JP2001271141A - HIGH Cr STEEL FOR SEAMLESS PIPE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high Cr steel for a seamless pipe in which the generation of cracking can effectively be suppressed in all production processes on and after a round billet production, i.e., in a piercing process, a drawing process, a sizing process and the subsequent cooling process. SOLUTION: This steel has a composition containing, by mass, 0.05 to 0.20% C, <=1.00% Si, <=1.00% Mn, 0.05 to 0.50% Ni, 8.00 to 10.00% Cr, 0.05 to 0.50% V, one or more kinds of metals selected from Nb, Ti and B of 0.01 to 0.20%, 0.50 to 3.00% Mo, 0.02 to 0.07% N, <=1.00% Cu and <=2.00% W, and the value of Ni-Bal. shown by the following formula (1) satisfies the range of 0.50 to 2.50, and the rest mainly composed of Fe: Ni-Bal.=Ni+0.5(Mn+Cu)+30(C+ N)-1.1(Cr+1.5Si+Mo+W)+8.2...(1); wherein, Ni, Mn or the like denote the mass percentage of each component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel for a high Cr seamless steel pipe, and more particularly to an effective prevention of cracks during the production of a seamless steel pipe.

[0002]

2. Description of the Related Art High Cr ferritic steels are disclosed in, for example, JP-A-8-229606, JP-A-8-232018, JP-A-60-155561, and JP-A-11-92827. Various techniques relating to improvement and processing methods have been proposed. In particular, JP-A-8-232018 discloses a method for preventing cracks caused by delta ferrite during rolling of a seamless steel pipe.

[0003] A seamless steel pipe is generally manufactured through a round billet for a seamless steel pipe, and the steps of piercing, stretching and constant diameter after reheating. The above-described technique is intended to prevent cracking of the steel pipe during drilling and drawing in these manufacturing steps.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the technology disclosed in Japanese Patent Publication No. 2018, in order to obtain good pipe formability in seamless rolling of high Cr seamless steel pipe steel,
Is used as an index to suppress the working ratio ε to 0.5 or less. However, due to the nature of this technology, there is a problem that the working limit value is determined by the working ratio ε.

[0005] Cracking during the production of steel pipes occurs during any of the processes of drilling, elongation and cooling after sizing. However, the above-mentioned technique is intended only for cracking during piercing and elongation. No consideration was given to cracking during cooling.

The present invention advantageously solves the above-mentioned problems. There is no limitation on the processing limit value due to the degree of processing ε and the like. An object of the present invention is to propose a high Cr seamless steel pipe steel capable of effectively eliminating cracks during subsequent cooling.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention realizes good manufacturability by making a high Cr ferrite alloy a component system suitable for seamless steel tube rolling. It is. That is, the inventors focused on the Ni-Bal. Value as a factor controlling the occurrence of cracks and flaws,
As a result of intensive studies to prevent the generation of cracks and flaws during pipe production by controlling the Ni-Bal.
It has been found that by controlling the Bal. Value in the range of 0.50 to 2.50, the intended purpose is advantageously achieved. The present invention is based on the above findings.

According to the present invention, C: 0.05-0.
20%, Si: 1.00% or less, Mn: 1.00% or less, Ni: 0.05-0.
50%, Cr: 8.0-10.00%, V: 0.05-0.50%, Nb, Ti
And one or more selected from B and B: 0.01 to
0.20%, Mo: 0.50 to 3.00%, N: 0.02 to 0.07%, Cu: 1.
Contains not more than 00% and W: 2.00% or less, and has the following formula
The Ni-Bal. Value represented by (1) satisfies the range of 0.50 to 2.50, and the balance is substantially Fe composition.
Cr Seamless steel pipe steel. Ni-Bal. = Ni + 0.5 (Mn + Cu) +30 (C + N) -1.1 (Cr + 1.5 Si + Mo + W) +8.2 --- (1) Here, Ni, Mn, etc. indicate the value of mass percentage of each component. .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, the reason why the composition of steel is limited to the above range in the present invention will be described. C: 0.05 to 0.20 mass% C is an austenite stabilizing element for forming martensite, and is also useful in precipitating carbide. Also, the influence on the Ni-Bal. Value is large, and it is also important as an element for stabilizing the Ni-Bal. Value.
The amount was limited to the range of 0.05 to 0.20 mass%.

Si: 1.00 mass% or less Si is useful as a deoxidizing agent. However, when it is contained in a large amount, it causes a decrease in toughness. In addition, in order to stabilize the Ni-Bal. It was to be contained.

Mn: 1.00 mass% or less Mn is also useful as a deoxidizing agent, like Si, but when contained in a large amount, it causes a decrease in high-temperature strength and toughness, and Ni-Ba
l. In order to stabilize the value, the content was set to 1.00 mass% or less.

Ni: 0.05 to 0.50 mass% Ni is an austenite forming element and has an effect of preventing a decrease in the Ni-Bal. Value. Therefore, it is necessary to contain at least 0.05 mass%. Limit for the purpose of
0.50 mass%.

Cr: 8.0-10.00 mass% Cr is an indispensable element for ensuring high-temperature oxidation resistance, and also has the effect of increasing the high-temperature strength by precipitating carbide. In addition, the influence on the Ni-Bal. Value is large, and a content of about 9.0 mass% is appropriate. From this viewpoint, the Cr content is limited to the range of 8.0 to 10.0 mass%.

V: 0.05 to 0.50 mass% V is useful as an element for increasing the high-temperature strength, but its effect is poor when the content is less than 0.05 mass%, while V is 0.50 mass%.
If it exceeds ss%, the amount of (Cr + Mo) carbide generated is reduced,
On the contrary, since the high temperature strength is reduced, the V amount is 0.05 to 0.50.
It was limited to the range of mass%.

One or more selected from Nb, Ti and B: 0.01 to 0.20 mass% All of Nb, Ti and B increase the high temperature strength and
Since it is effective in miniaturization of the structure, it is necessary to contain it at 0.01 mass% or more. However, even if it is added in excess of 0.20 mass%, it does not form a solid solution in the matrix and its effect is saturated, so the upper limit is set to 0.20 mass%.

Mo: 0.50 to 3.00 mass% Mo is a useful element not only useful for solid solution strengthening but also for stabilizing carbides and improving high-temperature strength. However, when the content is less than 0.50 mass%, the effect of improving the high-temperature strength is poor. On the other hand, when the content exceeds 3.00 mass%, cracks occur at the time of rolling. Therefore, the content is limited to the range of 0.50 to 3.00 mass%.

N: 0.02 to 0.07 mass% N precipitates nitride and effectively contributes to improvement in high-temperature strength. This effect is exerted at a content of 0.02 mass% or more, but has a large effect on the Ni-Bal. Value.
Limited to the range of 0.02 to 0.07 mass%.

Cu: 1.00 mass% or less Cu is an element useful for improving corrosion resistance and high-temperature strength. However, if added in excess of 1.00 mass%, there is a concern that external surface cracks may occur during rolling of the joint steel pipe and cooling. Therefore, it was limited to the range of 1.00 mass% or less.

W: 2.00 mass% or less W effectively contributes to the improvement of high-temperature strength.
If the addition exceeds the range, there is a concern that external surface cracks may occur during rolling and cooling of the joint steel pipe, so the content was limited to a range of 2.00 mass% or less.

The composition range of the steel of the present invention has been described above. However, in the present invention, it is not sufficient to limit each component to the above range, and the Ni-Bal. Value represented by the following formula (1) is not sufficient. Ni-Bal. = Ni + 0.5 (Mn + Cu) +30 (C + N) -1.1 (Cr + 1.5Si + Mo + W) +8.2 --- (1) It is important to regulate within the range of 0.50 to 2.50.

FIG. 1 shows that a round billet was manufactured from molten steel in which the Ni-Bal. Value was variously changed by adjusting the composition, and then a crack was formed when the pipe was made through a drilling process, a drawing process, and a sizing process according to a conventional method. The results of investigations on the occurrence of are arranged and shown in relation to the Ni-Bal. Value. In the figure,
Those shown in white are those in which cracking was not observed. As shown in the figure, when Ni−Bal. = 0.44,
Pipe end cracks (tip cracks) were observed after the drilling process.
When Ni-Bal. = 2.57, cracks on the outer surface of the steel pipe were observed in the cooling process after the constant diameter process. Therefore, in the present invention, the Ni-Bal. Value represented by the above formula is limited to the range of 0.50 to 2.50.

The tip crack is defined as shown in FIG.
A pipe end crack that occurs during the drilling process. The outer surface crack is a crack generated on the outer surface of the steel pipe after the piercing-rolling-constant diameter as shown in FIG.

[0023]

EXAMPLES A round billet for a seamless steel pipe having various component compositions shown in Table 1 was perforated, drawn, sized and cooled under the following conditions to produce a high Cr seamless steel pipe. Table 1 also shows the results of investigation on the state of occurrence of cracks after each of the above manufacturing processes.・ Punching condition A 230mmφ billet is heated to 1280 ° C, and a seamless steel pipe with an outer diameter of 273.0 mm and a wall thickness of 12.7 mm is obtained by the Mannesmann plug mill method (piercer → elongator → plug mill → reeler mill → overheating → sizer mill). Rolled.

[0024]

[Table 1]

As shown in Table 1, any steel (No. 2 to 10) whose steel component composition satisfies the proper range of the present invention,
A steel pipe of good quality could be obtained without cracking of the steel pipe.

[0026]

As described above, according to the present invention, in the steel pipe manufacturing process after the round billet, a sound quality high Cr seamless steel pipe can be stably manufactured without generating steel pipe cracks.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the Ni-Bal. Value and the state of occurrence of cracks in a pipe making process.

FIG. 2 is a view showing a tip crack (tube end crack) generated during a drilling process.

FIG. 3 is a diagram showing cracks on the outer surface of a steel pipe that occur during cooling after a constant diameter.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Nobuhiko Morioka 1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works

Claims (1)

[Claims] 1. In mass percentage, C: 0.05 to 0.20%, Si: 1.00% or less, Mn: 1.00% or less, Ni: 0.05 to 0.50%, Cr: 8.0 to 10.00%, V: 0.05 to 0.50%, Nb , Ti, B, one or more selected from: 0.01
0.20%, Mo: 0.50 to 3.00%, N: 0.02 to 0.07%, Cu: 1.00% or less and W: 2.00% or less, and the Ni-Bal. Value represented by the following formula (1) is 0.50.
A high Cr seamless steel pipe steel which satisfies the range of ~ 2.50 and the balance is substantially Fe. Ni-Bal. = Ni + 0.5 (Mn + Cu) +30 (C + N) -1.1 (Cr + 1.5 Si + Mo + W) +8.2 --- (1) Here, Ni, Mn, etc. indicate the value of mass percentage of each component. .