JPS59208055A - Martensitic stainless steel for seamless steel pipe - Google Patents

Abstract

PURPOSE:To provide a martensitic stainless steel from which a seamless steel pipe can be manufactured at a low cost with high productivity by contg. respectively C and Cr at prescribed ratios, regulating the content of ferrite at a specific high temp. and regulating respectively the contents of P and S to specific values or below. CONSTITUTION:The contents of S and P which are unavoidable impurities in a martensitic stainless steel pipe contg. by weight, <=0.30% C and 11-14% Cr and the ferrite content at 1,200 deg.C are regulated as follows: The content of S is regulated to <=0.003% and the content of P to <=0.02%, respectively. The resultant martensitic stainless steel permits production of a seamless steel pipe by a plug mill system or mandrel system without generating defects during the manufacture of the pipe. The productivity in the pipe manufacture is thus made higher than in the conventional manner and the cost is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to martensitic stainless copper used for seamless pipes such as oil country tubular goods and line pipes.

Martensitic stainless steel (which is represented by SUS 410 steel grade or SUS 420 Koshin) has a high carbon content (including CO2).4. Since it exhibits corrosion resistance under the condition of '1,
It is attracting attention as a material for oil country tubular goods, geothermal country tubular goods, line pipes, etc.

By the way, seamless stainless steel pipes are generally made by a tilted F rolling method such as a plug mill method or a mandrel mill method, or a hot extrusion method such as the Eugene Sejourne method or the Erhardt push bench method. Some kinds of steel ';jl'H)11 have poor hot workability, so when manufacturing seamless pipes using an inclined rolling method such as a plug mill method or a mandrel mill method,
When drilling with a piercing mill (piercer), defects may occur on the outer or inner surface. Therefore, such steel types are usually manufactured using a hot extrusion method typified by the Eugene-Cégir-Rne process.

However, when applying the hot extrusion method to directly perforate the billet (direct perforation method), the length of the billet is 50% of the diameter.
If it is ~7 times the thickness, the uneven thickness will be large, so the length of the long pipe is m4.
It is difficult to build. In order to solve this problem, a method has been adopted in the past that involves forming a guide hole in the center of the billet in advance by processing the roots, and then expanding the hole by pushing it out to create a long tube using the wave expansion method. ing. However, even in this expansion method, the length of the billet is approximately 15 times the diameter, 1 jll
Va is applied. Furthermore, in the Eugene Sejour method, which is a typical hot extrusion method, a glass lubricant is used, so after rolling the glass I'lff! Although it is necessary to peel off the lubricant, this peeling process has the disadvantage of requiring the same amount of effort and cost as A.

As mentioned above, in the hot extrusion method typified by the Eugene-Cégir René process, the billet length is reduced to a trill, so productivity cannot be increased beyond a certain level, and the yield is also reduced due to the use of short billets. I have no choice but to go low.
There is also the problem of being disadvantageous in terms of cost. On the other hand, both the plug mill method and the mandrel mill method use a piercing mill that utilizes the Mannesmann effect.
These methods can produce long tubes compared to hot extrusion methods such as the Eugene Ségir Ne method, and therefore have various advantages such as high productivity and cost advantages. However, as mentioned above, the actual situation is that it is difficult to apply it to some types of martensitic stainless steel due to the problem of defects occurring during pipe manufacturing.

This invention was made in view of the above situation, and it is made of martensitic stainless steel, which has been difficult to manufacture seamless steel pipes using the conventional plug mill method and mandrel mill method due to the problem of defects during pipe manufacturing. We have made it possible to practically apply the plug mill method and mandrel mill method to some of the materials, thereby making it possible to manufacture this type of seamless martensitic stainless steel R with high productivity and at low cost. ``J-'' is ``1''.

j-i' (straw, frag milling method or mandrel milling force, (, depending on the marten-leaite stainless steel field I 6in 'If of course 4), when ferrite;:1: is large , specifically, ferrite: 1. is 40φ j).'!:
For example, it is conventionally possible to produce a product without causing defects, but when the ferrite acid is as small as 40 and t > 784, At the time of construction, there were multiple defects on the inner and outer surfaces and cracks at one end.
It is said that it is difficult to use IJ as an actual process.
Therefore, the inventors of the present invention have determined that 1-ii is 40 or more -F's 2'i = (To! i As a result of iFc analysis, it was found that P and S as impurities in η exert a large influence ν + Iτ on this type of defect occurrence.
In addition, (01 yuan, if, `` Kokoro, S 0.0
0: 3 or more threads, 0.020 or less by regulating the number of threads to 0.020 or less, the plug mill method or mandrel mill method is used to avoid the above-mentioned defects. It was from Princess Ng's knowledge that it was possible to manufacture and use the product and this invention was made.

Specifically, the first invention has C0.30% or more)', Cr11
~Containing 1.1 candy and ferrite p in tzoo'c
Martensitic stainless steel type 4 with a value of 40 or more F
, p4 is 0.02% or less, S'r depression is 0.00
:Hot drilling 1 with a width of 3 or less.
We offer a completely new type of martensitic stainless steel. In addition to the above-mentioned components, the second invention also contains 111 elements (hereinafter referred to as REM) and Ca.

At least IA or higher of B, T7EM:4X (Attack S
) ~20X (%S), Ca:IX (person in charge) ~tox
(%S), B: 0. Added within the range of 001 to 0008, the hot porosity has been reduced (Ii multi-tensitic stainless steel for pipes).

The martensitic stainless steel of this invention will be described in more detail below.

First of all, to explain the reason for limiting each component in this Hikama steel, C is Moto Nitake, which is necessary to ensure strength.
If it exceeds 0.030 inches, the corrosion resistance will deteriorate, so it was limited to 0.030 inches or less.

Cr is an element that significantly improves corrosion resistance in a CO2 environment, and in order to prevent pitting corrosion and crevice corrosion, it is necessary to add a factor of 11 or more, 1ε. On the other hand, Cr is a ferrite-forming element, and if its addition exceeds 14, ferrite is formed.
;;, L increases, stress corrosion resistance increases by -1d
It is difficult to achieve a predetermined strength under heat treatment conditions (temperature: 2,000 yen).Therefore, the range of Cr was set to 11 to 14%.

S is an unavoidable impurity contained in steel, but it significantly deteriorates hot workability in steel A1a, which is the subject of this invention. The negative effect is particularly noticeable when manufacturing by the grab mill method or mandrel mill method, except for piercing with a piercing mill. Therefore, S needs to be regulated to 0.003% or more (.zeta).

■] is also an unavoidable impurity (contained in rlIll, but it significantly deteriorates the thermal processability at high temperatures of 1200°C or higher. In particular, This causes scratches to occur.P is 0
．． If it exceeds 0.2%, it will be difficult to drill without creating scratches.
1#, P must be set to 0.02% or less by -11.

In addition, the sea bream targeted in this invention has a ferrite content of 40 F or more at 1200°C.

9, where the amount of ferrite at 1200°C exceeds 40%,
In 1, as mentioned above, the plug mill or mandrel mill method can produce seamless seams without any defects or problems.
This is because it can be constructed in J. Huerai here)
The amount (%) is defined by the following equation (1).

Ferrite - Se (related) = -195X (%C) -185X
(%N)-18(%Ni)-6X (%Cu)-
5X(%Mn)-1-5X(%Si)+12X(%
Cr)+16X(%V)-5×(%Mo)+6×
(φNb)+5x(φTi)+50X(Ad)-12
0... (1) Furthermore, in the second invention of the present application, REM, Ca, B
Add one or more of the following.

REM or Ca is a strong sulfide forming element, R
By forming sulfides of FJ, 11, or Ca, they are effective elements for reducing the amount of solid solution S in steel and improving hot workability. /kohaS
'llt and this 1. 'j, the effect is small in the case of 71. On the other hand, 20 times of S, jji: or l
(If ΔJi is added to
Since there is a risk of increasing l<'t+'ir defects, for REM (4X (%S) to 20X (related S)) 635 songs, and for Ca, 1X (%S) to 10X
(%S) each limited to one box.

B changes its hot workability by adding 4rJ
3 stir, but 0. I) 01 %; Trust] island has no effect, while if it exceeds 0,008 %, it will reverse the effect and deteriorate the processing color 2 between ;:L. From Btd (limited to the range of 1,001 to 0008 fissures).

Table 1 shows the chemical composition and defect occurrence status of 'A', 1t(4) and Comparative Example of this invention. t
Add the billet consisting of J# to 1230"C and put it into a piercing mill (beam) for 1 degree. Cf = 185 +ir, t, ring opening 197
Observe the inner and outer surfaces of the holes drilled to form 6 gourds.If the defect is caused by scratches or cracks, mark it with an X; if the defect is fz, or if there is no ○ is marked for cases where there is no problem in practical use. Further, in Table 1, the ferrite resistance (φ) was determined by the equation (1) above, and the value was expressed as 0 for the negative side 1.

・Is it good for E1 table? 1 person who was sentenced to 1 bite;
it, Bu 517-2214, all P 4.1-1
: , S'+41 is the present invention, ε; the upper limit of one circle is 11~
All of these are missing 1s16.
No'd was born. -1' - 1' bowing voice] test t
23rd and 24th.

25, Uyoso A ('re REM, B, Ca is the second
The upper limit of the starting range of J was exceeded by iA, and defects occurred in all of these.

As is clear from the following explanation, the "1'1"shoulder" martenitic sudenless psi 1 of the present invention for use with the conventional plug mill method or mandrel mill method; ] Nothing ga・j ``'Jin's trend □′ to 1
;((Since the ferrite jij, which was considered to be 4o [
ir + (despite the fact that j can be achieved in the pillar, P , S”=
By suffering iill, you can go out into the world, especially public self-piercing i student:1/C, and therefore 1゛! iii, 11 Extrusion by 2 people without causing any defects using the plug mill method or mandrel mill method. By applying the plug mill method or the mandrel mill method to the two rods, productivity is improved compared to the 111-bottle. As the temperature increases, the yield can be lowered and costs can be reduced.

In addition, the second invention, the seamless colorless martensitic stainless steel e'+jJ for 1 steel, is P, S,! Rule ij+
By adding one or more of REM, Ca, and B at the same time as 1ill, the hot perforability is further improved, and therefore, it is possible to manufacture healthier seamless steel pipes using the mandrel mill method or plug mill method. can.

Applicant: Kawasaki Steel Corporation Agent: Patent Attorney Mori Takehisa Ta (1 other person)

Claims (1)

[Claims] (1) CO: 30% (contains 11 to 14 Cr and 1200°C)
Martensitic stainless steel with a ferrite r+・ili' of 40 or more! 1.], set P tit to 0.02 (IJ, IJ F, S P
'1 to o, o O3% or more) 1 layer Ull': 'Seamless with ¥ loss';, 1/4S Marten Size 1 Series Stainless Steel 1. -i +1 t2) CO, 30% or more F, Cr 1 , L ~ 14
% and +20+)'C ferrite,
l: Martensitic stainless steel with a diameter of 40° or higher? Here, P...4' (1.02% or less, S amount 1.1 (, less than 0.003φ), and one or more of the elements Ca, B, etc. (Du, 2 φ or more, rare earth elements: 4 × (S) ~ 2 (IX (%S), C
a: IX (%S) ~lOX (%S
), B: o, o ot~(1,008'its
] Muda, η
Martensitic stainless steel for pipes.