JPS6289848A - Two-phase stainless steel for rolling stock having high strength and high corrosion resistance and excellent in young's modulus and hot workability - Google Patents

Abstract

PURPOSE:To improve Young's modulus and hot workability and to prevent deterioration in strength in a weld zone after welding by limiting respective amounts of C, Si, Mn, Cr, Ni, Cu, Mo, rare earth elements, etc., and the value of Nibal represented by a specific expression. CONSTITUTION:The titled stainless steel consists of, by weight, <=0.05% C, 1-5% Si, 3-10% Mn, 17-22% Cr, 1-7% Ni, 0.5-3% Cu, 0.5-3% Mo, one ore more kinds among 0.005-0.04% rare earth elements, 0.005-0.04% Mg, 0.001-0.006% B and 0.002-0.01% Ca, and the balance Fe and has a Nibal value of -12--6. The above Nibal value is represented by -1.1{Cr(%)+1.5XSi(%)+0.5XNb(%)+Mo(%)}+30{ C(%)+N(%) }+0.5XMn(%)+0.3XCu (%)+Ni(%)+8.2.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a high-strength, high-corrosion-resistant duplex stainless steel for vehicles that has a high Young's modulus, good hot workability, and does not deteriorate the strength of the welded part after welding. It is about turbidity.

<Prior art and its problems> In recent years, from the viewpoint of labor and energy saving, there has been a strong demand for unpainted ML and @Ki (He), and thinning of materials by using high-strength stainless steel materials has been promoted. There are, but
To deal with these issues, currently 5US301 is mainly used.
The use of metastable austenitic stainless steel hard materials such as 5US304 and 5US201, mainly low carbon materials, has become common.

However, these metastable austenitic stainless steels (typically 5US301) are cold rolled (temper rolling) to generate deformation-induced martenite to obtain high strength. It is undeniable that the Young's modulus deteriorates due to inter-rolling and the amount of deflection of the material will inevitably increase, so when used as a vehicle material, the wall thickness should be thicker than calculated based on the strength value. The reality was that it was necessary and it was not possible to reduce the light to a sufficient degree.

Moreover, these metastable austenitic stainless steels are cold-rolled to achieve the desired strength, so the strength of the welded part after welding is significantly reduced, so reinforcing materials must be used or the thickness of the material must be increased. (1), and in this respect, it could not be said to be a sufficiently favorable material for making the vehicle light '+1.

In this way, 5U, which is currently commonly used as a material for vehicles,
S301, 5US304 and S U 8201 stainless steel hard materials had many unresolved problems such as a decrease in Young's modulus and deterioration in I6 joint strength.

<Means for Solving the Problems> Based on the above-mentioned problems found in current steel materials for vehicles, the present inventors have developed a method to improve cold rolling such as skin pass rolling, which causes a decrease in Young's modulus. We provide high-strength stainless steel materials that have sufficient strength, elongation, and corrosion resistance required for single-use materials without having to use them, and also have sufficient hot workability and weld strength, which are essential for manufacturing vehicle materials. As a result of conducting research, the following knowledge (aJ Hege) was obtained.

That is, (a) Various stainless steels are currently known in addition to the austenitic stainless steel mentioned above, but among these, two-phase stainless steel, which has two phases, a ferrite phase and an austenite phase, is a It has sufficiently high strength and elongation even without rolling, and there is no weakness in the strength of the welded part, and the strength of the welded part is almost the same as the base material. Something that can be easily achieved.

Figure 1 is a diagram showing the relationship between the structure of a stainless steel key, tensile strength, and elongation. From Figure 1, it can be seen that two-phase stainless steel consisting of a ferrite phase and an austenite phase has a good balance between strength and elongation. It is clear that the material has a tensile strength of 801'yf/- or more, which is sufficient as a key material for a vehicle. Note that the symbol "A" in No. 1 indicates the austenite phase, the symbol rMJ indicates the martenite phase, and the symbol rFJ indicates the ferrite phase.

fbl The Young's modulus of the above ferritic-austenitic duplex stainless steel is greatly influenced by the N1ha7 value calculated by the formula %, and by adjusting the Nihad value as small as possible, it can be fully satisfied as a steel material for vehicles. Young's modulus can be ensured. In addition, from now on, % representing the ingredient ratio is weight)
4i%.

Figure 2 is a diagram showing the relationship between the Ni ha value and Young's modulus of ferrite-austenite duplex stainless steel repair. It is clear that a ratio of 18nnnKqf/- or more can be maintained.

(C) However, the elongation of ferrite-austenite dual-phase stainless steel Tsukuda improves as the Ni hal value increases. Figure 3 shows the relationship between Ni ha/value of ferrite-austenite dual-phase stainless steel and elongation. It is clear from FIG. 3 that elongation of 20% or more can be ensured by adjusting the Ni had value to -12 or more.

(dl) Therefore, by adjusting Nihad (@) in consideration of both Young's modulus and elongation, a high-strength two-phase stainless steel key for vehicles with good Young's modulus and elongation and no deterioration in weld strength can be obtained. To be done, (el
When MO is added to the ferrite-tostenite duplex stainless steel described in A'l, the corrosion resistance of the stainless steel, particularly the corrosion resistance to non-oxidizing acids, pitting corrosion resistance, and plowing resistance, is improved by 1. .

(f) When one or more of rare earth elements, Mg, B, and Ca is added to a ferritic-austenitic duplex stainless steel, the hot workability of the stainless steel improves by -1. thing.

fgl Furthermore, when N is added or a combination of N and corner is added to the ferrite-austenite two-phase stainless steel key to which one or more of Mo, rare earth elements, Mg, B, and Ca is added, the stainless steel becomes cloudy. Improved strength.

This invention was made based on the above knowledge, and includes the following: Stainless steel material for vehicles, K: C: 0.0595 or less, si: more than 1 to 5%, Mn:
3S ~10%, Cr: 17~22%, N+: 1~7
%, Cu: 0.5-3%, Mo: 0.
Contains 5 to 3% rare earth elements: O, ('105 to 0.040%, Mg:
O,OO5~O,n4(1%,B:0.Onl
to O, 0f16%, Ca: 0. (102~0
．． (Contains one or more of 110Q4, or further contains 0.20% of N:O, (14) alone or in combination with 0.05 to 0.50% of Nb. , the remainder consists of Fe and unavoidable impurities, and Ni ba/value=1.1{Cr(Cr(%1 +1.
5 X5i (961 + 0.5 × Nbi system + Mo (%l
}+30(Cf%) 10N(%1}+0.5X Mn (
%}+0.3×Cu(%) +Ni [) −H,2 where the Ni had value according to the formula is [−12 to −6]
It is characterized by ensuring wearable base metal strength, Young's modulus, corrosion resistance, hot workability, and weld strength by being constructed of phase stainless steel.

Next, in the high-strength duplex stainless steel for vehicles of the present invention, the composition ratio and Ni ha7 value WO;

(1) C The C component has the effect of increasing the strength of stainless steel, and from this point of view it is a preferable element, but since a high C content causes deterioration in corrosion resistance, the C content should be 0.
05X or less.

1ii) Component 1 in St 8 has the effect of improving the strength of stainless steel as well as its Young's modulus, but if its content is less than 196, the desired effect cannot be obtained; on the other hand, If the Si content exceeds 596, the steel will harden and the elongation will deteriorate.
The value was set as 5 or less.

(Book Mn Mn component has the effect of securing the austenite phase at a relatively low cost, and it is preferable to add a large amount in order to save Ni, which has the same effect. However, if the content of M is 3% or less, the austenite phase tends to decrease significantly and become a single ferrite phase, which may lead to deterioration of elongation.
If the Mn content exceeds 10%, the Young's modulus deteriorates, so the Mn-containing U content was set at a value of more than 3 scratches and 10% or less.

Qφ Cr As with Si, there is work to be done to improve the strength and Young's modulus of the Cr component, but if the content is less than 17%, the desired strength cannot be secured; on the other hand, if the content exceeds 22% If it is contained, the elongation deteriorates significantly.1. Since E or σ embrittlement is likely to occur, Cr-containing liquid is 22g to 17.
It was set as 1.

Ni N1 component ensures complete austenite phase C: +j! ,
N
The i content was determined to be 1 to 7%.

(vD Cu The Cu component has the effect of significantly improving the plow corrosion resistance of stainless steel, and also has a great effect in preventing stress corrosion cracking that originates from plow corrosion, but its content is O, S *
If it is less than 3%, the desired effect cannot be obtained;
The Cu content was determined to be 0.5 to 395, since Cu content in excess of 0.5 to 395 significantly deteriorates the Young's modulus of steel, similar to Ni.

twill M.

The Mo component has the effect of improving the corrosion resistance of steel, particularly the corrosion resistance to non-oxidizing acids, pitting corrosion resistance, and plow corrosion resistance, but if its content is less than 0.5%, the desired effect is not achieved. On the other hand, when the content is widened by 3ii, σ
There is a tendency for phases to precipitate and cause brittleness, and it is also disadvantageous in terms of cost (both of which are disadvantageous), so the Mo content was set at 0.5 to 3%.

FIG. 4 is a graph showing the relationship between Mo content and pitting potential (in a 0.5 M NaCl aqueous solution at 140°C) in three types of Cr-Ni stainless steels. It is clear that when the Mo content is 3% or more, the deteriorated corrosion resistance can be stably improved.

lVi+) rare earth elements, Mg, Ca # and B
These components have the effect of improving the hot workability of stainless steel and suppressing corner cracks and cracks on the surface of steel sheets during hot rolling and forging, so they can be used alone or in combination of two or more. However, if each content is below the above-mentioned lower limit value, the desired effect will not be obtained in the above action, while on the other hand, if each content exceeds the above-mentioned upper limit value, the weld cracking susceptibility will be increased. The rare earth element content was reduced to 0.(105
~0.0409i, Mg-containing Fl 0.005~0
．． 040%, B content 0.001-0.006, and Ca content 1'&0.040%. (102-0,010gi
, respectively.

dN N is an unavoidable element that is normally contained in stainless steel at a concentration of about 0.0196, but it is a strong austenite-forming element and an interstitial element, so it strengthens the austenite phase and .296 It has strength-promoting effects such as proof stress and tensile strength. On the other hand, it is an element that is actively added when higher strength is required, but if the N content is less than 0.04, the desired effect cannot be obtained.
On the other hand, if the N content exceeds 0.20 gJ, the deterioration of hot workability will be significant, so the N content should be 0.04 to 0.
．． It was set at 20%.

(Phantom Nb N)) is added in combination with N to make the crystal grains of the skin finer and finer after solution f-treatment and to form Nb precipitates, increasing the 0.29151tt force and tensile strength. Since it has the effect of increasing strength, it is added or contained when higher strength is required.
If the content is less than 0.05%, the desired effect cannot be obtained; on the other hand, if the content exceeds 0.5096fr, the hardness of the steel becomes significant (D), which deteriorates the workability after cold rolling. The Nb content was determined to be 0.05 to 0.5 (195).

(X) Ni ha l Iroko [Ni han
As shown in FIGS. 2 and 3, a smaller g value is desirable for improving Young's modulus, but conversely, a larger value is more desirable for improving elongation. As a material for vehicles, considering its workability, the N1ha7 value [-12 to -6]
Is the Young's modulus and ductility of the ferritic-austenitic two-phase stainless steel adjusted in this way correct? N1ha/Iff is [knee 12~-s] because it is suitable as vehicle stainless steel 6!3 material.
] L determined.

Note that S, which is a random impurity in the ferritic-austenite two-phase stainless steel of this invention, does not cause any particular inconvenience as long as it is at a level that is always accompanied by Uno1. Since the hot workability of the steel is further improved by regulating it to .00296 or less, this is a highly recommended measure.Next, this invention will be specifically explained using actual cutting examples and comparing with comparative examples.

<Actual example> First, a 10 mm square steel ingot was melted in an experimental small high-frequency furnace, and this was made into a 7 IDP? 6 from 501 thickness at J temperature 1250℃
After hot rolling to a thickness of 1 mm, annealing at 1050°C and pickling were performed, the weaving properties, corrosion resistance, and hot workability were investigated.

In addition, the corrosion resistance test was conducted using C296FeCA3+0 at 25°C.
IMHC/;] A method of immersing in a water solution for 48 hours and visually inspecting the corrosion status was adopted, and the corrosion resistance was evaluated as follows: 1]... Pitting corrosion occurred, 0... Small pitting corrosion occurred, (◎... Pitting corrosion did not occur).

In addition, investigation of hot workability was carried out by observing a plate with corner cracks occurring 2 to 3 depths from the mill edge when a 50 m thick slab was hot rolled to a thickness of 6 mm. Shiγko.

The results are shown in Table 2.

As is clear from the results shown in Table 2, this Illusion Hori is conventionally -! It can be seen that compared to No. 1, the Young's modulus, corrosion resistance, and hot nO processing have aged well. Separately, the strength of the joint after welding was also measured, and it was confirmed that the bags of the present invention exhibited a cross-over γ of 1[σ even in the stray strength.

<Summary Effects> As explained above, according to the present invention, in addition to exhibiting the change in temperature and elongation without performing cold rolling such as temper rolling, it also has the desirable Young's modulus, corrosion resistance, and It has great benefits in terms of dyeing, such as providing hot workability and being able to provide duplex stainless steel suitable as a material for vehicles.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the structure of stainless steel and tensile strength and elongation. Figure 2 is a graph showing the relationship between Nt ha/ and Young's modulus of stainless steel. Figure 3 is a graph showing the relationship between stainless steel structure and tensile strength and elongation. Figure 4 is a graph showing the relationship between the MO content of stainless steel and the pitting corrosion 'dt position. Applicant: Nippon Stainless Co., Ltd. Tomi Tomi 1) Kazuo HakaX name Yang, Gu'f (Kgf/mm2)! Uu 6z (Kgf/mm21 ifv< °/=n A food 1r it (V) [V, S, C, E] Naka V ° Hak)

Claims (3)

[Claims] (1) In terms of weight percentage, C: 0.05% or less, Si: more than 1 to 5%, Mn: more than 3 to 10%, Cr: 17, 22%, Ni: 1 to
7%, Cu: 0.5-3%, Mo: 0.5-3%, rare earth elements: 0.005-0.040%, Mg: 0.005-0.040%, B: 0.001 to 0.006%, Ca: 0.002 to 0.010%, and the remainder consists of Fe and inevitable impurities, and Nibal value = -1.1 {Cr (%)+1.5×Si(
%)+0.5×Nb(%)+Mo(%)}+30{C(
%)+N(%)}+0.5×Mn(%)+0.3×Cu
(%) + Ni (%) + 8.2 The vehicle height is characterized by a Nibal value of [-12 to -6] according to the formula: -12 to -6, which has excellent Young's modulus and hot workability, and does not deteriorate the strength of the welded part. Duplex stainless steel with high strength and corrosion resistance. (2) In terms of weight percentage, C: 0.05% or less, Si: more than 1 and 5%, Mn: more than 3 to 10%, Cr: 17 to 22%, Ni: 1 to
7%, Cu: 0.5-3%, Mo: 0.5-3%, N: 0.04-0.20%, and rare earth elements: 0.005-0.040%, Mg: 0.005-0.040%, B: 0.001-0.006%, Ca: 0.002-0.010%, and the remainder consists of Fe and inevitable impurities. , and Nibal value = -1.1 {Cr (%) + 1.5 x Si (
%)+0.5×Nb(%)+Mo(%)}+30{C(
%)+N(%)}+0.5×Si(%)+0.3×Cu
(%) + Ni (%) + 8.2 The vehicle height is characterized by a Nibal value of [-12 to -6] according to the formula: -12 to -6, which has excellent Young's modulus and hot workability, and does not deteriorate the strength of the welded part. Duplex stainless steel with high strength and corrosion resistance. (3) In terms of weight percentage, C: 0.05% or less, Si: more than 1 to 5%, Mn: more than 3 to 10%, Cr: 17 to 22%, Ni: 1 to
7%, Cu: 0.5-3%, Mo: 0.5-3%, N: 0.04-0.20%, Nb
: 0.05 to 0.50%, and rare earth elements: 0.005 to 0.040%, Mg: 0.005 to 0.040%, B: 0.001 to 0.006%, Ca: 0.002 to 0.010%, and also contains one or more of the following, with the remainder consisting of Fe and unavoidable impurities, and Nibal value = -1.1 {Cr (%) + 1.5 × Si (
%)+0.5×Nb(%)+Mo(%)}+30{C(
%)+N(%))+0.5×Si(%)+0.3×Cu
(%) + Ni (%) + 8.2 The vehicle height is characterized by a Nibal value of [-12 to -6] according to the formula: -12 to -6, which has excellent Young's modulus and hot workability, and does not deteriorate the strength of the welded part. Duplex stainless steel with high strength and corrosion resistance.