JP2002301577A - Method of joining martensitic stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joining method which makes it possible to obtain a defectless joint part which does not give a cracking and other defects in a short joining work time in heating and joining of martensitic stainless steels. SOLUTION: In cooling after the heating and joining in the diffusion joining of the martensitic stainless steels, the heated areas are forcibly cooled and are then cooled at cooling rates from 0.6 to 10 deg.C/s during >=1,100 deg.C, from 2.4 to 25 deg.C/s between 300 and 1100 deg.C and from 0.6 to 8 deg.C/s between 100 and 300 deg.C. In the case of the martensitic stainless steel of <=0.05 mass% in (C+N) content, the stainless steels are cooled at a cooling rate 0.6 to 10 deg.C/s during >=1100 deg.C, from 2.4 to 30 deg.C/s between 100 and 1100 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining martensitic stainless steel used for piping of oil drilling pipes, chemical plants, and the like.

[0002]

2. Description of the Related Art Martensitic stainless steel such as SUS410 has excellent corrosion resistance and heat resistance and is inexpensive compared with austenitic stainless steel. It is widely used as a material for piping of various chemical plant equipment such as. In oil drilling, as the drilling operation progresses, casing tubes are sequentially joined and extended, and the total length is several thousand meters. Further, in the manufacturing process of a chemical plant, a large number of joining operations between martensitic stainless steel pipes are required in a local assembly process.
As these joining methods, mechanical joining methods such as flange joints and threaded joints are also used, but since the joints have good airtightness and good joining strength, it is necessary to frequently remove them. For joining non-existent parts, a method of melting and joining a joint portion, such as butt welding, is often used.

[0003] As a joining method involving heating (heating joining), in addition to the above-described welding joining such as butt welding, an insert material is inserted into a joint portion, the joint portion is heated to a high temperature, and the insert material is melted. Diffusion bonding in which diffusion is performed, a pressure welding method in which a bonding portion is heated to a high temperature and high pressure is applied to a bonding surface to perform bonding, and the like are performed.

[0004] By the way, since martensitic stainless steel is a material having self-hardening properties, when it is heated to a high temperature and joined, in the cooling process after the joining operation is completed, the molten metal and the heat affected zone of the weld are affected. The part heated to a high temperature hardens. Along with this, there is a possibility that the toughness may be reduced at the joint, or cracks may be generated due to thermal stress. In order to prevent these inconveniences, the cooling of the martensitic stainless steel after heating and joining is usually performed as slowly as possible. Furthermore, in order to strengthen the steel, a tempering heat treatment is performed after joining. Therefore, joining of martensitic stainless steel requires a long time, cooling after joining takes a long time, and redundancy of the joining operation is inevitable. In the field of assembly work such as joining of casing tubes for oil drilling and piping of chemical plants, it is desired to further shorten the joining work time of martensitic stainless steel from the viewpoint of improving efficiency and shortening the construction period. In the joining of martensitic stainless steel pipes for oil drilling, it currently takes 30 minutes as the time required from the setting of the material to be joined to the joining device to the end of the joining operation, but this time is reduced to 10 minutes or less. It is desired to do.

[0005] In order to improve the redundancy of the required time in the heating and joining of the martensitic stainless steel as described above, for example, in Japanese Patent Application Laid-Open No. H8-311563, an insert material is inserted into the joining surface and the material to be joined is inserted. A method in which heating is performed at a temperature of not higher than the melting point, heating and holding at a temperature of 840 to 950 ° C., and then cooling at a cooling rate of 30 ° C./h or less from the temperature during cooling after the liquid phase diffusion bonding by pressurizing. Has been proposed. According to this method, it is possible to obtain a joint having high toughness and ductility without performing any heat treatment after joining. However, this method requires a long working time of 20 hours or more per joint.

In diffusion bonding performed by heating a joint by high-frequency induction heating or high-frequency direct current heating, the melting point of the insert material, the thickness of the insert material, the surface roughness of the bonding interface, the bonding temperature, the bonding pressure, etc. The time required for setting the material to be joined in the joining apparatus and completing the joining operation is reduced to 12 minutes per joint by improving the joining conditions (JP-A-11-197853).
No.).

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a joining method which can provide a sound joining portion which does not cause cracks or other defects in a short joining operation time in heating joining of martensitic stainless steel. The purpose is to do.

[0008]

As a result of various studies to solve the above-mentioned problems, the present inventors have found that, in the heat joining of martensitic stainless steel, a portion heated at the time of cooling after the above-mentioned heat joining is removed. It has been found that by controlling the cooling rate in a specific temperature section while shortening the required cooling time by forcible cooling, a sound joint without cracks or other defects can be obtained. That is,
The method for joining martensitic stainless steel according to the present invention includes the following steps: (1) In heating and joining martensitic stainless steel, the temperature of the heated portion is set to 1100 by forcibly cooling the heated portion during cooling after the heat joining. Cooling at a cooling rate of 0.6 ° C./s to 10 ° C./s
Between less than 100 ° C and 300 ° C, 2.4 ° C / s to 25 ° C /
The cooling is performed at a cooling rate of 0.6 ° C./s to 8 ° C./s when the cooling rate is lower than 300 ° C. to 100 ° C. (2) In the heat bonding of martensitic stainless steel containing (C + N): 0.05% or less by mass%,
At the time of cooling after the heat bonding, the heated portion is forcibly cooled, so that the portion is cooled at a cooling rate of 0.6 ° C./s to 10 ° C./s while the temperature of the portion is 1100 ° C. or higher.
2.4 ° C / s to 30 ° C /
The cooling rate is s. (3) The method for joining martensitic stainless steel according to any one of (1) and (2), wherein the heat joining is diffusion joining.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for joining martensitic stainless steel according to the present invention, martensitic stainless steel as a material to be joined is set in a joining device, and then joined by a heating means provided in the joining device. After the material is heated to the joining temperature and the joining operation is performed to join the joining material, the portion heated by the heating is forcibly cooled using a cooling medium. Then, when the temperature of the portion is 1100 ° C. or more, cooling is performed at a cooling rate of 0.6 ° C./s to 10 ° C./s, and when the temperature is less than 1100 ° C. to 300 ° C., 2.4 ° C./s to 2 ° C.
Cool at a cooling rate of 5 ° C./s, less than 300 ° C. to 100 ° C.
During this period, cooling is performed at a cooling rate of 0.6 ° C./s to 8 ° C./s.

In the case where the (C + N) content of the martensitic stainless steel to be joined is 0.05% by mass or less, the above-mentioned forced cooling is performed at a temperature of less than 1100 ° C. to 100 ° C.
During this time, cooling may be performed at a cooling rate of 2.4 ° C./s to 30 ° C./s.

Here, the martensitic stainless steel is, for example, SUS403, SUS410, SUS41.
0J1, SUS416, SUS420J1, SUS43
C: 0.25% by mass or less, Cr: 11 to 11, etc.
The steel contains 17% by mass and undergoes martensitic transformation by quenching. These steels have self-hardening properties and undergo a martensitic transformation by air cooling from a temperature above the transformation point and harden.

As a method of joining with heating (heating joining), in addition to welding joining such as butt welding, an insert material is inserted into the joining portion to heat the joining portion to a high temperature and pressurize the joining surface, Diffusion bonding in which the insert material is melted and diffused, and a pressure welding method in which the joint is heated to a high temperature and high pressure is applied to the joint surface to join the joint. However, from the viewpoint of quickness of the heating and joining operations, it is preferable to carry out the diffusion joining method. In addition, from the viewpoint of rapidity of heating, the heating at the time of performing diffusion bonding and forging is preferably performed by high-frequency induction heating or high-frequency direct current heating. It is assumed that the joining apparatus includes at least means for gripping the material to be joined and heating means and joining means suitable for performing the above-described heat joining.

The forced cooling after the completion of the joining operation includes, for example, a control cooling mechanism including a temperature measuring means, a time measuring means, a cooling pattern setting means, an arithmetic circuit, a means for adjusting the amount of coolant jetted, and the like. It is preferable to use a coolant ejection mechanism.

Here, the temperature measuring means is for measuring the temperature of the heated portion. The timer means is for recording the time of the temperature measurement. The cooling pattern setting means is for setting the temperature at each time. The arithmetic circuit calculates the cooling rate from the data obtained by the temperature measuring means and the time measuring means. The calculated cooling rate is compared with the cooling rate set by the cooling pattern setting means, and the means for adjusting the amount of coolant jetted according to the difference is actuated, and cooling is performed along the set cooling pattern. To be done. As a means for adjusting the amount of coolant discharged, for example, an electromagnetic on-off valve can be used. The coolant ejection mechanism includes at least a coolant storage unit, a coolant transport mechanism, and a coolant ejection nozzle unit.

The arithmetic circuit calculates the cooling rate from the data obtained by the temperature measuring means and the time measuring means, and compares the calculated cooling rate with the cooling rate set by the cooling pattern setting means. The means for adjusting the coolant ejection amount and the coolant ejection means are operated according to the difference to adjust the amount of coolant ejected from the coolant ejection nozzle portion. As the cooling agent, in addition to air, an inert gas such as argon or nitrogen can be used, but water is preferably used.

Next, in the method for joining martensitic stainless steels of the present invention, the reason for limiting the cooling rate within a predetermined temperature zone during cooling after heating and joining will be described. When the martensitic stainless steel targeted by the present invention is heated to a high temperature of 1100 ° C. or higher, carbides and nitrides in the steel are dissolved and crystal grains are coarsened, which greatly affects the mechanical properties of the steel. . The Ms point of this steel is 3
At around 00 ° C., rapid cooling from a high temperature causes martensitic transformation, resulting in a large volume change and a large change in mechanical properties.

As a result of various experiments and investigations, the present inventor has set a temperature range of 1100 in cooling from the heating temperature at the time of joining.
℃ to 1100 ℃ to 300 ℃, less than 300 ℃ to 1
By dividing into three sections of 00 ° C. and adjusting the cooling rate in each temperature section, it has been found that cooling can be performed from a high temperature to 100 ° C. in a short time without causing harmful defects. That is,

The temperature zone above 1100 ° C. is 0.6 ° C./s
Cool at a cooling rate of 〜１０10 ° C./s. Cooling rate is 10 ℃
If it is higher than / s, cracks occur in the joints, so the upper limit of the cooling rate in the temperature section of 1100 ° C or more is set to 10 ° C / s. If the cooling rate is lower than 0.6 ° C./s, the cooling time becomes redundant, so the lower limit of the cooling rate in the temperature section of 1100 ° C. or more is set to 0.6 ° C./s.

In a temperature range of less than 1100 ° C. to 300 ° C., cooling is performed at a cooling rate of 2.4 ° C./s to 25 ° C./s. If the cooling rate is higher than 25 ° C./s, cracks occur at the joints. Therefore, the upper limit of the cooling rate in a temperature range of less than 1100 ° C. to 300 ° C. is set to 25 ° C./s. The cooling rate is 2.4 ° C.
If the cooling rate is lower than 1 / s, the cooling time becomes redundant.
4 ° C./s.

The temperature range from less than 300.degree. C. to 100.degree.
Cool at a cooling rate of 6 ° C / s to 8 ° C / s. If the cooling rate is higher than 8 ° C / s, cracks occur at the joints, so
The upper limit of the cooling rate in the temperature range from
° C / s. If the cooling rate is lower than 0.6 ° C./s, the cooling time becomes redundant. Therefore, the lower limit of the cooling rate in the section of less than 300 ° C. to 100 ° C. is set to 0.6 ° C./s.

When the (C + N) content of the material to be joined is 0.05% by mass or less, the change in volume due to martensite transformation is small and the toughness of the formed martensite structure is relatively large, so that the temperature is 1100 ° C. The upper limit of the cooling rate in a temperature range of less than 100C may be set to 30C / s. In this case, the lower limit of the cooling rate is set to 2.4 ° C./s in order to avoid redundant cooling time.

The reason that the lower limit temperature for cooling while controlling the cooling rate is set to 100 ° C. is that, in the martensitic stainless steel targeted by the present invention, a large structural change such as transformation occurs at a temperature of 100 ° C. or more. Will almost end. Further, at a temperature lower than 100 ° C., a mechanical effect such as a thermal stress becomes small. Further, in applications such as oil drilling, the ignition point of petroleum is sufficiently lower than 120 ° C., thereby preventing the risk of ignition due to residual heat stored in the bonding material.

At the time of heating and joining, not only the joint but also a whole area in the vicinity of the joint is heated together. Therefore, the cooling rate is controlled for all the heated areas as described above. Requires cooling.

As described above, according to the method of joining martensitic stainless steel, a sound joining portion that does not cause cracks or other defects can be obtained in a short joining operation time, but after joining, the joint is further heated to 700 to 750 ° C. Heat to temperature 6
It is preferable to perform a heat treatment after holding for 0 s or more. The post heat treatment can increase the toughness of the joining material.

[0025]

EXAMPLES SUS41 with (C + N) content of 0.2% by mass
Outer diameter 140mm, wall thickness 7 made of 0 equivalent steel (steel 1)
The end faces of the steel pipes were butt-joined by a liquid phase diffusion bonding method. The butt joining was performed using a high-frequency induction heating type joining apparatus. The joining apparatus is a holding unit that holds a material to be joined, a pressing unit that applies pressure to a joining surface,
A control mechanism including a high-frequency induction heating means for heating a joint portion, and having a temperature measuring means, a timing means, a heating / cooling pattern setting means, an arithmetic circuit, a means for adjusting a coolant ejection amount, and a coolant ejection. It has a mechanism.

An insert material is inserted between the respective end faces of the two steel pipes, the two steel pipes are gripped by the gripping means, and both steel pipes are pressed in the axial direction by the pressing means. Then, the insert material was pressed. As the insert material, a BNi-2 alloy foil having a thickness of 40 μm was used. Further, the pressure for clamping the insert material was 4 MPa.

A high-frequency induction heating coil provided in the high-frequency induction heating means is disposed so as to surround the joint, and a high-frequency current having a frequency of 3 kHz is passed through the coil to heat the joint. After the temperature was raised, it was heated and held for 30 seconds. Next, water was jetted from a coolant injection nozzle disposed around the joint with the high-frequency induction heating coil interposed therebetween to cool the joint and the heated region near the joint.

The temperature of the junction is measured by a radiation thermometer,
From the measured temperature data, the output of the high-frequency power supply and the amount of coolant jetted were controlled by the control mechanism so that the temperature of the junction became a preset temperature pattern. After the cooling is completed, the temperature of the joint and the heat-affected zone in the vicinity thereof is heated to 720 ° C. for 30 seconds using the high-frequency induction heating means and the control mechanism.
After cooling to ℃, heat treatment was performed to obtain a joined body.

The joined body was subjected to a penetrant test to check for cracks in the joint. Also, from the joined body,
A No. 3 test piece according to JIS Z 3121 was cut out and provided for a tensile test. Furthermore, JIS with a joint at the center and a V notch at the joint interface
A No. 4 half-size Charpy impact test piece according to Z2202 was cut out and subjected to a Charpy test. (C + N)
Regarding SUS410 equivalent steel (steel 2) having a content of 0.05% by mass, a joined body was obtained in the same manner as steel 1, and each test piece was prepared and tested.

Table 1 shows the test results. In Table 1, the time required for cooling after welding is taken as the cooling time, and the time from the setting of the material to be welded in the welding apparatus to the completion of cooling of the joined body (heating time 60 seconds + holding time 30 seconds) + Cooling time + post-heat treatment time of 120 seconds) was shown as the working time.

[0031]

[Table 1]

As is clear from Table 1, in the comparative example, the cooling time was short, but the cooling after the bonding caused cracks in the bonded portion.
On the other hand, in Examples, no cracks were observed in any of the joined bodies in the penetrant inspection test, and the results of the tensile test show that the fracture position was the base material and the joints were sound.

In Examples 5 and 8 in which the post heat treatment was not performed, the working time was shorter, but the Charpy impact value was inferior as compared with those in which the post heat treatment was performed. However, if a steel having a low (C + N) content such as steel 2 is used, it exhibits sufficiently practical impact resistance even if the post heat treatment is omitted. This is an effective means. If the cooling rate is lower than the range of the present invention, the cooling time is longer than 390 seconds, and the working time is longer than 10 minutes.

[0034]

As described above, according to the method for joining martensitic stainless steels of the present invention, a sound martensitic stainless steel which is free from cracks and other defects in a short joining operation time. Can significantly improve the efficiency of joining martensitic stainless steel at work sites, such as joining casing tubes for oil drilling and joining joints of chemical equipment pipes, and the economic effect is extremely large. I can say.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shigeyuki Inagaki 2-30, Datong-cho, Minami-ku, Nagoya-shi, Aichi F-term in the Technical Research Laboratory of Daido Steel Co., Ltd. 4E067 AA03 BA00 DC06 EA03 EC06 4K042 AA24 BA06 BA11 CA07 CA10 CA11 DA06 DE01 DE06

Claims (3)

[Claims] 1. In the heat joining of martensitic stainless steel, the temperature of the heated portion is 1100 by forcibly cooling the heated portion during cooling after the heat joining.
Cooling at a cooling rate of 0.6 ° C./s to 10 ° C./s during a temperature of not less than 1 ° C .;
Cool at a cooling rate of 25 ° C./s,
A method for joining martensitic stainless steel, wherein the martensitic stainless steel is cooled at a cooling rate of 0.6 ° C / s to 8 ° C / s during ° C. 2. In the heat joining of martensitic stainless steel containing (C + N): 0.05% or less by mass, by forcibly cooling the heated portion at the time of cooling after the heat joining. The temperature of the site is 1100
Cooling at a cooling rate of 0.6 ° C./s to 10 ° C./s during a temperature of not less than 1 ° C .;
A method for joining martensitic stainless steel, comprising cooling at a cooling rate of 30 ° C./s. 3. The method for joining martensitic stainless steel according to claim 1, wherein said heat joining is diffusion joining.