JPH05140764A - Cr-mo steel pipe excellent in carburizing resistance and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a steel pipe excellent in carburizing resistance by removing scales on the surface of a Cr-Mo steel pipe and thereafter forming a dense film of Cr oxide or applying hot dip aluminizing and alloying it. CONSTITUTION:Since porous iron oxide scales are present on the surface of a steel pipe produced by a hot process using a Cr-Mo steel contg., by weight, <=0.25$ C, 0.10 to 1.00$ Si, 0.30 to 1.00% Mn, <=0.030% P, <=0.030% S, 8.00 to 13.00% Cr, 0.80 to 2.50% Mo, <1.00% Ni and <0.15% Nb as stock, the scales are completely removed by methods such as pickling and abrasives. Next, this steel pipe is subjected to heat treatment in a bright atmosphere to form a dense Cr2O3 film on the surface. Or, the steel pipe in which the scales have been removed is subjected to hot dip aluminizing treatment at 680 to 700 deg.C and is thereafter annealed at 740 to 760 deg.C for 1 to 2hr, by which Al is diffused on the surface of the steel pipe and is alloyed with Fe. The objective Cr-Mo steel pipe excellent in carburizing resistance can be manufactured at a high yield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to an oil refining plant,
The present invention relates to a Cr-Mo steel pipe having excellent carburization resistance used for heating a process fluid in a heating furnace such as a petrochemical plant, and a method for producing the same.

[0002]

2. Description of the Related Art A steel pipe for a heating furnace used for heating a process fluid in a heating furnace of a petroleum refining plant, a petrochemical plant, etc. is defined in JIS G3467.
Of these, the chromium molybdenum steel pipes such as STFA26 are
It is used as a steel pipe for a heating furnace in an oil refining plant, but the inner and outer surfaces are significantly carburized during use by the inner surface fluid made of a crude gas and the outer surface combustion atmosphere gas. In particular, surface treatment for improving carburization resistance is strongly desired because carburization occurs in a short time due to high temperature operation due to recent increase in size and yield, and destruction due to carburization.

Steel pipes for heating furnaces for heating crude gas in petroleum refining plants are used at high temperatures of 600 ° C. or higher, and therefore are mainly specified in JIS G3467 for the purpose of ensuring high temperature oxidation resistance and high temperature strength. STFA26
9% Cr-1% Mo steel pipe of is used. 9% Cr-1
% Mo steel pipe is hot-manufactured by Mannesmann-mandrel mill, Mannesmann-plug mill, Eugene-Sejourne mill, etc., and if there are dimensional restrictions, after cold-finishing as necessary, the material has the specified strength. ,
It is manufactured by performing a heat treatment for imparting performance such as toughness. As the heating furnace tube, a panel structure is formed by bending and welding and then annealed for stress relief. In a heating furnace tube used in an oil refining plant, carburization occurs from the inner and outer surfaces by a crude gas as an inner surface fluid and an outer surface combustion atmosphere gas. In particular, when used at a high temperature of over 600 ° C., both the inner and outer surfaces are carburized to a depth of 1 mm or more in one year, leading to deterioration in ductility and toughness of the material.

As a method for improving the carburization resistance of steel materials, for example, Al and Zr are the most effective alloying elements effective for improving the carburization resistance of 25% Cr-20% Ni cast steel (Yamazaki Daizo et al., Mitsubishi. Heavy Industry Technical Report, Vol. 13, No.
5, P94 to P100 "Study on carburizing phenomenon of heat-resistant cast steel for reaction tubes"), C: 0.01% or less, Cr: 3 to 18
%, Mn: 0.1 to 1.5%, Si: 0.1% or less,
N: 0.004% or less, Al: 0.005-0.08%
It has been proposed to apply hot-dip aluminum plating to a steel sheet containing Al and the balance Fe and unavoidable impurities (Japanese Patent Laid-Open No. 61-6261).

[0005]

[Problems to be Solved by the Invention] Yamazaki Okura et al., Mitsubishi Heavy Industries Technical Report, Vol. 13, No. 5, P94-P100
Is to add 25% Cr-20% Ni cast steel base material to Al or Zr to improve the carburization resistance, and the addition of Al or Zr changes the mechanical properties of the base material. Carburizing properties cannot be improved without changing the mechanical properties of the base material. In addition, JP-A-6
The steel sheet disclosed in Japanese Patent No. 1-6261 improves corrosion resistance and prevents corrosion due to condensed water of an automobile muffler by applying hot dip aluminum plating to a 3 to 18% Cr steel sheet. Does not improve.

An object of the present invention is to provide a Cr-Mo steel pipe having excellent carburization resistance suitable for use in a carburizing atmosphere such as a heating furnace pipe in an oil refining plant, and a method for producing the same. ..

[0007]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies to achieve the above object. As a result, steel pipes that have been hot piped by Mannesmann mandrel mills, Mannesmann plug mills, Eugene Sejourne mills, etc. are generally exposed to the atmosphere at high temperatures during pipe production. Oxide scale is generated. In addition, since Cr is preferentially oxidized on the surface layer surface of the steel of the bare metal, a chromium-deficient dechromized layer having a thickness of 10 to 20 μm is formed. Therefore, corrosion resistance equivalent to the original Cr content is obtained. Is difficult to obtain. Therefore, the iron-based porous oxide scale formed on the surface of the hot-rolled Cr-Mo steel pipe is removed by grinding, pickling, etc., and heat-treated in a bright atmosphere to form a dense Cr ₂ O ₃ coating film on the surface. It was confirmed that it is possible to secure carburization resistance and corrosion resistance by forming it. In addition, hot-produced Cr-M
o The iron-based porous oxide scale formed on the surface of the steel pipe is removed by grinding, pickling, etc., and then subjected to hot dip aluminum plating at a specified temperature and annealed under specified annealing conditions to obtain carburization resistance. The present invention has been achieved by discovering that the value is significantly improved.

That is, according to the present invention, C: 0.25% or less, Si: 0.10 to 1.00%, Mn: hot-manufactured by using a Mannesmann mandrel mill, a Mannesmann plug mill, a Eugene Sejourne mill, or the like. 0.30-
1.00%, P ≦ 0.030%, S ≦ 0.030%, C
r: 8.00 to 13.00%, Mo: 0.80 to 2.5
0%, Ni: 1.00% or less, V: 0.40% or less, N
b: Cr- which contains 0.15% or less and which has a balance of Fe and unavoidable impurities and which has a fine Cr oxide coating formed on the surface layer of a descaled steel tube and which has excellent carburization resistance.
It is a Mo steel pipe.

[0009] Further, C: 0.25% or less, C: 0.25% or less, which was hot pipe-formed by using a Mannesmann mandrel mill, a Mannesmann plug mill, a Eugene Sejourne mill, or the like.
10-1.00%, Mn: 0.30-1.00%, P ≦
0.030%, S ≦ 0.030%, Cr: 8.00-1
3.00%, Mo: 0.80 to 2.50%, Ni: 1.
A dealuminized steel pipe containing 00% or less, V: 0.40% or less, Nb: 0.15% or less, and the balance being Fe and unavoidable impurities, with a hot dip aluminized coating film formed on the inner and outer surfaces thereof. It is a Cr-Mo steel pipe with excellent carburizing properties.

Further, a Mannesmann mandrel mill,
Hot pipemaking using Mannesmann plug mill, Eugene Sejourne mill, etc. C: 0.25% or less, Si:
0.10-1.00%, Mn: 0.30-1.00%,
P ≦ 0.030%, S ≦ 0.030%, Cr: 8.00
~ 13.00%, Mo: 0.80 to 2.50%, Ni:
1.00% or less, V: 0.40% or less, Nb: 0.15
% Of steel, the balance of which is Fe and unavoidable impurities, is completely descaled by pickling or grinding, and then heat-treated in a bright atmosphere furnace to form a dense C
It forms an r oxide film.

Further, C: 0.25 which has been subjected to an appropriate heat treatment for optimizing strength, workability, etc. by hot pipe forming using a Mannesmann mandrel mill, Mannesmann plug mill, Eugene Sejourne mill and the like. % Or less, S
i: 0.10 to 1.00%, Mn: 0.30 to 1.00
%, P ≦ 0.030%, S ≦ 0.030%, Cr: 8.
00-13.00%, Mo: 0.80-2.50%, N
i: 1.00% or less, V: 0.40% or less, Nb: 0.
A steel pipe containing 15% or less and the balance consisting of Fe and unavoidable impurities is completely descaled by pickling or grinding, and then subjected to hot dip aluminum plating treatment at 680 to 700 ° C. and then at 1 to 740 to 760 ° C. It is annealed for 2 hours.

[0012]

The reason why the steel composition of the present invention is limited as described above will be described in detail. C is an element that enhances strength, but since it tends to deteriorate corrosion resistance and workability,
From the viewpoint of workability and weldability, it was set to 0.25% or less. Si is added in an amount of 0.1% or more for the purpose of deoxidation, but if it exceeds 1.0%, hot workability is impaired, so 0.1 to 1.0% was made. Mn is an element effective for hot workability and strength increase, but it is effective at 0.3% or more, and 1.0% in this steel type.
% Is sufficient, so it was set to 0.3 to 1.0%. P is toughness, and S is 0.03 due to steel quality, workability and toughness.
It was set to 0%. Cr is an element effective in improving the corrosion resistance and oxidation resistance of steel, and when added in an amount of 8% or more, a dense Cr ₂ O ₃ film is formed on the surface of the steel material, and good corrosion resistance and oxidation resistance can be obtained. , 13%, the aspect of phase transformation is different and the hot workability is impaired, so the content was made 8 to 13%. Mo
Is an element that enhances high-temperature strength, but 0.80% is effective for showing an effect on strength at 600 ° C. or higher in 8 to 13% Cr steel.
%, It is necessary to add more than 2.5%, but if more than 2.5% is added, no further increase in strength can be obtained.
It was set to 2.50%. Ni, V, and Nb do not need to be added in particular for the purpose of improving the carburization resistance, which is the object of the present invention, but in the steel pipe containing Cr and Mo described above,
Ni may be added in an amount of 1.00% or less for the purpose of improving hot workability, and V may be added in an amount of 0.40% or less and Nb may be added in an amount of 0.15% or less for the purpose of particularly increasing strength.

In the present invention, hot-rolled Cr is used.
-To ensure corrosion resistance, the porous oxide scale mainly composed of iron formed on the surface of Mo steel pipe is removed by grinding, pickling, etc. and heat-treated in a bright atmosphere to form a dense Cr ₂ O ₃ coating on the surface. It becomes possible to obtain relatively good carburization resistance. This is because a steel pipe hot-manufactured by a Mannesmann mandrel mill, a Mannesmann plug mill, a Eugene Sejourne mill, etc. is generally exposed to the atmosphere at a high temperature during pipe making, and therefore a thick and porous iron-based surface is mainly used. Oxide scale is generated. In addition, since Cr is preferentially oxidized on the surface layer surface of the steel of the bare metal, 10 to 20
Since a chromium-depleted chromium-depleted layer with a thickness of μm is formed, it is difficult to obtain sufficient corrosion resistance equivalent to the original Cr content. By heat treatment in a bright atmosphere with the oxide scale completely removed by grinding, pickling, etc.,
This is because a dense Cr ₂ O ₃ film is formed on the surface.

According to the present invention, the iron-based porous oxide scale formed on the surface of the Cr-Mo steel pipe hot-rolled before hot dip aluminum plating is removed only when the oxide scale remains attached. This is because a normal aluminum plating film is not formed. The hot-dip aluminization treatment conditions were a temperature of 680 to 700 ° C. and a treatment time of 10 to 30 minutes, because the Fe-Al alloy layer was 50 to 150 μm, pure aluminum as the aluminum plating film thickness to satisfy practical carburization resistance. A
1 layer 20 to 50 μm, total adhesion amount 200 to 300 g / m
To obtain ² , 680-700, as shown in FIG.
This is because treatment at 10 ° C. for 10 to 30 minutes is required.

Annealing is performed after hot dip aluminum plating. The as-plated coating is a Fe--Al alloy layer on the steel side of the metal,
It has a two-layer structure of a pure Al layer on the surface side, and when used at high temperature, the pure Al layer of the surface layer peels off due to the difference in coefficient of thermal expansion, so annealing is performed in advance to form a diffusion alloy of the pure Al layer,
This is for forming a single layer in the e-Al alloy layer. The annealing condition in this annealing is set to 740 to 760 ° C. for 1 to 2 hours, in order to completely diffuse the pure Al layer in consideration of economical efficiency and efficiency, 1 hour or more is required at 740 ° C., 760
This is because if the temperature exceeds ℃, the temperature becomes higher than the final heat treatment temperature of the material after the hot pipe forming, and the strength of the base metal deteriorates.

There is a U-shaped bent portion in the panel structure of the heating furnace tube of the oil refining plant. Aluminum plated steel pipe is Fe
Since the ductility of the Al alloy layer is poor, cracking occurs due to bending. For this reason, it is a good idea to perform a bending process on the steel pipe that has been hot-rolled at the bent portion, and then perform a plating process.
The aluminum-plated steel pipe is thermally deformed due to the temperature of the plating bath in the hot-dip aluminum plating treatment, and it is necessary to straighten the bend. After that, panel assembly by welding is performed and finally stress relief annealing is performed. Since the Fe-Al alloy layer is hard and brittle, cracks are likely to occur with a small strain, while pure Al
Since the layer is soft and ductile, straightening after the plating treatment is preferably performed before annealing in the presence of the pure Al layer. In this case, it is not preferable to generate bending again in the annealing for diffusing the pure Al layer, and the diffusion annealing and the final stress relief annealing of the pure Al layer are performed at the same temperature and twice. Since it is uneconomical to anneal, it is preferable to perform panel assembly by welding a straightened steel pipe immediately after plating and then perform stress relief annealing to simultaneously diffuse the pure Al layer.

[0017]

【Example】

Example 1 A Cr-Mo steel pipe having a chemical composition shown in Table 1 and having an outer diameter of 88.9 mm and a wall thickness of 6.0 mm, which was hot-pipe-formed by using a Mannesmann mandrel mill, the conventional method 1 was 950 by heating in a bright furnace. Hold at ℃ for 10 minutes, then at 750 ℃ for 60 minutes
Heat treatment for 1 minute, cool to room temperature, then JIS G05
740 in the carburizing agent based on the carburizing test method specified in 51.
A carburization test was carried out by heating at 110 ° C for 110 hours. Conventional method 2
After heating at 950 ° C for 10 minutes by heating in a bright furnace, heat-treating at 750 ° C for 60 minutes, cooling to room temperature, then annealing at 740 ° C for 60 minutes by heating in the atmosphere, and then performing the carburizing test specified in JIS G0551. 110 hours at 740 ° C in carburizing agent, or 925
Carburization test was carried out by heating at 100 ° C. for 100 hours. Inventive method 1
For the Cr-Mo steel pipe, after removing 0.2 mm of the surface layer by grinding and descaling, holding at 950 ° C for 10 minutes by heating in a bright furnace, heat treatment at 750 ° C for 60 minutes, and cooling to room temperature. Then, a carburization test was performed by heating in a carburizing agent at 740 ° C. for 110 hours. According to the method 2 of the present invention, the surface layer of the Cr-Mo steel pipe is 0.2 m.
m was removed by grinding to be descaled, and then held at 950 ° C. for 10 minutes by heating in a bright furnace, and then at 750 ° C. for 6 minutes.
Heat treatment for 0 minutes, cool to room temperature, then anneal at 740 ° C. for 60 minutes by heating in the air, then in a carburizing agent for 7 minutes.
Carburization test was carried out by heating at 40 ° C. for 110 hours. According to the method 3 of the present invention, the Cr—Mo steel pipe is washed with sulfuric acid, then descaled by washing with fluorinated nitric acid, and heated to 9 in a bright furnace.
After holding at 50 ° C. for 10 minutes, heat treatment was performed at 750 ° C. for 60 minutes, cooling to room temperature, and then heating in a carburizing agent at 740 ° C. for 110 hours to perform a carburizing test. Inventive method 4 is
The Cr-Mo steel pipe was washed with sulfuric acid, then descaled by washing with fluorinated nitric acid, held at 950 ° C for 10 minutes by heating in a bright furnace, heat-treated at 750 ° C for 60 minutes and cooled to room temperature, and then heated at atmospheric pressure to 740 ° C. 60
After annealing for 7 minutes, in a carburizing agent at 740 ° C for 11
Carburization test was carried out by heating for 0 hours. The method 5 of the present invention comprises C
For r-Mo steel pipe, 1 at 950 ° C by heating in a bright furnace
After holding for 0 minutes, heat-treat at 750 ° C for 60 minutes, cool to room temperature, wash with sulfuric acid, descale by washing with fluorinated nitric acid, perform hot dip aluminum plating at 690 ° C for 20 minutes, then heat at atmospheric pressure for 60 minutes at 740 ° C. After annealing, a carburizing test was carried out by heating in a carburizing agent at 740 ° C. for 110 hours or at 925 ° C. for 100 hours.
The results are shown in Table 2. In the column of carburizing test results in Table 2, ⊚ indicates no carburizing, ∘ indicates local carburizing, × indicates whole carburizing, and the numbers in parentheses indicate carburizing depth.

[0018]

[Table 1]

[0019]

[Table 2]

As shown in Table 2, the Cr-Mo steel pipe descaled by grinding or pickling or the Cr-Mo steel pipe according to the present invention which was aluminized after being descaled by grinding or pickling was descaled and aluminized. Carburizing can be significantly reduced or eliminated in the carburizing test, as compared with the conventional Cr-Mo steel pipe that is not plated.

Example 2 Five kinds of steel pipes having an outer diameter of 88.9 mm and a wall thickness of 6.0 mm, which were hot-manufactured using a Mannesmann mandrel mill, and which had the chemical composition shown in Table 3, were ground to a surface layer of 0.2 mm. After removing and descaling, it is heated to 950 ° C in a bright furnace.
After holding for 10 minutes at 60 ° C, heat-treat at 750 ° C for 60 minutes, cool to room temperature, and then heat at atmospheric pressure for 6 minutes at 740 ° C
After annealing for 0 minutes, in a carburizing agent at 740 ℃ 1
Carburizing test was carried out by heating for 10 hours. The results are shown in Table 4. In addition, ○ in the carburizing test result column in Table 4 indicates local carburizing,
× indicates carburizing on the entire surface.

[0022]

[Table 3]

[0023]

[Table 4]

As shown in Table 4, the steel pipe of the method of the present invention is significantly improved in local carburization and carburization resistance as compared with the full-face carburization of the steel pipe of the comparative example.

[0025]

As described above, according to the present invention,
It is possible to obtain a Cr-Mo steel pipe having excellent carburization resistance suitable for a heating furnace tube of an oil refining plant and the like, and it is possible to prolong the life of the heating furnace tube and to cause carburization of the heating furnace tube. The destruction that occurs can be reduced.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship among the temperature in the Al plating treatment, the plating treatment time and the average adhesion amount, the alloy layer thickness, and the pure Al layer thickness.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C25D 11/38 B // C21D 9/08 Z

Claims (4)

[Claims] 1. C: 0.25% or less, Si: 0.10. Hot-pipe-formed by using a Mannesmann mandrel mill, a Mannesmann plug mill, a Eugene Sejourne mill, or the like.
˜1.00%, Mn: 0.30 to 1.00%, P ≦ 0.
030%, S ≦ 0.030%, Cr: 8.00-13.
00%, Mo: 0.80 to 2.50%, Ni: 1.00
%, V: 0.40% or less, Nb: 0.15% or less, and the balance is formed by forming a dense Cr oxide coating on the surface layer of a descaled steel pipe containing Fe and unavoidable impurities. Cr-Mo steel pipe with excellent carburizing properties. 2. C: 0.25% or less, Si: 0.10. Hot-pipe-made by using a Mannesmann mandrel mill, a Mannesmann plug mill, a Eugene Sejourne mill, or the like.
˜1.00%, Mn: 0.30 to 1.00%, P ≦ 0.
030%, S ≦ 0.030%, Cr: 8.00-13.
00%, Mo: 0.80 to 2.50%, Ni: 1.00
% Or less, V: 0.40% or less, Nb: 0.15% or less, and the balance is a carburization resistant carburized aluminum pipe coating formed on the inner and outer surfaces of a descaled steel pipe composed of Fe and unavoidable impurities. Cr-Mo steel pipe with excellent properties. 3. Hot-pipe-making C: 0.25% or less, Si: 0. 10 using a Mannesmann mandrel mill, Mannesmann plug mill, Eugene Sejourne mill, etc.
˜1.00%, Mn: 0.30 to 1.00%, P ≦ 0.
030%, S ≦ 0.030%, Cr: 8.00-13.
00%, Mo: 0.80 to 2.50%, Ni: 1.00
%, V: 0.40% or less, Nb: 0.15% or less, and the balance being Fe and unavoidable impurities, the steel pipe is completely descaled by pickling or grinding.
Cr with excellent carburization resistance, characterized by forming a dense Cr oxide film on the surface by heat treatment in a bright atmosphere furnace
-Method of manufacturing Mo steel pipe. 4. A C: 0.25% which has been subjected to an appropriate heat treatment for optimizing strength, workability, etc. by hot pipe making using a Mannesmann mandrel mill, a Mannesmann plug mill, Eugene Sejourne mill and the like. Below, Si: 0.1
0-1.00%, Mn: 0.30-1.00%, P ≦
0.030%, S ≦ 0.030%, Cr: 8.00-1
3.00%, Mo: 0.80 to 2.50%, Ni: 1.
A steel pipe containing 00% or less, V: 0.40% or less, Nb: 0.15% or less, and the balance of Fe and unavoidable impurities was completely descaled by pickling or grinding and then 680 to 700. Apply hot dip aluminum plating at ℃,
Then, a method for producing a Cr-Mo steel pipe having excellent carburization resistance, which is characterized by performing annealing at 740 to 760 ° C for 1 to 2 hours.