JPS581014A - Production of hot coil having high hydrogen induced cracking resistance - Google Patents

Abstract

PURPOSE:To produce a hot coil having high hydrogen induced cracking resistance by reducing the content of S in steel, adding Ca, finish rolling the steel and coiling the rolled steel plate in the stage of producing said hot coil. CONSTITUTION:In the steel material contg. 0.05-0.20% C, <0.5% Si, 0.5-1.0% Mn, <0.02% P, <0.002% S, <0.10% Nb, <0.1% Al, 0.001-0.006% Ca and further 1 or >2 kinds of 0.2-0.6% Cu, <0.2% Ni, <0.5% Mo, <0.5% Cr, and <0.1% V, the content of S is minimized, and a small amt. of Ca is added to control the shape of harmful non-metallic inclusions such as MnS. Such steel ingot is finish rolled in >=850 deg.C austenite recrystallization temp. region, and the rolled steel plate is coiled at >=650 deg.C or after it is finish-rolled in unrecrystallization gamma region, at 750-850 deg.C, it is coiled at 600 deg.C.

Description

[Detailed Description of the Invention] A hot coil material for electric resistance welded pipes, which has excellent resistance to hydrogen-induced cracking, and is used to form pipes for transporting oil, natural gas, etc., or storage tanks thereof, etc. The purpose of this invention is to provide an advantageous method for producing hot coil material suitable as a material for.

In recent years, with the increase in oil consumption, many plans have been made to develop oil fields and lay pipelines. Under the coexistence of hydrogen sulfide and water, the steel surface is severely corroded. In other words, hydrogen generated by corrosion under the conditions described in -F penetrates into the steel and aggregates around the elongated sulfide inclusions such as Mn8, increasing the internal pressure. Hydrogen-induced cracking occurs, and in some cases, it penetrates through the thickness direction and destroys the steel material. Conventionally, as a means to prevent hydrogen from entering steel in such a wet hydrogen sulfide corrosive environment, hydrogen induction is achieved by adding Co of 0.251 or more to steel K to form a retentive film with high corrosion resistance and hydrogen permeation resistance. This prevents cracks from occurring. However, the central segregation part of a practical steel ingot is S, C
, Mn, and other impurity elements or elements that increase susceptibility to hydrogen-induced cracking are concentrated, so it is difficult to completely prevent cracking with this Co addition treatment alone.
Even with u-added steel, the environmental conditions in which it is used are severe, for example, if the acidity of coexisting moisture is pli 4.6 or less, the above-mentioned corrosion-resistant film will not be formed, so there is a high possibility that hydrogen-induced cracking will occur frequently. For this reason, the steel used in such a severe corrosive environment must have a lower S content to reduce sulfide-based inclusions, which are the starting point for hydrogen-induced cracking, or a C1
It is necessary to control the shape of these nonmetallic inclusions by adding metals and rare earth elements to reduce the susceptibility to hydrogen-induced cracking. However, it is difficult to reduce the S content of the entire steel ingot at a uniform level, and it is also extremely difficult to effectively control the morphology of nonmetallic inclusions throughout the entire steel ingot. It is well known that inclusions of Ca and rare earth elements tend to accumulate particularly in the steel ingot precipitate part, which actually increases the cracking susceptibility.

On the other hand, the susceptibility to hydrogen-induced cracking in hot coil material is greater than that in plate material, and the cracks tend to connect in a step-like manner, so the risk of penetration in the thickness direction is extremely high.

Hot on the lid: To explain the susceptibility to hydrogen-induced cracking in coil material and plate material, hot coil material is strongly rolled down in one direction without the process of rolling in the width direction like in plate material, so the Mn8 is higher than in plate material. Since it has been significantly elongated, its cracking susceptibility increases accordingly. Also, since the plate thickness is generally thinner than hot coil material + S plate material, even if the inclusion content is the same, the hot coil material's direct force will be equivalent to 1 more per unit cross-sectional area in the thickness direction. There is also a greater risk that hydrogen-induced cracks that occur as cracks parallel to the plate thickness will connect in a step-like manner and develop into cracks that penetrate through the plate thickness. Furthermore, as mentioned above, the hot coil is rolled into a thin wall under conditions of strong reduction in one direction, so the rolling length is considerable, and the same
Even within a steel plate, the rolling conditions may vary considerably between the initial stage of production and the vicinity of the final stage, and hot coil manufacturing requires a unique process of rapid cooling with water on a run-out table followed by (coiling 1). The first point is that a wide range of materials can be obtained by controlling the rolling conditions such as warm finishing and winding temperature, or there are variations in rolling conditions within the same coil. and,
Regardless of whether this variation is unavoidable or intentional, there is a high degree of cracking susceptibility (a risk that the bainite structure is formed in a band shape and the hydrogen-induced cracking resistance is significantly deteriorated).

The present invention was created after repeated studies in view of the above-mentioned circumstances. In other words, the present invention has been studied from both the steel composition and the rolling method, and has been developed to withstand use under the harsh corrosive environment conditions mentioned above, and has excellent hydrogen resistance against changes in the rolling properties. API standards X42 to x6 indicating induced cracking characteristics
We succeeded in obtaining a hot coil material with a degree of s equivalent to s.

To further explain the present invention, the causes of hydrogen-induced cracking in hot coil materials generally include base metal elements, non-metallic inclusions (MnS inclusions stretched to 100%), and rolling conditions during hot coil manufacturing. Although there are changes in the microscopic structure due to fluctuations, in the present invention, the S content of steel is particularly reduced to 0.00.
By adding CAFT, the above-mentioned non-metallic inclusions are controlled, and the hydrogen-induced cracking resistance is improved. Moreover, by appropriately selecting the Mn content of the steel and rolling conditions, the microscopic structure can be controlled. By wholesale, the above-mentioned extremely low S and C&
It was confirmed that the effect of the addition was more pronounced and the hydrogen-induced cracking resistance could be significantly improved. In particular, variations in hot rolling conditions during hot coil manufacturing are sensitive to hydrogen-induced cracking, and as will be clarified in the examples described later, the greater the temperature difference between finish rolling and winding, the more susceptible to cracking. increases. However, by reconsidering the respective finish rolling temperatures, rolling at a certain temperature or higher results in a more favorable improvement in hydrogen-induced cracking resistance. The winding temperature is 65
By setting the rolling temperature to 0°C or higher and setting the winding temperature to 600°C or higher when finish rolling is completed in the non-recrystallized r region of 750'C or higher, excellent hydrogen-induced cracking resistance is exhibited. I found it.

That is, the one according to the present invention has c:o, os ~ 0.20%,
83: 0.5'i or less, Mn: 0.5-1. OS
, P: 0.02 or less, S: 0,0021 or less,
Nb: 0.10% or less, At: 0°1% or less, C
Cu: 0.20-0.60%, Ni:
0.20% or less, Mo: 0.50'4 or less, Cr
: 0.50% or less, V: 0.11 or less, and the temperature at which the hydrogen-induced cracking resistance of a pair of shoes is improved under the finishing temperature conditions of hot rolling. The above is the rolling process. Specifically, when finishing rolling is performed in the austenite recrystallization temperature range of 850°C or higher, the rolling temperature is set to 650°C or higher, and the finishing temperature is set to 750°C.
In the case of the unrecrystallized r region below 850°C, the winding temperature I# is 600°C.

The reason for the limited range of steel components in the present invention is as follows.

When C exceeds 0.20%, toughness and weldability KJI point occurs, and in large steel ingots and continuous cast materials, it is not preferable to prevent abnormal structures (martensite and bainite) from forming in the central segregation zone. However, if it is less than 0.05 mo, the required strength may not be obtained.

Si is added as a deoxidizing agent, but if it exceeds 0.504, the toughness deteriorates, so this is set as the upper limit.

Mu is also added as a deoxidizing agent and contributes to increasing toughness, but if it is less than 0.54, sufficient toughness cannot be achieved, and the abnormal structure in large steel ingots and continuous cast materials is caused by the combination of MI& and P. This is due to dense segregation, and addition of 1.04 or more promotes the development of this central abnormal structure that is harmful to hydrogen-induced cracking.

P is a harmful element that worsens tempering brittleness, and i1
As shown in R, it promotes the development of abnormal structures in the central part and significantly deteriorates the hydrogen-induced cracking resistance, so it is necessary to reduce its content, but there are constraints in steel manufacturing, so the upper limit cannot be set. 0.020 vomit.

As its content increases, S promotes the occurrence of hydrogen-induced cracking, and in large steel ingots and continuous cast materials, it also becomes the starting point of hydrogen-induced cracking in the irregular structure in the center. Note that reducing the S content to 0.005 # will further ensure the prevention of hydrogen-induced cracking, but hot coil materials are manufactured using a unique piezo resistance method and are therefore more susceptible to cracking. (Even if Ca is added, it is difficult to completely prevent cracking. Therefore, the upper limit of this S temperature is set to 0.0
02% Addition of NKCs made prevention of hydrogen-induced cracking more reliable than K.

At is necessary as a deoxidizing agent and is an effective element for refining the microscopic structure, but if it is contained in an amount of 0.1016 or more, it is undesirable because it causes deterioration in toughness and increases in nonmetallic inclusions. This was set as the upper limit.

Nb is an element that contributes to grain refinement and improvement of the strength and toughness of steel, but even if it is added in an amount of 0.1011 or more, its effect will be saturated and it is economically disadvantageous.
This is the upper limit.

Ca is added for the purpose of effectively controlling the morphology and composition of sulfide inclusions in steel, and for this purpose, an amount of 0.001 mm or more is required, but adding 0.006 mm or more increases the The effect is saturated and clusters of C4 inclusions are formed, increasing cracking susceptibility, so this is set as the upper limit.

The optional elements 011%N1, Mo%Or, and V are added as necessary to further improve the properties of the manufactured steel, and these elements improve hydrogen-induced cracking resistance,
They contribute to improving strength and toughness, and can be contained alone or in combination of two or more within an appropriate range, taking into consideration various properties required for steel, usage environmental conditions, etc. That is, as follows.

Cu is an element that is effective in improving strength and preventing hydrogen-induced cracking, but the effect is weak when added below 0.20% (,
On the other hand, if it is 0.6011 or more, weldability and hot workability are adversely affected.

Cr is an element that is effective in improving strength, but even if it is added in an amount of 0.50 or more, the effect is small and it is economically disadvantageous, so this is set as the upper limit.

Ni is an element that improves the strength and toughness of steel, but on the other hand, it is also an element that promotes the occurrence of water: It is preferable to keep the upper limit to 0.20%.

Mo%V is added for the purpose of obtaining the strength level required for -, but %MO is O, S, and even if V is added in excess of 0.1%, the effect is saturated, It is also economically disadvantageous.

Next, to explain the rolling conditions in the present invention, the final finishing temperature is 750°C or higher, specifically 850°C or higher.
There are cases where the temperature is 1: or higher and cases where the temperature is 750 to 850°C. In other words, if this final finish of 111 degrees becomes less than 750 degrees Celsius, rolling will occur in the ferrite-austenite two-phase region, and even in the hot coil state, the ferrite still retains considerable strain from rolling, making it resistant to hydrogen-induced cracking. This results in deterioration of the characteristics. The specific finishing temperatures of 850°C or higher and the range of 750 to 850°C are related to the following winding temperature. Winding temperature 6
As mentioned above, the winding temperature is set at 50°C or higher, and when finish rolling is completed in the non-recrystallized r region of 750 to 850°C, the winding temperature is set at 600°C or higher. That is, even when a steel that satisfies the steel composition conditions of the present invention as described above is used, it is rolled according to a conventional method, and the winding temperature is lower than that which does not satisfy the conditions in relation to the joint finish temperature. In some cases, sufficient hydrogen-induced cracking resistance is not obtained, and some cracking is observed at least in test results using H, S-saturated 0.5 euacetic acid + 5% saline. On the other hand, by setting the winding temperature to 650°C or higher or 600°C or higher in consideration of the strict finishing temperature as mentioned above, excellent hydrogen-induced cracking resistance is exhibited, and cracking does not occur under any of the test conditions. Or none at all. In other words, these relationships are as shown in Figures 1 and 2, and the steel having the chemical composition referred to in the present invention is finished rolled at a relatively high temperature of 850°C and then rolled at 700°C. (4), 65 in Figure 1
The one rolled up at 0℃ or the one rolled up at 550℃ has a microscope set m (200x magnification) as shown in the same figure (C). +5 Under no stress load in a corrosive environment in which a saline solution is saturated with hydrogen sulfide, 9
The state of hydrogen-induced cracking on the edge after 6 hours of immersion is shown in (4) above.
For TeG'l (A'), (Bl Ha(B')
% (C) and (C') are shown in Fig. 1, and % (A') and (B') cannot be found to have induced cracking at all, but (C') In some cases, multiple induced cracks with a length of -3 have occurred. Also, the finishing temperature is 750℃ as shown in Figure 2.The winding temperature is 650℃ (4) in the same figure, 600℃ is in the same figure (C).
), or the hydrogen-induced cracking conditions for these materials under the same test conditions as in Figure 1 are (
A' ) and (B) are shown as (B'), and (C) and K are shown as (C'), respectively, and 600
The samples (A') and (B') that were rolled up at temperatures above ℃ showed no induced cracks, whereas the samples (σ) that were rolled up at temperatures below 600 degrees Celsius still showed multiple induced cracks with a length of several ■. is occurring.

The following is a description of specific embodiments of the present invention.

First, the steels within the composition limit range of the present invention specifically adopted by the present inventors and the test steels as comparative steels are as shown in Table 1 below, and A-D are the comparative steels. Steel, E to H are steels in the present invention, E and J are those with basic components, F is one containing Mo, Cr, and V,
G is C-containing Ni, H is Cu.

It contains fCCr%V together with Ni.

Each of the above-mentioned steel slabs was heated to 1150-1250°C, and then rolled into a hot coil with a final plate thickness of 9.3cm, and the final rolling temperature in the hot strip mill was set at 750°C-1250°C. The temperature range was 850 DEG C., and the subsequent winding temperature f was varied within the range of 550 DEG to 700 DEG C., depending on the present invention and conventional methods.

In addition, hydrogen-induced cracking tests were conducted on such hot coil materials or ERW pipes made using the hot coil materials in a corrosive environment in which artificial seawater and 0.5 ml of acetic acid + 5 ml of saline solution were saturated with hydrogen sulfide. Ta. For this hydrogen-induced cracking test, the test piece shape was ioo ■t x 20■W x 7.5
After being immersed in the above corrosive environment for 96 hours with no stress applied, nine cross-sections were examined per steel type, and hydrogen-induced cracking was successfully detected.

That is, the rolling conditions and test results as described above are summarized as shown in Table 2 below for the comparison steel, and Table 3 for the steel produced by the method of the present invention.

@2 Table 3 In other words, cracking susceptibility is greatly influenced by the rolling conditions during hot coil manufacturing, and the lower the finishing rolling temperature and the larger the temperature difference from the subsequent winding temperature, the higher the cracking susceptibility, which has been known in history. In the case of a low temperature of 600° C. or lower, the cracking susceptibility increases and hydrogen-induced cracking occurs frequently.

However, by suppressing the amount of Mn and S and adding Nb and C, the steel with the composition range according to the present invention has excellent hydrogen-induced cracking resistance in conjunction with the rolling conditions during hot coil manufacturing as described above. and the acidity of the corrosive environment is pu < 4.
Even in the severe case of No. 6, no hydrogen-induced cracking occurs.

On the other hand, hot coil materials of steel that do not satisfy even one of the component ranges according to the present invention or electric resistance welded pipes made of the same are manufactured using artificial seawater saturated with hydrogen sulfide (pH: 5.
2) Among them, A, depending on the hot coil rolling conditions.
As in the case of steel B, hydrogen-induced cracking occurs frequently, and in a hydrogen sulfide-saturated 0.51 vinegar + 51i salt aqueous solution (3.8 in pil), which is even more corrosive, it is assumed that cracking does not occur according to the rolling conditions according to the present invention. cannot be prevented.

Historically, Cu-added steel exhibits excellent hydrogen-induced cracking resistance in H and S-saturated artificial seawater, or it has poor hydrogen resistance because a protective film due to Cu addition is not formed in the thigh corrosion environment described in Section 4.6 above. In some cases, the induced cracking resistance may be significantly deteriorated, and prevention of the formation of abnormal structures in the center and control of the shape of sulfide-based inclusions are essential conditions, especially in large steel ingots and continuous cast materials.

According to the present invention as explained below, a hot coil material with significantly improved hydrogen-induced cracking resistance can be appropriately manufactured, and it can be used as a line piezo material for transportation of petroleum and natural gas where HtS and water coexist. The present invention is also industrially highly effective since it can advantageously provide a hot-rolled material suitable for use as a storage tank material.

[Brief explanation of drawings]

The drawings show the technical content of the present invention, and Figure 1 shows a sample finished rolled at 850°C and rolled at 700°C (4
), photographs showing the microscopic structures of the coiled at 650°C (B) and the coiled at 550°C (C) at a magnification of 200x, and the hydrogen-induced cracking test results of these coil materials. An enlarged cross-sectional view with a magnification of 5 times showing the state of cracking (A (B))
Figure 2 shows the final pressure treated at 750°C and rolled up at 650°C (A), the rolled up at 600°C (B) and 55°C.
Photographs showing the microscopic structure of C) rolled at 0°C at 200x magnification, and cross-sectional enlargement at 5x magnification showing the state of hydrogen-induced cracking as a result of a hydrogen-induced cracking test on these hot coil materials. Figure (A') (B') (σ)
It is. Patent applicant Nippon Kokan Co., Ltd. Inventor Yutaka Inagaki Wama
Toshio Nakazawa #Mih Agent Patent Attorney Shirakawa --t・4j1+Chief of the Japan Patent Office Shima 1) Haruki Tono1. Display of the case ゛Showa origin f1゜, Application number q♂dog〃ッ3, Person making the amendment Name of the patent applicant related to the case (Mr. Button Nippon Steel Tube Co., Ltd. 4, Agent Showa Jie/July 2 (right) 1st Dispatch 6, Introducing the subject of the amendment Special i second...1 Lambda letter 7, Contents of the amendment As shown in the attached sheet, Contents of the amendment, Otsu main application number 1, line 14, line 13 and line 14, respectively. ``r(A)J'' and ``r(D)'' respectively.
Correct □ 2. Lines 13 and 14 of the same page are correct Ar(B).”
Correct each to r (E) J. 5 Lines 13 and 16 of the same page - Correct “(C)” to 7″Lr (F)J respectively ◇ 6 Lines 2 and 4 of page 15 of the same page: This is J. Correct ``(A)'' to t-Lr (D)J. In the third and fifth lines of the same page, correct r(BiJ to nr CE)j. Correct that as Ar'(F)J 02 same No. 22
There are 14 lines from the 6th line of the page and the 13th line of the same page, respectively.
r (J)) l) (F) Correct 0 to J and correct the attached drawings Figures 1 and 2 from the beginning of this application, respectively, as indicated in red in the attached sheet 0

Claims (4)

[Claims] (1) C: 0.05-0.204.81:0.5
1 or less, Mn: 0.5-1.0m, P: 0,0211
Below, 82, (k, OG2+1) or below, Nb: 0.
101G or less, Mut: 0.1% or less, Ca: 0.001
-0.006*, with the balance consisting of iron and unavoidable impurities, is hot-rolled and rolled at a certain temperature or higher under the finish rolling temperature condition, and has excellent hydrogen-induced cracking resistance. A method for manufacturing hot coils. (2) Co: 0.2-0.6”ll, Nl:
0.2 or less, Mo: 0.5 tatami or less, Cr: 0.5
96 or less, v: o, i's or less, the method for producing a hot coil with excellent hydrogen-induced cracking resistance according to claim 1, using steel containing one or more of the following: . (3) Production of a hot coil with excellent hydrogen-induced cracking resistance according to claim 1 or 2, wherein the finish rolling temperature is 850°C or higher and the winding temperature is 650°C or higher. Method. (4) Claim 1 in which the finish rolling temperature is 730 or more and less than 850°C, and the winding temperature is 600°C or more.
A method for producing a hot coil with excellent hydrogen-induced cracking resistance as described in item 1 or 2.