JPS59226152A - Heat resistant cr-mo-v steel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a carbon fiber used in a rotor shaft for a steam turbine.
Regarding r-MO-V steel.

[Background of the invention]

Conventionally, high-pressure and intermediate-pressure rotor shafts of steam turbines are exposed to high-temperature atmospheres with steam temperatures of 566C or 538C, and are therefore required to have high creep rupture strength at high temperatures. Furthermore, in recent years, nuclear power turbines have been used for base load, whereas steam turbines have come to be used under harsh conditions such as frequent load fluctuations, startup and shutdown operations. Since high thermal stress occurs when a steam turbine rotor starts and stops, materials with higher toughness than before have become necessary. Therefore, a steam turbine rotor shaft having the above-mentioned high creep rupture strength and high toughness is required as a high-pressure and intermediate-pressure turbine rotor material.

The high-pressure and intermediate-pressure steam turbine rotor shafts exposed to such high temperatures have a 538C, 100,000-hour creep rupture strength of 15.5 Ks+/ran! The above is required.

The low-pressure rotor shaft used at steam temperatures below 350C contains 365%N, which contains a relatively large amount of Ni, which has high low-temperature toughness.
i-1,71Cr-0,4596Mo-0,13%V
steel is used. This rotor shaft material has extremely low creep rupture strength and cannot be used for high-pressure and intermediate-pressure turbine rotor shafts.

[Purpose of the invention]

An object of the present invention is to provide a heat-resistant steel having mainly a bainitic structure and having high creep rupture strength and high toughness.

[Summary of the invention]

The present invention mainly focuses on C and Si of steel having a bainitic structure.
The Cr-Mo-V heat-resistant steel is characterized by having a D value expressed by the following formula within a range of 22.9 to 22.6.

JJ)=(f c x fsi)X100 (however, f
c and fsi mean hardenability multiples determined by the respective contents of C and Si).

The above-mentioned steel has a weight of C0.27 to 0.35, sio
, below A section, Mn 0.5-1%, Nio, 1-o
, ats, cr O, 9-1.3 ts.

MO1~1.5%, Vo, 2~0.31 and balance Fe
Hardened and tempered forged steel having a bainite structure is preferred.

In the present invention, heat-resistant steel refers to steel that is used in a temperature range in which members creep.

Like impurity elements, Bi is an element that lowers creep rupture strength and promotes embrittlement during use, and also reacts with oxygen to form nonmetallic inclusions of SiO□, deteriorating the quality of steel. , a manufacturing method using a vacuum carbon deoxidation method (Si reduction) is adopted. This production method uses At, which has conventionally been used as a deoxidizing agent.

Since Si is not used at all, a high quality steel ingot can be obtained.

Hardenability decreases as the amount of Si decreases, making it difficult to ensure toughness in the center of the steam turbine rotor where the cooling rate is slow. The decrease in hardenability due to the decrease in Si increases the D value from 22.9 to 26.
．． By adjusting it within the range of 6, even better effects can be obtained.

The appropriate range of D was obtained by determining the influence of C and Si on creep rupture strength and toughness from a large amount of experimental data. D is expressed as (fcXfsi)X100, and fc and fsj mean hardenability multiples determined by the respective contents of C and Si, which are determined from the relationships shown in FIGS. 1 and 2.

The heat-resistant steel of the present invention has a D value of 22.
It should be in the range of 9 to 26.6.

If D is lower than 22.9, the toughness decreases significantly, so it should be 22.9 or higher. When D exceeds 26.6, agglomeration and coarsening of carbides is promoted, and creep rupture strength is significantly reduced. By adjusting D within the range of 22.9 to 26.6, high toughness and high creep rupture strength at the center of the steam turbine rotor can be obtained.

The bainitic structure is obtained by quenching and tempering, and has the highest creep rupture strength among low alloy steels. It is particularly preferred to have an entirely bainite structure.

Bainite structure is obtained by quenching and tempering treatment, but to obtain this structure, C, Mn, Ni, Cr, MO1
&hi VJt(7) component adjustment is required. These components can be adjusted as appropriate depending on the purpose of use.

C is an element necessary to improve hardenability, combine with MO and Cr to form carbide, and improve creep rupture strength at high temperatures.

For this reason, it is preferable to contain 0.2% or more; conversely, if the content exceeds 0.35%, the carbide tends to become coarse and the toughness and creep rupture strength decrease, which is not preferable. Particularly preferred is 1.0.27 to 0.351.

Although Mn increases hardenability and strength, a large amount of Mn impairs toughness, so it is preferably 1% or less. In particular, 0.5 to 1% is preferable.

Ni is an extremely effective element for increasing hardenability and improving mechanical strength and toughness at low temperatures, but when added in large amounts it tends to promote embrittlement and reduce creep strength. Therefore, 1 inch or less is preferable.

In particular, 0.1 to 0.6 inches is preferable.

Cr is an effective element for increasing hardenability and improving toughness and creep rupture strength, but the effect is saturated even if added in large amounts, so 0.5 to 1.5 Cr is preferable. . In particular, 0.9 to 1.3% is preferable. If it is less than 0.9%, oxidation resistance tends to deteriorate.

Mo is an element that is effective in increasing the strength at high temperatures and suppressing high temperature embrittlement in coexistence with C and Cr, and is preferably 0.5 to 2 H. In particular, 1 to 1.5 inches is preferred.

(2) is the most effective element for increasing the strength at high temperatures, but if added in large amounts, it lowers the ductility at high temperatures, so it is preferably 0.1 to 0.5%.

In particular, 0.2 to 0.3 kt is preferable.

[Embodiments of the invention]

Table 1 of Examples is a table showing the chemical components (% by weight) of the samples used in the experiment.

The method for producing these steel ingots is as follows.

The raw material is melted into a steel ingot in a true induction melting furnace (vacuum level 10'-3 ug), forged into a specified shape, heated at 970C, and then cooled to the cooling rate of the center of a rotor for general business use. Equivalent to. It was controlled to cool to 100 C/b and quenched. After quenching, it was held at 660p for a predetermined time and then cooled in the furnace.

The invention steels are Nos. 1 to 3 and the comparative steels are Nos. 4 to 6, all of which have a completely bainitic structure.

Figure 3 shows a 2mm V notch Charpy FM piece (JISZ
No. 22024 test piece)
FIG. 2 is a diagram showing the relationship between absorbed energy and D determined in FIG.

As shown in the figure, the absorbed energy increases linearly as D increases.

The absorbed energy required for the central portion of the steam turbine rotor is 0.71 to 1n or more, but if D of Comparative Steels 4 and 5 is less than 22.9, the above required value is not satisfied. D
should be 22.9 or higher.

Figure 4 is a diagram showing the relationship between 1,538c, 100,000 hour creep rupture strength and D. As shown in the figure, the creep rupture strength decreases as D increases.

Strength required for steam turbine rotor: 15.5Kv-'
In order to satisfy the following, D should be 26.6 or less.

Comparison jil'16 (D=28.0) does not satisfy the required value.

From the results of Figures 3 and 4, it is D from the point of absorbed energy.
D should be 22.9 or more, and D should be 2 from the point of view of creep rupture strength.
It should be 6.6 or less.

〔Effect of the invention〕

As described above, the heat-resistant steel of the present invention has a D of 22.9 to 26.
By adjusting the C and Si components within the range of 6, it is suitable for manufacturing high-pressure and intermediate-pressure rotors for steam turbines having high creep rupture strength and high toughness.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the amount of C and the hardenability multiple fc, FIG. 2 is a diagram showing the relationship between the amount of Si and the hardenability multiple fsi,
FIG. 3 is a diagram showing the relationship between creep rupture strength and D, and FIG. 4 is a diagram showing the relationship between M yield energy and D. Figure 1c <y-noSt('t) p=Cchicx fs;)xtoo [SeD=C9XfSi)X100''

Claims (1)

[Claims] 1. C0, 20-0.35%, Mlll, 5% or less, Ni 1% or less, Cr 0.5-1.5%, Mo0.
In low alloy silver copper consisting of 5 to 2%, Vo, 1 to 0.5%, S: O, a% or less and the balance Fe, the amount of C and Si is expressed by the following formula % formula %) (However, fc, Or-Mo-V characterized in that D=22.9 to 26.6 when expressed as (fsi means hardenability multiple determined by each content of C and Si) Heat resistant steel.