JPH03180427A - Tube making for duplex stainless steel - Google Patents

Abstract

PURPOSE:To carry out tube making excellent in hot workability and corrosion resistance and free from the occurrence of scalelike flaw and wrinklelike flaw by subjecting a billet of a duplex stainless steel with a specific composition to heating up to a temp. region where ferrite content is limited and then carrying out diagonal rolling. CONSTITUTION:A billet has a composition consisting of, by weight, <=0.03% C, 0.10-2.0% Si, 0.10-2.0% Mn, <=0.05% P, <=0.002% S, 17.0-30.0% Cr, 1.0-11.0% Ni, 0.10-6.0% Mo, 0.01-0.50% V, 0.01-0.10% Al, 0.10-0.40% N, <=0.0050% O, one or more kinds among 0.0005-0.010% Ca, 0.0005-0.010% Mg, and 0.0005-0.010% REM, and the balance Fe with inevitable impurities, and further, this billet is composed of a duplex stainless steel in which ferrite content at ordinary temp. is regulated to 30-70vol.%. This billet is heated up to a region of 50-70% ferrite content and formed into a seamless steel tube by a diagonal rolling method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing seamless pipes using a Mannesmann plug mill system or a Mannesmann mandrel mill system using duplex stainless steel as a raw material.

[Conventional technology]

Duplex stainless steel pipes have excellent corrosion resistance and weldability, as well as superior seawater corrosion resistance and high strength compared to ferritic or austenitic stainless steels, so they are widely used as line pipes for submarine flow lines. It is being

However, on the other hand, since duplex stainless steel tubes consist of a two-phase structure of ferrite and austenite phases, their hot workability is poor, and they cannot be subjected to blooming or hot rolling. ! There was a problem that cracks occurred during tube rolling, resulting in poor yield.

As a countermeasure to this, we reduced the content of S, which is a factor that reduces hot workability, and added Ca and REM to fix solid solution S as sulfide, thereby preventing segregation at grain boundaries. There is a method of reducing the amount of ferrite (Japanese Patent Application Laid-open No. 60-262946 fW) 2 or mtII by setting the billet heating temperature of duplex stainless steel to a temperature range where the amount of ferrite is 70% or more (special method). Publication No. 80716/1983)
.

Problems to be solved by the invention C] The former method (adding Ca, REM, etc.) certainly improves hot workability, but it reduces the corrosion resistance that duplex stainless steel originally has. The latter method certainly eliminates scale-like defects on the outer surface of the tube, but on the other hand, the amount of ferrite increases, causing a wrinkling phenomenon due to non-uniform deformation, resulting in wrinkle-like defects on the outer surface of the tube. There has been a problem in that scale-like flaws occur when attempts are made to suppress wrinkle-like flaws.

The present invention has been made in view of the above circumstances, and has excellent hot workability and corrosion resistance, and is free from scale-like flaws and
To provide a method for manufacturing a duplex stainless steel pipe without wrinkle-like defects.

[Means to solve the problem]

The method for manufacturing a duplex stainless steel according to the present invention is as follows: % by weight, Mn: 0.03% or less, Si: 0. lO~
70% by volume Mn: 0.05%, P: 0.05
% or less S: 0.002% or less, Cr: 17
．． 0-30.0%.

Ni: 1.0~1■, 0%, Mo: 0.10~
6.0%.

V: 0.01-0.50%, AI! :0.01
~0.10%.

N: 0.10-0.40%, O: 0.005
0% or less, and Ca: 0.0005 to 0.010%.

Mg: 0.0005-0.010%.

REM: A billet made of duplex stainless steel containing 5 to 0.010% of O,0O0, or two or more types, with the remainder consisting of Fe and unavoidable impurities, and with a ferrite content of 30 to 70% by volume at room temperature. , ferrite content 5
It is characterized in that it is heated to a temperature range of 0 to 70% by volume and made into a pipe by an inclined rolling method.

Further, another duplex stainless steel pipe manufacturing method according to the present invention is as follows:
% by weight, Mn: 0.03% or less, Si: 0.0
5%.

Mn: 0.05%, P: 0.05% or less S
: 0.002% or less, Cr: 17.0-3
0.0%.

Ni: 1.0 = 11.0%, Mo: 0.
10-6.0%, V: 0.01-0.50%, Al
: 0.01~0.10%N: 0.10~0.40%
, O: 0.0050% or less, and Cu: 1.0 to 2%.

W: 0.01-1.50%.

Ti: 0.01~0.50% Nb: 0.01~0.50% Containing one or more types of Ca: O,0O05-0.010%.

Mg: o,oos~0.010%.

RE gate: 0.0005-0.010% type 1 or 2
A billet made of duplex stainless steel with a ferrite content of 30 to 70% by volume at room temperature, the remainder consisting of Fe and unavoidable impurities, and a ferrite content of 50 to 70% by volume at room temperature.
It is characterized in that it is heated to a temperature range of 70% by volume and made into a pipe by an inclined rolling method.

[Effect]

The reason why the content ratio of each component and the ferrite content ratio of the duplex stainless steel constituting the billet in the present invention are limited as described above is as follows.

A) Component content ratio C is an element that is unavoidably contained in steel, but if its content exceeds 0.03%, carbides will precipitate, especially in the weld heat affected zone, leading to a decrease in corrosion resistance. Therefore, the C content was determined to be 0.03% or less.

In order to ensure sufficient Ni corrosion resistance, it is essential to reduce the 0 content, and therefore it is essential to add Si for the purpose of deoxidation. In this case, if the Si content is less than 0.01%, a sufficient deoxidizing effect cannot be obtained, while if the Si content exceeds 70% by volume, it will cause embrittlement, so the Ni content should be 0.05%. Established.

Mn Mn is a component added for deoxidizing and desulfurizing steel, but if its content is less than 0.10%, the deoxidizing and desulfurizing effect will be small, while if it is contained in excess of 70% by volume, The Mn content was set at 0.05% since it adversely affected corrosion resistance.

Since P is an impurity element that is unavoidably contained in steel and deteriorates hot workability and corrosion resistance, it is preferable that its content be as low as possible. It was set at .05% or less.

S is also an impurity that is inevitably contained in copper, and is the element that has the greatest effect on the hot workability of duplex stainless steel, so the lower the content, the better.

In order to ensure sufficiently satisfactory hot workability, it is necessary to reduce S to a level of 0.002% or less, so the upper limit of the S content was set at 0.002%.

Cr Cr is one of the basic components of duplex stainless steel and is an important component governing corrosion resistance. In order to exhibit a two-phase structure of austenite and ferrite, 17.0% is required.
It is necessary to have a Cu content of 30.
If it exceeds 0%, the σ phase tends to precipitate, deteriorating corrosion resistance and toughness, so Cr-containing stars are 17.0~
It was set at 30.0%.

Ni Ni is a component added in consideration of the Cr-containing L Mo content and N content in order to obtain a two-phase structure.
When the Ni content is less than 1.0%, the ferrite phase becomes the main component and a two-phase structure cannot be obtained. On the other hand, if Ni is contained in an amount exceeding 11.0%, not only will it become a phase mainly composed of austenite, making it impossible to obtain a two-phase structure, but it will also cause economic disadvantages since it is an expensive element. Become. Therefore, the Ni content was determined to be 1.0 to 11.0%.

O The Mo component has the effect of improving the corrosion resistance of steel, but if its content is less than 0.10%, the desired effect cannot be obtained due to the above effect, while on the other hand, if it is contained in excess of 6.0%, Since Mo content significantly promotes the precipitation of 1.
It was set at 0 to 6.0%.

■■ component has the effect of improving pitting corrosion resistance when added in appropriate amounts along with Cr, Mo, and Cu, but if the content is less than 0.01%, the desired effect cannot be obtained; If the content exceeds 50%, hot workability deteriorates, so the content (2) was determined to be 0.01 to 0.50%.

4I! Al is also an essential component as a deoxidizing agent, and in order to ensure sufficient corrosion resistance, the deoxidizing action of Al was also utilized. l
It is essential to reduce However, its content is 0.01%
If it is less than 0.10%, the desired deoxidizing effect cannot be obtained;
If the Af content exceeds 0.01 to 0.0, AfN will precipitate and cause a decrease in corrosion resistance.
It was set at 0.4%.

N is an important component in forming a two-phase structure and is also effective in improving corrosion resistance, but if the N content is less than 0.10%, the above effects are poor, while if it exceeds 0.40%, The N content is 0.10 to 0.4 because it reduces hot workability and tends to cause blowholes during casting.
It was limited to 0%.

○ O is an undesirable impurity element that easily forms compounds with Ca, REM, etc. and easily becomes oxide-based inclusions that reduce corrosion resistance. It is necessary to reduce it to .0050% or less.

In order to improve corrosion resistance, the lower the O content, the better, and desirably it is preferably reduced to 0.0030% or less.

(Left below) Ca2M, and REM (rare earth element) Ca, 9,
Alternatively, since REMs such as La and Ce all have the effect of producing sulfides in steel, fixing S, and improving the hot workability of steel, one or two of these can be used. Although the above additions are essential, if the content of any of them is less than 0.0005%, the desired effect due to the above action cannot be obtained;
Even if the content exceeds 0.010%, the above effect will be saturated, so Ca.

Mg or REM (7) content is 0.0005 each
It was set at ~0.010%.

Cu, W, Ti, and Nb All of these components have the effect of producing stable carbides in steel and improving corrosion resistance, so one or more of these components may be added if necessary. However, the reason for limiting the content range for each individual component will be explained below.

a) Cu Cu component has the effect of improving the acid resistance of steel, but if its content is less than 1.0%, the desired effect cannot be obtained, while if it is contained in excess of 70% by volume, hot The Cu content is 0.05 because it greatly reduces workability.
%.

b) W Adding an appropriate amount of Cr and Mo to W can improve local corrosion resistance, but if the content is less than 0.01%, the desired effect due to the above action cannot be secured;
W content was set at 0.01 to 1.50%, since if the W content exceeds 0.01% to 1.50%, the hot workability would deteriorate.

c) Ti and Nb These elements generate stable carbides in steel and contribute to improving corrosion resistance, but if any of them is less than 0.01%, a sufficient effect cannot be obtained; Since the above effects would be saturated even if the content exceeds 50%, the Ti content and Nb content were determined to be 0.01 to 0.50%.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for manufacturing a duplex stainless steel pipe according to the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a flowchart showing the main steps of the pipe manufacturing method according to the present invention.
The heated billet is then heated in a temperature range of ~70% (step S2), and the heated billet is used in an inclined roll rolling mill called a piercer and its subsequent elongation mills such as a mandrel mill, a plug mill, an asocel mill, and a pilger. - A seamless pipe is manufactured by the Mannesmann pipe manufacturing method, which is finished using a mill or the like and a reducer or sizer, which is a sizing mill (step S3).

Each step will be specifically explained below.

1) Duplex stainless steel billet The materials used for the duplex stainless steel billet are as follows i):
Blossoming having the component composition as in ii) and having a ferrite content of 30 to 70% by volume at room temperature.

Manufactured by hot rolling or continuous casting.

i) % by weight, Mn: 0.03% or less, Si: 0.0
5%.

Mn: 0.05%, P: 0.05% or less.

S: 0.002% or less, Cr: 17.0~
30.0%.

Ni: 1.0 to 11.0%, Mo: 0
．． 10-6.0%.

V: 0.01-0.50%, AI! :0.01
~0.10%.

N: 0.10-0.40%, O: 0.0050%
Contains the following, and Ca: 0.0005 to 0.010%.

Mg: 0.0005-0.010%.

R song: Contains one or more of 0.0005 to 0.010%, with the remainder consisting of Fe and inevitable impurities.

ii) % by weight, Mn: 0.03% or less, Si: 0.0
5%.

Mn: 0.05%, P: 0.05% or less.

S: 0.002% or less, Cr: 17.0~
30.0%.

Ni: 1.0-11.0%, Mo: 0.1
0-6.0%.

V: 0.01-0.50%, Al: 0.0
1-0.10%.

N: 0.10-0.40%, O: 0.0050%
Contains the following, and Cu: 1.0 to 2%.

W: 0.01-1.50%.

Ti: 0.01~0.50% Nb: 0.01~0.50% Containing one or more of the following, Ca: 0.0005-0.01O%.

Mg: 0.0005~o, oto%.

REM: Contains one or more of 0.0O05 to o, oio%, with the remainder consisting of Fe and inevitable impurities.

FIG. 2 is a graph showing the results of a comparative test regarding the high-temperature ductility reduction ratio (%) of the two-phase stainless steel billet used in the method of the present invention described above and the two-phase stainless steel billet used in the conventional method, The horizontal axis shows the test temperature (t'), and the vertical axis shows the hot ductile reduction rate (%). The marks plotted in the middle of the graph show the results for the billet used in the method of the present invention, and the marks plotted with squares and squares show the results for the billet used in the conventional method.

As is clear from this graph, the billet used in the method of the present invention has a significantly improved high-temperature ductile drawing ratio in the range of 1000 to 1150'C, and no decrease in high-temperature ductile drawing ratio in the range of 1150 to 1300'C. I understand that there isn't.

2) Heating process of billet The content of ferrite structure in the billet made of duplex stainless steel, which is the material mentioned above, increases as the temperature increases, and when the content exceeds 70%, wrinkles after pipe production become large. The external skin needs to be taken care of.

Therefore, it is heated to a temperature range in which the ferrite content is 30 to 70% by volume, preferably 50 to 70% by volume, that is, in a temperature range of 1150 to 1250°C depending on the actual values of the components.

3) Pipe-making process The pipe-making process is piercing rolling using an inclined roll rolling mill called a piercer, mandrel girdle, and plug mill.

A Mannesmann pipe making method is used in which stretch rolling is performed using an Ansell mill and a pilger mill, and constant diameter rolling is performed using a reducer and a sizer.

For example, when using the Evermann-Mandrel mill method, a round billet is heated to obtain a hollow shell in a piercing mill, then stretched and rolled in a mandrel mill, reheated as necessary, and then stretched into a stretch reducer. to obtain a seamless pipe.

In addition, when using the Mannesmann plug mill method, the round billet is similarly heated and a hollow shell is obtained in a piercing mill, then stretched and rolled in an elongator, further stretched in a plug mill, passed through a reeler and a sizer, and then the seam is formed. Obtain no tube.

Among these, the cooling of the inclined rolls in the pipe manufacturing process using the inclined roll rolling method, particularly in the perforation and elongation rolling processes, is carried out as follows.

FIG. 3 is a schematic diagram showing the process of perforating and elongating a billet, and in the figure, 1.1 indicates a barrel-shaped or cone-shaped inclined roll, 2 indicates a plug, and 3, 3 indicates a guide shoe. The inclined rolls 1.1 are each provided with a gorge portion having a maximum diameter at the intermediate portion in the axial direction, and are located on both sides of the pass line of the Vilent hollow shell H, and have a predetermined intersecting angle, respectively.
They are arranged at an inclined angle, and are each driven to rotate in the direction of the arrow by a drive source (not shown). On the other hand, the plug 2 is supported by a mandrel (not shown) and is supported on the pass center of the billet hollow shell H. The guide shoes 3.3 are arranged around the pass line of the billet/hollow shell H alternately with the inclined rolls 1,1.

Then, the billet is rolled along the pass line with inclined roll 1,
The plug 2 is inserted between the plugs 1 and 2 and rotated and transferred in the axial direction, ie, so-called spiral movement, and the plug 2 is inserted into the center of the shaft, thereby manufacturing the hollow shell H.

Mist spray nozzles 11, 11 constituting a roll cooling system, air spray nozzles 12.12 constituting a roll draining system, and wipers 13.13 made of heat-resistant rubber are arranged on the outer periphery of each inclined roll 1, 1, respectively. There is. The mist spray nozzle 11.11 is located at a position away from the pass line of the billet and hollow shell H in the rotational direction of the inclined roll 1°1, and is set at a position where the mist does not directly scatter and adhere to the billet and hollow shell H surfaces. It is. The amount of water sprayed from the mist spray nozzle 11.11 is set according to the roll diameter of the inclined roll 1°, the roll barrel, etc.

In the rotational direction of the air spray nozzle l, the mist spray nozzle IL11
installation position, inclined roll 1.1 and billet.

It is set so that air is injected toward the direction opposite to the rotational direction of the inclined roll 1.1 at an intermediate portion between the point of contact with the hollow shell H and the direction of rotation of the inclined roll 1.1.

FIG. 3 is a schematic diagram showing how the wiper 13 is installed,
Wiper 13. 13 is an air spray nozzle 12.1 in the direction of rotation of the inclined roll 1.1. 12 and the point of contact between the inclined roll 1 and the billet or hollow shell H.

It is supported by a support member 14 so as to be in sliding contact with substantially the entire circumferential surface in the axial direction of L.

It should be noted that if pipe making is repeated, the temperature of the inclined rolls 1, 1 will increase, and it is predicted that the cooling capacity will decrease relatively.
In this case, the mist spray nozzles 11, 11 are operated after the completion of perforation and elongation rolling of the billet until the start of perforation of the next billet, that is, while there is no risk of water coming into direct contact with the billet. Inclined roll 1 by increasing the amount of mist sprayed from.

The cooling capacity will be increased compared to 1.

a mist spray nozzle 11.11 as described above;
Air spray nozzle 12. 12 and wiper 13.
13, etc., and cool the surfaces of the inclined rolls 1 and 1 and drain the water after cooling. This prevents the billet and hollow shell H from being locally cooled more than necessary due to contact with water, and prevents external surface flaws. It becomes possible to suppress the occurrence.

Next, comparative test results will be shown for a seamless pipe produced by the method of the present invention and a seamless pipe not produced by the method of the present invention.

The sample billet used was Sample A with component U as shown in Table 1.
Cave 2 A billet with a diameter of 213 m and a length of 3220 n is produced using B steel, and this is perforated and rolled with a piercing rolling machine to produce a hollow shell, which is then stretched and rolled with a stretching mill to form a joint as a finished product. A tubeless tube was manufactured and the occurrence of surface defects was observed.

The target dimensions of the hollow shell and finished product are as follows.

Hollow shell: Outer diameter: 223 mm: Length: 6400 mm: Wall thickness: 29.5 mm Finished product: Outer diameter: 171.2 mm: Length: 12,800 mm: Wall thickness: 17.2 mm Inclined roll of the piercing rolling machine used, mist spray nozzle,
The dimensions of the air spray nozzle are as follows.

Inclined roll: 1200n diameter mist spray nozzle Air pressure: 4kg/c+J Air supply amount: 17.2Nm'/h/individual water pressure
: 5kg/aJ Water amount: 14.61/min/piece Distance to roll surface: 200kg/aJ Number of nozzles
: 3 pieces/roll air spray nozzle Air pressure: 4 kg/crA Air supply amount: 80 ON 17 minutes/piece Distance to roll surface = 200 Number of nozzles: 5 pieces/roll The results are as shown in Table 2. Each part in the evaluation column in Table 2 shows the following contents.

◎ indicates external flaws: 0% Misroll 0 horse ○ indicates external flaws = less than 1.5% Misroll 0 pawn Δ indicates external flaws:
Less than 1.5% ξ Swirl less than 5.0% × indicates external flaws: 1.5% or more Dan scroll less than 5.0% × X indicates external flaws: 1.5% or more 5 swirl 5.0% or more ( As is clear from Table 2, when the present invention examples with test numbers NQI to 8 were used, the incidence of external defects was small for both A steel and B steel, and the misroll in the piercing mill was 0%. Most of the evaluations were ◎ and ○, and the evaluation was △ only when the inclined roll was not cooled. On the other hand, both the comparative example and the conventional example had a high incidence of external defects and were rated △.

It was marked with × and ××.

〔effect〕

As described above, the method of the present invention can reduce not only microscopic cracks on the outer surface of the outer bottom of a duplex stainless steel pipe but also wrinkle defects due to the ridging phenomenon, and also improve the corrosion resistance and hot workability of the product. This has an excellent effect in that a high quality seamless pipe can be obtained without any damage.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing the main steps of the method of the present invention;
FIG. 2 is a graph showing the results of a comparative test regarding the hot ductility drawing ratio between the billet used in the present invention and a conventional billet;
FIG. 3 is a schematic diagram showing the manner in which the inclined rolls are cooled during the inclined rolling process in the method of the present invention, and FIG. 4 is a schematic diagram showing the manner in which wipers are arranged.

Claims (1)

[Claims] 1. C: 0.03% or less, Si: 0.10 to 2.0%, Mn in weight percentage
: 0.10-2.0%, P: 0.05% or less, S: 0.
002% or less, Cr: 17.0-30.0%, Ni: 1
．． 0-11.0%, Mo: 0.10-6.0%, V: 0
．． 01-0.50%, Al: 0.01-0.10%, N
: 0.10-0.40%, O: 0.0050% or less, and Ca: 0.0005-0.010%, Mg: 0.0005-0.010%, REM: 0.0005-0 .010%, the remainder consists of Fe and unavoidable impurities, and the ferrite content at room temperature is 30 to 70%.
1. A method for making a pipe of duplex stainless steel, which comprises heating a billet made of duplex stainless steel with a ferrite content of 50% to 70% by volume, and manufacturing the billet by tilt rolling. 2. C: 0.03% or less, Si: 0.10-2.0%, Mn in weight percentage
: 0.10-2.0%, P: 0.05% or less, S: 0.
002% or less, Cr: 17.0-30.0%, Ni: 1
．． 0-11.0%, Mo: 0.10-6.0%, V: 0
．． 01-0.50%, Al: 0.01-0.10%, N
: 0.10 to 0.40%, O: 0.0050% or less, and Cu: 1.0 to 2%, W: 0.01 to 1.50%, Ti: 0.01 to 0.50. % Nb: 0.01-0.50%, Ca: 0.0005-0.010%, Mg: 0.0005-0.010%, REM: 0.0005-0 .010%, the remainder consists of Fe and unavoidable impurities, and the ferrite content at room temperature is 30 to 70%.
1. A method for making a pipe of duplex stainless steel, which comprises heating a billet made of duplex stainless steel with a ferrite content of 50% to 70% by volume, and manufacturing the billet by tilt rolling. 3. In the inclined rolling, the inclined rolls are cooled using a mist spray containing a mixture of air and water, and the water used for cooling is sprayed with air onto the inclined roll surface and with a wiper that is in sliding contact with the inclined roll surface. The method for making a duplex stainless steel pipe according to claim 1 or 2, which includes a step of removing.