JPS5952226B2 - Ferritic stainless steel with excellent rust and acid resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ferritic stainless steel that has excellent rust resistance, acid resistance, and good workability.

In general, ferritic stainless steel is inexpensive because it does not contain Ni, and has excellent stress corrosion cracking resistance, so it is widely used as a corrosion-resistant material.

However, its rust resistance, particularly its rust resistance due to aqueous solutions containing chloride ions, and its acid resistance are significantly inferior to austenitic stainless steel. Among ferritic stainless steels, steel types such as SUS434 containing MO have considerably improved rust resistance and acid resistance, but due to the recent rise in MO prices, MO-containing ferritic stainless steel,
Less steel has fewer advantages in terms of economy. For example, existing S
Materials like US43O steel do not have sufficient resistance.

Moreover, materials for such uses are strongly required to be economical in addition to good processability and surface quality after processing. The purpose of this invention is to greatly improve the rust resistance and acid resistance of inexpensive ferritic stainless steels. The objective is to provide stainless steel with excellent properties.

The feature of this invention is that, in addition to the combination of Cr, Cu, Nb, and other components, the impurity element S, which has not been studied in the past from the viewpoint of improving corrosion resistance, is strictly regulated.

As will be described in detail later, it has been confirmed from the numerous test results of the present invention that by suppressing S to an extremely low level, the rust resistance and acid resistance of ferritic stainless steel are surprisingly improved. This invention was made based on the above findings, and includes C: 0.05% or less, Si: 0.1 to 5.0%.
%, Mn: 0.1 to 5.0%, S: 0,005% or less,
Cu: 0.3~2.0%, Cr: 10,00~30
．． 00%, N: 0.05% or less, Nb: 0.2-1.
Contains 0% (however, Nb%≧C%×8+0.2%),
Ti: Q, 0.20% and Zr: as necessary
Contains one or two of 0.01 to 0.1% of Ni: Q. 3 to less than 1.5% and MO: Contains one or two of 0.1 to 2.5%, with the remainder consisting of Fe and other unavoidable impurities, and has particularly good rust resistance and It is a ferritic stainless steel with excellent acid resistance, moldability, and surface quality. Next, the reason why the composition range of the ferritic stainless steel of the present invention is limited as described above will be explained.

(a) C and N C and N components have a large effect on the rust resistance and acid resistance (rust and acid resistance) of steel, and the lower the content of C and N components in steel, the better the rust resistance. Acid resistance improves and becomes more stable.

Moreover, as the Cr content increases, the desired excellent rust and acid resistance cannot be ensured unless the contents of C and N components are conversely reduced. The allowable C and N values decrease significantly as the Cr concentration increases, and for example, a C+N value of 200 ppm or less is desirable around 19% Cr. Since the steel of the present invention also includes steel types with a low Cr concentration of 10.0%, the upper limit values were set at 0.05% for each. Reducing C and N also contributes to improving workability. (b) Si Si is a useful component with a deoxidizing effect, but if its content is less than 0.1%, sufficient deoxidation cannot be achieved; on the other hand, if it is contained in excess of 5.0%. The content may be reduced to 0.1 to 5.0%, as the processability may deteriorate.
It was determined that

(c) Mn Mn has a desulfurization deoxidizing effect and a hot workability improving effect, but if its content is less than 0.1%, the desired effect cannot be obtained in the above effects, whereas if it exceeds 5.0%, The content was determined to be 0.1 to 5.0% because even if it is contained, no further improvement effect can be obtained due to the above action.

(d) SS Standards for stainless steel only specify an upper limit of 0.03%1 or less, but there is no strict regulation of this, especially from the perspective of improving corrosion resistance. do not have.

FIGS. 1 and 2 are plots of the relationship between S content and acid resistance and rust resistance of ferritic stainless steels from Examples described later (test conditions will also be described later).

As is clear from FIG. 1, the acid resistance improves significantly as the S content decreases. In particular, S is 0.002
% or less, corrosion virtually disappears. 9 in Figure 2
As shown, the tendency of rusting due to NaCl aqueous solution also decreases as the S content decreases, and when the S content becomes 0.05% or less, large-scale rusting (red rust) disappears. Considering these test results and the harshness of the test conditions, practically,
It can be said that the object of the present invention can be achieved by regulating S to 0.005% or less. However, for applications with strict specifications such as automotive molding materials, S: 0,002%
The following is desirable. Methods for reducing S in this way include one method using basic slag, one using Ca-Si
, a method using additives such as metallic Ca, metallic Mg, and rare earth elements. (e) Cu The Cu component has the effect of imparting excellent rust and acid resistance to steel, but if its content is less than 0.3%, the desired effect cannot be obtained; on the other hand, 2. If the content exceeds 0%, hot workability deteriorates, so the content was set at 0.1 to 2.0%.

(f) If the Crj content is less than 10.0%, the normal corrosion resistance of ferritic stainless steel itself cannot be secured, while if the content exceeds 30.0%, embrittlement becomes noticeable. This not only causes manufacturing problems, but also prevents the ultra-low sulfurization effect from being seen.
．． It was set at 0 to 30.0%.

(g) Nb Nb has the effect of fixing the C and N components in the steel without deteriorating the surface properties, improving rust and acid resistance, and further improving formability by making the crystal grains finer. Therefore, in order to obtain the desired effect on these actions, 0.2
% or more, and in relation to the C content, an empirical formula determined based on various experimental results: Nb%≧C1%X
It is necessary to contain Nb in an amount that satisfies 8+0.2%, but if it is contained in excess of 1.0%, intermetallic compounds will be formed and workability will deteriorate, so the content should be 0.2 to 1.0%, Nb%≧C%X80.2
% shall be satisfied.

(h) Ti and Zr Since Ti and Zr are elements that strongly fix C and N components in steel together with Nb, they may be added depending on the application.

. Ti: less than 0.01%, and Zr: 0.
If the content is less than 0.01%, the desired improvement effect on the above action cannot be obtained, while if the content exceeds Ti: 0.20% and Zr: 0.1%, a large amount of grown products such as TiN and ZrO2 will be produced. Since the presence of Ti causes frequent ground scratches and makes it difficult to ensure excellent surface quality, the content is reduced to 0.01 to 0.2.
0%, Zr: 0.01 to 0.1%. (i)
Ni, MONi, and MO have the same effect of further improving the rust and acid resistance.

According to the present invention, by reducing the amount of S and adding Cu and Nb as described above, a ferritic stainless steel can be produced which has excellent rust and acid resistance without containing expensive alloying elements such as MO and Ni. is obtained.

However, the corrosion resistance is further improved by adding MO and/or Ni. If Ni: less than 0.3% and MO: less than 0.1%, no further improvement effect can be obtained due to the above action. Since the inclusion of Ni impairs the economic efficiency of steel materials, the content should be adjusted to Ni: 0.3 to 0.3, respectively.
MO: less than 1.5%, MO: 0.1 to 2.5%. Next, the ferritic stainless steel of the present invention will be specifically explained with reference to Examples. [Example 1] Steel having the composition shown in Table 1 was prepared with a capacity of 20 kg.
It is melted in a vacuum melting furnace and cast into an ingot.
Next, the ingot was hot-rolled to form a hot-rolled plate with a thickness of 3 mm, and after being held at a temperature of 1000°C for 10 minutes, an air-cooling annealing treatment was performed to obtain steels 1 to 10 of the present invention.
and Comparative Steels 11 to 18 were manufactured, respectively.

In addition, comparative steel 17 is made of SUS43O, and comparative steel 18 is made of SU
These have component compositions corresponding to those of S434. Inventive steels 1 to 7 and comparative steels 11 to 14 are 17Cr-based, and inventive steels 8 to 10 and comparative steel 15
, 16 are 22Cr stainless steel. A test piece with dimensions of 70 mm length x 30 mm width x 3 mm thickness was cut from these steels, and the surface of the test piece was wet polished with No. 1200 Emery paper, and then polished with 5% NaCl at a temperature of 50°C.
A rust resistance test was conducted by repeating wet and dry cycles, immersed in an aqueous solution for 25 minutes, taken out, and dried for 5 minutes.
After 10 cycles, 40 cycles, and 395 cycles of dry and wet cycles, the rusting state on the polished surface of the test piece was visually observed. The observation results are also shown in Table 1. Table 1 also shows the acid resistance test results.

For the acid resistance test, use the same test piece as in the rust resistance test above, immerse this test piece in a boiling 0.0 IN hydrochloric acid aqueous solution, and measure the average weight loss per 1 m2/1 hour. It was done by From the results shown in Table 1, 1
The 7Cr-based steels 1 to 7 of the present invention are the same as those of Lemo Comparison Ml7 (S
US43O) It has significantly superior rust resistance and acid resistance compared to the steels 1 to 6 of the present invention shown in Fig. 1 and comparative steels 11 to 14 (the numbers in the figure indicate the Corresponding to the steel types in the table, two points are shown for each steel), the relationship diagram between S content and corrosion rate, and the invention steels 1 to 7 and comparison steels 11 to 14 shown in Figure 2 (the numbers in the figure are As is clear from the relationship between the S content and the number of rusting points for the steel types in Table 1 (◆ indicates large rusting), S content is higher than 0.005%. It is clear that the steels 5 to 7 of the present invention, which contain either or both of Ni and MO, have even better rust resistance and acid resistance than Steels 11 to 14. be.

Particularly noteworthy is the fact that 17 does not contain Ni or MO.
Cr-based steels of the present invention 1 to 4 are SU containing about 1% MO.
It exhibits corrosion resistance comparable to S434 (Comparative Steel 18).

On the other hand, among the 22Cr-based steels, the low-S steel of the present invention exhibits excellent rust and acid resistance that far exceeds comparative steels of the same series. [Example 2] AOD (ArgOnOxygenDecarbariz)
The pitting corrosion resistance (test conditions: 0.01M
(in NaCl aqueous solution), crevice corrosion resistance and press formability were tested.

The test piece was a hot-rolled sheet manufactured under the same conditions as Example 1, further cold-rolled, and annealed at 950° C.
It was sampled from a cold-rolled sheet of 4 mmt. The test results are shown in Tables 3 and 4. These tables include SUS43O, 4 for comparison.
The test results of No. 34 (comparative steel No. 17 and No. 18 in Table 1, respectively) are also listed. From the results in Tables 3 and 4, the corrosion resistance of the 17Cr ferritic stainless steel of the present invention,
It far exceeds SUS43O and is comparable to SUS434, and has excellent press workability.
It can be seen that it surpasses both SUS43O and SUS434 and has excellent zinc resistance. Figure 3 shows the continuous spraying test of 5% NaCl aqueous solution according to JIS on cold rolled annealed steels of the invention steel 19 in Table 2 and SUS43O, 434 (comparative steels 17, 18 in Table 1) for comparison Q. This is the result.

The steel of the present invention did not rust at all even after 250 hours of testing, whereas SUS43O and 434 rusted after 60 hours and 85 hours, respectively. In Examples 1 and 2, 17Cr and 22Cr stainless steels were selected from the ferritic stainless steels of the present invention.
Although Cr type is selected as a representative example, the effect of reducing S of the present invention and improving rust resistance and acid resistance by adding Cu and Nb is in the range of Cr: 10.0 to 30.0%. It is exhibited in all ferritic stainless steels.

According to this invention, it is possible to obtain stainless steel that has corrosion resistance superior to steel types using such alloys and has excellent workability and surface quality after processing (no zinc) without using expensive alloy components. .

Such steel materials are ideal as exterior materials for mass-produced products where economy is emphasized, and rust resistance, workability, and aesthetics are required, as well as exterior case materials for various appliances.
It can be expected to have a wide range of uses, such as kitchen utensil materials.

[Brief explanation of the drawing]

Figure 1 shows the relationship between corrosion rate and S content in 0.01N boiling hydrochloric acid aqueous solution, Figure 2 shows the relationship between 5% NaC
FIG. 3 is a diagram showing the relationship between the rusting state and the S content in a dry-wet repeated test using a 5% NaCl aqueous solution. FIG. 3 is a diagram showing the results of a 5% NaCl aqueous solution spray test.

Claims (1)

[Claims] 1 C: 0.05% or less, Si: 0.1 to 5.0%, M
n: 0.1 to 5.0%, S: 0.005% or less, Cu:
0.3-2.0%, Cr: 10.0-30.0%, N:
0.05% or less, Nb: 0.2 to 1.0% (however, Nb
%≧C%×8+0.2%), and the remainder is substantially F.
Ferritic stainless steel with excellent rust resistance and acid resistance, characterized by having a composition (the above weight %) consisting of E and inevitable impurities. 2 C: 0.05% or less, Si: 0.1-5.0%, M
n: 0.1 to 5.0%, S: 0.005% or less, Cu:
0.3-2.0%, Cr: 10.0-30.0%, N:
0.05% or less, Nb: 0.2 to 1.0% (however, Nb
%≧C%×8+0.2%), and further contains Ti:0.
Zr: 0.01 to 0.20% and Zr: 0.01 to 0.1%. Ferritic stainless steel with excellent rust resistance and acid resistance. 3 C: 0.05% or less, Si: 0.1-2.0%, M
n: 0.1-2.0%, S: 0.005% or less, Cu:
0.3-1.0%, Cr: 10.0-30.0%, N:
0.05% or less, Nb: 0.2 to 1.0% (however, Nb
%≧C%×8+0.2%), and further contains Ni:0.
3 to less than 1.5% and one or two of Mo: 0.1 to 2.5%, with the remainder consisting essentially of Fe and unavoidable impurities (weight %). Ferritic stainless steel with excellent rust and acid resistance. 4 C: 0.05% or less, Si: 0.1 to 5.0%, M
n: 0.1-2.0%, S: 0.005% or less, Cu:
0.3-2.0%, Cr: 10.0-30.0%, N:
0.05% or less, Nb: 0.2 to 1.0% (however, Nb
%≧C%×8+0.2%), and further contains Ti:0.
01 to 0.20% and one or two of Zr: 0.01 to 0.1%, and Ni: less than 0.3 to 1.5% and Mo: 0.1 to 2.5%. A ferritic stainless steel having excellent rust resistance and acid resistance, characterized in that it contains one or two of the above, with the remainder essentially consisting of Fe and unavoidable impurities (weight percent).