JPS6077916A - Manufacture of alloy steel having superior resistance to corrosion and stress corrosion cracking - Google Patents

Abstract

PURPOSE:To provide superior resistance to pitting corrosion and stress corrosion cracking by explaining the interrelation between resistance to pitting corrosion and stress corrosion cracking and composition and the relation between the composition and conditions during heat treatment and by selecting them in specified ranges. CONSTITUTION:The composition of an alloy steel is composed of, by weight, <0.015% C, <1% Si, <1% Mn, <0.01% P, <0.01% S, 60-70% Ni, 22-35% Cr, <10% Mo, <0.01% N, <1% Cu, one or more among <1% Ti, <1% Nb and <0.1% Ca, and the balance Fe with inevitable impurities, and the value of DELTA1 represented by equation I is regulated to >=25. The alloy steel is subjected to soln. heat treatment of semi-soln. heat treatment at a temp. Tf which is in the range of 950-1,250 deg.C and satisfies conditions represented by equations II, III.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing alloy steel having excellent corrosion resistance and stress corrosion cracking resistance.

The corrosive environment in which metal materials are used has tended to become more severe in recent years. For example, oil wells, gas wells, geothermal wells, etc. are experiencing high temperatures, high pressures, and chloride contamination at the bottom of the wells due to the use of wells. In response to these changes in corrosive environmental conditions, the corrosion-resistant materials used are also changing from the conventional 9% chromium m,
Among the steel materials such as tan chrome fi, 48% chromium steel, and 5 US 304° 316 class steel materials, the use of high alloy steels known as Incoloy, Hastelloy, etc. is being considered. By the way, corrosion phenomena of high alloy materials in such a severe corrosive environment are pitting corrosion and stress corrosion cracking [hereinafter referred to as rsc
This is typified by localized corrosion such as cJ. The most commonly known effects of alloying elements on such localized corrosion are nickel for 8CC, and chromium and molybdenum for pitting corrosion. It is known that the SCC resistance of a chromium-nickel-iron alloy containing about 18% chromium in a magnesium chloride solution is the poorest at 8 nickels, and can be improved by reducing the amount of nickel added or increasing the nickel content. By setting the nickel content to 45 or more, extremely high SCC resistance can be obtained. It is also known that the pitting corrosion resistance is improved by increasing the chromium content, and that the pitting corrosion resistance becomes extremely high when the chromium content is about 22 to 35 or more. Furthermore, molybdenum shows its effect when added simultaneously with chromium.
It is about 1.5 times more effective than chromium. However, the influence of each component element as described above mainly has only the concentration of the component of interest as a variation factor, and the interaction of the component elements has not been studied in the past, and SCC
There are also very few examples where properties and corrosion resistance were considered at the same time.

In other words, the compositional design of highly corrosion-resistant alloys tends to increase the amount of nickel added to improve SCC resistance, and to increase chromium and molybdenum to improve pitting corrosion resistance, but the amount of each alloying element added varies individually. It is determined based on the effects of elements on individual phenomena, and there is still no known material that quantitatively considers the mutually optimal balance of nickel, chromium, molybdenum, etc. to improve FIIS CC properties and pitting corrosion resistance. In addition, in actual product manufacturing, especially solution treatment conditions and SCC resistance
At present, the relationship between corrosion resistance and pitting corrosion resistance has not been sufficiently elucidated.
By elucidating the interaction of alloying elements on CC properties and pitting corrosion resistance, and the relationship between this and solution treatment (or quasi-solution treatment) conditions, we have developed a structure that has even better pitting corrosion resistance and stress resistance than the conventional so-called Incoloy and Hastelloy. This was a successful achievement of producing high-alloy steel with corrosion cracking properties.

That is, in the present invention, C: 0.015 wt or less, Si: 1 wt $ or less, Mn: 1 wt % or less, P: 0.01 wt or less, S: 0.01 wt or less).
-, Ni:60wt96a~70wt%, Cr:22
~35wt%.

M□: 10 wt% or less, N: 0.01 wt% or less, Cu: 1 wt q6 or less, and 1 or 2 types of Ti, 1 wt or less, Nb, 1 wt or less, and Ca, 0.1 wt or less. Δ,=(Cr+ 1.5Mo+o, s'rt+0.
The value of Δ1 determined by 5Cu-ioo・c) is 25t%
) or more, a copper alloy having a composition of 950 to 1250
Solution treatment or semi-solution treatment is carried out at a temperature Tf that is within the temperature range of '0 and satisfies the conditions of equation 1.

Δ,=N1 [((Cr+1.5Mo-20)”/12
1-35C-27N+ 141 Tf≦60Δ, -550 The reasons for limiting the component composition and heat treatment conditions of the present invention will be explained in detail below. The reasons for limiting the component composition of the present invention are as follows.

There is a theory that Co is effective in suppressing intragranular type SCC, but as the carbon content increases, grain boundary type 800 tends to occur, especially in high Ni alloys where carbon solid solubility decreases.
f: f'L becomes larger. 'Also, there is a problem that carbide precipitates can easily become the starting point for pitting corrosion, so this
Therefore, C is strictly limited to 0.015 wt % or less.O 8t is necessary as a deoxidizing component, but it is a component that deteriorates hot workability, so it is not recommended to avoid such problems. The upper limit is set at 1%.

Like st, Mn has a deoxidizing effect. This Mn is SCC resistant
If the force exceeds 1 inch, precipitates such as manganese sulfide tend to become a starting point for pitting corrosion, so the upper limit is set at 1 inch.

Since P as an unavoidable impurity has the effect of increasing SCC sensitivity, it is necessary to reduce it as much as possible, and therefore its upper limit is set at 0.01 wt%.

S (τ) as an unavoidable impurity has the effect of deteriorating the hot working pipe and creates manganese sulfide etc., which deteriorates the pitting corrosion resistance, so its upper limit is set as o, oiwtq6, etc.

Ni is an effective element for improving 1iitscc property, and its effect becomes noticeable when the content is 20 wt or more, but as c and B increase, SCC resistance decreases, so it is necessary to satisfy sufficient corrosion resistance. Excellent SCC resistance compared to cr amount
In order to exhibit properties, it is necessary to contain at least 60 wt%, and the lower limit is 6°w.
It is defined as exceeding t%. Also, depending on the relationship with other components, especially the amount of 1ccr, the upper limit is 7 Owt.

Cr is an element that is effective in improving the t1 corrosion resistance of high alloy steel, especially in improving the corrosion resistance by strengthening the passive film. In order to obtain sufficient corrosion resistance, a content of i”t22wt% or more is required, but the content If it exceeds 35 wt %, deterioration of hot workability is inevitable, and therefore its content @Qma22~a
s wt %.

Mo&″l: 1.5 of Cr for strengthening the passive film
It is about twice as effective, but if its content exceeds 10 wt%, it will easily generate a σ phase that deteriorates corrosion resistance during hot processing, so the upper limit is set at 10 wt%.

Although N improves pitting corrosion resistance, the steel of the present invention has sufficient pitting corrosion resistance even without a nitrogen component.

On the other hand, when N exceeds 0.01 wt%, it has a sudden effect on SCC resistance, and for this reason, the upper limit is set at 0.01 wt%.
It is defined as tchi.

Cu helps to improve corrosion resistance of interest, but 1
Exceeding wt% leads to deterioration of hot workability, and therefore 1
wt % is set as the upper limit.

Each component (Ca, Ti, Nl) has the effect of improving hot workability, and furthermore, Tl and Nb have the effect of fixing carbon and, as a result, suppressing grain boundary SCC. Although each component exerts such an effect, Ca is 0.1wt.
%, Ti and Nl) are each below the lwt ratio, which is sufficient, and even if the content exceeds this upper limit, no further effect is expected. These ingredients are part 1
A species or two or more species may be contained.

In the present invention, it is necessary to satisfy the composition conditions of the component elements as described above, as well as the following conditions between the component sources, and by satisfying the mutual relationships between the component elements. τ, O at which the excellent pitting corrosion resistance aimed at by the present invention can be obtained; that is, in the present invention,
It is necessary to adjust each component value so that the value of Δ defined by the formula [Cu-100·C] is 25 or more. Figure 1 shows pitting corrosion resistance under severe corrosive environments.

The relationship between the value and the pitting corrosion rate was investigated, and the relationship between the value of Cr,
Regarding alloys with varying contents of Ni, M□, etc. 1
This figure shows the results of a pitting corrosion experiment using ferric chloride. As is clear from the figure, even with the component composition adopted by the present invention, the pitting corrosion resistance is greatly inferior in the range of Δ, >25, and in order to fully satisfy the pitting corrosion resistance, the mutual It turns out that fulfilling the relationship is essential.

In the present invention, after the steel having the above-mentioned compositional conditions is melted, so-called solution treatment or semi-solution treatment is performed in the steps after hot rolling. Here, quasi-solution treatment means that even if the trenches are not complete, the tissue is first subjected to heat treatment at a temperature of 950 to 125 degrees.
The condition is that it is carried out in a temperature range of 0°0. If the heat treatment temperature is less than 9500, the required uniformity of the metal composition cannot be obtained, so sufficient SCC resistance cannot be expected;
cc This is not preferable because it causes a decrease in c properties. Although there are differences depending on the component composition, generally 950 ~
In the temperature range of 1250°0, heat treatment on the high temperature side is solution treatment, and heat treatment on the low temperature side is vulgarization treatment. The heat treatment of the present invention is conditioned to be performed at a temperature Tf that further satisfies the condition of the first equation within such a temperature range.

Δ*=Ni[:(CCr+1.5Mo-20)”/1
21-35C-27N+14] Tf≦60Δ, -550 Temperature Tf is Δ determined in relation to the content of each component element.
1@((It is determined based on Figure 2 shows the SCC resistance in a severe corrosive environment based on the relationship between the value of Δ and the heat treatment temperature Tf.
Specifically, an sCc test was conducted in a zinc chloride solution, which is highly corrosive (like magnesium chloride), and the SCC resistance was determined based on the presence or absence of cracking after 600 hours. It is clear from the same figure') K, 950-1250
Even in the temperature range of °0, Tf>
Stress corrosion cracking resistance is poor in the range of 60Δ, -550, and in order to fully satisfy stress corrosion cracking resistance, it is essential to heat treat at a temperature based on the value of Δ determined by the relationship between the component elements. It turns out that there is something. In addition, as shown by the broken line in the figure, in the present invention, substantially Δ.

It is required that the value of is at least 25 or more.

The above-mentioned solution treatment or vulcanization treatment can be carried out at various stages after hot working. For example,
Cold rolling - solution treatment or obscene treatment, ■ hot rolling -
Processes such as solution treatment or obscene treatment-cold rolling can be employed. In addition, after the solution treatment, heat treatment to stabilize the structure by changing the solid solution C from a supersaturated state to a saturated state, a so-called stabilization treatment, can be performed.In this case, for example, hot rolling - Solution treatment - cold rolling - stabilization treatment, ■ hot rolling - solution treatment - stabilization treatment - cold rolling, ■ hot rolling - cold rolling - solution treatment - cooling 1) 1 rolling -
Various steps such as stabilization treatment, etc. can be taken. Here, the above-mentioned heat treatment is a heat treatment that progresses the dissolution of carbide in the structure to a certain extent, thereby making the component elements uniform (including the average ratio of the microscopic component tones). As mentioned above, the tissue obtained in this way is homogenized through solution treatment and stabilization treatment.
It becomes close to a stabilized organization. In addition, the above
, In the process shown by ■, cold rolling is performed between the solution treatment and stabilization treatment! L1 Through this cold rolling, N
b Since the precipitation of C* T I C% is promoted, a more stabilized structure can be obtained.

〔Example〕

Table 1 shows the present invention 1Q4 (C-1 to C-7) and comparative steel (
The chemical components of D-1 to D-8) are shown below. All of these are manufactured on regular stainless steel production lines.
After hot rolling-annealing-cold rolling, 950-1250'O
Solution treatment or obscene treatment was performed by heating in a temperature range of 10 to 30 minutes and rapidly cooling. Note that under some conditions, solution treatment or quasi-solution treatment was performed at a stage corresponding to the 4-degree annealing step, and the heat treatment after cold rolling was omitted.

The degree of heat treatment during the process or the holding time during the heat treatment do not affect the results, so these items are omitted.Table 1 shows the test results regarding pitting corrosion resistance and 14SCC property of each sample. It is also shown in .

As is clear from the same table, the steel of the present invention has excellent properties with both pitting corrosion resistance and SCC resistance titrated at the same time, whereas the comparative steel has both needle pitting corrosion resistance and SCC resistance. It can be seen that only i has an adverse effect on one or both.

As described above, according to the present invention, we have clarified the drilling corrosion resistance, stress corrosion cracking resistance, component composition, and their mutual relationship, as well as the relationship between such component conditions and heat treatment conditions, and adjusted them within a specific range. This selection makes it possible to manufacture alloy steel with unprecedented pitting corrosion resistance and SCC resistance, and this invention has great industrial effects regarding this type of alloy steel.

[Brief explanation of the drawing]

Figure 1 shows the relationship between Δ and pitting corrosion rate (pitting corrosion resistance). Figure 2 shows Δ. This shows the relationship between the value and the solution treatment (or the obscene treatment). U secret procedural amendment 1920 5g! [February 6]] Special FFIi Director Waka Iri, 111 No.N (Special Security 1 Examiner) 1 Indication of 1'1 1939 rco IIF Application No. 2 & 611. /7 Shi J2 brother Akira's 6 scoops; Relationship with the case of a person who makes an amendment Applicant Japan Pre-'LU'j+'+'jinkai r1-4 Agent 5 Amendment Order 1] Ij 6 Target of Amendment Amendment Content 1 "Claims" of the application Correct as follows. rc: 0.015wt% or less, Si: 1wt% or less, M
n: 1 wt% or less, P: 0.01 wt% or less, S20,01 wt% or less, Ni: more than 60 wt% to 70 wt%, Cr: 22 to 35 wt%, Mo
: 10wt% or less, N: 0.03wt% or less, CH
: 1wt% or less, and in addition to these, 1wt% or less of Ti, 1wt% or less of Nb, and 0.1wt% or less of Ca.
A composition containing one or more of the following, with the balance consisting of iron and unavoidable impurities, Mountain = [Cr + 1.5Mo + 〇, 8Ti + 0.5Cu
An alloy steel having a composition in which the value of Δl determined by -1ooc:] is 25 or more is solution-treated or made into a base material at a temperature Tf in the temperature range of 950 to 1250°C and satisfying the conditions of the following formula. A method for producing alloy steel with excellent corrosion resistance and stress corrosion cracking resistance, the method comprising: Δt=Ni-C((cr+t,5Mo-20)2/12
1-35C-27N +14) Tf<60Δ, -5504 From the end of line 13 to the beginning of line 14 on page 3 in the Ministry of Specification of the present application, the phrase "about 22 to 35% or more" is replaced with "about 22% or more".
I am corrected. 3 In the same book, page 5, line 7, the phrase "rN: 0.01 wt% or less" is revised to "rN: 0.03 wt% or less."4i', page 5, line 12, is corrected as follows. “Δs =CCr+1.5Mo+0.8Ti +0.5
Cu-10QC) JSadoho, page 8, line 13, “N is 0
．． The total fN that says "01 wt%" is corrected to "0.03 wt%". 1-8, line 15, correct the text "ro, 01 wt%" to "jO, 03 wt%". 7 Line 14 of page 9 of the same book is corrected as follows. r J1=[Cr+1.5Mo+0.8Ti+〇,5C
u tooc) J to page 10, line 3, “Δs>2
5" should be corrected as "Δ1<25J." In the circular, page 12, line 15, the phrase "[also after solution treatment]" should be changed to "r.
” he corrected.

Claims (1)

[Claims] Coo: 0.015wt% or less, Si: 1wt.96 or less. MH: 1 wt% or less, P: 0.01 wt% or less,
s: 0.01wt% or less, Nt: more than 60wt% ~ 70
wt%. Cr: 22 to 35 wt%, Mo: 10 wt% or less, N:
o, oxwt% or less, Cu: 1tvt% or less, and in addition to these, one of the following: 1wt% or less of Ti, 1 wt% or less of Nb, 0.1 wt% or less of Ca, or 21'! Δ, == [Cr-1-1,5Mo+0.8Ti
+○, 5Cu-too-c) The value of Δ1 is 2
Alloy steel having a composition of 5 or more, 950~125o
Temperature T that is in the temperature range of 0 and satisfies the conditions of the following formula
1. A method for producing an alloy steel having excellent corrosion resistance and stress corrosion cracking resistance, the method comprising solution treatment or humidification treatment. Δ*=Ni [((Cr+1.5Mo-20)”/12
1-35C-27N+14] Tf≦60Δ, -550