JPS5913053A - Stainless steel with superior corrosion resistance, workability and weldability - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance, workability and weldability of a stainless steel, by reducing the amount of Cr in the composition, restricting the amounts of elements to be added, and specifying the relation between Cr and C+P and the gammap value. CONSTITUTION:A stainless steel is composed of, by weight, <=0.030% C, <=2.0% Si, <=0.5% Mn, <=0.020% P, <=0.002% S, 11.5-15% Cr, <=1% Ni, <=0.2% Al, <=0.05% N, <=0.005% O and the balance Fe with inevitable impurities. The composition of the steel is regulated so as to satisfy equation Cr+100(C+P)<=18% and gammap=420C+470N+23Ni+7Mn-11.5Cr-11.5Si-52Al+189>=15%. To the steel may be added a proper amount of one or more among Mo, Cu, Ti, Nb, V and B. By the composition the characteristics of the weld zone of the low Cr stainless steel and the corrosion resistance, etc. of the steel are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inexpensive stainless steel with excellent corrosion resistance, mechanical properties, and weldability.

As the uses of stainless steel expand, there is a demand for stainless steel that is inexpensive, has good corrosion resistance, is easy to work into thin plates, and has good mechanical properties. Conventional stainless steel thin plate is S
n2304 (18Cr-8Nl) and 5US430 (
17Cr) steel, and the expansion of its applications requires thin stainless steel sheets at even lower costs.

The present inventor has discovered that the corrosion resistance of stainless steel can be greatly improved by high-purity refining, and based on this finding, it is possible to develop a steel material that is low in Cr but has corrosion resistance comparable to 17Cr steel. I found it. Moreover, these low Cr
Stainless steel is soft and can be easily cold rolled not only by Sendzimir cold rolling, which is conventionally used for stainless steel, but also by high-productivity tandem cold rolling for ordinary steel, and the final annealing is similar to that for ordinary steel. It was revealed that annealing is possible on a high-speed continuous annealing line. In this way, it was confirmed that low-Cr stainless steel, which is made with high purity refining, can be manufactured using the ordinary steel process, and has the remarkable advantage of increasing production speed and significantly reducing costs. but,
The inventor further found that: (1) Corrosion resistance and induction resistance are equivalent to 17% Cr stainless steel, and (2) Workability of thin plate is 17% Cr.
We aim to develop a low Cr stainless steel that is equivalent to or better than stainless steel, and has properties such as weldability and corrosion resistance of welded parts of 1710r or higher, and can be manufactured using the same process as ordinary steel. This is what the present invention is designed to provide.

The present invention will be explained in detail below. The present inventor has investigated and experimented with a wide range of Cr alloys, from about 9% CF to about 19% CF, but the alloy that satisfies the target 3 requirements has a Cr content of 1%.
more than 1.51 and less than 151, and high purity gold (C<,0
．． 030 excellent, S<0. QO2%, P≦0.020.

? 9 obtained by 0.0011+1).

First, regarding the corrosion resistance and induction resistance of low Cr steel,
It is necessary to reduce C2s, p, and o. S, 20pp
m.

Preferably 1.0. As soon as it is reduced below ppmJl,
7. It provides excellent corrosion resistance and resistance to corrosion. , Fig. 1 shows this situation, but when S is 20 ppm or less, s 14
% Cr provides φ induction resistance comparable to 17 To Cr stainless steel. 0 is charcoal (if it can be made below 50 ppm)
When g substances begin to precipitate, the induction resistance deteriorates. Cr increases,
When C is added, the solid solubility of C decreases and carbides are precipitated at grain boundaries.

In the case of ■ in Figure 1, the boundary is Cr14*.

Corrosion resistance and induction resistance deteriorate. Since P promotes the precipitation of carbides, it must be reduced together with C to a range that satisfies the following relational expression with the amount of Cr.

In improving the workability and weldability of thin plates with Cr +100 (C+P, )≦, the corrosion resistance of welds, and the rust resistance, the amount of r plays a major role when the composition changes to (α+γ) at high temperatures (5). γ of ``Hatashiru''
When present in a certain amount or more, the transformation progresses sufficiently to improve the thin sheet lubricating properties and deep drawing properties (1 value), as well as to transform the matsive martensite, which has low C toughness and corrosion resistance, during cooling during welding.・The properties and corrosion resistance of the welded part are greatly improved. For this, C5; γ at 0.020%, ≧1
5% is required.

5. rp is defined by the following formula by Ca5tro.

, Figure 2 shows the low C+ Fm-Cr alloy (C50,0021
゜N≦0.02% -Cr 9~1 ys, NlO
, 1%) shows the relationship between Orp and 7.

rp=4200+47ON+23Nl+9Cu+
7Mn-11,5Cr, -11,581-12Mo-2
3V-47Nb-49TI-52At+189° Here, Mo + V, Nb #Ti, etc. are selective addition elements.

By controlling the components as described above, the necessary requirements for characteristics can be satisfied. Finally, regarding Cr1l,
When the amount of Cr exceeds 15%, r decreases, and (6) carbides precipitate at grain boundaries, making it easier to rust than at grain boundaries. In addition, intergranular corrosion and rusting occur at welded parts. Therefore, Cr
It is desirable that the number is 15 or less. Also, in order to improve corrosion resistance, 1
1.41 or higher is required.

The reasons for limiting the additive components of the steel of the present invention will be described below.

C causes phase transformation in low Cr stainless steel, but if too much C precipitates as carbides, impairing intergranular corrosion resistance and lowering rust resistance. In addition, in terms of workability of the thin plate, it is better to have a lower C.
Cr +100[C+P]≦18 in relation to r, P
It is necessary to satisfy the following.

S improves the rust resistance of low Cr stainless steel, and the lower it is, the more preferably it is 0.0020% or less, preferably o, oo
It is necessary to be less than or equal to to*.

The lower P increases the rust resistance of low Cr stainless steel.

Therefore, it is necessary that p is 0.0201.

Furthermore, since it promotes the precipitation of carbides, the following relationship must be satisfied in relation to the amounts of C and Cr.

Cr +100(C+P)<180 acts as inclusions and deteriorates rust resistance. In particular, alloys with reduced S+P have a large negative effect and must be kept at 0.0050 or less.

As mentioned above, Cr is an essential element of stainless steel and increases corrosion resistance. If Cr is 11.5'% or less, corrosion resistance is insufficient.

The upper limit of Cr is regulated in many ways. When the Cr content increases, carbides tend to precipitate, which deteriorates the resistance to intergranular corrosion. Therefore, in relation to C and P, Cr + 100
CC0P ) < 18. Also, the workability of thin plates,
From the viewpoint of weldability, it is necessary to generate the (α+γ) phase at high temperature, r potential, γ.

is defined by the following equation.

γp =420 C+ 47 ON+23 Nk +9
Cu + 7 Mn 1l-5Cr-11,581
-12Mo-47Nb-49TI-52AL+189≧
15%, therefore, it is necessary to keep the Cr at 15% or less and to comply with the above regulations.

St is necessary for deoxidation and improving corrosion resistance, but it has a hardening effect, so it was set to 2 or less.

Mn is necessary for deoxidation and mechanical properties, but the lower the better for corrosion resistance, so it was set to 0.5 or less.

Nl is preferable for improving mechanical properties, welding properties, and corrosion resistance, but since it causes hardening, the content was set to 1 or less.

N does not significantly affect corrosion resistance or mechanical properties.

Therefore, for the purpose of controlling γ, which was already mentioned, 0
．． 05% or less. If it exceeds this range, hardening will increase.

At is effective for improving the processability of thin plates and for deoxidizing.

However, if the coefficient exceeds 0.2, the effect will be saturated, so the coefficient is set to 0.2 or less.

Mo T Cu + Tl, Nbrv, etc. are effective for improving corrosion resistance, and Tl, Nb, B, V, etc. are effective for improving workability of thin plates. However, these alloying elements have a hardening effect, so Mo51%, Cu≦0
．． 51. TI≦0.3% #NbS2.3%, VS
Depending on the application, one or more types can be selectively added within the range of 2.7%*B≦o, ots. However, especially when the purpose is to facilitate softening and recrystallization and to achieve high productivity, the total amount of major alloying elements added should also be regulated, and Cr/
15 + (Nl+Mo+Cu)+4(TI+Nb)<
35b.

(9) Examples of the present invention will be described below.

LD converter and VA, which is a normal stainless steel melting process
It was produced using the C treatment method, but the C and S were reduced.

Particular attention was paid to low P, and flux injection was carried out in a ladle. In addition, 00 reduction was carried out to ensure that deoxidation by At was sufficient. Examples of the composition of the steel of the present invention are steel numbers ① to ② in Table 1.

After that, after continuous casting, regular hot rolling and winding,
Hot-rolled plate pickled without annealing, steel, number ■.

■ is passed through the Sendzimir cold rolling, annealing, and pickling line in the stainless steel process, while ordinary steel cold rolling,
It passed through a tandem cold rolling continuous annealing line which is an annealing process. At this time, the annealing conditions were 850℃ for 1 minute or less, and the dew point was -40℃.
And so. After going through each of the above steps.

The mechanical properties of the resulting product plates were investigated. The comparative steels are a low C-12Or-Tl type steel that is conventionally manufactured using a tandem continuous annealing process and ordinary SUS.
430 steel was processed through the stainless steel process of Sendzimir cold rolling, annealing and pickling.

The results are shown in Table 2. Regarding rust resistance, (10) already mentioned 0, 54 NaCt + 0.2% H
Evaluation was made based on the degree of rusting when fogged with 2O2 solution at 30°C for 24 hours. While the comparative steels were ranked G and E, the steel of the present invention exhibited resistance to induction of ranks A-D despite its low Or, and exhibited excellent properties. In addition, as a result of investigating the workability of thin sheets using J5 JIS No. 5 tensile test pieces using thin sheet products, it was found that both the perfumes ■ to ■ manufactured using the ordinary steel process and the perfume ■ manufactured using the stainless steel process were compared to the comparative steel ■. 8US
The characteristics exceed those of the 430 class. The recrystallization conditions after cold rolling also indicate that recrystallization is completed within 850° C. for 1 minute from aroma adjustment ① to ②. The steel of the present invention also exhibited superior properties to the comparative steels in terms of induction resistance of welded parts.

1111 ゝゝ1 (11) (13)

[Brief explanation of the drawing]

Figure 1 shows 0.5% NaC1+ 0.24 H20□
Figure 2 shows the effects of Cr content, C content, and S content on the degree of rusting when a liquid (30°C) is sprayed for 24 hours. It is a diagram showing the relationship. (14) 碍欩 ＼Hehachi

Claims (3)

[Claims] (1) Weight/4 cents, C: 0.030 m or less, S
L: 2.0% or less, Mn: 0.5% or less, P:
0.020% or less, 80.002% or less, Cr:1
Contains 1.5% to 15%, Ni: 1% or less, AL: 0.2% or less, N: 0.05% or less, O: o, oos% or less, and the remainder consists of iron and inevitable impurities. , Cr+100 (C+P) 618% 7"p" 420 C+ 470 N+23
Ni + 7 RIIn-11,5Cr-11,5Si
A stainless steel with excellent corrosion resistance, workability, and welding properties, which satisfies the following relational expression: -52At+189≧15. (2) In weight percent, C: 0.030% or less, st
: 2.0% or less, Mn: 0.5% or less, P: 0.
020 or less, S: 0.002% or less, Cr:
11.5% to 15%, Ni: 1% or less, ht:o,
296 or less, N: 0.05'% or less, o: o, oo
ss or less and Mo 1% or less, CuO05 or less,
Contains one or more of the following: Tl O, 3 or less, NbO, 3 or less, vO 47 or less, BO 301 or less, the remainder consisting of iron and unavoidable impurities, and Or + '100X (C + P) ≦ 18 %r=420C+47ON+23Nl+9Cu+7M
n-11,5Cr-11,5Si-12Mo-47Nb
-49TI -52At+189≧15 A stainless steel with excellent corrosion resistance, workability and weldability, characterized by satisfying the following relational expression: -49TI -52At+189≧15. (3) Weight (- cents, c: o, oao 俤 or less, S
L: 2.0% or less, Mn: 0.5% or less, P:
0.020q or less, S: 0.002qIb or less, C
r: 11.596-15%. N1: 1 inch or less, At: 0.2 section or less, N: 0.05
Chi and O: 0.0051 or less and Mo 1% or less, CuO, 5% or less, T10.31 or less, Nb O, 3
1 or less, VO, 7 or less, Bo, 01 or less, the remainder consists of iron and unavoidable impurities, and Cr + 100X (C-1-P)≦18 coefficient r = 4
200+47ON+23Nl+9Cu+7Mn-11,
5Cr=1t, 5st-02,. -4゜Nb-49T
I-5°. □,,8゜≧15chi Cr/i5 + (N1+Mo+Cu)+4 (TI+N
b) Stainless steel with excellent corrosion resistance, workability and welding properties, which satisfies the relational expression <3%.