JPH0559176B2 - - Google Patents

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/mm ² or more. Specifically, the present invention relates to a method for producing high-strength oil country tubular goods having a 0.6% yield strength of 80 kg/mm 2 or more. The method relates to a method that allows production of oil country tubular goods having a strength equal to or greater than that obtained by adding expensive alloy components such as Mo, and a 0.6% proof stress of 80 kg/mm ² or more, by reconstitution. In general, high-strength oil country tubular goods (for example, 0.6% yield strength of 77 kg/mm ² or more) used for drilling deep oil wells are made of Mo
It is often manufactured by quenching and tempering steel containing expensive alloying elements such as.
In this method, tempering is usually performed at around 600°C, and in order to increase the tempering resistance and ensure strength, it is necessary to add expensive alloying components such as Mo. However, the content of Mo and other components is extremely high compared to other alloy components, which is a major drawback from an economic standpoint. Furthermore, in this method, the tempering temperature is too high, around 600°C, and even if an alloy component such as Mo is added, 600°C falls into the tempering brittle region, which is undesirable because toughness is impaired. The present invention aims to solve the above-mentioned drawbacks, and specifically, the present invention aims to solve the above-mentioned drawbacks, and specifically, without adding expensive alloy components such as Mo to steel,
We propose a method for manufacturing high-strength oil country tubular goods at low cost without impairing toughness by quenching and tempering this steel and performing the tempering at a relatively low temperature. That is, in the method of the present invention, when manufacturing high-strength oil country tubular goods by quenching and tempering steel after hot working without adding Mo to the steel, C 0.20 to
0.35%, Si 0.10~0.50%, Mn 1.0~1.6%, P
0.03% or less, S 0.02% or less, Al 0.02-0.10%,
In addition to containing Ti 0.005~0.050%, Cr 0.2~1.0
%, V 0.02~0.08% and B 0.0005~
0.0050%, and the remainder consists of Fe and unavoidable impurities.
It is characterized by being quenched at a temperature of Ac ₃ or higher, then tempered at a temperature of 450°C or higher and 580°C or lower to obtain a high strength of 0.6% yield strength of 80Kg/mm ^{2 or} higher. In addition, the method of the present invention can add 0.20 to 0.35% C to the steel when manufacturing high-strength oil country tubular goods by quenching and tempering the steel after hot working without adding Mo to the steel.
Si 0.10-0.50%, Mn 1.0-1.6%, P 0.03% or less, S 0.02% or less, Al 0.02-0.10%, Ti 0.005
In addition to containing ~0.050%, Cr 0.2~1.0%, V
Ni with 0.02~0.08%, B 0.0005~0.0050%
One or two of 0.10 to 0.30% or 0.015 to 0.035% of Nb is contained, and the remainder consists of Fe and unavoidable impurities, and this steel is heated after hot working.
After quenching at a temperature of ₃ points or above,
Tempered at 450℃ or higher and 580℃ or lower, 0.6% yield strength 80Kg/
It is characterized by obtaining high strength of mm ² or more. The method of the present invention will be explained in detail below. First, as mentioned above, high-strength oil country tubular goods used in oil wells are required to have a 0.6% yield strength of 77 kg/mm ² or more.
Conventionally, such high-strength oil country tubular goods are manufactured by adding alloy components such as Mo and Nb to a steel composition system and then subjecting the steel of this composition system to quenching and tempering treatment. 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.
Moreover, even if alloy components such as Mo are not added, avoid temperatures near 600℃, which enters the tempering expansion region.
By tempering under appropriate conditions, we manufacture oil country tubular goods that are excellent both in terms of material and economy. In other words, when manufacturing oil country tubular goods by quenching and tempering in the conventional manner, tempering is usually carried out at around 600°C, and it is necessary to add alloying elements such as Mo to increase tempering resistance and ensure strength. .
In this regard, the present inventors have conducted research on a method for 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, we added Cr and V without adding Mo as reinforcing elements, and also added B in an appropriate range.
If tempered at a relatively low temperature of 580℃,
Strength required for oil country tubular goods, especially 0.6% yield strength 80
In addition to obtaining Kg/mm ² or more, it is possible to avoid the so-called tempering embrittlement region (near 600℃).
It was discovered that oil country tubular goods with good toughness could be manufactured, and based on this knowledge, the method of the present invention was established. Therefore, the reasons for limiting the range of each component are as follows. C is the element that most affects the strength of steel,
If it is less than 0.20%, the target strength cannot be obtained, and if it is more than 0.35%, the susceptibility to quench cracking will increase significantly, so the lower limit should be set.
0.20%, with an upper limit of 0.35%. Si is an element necessary for deoxidizing steel, and 0.10% or more is necessary, but too much will harm the toughness, so the lower limit is set at 0.10%.
%, with an upper limit of 0.50%. Mn is an effective element for increasing the hardenability of steel and strengthening it, and requires a minimum content of 1.0%. Too much Mn 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 will deteriorate significantly, so the upper limit should be
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 used to improve hardenability and achieve high strength.
In particular, it is essential for achieving high strength without adding alloying components such as Mo.
From this point of view, a relatively large amount of Cr is added, and in particular, if it is less than 0.2%, it is ineffective, so the lower limit is set to 0.2%, and if it exceeds 1.0%, cracking susceptibility increases and toughness deteriorates, so the upper limit was set to 1.0%. . V is absolutely necessary to increase strength through precipitation hardening during tempering under conditions where alloying components such as Mo are not added. , is effective in stably obtaining strength after tempering.
If it exceeds 0.02%, it will not be effective, and if it exceeds 0.08%, it will cause cracking, so the lower limit should be set at 0.02%, and the upper limit should be set at 0.02%.
It was limited to 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 will cause a decrease in toughness, so the lower limit should be 0.02%. The upper limit was set at 0.1%. Ti is necessary to fix N in the steel and maximize the effects of B, such as improving the hardenability described below, and if it is less than 0.005%, it will not be effective, and if it is added more than 0.05%, it will significantly reduce the toughness. Since it causes deterioration, set the lower limit.
0.005%, with an upper limit of 0.05%. B, together with V, exhibits the effect of improving hardenability and stabilizing strength after tempering, and is an essential component under conditions where Mo is not added. This effect is significant in the range of 0.0005 to 0.005%, so
limited to this range. In addition, in the above component system, one or both of Ni or Nb can be added, and the addition of Ni improves the toughness, and in order to obtain this effect, at least about 0.10% is required, so the lower limit is 0.10%. did. The upper limit was set at 0.30% for economic reasons. Also,
Nb improves strength and toughness and is an effective component. From this point of view, the lower limit was set at 0.015%, and the upper limit was set at 0.035% from economical considerations. After hot working, steel with the above composition is quenched at a temperature of Ac ₃ or higher, and then heated to a temperature of 450℃ or higher to 580℃.
Temper in a low temperature range as shown below. The reasons for limiting the tempering temperature to a relatively low temperature range are as follows. That is, steel with the composition shown in D in Table 1 below
Figure 1 shows the relationship between the tempering temperature and strength (0.6% proof stress) as well as the fracture surface transition temperature in the impact test by quenching and tempering at temperatures of ₃ or more Ac points. Ta. As shown in Figure 1, when the tempering temperature exceeds 580℃, the target strength (0.6% proof stress 80Kg/mm ² )
cannot be obtained, especially since it does not contain Mo.
When it enters the temper brittle region, the toughness is poor. Furthermore, if the tempering temperature is lower than 450°C, precipitation of C in the martensite produced by quenching will be insufficient.
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 the toughness is good exists in a slightly lower temperature range than usual. For these reasons, the lower limit of the tempering temperature was set at 450°C and the upper limit was set at 580°C. 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 realize any of these methods. Next, examples will be described. Steels with the seven chemical compositions A to G shown in Table 1 are
Hardening was performed under the hardening conditions shown in Table 2, followed by tempering under the tempering conditions shown in Table 2, to produce oil country tubular goods shown in the notes of Table 2. The mechanical properties of these oil country tubular goods were determined and were as shown in Table 2. In Table 1, steels A and B have a composition system containing Cr and Mo, and steel C has a composition system that is reinforced by V, Nb, etc.
Steels D and E consist of the components included in the present invention, and steel E
also has components falling within 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, the method of the present invention
Although the composition does not contain Mo, it is clear that if tempered in the temperature range, it will exhibit a 0.6% yield strength of 80 kg/mm ² or more and notch toughness equivalent to CrMo steels A and B, regardless of the tempering method. be. As described above, the method of the present invention has the economic effect of saving effective elements such as Mo, as well as the economic effect of reducing the optimum tempering temperature by about 100 degrees Celsius compared to ordinary CrMo steel, thereby saving fuel. It will greatly contribute to the economical production of oil country tubular materials with extremely large, high strength and excellent toughness.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between tempering temperature and strength and toughness in the component system according to the present invention.

Claims (1)

[Claims] 1. When manufacturing high-strength oil country tubular goods by quenching and tempering steel after hot working without adding Mo to the steel,
This steel contains 0.20-0.35% C, 0.10-0.50% Si,
In addition to containing Mn 1.0-1.6%, P 0.03% or less, S 0.02% or less, Al 0.02-0.10%, Ti 0.005-0.050%, Cr 0.2-1.0%, V 0.02-0.08% and B 0.0005-0.0050%. The remainder is Fe.
After hot working, this steel is quenched at a temperature of Ac ₃ or higher, and then tempered at a temperature of 450°C or higher and 580°C or lower to achieve a yield strength of 0.6%.
A method for manufacturing high-strength oil country tubular goods characterized by obtaining high strength of 80 Kg/mm ² or more. 2. When producing high-strength oil country tubular goods by quenching and tempering steel after hot working without adding Mo to the steel, C 0.20 to 0.35%, Si 0.10 to 0.50%,
In addition to containing Mn 1.0-1.6%, P 0.03% or less, S 0.02% or less, Al 0.02-0.10%, Ti 0.005-0.050%, Cr 0.2-1.0%, V 0.02-0.08%, B
In addition to 0.0005 to 0.0050%, one or two of Ni 0.10 to 0.30% or Nb 0.015 to 0.035% is contained, and the remainder consists of Fe and unavoidable impurities, and this steel is heated at a temperature of Ac ₃ or higher after hot working. A method for producing high-strength oil country tubular goods, which is characterized by hardening and then tempering at 450°C or higher and 580°C or lower to obtain high strength of 0.6% yield strength of 80Kg/mm ² or higher.