JP2003328069A - Rolled stainless-clad steel superior in low-temperature toughness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolled stainless-clad steel superior in a low-temperature toughness of its base metal. <P>SOLUTION: The rolled stainless-clad steel employs the steel for the base metal, which comprises, by mass%, 0.02-0.2% C, 0.05-0.5% Si, 0.3-2.0% Mn, 0.03% or less P, 0.01% or less S, 0.0001-0.006% Mg, 0.01-0.06% Al, 0.006% or less N, further one or more elements of 0.5% or less C, 1.5% or less Ni, 0.5% or less Cr, 0.3% or less Mo, 0.05% or less Nb, 0.05% or less V, 0.05% or less Ti, 0.005% or less B, and 0.004% or less Ca, and the balance substantially Fe with inevitable impurities. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolled stainless clad steel, and more particularly to a stainless steel having excellent low temperature toughness of a base material and suitable for use in an icebreaker or an ice sea area.

[0002]

2. Description of the Related Art Icebreakers and offshore structures in ice areas are painted to improve corrosion resistance, but are often peeled off by ice, often requiring repairs up to the life of the structure, which is economical. Needless to say, the application of stainless clad steel, which has a large environmental load and does not require painting, has been desired.

The clad steel used for such a large structure is manufactured by a rolling method. However, in the case of stainless clad steel, the corrosion resistance of the stainless steel of the laminated material decreases as it is rolled. It has been feared that a solution treatment is required, and that the heat treatment causes the crystal grains of the base carbon steel to become coarse and the low temperature toughness to deteriorate.

Japanese Patent Laid-Open Nos. 5-293923 and 20
Japanese Patent Publication No. 00-1734 relates to a stainless clad steel by a rolling method which is excellent in low temperature toughness of a base material carbon steel and corrosion resistance of a stainless steel of a composite material. Improving the toughness of the base metal is to improve Nb (C, N) and Ti for the latter.
It is described that N prevents coarsening of austenite grains due to the solution treatment and provides excellent base material toughness.

[0005]

[Problems to be Solved by the Invention] However, TiN
If Nb (C, N) or Nb (C, N) is subjected to solution treatment at high temperatures, it may coarsen or partly dissolve in solid solution and deteriorate toughness, so stainless steel is used for icebreakers and marine structures used in ice waters. It was difficult to apply clad steel.

[0006] Therefore, it is an object of the present invention to provide a rolled stainless clad steel having excellent corrosion resistance of the stainless steel composite material and stable low temperature toughness of the base material.

[0007]

[Means for Solving the Problems] The inventors of the present invention have made earnest studies from the viewpoint of suppressing coarsening of the crystal grain size of the base metal in order to prevent deterioration of the toughness of the base metal due to solution treatment at high temperature. When the Mg-based oxide is finely dispersed in the alloy, it does not disappear like carbonitride even when the solution heat treatment temperature becomes high, and is much more stable and effective in suppressing coarsening of the crystal grain size. It was also found that it remains in the weld heat affected zone (HAZ) heated to 1300 ° C. or higher and is effective in improving the HAZ toughness.

The present invention has been made through further studies based on the above findings, that is, the present invention is as follows. In a stainless clad steel having stainless steel as a composite material and carbon steel as a base material, the base material is mass% and C:
0.02-0.2%, Si: 0.05-0.5%, M
n: 0.3 to 2.0%, P: 0.03% or less, S: 0.
01% or less, Mg: 0.0001 to 0.006%, A
Rolled stainless clad steel having excellent low-temperature toughness, in which l: 0.01 to 0.06%, N: 0.006% or less, and the balance substantially consisting of Fe and inevitable impurities.

In addition to the composition of the base material described in 2.1, in addition, in mass%, Cu: 0.5% or less, Ni: 1.5% or less, Cr:
0.5% or less, Mo: 0.3% or less, Nb: 0.05%
Hereinafter, V: 0.05% or less, Ti: 0.05% or less,
B: 0.005% or less, Ca: 0.004% or less, and a rolled stainless clad steel excellent in low-temperature toughness, which is added with one or more kinds.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The reason for limiting the composition of the base material in the present invention will be described in detail below.

C C is added to improve the strength. If it is less than 0.02%, the effect cannot be obtained, while if it exceeds 0.2%, the base metal and H
To reduce the AZ toughness, it is set to 0.02 to 0.2%.

Si Si is added for deoxidation. If it is less than 0.05%, the effect cannot be sufficiently obtained, while if it exceeds 0.5%, the HAZ toughness and weldability deteriorate, so the content is made 0.05 to 0.5%.

Mn Mn is added to improve the strength and toughness of the base material.
If it is less than 0.3%, the effect cannot be sufficiently obtained, while 2.
If it exceeds 0%, the HAZ toughness and weldability deteriorate significantly, so the content is made 0.3 to 2.0%.

In the present invention, P P is an impurity element, and is used as a base material and HAZ.
From the viewpoint of toughness, it is desirable to reduce as much as possible within the range allowed by economic efficiency, and the content is made 0.03% or less.

In the present invention, S S is an impurity element, and is a base material and HAZ.
From the viewpoint of toughness, it is desirable to reduce as much as possible within the range allowed by economic efficiency, and the content is made 0.01% or less.

Mg Mg is an important element in the present invention, and a fine oxide due to its strong oxidizing power is used even if the solution treatment required for recovering the corrosion resistance of rolled stainless steel is as high as 910 to 1200 ° C. It remains stably in the steel, the crystal grain size is refined, and it effectively acts to improve the low temperature toughness of the base material and HAZ.

Therefore, it is an essential addition element in the present invention, and is added in an amount of 0.0001% or more so as to obtain the above-mentioned effects. On the other hand, if it exceeds 0.006%, the number of oxides increases and the toughness is adversely affected.
It is set to 1 to 0.006%. Preferably, 0.001
It is in the range of 0.005%.

Al Al is added as a deoxidizing agent. If it is less than 0.01%, there is no effect, and if it exceeds 0.06%, the HAZ toughness deteriorates, so the content is made 0.01 to 0.06%.

N N forms a nitride and refines crystal grains to form a base material, HAZ.
The toughness is improved, but if it exceeds 0.006%, the HAZ toughness will decrease, so the content is made 0.006% or less.

The above is the basic composition of the present invention, and when further improving the strength and toughness, Cu, Ni, Cr, Mo,
One or more of Nb, V, Ti, B and Ca can be added.

Cu Cu is added in an amount of 0.5% or less so as not to impair the weldability when improving the toughness and strength of the base material.

Ni Ni improves the toughness and strength of the base material, but its effect is saturated when it exceeds 1.5%, so Ni is added in an amount of 1.5% or less.

Cr In the case of improving the strength of Cr, 0.5% or less is added so as not to deteriorate the HAZ toughness and weldability.

Mo Mo improves the toughness and strength of the base material, but if it exceeds 0.3%, its effect is saturated and the low temperature toughness and weldability deteriorate, so 0.3% or less is added.

Nb Nb improves the toughness and strength of the base material, but if it exceeds 0.05%, its effect saturates and deteriorates the HAZ toughness, so it is made 0.05% or less.

V V improves the toughness and strength of the base material, but if it exceeds 0.05%, its effect saturates and deteriorates the HAZ toughness, so it is made 0.05% or less.

Ti Ti forms TiN, suppresses the growth of the crystal grain size during slab heating and welding, and base material for refining the microstructure,
It is added to improve the HAZ toughness. If it exceeds 0.05%, the toughness will decrease, so 0.05% or less is added.

BB contributes to high strength by improving hardenability, but 0.0
If it exceeds 05%, the HAZ toughness deteriorates, so 0.005
% Or less.

Ca Ca improves the HAZ toughness by controlling the morphology of sulfide inclusions, but when it exceeds 0.004%, its effect saturates,
0.004% due to reduced cleanliness and reduced HAZ toughness
Below.

In the present invention, the base material may be produced by a conventional method, and it can be melted into the above-mentioned components, cast, and then hot-rolled to a predetermined slab thickness, and the production conditions are not particularly specified. .

Further, there is no particular restriction on the selection of the stainless steel for the joining material, and it is possible to select the one suitable for the structure of the icebreaker and the ice sea area.

The method for producing the rolled clad steel is not limited to any particular method, and it is not particularly specified. After the laminated material and the base material are assembled into a clad slab, the interface between the laminated material and the base material is vacuum-treated and then heated. Join by rolling. According to the present invention, after joining, solution treatment or normalizing treatment is performed in the range of 910 to 1200.
It is also possible to carry out at a high temperature of ° C and then temper to improve strength and improve toughness.

[0033]

EXAMPLES Commercially available ASTM S31254 steel (20Cr-18Ni) was prepared by rolling using base materials having various chemical compositions.
-6 Mo) was used as a composite material to manufacture a stainless clad steel. The clad steel had a total thickness of 10 to 70 mm, a clad ratio of 1: 4 to 1: 8, was solution-treated at 1100 ° C., was water-cooled, and was tempered at 550 ° C.

After that, 20 V-notch Charpy impact test pieces were taken from the central portion of the thickness of the base material, and the test temperature was -60 ° C.
Minimum value of absorbed energy at (vE-60min)
I asked.

HAZ toughness is BO with heat input of 500 kJ / cm
The minimum value of absorbed energy (vE-40 min) at a test temperature of −40 ° C. of 20 V-notch reproduction heat cycle Charpy impact test pieces to which a heat cycle equivalent to the ND portion was applied was determined.

Table 1 shows the chemical composition of the base material, the clad steel base material, and the test results of the simulated thermal cycle HAZ.

Steels 1 to 8 are base materials according to the present invention and are steels 9 to 9.
Outstanding base metal and HAZ toughness are obtained for 16 comparative steels.

Steel 9 has a high C content and is outside the range of the present invention.
Has no Mg added. Steel 11 has a high Si content, M
g was also not added. Steel 12 has a high Mn content and a high Mg content and is outside the scope of the present invention.

Steel 13 has a low C content, a high P content and a high B content, and is outside the range of the present invention. Steel 14 has a high S content and Cr content and is outside the scope of the present invention.

Steel 15 does not contain Mg and has a high Mo content, which is outside the range of the present invention. Steel 16 has a high Al content and a high Nb content and is outside the scope of the present invention.

[0041]

[Table 1]

[0042]

According to the present invention, it is not necessary to lower the solution heat treatment temperature in consideration of the low temperature toughness of the base metal, so that a rolled stainless clad steel excellent in corrosion resistance of the laminated material can be obtained on an industrial scale. Extremely useful.

Continued front page    (72) Inventor Shigeru Endo             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd.

Claims (2)

[Claims] 1. A stainless clad steel comprising stainless steel as a composite material and carbon steel as a base material, wherein the base material is mass%.
And C: 0.02 to 0.2%, Si: 0.05 to 0.5
%, Mn: 0.3 to 2.0%, P: 0.03% or less,
S: 0.01% or less, Mg: 0.0001 to 0.006
%, Al: 0.01 to 0.06%, N: 0.006% or less, and the balance is a rolling type stainless clad steel excellent in low temperature toughness consisting essentially of Fe and unavoidable impurities. 2. The component composition of the base material according to claim 1, further comprising:
Mass% Cu: 0.5% or less, Ni: 1.5% or less, C
r: 0.5% or less, Mo: 0.3% or less, Nb: 0.0
5% or less, V: 0.05% or less, Ti: 0.05% or less, B: 0.005% or less, Ca: 0.004% or less One or more types of rolling are added to achieve excellent low temperature toughness. Type stainless clad steel.