JPS6067618A - Preparation of thick hot rolled high tensile steel plate - Google Patents

Abstract

PURPOSE:To prepare a thick hot rolled high tensile steel plate excellent in hydrogen-induced cracking resistance under an adverse conditions, by hot rolling low C-low P-low S-a treated steel to form a plate material to which heat treatment is, in turn, applied under a specific condition. CONSTITUTION:A steel material, which contains 0.01-0.05% C, Si<0.8%, 0.5- 2.0% Mn, P<0.015%, S<0.003%, 0.01-0.08% sol. Al, 0.0005-0.0040% Ca or, further, at lerast one of Nb<0.10%, V<0.10% and Ti<0.10% or at last one of Mo<0.50%, Cu<0.50% and Cr<0.50% or B<0.0030%, is hot rolled at 1,100 deg.C or less under a processing ratio of 70% or more and hot rolling is finished at Ar3+ 50 deg.C-Ar3-30 deg.C. The obtained plate material is quenched to a temp. region of 650 deg.C-580 deg.C at a cooling speed of 5 deg.C/sec or more and cooled or held in air for 1-20sec as it is and again quenched to a temp. region of 550-200 deg.C at a cooling speed of 30 deg.C/sec or more to be wound in coil form.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing sour-resistant high-toughness hot-rolled high-strength steel, and is particularly suitable for manufacturing transportation pipes or storage tanks for oil and natural gas. The present invention relates to a method for manufacturing a hot-rolled high-strength steel plate having a thickness of about 61111 mm or more.

In recent years, as the production of oil and natural gas has expanded, the production conditions have become increasingly harsh.
Storage and even transportation have started to take place. However, under such harsh sour conditions, the surface of the steel material used is severely corroded, and hydrogen that has entered the steel aggregates around sulfide-based nonmetallic inclusions such as MnS, causing hydrogen-induced cracking. arise.

Therefore, it is desired to develop a steel material that is resistant to hydrogen-induced cracking even under such sour conditions, that is, has excellent sour resistance.

The manufacturing method for hot-rolled high-strength steel sheets suitable for such uses is as follows:
There is a method already disclosed in JP-A-58-1015, but its feature is that after hot rolling ultra-low carbon steel of 0.01%C or less, high temperature of 580 to 700℃ The purpose is to wind it up. This method certainly prevents hydrogen-induced cracking under severe sour conditions as mentioned above.
A high-toughness thick-walled hot-rolled high-strength steel sheet with excellent sour resistance, that is, excellent sour resistance, can be obtained.

However, the above method requires decarburization to an ultra-low carbon range of 0.01%C or less, making the resulting hot-rolled high-strength steel sheets expensive and economically unsuitable for general use. There were problems such as unavailability. Furthermore, since high-temperature winding is performed, crystal grains inevitably increase in I11, and satisfactory mechanical properties are not necessarily obtained.

In view of the state of these prior art, the present inventors have found that even if economical low carbon steel (0.01 to 0.05% C) is used, -1
- As a result of intensive investigation into whether it is possible to obtain thick-walled hot-rolled steel sheets with sour resistance and high tensile strength toughness equivalent to or higher than that of ultra-low carbon steel, we have found that low carbon steel (0.01 to 0.05%
)-Low P-low 5-Ca treated steel, the inventors have discovered that such objects can be achieved by performing controlled rolling, controlled cooling, and cryogenic winding, and have completed the present invention.

That is, the gist of the present invention is, in weight percent, C: 0.01 to 0.05%, St: 0.8% or less, Mn': 0.5 to 2.0%, P: o, oi
s% or less, S: 0.003% or less, sol, AC
! : 0.01-0.08%, Ca: 0.000
5 - A steel having a composition of 0.0040%, the balance Fe and impurities is processed at a processing rate of 70 at 1100°C or less.
% or more, Ar3+50℃ to Ar3-3
Hot rolling was completed at a temperature of 0°C, then rapidly cooled to a temperature range of 650 to 580°C at a cooling rate of 5°C/sec or more, air-cooled or held in this state for 1 to 20 seconds, and then rolled again at 30°C.
This is a method for producing a thick hot-rolled tensile strength steel sheet for sour resistant use, which is characterized in that it is rapidly cooled to a temperature range of 550 to 200°C at a cooling rate of 0°C/sec or more and then coiled.

The 1111 composition mentioned above includes the following group (
At least one additive selected from i) to (iii) may be added.

(i) Nb: 0.10% or less, V: 0.10% or less,
Ti: 0.10% or less, (ii) Mo: 0.50% or less, Cu:
0.50% or less, Ni: 0.50% or less, Cr
: 0.50% or less, and (iii) B: 0
．． 0030% or less, herein the steel composition and hot rolled strip in the present invention.

The reason for limiting the number of cases as mentioned above is as follows. Unless otherwise specified in the text, "%" means "% by weight."

C; C is an element that is extremely effective in strengthening steel by adding it to carbides or carbonitrides, but on the other hand, if it is added in an excessive amount in continuous casting, it can lead to solidification of steel. At times, it promotes center segregation of the CC slab, thereby forming a band-like structure extending in the longitudinal direction at the center of the thickness of the steel material, resulting in a significant deterioration of sour resistance performance. Therefore, in the present invention, C is contained in an amount of 0.01% or more in order to ensure high strength, and on the other hand, C is contained in an amount of 0.05% or less in order to prevent deterioration of strength. .

Si: Si is a preferable element that has deoxidizing and solid solution hardening effects, but if excessively contained, it impairs weldability, so the upper limit of its addition amount is set to 0.8%.

Mn: Mn causes solid solution hardening, fine grain hardening, and even transformation hardening, so it is a preferable element for ensuring toughness. Therefore, in the present invention, 0.5% or more of Mn is contained in order to ensure toughness.
If the content exceeds 2.0%, weldability will be impaired, so the upper limit should be 2.0% or less.

P: When a continuous casting method is adopted, P is a main element that causes center segregation of CC slabs, and in order to obtain the desired sour resistance, it is better to have as little as possible. However.

Therefore, P is preferably 0.010% or less, but from the viewpoint of economic efficiency, the allowable upper limit is set to 0.015%.

S: S becomes MnS in steel, and causes inclusions extending in the rolling direction, deteriorating the open sourability and the energy absorption characteristics at the time of impact. Therefore, the smaller the amount of S, the better. Preferably, it is 0.001% or less, but from the viewpoint of economic efficiency, the allowable upper limit of S is set to 0.003%.

sol, AQ: This is an element necessary for deoxidation. In order to obtain a deoxidizing effect, it is necessary to add at least 0.01%, but 0.01% is required.
If it exceeds 0.08%, the effect is saturated, so in the present invention it is limited to 0.01 to 0.08%.

Ca: Addition of Ca has the effect of converting the A-based inclusions of MnS and the B-based inclusions of A(2203) into C-based inclusions.

As described above, Ca is a preferable element that improves sour resistance and absorbed energy properties, but addition of a large amount lowers the 1Ili order of 1111 and rather deteriorates each of the above properties. Therefore, in the present invention, Ca
is added in an amount ranging from 0.0005 to 0.0040%.

Nl], (2), 1゛1: These elements are added as desired and are effective in increasing strength by forming carbonitrides, but if they are in too much, weldability deteriorates. Therefore, the upper limit of each addition is set at 0.10%.

Mo, Cu: tJi, Cr: These elements are also added as desired and have the same effect as Mn. However, if it is too much, welding performance will deteriorate. Therefore, the limit for each addition is set at 0.50%.

B: B is a desired additive element that improves hardenability to a large extent when added in a small amount. The upper limit of its addition is 0 when the 9JJ fruit is saturated.
, 0030%.

Steel having such a steel composition is then heated to 1100°C or higher.
1. Subjected to hot rolling with a processing rate of 70% or more. Note 1
, i! 11 In the case of continuous casting, the obtained CC slab may be reheated or directly hot rolled. 1100°C
The reason for applying a reduction that results in a processing rate of 70% or more is that even if the reduction amount is smaller than this or the reduction exceeds 70% at a temperature exceeding 1100°C, the austenite grain refinement does not progress much. , sufficient fine-grained ferrite could not be obtained even by controlled cooling in the subsequent process, and good @4J War II
This is because I and toughness cannot be obtained. Add the above here]
The second rate refers to the friction reduction rate of hot rolling margin.

The rolling finishing temperature is set to Ar3+50° to Ar330°C. However, if rolling is finished at a temperature higher than Ar3+50°C, sufficient ferrite transformation nuclei will not be introduced into the austenite, resulting in failure to obtain fine-grained ferrite, resulting in deterioration. This is to do so.

After rolling for 215 minutes, the hot rolled material is rapidly cooled to a temperature range of 650 to 580 °C at a cooling rate of 5 °C / sec or more, and then air cooled in this state for 1 to 20 seconds or held as it is. In this case, if the cooling rate is slower than 5° C./sec, ferrite grains not only become coarse because ferrite 1 transformation occurs at high temperatures, but also tend to form a band-like structure that particularly deteriorates sour resistance. Preferably, the cooling is performed at a rate of 10° C./second or more. Furthermore, if the temperature is higher than 650° C., ferrite 1 transformation also occurs on the high temperature side, resulting in the same shortcomings as described above. On the other hand, is it lower than 580℃? X! When rapidly cooled to the region of t, it is difficult to maintain sufficient pro-eutectoid ferrite i, resulting in significant deterioration of toughness.

In addition, even in the temperature range of 650°C to 580°C, air cooling and holding for less than 1 second are still sufficient to obtain (I) of pro-eutectoid ferrite H1.
゛I [It is difficult to maintain. On the other hand, even if it is held in this temperature range for 11.5 seconds longer than 20 seconds, the pro-eutectoid ferrite fit is almost saturated, and the effect of improving the strength and toughness is small, so air cooling or holding time in this temperature range is The upper limit is 20 seconds. Preferably it is 10 to 20 seconds.

After producing a sufficient amount of pro-eutectoid ferrite H in this way, the cooling rate was again 550 °C/sec or more.
It is rapidly cooled to an extremely low temperature range of ℃ to 200℃ and then rolled up. However, if the cooling rate at this time is closer than 30'c/sec, the untransformed austenite part will not be sufficiently quenched and hardened, making it difficult to obtain high strength. . That is, according to the present invention, by cooling at 30° C./second or more, the untransformed austenite portion is quenched and hardened to obtain a hard phase. Furthermore, if the winding is carried out at a temperature higher than 550°C, not only will the untransformed austenite portion not be sufficiently quenched and hardened, but rather the particles vi! becomes brittle and its sour resistance deteriorates. For this, 550°C preferably 500°
Wind up below C. 20 (If the coiling temperature is lower than 1°C, there will be less slow cooling after winding, and the hard phase will not be tempered, resulting in deterioration of both sour resistance and toughness. Practically, the preferred winding temperature is 300 to 40°C. 'C.

Thus, in this way low C (0,01-0.05%)-
According to the present invention, which is characterized in that low Y)-low 5-Ca treated steel is subjected to controlled rolling, controlled cooling, and cryogenic coiling, the resulting structure is free from only center segregation even by continuous casting. As a result, the sour resistance does not deteriorate and the toughness is significantly improved.1■
A tension 111i plate is obtained. And especially such a lino fruit is stomached by a thick hot-rolled high-tensile steel plate with a thickness of about 6II11 or more! Author:

Next, the present invention will be further explained by examples.

A series of test steels with compositions not shown in Table 1 were melted and a CC slab was obtained by continuous casting. A hot rolled steel plate was prepared according to the method according to the invention. The hot rolling conditions, cooling conditions and winding conditions at this time are summarized in Table 2.

The rolling start temperature was about 1150° C. when hot rolling was performed directly without adding 11f.

Table 2 also summarizes the results of mechanical tensile tests and sour cracking resistance tests conducted on test pieces from each of the hot-rolled steel sheets. The mechanical tensile test used a JIS No. 5 tensile test piece, and the Charpy FFI Y test (31J
The test was conducted using an IS'4 Charpy test piece.

In addition, the sour cracking resistance test was conducted at 0.5 in an autoclave.
%Ctl 3 C00II - H2 in 5% NaCl aqueous solution
Each test J11 was immersed for 96 hours in a test solution in which S gas was saturated and dissolved to give a pl+ of 3.5, and the occurrence of cracks at that time was observed. The results are shown as cracking rate (C%) under NACE conditions.

As is clear from the results shown in Table 2, all of the products obtained according to the present invention have excellent toughness and sour resistance.

On the other hand, the comparative examples have poor toughness or sour resistance. In particular, test number 12 had 110 (vTrs was poor due to insufficient pressure reduction below 1°C, R+
I: Piece number 13 has a low hot rolling finish temperature, so
Aspect 1 - Rewards are poor. Also, test number 14.1
Test No. 6 had insufficient cooling rate and low strength, and Test No. 14 in particular had poor sour resistance. Test No. 15 did not show that the air cooling (AC) temperature was too high, but the νTrs was poor and the sour resistance was insufficient.

Note that test number 17 shows an example in which the winding temperature was too low, and the vTrs was poor and the sour resistance was also poor.

Test numbers 18 to 25 all indicate cases where the steel composition is outside the scope of the present invention, and except for test numbers 18 and 21, which have low strength, all cases are 11i.
(The sourness is not sufficient.

Practical Example 1 In the present invention, Example 1 was repeated to evaluate how each characteristic is affected by the winding temperature, but in this example, after heating to 1180°C, the rolling The amount was set at 75%, and the hot rolling finishing temperature was set at 780°C.

After hot rolling, it is cooled to 600°C at a cooling rate of 20°C/second, air cooled for 15 seconds from that temperature, and then heated to 50°C.
It was cooled to each coiling temperature at a cooling rate of /sec. However, if the coiling temperature is 600°C, after the hot rolling
(Cooled at a cooling rate of 5°C/sec to a coiling temperature of 1'C.

A mechanical tensile test, a Charpy impact test, and a sour cracking resistance test were conducted on test pieces from each of the obtained hot rolled steel sheets, and the obtained results are summarized in a graph regarding the coiling temperature and are shown in the attached drawings. The procedures for each test were the same as those in Example 1.

As is clear from the results shown, the winding temperature is 550°.
C or lower, preferably 500 to 200°C, and even 300°C
At ~400°C, excellent results were obtained for all properties. I can see that you're getting jilted.

3rd Table Dan β” 1 red plate 0.020.1
3 1,520.0080.0010.0250.00
25 770

[Brief explanation of the drawing]

The attached drawings show each 11N11 of hot rolled steel sheet with respect to the coiling temperature.
1 is a graph summarizing changes in 1. Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Akira Hirose - Go Enshiro 2oo θθ Cθθ /θθ 3θo faθ ;i! -Torion Iwao (・C)

Claims (2)

[Claims] (1) In weight%, C: O, OL ~ 0.05%, Si: 0.8% or less, M
n: 0.5-2.0%, P: 0.015% or less, S: 0.003% or less, sol, AQ: 0
．． 01-0.08%, Ca: 0.0005-0.0
040%, with the balance consisting of Fe and impurities at a working rate of 70% at 1100°C or less.
% or more, rolled between j'L and Ar3 + 50℃ to A
Finish hot rolling at a temperature of r3-30℃, then 5℃/
Rapidly cool to a temperature range of 650 to 580°C at a cooling rate of 2 seconds or more, air cool or hold for 1 to 20 seconds, and then rapidly cool again to a temperature range of 550 to 200°C at a cooling rate of 30°C/second or more. A manufacturing method for sour-resistant thick-walled hot-rolled high-tension & 171 handling characterized by winding. (2) In weight%, C: 0.01-0.05%, Si: 0.8% or less, Mn: 0.5-2.0%, P: 0.015
% or less, S: 0.003% or less, sol, AC!
: 0.01-0.08%, Ca: 0.0005
~0.0040%, and at least one of Nb, ■, and Ti, each at 0.10% or less, and/or MOLCu, Ni, and Cr, each at 0.50% or less
and/or B: 0.0030% or less, the balance consisting of Fe and impurities at a working rate of 7 at 1100°C or less
Hot rolled at 0% or more, Ar3+5Q℃ or ^r33
Hot rolling was completed at a temperature of 0°C, then rapidly cooled to a temperature range of 650 to 580'c at a cooling rate of 5°C/sec or more, air cooled or held for 1 to 20 seconds, and then rolled again for 3
550-200℃ at a cooling rate of 0°c/Ll> or more
Rapidly cool down to a temperature range of . A method for producing a thick-walled, hot-rolled high-tensile strength steel plate for sour resistant use, which is characterized by winding the steel plate.