JPS6033312A - Manufacture of high strength oil-well pipe of 80kg/mm2 min. in 0.6% yield strength - Google Patents

Abstract

PURPOSE:To obtain the titled oil well pipe having the strength and toughness equal or superior to those of the case where high-priced alloy components are added, by quenching and tempering the steel of a specific composition having the zero or the minimum limit of additional amount of high-priced alloy components such as molybdenum or the like. CONSTITUTION:The steel of 0.20-0.35wt% C, 0.10-0.50% Si, 1.0-1.6% Mn, 0.3% max. P, 0.02% max. S, 0.2-1.0% Cr, 0.02-0.08% V, 0.02-0.10% Al, 0.005-0.050% Ti and 0.0005-0.0050% B, containing 0.10-0.30% Ni and/or 0.015-0.034% Nb when required, and remainder Fe is quenched from a temperature of not less than Ac3 point after hot rolling and successively tempered at 450-580 deg.C. Thereby, high strength oil-well pipe of 80kg/mm.<2> min. in 0.6% yield strength can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing high-strength oil country tubular goods having a 0.6% yield strength of 80 kg/mm2 or more. By minimizing the amount of alloying components added and quenching and tempering,
The present invention relates to a method for producing oil country tubular goods having strength and toughness equal to or greater than those obtained by adding expensive alloy components.

Generally, high-strength oil country tubing (oil country tubing) used for drilling deep oil wells (
For example, steel with a 0.6% yield strength of 77 kg/mm2 or more is often manufactured by quenching and tempering steel containing an expensive alloying element such as Mo. in this way,
Tempering is usually carried out at around 600°C, and in order to increase the tempering resistance and ensure strength, it is necessary to add expensive alloy components such as Mo, which is a major disadvantage from an economic point of view.

Furthermore, with this method, the tempering temperature is as high as around 600℃;
Since it fell into the tempered brittle region, it was also unfavorable from the viewpoint of toughness.

The present invention aims to solve the above-mentioned drawbacks, and specifically, Mo.
The steel is quenched and tempered without the addition of expensive alloying components, and even if it is added, the amount thereof is kept to a minimum. In this field, we develop a method for manufacturing high-strength oil country tubular goods at low cost and with excellent properties.

That is, the method of the present invention achieves C0.20 in weight percent.
~0.35%, Si0.10-0.50%, Mn1.0
~1.6%, P0.03% or less, S0.02% or less, C
r0.2-1.0%, V0.02-0.08%, Al0
．． 02-0.10%, Ti0.005-0.050%,
Contains B0.0005-0.0050%, the balance is Fe
After hot working, the steel containing unavoidable impurities is quenched at a temperature of AC3 or higher, and then tempered at a temperature of 450°C or higher and 580°C or lower.

In addition, the method of the present invention has C0.20 to 0 in weight percent.
．． 35%, Si0.10-0.50%, Mn1.0-1
．． 6%, P0.03% or less, S0.02% or less, Cr0
．． 2-1.0%, V0.02-0.08%, Al0.0
2-0.10%, Ti0.005-0.050%, B0
．． Contains 0.0005 to 0.0050% and Ni0.1
0-0.30% or Nb0.015-0.035%
A steel containing one or two of the above, with the remainder consisting of Fe and unavoidable impurities, is quenched at a temperature of Ac 3 or higher after hot working, and then tempered at a temperature of 450°C or higher and 580°C or lower.

The method of the present invention will be explained in detail below.

First, high-strength oil country tubular goods used in oil wells have a 0.
A 6% yield strength of 77 kg/mm2 or more is required. Such high-strength oil country tubular goods can be manufactured by adding alloy components such as Mo and Nb to the steel composition system and then quenching and tempering the steel of this composition system. However, this component system is expensive, and the method of the present invention reduces the amount of such expensive alloy components even if they are added without adding them, and also improves the material properties by tempering under appropriate conditions. The company manufactures oil country tubular goods that are both economical and excellent.

That is, when manufacturing oil country tubular goods by quenching and tempering according to conventional methods, the tempering is usually performed at around 600°C, and in order to increase the tempering resistance and ensure strength, Mo, Cr,
It is necessary to add things such as ■. In this regard, the present inventors have conducted research on a method of manufacturing oil country tubular goods by reducing the amount of expensive alloying elements, especially without adding Mo, and without causing deterioration of the material. As a result, if Cr and V are added without adding Mo as reinforcing elements and tempered at a relatively low temperature range of 450 to 580°C, the strength necessary for oil country tubular goods, especially 0.6%
It has been discovered that in addition to obtaining a yield strength of 80 kg/mm2 or more, it is possible to avoid the so-called tempering embrittlement region (near 600°C), so it is possible to manufacture oil country tubular goods with good toughness.Based on this knowledge, the method of the present invention has been developed. It has been established.

The reasons for limiting the range of each component are as follows.

C is the element that most affects the strength of steel, and is 0.20%
If it is less than 0.35%, the target strength cannot be obtained, and if it is more than 0.35%, the susceptibility to quench cracking increases significantly, so the lower limit was set to 0.20% and the upper limit was set to 0.35%.

Si is an element necessary for deoxidizing steel, and 0.10% or more is necessary, but too much will impair toughness, so the lower limit is 0.10%.
The upper limit was set at 0.50%.

M is an element effective in increasing the hardenability of steel and strengthening it, and requires a minimum content of 1.0%. Too much M increases cracking susceptibility, so the upper limit was set at 1.6%.

P is an impurity inevitably contained in steel, which causes temper brittleness and is harmful to toughness.

If it exceeds 0.03%, the toughness deteriorates, so set the upper limit to 0.
．． It was limited to 0.030%.

Like P, S is contained in steel as an impurity and causes brittleness, so the upper limit was set at 0.02%.

Cr is essential to improve hardenability and achieve high strength, and if it is less than 0.2% it is ineffective, so the lower limit is set at 0.2%, and if it exceeds 1.0%, cracking susceptibility increases. Since toughness also deteriorates, the upper limit was set at 1.0%.

(3) is essential for increasing strength through precipitation hardening during tempering, and is also effective for stably obtaining strength after tempering; if it exceeds 0.02%, it is ineffective; if it exceeds 0.08%, Since this may cause cracking, the lower limit was set at 0.02% and the upper limit was set at 0.08%.

Al is also used as a deoxidizing material, and if it is less than 0.02%, it has no deoxidizing effect, and if it is more than 0.1%, it causes a decrease in toughness, so the lower limit was set to 0.02% and the upper limit was set to 0.1%.

Ti is necessary to fix N in steel and exhibit the hardenability improvement effect of B, and if it is less than 0.005%, it has no effect, and if it is added more than 0.05%, it will significantly deteriorate the toughness. The lower limit was set to 0.005% and the upper limit was set to 0.05%.

As mentioned above, B shows the effect of improving hardenability, and this effect is 0.
Since the range of 0.0005% to 0.005% is significant, it is limited to this range.

In addition, in the above component system, one or two types of Ni or Nb can be added, and the addition of Ni improves toughness, and in order to obtain this effect, the lower limit is at least 0.10%. It was set to 0.10%. The upper limit was set at 0.30% for economic reasons. In addition, Nb improves strength and toughness and is an effective component, and from this point of view the lower limit is 0.
．． 0.015%, and the upper limit was set at 0.035% for economic reasons.

After hot working, the steel having the composition system as described above is quenched at a temperature of AC3 or higher, and then tempered at a low temperature range of 450° C. or higher and 580° C. or lower. The reasons for limiting the tempering temperature to a relatively low temperature range are as follows.

That is, the steel with the composition shown in D in Table 1 below was quenched and tempered from a temperature of Ac 3 or higher, and the tempering temperature and strength (0.6% proof stress) and fracture surface transition in the impact test were determined. The relationship with temperature was as shown in Figure 1.

As seen in FIG. 1, when the tempering temperature exceeds 580°C, the target strength (0.6% yield strength 80 kg/mm2) cannot be obtained, and furthermore, the tempering temperature falls into the brittle region, resulting in poor toughness. Furthermore, if the tempering temperature is lower than 450°C, the precipitation of C in the martensite produced by quenching is insufficient, resulting in very poor toughness.

In short, in the method of the present invention, since the steel has the above-mentioned compositional system, the tempering temperature range in which the target strength is achieved and good toughness is achieved usually exists in a slightly lower temperature range. For this reason, the lower limit of the tempering temperature is set at 450.
℃, and the upper limit was set at 580℃. As for the quenching method, there are conventional reheating quenching methods and surface quenching methods that have been developed in recent years, and the method of the present invention can implement any of these methods.

Next, examples will be described.

Steels having seven types of chemical composition, A to G shown in Table 1, were quenched under the quenching conditions shown in Table 2, and then tempered under the tempering conditions shown in Table 2. The oil country tubular goods shown in the figure were made. The mechanical properties of these oil country tubular goods were as shown in Table 2.

In Table 1, steels A and B have compositions containing Cr and Mo, and steel C has V
This is a component system that is reinforced with , Nb, etc. Steels D and E consist of components included in the present invention, and steel E also includes components included in claim (2). Furthermore, the quenching methods are compared between ordinary reheating quenching and direct quenching, which has been significantly developed in recent years.

As shown in Tables 1 and 2, although the method of the present invention uses a component system that does not contain Mo, if tempering is performed in the temperature range, any quenching method can achieve a yield strength of 0.6% of 80 kg/mm2 or more. It is clear that the notch toughness is equivalent to that of CrMo steels A and B.

As described above, the method of the present invention has the economic effect of saving expensive elements such as Mo, as well as the economic effect of reducing the optimum tempering temperature by about 100°C compared to the case of ordinary CrMo steel, thereby saving fuel. is extremely large and greatly contributes to the economical production of oil country tubular materials with high strength and excellent toughness.

Table 1 (chemical components) Table 2 (mechanical properties)

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between tempering temperature, strength, and toughness in the component system according to the present invention. Patent applicant Kawasaki Steel Co., Ltd. Agent Patent attorney Yoshikatsu Matsushita Attorney Vice Fumiyu Shima

Claims (1)

[Claims] 1) C0.2-0.35% by weight, Si0.
10-0.50%, Mn1.0-1.6%, P0.03
% or less, S0.02% or less, Cr0.2-1.0%, V
0.02-0.08%, Al0.02-0.10%, T
i0.005~0.050%, B0.0005~0.0
0.6 characterized in that the steel containing 0.050% and the remainder consisting of Fe and unavoidable impurities is quenched at a temperature of Ac 3 or higher after hot working, and then tempered at a temperature of 450°C or higher and 580°C or lower. A method for producing high-strength oil country tubular goods having a % proof stress of 80 kg/mm2 or more. 2) C0.20-0.35% in weight percent, Si0
．． 10-0.50%, Mn1.0-1.6%, P0.0
3% or less, S0.02% or less, CR0.2-1.0%,
V0.02-0.08%, Al0.02-0.10%,
Ti0.005~0.050%, B0.0005~0.
0.050% and Ni 0.10-0.30%
Alternatively, steel containing 0.015 to 0.035% of Nb or 0.035% and the remainder consisting of Fe and unavoidable impurities is quenched at a temperature of Ac 3 or higher after hot working, followed by 450%
0 characterized by tempering at a temperature of ℃ to 580℃
．． A method for manufacturing high-strength oil country tubular goods having a 6% yield strength of 80 kg/mm2 or more.