JPS5949284B2 - Method for producing high-strength oil well steel with excellent delayed fracture resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-strength oil well steel with excellent delayed fracture resistance, particularly at high temperatures (60 to 170
℃) This invention relates to a method for manufacturing high-strength oil well steel that has excellent resistance to delayed fracture that occurs in alkali.

Conventionally, the minimum yield strength in oil fields is 150k.
There is a great demand for materials having si, and a material commonly known as V-150 is used, although it is not an API standard.

This material has low Mo, V, and Nb content, so low-temperature tempering is required to obtain the necessary mechanical properties such as strength, and it also has defects that deteriorate delayed fracture resistance. In order to solve these defects, the present invention attempts to solve the current problems by adjusting the chemical composition of the steel itself and appropriately selecting the heat treatment conditions. As an excellent steel, the upper limit of strength is limited to a maximum tensile strength of 125 Y/K2 or less, and the γ grains are made finer, impurities, P, and S are reduced, and the grain boundary strength is strengthened by high-temperature tempering. This improves delayed fracture resistance. That is, the present invention provides (1) CO. 27-0.50 section, SiO. O8~0.3
Section 0, MnO. 9O to 1.30%, CrO. 5-0.9
%, NiO. O3 section and below, VO. O4~0, 11th Section, N
bO. Ol~0.10%, MOO. 6O~0.80%,
AIO. The balance consists of Fe and unavoidable impurities, and the PO. OO5% or less, 80.003%
(2) In the above (1), in addition to its chemical composition, TiO. OO2~0.020 Section, BO
．． Steel containing one or both of OOO2 to 0.00zs%,
(3) In (1) above, steel that further contains 3% or less CO in addition to its chemical components; (4) In (1) above,
In addition to its chemical components, TiO. OO2~0.02
0%, BO. A high-strength oil well product with excellent delayed fracture resistance characterized by quenching steel containing one or both of 2 to 0.0025% OOO and 3% or less of CO at 880 to 980°C and then tempering at 650 to 700°C. The gist is the method of manufacturing steel.

Next, the reason why the composition ratio of each additive element is limited in the present invention will be explained.

C: C is effective in improving strength, but if it exceeds 0.50%, quench cracking occurs during heat treatment, and when rapidly heated, it becomes difficult to form a uniform solid solution in austenite, causing uneven quenching. .

Further, if it is less than 0.27%, strength decreases and hardenability deteriorates, so it is limited to 0.27 to 0.50%. Si: 0.0s% or more is required to deoxidize Si steel and increase its strength, but if it exceeds 0.30%, delayed fracture resistance deteriorates, so 0.0s% or more is required.
．． 08 to 0.30%.

Mn: Mn is an additive element that is effective as a deoxidizing agent and improves hardenability, and improves hardenability, but
If it is less than 0.90%, the effect is too small.

If the content exceeds 1.30%, delayed fracture resistance deteriorates, so the content was set at 0.90 to 1.30%.

Cr: Cr is 0.0% to improve corrosion resistance and tempering resistance.
A ratio of 5% or more is required, but if the ratio exceeds 0.9, the delayed fracture resistance deteriorates, so the ratio was set at 0.5 to 0.9.

Ni: Ni is effective in improving strength and toughness, but 0.0
If it exceeds 3%, the delayed fracture property increases, so the coefficient was set to be 0.03 or less.

v: V is effective in improving strength, but if it is less than 0.04%, this effect cannot be obtained, and if it exceeds 0.11%, toughness deteriorates, so it is set to 0.04 to 0.11%.

Nb: Nb is an element that is effective in obtaining finer austenite grains during heating at the quenching temperature and is effective in preventing quench cracking during rapid cooling of materials with a high carbon content. If it exceeds the content, the toughness deteriorates, so the content was set to 0.1% or less.

MO: MO is effective in improving strength and corrosion resistance, but 0.
If it is less than 60%, it is difficult to satisfy a predetermined strength without causing corrosion resistance deterioration at a tempering temperature of 650° C. or higher.

On the other hand, 0. If s exceeds 0%, delayed fracture resistance deteriorates, so it was set at 0.60 to 0.80%. AI: AI is effective as a deoxidizing agent, and if it exceeds 0.10%, its effect will become saturated and cause deterioration of toughness. It was set to t0% or less.

P,s: In order to improve toughness and crack resistance, P
, S are desirable to be reduced as much as possible as impurities.
The upper limits are 0.005% and 0.003%, respectively.

Ti: Helps the hardenability effect of Ti4dB and is effective in improving the uniformity of material strength, and requires 0.00z% or more, but if it exceeds 0.02%, the toughness deteriorates, so 0.
0.002% to 0.02%.

B: B is effective for hardenability and requires a content of 0.0002% or more, but if it exceeds 0.0025%, it causes deterioration of toughness, so it was set to a ratio of 0.0002 to 0.0025. CO: C
O is effective for delayed fracture resistance, but if it is added in an amount exceeding 3%, the effect will be saturated and it will also be disadvantageous from an economic point of view, so it is set at a factor of 3 or less.

The present invention manufactures oil well steel having predetermined performance by combining chemical components and heat treatment, and the steel constructed based on the above reasons is first heated and quenched to 880 to 980°C.

This temperature range is necessary for sufficient development of austenite grains to obtain a hardened structure from austenite phase to hardened martensite phase, and at the same time to prevent deterioration of delayed fracture resistance due to coarsening of austenite grains. . Next, in the present invention, it is tempered at 650 to 700°C.
This is to prevent the uneven distribution of impurities in the austenite grain boundaries and to uniformly precipitate spheroidal carbides to meet the required strength and improve delayed fracture resistance. It is difficult to ensure delayed erosion resistance only by adjusting the yield strength 1
When trying to secure a material with a strength of 25bi (S7.9ky/0n2) or more, if the temperature exceeds 700°C, the required strength cannot be secured with this component system. Next, the effects of the present invention will be explained using examples.

Example 1 In order to test delayed fracture resistance, a 100k9 steel ingot having the chemical composition shown in Table 1 below was produced by induction welding and forged into a plate shape with a thickness of 60cm at 1250°C (after that,
Hot rolled at an average temperature of 1000℃ to a plate thickness of 12mm.
0 hot-rolled steel plate, quenched and tempered at each temperature shown in Table 1, with a thickness of 2W and ri11011.
A test piece with a DI of 1 and a length of 75 cages was prepared.

Each test piece was polished with No. 320 emery paper, degreased and dried, then bent into a U-shape to make a U-bend test piece.
A 200 hour boiling test was conducted by immersing the sample in a high temperature alkaline solution of 1% NaCl (PH adjusted with NaOH). After the test, each test piece was observed for cracking, and the results are shown in Table 2. Example 2 1.7 m thicker than the steel plate manufactured under the same conditions as Example 1
, a test piece with a width of 4.5 am and a length of 75 m was prepared, and 320
After polishing with emery paper, degreasing and drying, a shell type test was conducted.

That is, 0.5% CH3COO under H2S saturation at 20°C.
After being immersed in an H aqueous solution for 96 hours, bending stress was applied to the test piece using a four-point support type holder. Critical stress for crack initiation [SO
(KsiXlO-4)] was determined. The result is the second
As shown in the table. ○ As is clear from Table 2 showing the results of Examples 1 and 2,
The method of the present invention has extremely excellent delayed fracture resistance in high-temperature alkaline environments and environments containing hydrogen sulfide.

On the other hand, as seen in the results of comparative steel Nos. 6 to 10, even steels with the same composition as the steels subject to the present invention cracked when heat treatment conditions were different. As explained above, by the method of the present invention, it is possible to produce steel that has high strength and excellent delayed fracture resistance in a high-temperature alkaline environment.

Claims (1)

[Claims] 1 C0.27-0.50%, Si0.08-0.30
%, Mn0.90-1.30%, Cr0.5-0.9%
, Ni 0.03% or less, V 0.04-0.11%, Nb
0.01-0.10%, Mo0.60-0.80%, A
l0.1 or less, the balance consists of Fe and unavoidable impurities,
Steel containing impurities of P 0.005% or less and S 0.003% or less is quenched at 880 to 980°C, and then quenched at 650 to 980°C.
A method for producing high-strength oil well steel with excellent delayed fracture resistance, characterized by tempering at 700°C. 2 C0.27-0.50%, Si0.08-0.30
%, Mn0.90-1.30%, Cr0.5-0.9%
, Ni 0.03% or less, V 0.04-0.11%, Nb
0.01-0.10%, Mo0.60-0.80%, A
l0.1% or less, and Ti0.002 to 0.020%,
Consisting of one or both of B0.0002 to 0.0025%, the balance Fe and unavoidable impurities, P0.0 in the impurities
0.05% or less, S0.003% or less steel is 880-9
A method for producing high-strength oil well steel with excellent delayed fracture resistance, which comprises quenching at 80°C and then tempering at 650 to 700°C. 3 C0.27-0.50%, Si0.08-0.30
%, Mn0.90-1.30%, Cr0.5-0.9%
, Ni 0.03% or less, V 0.04-0.11%, Nb
0.01-0.10%, Mo0.60-0.80%, A
L0.1% or less, Co3% or less, the balance consisting of Fe and unavoidable impurities, P0.005% or less in the impurities,
A method for producing high-strength steel for oil wells with excellent delayed fracture resistance, characterized by quenching steel having S0.003% or less at 880-980°C and then tempering at 650-700°C. 4 C0.27-0.50%, Si0.08-0.30
%, Mn0.9-1.30%, Cr0.5-0.9%,
Ni 0.03% or less, V 0.04-0.11%, Nb0
．． 01-0.10%, Mo0.60-0.80%, Al
0.1% or less, and Ti0.002-0.020%, B
Consisting of one or both of 0.0002 to 0.0025%, and 3% or less of Co, residual Fe and unavoidable impurities,
Steel containing impurities of P 0.005% or less and S 0.003% or less is quenched at 880 to 980°C, and then quenched at 650 to 980°C.
A method for producing high-strength oil well steel with excellent delayed fracture resistance, characterized by tempering at 700°C.