JPS6077917A - Manufacture of alloy steel having superior resistance to stress corrosion cracking - Google Patents

Abstract

PURPOSE:To manufacture an alloy steel having superior resistance to stress corrosion cracking by explaining the interaction between alloying elements on resistance to stress corrosion cracking and the relation between the interaction and conditions during soln. heat treatment. CONSTITUTION:The composition of an alloy steel is composed of, by weight, <0.03% C, <2% Si, <2% Mn, <0.02% P, <0.01% S, 20-30% Ni, 12-25% Cr, <10% Mo, <0.3% N, <0.1% Ca and/or <2% Cu, and the balance Fe with inevitable impurities while satisfying equation I , and the value of DELTA represented by equation II is regulated to >=5. The alloy steel is subjected to soln. heat treatment or semi-soln. heat treatment at a temp. Tf which is in the range of 950- 1,200 deg.C and satisfies conditions represented by equation III.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing alloy steel with excellent stress corrosion cracking resistance. The present invention provides a metal-containing steel plate having stress corrosion cracking resistance.

Among the reports on the influence of alloying elements on chloride stress corrosion cracking (hereinafter simply referred to as rsccJ), one of the most common is the report on the influence of nickel on SCC resistance by Copson (plays i ca 1Meta+).
+urgy or 5tress corrosion
rracture.

P 247. Interscience, N.
Y. (1959)). According to this, 18
The SCC resistance of chromium-nickel i-based alloys containing about 8% chromium is currently the lowest at about 8% nickel, and it is said that reducing the amount of nickel added or increasing the nickel content improves SCC resistance. In the case of stainless steel, extremely high SCC resistance can be obtained by setting the nickel content to 45% or more. Among alloying elements other than nickel, carbon and silicon are generally recognized to be effective in improving SCC resistance, and phosphorus, nitrogen, molybdenum, chromium, etc. are known as elements that do not have an adverse effect. However, regarding the effects of each component element on SCC resistance described here, only the concentration of the component of interest was taken as a variable factor; on the other hand, there are no examples of studies regarding the interaction of component elements. less,
There are only a few reports on the combinations of carbon-nitrogen and phosphorus-nitrogen with small contents ([Yazawa, Fukase, Yoko, January 2, Thursday Journal of the Institute of Metals, 3G (1972) 170. J [Kowaka, Fuji: Japan Institute of Metals. Magazine, 34 (1970) 1047, J
). There, in the carbon-nitrogen combination J3, the SCC resistance of carbon is lost as nitrogen m increases, and in the phosphorus-nitrogen combination μ, reducing phosphorus is extremely effective. This has been confirmed.

Corrosion-resistant alloys used in severe corrosive environments containing chemical substances are
#4 SCC properties and pitting corrosion resistance are required, and in its component design, nickel is added to improve SCC resistance, and chromium and molybdenum are added to improve pitting corrosion resistance.
The amount of both is on the rise. However, in the J: sea urchin mentioned above, the amount of each alloying element added has conventionally been determined based on the effect on individual phenomena of the individual element system. There is still no known material in which the mutual optimum balance of alloying elements such as , molybdenum, and chromium is quantitatively considered.

Furthermore, the thermal history, which is one of the most important factors in actual product manufacturing, and in particular the interaction between solution treatment conditions, SCC resistance, and pitting corrosion resistance, are not fully understood. It is.

The present invention was devised in view of the current situation, and is
Interaction of alloying elements that affect CC properties and this and solutionization (
The relationship between the processing conditions (or vulgarization) and the conventional SU
S304. We have succeeded in obtaining an alloy steel with SCC resistance comparable to that of the No. 316-7 material using an economical range of alloying elements.

That is, in the present invention, J3 contains C: 0.03 wt% or less, 3i: 2 wt% or less, IVIII: 2 wt% or less, P
: 0.02wt% or less, 3: 0.01wt% or less,
Ni: 20W [% or more and 30W [less than %], Cr: 12
~25wt%, MO: 10wt% or less, N: 0.3
wt% or more, and in addition to these, 72wt% or less C
A composition containing one or more of u, 0.1 wt% or less of Ca, and 1 wt% or more of l-i, with the balance consisting of iron and unavoidable impurities, Or +1.5MO+0.8-1' -i + 0.5C
11≧15, ■ Δ= (N i +300-1-25N ) [((Cr
10L5M O-1-0,8-1-1-I-0,5Cu
-19) 2/ 12) -13] 8ItQ
Foamed gold r14+ having a composition of 5 or more, which is subjected to solution treatment or vulgarization treatment at a temperature in the temperature range of 950 to 1200 °C and satisfying the conditions of the following formula] - [ It is.

T [≦12Δ+900 The ingredient composition of the present invention and the reasons for limiting the heat-treated tea juice 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 C is effective in suppressing intragranular SCC, but if the C content exceeds 0.03 wj%, grain boundary SCC tends to occur, and in particular, if the CIN solubility decreases, With Ni alloys, this fear becomes more serious. For these reasons, the upper limit of C is limited to 0.03 wt% or less.

Si is necessary as a l1ji acid component, and also '#4S
Although it is an effective element for improving CC properties, M
Like Si, ll has a +12V effect. This M 11
has almost no effect on SCC resistance, but 2wt%
If it exceeds 2 wt%, precipitates such as manganese sulfide tend to become the starting point of pitting corrosion, and therefore the upper limit is set at 2 wt%.

Since 1] as an unavoidable impurity has the effect of increasing SCC susceptibility, it is necessary to reduce the amount of 1], and therefore its upper limit is set at 0.02 wt%.

S as an unavoidable impurity has the effect of deteriorating hot workability, and the upper limit of C1 is set at 0.0 hvt% to avoid deterioration of pitting corrosion resistance by forming manganese sulfide and the like.

Ni is an effective element for improving RI S CC properties, and its effect becomes noticeable at 20 wt% or more.
Therefore, the lower limit is 20w[%. On the other hand, since the upper limit of Crfii described below is 25 wt%, in balance with this upper limit of Crff1, the upper limit of Ni is 30 wt%.
% no vortex. In addition, the present invention allows the addition of alloying elements within an economical range while achieving SCC resistance of 1 phosphorus that is comparable to or better than that of conventional 5US304°316.
Therefore, adding more than 30W [%] will impair economic efficiency and deviate from the purpose of the present invention.

C and r are effective elements for improving the corrosion resistance of high-base metal steel, especially by strengthening the passive film, but if it is less than 12W (%), the effect is not sufficient, and if it exceeds 25wt%, the hot workability deteriorates. is difficult to avoid, therefore 12~25w
[Supposed to be in the range of %.

MO is about 1.5 times as effective as Or in strengthening the passive film, but if its content exceeds 10%, it easily forms a phase that deteriorates corrosion resistance during hot heating. Therefore, the upper limit is set at 10W%.

Although N is not necessarily an effective element for improving SCC resistance, it can be expected to increase pitting corrosion resistance in the steel of the present invention. SCC of high alloy steel often develops due to pitting corrosion, and preventing R1 of pitting corrosion leads to prevention of SCC. In addition, N suppresses grain boundary sensitization and suppresses grain boundary type SCC.
It has the effect of suppressing the occurrence of. However, if N exceeds 0.3%, it forms nitrides such as N, C1, T1, etc., which deteriorates pitting corrosion resistance and also reduces workability.
The upper limit is 3%.

Each of the components Ca, Ti, and C1 contains one or more of them. Among these components, Cu is useful for improving the corrosion resistance of the material, but at 2wt.
If it exceeds 1%, it will lead to deterioration of hot workability.
wt% is set as the upper limit. In addition, 1-i and Ca have the effect of improving hot workability, and Ti1. L.C.
This has the effect of suppressing grain boundary SCC by fixing it.

Although each component exhibits this kind of effect, Ca is 0.1wt%.
Hereinafter, it is sufficient if T1 is less than iwt%, and even if the content exceeds this upper limit, no further effect can be expected. Therefore, in these, Ca is Q, 1wt%, l-i is 1w
It can be contained up to t%.

In the present invention, in addition to the above compositional conditions of the component elements J and U, it is necessary to satisfy the following clause 1'1 among the component elements, and such a relationship between the component elements and the relative relationship is to be satisfied. By this, the purpose of the invention is to achieve excellent sc resistance.
C+1?
Each component value needs to be adjusted so that CU>15. In order to obtain corrosion resistance including general corrosion and pitting corrosion, it is necessary to satisfy the above conditions. Furthermore, in the present invention, in addition to the above composition A'1, 8-(N i 4-30G +25N )-[((Cr
+ 1.5Mo + 0.8'T'i〇, 5Cu
-19) 2 /12) -13] Δ
It is necessary to adjust the composition conditions so that the value is 5 or more, and if this Δ value is not satisfied, the desired S resistance
I can't get CC sex or 19.

Fig. 1 examines the relationship between the above Δ value and the resistance sc
+ 0.5 Cu) on the X axis, and % (N i to 30
c +25N) is expressed on the Y axis,
The SCC susceptibility in this case is determined by applying a stress 1.2 times the yield strength to test j′1 heat-treated at 950°C.
Immersed in 150℃ boiling magnesium chloride solution, G 00
Judgment was made based on the presence or absence of cracks after being stained for 11 yen. As is clear from the figure, (Cr + 1.5Mo 10
．． Even if the range is 8'l'i +〇,5Cu)≧15, the resistance s c should be satisfied only if J5 is in the range of △≧5.
c1q was obtained, and therefore, it can be seen that at least the above composition condition A'1 must be satisfied in order to sufficiently satisfy the SCC resistance aimed at by the present invention. NaJ
5 As shown by the broken line in the figure, (N i +30c +2
The value of tt 4 ; processing is performed. Here, the conditionalization treatment does not refer to a state in which the dissolution of carbide in the b-structure progresses until it is not complete, and the non-uniformity of the component elements is made uniform. In the present invention, first, such heat treatment is performed at 950 to 1200°C.
The condition is that the test be carried out within the humidity range of . Here, if the heat treatment temperature is less than 950°C, the metal structure cannot be made uniform to the required level! It has sufficient SCC resistance!
IJ could not hold and the temperature exceeded 1200℃ again! In heat treatment, the crystal grains become coarser and the yield angle decreases, so 1) I
Not good. Although there are differences depending on the component composition, in general, within the temperature range of 950 to 1200°C, heat treatment on the high temperature side is solution treatment, and heat treatment on the low temperature side is ff1l! I! becomes an obscene treatment. The heat treatment of the present invention is conditioned to be carried out within this temperature range at a temperature T[ that roughly satisfies the condition of the following formula in relation to Δ.

Tr ≦12Δ+900 Temperature] Δ is determined in relation to the mutual content of component elements.
By carrying out solution treatment or conditioning treatment at a temperature determined based on the phase relationship of the component elements, excellent SCC resistance can be obtained, which meets the objective of the present invention. You can get sex.

Figure 2 shows the investigation of SCC resistance from the relationship between Δ bean paste and heat 9J From the relationship with the Δ value, in the range of 1 Go > 12 Δ' + 900, the S resistance is
It can be seen that in order to achieve rusting that satisfactorily satisfies SCC resistance due to poor CC properties, heat treatment at a temperature based on the peak of Δ, which is determined by the relationship between the component elements, is essential.

The above-mentioned solution treatment or conditioning treatment can be performed at various stages after hot working, such as ■Hot rolling-cold rolling-melting treatment or conditioning treatment, ■Hot rolling Rolling-
Processes such as solution treatment or obscene treatment-cold rolling can be employed. Further, after the solution treatment, a so-called stabilization treatment, which is a heat treatment for changing the solid solution C from a supersaturated state to a saturated state and stabilizing the structure, can be performed. In this case, for example, hot rolling - solution treatment - stabilization treatment - cold rolling,
The following steps can be taken: (1) hot rolling, cold rolling, solution treatment, cold rolling, and stabilization treatment. Here, the above l
1I-Solution treatment is a term for heat treatment in which the dissolution of carbide in the structure is progressed to a certain extent, including uniformity of component elements and uniformity of microscopic concentration of components. As mentioned above, the structure obtained in this way becomes similar to a homogeneous and stabilized structure through solution treatment and stabilization treatment. It should be noted that solution treatment can be applied to the level of -4J: eel ni as indicated by (1) and (2) above.

"Example" Table 1 shows the steels of the present invention (Δ-1 to Δ-6) and comparative 1 (B-
1 to B-4) are shown below. All of these were manufactured on Tsutomi's stainless steel production line, and after hot rolling, annealing, and cold rolling, they were subjected to solution treatment, which involved heating at a temperature range of 950 to 1050°C for 10 to 30 minutes and then quenching. After that, I processed the situation. 113, under some conditions, solution treatment or conditioning treatment was performed at a stage corresponding to the above-mentioned annealing step, and the heat treatment after cold rolling was omitted. J on the process
The position of the heat treatment or the holding time after the heat treatment
Since the W interval did not affect the results, those items were omitted. The test results regarding the iIJ S CC properties of each sample steel are also shown in Table 1.

(Left below) As is clear from the table, the steel of the present invention has excellent SCC properties, whereas the comparative steel exhibits adverse effects at all heat treatment temperatures. I understand that.

As described above, according to the present invention, it is possible to clarify the phase H effect of alloying elements on SCC resistance and the relationship between them and heat treatment conditions, and to select them within a specific range, thereby achieving excellent resistance. This invention has made it possible to manufacture alloy steel having SCC properties, and is a highly effective invention for this type of alloy steel in the industry.

←1 method--Ten-ebo 44+H- Ida←4! I! Eeeee Hara--! i-→→4→

[Brief explanation of the drawing]

FIG. 1 shows the relationship between Δ value and SCC resistance. Figure 2 shows gl s from the relationship between Δftr+ and heat treatment temperature.
This is a study of cc characteristics. Patent Applicant: +Jhon Steel Tube Co., Ltd. Agent, Patent Attorney: Shozo Yoshihara (and 2 others) Mr. Wakasugi I. Kuchi, Commissioner of the Japan Patent Office (Mr. Patent Office Examiner) 1. Indication of the case Showa evening? 1 ShizJz4 ~ Core Alloy 4 Okameyoruka Kite 3 Relationship with the case of the person making the amendment Applicant Nippon Kokan Co., Ltd. 4, Agent 5 Correction of date of amendment order Contents 1 Specification of the application, middle chain page 2, line 14 r from the end of the second line to the beginning of the 15th line (physical Metalurg7
J toaruwoI+''(Pl+systemal rnetal
I corrected it as rugy Jl. Co. r170 at the end of page 3, line 14. JJ and a certain ir 170. Edit J J. 3. r'1047 at the beginning of page 3, line 16 of the same book. J) J and aru wo r 1047. J) Correct it as J. From the end of line 19 to the beginning of line 20 on page 4, ``
The phrase "not inferior to the materials" should be corrected to "superior to the materials." At the beginning of the 14th line of page 7 of Yodo Lip, the statement ``as good as 316 or better'' is corrected to ``excellent as compared to 316.'' 6 The first line of page 10 of the same book is corrected as follows. "△= (Ni+aoc+2sN)" The police station, page 10, line 12, replaces "boiling at 150 degrees Celsius" with "boiling at 154 degrees Celsius."
I am corrected. Same page ix, line 1 [(N Todo lOc+25N)J
Correct the statement to r (Ni+30C+ 25N)J. 7 Same column, page 12, line 20, “After solution treatment, solid solution C”
I am correcting it to say, ``After solution treatment (or obscene treatment), solid solution C love''. 70th edition, page 13, line 16 is corrected as follows. ``The precipitation of Nb C, Ti C, etc. is promoted depending on the site, but a stabilized structure of 7 tons was obtained.''//S-1
In the second line of page 6, the phrase ``in contrast to having the property'' is corrected to ``in contrast to having the property.''

Claims (1)

[Claims] (:, +0.03wt% or less, 3i: 2wL% or less, Mn: 2wt% or less, p: 0.02wt% or less,
S: 0.01wt% or less, Ni: 20wt% or more and less than 30Vlt%, Cr: 1
2-25wt% Mo: 10wt% or less, N + 0.3
wt% or less, and in addition to these, CI of 2wt% or less
A composition containing one or more of 10.1 wt% or less Ca, 1 wt% or less T1, and the balance consisting of iron and inevitable impurities, Cr + 1.5Mo + 0.8Ti + 0.5Cu
>15, and Δ= (Ni +30C+25N) [((Cr + 1.5MO+ 0.8T t+ 0,
5Cu -19) 2 /12) -13] I-stainless steel having a composition with a Δ value of 5 or more,
An alloy steel with excellent stress corrosion cracking resistance characterized by being subjected to solution treatment or vulcanization treatment at a temperature Tf in the range of 50 to 1200°C and satisfying the conditions of the following formula: manufacturing method. T"≦12Δ+900