JPS5983749A - Ferrite stainless steel having wheatherability - Google Patents

Abstract

PURPOSE:To achieve the enhancement of rust inhibiting property, by containing C, Si, Mn, S, Cr, N, Cu, Ni and Mo in predetermined ratios. CONSTITUTION:The titled steel contains 0.08% or less C, 1% or less Si, 0.3% or less Mn, 0.003% or less S, 10-20% Cr, 0.05% or less N and, in addition, one or more of 0.2-0.8% Cu, 0.2-0.8% Ni or 0.2-0.8% Mo. This steel excellent rust inhibiting property and especially suitable for an exterior material.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a weather-resistant ferritic stainless steel that has excellent rust resistance and is particularly suitable for exterior use.

Conventionally, ferritic stainless steel that can be used for decoration is 5US450°5tJS4.
34 is 8U8504 for austenitic stainless steel.
is used. Austenitic stainless steel S
Although TJ s304 has superior properties such as rust resistance, workability, and weldability compared to S U 8450 and 5TJS454, it is relatively expensive9.Because the surface has a yellowish tint, it cannot be used as a plated material. Ferritic stainless steel is preferred because the color tone does not harmonize with other materials. Among ferritic stainless steels, 5USd 30 is advantageous in terms of price, but it has poor rust resistance and cannot be used as an exterior material. On the other hand, 5us4s4 contains Mo,
Although it is widely used due to its relatively high rust resistance, its rust resistance is not sufficient in environments contaminated with chlorine ions and sulfur dioxide gas, such as coastal areas and industrial areas, and it is difficult to weld. When exposed to high temperatures, such as when exposed to high temperatures, Cr carbides are formed at grain boundaries during the cooling process, and a Cr-depleted layer is formed in the vicinity, resulting in deterioration of rust resistance. Furthermore, since it contains about 1 oz. of Mo, which is expensive and limited in terms of resources, it has the disadvantage that it is difficult to provide a stable supply industrially.

The present invention has been studied in view of the above-mentioned advantages and disadvantages.

Rust resistance is improved by reducing the impurity elements Mn and S in 5IJS430 series steel, and the effect is significantly increased by adding Nb. Cu or Mo, T
By adding i and further adjusting the composition if necessary, it is possible to obtain a steel that has rust resistance equivalent to or better than 5TJS304 and is optimal in terms of price as a weather-resistant ferritic stainless steel suitable mainly for exterior use. This is what I found.

The present invention basically consists of CD08% or less, Si1.0% or less, Mn0.5% or less, 80.003% or less, Cr10
Provided is a weather-resistant ferritic stainless steel containing up to 20% NO, 0.05% or less, and the balance consisting of iron and unavoidable impurities.

In addition to this basic composition, 0.2 to 0.8% Cu
, 0.2-0.8% Ni, 0.2-0.8%
Mo.

0.5-0.8% (1) Nb, 0.05-0.2% T
Provides steel with iwo added alone or in combination.

In preferred embodiments, these steels have an amount of C of 0.06
%J or less, and the amount of N is limited to 0.02% or less.

If Nb and '1'iAf are included, 0. j<(Nt+
+Ti)<0.8%.

The reasons for limiting the composition of the steel of the present invention are as follows.

C, N, 5US430 and 5TJS4 in terms of rust resistance
34, but when 2-strength forming or welding is performed, C and N should be low in terms of workability, rust resistance and intergranular corrosion resistance of welded parts, or toughness. The lower the value, the better. - Lowering the N content will lengthen the smelting time, leading to an increase in manufacturing costs. This content can be allowed to a certain extent by adding an appropriate amount of Nb, which has the effect of fixing C and N. In the steel of the present invention, C≦0.
008%, N<0. [35%, but if workability and corrosion resistance or toughness of the welded part are particularly required, c
kuo, os%, Nku [1.02%.

Si: Si has a deoxidizing effect, and in the steel of the present invention, it reduces Mn, which has a similar effect as described later, from the viewpoint of rust resistance, so the larger the amount, the better.

However, if there is too much, it hardens the steel and impairs workability.

It is also harmful to hot cracking during welding and to the toughness of bath joints, so the upper limit is set at 1.0%.

Mn: Mn has a strong sulfide-forming ability and forms MnS which is unstable in an aqueous solution and becomes a starting point for rusting due to s quasi-bonds in steel, which deteriorates rust resistance, so a lower value is preferable.

As the Mn content decreases, the pitting corrosion potential becomes more noble and the rust resistance is improved. In order to obtain significant rust resistance, Mn should be 0.
．． It is necessary to keep it below 5%.

S: As mentioned above, S combines with Mn and is harmful to rust resistance, so the lower the S content, the better. In order to obtain significant rust resistance,
S needs to be below 0.003-S L,I. i′i0.0 for materials used under particularly harsh conditions
It is desirable to keep it below 0.02%.

Cr: Cr1i general corrosion resistance (〆L has a good stilting effect, stainless steel (is an essential element for moss, and doubles the passive effect) requires at least 10% Cr.

Simply increasing Cr alone has a small effect on the rusting property ζ.

The steel of the present invention has good resistance and benign properties due to the reduction of Mn and S, or depending on the required inventive resistance, C
o, Mo o) An element with a strong effect of improving corrosion resistance Q) C++.

The effect of Mn is an increase for Cr [J makes it even more kennel. However, the increase in C+ jJ (Jζ magi
II work (14- cracks and rough firewood occur<)-a-<, and i! 6 (Qualitativeness is 1 yaw. From the talented Or's 1] i, the production is difficult and leads to an increase in the impurity value. 20% of these Koike are limited. .

Nb: Nb (', commonly known as an element that fixes N) is added to improve workability and properties of welded joints. The present inventors have found that Nb has an effect of improving corrosion resistance in addition to the above-mentioned effects. The lower limit of the amount of Nb is set from the point of preventing intergranular corrosion and the amount necessary for fixing C and N, and is set at 0.5% based on the results of the Queen's experiment. On the other hand, if the Nb content is too high.

The upper limit is set at 0.8% because it impairs the resistance to hot cracking during welding by 11% and impairs the toughness of 1m joints.

Ti: Ti has a stronger sulfide forming ability than Mn.

Moreover, like Nh, Ti sulfide is stable in an aqueous solution and is effective in improving invention resistance. Ti is effective in improving weld zone toughness and hot cracking resistance during welding, so if these properties are important, a small amount of Ti is added in addition to the above-mentioned Nb. If C is added at 105% or less, the effect of improving r1 cannot be obtained. However, the content of Ti is 0.20%.
Exceeding this limit will deteriorate the surface texture of the material, so set the second limit to 0.
It shall be 20%. Note that Ti is also a fixed element for C and N, so when adding Nb and I, 0.6< (N
h+T i )≦0.8%.

Cu, Ni, Mo: (, +i, Ni, Mo
] is an effective element for enhancing side food properties, and is also effective for improving inventiveness.

In the present invention, by reducing Mn, S ;i,',
Alternatively, Nh (silkworm JJa provides excellent 1 at 01, but the addition of C++, Ni, and Mo further increases the resistance to invention +<U;t.C++, M
Since o1iCr exhibits an effect of improving button erosion in a paleomorphic manner, it is desirable to increase the amount of Cr in order to effectively utilize these elements. The effects of C,'u, Ni, and Mo are JM when added in an amount of 0.2% or more;
Since oNi has low stress corrosion cracking susceptibility and may even precipitate martensite, the second limit is set at 0.8%. M+1 improves inventiveness resistance as the amount added increases, but
Since it is economically expensive and the features of the present invention are impaired, 08
The upper limit is %.

The invention will be explained in detail with reference to a first embodiment.

Table 1 shows the comparative composition of the uninvented steel used in the experiment and the comparison steel. These 1(i4) were melted by a conventional method and subjected to each of the following nine tests.

First, cut steel 1-7, 11, 15.16 into 10 x 10 plates, attach heat lead wires and embed them in hardening resin.
J I 5-(1+
Based on 0577, I used C117 with a porosity of about dL.

The results are shown in Figures 1-4. FIG. 1 shows the relationship between the Mn content and the pitting potential (relative to the standard Amagi electrode) for the steel of the present invention that does not contain Nb and the comparative @lti (16Crm). The pitting potential is a measure of rust resistance, and as is clear from Figure 1, the pitting potential increases as the Mn content decreases, with a significant increase at 0.5% or less. Note that the S content of these samples is all 0.001% or less.

Figure 2 shows a comparative fIA (17Cri) of the present invention steel containing Nb.
The relationship between Mn content and pitting potential of Nb steel is shown.

The S content of all samples in this test was Q,002% or less. As is clear from the figure, the amount of Mn is 0. A significant increase in pitting corrosion potential is seen below 'S%.

FIG. 6 shows the relationship between the S content and the pitting potential of the steel of the present invention that does not contain Nb and the comparison steel (16Cr steel). The Mn content of these samples is 0'5% or less. As is clear from the figure, a significant increase in pitting corrosion potential is observed when the amount of 8 is below 50 ppffL, that is, 0.005%.

From the above results, 2MnMn content is 0 or less, S content is 0.00!1
It is observed that a significant increase in pitting potential is achieved below %.

The effect of improving the invention resistance due to the reduction of Mn and S is due to the reduction of sulfides mainly consisting of MnS, which is the starting point for invention. It has already been known that rust resistance is improved by reducing S, but it is not sufficient to reduce the amount of S, so it is necessary to reduce the amount of Mn at the same time as mentioned above, or to increase the amount of Nb or By further adding T1 and improving the corrosion resistance of the sulfide itself, the rust resistance of the steel is further improved. The object of the invention is thus achieved.

The improvement in rust resistance due to the reduction of Mn is related not only to the reduction of sulfides but also to their qualitative changes.
When observed with PMA, it was observed that the Cr concentration in sulfide increased by reducing Mn.
It is thought that the improvement effect due to the reduction is due to the improvement in the corrosion resistance of the sulfide itself.

Next, steel 2.1, 5.6 was used as a short fence-shaped test piece of 10'0 x 150y+i, and a CASS test (acidic saline spray) shown in JISDO201 was conducted for 320 hours to examine the state of the invention. Figure 4 shows the appearance after the test. In this test,
8. It was found that the invention from the specimen surface decreases as Mn decreases, especially when Mn is 0.5% or less and S is 0.00%.
For steels 5 and 6 with 2% or less, there is no invention from the surface other than the periphery of the specimen.

In order to investigate the weather resistance of Steels 12 to 22, the present inventors cut out a 100 x 150 cold rolled steel plate and
After 00 polishing, an exposure test was conducted on the coast for 3 months.

For evaluation after the test, a transparent plate with 5 city square grids marked on it was placed on the test piece and observed, (number of invented grids/total number of grids) x1
00 is the invention rate, and 0 is further ranked according to the degree of invention.
．． The invention rate was multiplied by the red rust weighting coefficient of 0.01.0.02.0.05. The results are shown in Table 2. By comparing Steel 12 and 17.

The effect of lowering Mn and S was confirmed, and the weather resistance of Invention Steel 17 with increased Cr content and addition of Cu and Ni was compared to Comparison #42.
5 (SL+8504). Mn.

The weathering resistance improvement effect of Nb addition for steels with low S content was as follows: Steels 11 and 15.16 and Steels 15°14 and 18, -1
It is clear from the comparison of 9. The weather resistance of f1418 and f19 of the present invention is considerably superior to that of comparative fIA2'5.

Furthermore, from a comparison of Steel 16 and fM20 with Steel 18 and Steel 21, the effect of improving weather resistance by adding Ti was recognized.

In an atmospheric exposure test, N was added to steel containing Mn and S of normal density
Although no improvement in inventiveness is observed even when B is added, inventiveness is further improved when Nb is added to the steel of the present invention, in which Mn is lowered to 0.3% or less and S is lowered to 0005% or less. It is recognized that the effect of improving the invention resistance by Nb addition is low Mn,
iii Low S@l! It was found that it appears in iI.

The effect of Nb addition on improving inventiveness also seems to be related to changes in sulfide.

Nb is seen in the sulfide by EPMA observation. Nb sulfide is stable in an aqueous solution, and combined with the reduction in Mn and S, the sulfide becomes more stable, and it is thought that the invention resistance is improved.

Figure 5 shows 17-19% of the thickness of a cold-rolled plate of 1 m and m thickness.
TIG welding was applied twice to Cr steel.

Sulfuric acid based on JJS G0575 for intergranular corrosion test
A copper sulfate corrosion test was conducted, and cracking was determined by bending after the test, and it can be seen that intergranular corrosion can be prevented with an Nb content of 05 coefficient or higher.

As explained above, five aspects of the present invention include Mn, which is an impurity element,
By severely limiting the amount of S.

To provide an inexpensive steel that is almost comparable to 5TJS304 without relying entirely on the use of Mo or by including a small amount of Mo, and to provide a steel with a property superior to that of SUS 04 by adding Nb. , its contribution to industry is extremely large.

[Brief explanation of the drawing]

FIGS. 1 to 5 are diagrams showing the pitting corrosion potential of the steel of the present invention and comparative steel in saline water. FIG. 4 is a photographic diagram showing the invention resistance of the invention steel and comparative steel under acidic saline jetting. FIG. 5 is a diagram showing the intergranular corrosion resistance of the welded portion of the steel of the present invention and the comparative steel in a boiling sulfuric acid/copper sulfate solution. Patent applicant: Nisshin Steel Co., Ltd. Agent Patent attorney: Masahiro Matsui (2 others) Figure 1 Mn ('10) (The number in the figure is the example number) Second factor Mn ('10 (in the figure) The number is Example number 9 Third cause S (ppm) (The number in the figure is the example number) Figure 4 Steel 6 Steel 5 Figure 5 C+N (ppm) (The number in the figure is the example number)

Claims (1)

[Claims] 1. CD, 08% or less, Si1. l] 1 or less, Mn
0.5% or less, S0.005% or less, Crl O-
A weather-resistant ferritic non-stainless steel containing 20% NO, 05 or less, with the balance consisting of iron and unavoidable impurities. 2, C0.08% or less, 8i1.0% or less, Mn0.
5% or less, 80.003% or less, Cr10-2'O
%, NO, 05 or less and Cu O, 2-0,8%,
NiO, 2-0.8%, M. 0.2 to 0.8%] of one or more kinds. A weather-resistant ferritic stainless steel consisting of balance iron and unavoidable impurities. 3, C[], 08% or less, Si 1.0% or less, Mn0.
3% or less, 80.005% or less, Cr10-20%
Weather-resistant ferritic stainless steel containing NO, 05 or less, Nb 0.3 to 0.8%, the balance consisting of iron and inevitable impurities. 4, CD, 08% or less, Si 1.0% or less, MnO ，
! 1% or less, S0.005% or less, Cr10-20%
, NO, 05 or less, NbO, 5-0.8%, TiO,
A weather-resistant ferritic stainless steel containing 0.05 to 0.2%, the balance consisting of iron and unavoidable impurities. 5, CD, 0.8% or less, Si 1.0% or less, Mn0.
5% or less, 80.004% or less, Cr1O-20%, N
Below the O,05 ratio, NbO,3-0,8% and Cu O,2
-0.8%, NiO, 2~0.8%, MoO,
, 2-0.8% of one or more types, with the balance consisting of iron and unavoidable impurities. +S, C0.08% or less, Si1. '0% or less, M
n0.3% or less, S0.005% or less, Cr'1'
o -20%, NO, 05% or less, Nb0.5-08%
, Ti0.05-0.2% and CuO,2-0.8%,
A weather-resistant ferritic stainless steel containing one or more of NiO, 2-[ ], 88% Mo 0.2-0.8, and the balance consisting of iron and inevitable impurities.