JPH0791584B2 - Method for producing clad steel sheet for seawater resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION “Object of the Invention” The present invention relates to a method for producing a seawater-resistant clad steel sheet, and an object thereof is to provide a method capable of appropriately producing a product having high corrosion resistance as a seawater-resistant clad steel sheet. To do.

(Industrial application field) A technology for obtaining high corrosion resistance by optimizing the composition system and rolling conditions of the laminated material as a clad steel sheet for seawater resistance.

Conventional technology As a stainless steel sheet for seawater resistance, as represented by JP-A-52-95524, from the viewpoint of hot workability and corrosion resistance under the condition of rapid cooling from a high temperature range (1100 ° C or higher), C
Austenitic stainless steels with high r, Mo and N contents have been developed. In such stainless steel, a large amount of expensive Cr and Mo is added to enhance the corrosion resistance. Therefore, when considering the production of a thick plate, it is desirable to form a clad with carbon steel or a low alloy steel from the economical viewpoint. However, when considering the production of clad steel sheets for seawater resistance, rapid cooling from a high temperature range as in the case of conventional solid materials cannot be applied because it severely impairs the toughness of the base material. As described in JP-A-63-248583, the production of austenitic stainless clad steel has been studied from the viewpoint of suppressing the precipitation of σ phase during rolling cooling. However, in the production of the seawater-resistant clad steel sheet containing N ≧ 0.10%, which is the object of the present invention, the precipitation of Cr nitride is faster than that of the σ phase, and the corrosion resistance is greatly affected. The production of such clad steel for seawater resistance is thought to be possible by optimizing the component system of the composite material and rolling and cooling conditions.However, in consideration of the peculiar heat processing history at the time of clad steel production, during and after rolling From the viewpoint of precipitation of Cr nitride in the subsequent cooling process, there is no systematic study of the corrosion resistance of the clad steel composite.

(Problems to be Solved by the Invention) Generally, in clad rolling, hot rolling is performed after heating to 1100 ° C. or higher, and the rolling is finished in a temperature range of 800 to 1000 ° C. and then cooled or heated and cooled. However, due to restrictions on the base material, etc., 10 ° C / sec
It is difficult to secure the above cooling rate. FIG. 1 shows Japanese Patent Laid-Open No. 52-
20Cr-18Ni-6.2Mo-0.7Cu-0.20N steel, which is a typical austenitic stainless steel for seawater resistant to 95524, is used.
Results of pitting corrosion test using ferric chloride solution (ASTM G48, JIS G0578) to evaluate the corrosion resistance when the rolling finishing temperature was changed from 800 ℃ to 1000 ℃ after cooling to 0 ℃ and cooled at various cooling rates. The critical pitting temperature (CPT) at which pitting occurs
Shows almost no dependence on the rolling finish temperature, and increases with the cooling rate after rolling, and CPT = 55 ° C at 10 ° C / sec. For comparison, the CPT when heated to 1200 ° C and then rapidly cooled is also shown on the premise that a solid material is manufactured, but it is 75 ° C, and the corrosion resistance is greatly reduced when clad rolling is simulated. Figure 2 shows the relationship between the corrosion depth and the CPT in the ferric chloride test when a test piece artificially creviced with Teflon was immersed in natural seawater for 1 year. CPT of 60 ℃ or more is required to suppress. Judging on the basis of these results, 20Cr-18Ni-6.2Mo- which is a conventional typical seawater resistant stainless steel
0.7Cu-0.20N steel is not sufficient as a component for the cladding material, and it is desired to develop a component having CPT ≥ 60 ° C even when the thermal processing history of clad production is assumed.

"Structure of the Invention" (Means for Solving the Problems) The present invention was devised through repeated studies in order to solve the problems in the conventional ones as described above, and in the cladding material of clad steel, By optimizing the component system and defining the clad rolling conditions, we have succeeded in accurately obtaining the above-mentioned seawater-resistant clad steel having CPT ≧ 60 ° C. That is, the present invention is as follows.

1.Si:0.02〜1.0wt%, Mn: 0.05〜2.0wt%, Cr: 18.0〜27.0wt%, Mo: 4.0wt% over 7.0wt%, Ni: 15.0〜30.0wt%, B: 0.0010〜 It contains 0.0055wt%, Al: 0.001-0.30wt%, N: 0.10-0.25wt%, and satisfies Cr + 3Mo + 17N ≧ 41.0, 0.030wt% or less of C as unavoidable impurities, P of 0.050wt% or less,
When rolling a clad steel sheet in which stainless steel containing 0.010 wt% or less of S and the balance Fe is laminated on at least one side of the steel sheet, after heating to 1100 to 1250 ° C, hot rolling is performed, and rolling is completed at 800 ° C or more. And then cooling at 1 ° C./sec or more, a method for producing a clad steel sheet for seawater resistance.

2.Si:0.02〜1.0wt%, Mn: 0.05〜2.0wt%, Cr: 18.0〜27.0wt%, Mo: 4.0wt% to 7.0wt%, Ni: 15.
0〜30.0wt%, B: 0.0010〜0.0055wt%, Al: 0.001〜0.30wt%, N: 0.10〜0.25wt%, 2.0wt% or less Cu, 0.5wt% or less W, 1.0wt% or less Ti, 1.0 wt% or less of Nb, 1.0 wt% or less of V, 1.0 wt% or less of Zr, 0.02 wt% or less of La, 0.02 wt% or less of Ca, 0.02 wt% or less of Ce or Contains two or more types, and Cr + 3Mo + 1
A clad steel plate obtained by superposing on at least one side of a steel plate a stainless steel which satisfies 7N ≧ 41.0 and contains 0.030 wt% or less of C as unavoidable impurities, P of 0.050 wt% or less, S of 0.010 wt% or less and the balance Fe. 1100 ~ 12 when rolling
A method for producing a clad steel sheet for seawater resistance, which comprises heating to 50 ° C, hot rolling, finishing rolling at 800 ° C or higher, and then cooling at 1 ° C / sec or higher.

The details of the present invention as described above will be described. The present inventors describe the following first by wt% (hereinafter simply referred to as “%”).
Steels 1 to 10 as shown in the table were prepared.

When these steels 1 to 10 are heated to 1200 ° C., hot rolled at 850 ° C. and then cooled at 1 ° C./sec, the CPT is as shown in FIG. That is, 20Cr-18Ni-6Mo system and 25Cr-22Ni system
In any case of -4.5Mo system, the CPT increases with the increase of the B amount, but after saturation at the B amount of 0.0015% or more, the CPT decreases again at 0.0060%. 0.0010% in any system to satisfy CPT ≧ 60 ° C (in 10% ferric chloride solution), which is the condition to prevent crevice corrosion in natural seawater
The above B addition is required. On the other hand, the addition of B exceeding 0.0050% lowers CPT. Therefore, the B addition amount is preferably 0.0010% or more and 0.0055% or less. Generally, pitting corrosion resistance and crevice corrosion resistance of austenitic stainless steel are C
It is said that it can be sorted by r, Mo, N amount, for example P
Cr ＋ 3Mo ＋ 17N has been proposed as an itting index. However, it has been found by the present invention that B plays an important role on the assumption of clad rolling.

In addition, Fig. 4 shows the CPT when the steel whose composition is shown in Table 2 below is heated to 1200 ° C, rolled at 900 ° C, and then cooled at 1 ° C / sec.
The results of sorting with Cr + 3Mo + 17N are shown below.

That is, the Pitting Index (= Cr
It can be seen that ＋ 3Mo ＋ 17N) is 41. Also this Pittin
Even if g Index ≥ 41.0 is satisfied, Steel 17 containing more than 27% of Cr and reduced Mo has a C content higher than that of the same Pitting Index Steel.
PT is inferior. Further, Steel 16 having a Ni content of less than 15% does not become a complete austenite single phase even after hot rolling, and a ferrite phase is present, which causes a decrease in CPT, which is considered to be caused by that. Considering that 18% or more of Cr is required from the viewpoint of improving pitting corrosion resistance and intergranular corrosion resistance, 18.0% ≤
Cr ≦ 27.0%, 15% ≦ Ni, 0.0010% ≦ B ≦ 0.0055% and
It is necessary to satisfy Cr + 3Mo + 17N ≧ 41.0.

Next, using Steel 3 having the above components, the optimum rolling cooling conditions were studied in consideration of the peculiar heat processing history during clad production. That is, Fig. 5 shows the CPT when the heating temperature and rolling finishing temperature are changed and cooling is performed at 1 ° C / sec. When compared at 900 ° C finishing, CPT = 70 when heating at 1100 ° C or higher.
℃ is obtained. On the other hand, CPT = 5 for 1050 ℃ heating material
The temperature decreased to 5 ℃, and the CPT decreased to 55 ℃ in the 750 ℃ finished material even after heating at 1220 ℃.

Moreover, in Fig. 6, after heating the above-mentioned steel 7 to 1200 ° C, 900 ° C
Shows the change in CPT when the rolling is completed and the cooling rate is changed drastically thereafter. That is, the CPT decreases as the cooling rate decreases, but especially at less than 1 ° C./sec, a sharp decrease occurs. Note that the heating, rolling, and cooling conditions shown above were simulated by simulating the thermal processing history of the laminated material in clad rolling, but in the actual clad rolling, it is necessary to consider the characteristics of the base material as well, and the temperature exceeds 1250 ° C. Such heating is not desirable due to the toughness of the base material. Although the rolling finishing temperature is lower than the heating temperature, it is generally 1100 ° C or lower in consideration of the toughness of the base material. Therefore, as the rolling and cooling conditions for seawater-resistant stainless steel, after heating to 1100 ° C or higher and 1250 ° C or lower,
It is necessary to finish rolling at 800 ° C or higher and then cool at 1 ° C / sec or higher.

(Function) Si is required to be 0.02% or more for deoxidation, but if it exceeds 1.0%, the corrosion resistance deteriorates, so this is made the upper limit.

Mn is also required to be 0.02% or more for deoxidation, but if it exceeds 2.0%, corrosion resistance deteriorates, so this is made the upper limit.

Cr is effective for improving pitting corrosion resistance and crevice corrosion resistance, and 18% or more is required for this purpose, but if it exceeds 27%, the formation of the σ phase is significantly promoted. The upper limit is 27%.

Mo is also effective for improving pitting corrosion and crevice corrosion resistance, and it is necessary to exceed 4.0%, but if it exceeds 7.0%, the formation of the σ phase is remarkably promoted. It is necessary to set% as the upper limit.

From the viewpoint of austenite phase stability, Ni is required to be 15% or more in such a component system as shown in FIG. However, since it is an expensive element, the upper limit must be 30%.

B is a particularly important element in the present invention, and if thermal processing history of clad rolling is presupposed, 0.0010% or more is necessary as shown in FIG. Also, if added in excess of 0.0055%, corrosion resistance and hot workability deteriorate, so
The upper limit was 0.0055%.

N has the effect of increasing the corrosion resistance, and it is necessary to contain 0.10% or more. On the other hand, addition of more than 0.25% is difficult within the range of the components of the present invention, so this is the upper limit.

Al is required to be 0.001% or more for deoxidation, but if it exceeds 0.30%, corrosion resistance deteriorates, so this is made the upper limit.

P and S are preferably as low as possible, but the lower limit is set due to steelmaking restrictions.
It was set to 0.0005%. If 0.050% <P and 0.010% <S, hot workability is impaired. Further, in order to further improve the hot workability or the corrosion resistance, the one according to the present invention has Cu ≦ 2.0%, W ≦
0.5%, Ti ≦ 1.0%, Nb ≦ 1.0%, V ≦ 1.0%, Zr ≦ 1.0
%, La ≦ 0.02%, Ca ≦ 0.02%, or one or more of them can be contained.

As described above, the present invention makes it possible to produce a seawater-resistant clad steel sheet by optimizing the components of the laminated material and the rolling conditions, and the conventional seawater-resistant stainless steel (solid) is 1100 ° C. By quenching from the above high temperature range, precipitation of intermetallic compounds such as Cr carbonitride and σ phase was suppressed, but the corrosion resistance in this case was mainly controlled by the amounts of Cr, Mo and N. However, if it is difficult to quench rapidly due to the characteristics of the base metal, such as clad rolling, in addition to the above components, B
Plays a big role. That is, as shown in FIG.
The reason that the addition of 0010% to 0.0055% improves the pitting corrosion resistance is that B suppresses the precipitation of Cr nitride in the cooling process after rolling.

In the rolling and cooling conditions, the heating temperature was set to 1100 ° C. or higher.
This is because in Mo and high N steels, Cr nitrides do not completely form a solid solution and impair pitting corrosion resistance. Also, when the rolling finishing temperature is less than 800 ° C. and the cooling rate is less than 1 ° C./sec, Cr nitrides are precipitated during rolling or cooling even if B is added, and the pitting corrosion resistance is lost. .

(Examples) Specific examples of the present invention are described below.

Example 1 The following Table 3 shows the stainless steel plates whose components are A to G.
Superposed on carbon steel having a composition of 0.20C-0.22Si-0.80Mn, heated to 1200 ° C, finished rolling at 850 ° C, and then 1.5
The results of evaluating the pitting corrosion resistance of the laminated material when cooled at ℃ / sec in a 10% ferric chloride solution are shown. The total thickness of the finished plate is 20 mm, including 3 mm for the laminated material and 17 mm for the base material.

Steels A and D satisfy the Pitting Index (= Cr + 3Mo + 17N) ≧ 41.0, but one of the gist of the present invention is the regulation of the amount of B; 0.0010% ≦ B ≦ 0.0055%, so the CPT is
As low as 55 ℃. Steels F, G, and H satisfy the regulation of the amount of B, but steel F regulates the amount of Cr; 18.0% ≤ Cr ≤ 27.0%, steel G regulates the amount of Cr and N amount; 0.10% ≤ N ≦ 0.25%, Steel H does not meet the regulations of the Pitting Index, so that the CPT is 55 ° C or less in all cases. On the other hand, Steels B, C and E satisfying all of the compositional ranges of the present invention have good corrosion resistance with a CPT of 65 ° C or higher.

Example 2 The following Table 4 shows the steels B and E satisfying the composition requirements of the present invention.
Laminated on low alloy steel with composition of 03-0.25Si-1.45Mn-0.03Nb-0.06V, and under various conditions, 30mm (laminating material 2mm, base material 28mm), 10mm (laminating material 2mm, base material 8mm)
The results of evaluating the pitting corrosion resistance of the laminated material in the case of rolling to 10% in a 10% ferric chloride solution are shown.

Condition J is that the cooling rate after rolling is the cooling condition of the present invention 1
C./sec or more, the condition L does not satisfy the heating temperature of 1100 ° C. or more and 1250 ° C. or less, which is the temperature range of the present invention, and the conditions K and O are the rolling finishing temperature of the present invention. Since it does not meet the requirement of 800 ° C or higher, both are C
PT is as low as 55 ℃ or less. On the other hand, all of the conditions I, M and N satisfying the conditions of the present invention show good corrosion resistance of CPT ≧ 60 ° C.

Example 3 The following Table 5 shows the stainless steel plates showing the components from P to U.
0.04C-0.3Si-1.1Mn-0.01Nb-0.01Ti superposed on a low alloy steel having a composition, heated to 1150 ° C, finished rolling at 850 ° C, and then cooled to 1.5 ° C / sec. The result of having evaluated the pitting corrosion resistance in a 10% ferric chloride solution is shown.

The total thickness of the finished plate is 23 mm, which is 3 mm of laminated material and 20 mm of base material.
In order to further improve the corrosion resistance or hot workability, steels P, W containing Cu, steels Q containing Ca, steels R containing Zb, Ce, steels S containing Ti, La, and Ti, In all of the steels T added with V, the conditions of the present invention are satisfied, so CPT ≧ 6
It has good corrosion resistance of 5 ℃. On the other hand, the steel U which does not satisfy the regulation of the amount of B in the present invention has a low CPT of 40 ° C.

"Effect of the Invention" According to the present invention as described above, the critical pitting temperature (CPT) in the 10% ferric chloride test is optimized by optimizing the composition system, rolling and cooling conditions in the clad material.
Is 60 ° C. or higher, and a clad steel sheet for seawater having excellent corrosion resistance in seawater can be appropriately produced and provided, and the invention has a large industrial effect.

[Brief description of drawings]

The drawings show the technical contents of the present invention. Fig. 1 is a diagram showing changes in the critical pitting temperature due to rolling and cooling conditions, and Fig. 2 is the maximum by ferric chloride test and seawater immersion. Chart showing the relationship with crevice corrosion depth, Figure 3 shows a summary of changes in critical pitting temperature with B content, and Figure 4 shows Pitt.
Chart showing the relationship between the ing index and the critical pitting temperature, No. 5
FIG. 6 is a diagram showing changes in critical pitting temperature with rolling temperature and rolling finishing temperature, and FIG. 6 is a diagram showing changes in critical pitting temperature with cooling rate after rolling.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C22C 38/54

Claims (2)

[Claims] 1. Si: 0.02 to 1.0 wt%, Mn: 0.05 to 2.0 wt%, Cr: 18.0 to 27.0 wt%, Mo: over 4.0 wt% to 7.0 wt%, Ni: 15.0 to 30.0 wt%, B : 0.0010 to 0.0055wt%, Al: 0.001 to 0.30wt%, N: 0.10 to 0.25wt%, Cr + 3Mo + 17N ≧ 41.0, 0.030wt% or less C as unavoidable impurities, P of 0.050wt% or less ,
When rolling a clad steel sheet in which stainless steel containing 0.010 wt% or less of S and the balance Fe is laminated on at least one side of the steel sheet, after heating to 1100 to 1250 ° C, hot rolling is performed, and rolling is completed at 800 ° C or more. And then cooling at 1 ° C./sec or more, a method for producing a clad steel sheet for seawater resistance. 2. Si: 0.02 to 1.0 wt%, Mn: 0.05 to 2.0 wt%, Cr: 18.0 to 27.0 wt%, Mo: over 4.0 wt% to 7.0 wt%, Ni: 15.0 to 30.0 wt%, B : 0.0010 to 0.0055 wt%, Al: 0.001 to 0.30 wt%, N: 0.10 to 0.25 wt%, 2.0 wt% or less Cu, 0.5 wt% or less W, 1.0 wt% or less Ti, 1.0 wt% or less Nb, V of 1.0 wt% or less, Zr of 1.0 wt% or less, La of 0.02 wt% or less, Ca of 0.02 wt% or less, Ce of 0.02 wt% or less, or one or more of And Cr ＋ 3Mo ＋ 1
A clad steel plate obtained by superposing on at least one side of a steel plate a stainless steel which satisfies 7N ≧ 41.0 and contains 0.030 wt% or less of C as unavoidable impurities, P of 0.050 wt% or less, S of 0.010 wt% or less and the balance Fe. 1100 ~ 12 when rolling
A method for producing a clad steel sheet for seawater resistance, which comprises heating to 50 ° C, hot rolling, finishing rolling at 800 ° C or higher, and then cooling at 1 ° C / sec or higher.