JPS6013056A - Heat resistant martensitic steel - Google Patents

Abstract

PURPOSE:To obtain a heat resistant martensitic steel with superior strength at high temp. and superior toughness by adding a proper amount of Mo or W to a steel having a specified composition contg. Si, Mn, Ni, Cr, V, Nb, Al, etc. CONSTITUTION:This heat resistant martensitic steel has a composition consisting of, by weight, 0.10-0.20% C, 0.01-0.06% N, <=0.5% Si, <=0.5% Mn, <=0.6% Ni, 9-12% Cr, 0.1-0.3% V, 0.01-0.06% Nb, <=0.015% Al, <=6% Co, 1-3% Mo and/or 1-4% W and the balance Fe with inevitable impurities and satisfying relation represented by an equation Co%>=Mo%+0.5W%-2.3. By the steel composition, the formation of delta-ferrite can be inhibited, so superior strength at high temp. and high toughness are provided while avoiding the purposeless addition of Co.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a martensitic heat-resistant steel having excellent high-temperature strength and toughness.

Martensitic 120R, which has high high temperature strength and resistance to thermal fatigue (and has large damping capacity), is used for various parts such as power generation plants, chemical plants, pinch rollers for continuous casting, and heat treatment trays.
Heat-resistant steel has traditionally been used. In recent years, this type of plant/equipment has been required to operate at high temperatures and
With the aim of improving efficiency through high-pressure operation, the operating conditions for each component have also tended to be higher temperatures and higher stress. Therefore, conventional steels such as 80840 B and 8UH616 lack high-temperature strength, and martensitic heat-resistant steels having higher high-temperature strength have been required. In addition, steam turbine power generation plants in particular have come to be operated in accordance with electricity demand, resulting in an increase in the number of starts and stops due to intermittent operation, and the need for toughness and fatigue strength in components such as blades and rotors. . An object of the present invention is to provide a martensitic heat-resistant steel that has high high-temperature strength and high toughness and is suitable for such severe usage conditions.

The gist of the present invention is as follows: (1) C: 0.10-0.20%, N: 0.0
1 to 0.06%, si: 0.5% or less, Mn: 0.
5% or less, Ni: 0.6% or less, Or: 9-12%
, v: o, i~o, s%, Nb: 0.01~0.0
6%, Mo: 0.015% or less and 1 to 8% Mo, 1 to 4
At least one type of W in the form, and if necessary, 6% or less of c.

A high-temperature steam turbine with high high-temperature strength and toughness characterized by containing CoQ6≧Mo%+0.5W%-2,8 to satisfy the relationship, and the remainder consisting of Fe and unavoidable impurities. Heat-resistant steel for blades, discs, rotors, and bolts.

The steel of the present invention suppresses Ni, which is harmful to high-temperature strength, to a low level, and
By adding a larger amount of W than conventional steel to obtain excellent high-temperature strength, at the same time suppressing the addition of C to the minimum necessary to ensure room-temperature strength, and achieving an overall balance of components to suppress δ-ferrite. It is characterized by the fact that high toughness can be obtained by using .

According to the present invention, the effect of suppressing δ-ferrite is remarkable.If the component balance of the amount of Go added is defined in relation to the amount of MOLW added, δ-ferrite, which deteriorates high temperature strength and toughness,
- Generation of ferrite can be suppressed and pointless addition of cobalt can be avoided.

Next, the reasons for limiting each component will be explained.

c: o, i ~ 0.2% C is dissolved in the matrix martensite and at the same time (3r,
It is a basic element required to combine with carbide-forming elements such as Mo, W, and Nb%V to form carbides and obtain strength at room temperature and high temperature. If it is less than 0.1%, no strength will be obtained, and if it exceeds 0.2%, the amount of carbides will increase,
Since this impairs the toughness and at the same time lowers the creep rupture strength, 0.1 to 0.2% is appropriate. Preferably, in relation to N described below, 0+2N: 0.15 to 0.24.

N: 0.01-0.06% Like C, N is also dissolved in the matrix martensite, and Nb
, V, etc., to form nitrides, and is an element necessary to obtain strength at room and high temperatures. If it is less than 0.01%, there is no effect, and if it exceeds 0.06%, 3riN will precipitate and deteriorate the toughness and high temperature strength.
06% is appropriate, preferably 0+2N as in the previous section:
The content is preferably 0.15 to 0.24%.

8i: 0.5% or less 8 Blood is added as a deoxidizer, but if added in large amounts, δ-
Since it promotes the formation of ferrite, it should be 0.5 type or less.

Mn: 0.5% or less Mn is also added as a deoxidizing agent like 81, or it is set to 0.5% or less since it promotes the formation of retained austenite.

Ni: 0.6% or less Ni is usually added to suppress δ-ferrite and improve toughness by solid solution in the martensite matrix, but it also lowers the Aat point and increases the creep rupture strength at high temperatures. Therefore, in the steel of the present invention, which places particular emphasis on high-temperature strength, the
．． The limit is 6%.

(3r: 9-12% Or is an essential element for the steel of the present invention like C, and at the same time imparts corrosion resistance and oxidation resistance, it also forms carbides and imparts high temperature strength. Furthermore, Or is %, austenite forming elements such as co and Mo.

It is a powerful element that adjusts the balance with ferrite-forming elements such as W%V%Nb when suppressing the formation of δ-ferrite and retained austenite. 9
If it is less than 12%, the corrosion resistance and oxidation resistance will deteriorate, and if it exceeds 12%, the ability to adjust the above component balance will be lost, and δ-ferrite will be produced, reducing toughness and high-temperature strength.
~12% is suitable.

V: 0.1 to 0.8 V combines with O and N to form fine carbonitrides, increasing strength at room temperature and high temperature, and at the same time making crystal grains finer and improving toughness.

If the content is less than 0.0, iq6, the effect will be small, and if it exceeds 0.8%, the reinforcing effect will be saturated, so 0.1 to 0.8% is appropriate.

Nb: 0.01-0.06% Nb combines with C%N to form carbonitrides, making crystal grains finer and improving toughness.

Nb carbonitride exists relatively stably even in the austenitic state, so it prevents crystal grains from becoming coarser, and compared to steel in which Nb is not intentionally added, the effect of making the crystal grains finer is greater even with a relatively small amount of Nb. big. If it is less than 0.01%, there will be no effect, and if it exceeds 0.06%, the effect will be saturated.
01 to 0.06% is appropriate.

At: 0.015% or less M is added as a deoxidizing agent, but since it has a strong affinity with N, it forms AtN, reducing the amount of nitride in solid solution N'M1V,
As a result, the strength at room temperature and high temperature is reduced, so the upper limit is set at 0.015%.

MO: 1 to 8% Mo forms carbides and increases the strength at room temperature and high temperature, increases resistance to temper softening, and causes secondary hardening. In particular, No is dissolved in Ms+sOs type carbide,
Suppresses agglomeration and coarsening of MxsOs and increases creep rupture strength on the high temperature and long time side. If it is less than 1911, the effect will be small, and if it is more than 8%, it will be difficult to suppress the production of δ-ferrite even if other components are adjusted, and a large number of MsO type carbides will be formed, reducing high temperature strength. % is appropriate.

W: 1-4% W is an element that has the same effect as Mo, and when compared at equal atomic % (approximately twice that of Mo in weight %), it is slightly more effective than Mo, providing particularly excellent high-temperature strength. It is valid in some cases. If it is less than 1%, the effect is small, and if it exceeds 4%, it becomes difficult to suppress δ-ferrite, and at the same time, a large amount of M2C type carbide is formed, resulting in a decrease in high-temperature strength.

Co: 6% or less CO is added for the purpose of suppressing the formation of δ-ferrite, but unlike Ni, it does not significantly lower the A (11 points).
Since it does not reduce the creep rupture strength, Mo,
It is extremely effective when adding a large amount of a ferrite-forming element such as W.

When Mo and W are added, the amount of Co added is Co%≧Mθ
%+0.5W%-2.8, the amount δ that harms the characteristics
-No ferrite is produced. However, even if Co itself is dissolved in martensite, it does not have the effect of increasing the creep rupture strength and is therefore expensive, so the upper limit is set at 6%.

Next, the characteristics of the steel of the present invention will be explained using examples.

The inventive steel and comparative steel having the compositions shown in Table 1 were produced by vacuum melting, hot forged to a diameter of 25 f6, and then quenched and tempered to investigate their properties. Comparison steel P1Q1 is 8UI each
(616,8U840 B, steel equivalent to [58).

Table 2 shows the sample materials heated at 1000℃ for 30 minutes and then oil quenched.
The room temperature strength, impact properties, and creep rupture strength when tempered by heating at 700° C. for 1 hour and then air cooling are shown. From this, it can be seen that the steel of the present invention has a room temperature strength comparable to that of the conventional steel P%, and has excellent toughness and creep rupture strength as shown in Table 2.

In addition, in comparison steel S, the amount of Co added is smaller than the amounts of Mo and W.
Comparative Steel V, which is a steel that does not satisfy 8, is a steel in which the amount of Mo added exceeds the upper limit, but both have a low impact value and creep rupture strength because a large amount of δ-ferrite is generated. In addition, Comparative Steel T has Ofi exceeding the upper limit,
Since many coarse carbides are formed, the impact value is reduced.

Comparative steel U has Ni added beyond the limit, and has a relatively good impact value, but has a low creep rupture strength.

As described above, the heat-resistant steel according to the present invention has excellent toughness and extremely high high-temperature strength, and is useful as a high-temperature member that requires toughness.

Applicant Daido Steel Co., Ltd. Agent Yoshio Kawaguchi Procedural amendment dated September 6, 1986 Kazuo Wakasugi, Commissioner of the Patent Office1, Indication of case Patent application No. 1981-14319782, Jllll name marten pipe) Heat-resistant steel 3, relationship with the case of the person making the amendment Applicant's address: 66 Kade, Hoshizaki-cho, Minami-ku, Nagoya, Aichi Prefecture Name
(371) Father Shodaka Co., Ltd. Representative: Monzan 1i 4, Agent Address: 1-7-13-5 Nishi-Shinbashi, Minato-ku, Tokyo 1-7-5 Date of amendment order (1 issue) 8. Details of the amendment Copy the entire text (without any changes) as shown on the attached sheet.

Claims (2)

[Claims] (1) In weight form, O: 0.10-0.20%, N: 0.
01-0.06%, 8i: 0.5 form or less, Mn:
0.5% or less, Ni: 0.6q6 or less, Cr: 9
~12%, v:o, t~o, s%, Nb:0.01~0
．． 06%, Mo 1: 0.015% or less and 1 to 8% Mo,
Contains at least one type of W from 1 to 4q6, and the remainder is F
Martensitic heat-resistant steel with excellent high-temperature strength and toughness, characterized by consisting of E and irreversible impurities. (2) Weight 4 TeO: 0.10-0.20q6, N
: 0.01No, 06 type, Si: 0.5q6 or less, Kn: 0.596 or less, Ni: 0.696 or less, Cr: 9-12%, V: 0.1-0.8%, Nb
: 0.01-0.06 type, Mu1: 0.015% or less,
(3o: 6g6 or less and 1-8q6Mo, 1-4%W
containing at least one of the following, the remainder consisting of Fe and irreversible impurities, and co. A martensitic heat-resistant steel having excellent high-temperature strength and toughness, characterized in that Mo and W satisfy the relationship (3o%≧Mo%+0.5W%−2.8).