JPS6147885B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an electric resistance welded steel pipe for upset tubing, and more specifically, it has mechanical properties equivalent to the J-55 class for upset tubing specified by the API standard, and has relatively low carbon and
The present invention relates to a method for manufacturing ERW steel pipes that can maintain formability and weldability with a low alloy composition. Recently, with the development of deep-seated oil fields and offshore oil fields, high-strength materials have been required for upset tubing materials for oil well drilling and oil extraction.According to the API-J55 tubing standard, its mechanical properties include yield strength
38.7-56.2Kg/mm ² , tensile strength 52.7Kg/mm ² or more, elongation
It is stipulated to be 24% or more. Conventionally, in order to meet the strength standards for this grade of upset tubing, a seamless tube with a high carbon and high alloy composition has been used as the original tube and has been hot upset-processed. However, this steel pipe has the drawback of high cost. From this point of view, it is conceivable to use ERW steel pipes as an alternative to seamless steel pipes, but J55 class tubing materials are sometimes used without heat treatment after upset processing, and sometimes are normalized. It is difficult to manufacture using materials with the same composition, and this creates the complexity of requiring materials with two different compositions. In other words, if a steel pipe that is intended to be used without normalizing is heat treated, the yield strength will be low and it will not be able to meet the standard value of API-J55. If the assumed material is used without heat treatment, there is a risk that the yield strength will exceed the upper limit of the specification. Furthermore, when heat treatment is applied after upset processing,
Since the material composition is high carbon and high alloy, it has poor cold workability and weldability, which is a major drawback in manufacturing ERW steel pipes. In order to improve these, the present inventor believes that it is important to maintain formability and weldability with a relatively low carbon and low alloy material composition, and to ensure the strength of the steel pipe, it is necessary to regulate the cooling conditions immediately after upset processing. In addition, research focused on regulating the conditions for heat treatment after upset processing, that is, normalizing or quenching and tempering, and found that if this manufacturing method was used, it would be possible to create a product with only one type of composition, good productivity, and low cost. of cost
It has been found that electric resistance welded steel pipes for J55 class upset tubing can be obtained. The present invention was established as a result of the above and repeated experiments, and specifically, C: 0.13 to 0.20.
%, Si≦0.25%, Mn: 1.0-1.5%, P≦0.03%,
S≦0.01%, Nb: 0.01~0.05%, Al: 0.005~0.06
%, the remainder iron and impurities are slitted, formed, and electrically welded to form a pipe of a specified size, and then upset processing is performed, and the cooling conditions immediately after and heat treatment conditions after upset processing are regulated. We propose a method for manufacturing ERW steel pipes that meet the API-J55 tubing standard. The present invention will be explained in detail below. First, the composition of the steel pipe material is relatively low carbon and low alloy to ensure formability and weldability, which are important factors in the manufacture of ERW steel pipes, and properties specified in the API-J55 standard. Therefore, the composition of the steel pipe material will be explained as follows. C: 0.13-0.20% and Mn: 1.0-1.5% The lower limits of C and Mn are 0.13% and 1.0, respectively.
% because if it is less than this, the strength of the main tube in the as-formed state without heat treatment cannot satisfy the API standard. Also, C and
The reason why the upper limits of Mn are set at 0.20% and 1.5%, respectively, is that if added in excess of this, the yield strength of the main tube will exceed the upper limit of the API standard value when quenching and tempering are performed after upset processing. This is because the weldability deteriorates and the incidence of panel defects rapidly increases. Si≦0.25% Si is an element that is inevitably contained in steel during steel manufacturing, and if added in excess of 0.25%, weldability will deteriorate and the incidence of penetrator defects will increase.
The upper limit was set at 0.25%. P≦0.03%, S≦0.01% P and S are impurities and elements that inhibit weldability, and if their respective upper limit values of 0.03% and 0.01% are exceeded, cracks may occur near the electric resistance welding part. Nb: 0.01-0.05% Nb is an element necessary to ensure the strength of the main tube in the as-formed state without heat treatment, and it is necessary to add 0.01% or more to meet the API strength standards. If it exceeds 0.05%, the yield strength may exceed the standard value, so this was set as the upper limit. Al: 0.005-0.06% Al is a necessary element for deoxidizing steel, and if the amount of oxygen in the steel is not reduced, penetrator defects will occur in the ERW weld, so it is necessary to contain it at 0.005% or more. Also, if it exceeds 0.06%, it becomes coarse.
Al ₂ O ₃ based inclusions are generated and there is a risk of cracking near the electric resistance welding area. Next, the steel pipe material having the above composition is hot-rolled according to a normal process, and then the hot-rolled coil is slitted, formed, and electric resistance welded to produce a mother pipe for upset tubing. Subsequently, both ends of this main tube are heated to 1100 to 1250°C for upset processing, and then heat treated under the following heat treatment conditions. Upset processing is usually performed on pipe ends with a diameter of 1100~
Processing is performed after heating to 1250℃, and at the end of the process, the upset part temperature has been cooled to approximately 1000℃. From this temperature, it is cooled by air cooling, etc., and during this cooling, the cooling rate is reduced between 800 and 500℃. It is cooled at a rate of 1.5 to 5°C/sec. That is, if a steel pipe with the above composition is cooled in the atmosphere immediately after upset processing, the yield strength of the upset portion will be lower than the API standard. In order to meet the standard value of yield strength, the temperature must be between 800 and 500℃.
If it is necessary to cool at a rate of 1.5℃/second or higher, the yield strength will be 38.7Kg/ ^mm2 or higher, and if the cooling temperature in the same temperature range is 5℃/second or lower, the yield strength will be 56.2. Kg/mm ² or less. In addition, when steel in the above composition range is cooled between 800 and 500 degrees Celsius at a rate of 1.5 to 5 degrees Celsius/second, it changes from austenite to ferrite,
Since the transformation to pearlite and bainite is completed by 500°C, there is no need to particularly limit the cooling conditions below 500°C. In addition, when performing normalizing treatment after upset processing, the cooling rate at 800 to 500℃ should be increased to 15 to 30°C.
Cool as °C/sec. In other words, if the cooling rate is less than 15°C/sec, the yield strength will be below the lower limit of the specified value;
This is because if the temperature exceeds °C/sec, the yield strength exceeds the upper limit of the standard value. In this case too, the bainite metamorphosis
Since the cooling process is completed by 500°C, there is no need to particularly limit the cooling conditions below 500°C. When quenching and tempering are performed after upset processing, the material is cooled between 800 and 300°C at a rate of 30 and 60°C/second, and then tempered at 550 and 650°C. In other words, if the cooling rate between 800 and 300℃ during quenching is less than 30℃/second, the yield strength of the upset part after tempering will be below the standard value, and if it exceeds 60℃/second, the yield strength of the upset part after tempering will be lower than the standard value. This is because the yield strength of the pipe exceeds the standard value. If the tempering temperature is less than 550℃, the yield strength when the cooling rate during quenching is increased will exceed the standard value, while if it exceeds 650℃, the yield strength when the cooling rate during quenching is decreased will exceed the standard value. The temperature was limited to 550 to 650°C. Next, examples will be described. The steel pipe materials having the compositions of the present invention and the conventional example shown in Table 1 are hot-rolled, slitted, formed, and electrically welded to obtain a main pipe with the strength shown in Table 2. As determined by ultrasonic flaw detection, the results were as shown in Table 3.

【table】

【table】

[Table] As is clear from Tables 2 and 3, the method of the present invention has good formability and weldability, and satisfies the API J55 standard even when the pipe is made as is. On the other hand, although conventional steel pipe E is constructed to be subjected to normalizing treatment, welding defects are likely to occur due to its composition, and the yield strength exceeds the standard value if the pipe is made as is. It's on. As shown in Table 4, the strength of conventional steel pipes D and E after upset processing and normalizing treatment (held at 900°C for 5 minutes and then air cooled) is based on the assumption that they will be used as they are. The yield strength of steel pipe D is below the lower limit.

[Table] On the other hand, when steel pipes A, B, and C are subjected to the respective heat treatments as shown in Table 5 after upset processing by the method of the present invention, the strengths shown in Table 5 are obtained.

[Table] From these points, when manufactured by the method of the present invention, the resistance welded pipe satisfies the strength standards in all cases. As explained in detail above, by manufacturing pipes from low-carbon, low-alloy materials and heat-treating them according to the present invention, it is possible to create ERW steel pipes with contradictory properties such as strength, formability, and weldability, which were previously considered difficult. J55 as main pipe
A class of upset tubes can be manufactured.

Claims (1)

[Claims] 1% by weight: C: 0.13-0.20%, Si≦0.25%,
Mn: 1.0-1.5%, P≦0.03%, S≦0.01%, Nb:
After forming a hot rolled coil consisting of 0.01~0.05%, Al: 0.005~0.06%, and the balance iron and impurities into a specified size by slitting, forming, and electric resistance welding,
Upset processing is performed by heating to 1100 to 1250℃, and during the cooling process the temperature is 1.5 to 5℃/800 to 500℃.
A method for manufacturing an electric resistance welded steel pipe for upset tubing, which is characterized by cooling at a speed of seconds. 2 In weight%, C: 0.13-0.20%, Si≦0.25%,
Mn: 1.0-1.5%, P≦0.03%, S≦0.01%, Nb:
After forming a hot rolled coil consisting of 0.01~0.05%, Al: 0.005~0.06%, and the balance iron and impurities into a specified size by slitting, forming, and electric resistance welding,
An upset tube characterized by performing upset processing by heating to 1100 to 1250°C, and cooling at a rate of 15 to 30°C/second between 800 and 500°C as a cooling condition during normalizing treatment after the upset processing. Manufacturing method of ERW steel pipe for Bing. 3 C in weight%: 0.13-0.20%, Si≦0.25%,
Mn: 1.0-1.5%, P≦0.03%, S≦0.01%, Nb:
After forming a hot rolled coil consisting of 0.01~0.05%, Al: 0.005~0.06%, and the balance iron and impurities into a specified size by slitting, forming, and electric resistance welding,
Upset processing is performed by heating to 1100 to 1250℃, and the cooling conditions for quenching after upset processing are cooling between 800 and 300℃ at a rate of 30 to 60℃/second, and then tempering at 550 to 650℃. A method for producing an ERW steel pipe for upset tubing, characterized by: