JP3489535B2 - Method for producing martensitic stainless steel pipe with excellent weather resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of martensitic stainless steel pipes used for oil wells or gas wells, various plant or construction structural materials, and more particularly to a composition containing 9 to 15 mass% of Cr. Therefore, the present invention relates to a method for producing a martensitic stainless steel pipe having excellent weather resistance (rust resistance) during pipe manufacturing, heat treatment, before and after storage, and during transportation.

[0002]

2. Description of the Related Art Conventionally, martensitic stainless steel pipes have been widely used for oil wells, various plants, or construction structures, and can be classified into seamless steel pipes and welded steel pipes depending on the pipe manufacturing method.

In the case of a seamless steel pipe, the Mannesmann-mandrel mill system is usually applied because it is advantageous in terms of dimensional accuracy and productivity. In this method, a material billet manufactured by continuous casting is heated to 1100 to 1300 ° C., then a hollow shell is formed by piercing and rolling with a piercer, and further stretched and rolled by a mandrel mill to prepare a shell tube for finish rolling. Next, this raw material tube for finish rolling is in a state of being stretch-rolled or reheated to 850 to 1100 ° C. and then passed through a stretch reducer to finish a seamless steel tube of a predetermined dimension.

On the other hand, in the case of a welded steel pipe, a strip steel is used as a raw material to finish the product into a predetermined size by ERW (electric resistance welding) pipe manufacturing method, TIG welding pipe manufacturing method, laser welding pipe manufacturing method, or the like.

Whether it is a seamless steel pipe or a welded steel pipe, a martensitic stainless steel pipe finished to a predetermined product size is generally fired from 900 ° C. or higher in order to secure a desired strength. And then 600-750
Tempering heat treatment is performed at ℃. Therefore, in the case of a seamless steel pipe, it is heated to 600 to 1300 ° C in each process, and in the case of a welded steel pipe, there is a temperature rise of 600 to 1000 ° C in the heat treatment process. , Unavoidable oxide film (mill scale) is generated.

Normally, the oxide film formed on the surface of the steel pipe is
It is completely removed by shot-blasting and pickling. Such removal of the oxide film is to remove the Cr-free layer existing in the base material immediately below the oxide film. That is, in the Cr-free layer, the Cr content is less than 9% required for forming the non-conductive coating of stainless steel, which is the starting point of rusting in the atmospheric environment.

Furthermore, after the shot blasting treatment, a pickling treatment is applied to completely remove the oxide film and the Cr-free layer. Recently, the pickling treatment requires a large number of steps and a large cost as compared with the shot blasting treatment. Therefore, a method of removing the oxide film and the Cr-free layer by only the shot blasting treatment is also adopted.

In view of such circumstances, various proposals have been made regarding the shot blasting method. For example, in Japanese Patent Laid-Open No. 11-236651, a martensitic stainless steel pipe is targeted, and after removing an oxide film formed and adhered to the surface, the surface roughness has a maximum height R defined by JIS B0601.
A method has been proposed in which y is 50 μm or less, the size of the oxide film remaining on the surface is 0.01 mm ² or less, and the remaining area ratio of the oxide film in a 1 mm ² visual field is 2% or less.

In the proposed method, surface roughness is
By setting Ry to 50 μm or less, the pitting potential is significantly increased to improve the corrosion resistance, and the size of the oxide film remaining on the surface is 0.01 mm ² or less to prevent substantial rusting. Prevents the generation of the oxide film
This is because when the residual area ratio in the visual field of mm ² is 2% or less, a non-conductor holding current is generated due to the anodic polarization behavior, and a non-conductor film is formed around the remaining oxide film. Thus, by defining the surface roughness on the surface of the steel pipe after shot blasting, the residual area of the oxide film, and the residual area ratio, the martensitic stainless steel pipe treated by the proposed method has excellent weather resistance. You will be able to exercise your abilities.

By the way, in the method proposed in the above publication, the surface roughness is defined as 50 μm or less at the maximum height Ry as described above. The shot condition of the cleaning material becomes important. In other words, in order to secure the above-mentioned surface roughness after shot blasting, it is necessary to limit the size of the polishing / cleaning material to be used, and the collision angle of the polishing / cleaning material must be reduced. As described above, when the polishing / cleaning material is small, the life is shortened and the manufacturing cost is increased, and when the collision angle of the polishing / cleaning material is further reduced, the cleaning / cleaning force is reduced and the work efficiency is reduced.

[0011]

As described above, although the method conventionally proposed and carried out as the shot blasting treatment suitable for the martensitic stainless steel pipe is effective for exerting the weather resistance of the treated steel pipe, In order to secure the surface roughness of the steel pipe after treatment, it is necessary to limit the operating conditions such as the size of the polishing and cleaning material and the collision angle. Therefore, in order to achieve more efficient production in the future production of martensitic stainless steel pipes, it is necessary to develop a shot blast treatment that can reduce the production cost.

The present invention has been developed from the above viewpoint, and it is possible to reduce the manufacturing cost of the shot blasting treatment after the final heat treatment of the steel pipe by defining the characteristics of the abrasive material used for the shot blasting treatment. It is an object of the present invention to provide a method for producing a martensitic stainless steel pipe capable of exhibiting excellent weather resistance while aiming.

[0013]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventor has conducted extensive research on various abrasives used for shot blasting, and as a result, has found that the weather resistance of steel pipes (corrosion resistance to rust). The magnetic properties of the polishing and cleaning material are affected by contamination, and limiting the content of the magnetic iron content in the polishing and cleaning material prevents rusting of the steel pipe and improves weather resistance. It was found that the above can be improved.

The present invention has been completed on the basis of such knowledge, and has as its gist the following method for producing a martensitic stainless steel pipe.

That is, after martensitic stainless steel having a Cr content of 9 to 15% by mass is made into a pipe and then heat-treated, a non-ferrous oxide-based or non-ferrous carbide-based iron component is formed on the surface of the steel pipe . A method for producing a martensitic stainless steel pipe having excellent weather resistance, characterized by colliding a cleaning material controlled to contain magnetic iron content of 5% or less by separation to remove an oxide film formed on the surface. is there.

In this manufacturing method, in order to reduce the manufacturing cost, the above-mentioned abrasive cleaning material is recovered and reused after the oxide film formed on the surface of the steel pipe is removed, but it is desirable to recycle it.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION In the production method of the present invention,
It is made of martensitic stainless steel with a Cr content of 9-15%. If the Cr content is less than 9%, desired corrosion resistance, specifically CO ₂ corrosion resistance cannot be secured. On the other hand, when the Cr content exceeds 15%, a delta / ferrite phase is easily generated, corrosion resistance (SSC resistance) and hot workability deteriorate, and excessive addition causes an increase in manufacturing cost.

In the present invention, only the Cr content is specified with respect to the chemical composition of the material, but in addition, C: 0.5% or less, Si: 1
% Or less, Mn: 5% or less, Ni: 8% or less, Mo: 7% or less,
Ti: 0.1% or less, Zr: 0.1% or less, Nb: 0.1% or less, sol.A
l: 0.1% or less of elements and the like can be appropriately contained.

FIGS. 1 and 2 are diagrams showing the relationship between the content of magnetic iron in the abrasive material used for the alumina shot blasting treatment and the weather resistance of the steel pipe. The steel pipe used for the test was 13Cr martensitic stainless steel shown in Table 1 in the examples described later, and the steel pipe was used as the final heat treatment.
After quenching at 0 ° C and tempering at -600 to 750 ° C, shot blasting treatment was performed so as to secure a predetermined surface roughness and a residual area ratio of an oxide film. After that, a weather resistance test is carried out by taking a test material of size 50 mm width × 300 mm length × 6 mm thickness from the test steel pipe.

The test for evaluating the weather resistance is based on a rust simulation test during sea transportation. Specifically, after immersing the test material in an aqueous solution prepared by diluting artificial seawater with 100 times of water, taking it out and drying it, and attaching salt on its inner and outer surfaces, the temperature was 50 ° C and the relative humidity was It was exposed to an atmosphere of 98% and the surface was visually observed to measure the time (days) until a discolored portion, that is, a rust (red rust), which can be clearly confirmed by visual observation, was generated.

In the test shown in FIG. 1, the surface roughness after shot blasting was adjusted so that Ry was 15 to 25 μm, and the surface roughness was 1 m.
The residual area ratio of the oxide film in the m ² visual field is varied within the range of 0 to 3.0%. From the results shown in FIG. 1, it is understood that the weather resistance is remarkably improved when the content of the magnetic iron component in the alumina abrasive cleaning material is 5% or less, regardless of the residual area ratio of the oxide film. It is more preferably 1% or less. Further, it should be noted that even when the residual area ratio of the oxide film is out of the range specified in the above-mentioned JP-A-11-236651 (area ratio: 2.1 to 3.0%), the weather resistance is improved. Is to be seen.

Next, in the test shown in FIG. 2, the residual area ratio of the oxide film in the 1 mm ₂ field of view after shot blasting was 0.8.
.About.1.4%, and the surface roughness Ry varies from less than 15 .mu.m to 55 .mu.m. From the results of FIG. 2, it is clear that weather resistance is improved when the content of the magnetic iron component in the alumina abrasive cleaning agent is 5% or less, regardless of the surface roughness, as in the case of FIG. Become. It is more preferably 1% or less. This means that when the surface roughness deviates from the range specified in the above-mentioned JP-A-11-236651 (surface roughness Ry: ~ 5
5 μm) also shows similar results.

From the results shown in FIGS. 1 and 2, it is not necessary to strictly regulate the surface roughness of the steel pipe and the residual area ratio of the oxide film by controlling the content of the magnetic iron content in the abrasive. I understand. This makes it possible to relax the operating conditions that define the size of the polishing / cleaning material, the collision angle of the polishing / cleaning material, and the like, leading to a reduction in manufacturing cost.

The polishing agent used in the present invention may be a non-ferrous oxide-based material, such as alumina or silica sand, or a non-ferrous carbide-based material, for example, as long as the magnetic iron content can be controlled to 5% or less. It may be silicon carbide or the like.
Further, in order to judge the degree of removal of the oxide film (mill scale) on site, it is effective to judge whether or not it takes 15 seconds or more for the discoloration to take place after the ferroxile liquid is attached to the surface. That is, when the time until discoloration takes 15 seconds or more, it can be determined that the degree of removal of the oxide film on the surface or the content of the magnetic iron component in the abrasive material is inappropriate.

Furthermore, in the present invention method, in order to reduce manufacturing cost, abrasive cleaning agent is recovered once after removal of the oxide layer, it circulating reused. In this case, it is necessary to control the content of magnetic iron mixed in the polishing / cleaning material to be recycled by installing an iron separator in the shot blasting machine. In any case, the separation of the magnetic iron component in the abrasive material and the measurement of the content are basically magnet separation and weighing, and do not require complicated work.

Further, when the polishing / cleaning material that has been used once is circulated, a new polishing / cleaning material is added in order to separate the magnetic iron content in the polishing / cleaning material and to supplement the amount reduced by abrasion and powdering of the polishing / cleaning material. Can be added. In this case, the additional amount is within a range that does not hinder the grinding work.

[0027]

EXAMPLES In order to confirm the effect of the martensitic stainless steel pipe manufactured by the method of the present invention, material billets having the chemical composition shown in Table 1 were prepared.

[0028]

[Table 1] After heating the above material billet to 1100-1300 ° C in a heating furnace,
A hollow shell was pierced with a piercer to produce a hollow shell, and subsequently, a finish rolling shell was manufactured by mandrel mill rolling. Next, the finished rolling stock tube was reheated to 1100 ° C. and passed through a stretch reducer to produce a seamless steel tube having an outer diameter of 88.9 mm, an inner diameter of 70 mm and a length of 1000 mm.

After that, the manufactured steel pipe was heated at 950 ° C. for 60 minutes, then air-cooled and quenched, and tempered at 650 ° C. for 30 minutes to produce a seamless steel pipe having an oxide film formed on its surface. A shot cleaning treatment was performed by spraying a polishing agent on the inner and outer surfaces of the manufactured steel pipe with an injection type alumina shot machine.

The conditions for the alumina shot were as follows: using the alumina abrasive cleaning material # 16 by recycling and recycling, the injection angle was 10 to 35 °,
The injection pressure was 4 to 6 kgf / cm ² (392 to 588 kPa). At this time, the alumina shot was carried out while varying the content of the magnetic iron component in the abrasive material in the range of 1 to 16% and grasping the surface roughness and the remaining area ratio of the oxide film.

A test piece having a size of 50 mm width × 300 mm length × 6 mm thickness was taken from a steel tube subjected to alumina shot.
As a test for evaluating the weather resistance, a rust simulation test during marine transportation was carried out under the same conditions as in FIGS. 1 and 2 above, and the number of weather resistance days until rust (red rust) occurred was investigated. The results are shown in Table 2.

[0032]

[Table 2] From the results of Table 2, Comparative Examples Nos. 1 to 7 all have a magnetic iron content of more than 5% contained in the abrasive.
The number of weather-resistant days is as short as 11-18 days. On the other hand, in the examples of the present invention, since the magnetic iron content in the abrasive material is 5% or less, the weather resistance is 26 to 34 days, which is a marked improvement in weather resistance. Further, even when the surface is relatively rough as in the present invention examples No. 13 and 15, the present invention examples No. 10, 14, 1
It can be seen that the weather resistance can be maintained even when the residual area ratio of the oxide film is relatively high as in No. 5.

[0033]

According to the manufacturing method of the present invention, by controlling the magnetic iron content contained in the non-ferrous oxide-based or non-ferrous carbide-based abrasive, a martensitic stainless steel pipe having excellent weather resistance, It can be efficiently manufactured at a low manufacturing cost.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the content of magnetic iron in a polishing and cleaning material used for alumina shot blasting and the weather resistance of a steel pipe when the residual surface contact ratio of an oxide film is used as a parameter.

FIG. 2 is a diagram showing the relationship between the content of magnetic iron in the abrasive material used for the alumina shot blasting treatment and the weather resistance of the steel pipe when the surface roughness is used as a parameter.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI // C21D 9/08 C21D 9/08 EF (58) Fields investigated (Int.Cl. ⁷ , DB name) B21B 45/04 B24C 1/00-11/00 C22C 38/00-38/18 C21D 9/08

Claims (2)

(57) [Claims] 1. A martensitic stainless steel having a Cr content of 9 to 15% by mass is made into a pipe, which is then heat treated. Then, the surface of the steel pipe is made of a non-ferrous oxide-based or non-ferrous carbide-based material . A method for producing a martensitic stainless steel pipe having excellent weather resistance, which comprises colliding a polishing / cleaning material having a magnetic iron content controlled to 5% or less by separation to remove an oxide film formed on the surface. 2. The martensitic stainless steel pipe with excellent weather resistance according to claim 1, wherein the abrasive cleaning material is recovered after the oxide film formed on the surface of the steel pipe is removed and recycled. Production method.