JPS6240345A - High tension steel pipe for oil well having superior delayed fracture resistance - Google Patents

Abstract

PURPOSE:To manufacture a high tension steel pipe for an oil well having superior delayed fracture resistance by using a low-alloy steel contg. specified amounts of Cr, Mo, V and Nb as a material for a steel pipe for an oil well. CONSTITUTION:A low-alloy steel contg., by weight, 0.10-0.25% C, 0.15-1.0% Si, 0.3-1.5% Mn, 0.5-5.0% Cr, 0.5-3.0% Mo, 0.05-1.2% V and 0.005-0.10% Al and having 0.5-1.5 as value for X represented by formula I is used as a material for a steel pipe for an oil well. The low-alloy steel may further contain 0.01-0.5% Nb. At this time, the steel has 0.5-1.5 as valve for X represented by formula II. The low-alloy steel may further contain 0.1-1.5% Cu, 0.005-0.040% Ti, 0.1-1.5% Ni and 0.0003-0.0030% B. At this time, the steel has 0.5-1.5 as value for X represented by two formulae III. A high strength steel pipe for an oil well having superior delayed fracture resistance can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention The present invention relates to the creation of a tubular tension oil well steel pipe with excellent delayed fracture resistance.
The present invention aims to provide a high-strength steel pipe for oil wells that has a yield strength exceeding 100% and has significantly delayed fracture properties superior to conventional steels.

Industrial applications High-tensile oil well steel pipe with high yield strength.

Conventional oil country tubular goods have a yield strength of 150 Kml (4f layer on 1055) or more, and 170 Ksi (119,5-/
-) or above are required, each with V-150
Or it is called as U-170.

By the way, such high-strength oil well steel pipes are manufactured by quenching and tempering, and high-temperature tempering is effective in improving their delayed fracture resistance.

Problems to be Solved by the Invention However, in order to obtain high strength in the conventional products as described above, it is necessary to lower the tempering temperature.
If the tempering temperature is lowered in order to obtain such high strength, the delayed fracture resistance W& characteristics will inevitably be inferior.

"Structure of the invention" Means for solving the problem 1, C: 0.10-0.25wt%, st:
0.15-1.0wt%.

Myr: 0.3-1.5wt%, Cr:
0.5-5.0wt%.

Mo: 0.5-3. (hwtchi, V: 0.
05-1.2wt%.

, u: o, oos ~ 0.10 wt%, the remainder consists of Fe and unavoidable impurities, and (M'(drive Ti3'' ■(%)X, )/c(
A high-tensile steel pipe for oil wells that is custom-made for delayed fracture resistance, characterized in that X in the formula 'rX satisfies 0.5≦X≦1.5.

2. C: 0.10-0.25wt%, S
i: 0.15 to 1.0 wt%.

kh: 0.3-1.5wt%, Cr:
0.5-5.0wt%.

MO: 0.5-3.0wt%, V:
0.05-1.2wt%.

Contains At: 0.005 to 0.10 wt%, Nb: 0.01 to 0.1 wt%, the shallow part consists of Fe and inevitable impurities,
Moreover, (M+) (# x 1/16 + Nb (%) x soil + 'IC'l
l ”)/c(%5X, where X is 0.5≦X≦
1.5 A high-tensile oil well steel pipe with excellent delayed fracture resistance.

3. C: 0.10-0.25wt%, jf;
4: 0.15-1.0wt To-Mpg: 0
．． 3-1.5wt%, Cr: 0.5-5.0
wtfb-Mo: 0.5-3.0wt%,
V: 0.05-1.2wt%.

AI: Contains 0.005 to 0.10 wt%, Cu: 0.1 to 1.5 wt%, n: 0.0
Between 05 and 040 wt%.

Nt: o, 1 to 1.5 wt%, B: 0.00
0&-01)030wt%Nb: 0.01~0. lw
t%.

or 2a or more, the remainder consists of Fe and unavoidable impurities, and (Mx-L+v(Go-L)xq(kaX...... Engineering) (%)X
−+Nb(%)X −+V(%)X”)/C(%9
=X・・・・■X in each formula is 0.5≦X≦1
．． A high-tension oil well m-tube with delayed fracture resistance that satisfies condition 5.

Strength is obtained by having c: o, to% or more in the action wt% (hereinafter simply referred to as "chi"), and & is 0.
Deoxidation is achieved by containing 15% or more of Mn and 0.3% or more of Mn, and 1.0% or less of Si and 1.5% of Mn.
Hereinafter, the deterioration of toughness is suppressed by setting ■ to 1.2% or less and M to 0.10- or less. □Cr 0.5
By increasing Mo content to 0.51% or more, the hardenability is improved and the tempering temperature is increased.

Good delayed fracture properties can be achieved by containing Mo (3.0% or more) and 0.05% U (U).Nb (0.01% or more) makes austenite grains finer and improves toughness. In order to improve the delayed bankruptcy resistance, Nb carbide is precipitated during tempering.

By setting the content to 0.01% or less, deterioration of toughness is completely avoided.

By containing Cu: 0.1% or more and Ni: 1.5% or less, delayed fracture resistance is improved, and the Ni
: 0.1% or less, n: 0.0051 or more, B:
Hardenability is improved by containing 0.0003% or more.

Furthermore, (MO(%) ×” ■(plow×l −t )/C@)=
X “==・” X in each equation of 1 is 0.5≦X≦
By satisfying the condition 1.5, the delayed fracture resistance described above should be improved and the toughness % should be improved.

EXAMPLE To further explain the present invention as described above, the present inventors have conducted repeated research into obtaining a material for oil country tubular goods that has delayed fracture resistance and high strength, and as a result, the chemical composition of steel has been improved. Adjustment and high-temperature tempering make it resistant to delayed fracture! Cementite, which is considered to be harmful to its properties (
It has been found that it is possible to significantly reduce #m3C), and as a result, properties superior to conventional steels can be obtained.

That is, the reason for limiting the composition range of each element in the present invention as described above is as follows.

C is effective in increasing the strength C, and for this purpose it is necessary to contain it at 0.10% or more in wt (hereinafter simply referred to as -); Also C
There is a possibility that quenching may occur during hardening, so this is the upper limit. In addition, if C is less than 0.10%, hardenability will deteriorate! ,
Even if it is 5, there will be a significant decline.

It is necessary to contain 0.15% or more of Si for the purpose of deoxidizing the pot. However, if the content is 1.0% or more, the toughness and ductility will be poor, so this should be the upper limit.

Mn is an element that is effective as a deoxidizing agent and improves hardenability, and these effects are not ensured if the amount is less than 0.3%. On the other hand, if the content exceeds 1.5%, the toughness deteriorates, so this is set as the upper limit.

Cr is an element that improves hardenability and is effective in increasing the tempering temperature, and if it is 0.5% or less, these effects are insignificant.

However, if the content exceeds 5.0%, the effect becomes saturated and becomes economically disadvantageous, so this is set as the upper limit.

Mo is an element that improves hardenability, is effective in increasing the tempering temperature, and is effective in reducing IJsC, and these effects are reduced at 0.5% or less. It is insufficient.

However, if the content is 3.0% or more, M during tempering.

This is set as the upper limit because carbides are precipitated and this is harmful to delayed fracture resistance.

(2) is an element that is effective in increasing the tempering temperature (1) and is also effective in reducing the amount of h g C that is harmful to delayed fracture resistance by precipitating U carbides during tempering, If it is less than 0.05%, these effects cannot be obtained appropriately.

However, if the content exceeds 1.2 inches, the toughness will deteriorate, so this is set as the upper limit.

M is essential as a deoxidizing agent and is effective in refining austenite grains at the quenching temperature, and in order to obtain these effects, it is necessary to contain at least o, oo s- or more. It is. However, if the content exceeds 0.100 h, the toughness deteriorates, so this should be the upper limit.

Nb is effective in refining austenite grains during heating at the quenching temperature, and addition of an appropriate amount improves toughness and reduces the amount of h3C that precipitates Nb carbides during tempering, which is harmful to delayed fracture resistance. It is effective in reducing the amount of carbon, and for this purpose, it is necessary to contain 0.014 or more. However, if Nb is contained in excess of 0.1%, the toughness will deteriorate, so this should be the upper limit.

Cu is effective in improving delayed fracture resistance and corrosion resistance, but the effect is insufficient if it is less than 0.14. Again 1
．． If it exceeds 5%, the above-mentioned effect on delayed fracture resistance is saturated and it is not economical, so it should be kept at 1.5% or less.

Ni is an element that improves hardenability and also improves toughness. The effect is small if it is less than 0.1%, and on the other hand, if it exceeds 1.5%, the delayed fracture resistance will be adversely affected, so this was set as the upper limit.

n is an element that is effective in securing solid solution B that combines with N in steel to prevent the formation of BN and is effective in improving hardenability. The following is insufficient. However, if it exceeds 0.040%, it will become saturated, so this is set as the upper limit.

Hardenability improves when B is added in an amount of 0.0003% or more.

However, even if added in excess of 0.0030%, the effect will be saturated, so this should be the upper limit.

Furthermore, in the present invention, between Mo%V and C, the following formula or π formula is used: (Mo(@x-+v(%)x)/C(%)=X-・
−n(Mo(%)x −+Nb(drive+M%)X”
)/C<%SX-...n It is necessary that the value of X falls within the range of 0.5 to 1.5. That is, when tempering the martensitic phase after quenching at a temperature of 600°C or higher and lower than Ae1 point, Mo, V or Mo * V + N
By precipitating a large amount of carbide b and fixing C, A3 ((n) is a necessary condition to reduce the precipitation amount and improve delayed fracture resistance, and X in the above I% ■ formula is 0. #*3C amount decreases even if it is less than 5, but
The improvement in delayed fracture resistance is small. If the value of X in the π equation entered by the father exceeds 1.5, toughness will deteriorate.

In addition, in specific manufacturing, it is preferable that steel having a chemical composition within the above range be quenched at a temperature of 900° C. or higher. In other words, in order to obtain a uniform martensite phase, it is appropriate to cool a sufficiently uniform austenite phase at a cooling rate higher than the critical cooling rate, and a temperature of 900°C or higher is necessary to effectively obtain a sufficiently uniform austenite phase. It is practically necessary.

After hardening, tempering is performed at a temperature of 600°C or higher and lower than the Act point. This temperature range is a preferable range for precipitating Mo+VsNb carbides and reducing the amount of hsC precipitation. F1s at tempering temperature
The amount of decrease in c'M is small.

A specific manufacturing example of the product according to the present invention will be described below.

That is, Table 1 below shows the chemical compositions of the steels of the present invention examples and comparative examples used by the present inventors.

In addition, the heat treatment conditions for these steels, the results of measuring the yield strength and tensile strength of the test pieces, and the values of X in the above formulas I and II are summarized in Table 2 below. However, the delayed fracture test uses a cantilever type testing machine, and the test piece 1 is 10 x 1 as shown in Figure 1.
A fatigue crack 2 with a depth of 3 cm was introduced in the center of the upper row in the rolling direction and in a direction perpendicular to the rolling surface using a 5×150 earthquake.

The details of the test method are as follows: Using a testing machine, a bending moment is applied in the direction in which the fatigue crack 2 of the test piece 1 opens, and the + value of the fatigue crack is increased to 260 Kff.
/*j, and was kept in a test environment and the rupture time was measured. The test environment was a 35% Na (J aqueous solution (pH approximately 7) at 30°C, and the maximum holding time was 500 hours.

The rupture time and the relationship between yield strength and rupture time obtained as a result of such a delayed rupture test are shown in FIG.

That is, as is clear from FIG. 2, the device according to the present invention is 500
Delayed fracture does not occur even after holding for a long time, and exhibits significantly better delayed fracture resistance than that of the comparative example.

In other words, comparison A and B are SN0M439 steel and comparison steel C.
, D are S 0M435 steel and S 0M430 steel, respectively, and these are steels that are widely used for mechanical structures, but their chemical composition is outside the scope of the present invention, and their recirculating temperatures are similar to those mentioned above. Unlike the preferred range, it is clear that the fracture resistance is inferior when compared with the examples of the present invention.

Furthermore, the chemical composition and tempering temperature of comparative steels ESF, G, and H are outside the range of the present invention, and their delayed fracture resistance is inferior.

Steel I has a chemical composition within the range of the present invention, but because the tempering temperature is low, the decrease in Fa3C is small and the delayed fracture resistance is poor. @J has a low C content and therefore exceeds the standard of V-150. This is an example where strength cannot be obtained.

As described above, by adjusting the chemical components within the range of the present invention and also performing the excessive heat treatment specified by the present invention, it is possible to accurately manufacture a high tension oil well well tube with good delayed fracture resistance. becomes.

"Effects of the Invention" According to the present invention as explained above, it is possible to manufacture a steel pipe that has appropriate high strength and excellent delayed fracture resistance as a steel pipe for oil wells. This is an invention with great industrial effects.

[Brief explanation of drawings]

The drawings show the technical content of the present invention, and FIG. 1 is an explanatory diagram of the shape of a delayed fracture test piece, and FIG.
It is a chart summarizing the results of a delayed fracture test in a 35% Nact aqueous solution environment at 0° C. for the inventive material and the comparative material.

Claims (1)

[Claims] 1. C: 0.10-0.25wt%, Si: 0.15-0.15wt%
1.0wt%, Mn: 0.3-1.5wt%, Cr: 0
．． 5 to 5.0 wt%, Mo: 0.5 to 3.0 wt%, V
:0.05~1.2wt%, Al:0.005~0.1
0 wt%, the remainder consisting of Fe and unavoidable impurities,
Moreover, {Mo(%)×1/16+V(%)×3/17}/C(
%) = 2, C: 0.10~0.25wt%, Si: 0.15~
1.0wt%, Mn: 0.3-1.5wt%, Cr: 0
．． 5 to 5.0 wt%, Mo: 0.5 to 3.0 wt%, V
:0.05~1.2wt%, Al:0.005~0.1
0 wt%, and Nb: 0.01 to 0.1 wt%, with the remainder consisting of Fe and inevitable impurities,
Moreover, {Mo(%)×1/16+Nb(%)×4/31+V(
%)×3/17}/C(%)=X, where X is 0
．． A high-tensile oil well steel pipe with excellent delayed fracture resistance, characterized by satisfying 5≦X≦1.5. 3, C: 0.10~0.25wt%, Si: 0.15~
1.0wt%, Mn: 0.3-1.5wt%, Cr: 0
．． 5 to 5.0 wt%, Mo: 0.5 to 3.0 wt%, V
:0.05~1.2wt%, Al:0.005~0.1
Cu: 0.1 to 1.5 wt%, Ti: 0.005 to 0.0 wt%.
040 wt%, Ni: 0.1 to 1.5 wt%, B: 0.
0003~0.0030wt%Nb:0.01~0.1
wt%, and the remainder consists of Fe and unavoidable impurities, and {Mo(%)×1/1
6+V(%)×3/17}/C(%)=X... I {
Mo (%) × 1/16 + Nb (%) × 4/31 + V (%
)×3/17}/C(%)=X...II A high-tension oil well with excellent delayed fracture resistance characteristics, characterized in that steel pipes.