and then hot-worked and stretched, or if necessary, subsequently heat-treated, cold-worked + heat-treated. However, with respect to the Fe-based alloy containing high Al and Si as described above, it is extremely important to secure workability during hot working, and in particular, the presence of a metal diffusion layer as an intermediate layer between the outer layer and the inner layer is essential. .

[0005]

From the viewpoint of solving the above-mentioned problems, the present invention has excellent high-temperature corrosion resistance to chloride and HCl gas in a waste combustion environment and the like, and An object of the present invention is to provide a multi-layer steel pipe having good hot workability during production, a multi-layer steel material, and a method for producing the same.

[0006]

The subject matter of the present invention is as follows. (1) The outer layer, in% by weight, is C: 0.08% or less,
Mn; 0.3-2.0%, Cr; 18-27%, N
i; 17 to 50%, Mo; 0.5 to 3.0%, T
i; 0.03 to 0.3%, Nb; 0.05 to 0.6
%, B; 0.001-0.01%, P; 0.0
4% or less, S; 0.005% or less, N; 0.0
2 to 0.3% and further Al; 0.5 to 9.0
%, Si; 0.7 to 7.0%, one or more kinds, and
Ca; 0.0005 to 0.05%, Y; 0.00
1-0.2%, La; 0.001-0.2%, Ce;
Coating formed by hot isostatic pressing (HIP) treatment and hot working of an austenitic stainless steel powder containing at least one of 0.001 to 0.2% and the balance being Fe and unavoidable impurities. Layer, an inner layer is a steel pipe for a boiler, and an intermediate layer consisting of a metal diffusion layer of 5 μm or more formed by HIP-hot working is provided between the outer layer and the inner layer, which is excellent in high temperature corrosion resistance Steel pipe.

(2) The outer layer is a coating layer formed by HIP-treating the powder of austenitic stainless steel according to the preceding paragraph 1, the inner layer is boiler steel, and the space between the outer layer and the inner layer is 10 μm or more formed by HIP treatment. A material for multi-layer steel material having excellent high-temperature corrosion resistance characterized by having an intermediate layer composed of a metal diffusion layer. (3) The multi-layer steel pipe or multi-layer having excellent high-temperature corrosion resistance according to the above 1 or 2, wherein the HIP treatment conditions are a temperature of 1050 to 1240 ° C., a pressure of 29 MPa or more, and a holding time of 0.5 hour or more. Manufacturing method for steel materials.

(4) The high temperature resistance according to item 1 above, which is characterized in that the raw material for a multi-layer steel product according to item 2 above produced by HIP treatment under the conditions described in item 3 above is produced by drawing by hot working. A method for producing a multi-layer steel pipe having excellent corrosion characteristics. (5) The high-temperature corrosion resistance according to the preceding clause 1, characterized in that the raw material for a multi-layer steel material according to the preceding clause 2 produced by HIP treatment under the conditions of the preceding clause 3 is drawn by hot working and then further heat-treated. A method for producing a multi-layer steel pipe with excellent characteristics.

(6) The raw material for a multi-layer steel product according to item 2 produced by HIP treatment under the conditions described in item 3 above is drawn by hot working, and then subjected to cold working and heat treatment at least once. A method for producing a multi-layer steel pipe excellent in high-temperature corrosion resistance as set forth in the preceding paragraph 1, which is characterized. (7) The multi-layer steel material according to item 2 produced by HIP treatment under the conditions described in item 3 above is drawn by hot working, and then further heat treated, and then cold worked and heat treated once or more. The method for producing a multi-layer steel pipe excellent in high-temperature corrosion resistance according to the above item 1, characterized in that.

[0010]

In the following, the reasons for limiting the components of the austenitic stainless steel for the outer layer will be described first. First, Ni, Al, and Si, and Ca, Y, and L are alloying elements that improve high-temperature corrosion characteristics with respect to chloride and HCl gas.
It is effective to add a and Ce in combination.

The hot corrosion depth decreases with increasing Ni content (FIG. 1). It is considered that this is because the Ni-rich layer formed in the scale has protection against chloride and HCl gas. The effect is not sufficient if less than 17%, so the lower limit was made 17%. The upper limit of Ni was set to 50% because the hot workability deteriorates as the Ni content increases and the cost increases as the Ni content increases.
Therefore, the amount of Ni is limited to 17 to 50%.

The addition of Al and Si reduces the hot corrosion depth (FIG. 2). It is considered that this is because protective scales of Al ₂ O ₃ and SiO ₂ series are formed in the scale. The effect is Al; less than 0.5%,
Since Si is less than 0.7%, the lower limit of Al is 0.5% and the lower limit of Si is 0.7%. In addition, Al
Since the hot workability decreases as the amount of Si and Si increases,
In order to secure both properties, it is necessary to set the Al content to 6.0% or less and the Si content to 3.0% or less in a general melting or casting material, but use the outer layer powder according to claim 1. The multi-layer steel material according to claim 2 under the H condition of claim 3.
In the case of manufacturing by the IP treatment, it becomes possible to extend the upper limits to 9.0% in the amount of Al and 7.0% in the amount of Si by improving the hot workability. Furthermore, the outer layer of the multi-layer steel pipe after hot working when the material for hot working by hot isostatic pressing of the powder for the outer layer is melted,
Compared to the case of using a cast material, the composition distribution is more homogenized and melts,
When a cast material is used, the amount of Al is 6.0% and the amount of Si is 3.
No deterioration of the high-temperature corrosion resistance due to the segregation of the constituents observed in the materials exceeding 0% is observed. For these reasons, the amount of Al is 0.5 to 9.0% and the amount of Si is 0.7.
It was set to 7.0%.

Similar effects can be obtained by adding Al or Si alone or in combination. However, from the viewpoint of ensuring hot workability, the upper limit in the case of composite addition is 9.0% in total of Al and Si.
Is desirable. When one or more of Ca, Y, La and Ce are added alone or in combination with Al and Si, the high temperature corrosion depth is reduced. By adding Al and Si, as described above, Al ₂ O ₃ and SiO ₂ -based protective scales are formed in the scale, respectively, to improve the protection against chloride and HCl gas. If at least one of Ce and Ce is added, the scale becomes dense and the high temperature corrosion resistance is improved. Further, these elements have a deoxidizing / desulfurizing action and improve the hot workability by reducing the grain boundary segregation of O and S. These effects are Ca; 0.0
Less than 005, Y; less than 0.001%, La; 0.001
%, Ce: Since less than 0.001% is not sufficient,
Lower limit of Ca is 0.0005%, lower limit of Y is 0.001
%, The lower limit of La is 0.001%, the lower limit of Ce is 0.00
It was set to 1%. If the Ca content exceeds 0.05% and the Y, La, and Ce contents exceed 0.2%, respectively, the cleanliness of the steel decreases, and the hot workability and creep rupture strength decrease, so both properties are secured. In order to do this, the amount of Ca should be 0.05% or less,
It is necessary to set the Y content to 0.2% or less, the La content to 0.2% or less, and the Ce content to 0.2% or less. For these reasons, the amount of Ca is 0.0005 to 0.05%, the amount of Y is 0.001 to 0.2%, and the amount of La is 0.001 to 0.2%.
%, And the amount of Ce was 0.001-0.2%. Ca,
The above effects can be obtained by adding one or more of Y, La and Ce, but from the viewpoint of ensuring hot workability and creep rupture strength, the upper limit in the case of compound addition is C
A total of 0.2% of a, Y, La and Ce is desirable.

Next, components other than the above will be described. C
Generates a carbide such as Cr ₂₃ C _{6 at a} grain boundary by being combined with Cr during use in a high temperature environment of 400 ° C. or higher. Therefore, a Cr-deficient portion is generated in the vicinity of the grain boundary, which hinders the formation of the Cr-containing protective coating layer and promotes high temperature oxidation and high temperature corrosion. Further, in order to prevent hot cracking during welding, it is necessary not to excessively increase the C content. From the above viewpoints, the upper limit of C is set to 0.08%.

Mn is necessary for sufficient deoxidation to obtain a sound cast piece. It fixes the S component contained as an impurity in steel, prevents hot brittleness, weldability and hot workability. In order to improve the property, 0.3% or more is necessary. However, if too much is added, the oxidation resistance will be impaired, so the upper limit is 2.0%.
And Cr is an essential element for heat-resistant alloys because it improves the high-temperature corrosion resistance and high-temperature oxidation resistance against sulfates and the like. SUS347H (18Cr-12N
Since i-0.7Nb) requires a high temperature oxidation resistance equal to or higher than that of i-0.7Nb), the lower limit of the Cr content is set to 18%, which is the same as the Cr content of SUS347H. However, if the Cr content is large, σ embrittlement easily occurs due to heating for a long time, so the upper limit of the Cr content was set to 27%.

Mo improves the high temperature corrosion resistance in a high temperature chloride environment, so the lower limit was made 0.5%. However, Mo promotes the formation of the σ phase and tends to cause embrittlement during long-term use, so the upper limit of the addition amount was made 3.0%. Ti and Nb are charcoal and nitride forming elements, and suppress the large amount of precipitation of Cr ₂₃ C _{6 at} the grain boundaries.
Improves high temperature corrosion resistance and oxidation resistance. Further, it has an effect of improving the creep rupture strength, and the creep rupture strength becomes highest when the carbon and nitride are finely dispersed by the combined addition. For these effects, the precipitation amount of carbon and nitride is not sufficient if the Ti amount is less than 0.03% and the Nb amount is less than 0.05%, while the Ti amount is 0.3% and the Nb amount is Is 0.
When Ti and Nb are added in excess of 6%, carbon and nitride are aggregated and coarsened, and the effects on high temperature corrosion resistance and oxidation resistance are saturated, and also creep rupture strength is reduced. Considering the above points, the amount of Ti is 0.03 to 0.3% and the amount of Nb is 0.05 to 0.6%.

B is an element that further improves the hot workability, and is particularly effective when performing severe hot work. A B content of 0.001% or more is necessary to improve hot workability,
If the addition amount is large, the weldability and ductility deteriorate, so the upper limit of the addition amount was made 0.010%. If P is added in a large amount, it deteriorates the high temperature corrosion resistance, so P is preferably as low as possible, and the upper limit was made 0.04%.

Since S also segregates at the grain boundaries and deteriorates the high temperature corrosion resistance, the upper limit was made 0.005%. N is an element effective in high temperature intergranular corrosion resistance, and for this purpose, it is necessary to make it 0.02% or more. However, excessive addition of N deteriorates hot workability, so the upper limit was made 0.3%.

The boiler steel for the inner layer is made of carbon steel, depending on the operating environment (temperature, steam pressure) of the multi-layer steel pipe.
Low alloy steel, stainless steel, high Cr-high Ni steel, etc. can be selected. Specifically, STB410 (0.5
Mn steel), STBA24 (2.5Cr-1Mo steel), A
SME SA213 T91 (9Cr-1Mo steel),
SUS304HTB (19Cr-10Ni steel), SUS
347HTB (18Cr-12Ni-0.7Nb steel),
NCF800HTB (22Cr-33Ni system steel) and various high strength high Cr-high Ni steels can be mentioned.

Next, the outer layer of the multi-layer steel pipe of the present invention comprises Al:
0.5 to 9.0%, Si: 0.7 to 7.0%, at least one of which is contained, but a normal melting / casting material is used as the outer layer material of the multi-layer steel pipe or the material for the single layer pipe. And Al is 6.
If the composition range of 0% and Si exceeds 3.0%, bald defects or cracks occur during pipe forming and stretching by hot working. This problem was solved by using the powder-HIP as the outer layer of the above components.
This is a manufacturing method using a multi-layer material for hot working formed as a metal layer on the surface of the hot working material for inner layer by the method, and the method will be described below.

In the present invention, it is necessary to form a metal diffusion layer having a thickness of 10 μm or more as an intermediate layer between the outer layer and the inner layer of the multilayer material for hot working in order to secure hot workability. This is because when the thickness of the metal diffusion layer is less than 10 μm, the hot workability is insufficient and the outer layer and the inner layer are separated from each other during the hot working, or the outer layer is cracked or has a bald defect caused by the peeling. In addition, after hot working, or after further heat treatment or a combination of cold working and heat treatment, one or more times, or both, as an intermediate layer between the outer layer and the inner layer of the multi-layer steel pipe as a product pipe, 5 μm or more It is necessary to have a thickness of the metal diffusion layer. By this,
While ensuring the heat transfer properties of the outer and inner surfaces of boiler steel pipes,
It is possible to avoid the occurrence of interfacial peeling or the like due to the difference in thermal expansion between the outer and inner layers with respect to the temperature change during use. If the thickness of the metal diffusion layer between the outer layer and the inner layer of the multi-layer steel pipe is less than 5 μm, these characteristics cannot be secured.
m or more. The thickness of the metal diffusion layer, in relation to the thickness of the multilayer material for hot working, acts in the direction of becoming smaller according to the cross-sectional reduction rate in hot working and cold working,
It is also affected by the diffusion of outer and inner layer components due to heating during hot working and heat treatment. As a result, when a metal diffusion layer having a thickness of 10 μm or more is provided as an intermediate layer between the outer layer and the inner layer of the multilayer material for hot working, the metal diffusion layer as the intermediate layer between the outer layer and the inner layer of the multi-layer steel pipe of the product pipe. Can be secured to 5 μm or more.

In the production, first, the powder of the austenitic stainless steel for the outer layer of claim 1 is filled in the HIP capsule on the surface of the steel material for the boiler as the inner layer,
Then, after vacuum deaeration, it is sealed. Then, HIP treatment is performed to form the outer layer powder as a metal layer on the outer surface of the inner layer material. The powder is filled, the inside of the HIP capsule is evacuated when closed, and the HIP treatment is performed at a temperature of 1050 to
1240 ° C, pressure: 29 MPa or more, holding time: 0.5
By setting the condition to be longer than time, it is possible to form a metal diffusion layer of 10 μm or more as an intermediate layer between the outer layer and the inner layer without leaving pores in the outer layer, and to obtain sufficient bonding strength at the bonding interface. You can have it. The reason for setting the HIP treatment temperature to 1050 to 1240 ° C. is not practical because the holding time becomes several tens of hours when the HIP treatment temperature is less than 1050 ° C., and it is not practical when the HIP treatment temperature exceeds 1240 ° C. Is caused and the hot workability in the next step is deteriorated. The pressure is set to 29 MPa or more because a pressure of less than 29 MPa cannot form a metal diffusion layer of 10 μm or more as an intermediate layer between the outer layer and the inner layer, no matter how the HIP treatment temperature and the load holding time are selected, and This is because the outer powder layer is not sufficiently sintered and hot workability cannot be ensured. Furthermore, if the holding time is less than 0.5 hours, a metal diffusion layer of 10 μm or more cannot be formed as an intermediate layer between the outer layer and the inner layer, no matter how high the HIP treatment temperature is within the above temperature range, and the outer layer is not formed. This is because the sintering of the powder layer for use is insufficient and hot workability cannot be secured.

Next, the multi-layer material for hot working is pipe-formed and stretched by hot working such as hot extrusion or hot rolling. According to the above HIP treatment conditions, a multilayer material for hot working, which does not leave pores in the outer layer and has a metal bond at the interface between the outer and inner layers to give a sufficient bonding strength to the bonding interface, Hot working can be performed without causing bald marks and cracks. The purpose of hot working in the present invention is to produce a long multi-layer steel pipe, and it is necessary to select appropriate temperatures for both the outer layer and the inner layer when selecting the working temperature.

Next, in the present invention, the multi-layer steel pipe drawn by hot working is optionally heat treated in claim 5, and in claim 6 cold worked and heat treated at least once. In item 7, after the heat treatment, cold working and heat treatment 1
Apply more than once. Here, the purpose of cold working in the present invention is to
The main purpose is to accurately manufacture multi-layer steel pipes up to the size of the final product, and cold working methods such as cold drawing and cold rolling can be applied depending on the shape of the product.

The purpose of the heat treatment after hot working is to build up the material of the outer and inner layers as a product, or to further improve the cold workability in the cold working which is the next step. If the inner layer is a low alloy steel or 9Cr steel, it is necessary to soften the quenched structure after hot working.
If the inner layer is an austenitic stainless steel, it is possible to perform solution heat treatment for further improving the cold workability of the outer layer.

The heat treatment after the cold working is intended for softening, etc. if there is a cold working step in the subsequent step, and for the purpose of assembling outer / inner layer products after the final cold working. It is possible to perform solution heat treatment, normalization, tempering heat treatment, etc. depending on the steel type of the inner layer.

[0027]

EXAMPLES Next, examples of the present invention will be described more specifically. Table 1 shows the chemical composition of the powder which is the material for the outer layer of the present invention example, Table 2 shows the chemical composition of the steel for boiler which is the material for the inner layer used in the present invention example, and Table 3 shows the outer layer of the comparative example. The chemical composition of the powder, which is the raw material, is shown below. The boiler steel, which is the material for the inner layer, is manufactured by the melting / casting method.

Next, Table 4 shows the combination of the materials for the outer layer and the inner layer, the manufacturing method, and the hot workability and high temperature corrosion resistance of the outer layer which are the characteristics of the multi-layer steel pipe of the multi-layer steel pipe of the present invention. Further, Table 5 shows the combination of the materials for the outer layer and the inner layer, the manufacturing method, and the hot workability and high temperature corrosion resistance of the outer layer which are the characteristics of the multi-layer steel pipe of the multi-layer steel pipe of the comparative example. In the high temperature corrosion test, synthetic ash of 37% NaCl + 63% FeCl ₂ was applied to the surface of the test piece cut from the outer layer of the multi-layer steel pipe, and 0.2
% HCl + 0.5% SO ₂ + 5% O ₂ + 15% CO ₂ +
bal. The specimen was heated in N ₂ gas at 550 ° C. for 30 hours, and the corrosion depth of the vertical cross section of the test piece was measured. The hot workability was evaluated by the presence or absence of outer layer cracking during hot extrusion or hot rolling.

Inventive Examples A to U shown in Table 1 are the outer layer material powders used in claims 1 to 7, and Inner layer material examples AA to FF in the invention shown in Table 2 are claims 1 to 7. It is a standard steel for the inner layer material used in Item 7. Inventive Examples A to D shown in Table 1
Contains 20Cr-25 to 29Ni as a basic component and contains 1 to 9% of Al, and E to H contain 20 to 23Cr.
-25 to 29Ni as a basic component and 1 to 7% of Si.

Inventive Examples I to K are 24Cr-35N.
i is a basic component, Al is contained in 2 to 7%, and L is the same basic component and Si is contained in 3%. Next, M and N are 20Cr-25Ni as a basic component, Al and Si are 4% and 3%, respectively, and N is 5% and 2% respectively, and O and P are 24.
Cr-35Ni is used as a basic component, and Al and Si are contained in a composite of O of 3% and 2%, and P of 3% and 3%, respectively.

Inventive Example Q is B of 20Cr-25Ni-3.
Compared to Al, Ni is as low as 18% in the composition range of the present invention, and R is 24Cr-35Ni-3Al of J,
Within the composition range of the present invention, Ni is as high as 48%. S to U are 2.9% Mo and Ti within the range of the component of the present invention, respectively, as compared with B or C 20Cr-25Ni-3 to 6Al.
Is as high as 0.25% and Nb is 0.57%.

The invention examples A to U contain at least one of Ca, Y, La and Ce. The inner layer material example AA for the present invention shown in Table 2 is STB41 of JIS G 3461.
Carbon steel equivalent to 0, BB is JIS G 346
2 is a low alloy steel equivalent to STBA24, CC is A
9Cr-1Mo corresponding to T91 of SME SA213
Steel, DD and EE are JIS G 3463 SUS
Austenitic stainless steel equivalent to 304HTB and SUS347HTB, FF is JIS G 490
4 is a high Cr-high Ni steel equivalent to NCF800HTB of No. 4.

Next, in the outer layer material powders HA to HG of the comparative example shown in Table 3, Ni was 9.3%, 13.1% and 1%, respectively.
It is an austenitic stainless steel containing 7.3%, 25.3%, 34.8%, 47.1% and 54.5%, and Al and Si are the lower limits of the composition range of the present invention. Less than 0.5% and 0.7%. In addition, HA
Is a material equivalent to SUS304, Ni is lower than the component range of the present invention (17 to 50%), and HG has Ni higher than the component range of the present invention.

Comparative Example HH contains 3% Al, but Ni
Is 14.2%, which is lower than the component range of the present invention. HI, HJ
Is a steel containing 24Cr-35Ni as a basic component, HI having 9.8% Al and HJ having 7.8% Si, both of which exceed the composition range of the present invention. Furthermore, HK is 2
Steel containing 4Cr-35Ni as a basic component, Al and Si at 9.8% and 7.3%, respectively, and both components exceeding the component range of the present invention.

Next, Tables 4 and 5 (continued from Table 4-1),
All of WA to WU of the multi-layer steel pipe of the present invention shown in Table 6 (Continued-2 of Table 4) are the outer layer raw material powders A to U of the present invention shown in Table 1 and those of the present invention shown in Table 2. In combination with the example of the inner layer material, HIP treatment is performed under the conditions shown in claim 3 to form a coating layer, and then the hot working shown in claim 4 is performed, and then, if necessary, in steps 5 to 7. It has been subjected to the heat treatment, cold working and heat treatment shown. Classified by the steps after hot working, claim 4 corresponds to WJ and WK, and claim 5 corresponds to WB to WD, WG, WH, and WL to W.
S and WU correspond, claim 6 corresponds to WA and WF,
Claim 7 corresponds to WE, WI, and WT.

The multi-layer steel pipe of the present invention and the hot working materials WA to WU thereof each have a metal diffusion layer of 10 μm or more as an intermediate layer between the outer layer and the inner layer after HIP treatment, and are cracked only during hot working. It has good hot workability and the product tube has a metal diffusion layer of 5 μm or more in the intermediate layer,
It has good high temperature corrosion characteristics with the high temperature corrosion depth of the outer layer being 20 μm or less.

On the other hand, Tables 7 and 8 (continued from Table 7-1),
H of the multi-layer steel pipe of the comparative example shown in Table 9 (continued-2 in Table 7)
WA to HWK are the outer layer material powder H of the comparative example shown in Table 3.
HIP by combining A to HK with the inner layer material examples shown in Table 2
It is the one that has been subjected to treatment, hot working, and then heat treatment, cold working, and heat treatment, if necessary. Sorted by the process after hot working, and compared with claim 4, HWE,
HWG and HWI to HWWK correspond, HWB to HWD and HWF correspond to the comparison with claim 5, HWA corresponds to the comparison with claim 6, and HWH corresponds to the comparison with claim 7. To do.

Tables 7 and 8 (continuation of Table 1-1),
H of the multi-layer steel pipe of the comparative example shown in Table 9 (continued-2 in Table 7)
WL to HWO are obtained by combining the outer layer material powder B of the present invention example with the inner layer material example DD (equivalent to SUS304HTB).
P processed and hot extruded, but both are HIP
The processing condition is out of the condition range of the present invention. That is, HWL has a HIP treatment temperature of 1000 ° C., which is lower than the lower limit temperature of 1050 ° C. of the present invention, and HWM has a HIP treatment temperature of 1270 ° C., which is higher than the upper limit temperature of 1240 ° C. of the present invention. HWN has a HIP treatment pressure of 25 MPa, which is lower than the lower limit pressure of 29 MPa of the present invention, and HWO has a load holding time of 0.3 hours, which is shorter than the lower limit time of the present invention.

These comparative examples are compared with the examples of the present invention.
There is a problem in at least one of the hot workability during manufacturing and the high temperature corrosion resistance of the outer layer of the product tube.
That is, HWA using an outer layer in which both Al and Si are lower than the lower limit of the composition range of the present invention, HWH containing 3% of Al, but Ni lower than the lower limit of the composition range of the present invention has a high temperature corrosion depth of more than 20 μm. Therefore, the high temperature corrosion property is inferior to that of the steel of the present invention.

HI with Al 9.8% and Si 7.8
% HJ for the outer layer of multi-layer steel pipes HWI, HWJ and A
HK in which l and Si are each higher than the upper limit of the component range of the present invention.
In the multi-layer steel pipe HWK using as the outer layer, bald defects or cracks occurred during hot extrusion. Further, even in a multi-layer steel pipe HWG using HG containing Ni in an amount of 54.5% exceeding the composition range of the present invention as an outer layer, a bald defect occurred during hot extrusion. Although these comparative examples have a metal diffusion layer of 10 μm or more as an intermediate layer between the outer layer and the inner layer after the HIP treatment, the outer layer component exceeds the component range of the present invention and the hot workability is poor, so that the hot extrusion is performed. Occasionally, bald spots or cracks occurred.

Further, using the raw material powder B for the outer layer of the present invention, but the HIP treatment condition is outside the condition range of the present invention, in any of HWL to HWO, any of the blistering flaws or cracks occurs in the outer layer during hot extrusion. It was That is, in HWL, HIP
The processing temperature is low, and HIP processing pressure is low in HWN.
Since the load holding time was short in WO, HIP
After the treatment, the metal diffusion layer, which is an intermediate layer between the outer layer and the inner layer, is
It is less than m, the outer layer is not sufficiently sintered, and a bald defect or a crack is generated during hot extrusion. on the other hand,
HWM had a high HIP treatment temperature of 1270 ° C., segregation of constituent elements occurred during cooling, and hot workability was not sufficient, so that bald defects occurred during hot extrusion.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

[0047]

[Table 6]

[0048]

[Table 7]

[0049]

[Table 8]

[0050]

[Table 9]

[0051]

Industrial Applicability According to the present invention, it is possible to apply chlorides and hydrogen chloride (HCl) gas in a combustion environment, which can be applied to waste plastics and superheated organs of waste combustion boilers such as automobile shredder dust. On the other hand, it becomes possible to supply a multi-layer steel pipe having extremely excellent high-temperature corrosion resistance and good hot workability at the time of production, which brings a very useful effect in the fields of energy and environment.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of the Ni content of the outer layer on the hot corrosion depth.

FIG. 2 is a diagram showing the influence of the Al and Si contents of the outer layer on the hot corrosion depth.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shinji Niinuma 3434 Shimada, Hikaru City, Yamaguchi Prefecture, Nippon Steel Works, Ltd., Hikari Works, Ltd. (72) Inventor Tetsuo Ishizuka 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Co., Ltd. Technology Development Headquarters

Claims (7)

[Claims] 1. The outer layer, in wt%, is C; 0.08% or less, Mn; 0.3 to 2.0%, Cr; 18 to 27%, Ni; 17 to 50%, Mo; 5-3.0%, Ti; 0.03-0.3%, Nb; 0.05-0.6%, B; 0.001-0.01%, P; 0.04% or less, S; 0.005% or less, N; contains 0.02 to 0.3%, and further contains Al; 0.5 to 9.0%, Si; 0.7 to 7.0%, and one or more types thereof, and Ca; 0.0005 to 0.05%, Y; 0.001 to 0.2%, La; 0.001 to 0.2%, Ce; 0.001 to 0.2% ,
Hot isostatic pressing (HIP) of austenitic stainless steel powder with the balance Fe and unavoidable impurities
A coating layer formed by treatment and hot working, wherein the inner layer is a steel pipe for a boiler, and an intermediate layer composed of a metal diffusion layer of 5 μm or more formed by HIP-hot working is provided between the outer layer and the inner layer. A multi-layer steel pipe with excellent high temperature corrosion resistance. 2. The outer layer is a coating layer formed by HIP-treating the powder of austenitic stainless steel according to claim 1, the inner layer is steel for boiler, and the inner layer is 10 μm or more formed by HIP treatment between the outer layer and the inner layer. A material for multi-layer steel material having excellent high-temperature corrosion resistance characterized by having an intermediate layer composed of a metal diffusion layer. 3. The HIP processing condition is set to a temperature of 1050 to 124.
The method for producing a multi-layer steel pipe or a raw material for a multi-layer steel material excellent in high-temperature corrosion resistance according to claim 1 or 2, wherein the temperature is 0 ° C, the pressure is 29 MPa or more, and the holding time is 0.5 hours or more. 4. The multi-layer steel material according to claim 2, which is produced by HIP treatment under the conditions of claim 3, is produced by drawing by hot working.
A method for producing a multi-layer steel pipe having excellent high-temperature corrosion resistance as described above. 5. The multi-layer steel material according to claim 2, which is produced by HIP treatment under the conditions of claim 3, is drawn by hot working, and then further heat-treated. A method for producing a multi-layer steel pipe having excellent high-temperature corrosion resistance as described above. 6. The multi-layer steel material according to claim 2, produced by HIP treatment under the conditions of claim 3, is drawn by hot working, and then subjected to cold working and heat treatment once or more. The method for producing a multi-layer steel pipe excellent in high temperature corrosion resistance according to claim 1. 7. The multi-layer steel material according to claim 2 produced by HIP treatment under the conditions of claim 3, is drawn by hot working, and then further heat treated, and further cold worked and heat treated. The method for producing a multi-layer steel pipe excellent in high-temperature corrosion resistance according to claim 1, wherein the method is performed once or more.