JPS58147545A - Manufacture of martensitic stainless steel with superior resistance to stress corrosion cracking due to hydrogen sulfide - Google Patents

Abstract

PURPOSE:To obtain the titled stainless steel without deteriorating characteristics peculiar to a martensitic stainless steel by restricting the Ni and C+Ni contents of the martensitic stainless steel having a specified composition and by providing a specified structure. CONSTITUTION:This martensitic stainless steel consists of <=0.25% C, <=1.00% Si, <=1.00% Mn, <=0.040% P, <=0.030% S, 11.50-14.00% Cr, 0.05-0.5% Ni and the balance Fe with inevitable impurities while satisfying C(%)+Ni(%)/30>=0.15% and has a mixed structure composed of tempered martensite, unsolubilized carbide and carbide precipitated during tempering. A steel having said composition is heated to a region where austenite coexists with undissolved carbide, and the heated steel is hardened at a cooling rate above the air cooling rate and tempered to obtain the desired martensitic stainless steel.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing martensitic stainless steel that has excellent resistance to stress corrosion cracking caused by sulfide water volume.

Conventionally, 111K steel and low-pitched gilt copper have been used as O steel for natural gas development, but in recent years, O steel has been actively developed for natural gas containing a large amount of vertical gas. This rounded stainless steel 01 has excellent corrosion resistance as this type of O-steel pipe for natural gas, which is hard to compare with the fI14ii mentioned above which has sufficient corrosion resistance. The use of %
M1B1 41G and 42G are representative stainless steels that provide 1 strength and are economical. 8~! Martensitic stainless steel is attracting attention. It has good corrosion resistance against vertical acid gas contained in this stainless steel work gas and stress corrosion cracking caused by chlorination caused by seawater, and has a yield point of SO~7011d/-I of 4 degrees due to Sika 4 heat treatment INK. It has nine excellent properties:

However, this martensitic stainless steel is sensitive to stress corrosion cracking due to the bulk of water sulfide, which is often enriched in natural gas, and despite its excellent f# characteristics mentioned above, it cannot be used in W gas rich in hydrogen sulfide. It also has the disadvantage that it is almost unusable, and this point becomes a big problem when it comes to the axial circumference as a material for natural gas steel pipes.

As a result of careful consideration and consideration, the above-mentioned martensitic stainless copper was used as the basic component, and Ni
However, by adding a limited heat treatment for 4 hours to this, the martensitic stainless copper has corrosion resistance against vertical acid gas and resistance to stress corrosion cracking caused by chloride. Yield point 50-70-f
This product successfully improved the resistance to stress corrosion cracking caused by hydrogen sulfide without sacrificing the characteristics of ♂.

The above-described martensitic stainless steel of 1~10R is crimped in 9 areas of complete austenite single phase, made into martensitic fiber paper by air cooling, and has a yield point of SO~
70*f/wm", but in reality, the metal structure during solution treatment is affected by temperature, and the austenite-undissolved carbide family is austenite-unseaside-ferrite. The present inventors investigated the relationship between the metal weave due to the solution temperature such as ζO and the stress corrosion cracking resistance due to hydrogen sulfide, but the conclusion was that it was O. In this case, the heterogeneity of the metallographic structure is favorable, and the susceptibility to stress corrosion cracking increases.
4IlII14 It is known that the undissolved carbides that are uniformly dispersed and converted into a solution greatly contribute to the formation of metal composite fibers 4DJI and 4JI resistant to corrosion cracking caused by hydrogen sulfide.
Shi9. It has been found that if the aging treatment temperature is set to the coexistence region of austenite and undecomposed material, a metal structure with high resistance to stress corrosion cracking caused by hydrogen sulfide can be obtained. be. However, as mentioned above, M1B1
In the component system represented by 41m) and 41O, it is possible to obtain such composite fibers in a beautiful manner, due to the state-of-the-art austenite-undissolved carbide coexistence region in the bulk yarns. What is the metal structure? II! In some cases, it is extremely unstable;
The distribution of undissolved carbides is uneven, and ferrite formation occurs in areas with uneven composition. Based on these facts, we have further investigated whether N1, which is known as an element that stabilizes austenite, is particularly effective as a factor controlling the metal structure of martensitic stainless steel. The addition of an appropriate amount of N1 to the alloy is effective in softening the metal structure in the austenite-non-IM carbide coexistence region and obtaining an optimal metal structure that is resistant to stress corrosion cracking caused by hydrogen sulfide. This is what we have learned. For these reasons, the present invention basically involves adding a component system of martensitic stainless steel represented by Mu III 41G and 420, and sometimes adding an appropriate amount of N.
1ta was added, and the solution treatment was set at 11 degrees in the above-mentioned austenite-non-11% eufined region to perform nine-heat treatment.

The present invention is based on the compositional system of martensitic stainless copper represented by MU 1111410 and 4-layer O as mentioned above, and the compositional system wholesale c: o, zs * below,
81:1. OQ sound or less, Mn: 1.00 sound or less, P
: 0.0404 or less, 8:0J30 or less, Cr:
KC (I
G)+Ni m/30≧0. In order to satisfy IS4, N1 of O, OS ~ 0] is contained.

The above basic components will not be described in detail here, but in particular P and 8Fi, if these are too large, the stress corrosion cracking properties that are the object of the present invention will deteriorate, and in this sense the preferable upper limit is P: 0
．． 018 Sorry, B2G, 01 Sorry. As mentioned above, Ni is added to stabilize the austenite-undissolved carbide coexistence region, and the stabilizing effect is expected at less than 0 and 0, but 0. ! If the corrosion resistance is exceeded, the corrosion resistance deteriorates, and the resistance to stress corrosion cracking caused not only by sulfides but also by chlorides becomes poor. Like this N
The content range of i' is defined, but in order to ensure the stabilizing effect of this, it is necessary to
Setting it to 0 is not enough. In other words, the Ni content is related to C, C@)+kN-)/84J≧0.1
It is necessary to add K, but only by adding K can ferrite not be mixed in, and undissolved carbide be uniformly dispersed to obtain a nine austenite-dissolved oxycarbide coexistence region.

Since the figure shows the range of N1 as shown above, the shaded area in the figure is the Ni content range that can be adopted in the present invention.
The group is above 0.05~O, S 小O*l! If the above relational expression is not satisfied, ferrite will be formed due to microsegregation of the bond, and a stable 93-phase structure will not be obtained.

In the present invention, steel with the above-mentioned composition system is solution-treated in the austenite-undissolved carbide coexistence region as shown by the diagonal lines in Figure 2, and from this temperature it is cooled at a cooling rate higher than air cooling, generally air cooling. Or oil cooling (20-5O'O/min)
Since the above-mentioned coexistence region is extremely stabilized by addition of an appropriate amount of Ni and Ni, it becomes possible to perform such thermal I & ring stably. Next, a tempering treatment is performed on the tube to a predetermined strength, but this treatment itself is a special 4, so it is expressed as Fi.

That is, for example, tempering of 1 (b) or more is performed at 600° C. or higher.

The structure of the rutinsite stainless steel obtained in the above manner does not contain ferrite, and is a mixed structure consisting of tempered martensite in which undissolved carbides are uniformly dispersed, undissolved carbides, and tempered carbides. Due to the action of undissolved oxides that are uniformly dispersed in the structure during solution treatment, it becomes a dense structure with prior austenite grain size of MU IiTM 7 or higher, which significantly improves resistance to stress corrosion cracking caused by hydrogen sulfide. be done. The four true marks in 3-1) or el) indicate the differences in the structure obtained due to the above solution treatment conditions. (C) is the austenite-undissolved carbide coexistence region, and (C) is the austenite-undissolved carbide coexistence region, which is air-cooled from the austenite-undissolved carbide coexistence region. , the Fi grain size of 4 in (1) is the origin, and while in (a) ferrite is formed,
It can be seen that the specimen in (b) has an extremely dense structure.

The table below shows the stress corrosion cracking resistance due to hydrogen sulfide of steels using the IjII method of the present invention, together with that of Hibori materials. (b) and (a) each integrated treatment is air-cooled and the yield point is 65f/=”
It is tempered to look like this. The solution treatment temperatures in (a) to (・) above are C niostenite single phase region b niostenite coexistence region b niostenite undissolved carbide coexistence region C niostenite coexistence region undissolved carbide-17 elite; is also an application of the phase diagram obtained from each composition. The stress corrosion cracking resistance test using hydrogen sulfide was conducted by applying a CG test piece to which stress was applied to the yield point by adding *m gas containing 30 bags of water to the sIs saline solution. The samples were immersed for 1 month and examined for cracking. In addition, the following (1) is shown in Figure 1.
) to (7) are illustrated.

According to the above table, steels (11 to (
In 3), the nine lines in which air cooling is performed from the solution geological conditions of (a) and (a), i.e., the austenite single-phase region and the austenite-un-II Sakai carbide-ferrite coexistence region, all show cracking. ing. On the other hand, under the conditions of the present invention (b) and C) solution treatment conditions, that is, when air cooling is applied from the austenite-undissolved carbide coexistence region, the formation of cracks is stopped in all nine cases. In addition, for this reason, in the present invention, the above-mentioned austenite-non-#
It can be seen that the region where l-membered compounds coexist is extremely stabilized. On the other hand, among the comparative materials nine-pots (4) to (7), steel (4)
The amount of steel (5) was too small, and the amount of gNi in steel (5) was too large, causing cracks in both cases. 9. Steels (6) and (7) do not satisfy the following formula: 04%)+81m)/so≧0.11 of the amount of Nl in fkll of o, os ~ o, s. The nine-austenite-undissolved member coexistence region obtained from 1 ml of real KFi is extremely unstable and does not have a strict atksm structure, -therefore, (
Steel produced under the treatment conditions b) also shows no improvement in cracking resistance. The round steel obtained by the method of the present invention not only has the above-mentioned resistance to stress corrosion cracking caused by hydrogen sulfide, but also has the corrosion resistance to vertical acid gas corrosion and resistance to stress corrosion cracking caused by chloride, which conventional martensitic stainless steel copper has. 11 have been recognized as having the following.

As described above, according to the present invention, conventional martensitic stainless copper has corrosion resistance against coal gas, resistance to stress corrosion cracking due to chlorides, and yield point SO.
~? Since it is possible to manufacture steel that has good resistance to stress corrosion cracking caused by hydrogen sulfide without any loss of strength as high as Ol This invention is extremely useful and has high industrial utility value.

[Brief explanation of drawings]

Figure 1 shows the Ni content conditions in the present invention. FIG. 1 shows an equilibrium state 11WA of r.-Cr system. Atsushi 8m11(a) or a) are each ms
This is a 400x magnified nine-point mirror photograph of the round steel 0 silver weave obtained through %mmmm. Patent Applicant: Nippon Kokan Co., Ltd. Employee: Sumi Shimomura
Sawa Yoshi - same island 1) Toru 1
5-; t7 Daikyorinbenhoshi Kaiho Ministry Santon: Shoulder Responsibility ＼: 111.... (%)! N (tsu.) 1/V Display of the incident Showa s1 Token license test number! No. 9845 Yuya @O Name Rutinsite stainless steel with excellent resistance to stress corrosion cracking due to hydrogen mercenide and method of manufacturing the same 1 Part of the case involving the person making the amendment License applicant 1 Marunouchi, Chiyoda-ku, Tokyo Chome lI! No. (411) Representative of Nippon Steel Tube Co., Ltd. Mr. Kaneo, Representative of Butshu Daisho ◆ O Date 1. Correction Contents <Military imor development name" 1. Stress corrosion cracking resistance due to hydrogen sulfide It has been corrected to say, ``fw siltinsite stainless steel with excellent properties and the OII manufacturing method''. 1. The entire text of the attached document is corrected in the specification of the application. The number of patent failures for the three applications is increased by one term, and the number of inventions is eight. W14JII Book 1 Name of the invention Martenitic stainless steel with excellent resistance to stress corrosion cracking due to hydrogen sulfide and its preparation method (7) O range (1) C, O,! 5s or less, gi:i, oo* or less@MHs tIA returned martenphyte, undissolved members (
2) C: (1,25- or less, Sl: x, 001 or less,
Mn: 1.0091 or less, P: 0.04 (l or less, 8:
0. Q30-below, c, ; ls, so ~14
．． Oofk and this K CC illusion + Ni (%
)/3 G≧0. o, os-o to satisfy li-
Detailed description of the invention * Rutinite stainless steel with excellent resistance to stress corrosion cracking caused by sulfurized water IK and its Omlml
Conventionally, carbon steel and low-alloy steel are generally used as steel pipes for producing natural gas wU, but the development of these pipes is being actively carried out for natural gas that contains a large amount of carbon dioxide gas. Although the above steels have sufficient corrosion resistance, the use of stainless steel, which has excellent corrosion resistance, has been considered as a steel pipe for 110 natural gas. As a strong and economical stainless steel, Al81410 and 410K are representative stainless steels.
Martenite stainless steel with 1s Cr is attracting attention. This stainless steel has good corrosion resistance against carbon dioxide contained in gases and stress corrosion cracking caused by chlorides in seawater. It has an excellent property that a yield point of 50 to 70 K4t/wP can be obtained by heat treatment 11. However, this martenitic stainless steel is sensitive to stress corrosion cracking due to hydrogen sulfide, which is often contained in natural gas, and despite its excellent properties, it can hardly be used in gases containing hydrogen sulfide. Trout also has the disadvantage of being hard to look at), and this point is a major reason for preventing its use as a material for steel pipes for natural gas. The present invention has been developed as a result of repeated studies in view of the above-mentioned circumstances, and has been developed using the above-mentioned 1 rutinite stainless steel composition as a basic component.
By containing K, the martenphyte stainless steel has corrosion resistance against carbon dioxide gas and resistance against stress corrosion cracking due to chloride, and further improves the yield point of 50~
70 N9 f/J -(1m
This product successfully improved resistance to stress corrosion cracking caused by hydrogen chloride. The above-mentioned 12~*s@cl (6 martenbutite stainless steel is a complete austenite single phase region with no solution habitat)
It is then air-cooled to form a martenitic structure with a yield point of 5.
0~to61/JKfi is often returned and used, but in reality, the gold structure during solution treatment changes depending on the temperature, and it may become an austenite-undissolved carbide or austenite-undissolved carbide-ferrite structure. The present inventor, Hiromu, has repeatedly investigated the relationship between the metal structure due to solution temperature and the stress corrosion cracking resistance due to hydrogen sulfide. As a result, when 7-elite exists, the metallographic structure is highly heterogeneous and susceptibility to stress corrosion cracking increases. High metal! In other words, if the solution treatment temperature is set to the austenite-undissolved carbide coexistence region, the sulfide water volume contributes greatly to the formation of liI, which has a high resistance to stress corrosion cracking of 1n#t.
It was 41tIa that jl1 tissue was obtained, and
This high resistance to stress corrosion cracking caused by hydrogen sulfide is due to the tempered martenite, which does not contain ferrite and has undissolved carbides evenly dispersed, and the dense structure consisting of undissolved carbides and solid matter precipitated during tempering. However, it is difficult to uniformly obtain such a texture with component yarns such as Al8I410 and Al8I420 as mentioned above. That is, the metal structure in the phase diagram of the austenite-undissolved carbide coexistence region in the above-mentioned component system is actually extremely unstable, and the undissolved carbide distribution 111 is non-uniform, and the composition is uneven. Ferrite formation is inevitable. As a result of further investigation, we found that N1, which is known as an element that stabilizes austenite, is a factor that controls the metallographic structure of martempuit stainless steel.
is IIIiK effective, 4! The addition of an appropriate amount of Ni to the above component system stabilizes the metal structure in the austenite-undissolved carbide coexistence region and is effective in obtaining an optimal metal structure that is resistant to stress corrosion cracking caused by hydrogen sulfide. The present invention is based on the knowledge that there is a good thing. For the basic martenitic stainless steel composition represented by KAISI 410 and 420, an appropriate amount of Ni is added to 41 to change the composition of the steel to tempered martensite,
It is characterized by a mixed structure consisting of undissolved carbides and good carbides precipitated during tempering. KAISI 410 and 420 as described above
Assuming the martenite stainless steel pot OH represented by K, the component system is C; 0.2111 or more - F
, 81: 1.00s or less, Mn: 1.0G- or less, P: 0.040% or less, s: o, oaos or less, C
r: The steel containing 11.10-14.00- is further made to satisfy C (10 Ni (嗟)/3G>0.15%) and contains 0.05-0.5-0.5-N1 of stone. I will not explain the above basic ingredients in detail here, but @tcp
and 8, if these amounts are too large, the stress corrosion cracking properties which are the object of the present invention will deteriorate. In this sense, the preferable upper limit is P: 0.015% S
:0.01%. As mentioned above, Ni#i is added to stabilize the austenite-undissolved carbide coexistence region, and if it is less than O,OS-, the stabilizing effect cannot be expected.However, if it is less than 0. ! ! If the IG is exceeded, the corrosion resistance deteriorates, and the resistance to stress corrosion cracking caused not only by sulfides but also by chlorides deteriorates.In this way, the content range of K Ni is specified, but this does not limit the stabilizing effect of K. In order to reliably obtain the content, it is not enough to simply set the content range like this.In other words, the content of N1 is related to C and O, and c (s
) It is necessary to satisfy 10Ni (*) / s o ≧ 0.15-, and by this, 7-elite is not mixed in the solution body, and moreover, undissolved carbide is uniformly dispersed in austenite-undissolved carbide. The coexistence region can be stably obtained.・Summary 1WA shows the range of the above set, and the diagonally shaded part in the figure is the Ni O content range that can be adopted in the present invention. Even in the ~0, iso range, unless the above relational expression is satisfied, ferrite will be formed due to black segregation in the material, and a stable eight-phase structure will not be obtained. The structure of the martenitic stainless steel of the present invention, which is composed of such components, does not contain 7-elite as described above, and undissolved carbides are uniformly dispersed, resulting in well-tempered martenite, undissolved carbides, and precipitated during tempering. This is a mixed structure consisting of carbides.This O mixed structure is created during solution treatment! l
Due to the action of undissolved members that are uniformly dispersed in the air), the prior austenite grain size is denser than BTM7.
The resistance to stress corrosion cracking caused by hydrogen sulfide has been significantly improved, making it a better product.The above-mentioned rutinite-based stainless steels are the same as steels with the above-mentioned compositions. Solution treatment is carried out in the austenite-undissolved carbide coexistence region shown by the diagonal line O, and from this temperature the cooling is performed at a cooling rate higher than that of air cooling, generally air cooling or oil cooling (20~B A), with the addition of an appropriate amount of N1. Since the above-mentioned coexistence region is extremely stabilized by this, the tempering process ffi is performed to a predetermined strength with the primary i that makes it possible to perform such heat treatment stably, but this J6111 itself is not special.
That is, for example, the photos of one sheet, one figure, and one (fake) or (e) in which tempering of 11g1 or more is performed at 5ooc or more show the difference in the structure obtained due to the difference in the above-mentioned solution heat treatment, and among these, the fake ) is the austenite single-phase region % conflict) is the austenite-undissolved carbide coexistence region targeted by the military @
(C) is air-cooled from the austenite-unreleased material-noelite coexistence region, and shows the metal structure of the in-situ metal during tempering. The non-containing particles are coarse and have good quality, whereas ferrite is formed in the ones with good quality.
It can be seen that in the case of (3), an extremely dense structure was obtained due to the action of undissolved carbides, undissolved ortenite, and tempered carbides. The table below shows the stress corrosion cracking resistance due to hydrogen sulfide of the steel according to the present invention, together with that of comparative materials.
) to (7) steel, -), 伽). (c) Air cooling from O each solution treatment salt temperature, yield point is 61
*Tempered to #//-. -) ~ (s) above
The Oi 1 body formation process is (a) austenite single phase region (b) niostenite-undissolved carbide coexistence region (c) niostenite-undissolved carbide-7 elite coexistence region), both of which have a shape 11 diagrammatically from each composition. The test for stress corrosion cracking resistance due to 1+ hydrogen sulfide was conducted by bubbling nitrogen gas containing 30-sulfide water into 6-salt water [K, yield point @ A C-type test piece to which a tremendous stress was applied was immersed for 1 month and 3 hours to determine whether or not cracks occurred. In addition, the following (1) is shown in Figure 1.
) to (7) are illustrated. According to the above table, steels (l) to (
3) Kk, -) and (Cl solution II & wear conditions, i.e. austenite single phase region and austenite -
Cracks occurred in all samples that were air-cooled from the unmelted carbide-7elite coexistence region. On the other hand, under the solution treatment conditions of the can (which is the condition of the present invention), that is, when air cooling is performed from the austenite-undissolved carbide coexistence region,
All of them were prevented from cracking and were worn one time. From these facts, it can be seen that the austenite-undissolved carbide coexistence region described above is extremely stabilized. On the other hand, among the comparative steels (4) to (7), steel (4) is N1
The amount of steel (5) is too small, and the amount of ttNi is too large, causing cracks in both steels (6) and (7) Fi.
The amount of Nl is o, oi~o. 6!4C) in the 510 range,
C (%) 10 Nl (1)/a O> o, ls Excellent is not satisfied, and therefore the austenite-undissolved carbide coexistence region obtained from the phase diagram is actually extremely unstable and does not match the original 2 The IIJI of Rasu is a phase organization.
It should be noted that even steel produced under 111 conditions shows no improvement in cracking resistance. Unexploded Ijio steel not only has resistance to stress corrosion cracking caused by sulfide water, but also A11R, which has the same corrosion resistance as conventional martensite stainless steel to carbon dioxide corrosion and resistance to stress corrosion cracking caused by sodium chloride. It has been masturbated. As described above, according to the present invention, the conventional martenitic stainless steel has corrosion resistance against carbon dioxide gas, resistance against stress corrosion cracking due to chloride, and yield point SO.
It has good resistance to stress corrosion cracking caused by hydrogen sulfide without any loss of high strength of ~70-1/-%.
In addition, since such steel can be manufactured stably, its industrial use in the field of steel pipes for coal, iron, and gas is possible.4a
It can be said that this invention has a high value.A simple diagram with a weak direction shows the NIO content conditions in the present invention. FIG. 2 is an equilibrium diagram 111 of the re-cr system. No. 8 m(a) to cl are micrographs magnified by 400 times of the structures of round steel obtained by solution treatment and tempering treatment, respectively. Tatami permit applicant Nippon Steel Pipe Co., Ltd. Kinsha

Claims (1)

[Scope of Claims] c: o, zi 戉 or less, 81 21.0011 or less, Mn
:1, OO regret or less, P: 004G- or less, a: o, oa
. Below the capsule, Cr: l 1. l$ @〜14.0011
and this KC■+Ni ell)/go≧
01! + o to satisfy san, os-o, i regret Nl
The round steel containing the fi
9. A method for producing martensitic stainless steel that has mixed corrosion aIIk consisting of tempered martensite, undissolved carbides, and tempered vertical grains by performing MLJ6, and has excellent stress corrosion cracking resistance due to hydrogen sulfide.