JPH10102206A - Duplex stainless steel having high corrosion resistance and high corrosion fatigue strength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a duplex stainless steel excellent in corrosion resistance, corrosion fatigue strength, etc., and useful, e.g. for a material for the barrel of a suction roll for a paper-making machine. SOLUTION: This duplex stainless steel has a composition consisting of <=0.03% C, 0.1-2.0% Si, 0.1-2.0% Mn, 19.0-21.0% Cr, 1.5-3.0% Ni, 1.0-2.5% Mo, <=1.0% Cu, 0.1-0.3% N, and the balance essentially Fe and also has a two-phase structure in which the amount of ferrite is regulated to 40-65area%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duplex stainless steel having excellent corrosion resistance, corrosion fatigue strength and the like, which is useful as a suction roll body member for papermaking.

[0002]

2. Description of the Related Art The body member (sleeve) of a suction roll for dewatering wet paper in a papermaking process is made of water squeezed from wet paper, so-called "white water" (chlorine ion Cl ^- and sulfate ion SO ₄ ^- etc.). Is a hollow cylindrical member with a large number of small holes (suction holes) dispersed and perforated to suck out and remove the highly acidic corrosive liquid containing water. Corrosion resistance of wet paper to moisture, wet paper to white water It is required to have both mechanical strength and corrosion fatigue strength that can withstand the repetitive load of the pressing force (nip pressure) of the press roll for extracting the water. Conventionally, duplex stainless steel has been used as the sleeve material of the suction roll. Duplex stainless steel is a corrosion-resistant alloy having strength and toughness due to a mixed phase structure of a δ-ferrite phase and an austenitic phase.Precipitation hardening type duplex stainless steel with an increased content of Cu and the like has recently been widely used. It is used.

[0003]

SUMMARY OF THE INVENTION In the papermaking process, as the speed of a line is increased, the load on a suction roll is increasing. In order to increase the durability of suction rolls and ensure stable use in response to the harsh operating environment, it is necessary to improve and strengthen the strength, toughness, corrosion resistance, corrosion fatigue strength, etc. of roll body members. It is. The present invention provides a duplex stainless steel useful as a constituent material of such a suction roll body member and the like.

[0004]

The duplex stainless steel according to the present invention comprises C: 0.03% or less, Si: 0.1 to 2.0%,
Mn: 0.1 to 2.0%, Cr: 19.0 to 21.0
%, Ni: 1.5 to 3.0%, Mo: 1.0 to 2.5
%, Cu: 1.0% or less, N: 0.1 to 0.3%, balance substantially consisting of Fe, amount of falite: 40 to 65%
(Area).

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the components of the duplex stainless steel of the present invention are as follows. All elemental contents are% by weight. C: 0.03% or less C is an austenite-forming element and solid-solution strengthens the austenite phase. However, when the content is increased, chromium carbides are easily generated, which causes a decrease in toughness due to precipitation of chromium carbides, a decrease in corrosion resistance due to a decrease in Cr concentration near chromium carbide particles, and the like. Therefore, in the present invention, the content is limited to a low content region of 0.03% or less.

[0006] Si: 0.1 to 2.0% Si is a deoxidizing agent at the time of smelting steel and is an element that improves the flowability of molten metal in the casting process. For this purpose, at least 0.1% is required, but if added in a large amount, the toughness and weldability of the steel are reduced, so the upper limit is 2.0.

Mn: 0.1 to 2.0% Mn is added as a deoxidizing / desulfurizing element for molten steel. To obtain this effect, 0.1% or more is required. However, if it exceeds 2.0%, the corrosion resistance is reduced.

[0008] Cr: 19.0 to 21.0% Cr is an element for improving corrosion resistance, and is an element necessary as a ferrite-forming element to balance the quantitative ratio of the two phases and to secure the strength. For this reason, 19.0%
Need more. However, if the amount increases, the corrosion resistance and toughness become insufficient due to a relative decrease in the amount ratio of the austenite phase, so the upper limit is 21.0%.

Ni: 1.5 to 3.0% Ni is an austenite-forming and stabilizing element, and is necessary for balancing the two-phase ratio in the two-phase structure and ensuring toughness and corrosion resistance. . The amount must be 1.5% or more, but if it is too large, the corrosion fatigue strength and the like are impaired, so the upper limit is 3.0%. The reason that the required two-phase structure, toughness, corrosion resistance, and the like are ensured with such a small amount of Ni corresponds to the fact that the amount of Cr is specified to be as low as about 20%. Ni is an expensive element, and limiting the amount of Ni to such a small amount increases the economics of the alloy.

Mo: 1.0 to 2.5% Mo has an effect of improving corrosion resistance. This effect
It can be obtained by adding 1.0% or more. If added in a large amount, the toughness is impaired, so the upper limit is 2.5%. Preferably, it is 1.5 to 2.5%.

Cu: 1.0% or less Cu is added as an element for improving corrosion resistance. If the amount exceeds 1.0%, the toughness is impaired, and the corrosion fatigue strength is lowered. Therefore, it is added in a range of 1.0% or less.
Preferably, it is 0.3 to 1.0%.

N: 0.1 to 0.3% N is a strong austenite-forming element, and forms an interstitial solid solution in the austenite phase to strengthen the matrix of the alloy. It also has a great effect on improving pitting corrosion resistance and crevice corrosion resistance. This effect can be obtained by adding 0.1% or more.
However, if it exceeds 0.3%, nitrides such as Cr and Mo are generated, the action of corrosion-resistant elements is hindered, and the toughness of the alloy is impaired.

[0013] The heat treatment of the duplex stainless steel according to the present invention is carried out in a temperature range of about 1000 to 1100 ° C for a suitable time (about 1 to 5 hours per inch of wall thickness of the cast material).
This is done by cooling. The cooling from the solution temperature can be air cooling (cooling rate: about 5 to 15 ° C./min). Therefore, even for thick and large diameter cast materials,
There is no difficulty in the cooling operation, and by applying such slow cooling conditions, the residual stress is reduced and alleviated.

[0014]

EXAMPLE A sample material is obtained by subjecting a duplex stainless steel centrifugally cast material (hollow cylindrical body) to a solution heat treatment. Table 1 shows the chemical composition of the test materials. Nos. 1 to 6 are invention examples, Nos. 11 to 19
Is a comparative example (in the table, the underline indicates that the element content is out of the range of the present invention). Table 2 shows the material properties of each test material. Casting material size: Outer diameter 600, wall thickness 50, length 4000 (mm) Heat treatment (solution heat treatment): 1050 ° C x 4 Hr → controlled air cooling (10 ° C / min)

[Corrosion Test] A test piece is immersed in a corrosive liquid to determine a corrosion rate (g / m ² h). Corrosion test solution: Ferric chloride solution (FeCl _3, concentration 6%), liquid temperature 50 ° C Test time: 72hr

[Corrosion Fatigue Test] An Ono-type rotary bending fatigue tester was used. Test piece: φ10 × 35 ^L (parallel part) Corrosion test _{^{solution: Cl - 1000 ppm, SO 4}} 2- 1000 ppm (Tappi
II solution) Speed: 3000 rpm Number of cycles: 10 ⁸

As shown in Table 2, the materials of the present invention (Nos.
) Has superior mechanical properties such as strength and toughness, corrosion resistance, corrosion fatigue strength, etc. as compared with the comparative material (Nos. 11 to 19). It is suitable as a component material used in an environment where a high load is superimposed.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

The duplex stainless steel of the present invention has various properties such as strength, toughness, corrosion resistance and corrosion fatigue strength in a well-balanced manner. Therefore, it is suitable as a part material used in an environment where corrosion and mechanical stress load are superimposed, such as suction rolls for paper machines, etc., contributing to improved durability of members and more stable and efficient line operation. Is what you do.

Claims (1)

[Claims] 1. C: 0.03% or less, Si: 0.1 to
2.0%, Mn: 0.1-2.0%, Cr: 19.0-
21.0%, Ni: 1.5 to 3.0%, Mo: 1.0 to
2.5%, Cu: 1.0% or less, N: 0.1 to 0.3
%, The balance being substantially composed of Fe, the amount of ferrite: 40 to
High corrosion resistance and high corrosion fatigue strength duplex stainless steel with 65% (area).