JPH0649601A - 5cr series heat resistant steel - Google Patents

Abstract

PURPOSE:To obtain a 5Cr series heat resistant steel excellent in high temp. strength and capable of providing an excellent service life and reliability according to the purpose of use by specifying the compsn. constituted of C, Si, Mn, Ni, Cr, Mo, V, N and Fe. CONSTITUTION:The 5Cr series heat resistant steel has a compsn. contg., by weight, 0.05% to 0.30% C, <=0.3% Si, 0.1 to 1.5% Mn, <=1.0% Ni, 4.0 to 6.0% Cr, 0.1 to 1.5% Mo, 0.05 to 0.3% V and <=0.1% N and furthermore contg., at need, 0.01 to 0.20% Nb, and the balance Fe with inevitable impurities and is excellent in high temp. strength compared with that of the conventional one. This 5Cr series heat resistant steel can be obtd. by melting the steel having the prescribed compsn. by an electric furnace or the like, subsequently executing electronics melting or vacuum arc melting according to necessity into an ingot, subjecting it to heating to about 1000 to 1200 deg.C, executing hot working into the element assembly of each parts, thereafter heating it to about 900 to 1100 deg.C, subjecting it to oil hardening and subsequently executing tempering at about 550 to 700 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a 5Cr heat resistant steel, and is particularly used for nuts, bolts, shrouds, valve seats and nozzle plates of steam turbine members, gas turbine members and boiler members.

[0002]

2. Description of the Related Art Conventionally, as a nut material for a high temperature bolt of a steam turbine, a 5Cr steel having excellent seizure resistance and oxidation resistance has been used.

[0003]

However, the conventional 5Cr steel cannot be said to have sufficient high-temperature strength, and it has been dealt with by design measures such as dimensional change. The present invention has been made in view of these circumstances, and an object thereof is to provide a 5Cr heat resistant steel having excellent high temperature strength properties as compared with conventional ones.

[0004]

The first aspect of the present invention is to provide C: 0.05 to 0.30% by weight, Si: 0.3% or less by weight,
Mn; 0.1 to 1.5%, Ni; 1.0% or less, Cr;
4.0-6.0%, Mo; 0.1-1.5%, V;
05-0.3%, N; 0.1% or less, balance Fe
And a 5Cr-based heat-resisting steel.

The second invention of the present application is C; 0.05% by weight.
~ 0.30%, Si; 0.3% or less, Mn; 0.1
1.5%, Ni; 1.0% or less, Cr; 4.0 to 6.0
%, Mo; 0.1 to 1.5%, V; 0.05 to 0.3
%, Nb: 0.01 to 0.20%, N: 0.1% or less, and the balance is Fe and incidental impurities. In the present invention, the reason for limiting the composition is as described below. (1). C (carbon)

[0006] C is an element that forms an alloy carbide and significantly changes the material strength and the toughness at room temperature, and is an element necessary for ensuring the tensile strength and creep rupture strength. If C is less than 0.05%, the hardenability is insufficient and the required properties cannot be obtained. On the other hand, if C is added in excess of 0.30%,
The toughness at room temperature decreases, and the coarsening of carbides becomes remarkable, resulting in a decrease in creep rupture strength for a long time. (2). Si (silicon)

Si is an element effective as a deoxidizer,
Addition of a large amount reduces toughness. Since the reduction in Si reduces the deterioration of toughness after long-term use and improves the high temperature characteristics, Si is set to 0.3% or less. (3). Mn (manganese)

Mn is added as a deoxidizing agent, but 0.1
If it is less than%, the effect is insufficient and the effect is small. If added in excess of 1.5%, it hardens the steel, impairs workability, and lowers the creep rupture strength. (Four) . Ni (Nickel) Ni improves hardenability and toughness at room temperature,
Since the creep rupture strength is reduced, Ni is set to 1.0% or less. (Five) . Cr (chrome)

Cr is necessary to improve mechanical properties, oxidation resistance and corrosion resistance, and creep rupture strength, and is set to 4.0% to 6.0% in order to secure stable seizure resistance. (6). Mo (molybdenum)

Mo is effective in improving creep rupture strength as a solid solution strengthening element and a fine carbide precipitation strengthening element.
If it is less than 1%, a sufficient effect cannot be obtained, and if it exceeds 1.5%, the toughness decreases. (7). V (vanadium)

V forms fine precipitates of VC and improves the creep rupture strength, but if it is less than 0.1%, a sufficient effect cannot be obtained, and if it exceeds 0.3%, the solid solution V increases, On the contrary, the strength and toughness are impaired. (8). Nb (niobium)

[0012] Nb forms carbides and NbC similarly to V, significantly improves creep rupture strength, and is also effective for refining crystal grains, but if it is less than 0.01%, the above effect cannot be obtained. . On the other hand, if it exceeds 0.2%, undissolved NbC is increased by quenching and coarse NbC is also generated, which reduces ductility and toughness and further reduces long-term creep rupture strength. (9). N (nitrogen)

N is an element effective for improving the high temperature creep rupture strength. However, if N is added in excess of 0.1%, not only the toughness at room temperature is lowered, but also the nitrides are aggregated to form coarse particles. To decrease creep rupture strength, so
It was set to 1% or less.

[0014]

The 5Cr heat-resisting steel according to the present invention is obtained by melting in an electric furnace or the like, or by electronic melting or vacuum arc melting to obtain a steel ingot, and then the steel ingot
After heating to 1200 ° C. to perform hot working into each element body, after heating to 900 ° C. to 1100 ° C., quenching in oil and the like are performed, and subsequently tempering heat treatment is performed at 550 ° C. to 700 ° C.

[0015]

Embodiments of the present invention will be described below.
The following "Table 1" shows the chemical composition of the 5Cr heat resistant steel according to the present invention (invention steel) and the comparative steel.

[0016]

[Table 1] Specimen No. 1-No. No. 5 is the steel of the present invention, and the test material N
o. 6, No. Reference numeral 7 is a comparative steel, which is 5Cr steel used as a current nut material.

All the test materials were melted in a high-frequency induction furnace, forged into a steel ingot, heated at 900 ° C to 1100 ° C, and then rapidly cooled in oil, followed by quenching treatment. kgf / mm ² ~ 95 kgf / mm ² To be 640
Tempering was performed in the range of ℃ to 680 ℃. Next, a room temperature tensile test piece, a high temperature tensile test piece and a creep rupture test piece were sampled from each test material and tested. "Table 2" below
Indicates the results of normal temperature tensile test.

[0018]

[Table 2] The high temperature tensile test is performed at 600 ℃, the creep rupture test is 600 ℃, and the stress is 20 kgf / mm ² It was performed under the conditions of. The following "Table 3" and "Table 4" show the respective results.

[0019]

[Table 3]

[0020]

[Table 4]

As is apparent from Table 3, the steel of the present invention has higher high temperature strength than the comparative steel. Also, regarding the creep rupture properties of Table 4, it can be confirmed that the steel of the present invention has a significantly improved rupture life as compared with the comparative steel and has a sufficiently large rupture ductility.

As described above, according to the above-mentioned embodiment, the high temperature strength is high, the creep rupture life is remarkably improved, and the fracture ductility is sufficiently large as compared with the conventional one (comparative steel).
Cr-based heat resistant steel can be obtained.

[0023]

As described above in detail, according to the present invention,
It is possible to provide a 5Cr heat-resisting steel which is superior in high-temperature strength properties to conventional applications and which has a life and reliability superior to those of conventional steels when used in applications requiring high-temperature strength properties.

Claims (2)

[Claims] 1. C in weight%; 0.05 to 0.30%, S
i: 0.3% or less, Mn: 0.1 to 1.5%, Ni;
1.0% or less, Cr; 4.0 to 6.0%, Mo; 0.1
˜1.5%, V: 0.05 to 0.3%, N: 0.1% or less, and a balance of Fe and incidental impurities. 2. C by weight%; 0.05-0.30%, S
i: 0.3% or less, Mn: 0.1 to 1.5%, Ni;
1.0% or less, Cr; 4.0 to 6.0%, Mo; 0.1
~ 1.5%, V; 0.05 to 0.3%, Nb; 0.01
.About.0.20%, N; 0.1% or less, and a balance of Fe and incidental impurities.