JPS61270355A - High strength steel excelling in resistance to delayed fracture - Google Patents

Abstract

PURPOSE:To develop a high strength steel having superior yield strength and resistance to delayed fracture by subjecting an Ni-Cr-Mo low alloy steel containing trace constituents of various kinds to heat treatment under specific conditions. CONSTITUTION:The low alloy steel contains, by weight, 0.15-0.45% C, <1.50% Si, 0.01-1.50% Mn, 0.10-4.00% (not including 0.10%) Ni, 0.50-2.00% Cr, either or both of Mo and W in the amount satisfying Mo+1/2W=0.30-1.50%, 0.01-0.20% V, 0.005-0.20% Nb, 0.01-0.15% Zr and 0.01-0.10% Al, to which specific small amounts of Cu, Ca, Ti and B are further added independently or in combination. This steel is subjected to hardening from the temp. of AC3 point or above and then to tempering from the temp. between 580 deg. and AC1 point under the condition that PLM represented by expression (1) is 16.8X10<3> or more. In this way, the steel stock having austenite grains of ASTM No.8.5 or above, excelling in resistance to delayed fracture and suitable for ultra-high strength oil well pipes can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a
The present invention relates to a high-strength steel that has a yield strength exceeding 0.2% yield strength) and excellent delayed fracture resistance, and is suitable for uses such as oil country tubular goods.

Conventional technology In recent years, in response to the growing need to secure energy from a long-term perspective, the development of new oil and gas fields has become active in various parts of the world. Energy extraction is becoming more common than ever, and development is now being focused on oil and natural gas in harsh environments such as those deep beneath the surface of the earth, which had previously been abandoned. Advanced technology is becoming necessary.

For example, in recent years, extremely deep areas (over 15,000 feet deep) and 0.5 psi per foot of depth have been
Increasingly, wells for oil and natural gas extraction are being drilled into geological formations with higher ground pressure than the so-called "standard state", where pressure increases of more than (0,3515 gf/mm2) are expected. . To perform stable work in such an environment, a V-150 class or higher CS MYS
(Specified Minimum Yield
Strength, standard minimum yield strength) is 150ksi
Oil country tubular goods having extremely high strength (105.5 kgf/mm2 or more) are required, and the current situation is that the demand for a stable supply thereof is increasing.

However, when low-alloy steel, which has traditionally been used as oil country tubular goods, has a high strength of V-150 class or higher, the static temperature drops below the yield point due to embrittlement of the austenite grain boundaries. There was an inherent risk of ``delayed failure'' in which failure occurred even under heavy loads. Generally speaking, in oil fields, when a well becomes old and no longer produces self-gushing water, the pumping efficiency is improved by applying water or gas pressure or adding acid (acidizing), which is called secondary recovery. When acid is added or in oil fields under acidic environments, low alloy steels have conventionally had the problem of increased risk of delayed fracture due to the influence of hydrogen.

On the other hand, maraging steels such as 18Ni-5Mo-7,5Co series, austenitic high alloys, and high alloy steels are known to have better delayed fracture resistance than ordinary low alloy steels. However, maraging steel
Since it contains, there are problems such as high cost and poor low temperature toughness. On the other hand, austenitic high alloys and high alloy steels require a large amount of cold working to obtain strength, which is inefficient, and high N1, Cr, etc. contents, resulting in high costs. There is a problem that
None of these have been used simply for high-strength oil country tubular goods, and have only been put to practical use in some extremely limited environments, especially from the point of view of economic efficiency.

On the other hand, JP-A-58-61219 and JP-A-58-84
No. 960 discloses a high-strength steel with excellent delayed fracture resistance. However, the steel described in JP-A No. 58-61219 only pursues the effect of cleaning grain boundaries by reducing P and N, and furthermore, since the austenite grain size is large, the above-mentioned severe It cannot exhibit sufficient delayed fracture resistance in the environment.

On the other hand, the steel described in JP-A-58-84960 is also exclusively L.
The steel described in this publication is also unable to exhibit sufficient delayed fracture resistance in the above-mentioned harsh environment, simply by pursuing the effects of suppressing the segregation of P by a and controlling the sulfide morphology by Ca.

Problems to be Solved by the Present Invention The present invention has been made in view of the problems of the prior art as described above.
It has a yield strength exceeding ksi (105.5 kgf/mm2), has a delayed fracture resistance that is far superior to conventional low alloy steels, and is suitable for use with 18N1 maraging steel, austenitic high alloy steels, and high alloy steels. The purpose of the present invention is to provide a high-strength steel that is much cheaper than alloy steel and is suitable for use as oil country tubular goods.

Means for Solving the Problems In order to achieve the above objectives, the inventors conducted detailed research on the chemical composition of steel materials, manufacturing conditions including heat treatment, and the relationship between the resulting structure and properties. As a result of repeated efforts, the findings shown in (a) to (e) below were obtained. That is, (a) Delayed fracture is a phenomenon in which steel suddenly exhibits brittle fracture after a period of time has elapsed when it is placed under a static load.
It is said to be a type of hydrogen embrittlement that occurs due to hydrogen that has entered the steel from the external environment or hydrogen that has entered the steel due to plating, etc., but the austenite grain size of the steel is
It has been found that the occurrence of delayed fracture can be suppressed by adjusting the grains to fine grains with a TM No. of 8.5 or more and quenching to obtain a martensite or low-temperature bainite structure, followed by tempering.

(3) Carbides in steel serve as a place for hydrogen to accumulate. Therefore, if these carbides exhibit a notch defect shape such as needles or rods, or coarsely aggregate, this will become the starting point for delayed fracture. Although it is easy to do so, it has been found that when Zr is contained in steel, the carbides are finely dispersed into spherical shapes, and the delayed fracture resistance is significantly improved.

(C) Quenched steel is heated at a high temperature of 580°C or higher and lower than the Act point.
= T (20+ l og t), T: tempering temperature (K), t: holding time (hr)], the carbides become spheroidized and the occurrence of delayed fracture is suppressed. It turns out.

(d) C: 0.15-0.45%, Si: 1.5
0% or less, Mn: 0.01 to 1.50%, as alloy components Ni: 0.10% to 4.00% (but not including 0.10%), Cr: 0, 50-2.0
0%, Mo+'AW: 0.30-1.50%
, V: 0.01-0.20%, Nb: 0.005-0
．． If it contains 20%, Ac.

After heating and quenching, the temperature is 580℃ or higher and Ac1 point or lower, and the above P+, w value is PLM≧16.8
Even if tempered under the conditions of X103, if the austenite grain size A STM No. is 8.5 or more,
Yield strength: 150ksi (105.5kgf/mm2
), it was found that it was possible to obtain stable strength and to have excellent delayed fracture resistance.

(e) Refinement of austenite grains increases the yield ratio (yield strength/tensile strength), and therefore improves delayed fracture resistance because tensile strength can be suppressed for the same yield strength. It was found to be effective.

The present invention was made based on the above findings, and includes: C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10 % to 4.00% (excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: 0.30 to 1.50% for Mo+ZW, Contains V: 0.01-0.20%, Nb: 0.005-0.20%, Zr: 0.01-0.15%, 8]: 0.01-0.10%, and as necessary. Accordingly, further: 1st category: Cu: 1.5% or less 2nd category: garbage: 0.01-0.10% 3rd category: B: 0.0003-0.0050% 4th category: Ca: 0. 001 to 0.030% of one or more types, the remainder consisting of Fe and unavoidable impurities,
Quenched after heating to C3 point or higher, then at a temperature of 580℃ or higher and Ac+ point or lower, and P LX≧16.8 x10
3 [However, P pg −T (20+ log t),
T: tempering temperature (°K), t: holding time (hr)], the austenite grain size is ASTM
No. It is characterized in that it provides a high-strength steel with excellent delayed fracture resistance of 8.5 or more.

Function Next, in the present invention, the reason why the chemical composition, heat treatment, and grain size of the steel are limited as described above will be explained.

(1) Reason for limiting the component composition C: C is an effective component for increasing the hardenability and strength of steel, as well as refining the grains, but if it is less than 0.15%, it decreases the strength and hardenability. As a result, the desired strength cannot be tempered at high temperatures for carbide spheroidization, and it becomes difficult to obtain the desired fine-grained steel, resulting in increased delayed fracture susceptibility.

On the other hand, if C content exceeds 0.45%, susceptibility to quench cracking during quenching increases and also causes deterioration of toughness, so the C content is set at 0.15 to 0.45%.

Si: Si is an element necessary for deoxidizing steel and increasing its strength, and is also effective for raising the transformation point so that high temperature tempering can be performed stably.

However, if the Sl content exceeds 1.50%, the toughness will deteriorate significantly, and in a low pH environment, the delayed fracture resistance will also deteriorate, so the upper limit is set at 1.50%.
And so.

In addition, in order to further improve delayed fracture resistance by making the austenite grains as small as possible, the Si content should be set to 0.80.
% or less, and furthermore, in order to further improve delayed fracture resistance in a low pi environment, it is preferable that the value of (Si + Mn) be 0.80% or less.

Mn: Mn is an effective element for deoxidizing, desulfurizing, and improving hardenability, but if it is contained in large amounts, it will deteriorate the workability and delayed fracture resistance of steel, so the upper limit has been set to 1. .5
It was set to 0%. In the case of low alloy steel, the value of (Si + Mn) should be set to 0.80 in order to reduce delayed fracture susceptibility in a low p+ environment.
It is effective to reduce the Mn content to 0.
．． It is extremely difficult to make the Mn content less than 0.01% and increases costs.
The content was set at 1 to 1.50%. 0.0 to obtain stable fine-grained steel.
Addition of 10% or more is preferred.

Ni: Ni is an element that has the effect of increasing the strength of steel and further improving its toughness, but at 0.10%
The following effects cannot be obtained.

On the other hand, Ni is expensive, and addition of a large amount of Ni significantly lowers the transformation point, which impedes the effect of the present invention, which aims to improve delayed fracture resistance by high-temperature tempering. Therefore, assuming that the upper limit of the N1 content range is 4.00%, the content should be 0.10% to 4.00% (however, 0.10%
(excluding %).

Cr: Cr has the effect of increasing the hardenability, strength, and temper softening resistance of steel, and is an effective element for obtaining high-strength steel by high-temperature tempering treatment, but its content is 0.5%. If the content is less than 0.50 to 2.00%, the desired effect cannot be obtained, while if the content exceeds 2.00%, the toughness will deteriorate and the susceptibility to quench cracking will increase. did.

Mo, W: Both Mo and W increase the hardenability, strength, toughness, corrosion resistance and temper softening resistance of steel,
Since it has the effect of enabling high-temperature tempering treatment and improving delayed fracture resistance, it was decided to contain one or both of Mo and W.

Regarding the content of IJo and W (Mo + 'A W)
The atomic weight of W is approximately twice that of Mo, and
This is because the effect described above is about half that of Mo.

If the value of (Mo+ZW) is less than 0.30%, the desired effect cannot be obtained in the above action, while if this value exceeds 1.50%, the effect of these additions will be saturated, and the effect of increasing strength will be further increased. can not be obtained, and a substantially unnecessary amount of M
The content of Mo and/or W is set to 0.02 at a value of (Mo 10% W) because the content of Mo and W causes an increase in cost.
It was set at 30 to 1,50%.

■: ■ is an element that is effective in increasing the strength of steel, imparting resistance to temper softening, and refining the grain, and is effective in enabling high-temperature tempering treatment and improving delayed fracture resistance, but 0.01%
If it is less than 0.2%, the above-mentioned effect will be impaired. On the other hand, if it is added in a large amount exceeding 0.20%, the toughness will be deteriorated, so it is set at 0.01 to 0.20%.

Nb: Nb is effective in improving the strength and toughness of steel, imparting temper softening resistance, and grain refinement, and is also effective in improving delayed fracture resistance, but if it is less than 0.005%, The effect was not sufficient, and on the other hand, if the content exceeded 0.20%, the effect would be saturated, and it would also cause deterioration of toughness, so it was set at 0.005 to 0.20%. .

Zr: Zr is an important element in the present invention and has the effect of dispersing carbides into fine spherical particles in the steel and significantly improving delayed fracture resistance, but if it is less than 0.01%, the effect is small; If it exceeds .15%, the toughness deteriorates, so it is set at 0.01 to 0.15%.

Al: Al is effective in stabilizing the deoxidation of steel, making it homogenized, and making the grains finer, but if it is less than 0.01%, the desired effect cannot be obtained, and if it is less than 0.10% Even if the content exceeds 0.01 to 0.1, the effect will be saturated, and the increase in inclusions will cause cracks and deteriorate the toughness.
It was set to 0%.

Cu: Cu is an element that has the effect of increasing strength and further improving corrosion resistance. 1.5% Cu
Since hot workability deteriorates if the content exceeds 1.5%, the upper limit of the content range was set at 1.5%. Further, when adding 0.5% or more of Cu, it is preferable to add the same amount or more of Ni to prevent hot embrittlement.

Ti: Ti is an effective element for increasing the strength and refining steel, but if it is less than 0.01%, the above effects cannot be obtained;
Addition of more than 10% leads to deterioration of toughness, so the content is set in the range of 0.01 to 0.10%.

B: B is effective in improving hardenability, and thereby improving strength, toughness, and delayed fracture resistance. However, if the amount of B is less than 0.0003%, it is difficult to obtain the effect of addition, and even if it is added in excess of 0.0050%, the effect of addition is saturated and no further property improvement effect can be expected; Since this may lead to deterioration of toughness and delayed fracture resistance, the B content is set to 0.0003 to 0.0050%.

Ca: Ca is effective in spheroidizing inclusions in steel and improving the toughness in the direction perpendicular to the rolling direction, especially in high-strength steel, but if it is less than 0.001%, this effect cannot be obtained; If it exceeds 0.030%, the effect not only becomes saturated, but also non-metallic inclusions such as oxides of the steel increase, reducing the cleanliness of the steel and increasing the susceptibility to delayed fracture. Therefore, the Ca content range is 0.001 to 0.
．． 030%.

(2) Reason for limiting heat treatment and particle size Conventionally, the yield strength was 150 ksi (105,5 kgf/
Ac-ac.

It is manufactured by intentionally reheating and then quenching, or by hot-forming, directly quenching at a temperature of Ar 3 or higher, and then tempering at a temperature of Ac 1 or lower.

However, directly quenched steel pipes have coarse austenite grains (ASTM No. 7 or less) and are extremely susceptible to delayed fracture. On the other hand, research by the present inventors has revealed that in the case of reheated and quenched steel, the delayed fracture characteristics vary greatly depending on the austenite grain size and tempering temperature.

That is, the present inventors discovered that C, Si, Mn, N1%,
Mo.

Using various steels whose contents of W, ■, Nb, Zr, and Al are within the range of the present invention, the austenite grain size is changed using various means such as heat treatment, processing heat treatment, and a combination of cold working and heat treatment. This was tempered at 450 to 650°C for 30 minutes. A round bar tensile test piece with a parallel part of 8.5-φ was taken from each steel plate and subjected to a tensile test.
(119.5kgf/mm2) yield strength is 0.
Delayed fracture characteristics were investigated only for those that were confirmed to have a 2% yield strength).

The delayed fracture characteristics are shown in Fig. 1(a), a perspective view of the whole, and Fig. 1(a).
Five specimens with details of the U-notch shown in Fig. 2) were cut out from one tempered steel plate, a wedge was inserted into the U-notch, and then immersed in hot water at 80°C for 5,000 hours to prevent cracking. A survey was conducted to determine the presence or absence of the virus, and the results are shown in Figure 2. In FIG. 2, 0 indicates that no cracking was observed in any of the five test pieces, and × indicates that cracking was observed in any or all of the five test pieces.

As shown in Figure 2, the austenite grain size is ASTMN
If the tempering temperature is lower than 580°C, cracks will occur even if the austenite grain size is ASTM No. 8.5 or higher, even if the austenite grain size is fine. It was found that it occurs. Therefore, in the present invention, the sea bream is limited to sea bream that has been quenched with the austenite grain size adjusted to ΔSTMNα of 8.5 or higher and tempered at 580° C. or higher.

Next, the reason why the heating temperature for quenching is set to Ac3 or higher is to quench from a uniform austenite structure. The upper limit of the heating temperature for quenching is preferably below the austenite grain coarsening starting temperature, and as mentioned above, it is necessary to obtain fine austenite grains with an ASTM No. of 8.5 or higher in the final quenching process. There is.

The present invention has an austenite grain size of ASTM No. 8.5.
One of the features is that it can be adjusted to the above level,
The austenite grain size is determined by ASTM No. To adjust the value to 8.5 or higher, there are, for example, the following methods.

■ Instead of direct quenching, quenching is performed by reheating in a furnace to a temperature below Ac3 point + 150°C, or by rapid heating quenching.

0 Quenching is performed two or more times or after cold working. If the product is directly quenched, it will become finer if it is quenched two or more times (furnace heating or rapid heating may be used), and if it is cold worked, even if it is as quenched,
It may be tempered, and if it is tempered again, it becomes fine grains.

Next, the present inventors discovered that 0°28%C-0,45%5i-
0,25%Mn-1,37%Ni-0,94%Cr-
0,56%Mo -0,04%V -0,044%Nb
-0,045%Zr -0,043%Al (Ac,
Using a steel having a composition of 40°C at the point nearer and 840°C at the 3rd point Ac, the austenite grain size was determined to be ASTM No. 10.
5, and then heated to 600°C and tempered with holding times of 5, 10, 15, and 30 minutes, respectively, and the same delayed fracture test as above was conducted on the steel pieces after tempering. Ta. From this experimental result, 5 minutes and 10 minutes
Cracks were observed at a rate of 215.115 in each of those subjected to tempering treatment. However, no cracks were observed in the samples tempered for 15 and 30 minutes.

For tempering at 600°C for 10 minutes, PLM216
．． 78 x 10', and for tempering at 600°C for 15 minutes,
6.93×103.

Therefore, in the present invention, the condition that PLM≧16.8×103 is set. Note that this condition indicates that at a tempering temperature of 580°C, tempering for 30 minutes or more is required.

That is, as mentioned above, the temperature is 580°C or higher, and the PLM
It was confirmed in the above experiment that when ≧16.8 x 103, the carbide is well spheroidized and the delayed fracture susceptibility is reduced.

On the other hand, the above steel was tempered at 545°C for 4 hours (
When the delayed fracture test was performed on PLM=16.9×103), cracking occurred at a rate of 215. From this, it is clear that with regard to tempering, even if either one of the conditions of 580° C. or higher and P LM ≧16.8×103 is missing, it is not preferable for improving delayed fracture resistance.

Therefore, in the method of the present invention, the temperature is 580°C or higher and P
The condition for tempering is defined as ≧16.8×103.

Furthermore, in this case, if the tempering temperature exceeds the Act point, not only will the strength of the steel material vary significantly, but also the delayed fracture susceptibility will increase, so the tempering temperature was determined to be below the Ac point.

Next, the present invention will be explained using examples and comparing with comparative examples. It should be noted that these Examples are merely illustrative of the effects of the present invention, and of course do not similarly limit the technical scope of the present invention.

Example 1 First, steels 1 to 25 having the chemical compositions shown in Table 1 were melted. These steels were then heated and rolled, quenched and tempered under the conditions shown in Table 2.

Austenite & once (AS) for those before tempering
T M No.) was measured, and the tensile test and delayed fracture test were conducted on the tempered material.

The tensile test was conducted using a round bar test piece with a parallel portion of 8.5 mmφ, and the delayed fracture test was conducted under the following conditions. That is,
Five test pieces shown in FIG. 1 were cut out from each type of steel material. FIG. 1(a) shows the overall shape of the U-notched test piece, and FIG. 1 et al.) show details of the U-notched test piece.

After statically inserting a wedge into this U-notch, it was immersed in warm water at 80° C. for 5,000 hours to check for cracks.

The test results obtained are also shown in Table 2.

From the results shown in Table 2, the steel with the chemical composition range of the present invention is 5
Even if tempered under the conditions of 80℃ or higher and PLM≧16.8
A yield strength exceeding 0.2% proof stress) is obtained, and there is no occurrence of delayed fracture, and either or both of strength and delayed fracture resistance are superior to comparative steels. It is clear that the balance of destructive properties is extremely good.

Example 2 Steels 26 to 28 having the chemical composition shown in Table 3 were melted.

Next, these steels were heated and rolled, quenched under the conditions shown in Table 4, and then tempered.

Austenite grain size (AST
M No. ) was measured, and the tensile test and delayed fracture test were conducted under the same conditions as in Example 1 for the tempered product.

The test results thus obtained are also shown in Table 4.

From the results shown in Table 4, steel within the chemical composition range of the present invention is 580°C or higher, PLOT≧16.8 x 10'
Even if tempered under the conditions of 150ks i (105,5k
Large yield strength exceeding 0.2% yield strength (gf/mm2)
Moreover, the occurrence of delayed fracture was zero, and it is clear that both strength and delayed fracture resistance are superior to comparative steels, and the balance between strength and delayed fracture resistance is extremely good. .

Example 3 Steel 27, which is a target steel having the chemical composition range prescribed by the present invention in Table 3 above, was heated and rolled, quenched under the conditions shown in Table 5, and then tempered.

Austenite grain size (ASTM
No. ), and a tensile test and a delayed fracture test were conducted on the tempered product under the same conditions as in Example 1. The test results are also shown in Table 5.

From the results in Table 5, it can be seen that the delayed fracture resistance of target steels within the chemical composition range defined by the present invention becomes good only when the processing conditions within the range of the present invention are satisfied.

Example 4 Steel 26, which is a target steel having the chemical composition range prescribed by the present invention in Table 3 above, was heated and rolled, then quenched under the conditions shown in Table 6, and then tempered.

Austenite grain size (ASTM
After tempering, a tensile test and a delayed fracture test were conducted under the same conditions as in Example 1. The test results are also shown in Table 6.

From Table 6, it can be seen that in the present invention, regardless of the method of refining austenite grains, the austenite grain size is
After adjusting the M No. to 8.5 or higher and quenching it, you can obtain high-strength steel with excellent delayed fracture resistance by tempering it at 580℃ or higher and under the conditions of PLM≧16.8×103. It turns out that it can be done.

Example 5 Of the steels shown in Table 1 above, Steel 1.2.14.15, which is the target steel within the chemical composition range specified by the present invention, and Comparative Steel 24, which is outside the scope of the present invention, were heated and rolled, Hardening was performed under the conditions shown in Table 7, and then tempering was performed. The austenite grain size (△STMNα) was measured for the one before tempering, and the tensile test was conducted on the one after tempering under the same conditions as in Example 1. A delayed fracture test was conducted by immersing the sample in a 5% saline solution (at room temperature) adjusted to 5% for 1000 hours. In addition, the test liquid is 48
Replaced every hour.

The test results thus obtained are also shown in Table 7.

From the results shown in Table 7, among the target steels within the chemical composition range specified by the present invention, steel 1.2 with (Si + Mn) of 0.80% or less has delayed fracture resistance even in a low pH environment. It can be seen that the balance between strength and strength is extremely good.

Effects of the Invention As mentioned above, the steel of the present invention has a strength of 150 ksi (10
It has become possible to manufacture inexpensive ultra-high strength oil country tubular goods that have high strength exceeding 5.5 kgf/mm') and excellent delayed fracture resistance, and the industrial effects thereof are extremely large. .

The steel of the present invention can be widely applied not only to ultra-high-strength oil country tubular goods but also to high-strength bolts having the same strength level as described above.

Note that in this specification, the percentages used to indicate the chemical components of steel are percentages by weight.

[Brief explanation of the drawing]

Figure 1 shows the shape of the delayed fracture test piece. Figure 1 (a) is a perspective view of the entire test piece, and Figure 1 (a) shows its U.
This figure shows the details of the notch part. Figure 2 shows 170 ksi (119,5 kgf/mm2
FIG. 2 is a diagram showing the influence of tempering temperature (when held for 30 minutes) and austenite grain size on the delayed fracture resistance of a steel subject to the present invention having a yield strength near ).

Claims (16)

[Claims] (1) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ 0.10%, the balance consists of Fe and unavoidable impurities, and A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (2) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ 0.10%, Cu: 1.5% or less, the balance consists of Fe and inevitable impurities, A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (3) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ 0.10%, Ti: 0.01~0.10%, the balance consists of Fe and inevitable impurities, and A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (4) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ 0.10%, B: 0.0003 to 0.0050%, the balance consists of Fe and inevitable impurities, and A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (5) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ 0.10%, Ca: 0.001-0.030%, the balance consists of Fe and inevitable impurities, A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (6) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ Contains 0.10% Cu: 1.5% or less, Ti: 0.01 to 0.10%, the balance consists of Fe and inevitable impurities, and A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (7) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ Contains 0.10% Cu: 1.5% or less, B: 0.0003 to 0.0050%, the balance consists of Fe and inevitable impurities, and A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (8) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ Contains 0.10% Cu: 1.5% or less, Ca: 0.001 to 0.030%, the balance consists of Fe and inevitable impurities, and A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (9) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ Contains 0.10% Cu: 1.5% or less, Ti: 0.01 to 0.10%, B: 0.0003 to 0.0050%, and the balance consists of Fe and inevitable impurities, A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (10) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ Contains 0.10% Cu: 1.5% or less, Ti: 0.01 to 0.10%, Ca: 0.001 to 0.030%, and the balance consists of Fe and inevitable impurities, A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (11) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ Contains 0.10% Cu: 1.5% or less, B: 0.0003 to 0.0050%, Ca: 0.001 to 0.030%, with the balance consisting of Fe and inevitable impurities, and A
Quenched after heating to C_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower each time.
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (12) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ Contains 0.10% Ti: 0.01~0.10%, B: 0.0003~0.0050%, the balance consists of Fe and inevitable impurities, A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (13) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ Contains 0.10% Ti: 0.01 to 0.10%, Ca: 0.001 to 0.030%, the balance consists of Fe and inevitable impurities, and A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (14) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ Contains 0.10% Ti: 0.01 to 0.10%, B: 0.0003 to 0.0050%, Ca: 0.001 to 0.030%, and the balance consists of Fe and inevitable impurities, A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (15) In weight%, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ Contains 0.10% B: 0.0003 to 0.0050%, Ca: 0.001 to 0.030%, the balance consists of Fe and inevitable impurities, and A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr), (16) As component elements, C: 0.15 to 0.45%, Si: 1.50% or less, Mn: 0.01 to 1.50%, Ni: 0.10% to 4.00% (but , excluding 0.10%), Cr: 0.50 to 2.00%, Mo or W or both: Mo+1/2
W: 0.30~1.50%, V: 0.01~0.20%, Nb: 0.005~0.20%, Zr: 0.01~0.15%, Al: 0.01~ Contains 0.10% Cu: 1.5% or less, Ti: 0.01 to 0.10%, B: 0.0003 to 0.0050%, Ca: 0.001 to 0.030%, and the remainder Consisting of Fe and unavoidable impurities, A
Quenched after heating to c_3 point or higher, then P_L_M≧16.8× at a temperature of 580℃ or higher and Ac_1 point or lower
10^3, the austenite grain size is ASTM No. High strength steel with excellent delayed fracture resistance of 8.5 or higher. However, P_L_M=T(20+logt) T: Tempering temperature (°K), t: Holding time (hr),