JPH0776728A - Production of 13% cr steel pipe excellent in toughness - Google Patents

Abstract

PURPOSE:To remarkably improve the toughness of a 13% Cr steel pipe. CONSTITUTION:In a producing method for a 13% Cr steel pipe in which a 13% Cr steel pipe is heated to the A3 point or above, is hardened, is thereafter tempered at the A1 point or below and is then subjected to warm bend straightening, the engaging temp. of a warm bend straightening machine is regulated to 600 to 680 deg.C. Thus, its toughness can remarkably be improved without deteriorating its strength and hardness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a 13% Cr steel having excellent toughness which can improve toughness during warm straightening of a 13% Cr steel pipe.
The present invention relates to a method for manufacturing a steel pipe.

[0002]

2. Description of the Related Art In manufacturing a steel pipe, the steel pipe bends regardless of whether it is hot or cold. Steel pipes, especially oil well steel pipes, are required to be threaded at both ends, and machine structural steel pipes are required to have high dimensional accuracy, and therefore high straightness is required. As a particularly severe example,
Some users are demanding 1.0 / 1000 as the nose bend at the tube end. Conventionally, straightening of a steel pipe is generally straightened cold or warm by a straightening machine such as a rotary housing type or an inclined roll type.

In recent years, oil wells for crude oil and gas wells for natural gas have tended to become deeper and deeper, and in particular, as the development of oil and natural gas in the deep sea has progressed, the depth has become higher and higher. Furthermore, with the increase of hydrogen sulfide in oil and gas,
Some steel materials are required to have corrosion resistance such as sulfide stress corrosion cracking resistance (SSCC resistance). The 13% Cr steel pipe can be warm-corrected to reduce the Bauschinger effect, stabilize the tensile strength and reduce the residual stress. It has the drawback of being low.

To improve the toughness of a 13% Cr steel pipe, the workability is increased in the rolling process for the purpose of refining the crystal grains, the coarsening of the crystal grains is prevented by the effect of the precipitation of fine carbides by the addition of a trace amount of alloying elements, and during quenching. Measures such as prevention of crystal grain coarsening are implemented by setting the material temperature of the above to a point A ₃ above. But,
As shown in FIG. 4, which shows the relationship between hardness (HRC), V fracture surface transition temperature (vTrs) in the Charpy impact test, and heat treatment conditions, these measures increase the strength and thereby reduce the toughness.

As a method for preventing a decrease in strength in straightening a steel pipe, the steel pipe is straightened in a temperature range of 100 to 500 ° C. by a straightening machine and the strength is adjusted (Japanese Patent Laid-Open No. 54-130466). No.), a steel pipe of a predetermined component is heated to 880 ° C. or higher and quenched,
A method of tempering at ~ 700 ° C, then straightening at 150 ~ 450 ° C, and then cooling to normal temperature while keeping it in a state where no bending occurs (Japanese Patent Publication No. 60-47327), inside of steel pipe A method of sending warm air from the pipe end to heat the vicinity of the inner surface to 400 ° C. or lower (Japanese Patent Laid-Open No. 4-111926).
No. publication) is proposed. In addition, the 13% Cr steel steel pipe is effective for manufacturing a corrosion-resistant oil country tubular good, because the Bauschinger effect is reduced, the tensile strength can be stabilized, and the residual stress can be reduced by performing warm straightening. The outgoing material control temperature for this warm correction is the American Petroleum Institute (AP
I) It is specified in the standard that the temperature is 510 ° C or higher.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The methods disclosed in Japanese Patent No. 0466, Japanese Patent Publication No. 60-47327, and Japanese Patent Laid-Open No. 4-111926 all perform quench straightening on a quenched and tempered steel pipe at a temperature of 500 ° C. or less to obtain tensile strength. It is effective for stabilization and reduction of residual stress, but has a drawback that it is not sufficient for improving toughness. In addition, the warm-up according to the API standard implemented with 13% Cr steel pipes has a delivery side control temperature of 5
Since the temperature is 10 ° C. or higher, it is effective for stabilizing the tensile strength and reducing the residual stress as described above, but the toughness is not sufficiently improved.

The object of the present invention is to quench and temper 1.
It is an object of the present invention to provide a method for producing a 13% Cr steel pipe excellent in toughness, which can significantly improve the toughness in warm straightening of a 3% Cr steel pipe.

[0008]

[Means for Solving the Problems] The present inventors conducted various test studies in order to achieve the above object. As a result, in the warm straightening of the quenched and tempered 13% Cr steel pipe,
It was clarified that the toughness can be significantly improved by setting the biting temperature of the warm bending straightening machine at the time of warm straightening to be higher than the conventional control temperature of 510 ° C or higher and 600 ° C or higher in the high temperature range. Arrived

That is, according to the present invention, a 13% Cr steel pipe is heated to a temperature of A ₃ point or higher and quenched, and then tempered at a predetermined temperature of A ₁ point or lower, and then, straightening is performed warm. In the method for producing a 13% Cr steel pipe, the method for producing a 13% Cr steel pipe having excellent toughness is characterized in that the warm bending straightener biting temperature is 600 to 680 ° C.

[0010]

According to the present invention, in the method for manufacturing a 13% Cr steel pipe in which quenching and tempering are carried out, and then the straightening is carried out in a warm state, the warm bending straightening machine biting temperature is 600 to 6
By setting the temperature to 80 ° C, tensile strength, yield point, hardness H
The Charpy value can be significantly improved and the toughness can be significantly improved without lowering the RC. In the present invention, the warm bending straightener biting temperature is set to 600 to 680 ° C. The reason why the increase in Charpy value is small at 600 ° C. or lower, and the increased Charpy value decreases 680 ° C. conversely decreases, This is because it remains the same as the Charpy value of 600 ° C. or lower.

[0011]

[Example] Outer diameter 177.8 mm, wall thickness 11.51 mm,
API standard 5CT2-L80-1 with a length of 12,500 mm
After heating the 3CR steel pipe to 980 ° C to quench it,
After tempering was performed at 715 ° C., the biting temperature of the hot straightener was changed to 495 to 680 ° C. to correct the bending, and then the bending was maintained in a state where the bending was not generated and the temperature was cooled to room temperature. Metal material impact test piece from each obtained steel pipe,
Cut out metal material tensile test pieces and hardness test samples, and
Charpy impact test method specified in IS Z2242, J
Charpy impact value, tensile strength, yield point and Rockwell hardness (HRC) were measured according to the metal material tensile test method specified in IS Z2241 and the Rockwell hardness test method specified in JIS Z2245. The relationship between the hot straightener biting temperature and the Charpy impact value is shown in FIG. 2 shows the relationship between the hot straightener biting temperature, the tensile strength, and the yield point. Further, FIG. 3 shows the relationship between the hot straightener biting temperature and the Rockwell hardness (HRC).

As shown in FIG. 1, when the hot straightener biting temperature exceeds 600 ° C., the Charpy impact value sharply improves, and when it exceeds 680 ° C., the increased Charpy impact value conversely decreases to a value of 600 ° C. And the hot straightener biting temperature is 600-680
By controlling the temperature to be 0 ° C, the toughness can be significantly improved as compared with the case where the straightening is performed at the conventional temperature of 510 ° C or higher. Further, as shown in FIGS. 2 and 3, there is almost no change in tensile strength, yield point and Rockwell hardness due to fluctuations in hot straightener biting temperature.

[0013]

As described above, according to the method of the present invention, the strength and hardness are reduced by setting the biting temperature of the 13Cr steel pipe to the hot straightener in the warm straightening to be 600 to 680 ° C. In addition, the toughness can be significantly improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between hot straightener biting temperature and Charpy impact value.

[Fig. 2] Hot straightener biting temperature and tensile strength,
It is a graph which shows the relationship with a yield point.

FIG. 3 is a graph showing the relationship between hot straightener biting temperature and Rockwell hardness (HRC).

FIG. 4 is a graph showing the relationship between hardness (HRC), fracture surface transition temperature (vTrs) in a V Charpy impact test, and heat treatment conditions.

Claims (1)

[Claims] 1. A 13% Cr steel tube is heated to a temperature of A ₃ point or higher to quench it, and then tempered at a predetermined temperature of A ₁ point or lower, and then is warmed to straighten a 13% C steel.
In the method for producing a r steel pipe, the method for producing a 13% Cr steel pipe having excellent toughness is characterized in that the warm bending straightener biting temperature is 600 to 680 ° C.