JP4529640B2 - Stainless steel pipe manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing a stainless steel pipe manufactured by mandrel mill rolling, and more specifically, scales generated on the surface of a steel pipe by mandrel mill rolling and stretch reducer rolling and subsequent heat treatment are easily removed by pickling treatment. The present invention relates to a method for manufacturing a stainless steel pipe.

  In recent years, there has been a growing demand for steel pipes made of stainless steel for heat exchangers for oil wells, boilers, chemical industries, petroleum industries, etc., and mandrel as a manufacturing method for hot seamless steel pipes in order to produce them with high quality and efficiency. Production by mill rolling is increasing.

  In manufacturing by mandrel mill rolling, the raw stainless steel billet is heated in a rotary hearth heating furnace, a hollow shell is manufactured by piercing (piercer) rolling, and then the finishing tube is drawn and rolled by mandrel mill rolling. To do. Then, after reheating as needed, finish rolling is performed by a stretch reducer.

  Conventionally, in the production process of stainless steel, solution treatment is performed after hot rolling in order to improve the corrosion resistance by solidifying Cr carbonitride precipitated during hot rolling and to ensure mechanical properties. Usually, in the production of a stainless steel plate, a mechanical method such as shot blasting, pickling, or a combination thereof is performed in order to remove the scale generated on the surface after the solution treatment. Various proposals have been made for removing the scale of the stainless steel plate.

  For example, in Patent Document 1, in an austenitic stainless steel sheet, as a solution treatment after hot rolling, heat treatment is performed by heating to about 1010 to 1150 ° C. and quenching, and after pickling, cold rolling, finish annealing, acid Instead of the conventional technology that is manufactured after washing, in the hot rolling, by specifying the total rolling reduction and rolling end temperature of rough rolling and finish rolling, and by further limiting the winding temperature and cooling conditions of the hot rolled steel strip A method of manufacturing a stainless steel strip that can eliminate the solution treatment has been proposed.

  Further, in Patent Document 2, instead of solution treatment at high temperature in an austenitic stainless steel sheet, generation of a Cr-depleted layer immediately below the scale layer accompanying solution treatment is limited to low-temperature heat treatment in a temperature range of 1000 ° C. or lower. A method for producing a stainless steel cold-rolled sheet is proposed in which after mechanical pre-scaling by shot blasting is performed, the scale is removed by pickling in a simple pickling bath of hydrochloric acid. Yes.

  On the other hand, in steel strips obtained by batch annealing of ferritic stainless steel strips and hot-rolled steel strips, grain boundary erosion grooves in sulfuric acid pickling may be a factor, which may deteriorate the quality of the steel sheet surface. For this reason, in Patent Document 3, paying attention to the reduction of the quality by reducing the P concentration of the grain boundary, heat treatment of the hot-rolled steel strip and the batch-annealed steel strip before the pickling is performed before the pickling. Thus, a method for producing a ferritic stainless steel sheet is proposed in which P segregated at the grain boundaries is diffused to prevent the occurrence of grain boundary erosion grooves in sulfuric acid pickling.

  According to the manufacturing methods proposed in Patent Documents 1 to 3, desired scale removal can be achieved, and deterioration of the steel sheet surface due to descaling with an aqueous sulfuric acid solution can be prevented. However, the manufacturing method proposed here exerts a predetermined effect on a stainless steel plate, and the effect is not effective even when applied to the removal of scale generated on the surface of a stainless steel tube manufactured by mandrel mill rolling. In particular, the scale partially remains on the inner surface of the steel pipe, and reliable scale removal cannot be performed.

JP 60-59022 A Japanese Patent Laid-Open No. 56-158819 JP 2002-60911 A

The present invention was made in view of the problem of scale removal generated on the surface of the stainless steel pipe manufactured by the mandrel mill rolling described above, and per unit area of the lubricant adhering to the mandrel bar surface in the mandrel mill rolling. Provided is a stainless steel pipe manufacturing method capable of efficiently removing scale by appropriately selecting the carbon equivalent weight (g / m ² ) and the heat treatment conditions of the stainless steel pipe rolled using the mandrel bar. That is the purpose.

  In order to solve the above-mentioned problems, the present inventors have conducted a detailed investigation on the surface properties of a stainless steel pipe manufactured by mandrel mill rolling. It was clarified that it was caused by the lubricant used.

  When rolling stainless steel with a mandrel mill, in order to prevent seizure between the mandrel bar and the material to be rolled, a lubricant is sprayed on the mandrel bar before rolling to form a lubricating film on the surface. After the mandrel mill rolling, if the lubricant on the mandrel bar surface adheres and remains on the inner surface of the steel pipe, and if subsequent reheating or stretch reducer rolling is performed, the air permeability is poor on the inner surface of the steel pipe, the lubricant will abnormally oxidize. Then, an abnormal oxide scale is locally generated on the inner surface of the obtained stainless steel pipe, where the scale becomes thick locally.

  The lubricant sprayed on the mandrel bar contains a large amount of graphite and an organic binder, and an abnormal oxide scale is generated due to carbon (C) contained in the graphite and the binder. The abnormal oxidized scale is thick, and the pickling solution used for removing the scale is difficult to permeate, making it difficult to remove the scale.

  The manufacturing method proposed in Patent Documents 1 to 3 is an improvement of heat treatment and pickling treatment applied to a stainless steel plate, and has been confirmed to be more efficient than conventional mechanical scale removal. However, when hot rolling a stainless steel plate, an abnormal oxide scale as observed in a stainless steel pipe manufactured by mandrel mill rolling is not generated.

  For this reason, even if the improvement of the heat treatment and pickling treatment applied to the stainless steel plate proposed above is adopted for a stainless steel pipe manufactured by mandrel mill rolling, the occurrence of abnormal oxidation scale cannot be avoided and the scale can be reliably increased. Can not be removed. Therefore, when scale removal is performed by pickling treatment combined with heat treatment on a stainless steel pipe rolled into a mandrel mill, new improvements are required.

Based on this recognition, using steel pipes with abnormal oxidation scales generated by actual mandrel mill rolling, experimentally changing the heat treatment conditions and confirming the removal of the scale by pickling treatment, Efficient removal of scale by properly selecting the carbon equivalent weight (g / m ² ) per unit area of lubricant adhering to the mandrel bar surface and the heat treatment conditions of the stainless steel pipe rolled using the mandrel bar I found out that I can do it.

Here, the carbon equivalent weight (g / m ² ) means the carbon equivalent weight (hereinafter referred to as “C equivalent weight” contained in the graphite and the organic binder in the lubricant per unit area of the lubricant adhering to the mandrel bar surface. ")". The C equivalent weight is a value obtained by dividing the C equivalent weight in the lubricant sprayed onto the mandrel bar by the surface area of the mandrel bar to be applied.

In order to explain the above findings, FIG. 1 shows the case where the C equivalent weight (g / m ² ) is taken as the X axis and the heating temperature (° C.) of the stainless steel tube rolled using the mandrel bar is taken as the Y axis. It is a figure which shows the relationship. According to the study by the present inventors, it is clear that the scale can be efficiently removed by heat-treating the stainless steel pipe under conditions within a range connecting the points in FIG. 1 with straight lines.

The present invention has been completed on the basis of the above findings, and has the following (1) and (2) methods for producing a stainless steel pipe.
(1) A method for producing a stainless steel pipe in which a stainless steel pipe produced by mandrel mill rolling and stretch reducer rolling is subjected to heat treatment and scales formed on the surface by pickling treatment are removed, and the C equivalent weight in the mandrel mill rolling (G / m ² ) is the X axis, and when the heat treatment of the stainless steel pipe is represented by the relation diagram with the heating temperature (° C.) of the stainless steel pipe rolled using the mandrel bar as the Y axis, A (2 g / m ² , 1000 ° C.), B (20 g / m ² , 1000 ° C.), C (100 g / m ² , 1150 ° C.), D (100 g / m ² , 1300 ° C.), E (20 g / m) m ^2, 1300 ° C.) and F (after heating each point of 2g / m ^2, 1300 ℃) under the conditions of within a range connected by a straight line, producing side of the stainless steel tube, characterized in that quenching It is (hereinafter referred to as "first production method").
(2) During the heat treatment of the stainless steel pipe, B (20 g / m ² , 1000 ° C.), C (100 g / m ² , 1150 ° C.), D (100 g / m ² , 1300 ° C.) and E ( ^{2. The} method for producing a stainless steel pipe according to claim 1, wherein heating is performed within a range in which each point of 20 g / m ² and 1300 ° C. is connected in a straight line, and then rapidly cooling (hereinafter referred to as “second”). Is called "Manufacturing method").

According to the method for producing a stainless steel pipe of the present invention, by appropriately selecting the C equivalent weight (g / m ² ) in mandrel mill rolling and the heat treatment conditions of the stainless steel pipe rolled using the mandrel bar, While suppressing the abnormal oxidation scale which generate | occur | produces in a steel pipe inner surface, the scale formed in the stainless steel pipe surface can be efficiently removed by the rapid cooling after heat processing.

The contents of the present invention will be described in relation to the relationship between the C equivalent weight (g / m ² ) and the heating temperature (° C.), the applicable stainless steel, the first production method, and the second production method.

1. Relationship between C equivalent weight (g / m ² ) and heating temperature (° C.) The C equivalent weight (g / m ² ) in the mandrel mill rolling and the heating temperature of the stainless steel pipe, which became the technical basis for completing the present invention In order to obtain the relationship with (° C.), a steel pipe in which an abnormal oxidation scale was generated by actual mandrel mill rolling was manufactured, and the pickling test was carried out by experimentally changing the heat treatment conditions. Table 1 shows the chemical compositions of the steels A and B used.

Billets having a diameter of 200 mm and a length of 3000 mm were produced using the steels A and B shown in Table 1. The obtained billet was heated to 1200 ° C., and a hollow shell having an outer diameter of 192 mm and a wall thickness of 16 mm was manufactured by Mannesmann Piercer rolling, and the boric acid type in which the C equivalent weight was changed in the range of ² to 100 g / m ² and Using a mandrel bar coated with a graphite-based lubricant, a finishing blank having an outer diameter of 151 mm and a wall thickness of 6.5 mm was manufactured by mandrel mill rolling at a finishing temperature of 1100 ° C. After that, it was heated at 1000 ° C. for 20 minutes in a reheating furnace, and finished and rolled to an outer diameter of 63.5 mm and a wall thickness of 5.5 mm with a stretch reducer.

Mandrels adjustment of C corresponding weight of the bar surface attached to lubricants, C corresponds weight ^{2g / m 2, 10g / m} 2 and boric acid consisting 20 g / m ² lubricants, C corresponds weight 40 g / m ² and borate consisting 60 g / m ² lubricants and formulation of the graphite-based lubricant, and selectively using graphite-based lubricant composed of 80 g / m ² and 100 g / m ^2, further lubricant to the mandrel bar surface The amount of adhesion was also changed.

  The finish-rolled steel pipe was cut to a length of 250 mm, heated in an electric furnace while changing the heating temperature in the range of 950 to 1300 ° C., held for 20 minutes, and then immersed in a water bath and rapidly cooled. The obtained steel pipe was immersed in a 5% NaOH solution bath for 15 minutes, then immersed in a 5% hydrofluoric acid + 8% nitric acid hydrofluoric acid solution for 6 minutes, and finally washed with high-pressure water. The outer surface of the steel pipe after cleaning was visually observed to confirm the scale removal status.

FIG. 2 is a diagram showing a scale removal situation when a C equivalent weight (g / m ² ) in mandrel mill rolling and a heating temperature (° C.) of a stainless steel pipe rolled using the mandrel bar are changed. . From the results shown in FIG. 2, it can be seen that the scale can be efficiently removed by appropriately selecting the weight of carbon contained in the graphite and the organic binder in the lubricant, that is, the weight corresponding to C and the heating temperature.

  As shown in FIG. 2, the remaining scale due to the occurrence of abnormal oxide scale is affected by the C equivalent weight, and as the C equivalent weight increases, the area where the abnormal oxide scale occurs increases and the scale thickness also increases. come.

The C equivalent weight can be changed depending on the amount of graphite added and the amount of C in the organic binder. Usually, the boric acid lubricant has a C equivalent weight of ² to 30 g / m ² , the graphite lubricant has a C equivalent weight of 80 to 100 g / m ² , and the C equivalent weight of 30 to 80 g / m ² . When doing so, both lubricants are blended and used. Therefore, the C equivalent weight can be adjusted by the type and composition of the lubricant and the amount of lubricant adhering to the mandrel bar surface, and the frequency of occurrence of abnormal oxidation scale can be controlled.

  Furthermore, in order to reliably remove the scale having a predetermined thickness or more by the pickling treatment, it is necessary to generate cracks in the scale so that the pickling solution can penetrate the scale. For this reason, heat treatment is performed before the pickling treatment, and rapid heating and cooling are performed, thereby applying thermal strain to the scale to generate microcracks (cracks). By allowing the pickling solution to penetrate through the generated crack, the scale can be efficiently removed.

  In order to generate cracks in the scale, the higher the heating temperature, the more rapid thermal cooling can be applied to the scale, and cracks can be generated effectively. Therefore, an appropriate heating temperature should be selected according to the weight of graphite in the lubricant and the C equivalent weight in the organic binder. Specifically, conditions within a range connecting the points in FIG. 1 and FIG. After heating the stainless steel tube with the above, it is possible to perform efficient and reliable descaling by quenching.

2. Applicable stainless steels As stainless steels applicable in the present invention, steel types that may cause abnormal oxidation scales on the inner surface of steel pipes during mandrel mill rolling are targeted, including austenitic stainless steel, duplex stainless steel, ferritic stainless steel, Any martensitic stainless steel can be applied.

  In particular, since austenitic stainless steel and duplex stainless steel produce thin and dense scales compared to other stainless steels, the part where abnormal oxidation scale is generated is a relatively significantly thicker scale than other parts. It becomes. Therefore, when pickling is performed under normal conditions, pickling of the abnormally oxidized scale portion becomes insufficient and residual scale spots become noticeable, so the pickling time is made longer than usual for removing the scale. There is a need.

  For this reason, in the present invention, austenitic stainless steel or duplex stainless steel, which has a longer pickling time due to an abnormal oxidation scale and deteriorates pickling characteristics, is used as a suitable steel type. There are no particular restrictions on the steel types that can be applied in the present invention. And austenitic stainless steels such as SUS347 and SUS347H, duplex stainless steels such as SUS329J1, SUS329J3L and SUS329J4L, and their corresponding steel types. Further, since Ni has little influence on the generation of scale, it can be applied to high Ni austenitic stainless steels such as NCF800 and NCF800H.

  Examples of applicable steel chemical compositions include, by mass%, C ≦ 0.15%, Si ≦ 1.5%, Mn ≦ 2.0%, P ≦ 0.05%, S ≦ 0.03%, Cr: 15 to 28% and Ni: 3 to 35%, Mo: 5% or less, Cu: 2.5% or less, Ti: 1% or less, Nb: 1% or less, and Al: 1% as necessary An austenitic stainless steel or a duplex stainless steel that can contain one or more of the following.

3. About a 1st manufacturing method The 1st manufacturing method of this invention is the conditions in the range which connects each point of A, B, C, D, E, and F in the said FIG. 1 in the straight line in the case of the heat processing of a stainless steel pipe. It is characterized by rapid cooling after heating.

In other words, the structure of the first manufacturing method is intended for a stainless steel pipe rolled using a mandrel bar having a C equivalent weight of ² to 100 g / m ² in mandrel mill rolling, and in the heat treatment of the steel pipe, When the C equivalent weight is less than 20 g / m ² , the heating temperature is 1000 to 1300 ° C., or when the C equivalent weight X is 20 g / m ² or more, the heating temperature is 1000 to 1300 ° C., And after satisfying the relationship shown in the following formula (1) of the C equivalent weight X and the heating temperature Y corresponding to the straight line connecting B and C in FIG.

Y ≧ (15/8) X + 962.5 (1)
In the first manufacturing method, the C equivalent weight in mandrel mill rolling is set to ² to 100 g / m ² . The reason why the lower limit of the C equivalent weight is set to 2 g / m ² is that the boric acid-based lubricant is the minimum amount necessary for developing the original characteristics (lubricating effect) of the lubricant necessary for mandrel mill rolling. On the other hand, the upper limit of the C equivalent weight was set to 100 g / m ² because the lubrication effect was saturated even when more lubricant was applied, and dripping occurred with the application to the mandrel bar. This is because the lubricant cannot be applied due to its thickness.

When the C equivalent weight is as low as less than 20 g / m ² , the heating temperature is set to 1000 to 1300 ° C. because the generation of abnormal oxide scale is small and the dependence on the heating temperature is small. Here, the lower limit of the heating temperature is 1000 ° C., which is the minimum temperature required for softening and solution treatment for cold working performed after mandrel mill rolling, and the C equivalent weight is small. Depending on the temperature at which descaling is possible.

  On the other hand, the upper limit of the heating temperature is set to 1300 ° C. The higher the heating temperature, the greater the subsequent rapid cooling, the greater the thermal strain applied to the scale, the more likely to crack, and the more reliable removal of the scale by pickling. When the temperature is higher than 1300 ° C., not only the scale generation amount is increased and the product yield is decreased, but also the energy intensity is deteriorated.

  In the production method of the present invention, the heating and holding time of the stainless steel pipe is not specified, but the effect of softening treatment or solution treatment is exhibited and the mechanical properties after heat treatment are stabilized in order to maintain the holding temperature. 1 minute or more is desirable.

When the C equivalent weight X is as large as 20 g / m ² or more, it is necessary to set the heating temperature to 1000 to 1300 ° C. and satisfy the relationship of the C equivalent weight X and the heating temperature Y to the following formula (1). is there.

Y ≧ (15/8) X + 962.5 (1)
The reason why the above equation (1) is satisfied is that, depending on the thickness of the abnormal oxide scale, the heating temperature is increased and quenched to increase the thermal strain on the scale and facilitate the generation of cracks. is there. In addition, the lower limit of the heating temperature is the above formula (1), which is a temperature required for softening or solution treatment for cold working, and scale removal is possible according to the C equivalent weight. Depending on the temperature. On the other hand, the upper limit of the heating temperature is set to 1300 ° C. for the same reason as in the case where the C equivalent weight is less than 20 g / m ² .

  In the first manufacturing method, the stainless steel pipe is heated and then rapidly cooled. In order to surely remove scales of a predetermined thickness or more by pickling treatment, thermal strain is applied to the scales by rapid cooling to generate cracks. As the means for rapid cooling, water cooling, oil cooling or the like is appropriately selected depending on the stainless steel type. As a general means, water cooling is adopted.

  In the production method of the present invention, the pickling conditions after the heat treatment are not defined. Depending on the type of stainless steel, conditions such as sulfuric acid washing, hydrochloric acid washing, and hydrofluoric acid washing may be appropriately selected. When descaling austenitic stainless steel, a nitric acid solution containing nitric acid, hydrofluoric acid and water is often used because the pickling time is shortened and the pickling properties are excellent.

4). About the 2nd manufacturing method The 2nd manufacturing method of the present invention, in the case of the heat treatment of the stainless steel pipe, after heating under the conditions within the range connecting the points B, C, D and E in FIG. It is characterized by rapid cooling.

In other words, in the second manufacturing method, a stainless steel pipe rolled using a mandrel bar having a C equivalent weight of 20 to 100 g / m ² in mandrel mill rolling is used as a target for heat treatment of the steel pipe. The temperature Y is 1000 to 1300 ° C., and after satisfying the relationship represented by the following formula (1) of the C equivalent weight X and the heating temperature Y, the temperature is rapidly cooled.

Y ≧ (15/8) X + 962.5 (1)
In the second manufacturing method, the C equivalent weight in mandrel mill rolling is limited to ²⁰ to 100 g / m ² . In consideration of the lifetime of the mandrel bar, it is desirable that the lubricant is applied uniformly over the entire surface of the mandrel bar, but the lubricant may not be applied uniformly over the entire surface of the mandrel bar. Therefore, the weight equivalent to C is 20 g / m ^2. If applied above, the lubricant is applied over the entire surface, so the lower limit was set to 20 g / m ² . The upper limit is due to the same reason as in the first manufacturing method.

  In the second manufacturing method, the heating temperature is defined as 1000 to 1300 ° C. As with the first manufacturing method, this ensures the minimum temperature required for softening and solution treatment for cold working, ease of scale cracking, product yield, and energy intensity. This balance is taken into consideration. Furthermore, in order to easily generate scale cracks according to the thickness of the abnormal oxide scale, the relationship represented by the following formula (1) between the C equivalent weight X and the heating temperature Y is satisfied.

Y ≧ (15/8) X + 962.5 (1)
Also in the second manufacturing method, rapid cooling after heating is performed in order to reliably remove scales of a predetermined thickness or more by pickling treatment.

  In order to confirm the effect of the production method of the present invention, a stainless steel pipe that has been mandrel-rolled and finish-rolled using a billet manufactured from steel A and steel B of the steel types shown in Table 1 above, is heat-treated in an actual operation line, Thereafter, pickling treatment was performed.

  A billet made of steel A and steel B having a diameter of 200 mm and a length of 3000 mm is heated in a temperature range of 1100 ° C. to 1250 ° C. in a rotary hearth heating furnace, and is hollow with an outer diameter of 192 mm and a wall thickness of 16 mm by Mannesmann Piercer rolling. A tube was manufactured, and then a finishing tube having an outer diameter of 151 mm and a wall thickness of 6.5 mm was manufactured by mandrel mill rolling. Then, after heating at 1000 to 1050 ° C. for 20 minutes in a reheating furnace, finish rolling was performed to an outer diameter of 63.5 mm and a wall thickness of 5.5 mm by a stretch reducer.

In the mandrel rolling of steel A, lubricants having a C equivalent weight of 20 g / m ² (boric acid-based lubricant) and 60 g / m ² (comprising boric acid-based lubricant and graphite-based lubricant) were applied to the mandrel bar. . On the other hand, in mandrel rolling of steel B, lubricants with a C equivalent weight of 40 g / m ² (mixed with boric acid type lubricant and graphite type lubricant) and 80 g / m ² (graphite type lubricant) are applied to the mandrel bar. did.

  After the finish-rolled stainless steel pipe was cut to 15 m, the heating temperature was changed in the range of 950 to 1200 ° C., and after the heating, a heat treatment was carried out by quenching with water spray. The heat-treated steel pipe was immersed in a 5% NaOH solution bath for 15 minutes, then immersed in a hydrofluoric acid solution of 5% hydrofluoric acid and 8% nitric acid for 6 minutes, and finally washed with high-pressure water. Table 2 shows the results of visually observing the outer surface of the washed steel pipe and confirming the removal status of the scale.

  As shown in Table 2, in both steel A and steel B, when the heating temperature was 950 ° C., the temperature was not sufficient for scale removal, and scale residue occurred even when any C equivalent weight of lubricant was used.

In steel A, when the C equivalent weight in the mandrel rolling was 20 g / m ² , the scale was sufficiently removed at a heating temperature of 1000 ° C. or more, but in the case of 60 g / m ² , the heating temperature was 1100. A scale residue occurred until the temperature reached ℃.

In steel B, when the C equivalent weight in mandrel rolling was 40 g / m ² , a scale residue was generated at a heating temperature of 1000 ° C., and the scale was removed at a heating temperature of 1050 ° C. or more. In the case where the equivalent weight of C was 80 g / m ² , scale residue was generated even at a heating temperature of 1100 ° C.

  When the heating temperature reached 1200 ° C., no scale residue occurred at any C equivalent weight.

According to the method for producing a stainless steel pipe of the present invention, by appropriately selecting the C equivalent weight (g / m ² ) in mandrel mill rolling and the heat treatment conditions of the stainless steel pipe rolled using the mandrel bar, While suppressing the abnormal oxidation scale which generate | occur | produces in a steel pipe inner surface, the scale formed in the stainless steel pipe surface can be efficiently removed by the rapid cooling after heat processing. Thereby, it can apply widely as a manufacturing method of a hot seamless stainless steel pipe.

It is a figure which shows the relationship when C equivalent weight (g / m < ² >) is made into an X-axis, and the heating temperature (degreeC) of the stainless steel pipe rolled using the said mandrel bar is made into a Y-axis. It is a figure which shows the scale removal condition at the time of changing the heating temperature (degreeC) of the stainless steel pipe rolled using the C equivalent weight (g / m < ² >) and the said mandrel bar in the mandrel mill rolling.

Claims (2)

A stainless steel pipe manufactured by mandrel mill rolling and stretch reducer rolling is subjected to heat treatment, and the scale generated on the surface is removed by pickling treatment.
The carbon equivalent weight (g / m ² ) per unit area of the lubricant adhering to the mandrel bar surface in the mandrel mill rolling is defined as the X axis, and the heating temperature (° C.) of the stainless steel pipe rolled using the mandrel bar is defined as When expressed in a relationship diagram with the Y-axis,
In the heat treatment of the stainless steel pipe, A (2 g / m ² , 1000 ° C.), B (20 g / m ² , 1000 ° C.), C (100 g / m ² , 1150 ° C.), D (100 g / m) in the relationship diagram. ² , 1300 ° C.), E (20 g / m ² , 1300 ° C.) and F (2 g / m ² , 1300 ° C.) are heated under conditions within a straight line and then rapidly cooled. Stainless steel pipe manufacturing method.
Here, the carbon equivalent weight (g / m ² ) represents the carbon equivalent weight contained in the graphite and the organic binder in the lubricant per unit area of the lubricant adhering to the mandrel bar surface. In the heat treatment of the stainless steel pipe, B (20 g / m ² , 1000 ° C.), C (100 g / m ² , 1150 ° C.), D (100 g / m ² , 1300 ° C.) and E (20 g / m) in the relationship diagram. ^{2. The} method for producing a stainless steel pipe according to claim 1, wherein the stainless steel pipe is rapidly cooled after being heated under conditions within a range connecting points of 1300 ° C.).

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