JPS6047885B2 - Manufacturing method for line pipe steel with excellent resistance to hydrogen-induced cracking - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing line pipe steel materials having strength levels AP1X-42 to X-80 class and having excellent resistance to hydrogen-induced cracking.

The use of pipelines has become very large-scale in recent years, and in such cases, embrittlement of materials due to corrosion has become a very big problem.

Particularly in oil and natural gas pipelines, crude oil or natural gas often contains hydrogen sulfide, and there is a high probability that water, such as seawater or fresh water, and hydrogen sulfide coexist and contribute to corrosion of the steel surface. In this case, destruction due to penetration of hydrogen into the steel due to corrosion has become a problem. This phenomenon is different from the previously known stress corrosion cracking caused by sulfides, in which cracks occur inside the steel under no stress and are continuous in the thickness direction. This crack has the property of leading to damage to the pipeline, such as oil leakage, if it becomes a through crack in the plate thickness direction, and in the present invention, such cracks are tentatively referred to as ``hydrogen-induced cracks.'' Furthermore, in recent years, in order to supply inexpensive steel materials for line pipes, the frequency of using large-sized requiems with a thickness of 40077Z77I or more has increased significantly.

In such cases, hydrogen-induced cracking may occur along the abnormal structure of martensite or baijite based on microsegregation, and may also be connected to other step-like cracks or affected by minute load stress. There is a high possibility that this will lead to a serious pipeline destruction accident. The present invention has been researched and developed in order to cope with the new environmental embrittlement of materials under such severe environments, and has toughness and conforms to the abnormal structure described above. The purpose of this invention is to provide line pipe materials that are resistant to hydrogen-induced cracking, including cracking, at low cost.

That is, the steel according to the present invention has a carbon content of 0.05 to 0.20%, which is produced by a large-scale steel mill with a thickness of 4007 Kfit or more;
5i<0.5% ■Mn0.9-1.60%; P<0.0
3%■50.002~0.015・%; A1<0.1%
It relates to steel containing the components of AP
0.1% or less NbNV; 1% or less Mo: 0.5% or less Cu, depending on the strength level of 1X42 to X80, etc.
Cr; 0.3 or less Ni; 0.001% or less B; 0.
This invention relates to a material containing 1% or less of Ti; 0.0001 to 0.005% of Ca, singly or in combination.

In addition, the present invention also provides a steel slab having these components (a slab made by blooming the above-mentioned large-sized Chikon in a conventional manner).
It is characterized by applying a long soaking treatment before hot rolling, which homogenizes the micro-segregation during ingot making and converts martensite into martensite by normal hot rolling and cooling. Or prevent the formation of abnormal tissues such as bainite,
This reduces susceptibility to hydrogen-induced cracking. The conditions for this soaking treatment are limited to the soaking temperature and time range shown in Figure 1 of the attached drawings, and point A (
13000C)O, 5hr), B(1250℃, 2,O
hr), C (1200°C, 3 Ohr), D (1150
°C, 5, Ohr), E (11500C) 150hr),
F (1200℃, 65hr), G (1250℃, 25hr
r), H(13000C) 10hr). The reason for this will be explained below. In the present invention, the reason why the slabs made by large-scale refining with a thickness of 4 or more are limited is because the abnormal structure based on micro-segregation is caused by the slow solidification rate during agglomeration, and the large-scale refining with large micro-segregation. Limited to products made from
In addition, eliminating microsegregation by soaking the slab requires soaking at extremely high temperatures and for a long time, which is impractical due to the furnace life and soaking cost. This is because the feature of the manufacturing method according to the present invention, which is a combination, is really needed. The reasons for limiting the components are as follows: If C is 0.20% or more, there will be problems in weldability, manufacturing process, etc., but if it is 0.05% or less, the required strength cannot be obtained. Si is added as a deoxidizing agent, but if it exceeds 0.5%, brittleness increases and the development of abnormal structures is promoted. If Mn is 0.9% or less, strength cannot be obtained, and if it is 1.6% or more, brittleness increases. P is an element related to hydrogen-induced cracking, and the lower the content, the more effective it is in preventing hydrogen-induced cracking. A large steel ingot with a thickness of 40 cy1 m or more containing OOOl ~ 0.005% is bloomed by a normal method, and before the slab is hot rolled, the attached drawing No. 1 is shown.
Points A (1300°C 10.5hr) and B (12
50℃, 2.011r), C (1200℃, 3.0hr
), D (1150℃, 5.0hr), E (1150℃,
150hr), F (1200℃, 6511r), G (1
250℃, 2511r), H (1300℃, 10hr)
1. A method for producing a steel material for a line vibrator having excellent resistance to hydrogen-induced cracking, characterized in that the steel material is soaked at a soaking temperature and soaking time within the range of the shaded area surrounded by and then rolled. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a steel material for line vibrators having a strength level of APIX-42 to X-80 class and having excellent resistance to hydrogen-induced cracking.

In recent years, the use of vibrine has become very large-scale, and in such cases, material embrittlement due to corrosion has become a very big problem.

In particular, oil and natural gas vibrating lines often contain hydrogen sulfide in the crude oil or natural gas, and there is a high probability that water, such as seawater or fresh water, and hydrogen sulfide coexist and contribute to corrosion of the steel surface. In this case, destruction due to penetration of hydrogen into the steel due to corrosion has become a problem. This phenomenon is different from the previously known stress corrosion cracking caused by sulfides, in which cracks occur inside the steel under no stress and are continuous in the thickness direction. This crack has the property of leading to damage to the vibration line, such as oil leakage, if it becomes a through crack in the plate thickness direction, and in the present invention, such a crack is tentatively referred to as "゜Hydrogen-induced crack!'' Furthermore, in recent years, large steel ingots with a thickness of 400 Twt or more have been used very frequently in order to supply inexpensive steel materials for line vibrators.

In such cases, hydrogen-induced cracking may occur along the abnormal structure of martensite or bainite based on microsegregation, and may also be connected to other step-like cracks or affected by minute load stress. There is a high possibility that this will lead to a serious vibration line destruction accident. The present invention has been researched and developed in order to cope with the new environmental embrittlement of materials under such severe environments, and has toughness and conforms to the abnormal structure described above. The purpose of this invention is to provide a line vibrator material that is resistant to hydrogen-induced cracking, including cracking, in an inexpensive manner.

That is, the steel according to the present invention has a CO. O5~0.20%; Si<
0.5%; MnO. 9-1.60%; P<0.03%:
S.O. OO2~0.015%; relates to steel containing 0.1% of A1, and furthermore APIX42
~0.1% or less Nbl depending on the strength level of X8O etc.
; 1% or less MO: 0.5% or less Cu, . Cr;0.
3 or less Ni; 0.001% or less B; 0.1% or less Ti; CaO. This relates to a material containing OOOl to 0.005% either singly or in combination.

In addition, the present invention also provides a steel slab having these components (a slab made by blooming the above-mentioned large steel ingot by a normal method).
It is characterized by subjecting it to a long soaking treatment7 before hot rolling, which homogenizes the micro-segregation during ingot making and converts it into martensite by normal hot rolling and cooling. Or prevent the formation of abnormal tissues such as bainite,
This reduces susceptibility to hydrogen-induced cracking. The conditions for this soaking treatment are limited to the soaking temperature and time range shown in Figure 1 of the attached drawings, and point A (
1300℃, 0.511r), B(1250℃, 2.0
hr), C (1200℃, 3.0hr), D (1150
°C, 5.0hr), E(1150'Cll5Ohr),
F (1200℃, 65hr), G (1250℃, 251
1r), H (1300°C, 10F1r). The reason for this will be explained below. In the present invention, the thickness is 400Tr! The reason for limiting this to slabs made from large steel ingots of Ift or higher is that abnormal structures based on microsegregation occur because the solidification rate during ingot formation is slow and products made from large steel ingots with large microsegregation. In addition, eliminating micro-segregation by soaking the steel ingot requires soaking treatment at extremely high temperatures and for a long time, which is impractical due to the furnace life and soaking cost. This is because the feature of the manufacturing method according to the present invention, which is a combination of and soaking treatment of the slab, is really needed. The reasons for limiting the components are as follows: If C is 0.20% or more, there will be problems in weldability, manufacturing process, etc., but if it is 0.05% or less, the required strength cannot be obtained. Si is added as a deoxidizing agent, but if it exceeds 0.5%, brittleness increases and the development of abnormal structures is promoted. If Mn is 0.9% or less, strength cannot be obtained, and if it is 1.6% or more, brittleness increases.
P is an element related to hydrogen-induced cracking, and the lower the value, the more effective it is in preventing hydrogen-induced cracking, but the upper limit is set to 0.
03%. S has a very sensitive effect on hydrogen-induced cracking, and SO. If Ol exceeds 5%, the cracking susceptibility increases, while if it becomes less than 0.002%, the manufacturing process becomes difficult, and if it exceeds 0.1%, the steel quality deteriorates. CuNcr
are added for strength reasons, but if each exceeds 0.5%, there will be difficulties in manufacturing such as weldability. Ni is added to improve strength, and when Cu is added, it is added to improve hot workability and weldability.
Up to 0.3%, it does not have a significant effect on hydrogen-induced cracking properties. Nb. ．． V,. MO is added to increase strength and toughness, and the upper limit is mainly for economic reasons. B
is added to improve hardenability and is 0.001
% or more, the steel quality deteriorates. Further, Ti is added to make the effect of B addition effective, and if it exceeds 0.1%, it causes embrittlement of the steel. The restrictions on Ca treatment are mainly set from the viewpoint of manufacturing issues and quality stability, and it is very effective in changing the morphology and formation of sulfide inclusions in steel.
A content of 0.0001% or more is very effective in preventing hydrogen-induced cracking, while a content of 0.005% or more does not improve the effect much, but causes great difficulties in manufacturing. As shown in Figure 1 of the drawing, soaking steel slabs for a long time has manufacturing problems, economical reasons such as too long treatment, and has an effect on preventing abnormal structures, and is not effective in improving quality. On the contrary, the range of soaking treatment conditions is limited in view of the quality deterioration of steel for line vibrators, such as coarsening of crystal grains and roughening of the surface of the steel piece. be. The hydrogen-induced cracking resistance of steel materials with the above-mentioned components and subjected to long-time soaking treatment prior to rolling cannot be determined by manufacturing methods such as after rolling or by appropriate quenching, tempering, or normalizing treatment. ) It is a meaningless thing.

Therefore, the steel material for line vibrator of the present invention obtained by rolling after soaking treatment may be used before rolling, or may be used after being subjected to appropriate heat treatment. Next, features of the present invention will be explained according to examples.

Example 1 200 mm was made by blooming and rolling a 25-ton large steel ingot having the components shown in Table 1 below under normal conditions.
77! 77! From various rolled materials manufactured by hot rolling after changing the soaking treatment conditions of large-diameter pipe slabs, the second
A test piece as shown in Fig. 3 was taken and immersed in a solution of artificial seawater or fresh water saturated with H2S for % time without stress loading, and then hydrogen-induced cracking was determined by microscopy of 9 cross sections per steel type. I went. This test method has been tested on several tens of different types of steel, and has been found to be an extremely simple method for distinguishing between breakable materials and hard-to-break materials. The influence of soaking treatment on hydrogen-induced cracking is shown in Table 2 below.
The effect of long-time soaking treatment is obvious, and in contrast to the material that was not heated for a long time in the slab, linear cracks along martensite 7 or bainite occurred, whereas the material that was soaked So, for example, at 13000C, 0. Time: 2 hours at 1250℃; 3 hours at 1200℃
When the temperature is 1150°C, the effect starts to appear after about 5 hours, and the effect on preventing hydrogen-induced cracking is great. Example 2 25 with various intensity levels as shown in Table 3 below
A steel plate was produced in the same manner as in Example 1 by casting into a ton steel ingot, and after pipe-making, specimens were prepared and subjected to a tensile test and a hydrogen-induced cracking test.

As is clear from the results, it can be seen that the material produced by the method of the present invention is very effective in preventing hydrogen-induced cracking.

[Brief explanation of the drawing]

In the accompanying drawings, FIG. 1 shows the range of soaking treatment conditions in the method of the present invention, and FIGS. 2 and 3 are explanatory diagrams showing the method and shape of specimen collection in the present invention.

Claims (1)

[Claims] 1 C0.05-0.02%, Si<0.5%, Mn0
．． 9-1.60%, P<0.03%, S0.002-0
．． A large steel ingot with a thickness of 400 mm or more containing 0.015%, Al<0.1%, and the remainder iron and impurities is bloomed in a conventional manner, and prior to hot rolling the slab, the attached drawing No. 1 Points A (1300℃, 0.5hr), B (
1250℃, 2.0hr), (1200℃) 3.0hr
), D (1150℃, 5.0hr), E (1150℃,
150hr), F (1200℃, 65hr), G (12
50°C, 25hr) and H (1300°C, 10hr), which is characterized by being soaked at a soaking temperature and soaking time within the shaded range and then rolled. Method of manufacturing steel materials for industrial use. 2 C0.05-0.02%, Si<0.5%, Mn0
．． 9-1.60%, P<0.03%, S0.002-0
．． A large steel ingot with a thickness of 400 mm or more containing 0.015% Al, <0.1% Al, the balance consisting of iron and impurities, and 0.0001 to 0.005% Ca is bloomed by a conventional method, and the ingot is Prior to hot rolling the slab, points A (1300°C, 0.5 hr) and B (1
250℃, 2.0hr), C(1200℃, 3.0hr
), D (1150℃, 5.0hr), E (1150℃,
150hr), F (1200℃, 65hr), G (12
50°C, 25hr) and H (1300°C, 10hr), which is characterized by being soaked at a soaking temperature and soaking time within the shaded range and then rolled. Method of manufacturing steel materials for industrial use. 3 C0.05-0.20%, Si<0.5%, Mn0
．． 9-1.60%, P<0.03%, S0.002-0
．． 015%, Al<0.1%, the balance consisting of iron and impurities, V<0.1%, Nb<0.1%, Mo<1
%, Cu<0.5%, Cr<0.5%, Ni<0.3%
, B < 0.001%, Ti < 0.1%, singly or in combination, a large steel ingot with a thickness of 400 mm or more is bloomed in a conventional manner, and the slab is prior to hot rolling. Point A (1300°C, 0.5r) shown in Figure 1 of the attached drawings,
B (1250℃, 2.0hr), C (1200℃, 30
hr), D (1150°C, 5.0hr), E (1150
℃, 150hr), F (1200℃, 65hr), G(
1250℃, 25hr), H (1300℃, 10hr)
1. A method for producing a steel material for line pipes having excellent resistance to hydrogen-induced cracking, the method comprising soaking the steel material at a soaking temperature and soaking time within the range of the shaded area surrounded by and then rolling. 4 C0.05-0.20%, Si<0.5%, Mn0
．． 9-1.60%, P<0.03%, S0.002-0
．． 015%, Al<0.1%, the balance consisting of iron and impurities, V<0.1%, Nb<0.1%, Mo<1
%, Cu<0.5%, Cr<0.5%, Ni<0.3%
, B < 0.001%, Ti < 0.1% singly or in combination, and further containing Ca 0.0001 to 0.005%, a large steel ingot with a thickness of 400 mm or more is bloomed by a normal method. Prior to hot rolling the slab, point A (1300°C, 0.5hr) shown in Figure 1 of the attached drawings,
B (1250°C, 2.0hr), C (1200°C, 3.
0hr), D (1150℃, 5.0hr), E (115
0℃, 150hr), F (1200℃, 65hr), G
(1250℃, 25hr), H (1300℃, 10hr
) A method for producing a line pipe steel material having excellent resistance to hydrogen-induced cracking, characterized in that the steel material is soaked at a soaking temperature and soaking time within the range of the shaded area surrounded by ) and then rolled.