JPS58221260A - Steel for steel pipe welded by electric resistance welding - Google Patents

Abstract

PURPOSE:To remarkably improve the resistance of the titled steel to cracking due to hydrogen embrittlement and to blister due to hydrogen, by restricting the amount of Mn in a steel having a specified composition as well as the amount of Ca and REM, restricting the amount of S at the same time, and specifying the quantitative relation among Ca, REM and S. CONSTITUTION:This steel consists of, by weight, 0.05-0.25% C, 0.010-0.50% Si, 0.05-1.15% Mn, 0.01-0.10% Al, <=0.030% P, <=0.0010% S, 0.0005-0.0030% Ca and/or 0.0010-0.010% REM satisfying the equation, and the balance Fe or further contains one or more among <=0.6% Cu, <=0.6% Ni and <=3.0% Cr and/or one or more among <=1.0% Mo, <=0.10% Nb, <=0.15% V and <=0.10% Zr and/or <=0.0050% B or <=0.0050% B and <=0.10% Ti. The steel contains coarse nonmetallic inclusion having <=1 coarse grain of >=50mumphi grain size per 1kg slab, and the steel is rolled with a hot strip mill and coiled.

Description

[Detailed Description of the Invention] This invention improves the resistance to hydrogen-induced cracking and hydrogen blistering of steel for electrical resistance welded steel pipes, particularly steel for line pipes or oil country tubular goods used in humid environments containing hydrogen sulfide. This is an attempt to significantly improve the situation.

In recent years, there have been reports of leakage or breakage accidents caused by hydrogen-induced cracking in line pipes used to transport crude oil and natural gas containing hydrogen sulfide, and the resistance to hydrogen-induced cracking of line pipe steel has become an important issue. Various studies have been conducted and some effective countermeasures have been established.

Recently, however, with the decline in high-quality oil resources, so-called sour gas fields and sour oil fields with high concentrations of hydrogen sulfide have been developed in large numbers, and the operating pressure of lines has often been increased to increase transportation efficiency. Steel materials are now required to be used in harsher environments with lower pH values and higher hydrogen sulfide concentrations than in the past.

The demands are also becoming more demanding.

In other words, conventional hydrogen-induced cracking occurs when hydrogen generated by the corrosion reaction of steel invades the steel, causing non-metallic inclusions in the steel, especially Mn, which tends to cause stress concentration due to the notch effect at the tip of the inclusion.
Anomalous low-temperature transformation structures (hereinafter abbreviated as abnormal structures) such as band-shaped martensite and bainite that accumulate at the interface between A-based inclusions such as S and the base steel and generate cracks, and occur in the segregated area at the center of the plate thickness. ) is known to propagate and expand. Therefore, conventionally, as a measure to improve resistance to hydrogen-induced cracking, sulfide-based inclusions, which are the starting point of cracks, have been treated with Oa.

It was sufficient to make the dispersion spherical by adding REM and at the same time take measures to reduce abnormal tissue.

However, recently required usage environment (pH'4.0
In addition to hydrogen-induced cracking as described above, at hydrogen sulfide concentrations of 2,500 ppm or higher, blisters often occur starting from B-based or C-based inclusions near the steel surface, which penetrate the surface and cause partial damage. In recent years, under high-pressure operation, blistering on the steel surface, which has not been considered a major problem in the past, has been considered to cause a reduction in plate thickness. Hydrogen blisters, which can be seen with the naked eye, are now becoming a major problem.

According to the inventors' research, such hydrogen blisters are caused by large inclusions in the steel, and the results of investigating the relationship between large inclusions in the slab and hydrogen blisters using X-ray transmission method. It was discovered that hydrogen blistering does not occur if the amount of large inclusions of 50 μφ or more in the slab is less than 1 piece per 1 kg of slab (9.5 teeth per piece). In addition, the number of large inclusions of 50 μφ or more in the slab was 9.5 per piece.
In order to reduce the tee to 1 or less, Oa or REM added to control the form of inclusions is o, o o, respectively.
It has been found that it is effective to make the content less than so% and less than 0.01ti%.

In addition, in order to obtain sufficient hydrogen-induced cracking resistance with the addition of such a small amount of Ca or REM, it is necessary to increase the electrical resistance through the rolling history of rolling with a hot strip mill and generally winding as a hot coil. □゛Welding (hereinafter referred to as E)
RW) For #i pipe steel materials, Mnm is 1.15%.
It has also been found that it is necessary to reduce S to 0.0010% or less to suppress the formation of abnormal tissues, and at the same time to reduce S to 0.0010% or less, and to add S to the above-mentioned level. - Based on the above new knowledge, this invention has succeeded in significantly improving the hydrogen-induced cracking resistance and hydrogen blistering resistance of FRWM pipe steel materials rolled by hot strip mills.

During a series of manufacturing experiments on hydrogen-induced cracking-resistant steel, the inventors found that hydrogen blistering sometimes occurred regardless of the hydrogen-induced cracking resistance.As a result of investigating the cause of this, they found that We were able to clarify the relationship between large inclusions inside and hydrogen blisters. This invention is based on such knowledge. 1. Conventionally, there have been many proposals for improving hydrogen-induced cracking resistance, but none have been able to simultaneously improve hydrogen blistering resistance.

Furthermore, according to the inventors' research, there is no clear relationship between hydrogen-induced cracking resistance and hydrogen blistering resistance. It is necessary to reduce the

It is useful to implement.

Also, 1 large inclusion with a diameter of 50 μm or more in the slab/k
In order to reduce g・5tee to 1 or less, it is essential to reduce Oa or REM to 0.0080% or less and 0.010% or less, respectively.
It has been found that in order to obtain sufficient hydrogen-induced cracking resistance with the addition of M, it is necessary to suppress the generation of low-temperature transformation abnormal groups m (hereinafter abbreviated as abnormal structures) generated during the cooling process after rolling.

As a result of researching the causes of the abnormal structure, it was found that the abnormal structure is strongly influenced by the amount of 14n in the leaf material and the cooling rate after rolling. It has become clear that the larger the number of ′ and the faster the cooling rate, the easier it is for abnormal structures to form.

Specifically, the ERW filI pipe steel material that is the object of this invention is rolled by a plate mill and then cooled in the air by submerged arc welding (hereinafter referred to as SAW) in order to be wound up as a pot coil after rolling. It has become clear that the cooling rate after rolling is slower than that of steel pipe materials, which causes the abnormal structure to develop and grow.For this reason, ERW steel pipe materials and SAW steel pipe materials have a lower Mn content (above the limit). In M, abnormal tissue develops and impairs HIC resistance.
It was found that it was necessary to change the management target for inclusion form control (N amount), and that ERW steel pipe material has a higher limit Mn content than SAW steel pipe material, and even milder inclusion form control is sufficient to achieve 1" resistance. It was found that hydrogen-induced cracking resistance (HIC resistance) was obtained.

That is, in the steel material for ERW steel pipes that is rolled by a hot strip mill and wound as a hot coil, the amount of Mn is reduced to 1.15% or less to suppress the formation of abnormal structures, and at the same time, the S content is reduced to 0.0010% or less. Low/S)〉1.0
It was clarified that by adding hydrogen so as to achieve this and controlling the morphology of inclusions, a product with excellent resistance to both hydrogen-induced cracking and hydrogen blistering can be obtained.

In addition, Oa and REM necessary for inclusion morphology control here
Since the S inside forms a 1=1 compound with aa or REM atoms and is spheroidized, the atomic weight must be about 8 times that of Ca in order to form Qa and REM with the same formula. be.

In short, the basic matters of this invention are c:o, o5~
0.25%, 3. i: 0.010-0.50%,
P: 0.03'0% or less, Mn 70.50-1
．． 15%, S: 0.0010% or less, A/
Contains 70.01-0.10% and Oa: 0.
0005~o, 003 o % or REM: 0.
0010 to 0.010%,
Kakeke: A hot coil obtained by rolling a steel slab, which is essentially made of Fe and has a reduced amount of large nonmetallic inclusions of 50μφ or more to 9.5teex or less per unit, using a hot strip mill, is resistant to hydrogen-induced cracking. It has excellent properties of water resistance and hydrogen blistering resistance.
5) It is compatible with steel materials for use, and the above-mentioned steel components include Cu: 0.15 to 0.60%, Ni: 0.10
-0.60%, Or: at least one selected from 0.1-8.0% MOj 0.01-1.0%
, Nb: 0.01-0.10%, V: 0.0
At least one yuzu selected from 1 to 0.15%, Zr: 0.01 to 0.10%, and B: 0.0005
~0.005%, or B: 0.0005~0.0
0.05% and Ti: 0.01 to 0.10% to achieve the effect of their addition, this also satisfies the purpose of the present invention.

The features of this invention are that it suppresses the formation of abnormal tissue by reducing the S content to 4n (low), and further has an extremely low S content (S <0.0010%).
Then, Qa added to obtain hydrogen-induced crackability
Alternatively, by reducing the amount of REM added, large inclusions (50 μmφ or more) in the slab can be completely reduced.
In this way, hydrogen-induced cracking resistance and hydrogen blistering resistance are ensured at the same time. Note that this invention relates to steel materials for ERW steel pipes rolled by a strip mill, and therefore the effects of this invention are as follows: □゛(16) No deterioration due to other alloying elements or heat treatment, etc. It does not have any adverse effect on the mechanical properties and weldability.

Next, the reason for limiting the range of steel components and the reason for limiting the amount of inclusions in this invention will be described. -・o:
o, o a~0.25% If 0 is less than 0.05%, the required strength cannot be obtained, so 0.25%
If it exceeds 0.05 to 0.0.0, the toughness of the weld will be damaged.
It was limited to a range of 25%.

Si: 0. (110~0°50% Sj- is a necessary element for deoxidation, but if it is less than 0.01%, it has no deoxidizing effect, and if it exceeds 0.50%, it deteriorates the toughness of the steel, so 0. limited to the range of 01 to 0.50%,
Ta.

Mn i 0.50-1.15% In is less than 0.50%, which is undesirable in terms of ensuring the required degree, and if it exceeds 1.15%, it is undesirable.
0.50~], 16 because abnormal structures are generated in steel materials rolled by J mill and have a negative effect on hydrogen-induced cracking resistance.
% range.゛2Pa It:
0.01 to 0.10% A/ is necessary for deoxidation,
It is also an element that improves the yield of Oa, but 0°01
It has no effect at the end of 0.10%, and if it exceeds 0.10%, it causes coarsening of crystal grains and deteriorates the quality of the material, which is undesirable, so it was limited to a range of 0.01 to 0.10%.

P: 0.080% or less P is a harmful impurity element, and the smaller the amount, the better, but it was set to 0.080% or less in relation to manufacturing costs.

S: 0.001% When the marginal S content exceeds 0.0010%, in order to obtain sufficient hydrogen-induced cracking resistance, it is necessary not to add Oa and REM in a large amount beyond the limit of this invention. Therefore, sufficient hydrogen blistering resistance cannot be obtained.

For this reason, the S content was limited to 0.0010% or less.

Oa: 0.0005-0.0080% Si 0.0010% is required to ensure hydrogen-induced cracking resistance by adding Oa.
Even in the case of ultra-low S, less than 0.0005%
However, adding more than o, o o %1 may increase large inclusions in the slab and reduce the hydrogen blistering resistance, so it should be added from 0.0005 to o, o o.
It was limited to the range of ao%.

REM 70.0010 to 0.010% REM requires addition of at least 0.0010% even if S is reduced to 0.0010% or less in order to ensure hydrogen-induced cracking resistance, and exceeds 0.010%. 0 because large inclusions in the slab may increase and impair its hydrogen resistance properties.
．． It is limited to a range of 0.0010 to 11.10.010% and is advantageously used as Mitsushi metal.

Note that both Oa and RIICM mentioned above are necessary elements to ensure hydrogen-induced cracking resistance and have the same effect, but in order to obtain sufficient hydrogen-induced cracking resistance 1', S must be added. It is necessary to add it after reducing it to 0.0010% or less. However, it is difficult to stably add Oa and REM, and with the current technology, Oa is 0.0005%.

It is practically difficult to stably add REM below 0.0010%4
1 (19), so the lower limits are 0°0005% and 0.00, respectively.
It was set at 10%.

In addition, the upper limit is the range that does not increase large inclusions in the slab in order to ensure hydrogen blistering resistance.
a is o, o o a o% lieutenant, REM is ・0.0
Limited to 10% or less, Ca is 0.0005 to 00008
0%, and REM was limited to a range of 0.0010 to 0.010%.

Qu: 0.60% or less Ou improves corrosion resistance and hydrogen-induced sidewall resistance 1.
Although it is effective, it is preferably effective at 0.15% or more, but if it exceeds o, e o%, hot workability is impaired, so it is limited to a range of 0.60% or less.

wi: o, a o% or less Ni is effective in improving corrosion resistance and toughness. 1' Also, when containing 0.2 to 0.6% of O as above, to prevent embrittlement due to O. It is preferable to add 0.10% or more of Ni, but adding 0.60% or more of Ni will damage the sulfide stress corrosion cracking resistance.
% or less.

(20) Or: 8.0% or less Qr is effective in improving corrosion resistance, strength, and toughness, but 0.0% or less is effective in improving corrosion resistance, strength, and toughness.
If it exceeds 0.01%, the effect will be diminished, and if it exceeds 8.0%, it will have a negative impact on workability, so it was limited to a range of 3.0% or less.

MO? MO below 1.0% is effective in improving hardenability and strength, but 0.01%
Although the above effects can be summarized, addition of a large amount exceeding 1.0% will actually lead to deterioration of toughness, so the range is set to 1.0% or less.

Nb, V and zr have almost the same effect as MO, but for the same reason as No, Nb is 0.1% or less, and ■ is 0.
The content was limited to 15% or less, and zr was limited to 0.10% or less.

Ti: 0.10% or less Ti is effective in improving strength and corrosion resistance, and when it coexists with B, it has the effect of increasing the effect of B.
It is desirable to use more than 0.01%, but if it exceeds 0.1%, the toughness may deteriorate, so it is limited to less than 0.10%. Pa″B: 0.005%
Below, B is an element that improves hardenability (1,0(10
If it is 5% or more, the effect will be diminished, and if it exceeds 0.005%, the toughness will be impaired, so it was limited to a range of 0.005% or less.

Note that in this invention, there are no conditional expressions regarding Oa, REM, and S. If this value is exceeded, sufficient inner/first water chapter induced cracking resistance cannot be obtained.

In addition, 11 large inclusions of 50μφ or more were found in the slab.
It must be reduced to less than kg・5tee1.

If this is not the case, sufficient hydrogen blistering resistance cannot be obtained.

The inventors changed the Mn level in order to clarify the effects of improving water resistance and blistering properties due to the low range of large inclusions in the slab, and improving hydrogen-induced cracking resistance by adding low Mn, low S, and the addition of Oa and REM4. Types of conventional silver based Oa,
A REM addition experiment was conducted.

All samples were manufactured using the continuous casting method and were Oa.

REM is the continuous addition of granular alloys to tundish.
This was done using the following method.

In addition, as shown in Fig. 1, a test piece for X-ray transmission (5 mm x 80 mm x 2
Ten pieces were cut out (80 pieces) and the amount of large inclusions was investigated using an X-ray transmission method.

Next, the steel slab produced in this manner was rolled using a hot strip mill, and the obtained hot coil plate was used to conduct hydrogen-induced cracking resistance and hydrogen blistering resistance tests.

Table 1) shows the chemical composition of the sample, 2) and mechanical properties, and Table 3) shows the hydrogen-induced cracking resistance and hydrogen blistering resistance test results.

/2.7/ Evaluation of hydrogen-induced cracking resistance and hydrogen blistering resistance was carried out in accordance with the so-called BP test method.

That is, test 1 was mixed with NAOE solution (H, 2S saturated, 0°5%
After being immersed in acetic acid + 5% saline solution (7 pH approx. 8.0) for 96 hours, the blistering on the surface of sample 1 was visually evaluated to determine its water resistance.
The blistering property was evaluated, and the cross section of the sample was examined under a microscope to evaluate the resistance to hydrogen-induced cracking.

A test piece was taken from a position corresponding to the center of the width of the continuously cast slab, which is considered to have the largest segregation, as shown in Figure 2. The test consisted of 8 11 yuzu trees each. 1'□Evaluation of hydrogen-induced cracking resistance was carried out using 8 cross sections for each test piece as shown in Figure 8.
The cross-sections of nine needles of each steel type were examined using a microscope (10x magnification). Hydrogen blistering resistance was evaluated by checking the number of visible hydrogen blisters on the surface of each sample and using the average number of hydrogen blisters per sample. 1' As is clear from Table 1.3, all the steel materials according to the present invention exhibit excellent hydrogen-induced cracking resistance, but steel 5.
Even if the S content is 0.0010% or less, as in No. 14 and 19.24, the amounts of REM and Oa added are small and the blistering property is good, but sufficient hydrogen-induced cracking resistance cannot be obtained.

Also, like steel 7.12 and 18.20, Ca or RE
Those with an excessive amount of M added have good resistance to hydrogen-induced cracking, but do not have sufficient resistance to hydrogen blistering.

However, since the S content is 0.0010% or more, sufficient hydrogen-induced cracking resistance cannot be obtained, and 1il125 and 26 are Mn
If it is 1°15% or more, an abnormal structure develops and sufficient hydrogen-induced cracking resistance cannot be obtained.

From the above results, it is clear that the present invention can provide a steel material for ERW steel pipes that has sufficient hydrogen-induced cracking resistance and hydrogen blistering resistance at the same time. 1 This invention simply
It is thought that it can be applied not only to steel for pipes, but also to steel for pressure vessels, where hydrogen-induced cracking or hydrogen blistering is a problem, and cast and forged materials for petrochemical plants.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the method for collecting X-ray transmission test pieces from steel slabs for investigating inclusions. Figure 2 is a perspective view of the shape and collection method of hydrogen-induced cracking and hydrogen blistering test pieces. Figure 8 is FIG. 2 is an explanatory diagram of a hydrogen-induced crack observation method. Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Claims] LO: 0.05 to 0.255 weight, si: 0.0
10-0.500 weight, Mn: 0.50-1.
15 weight %, Al: 0.01 to 0.100 weight included, P: o, o a o weight % or less, S: 0
．． 0010% by weight or less, and 0.0005 to o, o
o a o weight % Oa, 0. o o ] o ~
o, o Contains at least one type of REM of 10% by weight under the conditions of the following formula, and the remainder has a substantially Fe composition,
It consists of a coil rolled by a hot strip mill of a steel slab in which large nonmetallic inclusions with a diameter of 50 μm or more are present in a volume equivalent to 111 kg of a unit mold, and the coil is rolled by a hot strip mill and has excellent hydrogen-induced 1111 resistance and Steel for electric resistance welded pipes characterized by excellent hydrogen blistering resistance. 11.0:0.05 to 0.25 weight M%, Si
: 0.010"□~0.50% by weight, Mn
: 0.50-1.15 weight 1%, Al: 0
．． 01 to 0.10% by weight, P: o, o a o weight% or less, S: 0゜0010% by weight or less, o,
o o o b ~ 0.0080% by weight (7) Oa, 0
．． 0010 to 0.010% by weight of REM・ under the conditions of the following formula, glaze at least one of 0.6% by weight or less of Cu, Ni and 3.0% by weight or less of Or. Both "□" are contained, and the remainder has a composition of substantially Fe, and among the nonmetallic inclusions, large ones with a diameter of 50 μm or more have a unit weight of 1
Consists of a hot strip mill rolling fill of steel slabs with not more than 1 piece in a volume equivalent to 1c9, and has a hydrogen resistance reading. A steel for electrical resistance welded pipes that is characterized by quick cracking and hydrogen blistering resistance. 8.0: 0.115-0.255 weight, Si: 0
．． 010~0.50% by weight, Mn: o, 50~
1.15% by weight, Al: 0.01-0.10% by weight
Contains P: 'o, o a o weight% or less, S: 0
．． 0010% by weight or less, and 0.0005 to 0.0010% by weight.
0080% by weight Oa, 0. o 010~0.010
At least one type of REM in weight% is mixed with MCI of 1.0% by weight or less and 0.10% by weight under the conditions of the following formula.
It contains at least one of the following Nb, 0.15% by weight or less of V, and 0.10% by weight or less of zr, and the remainder has a composition of 1re substantially, and 50 μm or more of nonmetallic inclusions The large-sized coil is made of a steel slab rolled by a hot strip mill, with not more than one coil in a volume corresponding to 1 kg of unit weight, and has hydrogen resistance induction II.
A steel for electrical resistance welded pipes characterized by excellent resistance to corrosion and hydrogen blistering. 4, 0:0.05-0.25 weight=”, si:
o, o 1° to 0.50% by weight, In: 0.50
~1.151ifi%, A/: 0.01~0.1
Including 0 weight%, P: o, o a o weight% or less, S
: 0.0010% - “□Saishita, 0.00
05~o, o o ao weight M1% (7) Oa, 0.
0010-at least 1 of 0.010% by weight REM
The seeds are mixed with up to 0.0050% by weight of B or 0.00% by weight under the following conditions:
It is contained together with 50% by weight or less of B and 0.10% by weight or less of Ti, and the remainder is substantially composed of Fe, and among the nonmetallic inclusions, large ones with a diameter of 50 μm or more are compatible with the unit weight of 11c9. □"A steel for electric resistance welded steel pipes, consisting of one or less rolled coils of steel slabs in the relevant volume by a hot strip mill, and characterized by excellent resistance to hydrogen-induced cracking and hydrogen blistering. 〇: 0.05-0.25% by weight, Si:
0.010~0.50% by weight, Mn: 0.50~
1.15% by weight, A/: 0001 to 0.10% by weight, P: o, o a o weight% or less, SF 0
．． 0010% by weight or less, and 0.0005 to 0.0
080 wt 1% Oa, 0.0010-0.010 wt% REM. At least one of them is combined with 0.60% by weight or less of O, Ni and
and at least one of Qr of 8.0% by weight or less, Mo of 1.0% by weight or less, Nb of 0.10% by weight or less,
It contains at least one of V of 0.15% by weight or less and Zr of 0.10% by weight or less, with the remainder being substantially Fe, and 50% of the nonmetallic inclusions.
Consists of hot strip mill rolled coils of steel slabs in which there is no more than 1 large piece of μmφ or larger in a volume corresponding to 1 to 9 unit weight, and has excellent hydrogen-induced cracking resistance and hydrogen blistering resistance. A steel for M1 air resistance welded pipes, which is characterized by a temperature of 1°. 60: 0.05-0.25% by weight, si-: o, o
1°~0. bO weight i%, Mn: 0.50-1
．． 15% by weight, A/: 0.01-0.10% by weight
Contains P: o, o a o weight% or less, S F 0.
0010% by weight or less, and from 0.0005 to 0.0010% by weight.
0080 superposition 1% (7) Oa, 0.0010~0.0
At least one type of REM of 10% by weight is mixed with at least one type of Ou, Ni, 0.60% by weight or less, and Or, 8.0% by weight or less, under the conditions of the following formula,
o, o o 5% or less of B or 0.005% by weight
It is contained together with the following B and 0010% or less of Ti, and the remainder has a composition of substantially 1pF8, and among the nonmetallic inclusions, large ones with a diameter of 50 μm or more are in units of 1i1
For electric resistance welded steel pipes, it consists of one or less coils rolled by a hot strip mill of a steel slab in a volume equivalent to 11C9, and is characterized by excellent hydrogen-induced cracking resistance and hydrogen blistering resistance! i#. 7.0: 0.05 to 0.25% by weight, Si: 0.
010~0.50Ti%, In: 0.50~1
．． 15% by weight, A/: 0.01-0.10% by weight
Contains Pi""0.080% by weight Satoshita, S: 0.
0010% by weight 1 or less, and 0.0005 to 0.0
030% by weight l7) Oa, 0.0010-0.010
At least one type of REM with a weight of t1j% is mixed with 1.0% by weight or less of No, 0゜100% by weight or less of Nb, 0゜]5% by weight or less of V, and 0.10% by weight or less under the conditions of the following formula. % or less of Zr and 0.005
0% by weight or less of B1 or ゛・' is contained together with 0.0050% by weight or less of B and 0.1% by weight or less of Ti, and the remainder is substantially composed of Fe, and 50 μmφ of the nonmetallic inclusions. The above-mentioned large-sized coil is made of hot-strip mill rolled coils of steel slabs, with less than one coil per unit weight of 1 kg, and has excellent resistance to hydrogen-induced cracking and blistering. Characteristic electrical resistance, steel for welded steel pipes. 8, (3: 0.05-0.25 weight-%, s
i: o, o 1o"~0.50% by weight, Mn:
0.50-1.15 weight 1%, Al: 0.01
~0.10% by weight i1'%, P: 0.080% by weight or less, S F (1,0010% by weight or less, o,
o o o 5-0.0080% Oa, 0. O
o 10 to 0.010% by weight of REM ・ At least one frame is filled with 0.6% by weight or less of O, Ni, and 3 under the conditions of the following formula.
．． At least one glaze of Qr of 0% by weight or less and Pa□1.
0 wt- or less MOlo, 10 wt% or less Nb, 0.
At least one of ■ below 155 weight and zr below 0.100 weight and B below 0.0050 weight%
, or contains 0.0050% by weight or less of B and 0.10% by weight or less of T11, with the remainder being substantially Fe.
The composition of the Shoken coil is made by hot strip milling of a steel slab, and there is less than one large nonmetallic inclusion with a diameter of 50 μm or more in a volume corresponding to a unit weight of 11c9, and the hydrogen resistance reading □ A steel for electric resistance welded fM pipes characterized by excellent cracking resistance and hydrogen blistering resistance.