JP2001073092A - 9-12% Cr HEAT RESISTING STEEL EXCELLENT IN HIGH TEMPERATURE STRENGTH AND TOUGHNESS, AND ITS MANUFACTURE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent high temperature strength and toughness by providing a composition consisting of, C, V, Si, Nb, Mn, N, Ni, B, Cr, either or both of Mo and W, and the balance Fe with inevitable impurities. SOLUTION: The steel is a 9-12% Cr heat resisting steel excellent in high temperature strength and toughness and having a chemical composition consisting of, by weight, 0.01-0.16%; C, 0.10-0.30% V, <=0.10%; Si, 0.02-0.10% Nb, <=0.20% Mn, 0.01-0.07% N, 1.6-2.8% Ni, <0.001% B, 9.0-12.0% Cr, either or both of 0.5-1.7% Mo and 0.1-2.0% W, and the balance Fe with inevitable impurities. A material having the chemical composition is prepared, and this material is subjected to forging under the conditions of 1,050-1,500 deg.C heating temperature at final forging, 700-900 deg.C material-surface temperature at the completion of forging, and >=20% draft, to quenching heat treatment at 1,030-1,090 deg.C quenching temperature, and then to tempering heat treatment at 500-650 deg.C tempering temperature, by which the steel having crystal grains finer than those of grain size number No.3.0 can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a 9-12% Cr heat-resistant steel excellent in high-temperature strength and toughness, and a method for producing the same, and in particular, a gas turbine disk and / or a compressor, which are important parts constituting a gas turbine. Disc material.

[0002]

2. Description of the Related Art In order to improve power generation efficiency, the gas combustion temperature of gas turbines has been increased, and accordingly, the metal temperature of gas turbine disks and compressor disks has also increased. Conventional low alloy CrMoV steel and 3.5N
iCrMoV steel and the like have been used. However, it cannot be used in a high temperature region where the metal temperature exceeds 440 ° C., and steel having higher strength and higher toughness is required. Ni-based alloys have sufficient high-temperature strength, but are extremely inferior in hot workability and machinability, and their production costs are extremely high. On the other hand, 12
As for the% Cr-based steel, Japanese Patent Publication No. 6-50041 is known.
However, this material has sufficient high-temperature strength, but lacks toughness. This is because elements that contribute to toughness and high-temperature strength have not been optimized.

[0003]

Generally, in conventional materials, when the strength at high temperatures is increased, the toughness tends to decrease. In order to increase the toughness, it is most effective to increase Ni, but the high-temperature strength tends to decrease. On the other hand, in order to improve the high-temperature strength, it is necessary to lower Ni and increase B. An object of the present invention is to provide a 9 to 12% Cr heat-resistant steel excellent in high-temperature strength and toughness by optimizing Ni and B under such a technical background, and a method for producing the same. I do.

Further, according to the present invention, the metal temperature is 440 ° C.
It is an object to provide a gas turbine disk or / and compressor disk material for a gas turbine that exceeds 100%.

[0005]

In order to achieve the above-mentioned object, the present invention relates to 9-1 to 9-1 having excellent high-temperature strength and toughness.
2% Cr-based heat-resistant steel is expressed in terms of% by weight: C: 0.10 to 0.16 V: 0.10 to 0.30 Si: ≤ 0.10 Nb: 0.02 to 0.10 Mn: ≤ 0.20 N: 0.01 to 0.07 Ni: 1.6 to 2.8 B <0.0010 Cr: 9.0 to 12.0 Mo: 0.5 to 1.7 or W: 0.1 to 2. One or two kinds of 0 and the balance have a chemical composition composed of Fe and inevitable impurities (Claim 1).

A 9-12% Cr heat-resistant steel excellent in high-temperature strength and toughness according to another aspect of the present invention has a Ni ≦ 600.
0 × B (claim 2). Further, according to another aspect of the present invention, 9 to
The 12% Cr heat-resistant steel is characterized in that the working ratio at the time of final forging is 20% or more and the grain size (ASTM No.) is finer than 3.0 (Claim 3). 9 to 9 having excellent high-temperature strength and toughness constituted by the above embodiments of the present invention.
The 12% Cr heat-resistant steel is suitably used as a gas turbine disk and / or compressor disk material for a gas turbine (claim 4).

Next, according to the method for producing a 9-12% Cr heat-resistant steel excellent in high-temperature strength and toughness according to the present invention, the chemical composition is expressed in terms of% by weight, and C: 0.10 to 0.16. 10-0.30 Si: ≦ 0.10 Nb: 0.02-0.10 Mn: ≦ 0.20 N: 0.01-0.07 Ni: 1.6-2.8 B <0.0010 Cr : 9.0 to 12.0 Mo: 0.5 to 1.7 or W: 0.1 to 2.0 One or two kinds and a material whose balance is composed of Fe and unavoidable impurities, or
In the above-mentioned material, the material is further adjusted under the condition of Ni ≦ 6000 × B, and the final forging heating temperature is 1050 to 1150 ° C., the material surface temperature at the end of forging is 700 to 900 ° C. Forging at a rate of 20% or more, 10
Quenching heat treatment at a quenching temperature of 30 to 1090 ° C.
By performing one or more tempering heat treatments at a tempering temperature of 00 to 650 ° C., the grain size (ASTM No.) is 3.0.
It is characterized by having finer grains (claim 5).

The reasons for limiting the composition range of each element in the 9 to 12% Cr heat-resistant steel excellent in high-temperature strength and toughness according to the present invention will be described below.

[0009]

C: 0.10 to 0.16 If C is less than 0.10, desired strength such as tensile strength and proof stress cannot be obtained, so the lower limit was made 0.10%. On the other hand, if it exceeds 0.16%, the toughness is reduced, and during use at a high temperature, the carbides are remarkably agglomerated and coarsened to lower the high-temperature strength. Si: ≦ 0.10 Si is added as a deoxidizing element for molten steel, but may be ≦ 0.10% when carbon deoxidation is performed due to recent advances in steelmaking technology. Also, 0.10
%, It becomes embrittled by long-term use at 400 to 500 ° C.

Mn: ≦ 0.20 Mn is an element conventionally required as a deoxidizing and desulfurizing material. On the other hand, it is an element that promotes tempering embrittlement and lowers high-temperature strength. However, due to recent advances in steelmaking technology, the function as a deoxidizing and desulfurizing material is becoming unnecessary, and it is desirable that it be as low as possible under the conditions used as a gas turbine material.
If it exceeds 0.2%, the high-temperature strength deteriorates.
20%. Ni: 1.6 to 2.8 Ni is an element that increases hardenability and improves toughness, but is an element that, when added excessively, lowers high-temperature strength. If it is less than 1.6%, the toughness is not sufficient, and if it exceeds 2.8%, the high temperature strength is significantly reduced. Ni is superior in toughness when Ni> 6000 × B, but the high-temperature strength is slightly deteriorated.
Let i ≦ 6000 × B.

Cr: 9.0-12.0 Cr is an element that improves toughness and strength by suppressing high-temperature oxidation and increasing hardenability. If it is less than 9%, the oxidation resistance and hardenability are insufficient, and if it exceeds 12%, a delta ferrite phase tends to precipitate and the toughness is reduced. V: 0.10 to 0.30 V is an element that combines with C and N in steel to form an MX-type carbonitride and significantly enhances high-temperature strength. However, if it is less than 0.10%, the precipitation of carbonitride is not sufficient, and the above effect is small.
If it exceeds 0%, a delta ferrite phase precipitates and lowers toughness.

Nb: 0.02 to 0.10 Nb is an element that forms an MX-type carbonitride by combining with C and N in steel to increase the high-temperature strength. However, if it is less than 0.02%, the above-mentioned amount of precipitation is small, and if it exceeds 0.10%, coarse Nb-containing carbonitride precipitates, and the toughness and high-temperature strength are reduced. N: 0.01 to 0.07 N is an effective element that improves the strength together with C. However, if it is less than 0.01%, the above effect is small, and if it exceeds 0.07%, production of a steel ingot becomes difficult, and hot workability deteriorates.

B: <0.0010 B is an element that, when added in a small amount, improves the hardenability of steel and improves the high-temperature strength. However, if the content is 0.001% or more, the toughness and hot workability are significantly reduced, so the content is made less than 0.0010%. Mo: 0.5 to 1.7 Mo is an element that remarkably improves the high-temperature strength and is an element indispensable in heat-resistant steel, and is therefore used selectively or together with W. However, if the content is less than 0.5%, the high-temperature strength is insufficient, and if it exceeds 1.7%, unstable precipitates such as harmful intermetallic compounds Fe ₂ Mo are formed during long-time use at high temperatures. And high-temperature strength and toughness decrease.

W: 0.1 to 2.0 W is an element which remarkably improves the high-temperature strength and is an indispensable element in heat-resistant steel. Therefore, W is used selectively or together with Mo. However, if it is less than 0.1%, the above effect is small,
If it exceeds 2.0%, a delta ferrite phase or a Laves phase is formed, and the high-temperature strength is deteriorated. Next, the final forging heating temperature, the material surface temperature at the end of forging, the working ratio, and the subsequent quenching and tempering heat treatments in the manufacturing method according to the present invention will be described. Generally, crystal grains are required to be fine from the viewpoint of improvement in toughness and ultrasonic transmittance at the time of ultrasonic inspection. In order to refine the crystal grains of a martensitic heat-resistant steel such as the steel of the present invention, annealing such as pearlite transformation is performed before quenching. However, in the steel of the present invention, pearlite transformation is difficult due to high Ni. For this reason, there is no other way to refine the crystal grains after austenitization such as quenching, except to refine the crystal grains after the final forging step. This is especially true when employing high quenching temperatures to increase high temperature strength.
In quenching, crystal grains are indispensable because they grow large and easily. On the other hand, it is generally known that the crystal grain after final forging becomes finer as the working temperature is lower and the strain rate is higher (that is, the dynamic recrystallization grain size is smaller) (“Hot working of steel”). Metallurgy ”edited by High Temperature Deformation Working Group, P68 As for the processing temperature and the strain rate, there are optimum temperatures and strain rates depending on the forgeability and composition of the steel. In order to increase the strain rate, it is necessary to increase the working rate per unit time. In the case of the steel of the present invention, the final forging heating temperature is 1050 to 1150 ° C and the forging material surface temperature at the end of forging is 700 to 900 ° C. It has been found that setting the final forging reduction (working rate) to 20% or more is the most effective for the refinement of crystal grains.

If the heating temperature is 1050 ° C. or less and the forging material surface temperature at the end of the forging is 700 ° C. or less, the hot deformation resistance is large and forging is difficult and cracks easily occur. In the following, since recrystallization is difficult, the crystal grain size becomes non-uniform. When the forging heating temperature exceeds 1150 ° C., the Nb-containing carbonitride completely dissolves at this point, and the precipitation amount of these carbonitrides during forging is small. However, the crystal grains after forging are coarsened. Further, if the forged material surface temperature at the end of forging is 900 ° C. or higher, the crystal grains are likely to become coarse.

Accordingly, the heating temperature at the time of final forging is set to 1050 to 1
150 ° C., forging material surface temperature at the end of forging 700 to 90
0 ° C. At this time, if the processing rate is less than 20%, the effect of refining the crystal grains is low, so the content is set to 20% or more. The steel of the present invention
After forging, quenching and tempering are performed. At this time, in the steel of the present invention, even if the crystal grains are refined during forging, if the quenching temperature exceeds 1090 ° C., the crystal grains are likely to grow and become coarse and toughness is reduced. On the other hand, if the temperature is lower than 1030 ° C., the solid solution of the Nb-containing carbonitride is insufficient, so that sufficient high-temperature strength cannot be obtained. The tempering process needs to be performed one or more times in order to adjust to a desired strength. However, tempering temperature is 500 ℃
If it is less than 650 ° C., a sufficient tempering effect cannot be obtained, and if it exceeds 650 ° C., a desired strength cannot be obtained.
~ 650 ° C.

As described above, the final forging heating temperature, the material surface temperature at the time of final forging, and the final working ratio specific to the steel of the present invention are selected, and quenching is performed in the above-mentioned temperature range. Fine grains having a crystal grain size (ASTM No.) of more than 3.0 are obtained.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of a 9 to 12% Cr heat-resistant steel excellent in high-temperature strength and toughness according to the present invention and a method for producing the same will be described below. Table 1 shows inventive steels 1 to 9 and comparative steels 10 to 13.

[0019]

[Table 1]

Table 2 shows the test results of the mechanical properties of Table 1.

[0021]

[Table 2]

The steel of the present invention having the composition shown in Table 1 1 to N
o. 9 and Comparative Steel No. 10-No. 13 was melted in a vacuum melting furnace to produce a 90 kg steel ingot, and the final forging heating temperature was 11
After heating to 00 ° C., forging was completed at a final material surface temperature of 800 ° C. and a final forging rate of 20%. As a simulation of heat treatment of the high strength disk material, a test piece material was cut out from these forged materials, held at a quenching temperature of 1050 ° C., cooled in a simulation heat treatment furnace, then first tempered at 550 ° C., and further at 650 ° C. The material was subjected to a ^second tempering to have a tensile strength of 80 to 90 kgf / mm ² to obtain a test material. Tensile test results of these test materials, FATT and 50
Creep rupture strength at 0 ° C. -10 ⁵ h the (MPa) shown in Table 2.

The steel of the present invention has a longer creep rupture time and a lower FATT than the comparative steel. No. 8 and 9 are claims 1
Is satisfied, and No. 2 is not satisfied. 1-7
Slightly lower creep strength. No. In No. 10, since B was too high, the creep strength was excellent, but the FATT deteriorated. No. No. 11 has excellent FATT because Ni is too high, but has poor creep strength. No. In No. 12, although Mn is too high, FATT is excellent, but creep deteriorates. N
o. No. 13 is excellent in creep because Ni is too low, but FA
TT worsens.

FIG. 1 shows that the steel of the present invention and the comparative steel having the compositions shown in Table 1 were melted in a vacuum melting furnace, and a 90 kg steel ingot was melted.
The final forging temperature and the final processing rate were changed, forging was performed at a material surface temperature of 800 ° C. at the time of the final forging, and a test piece material was cut out of these forged materials. After cooling in a simulation heat treatment furnace, the first tempering was performed at 550 ° C., and the second tempering was further performed at 650 ° C. to measure the crystal grain size (ASTM No.). Thus, the forging heating temperature of the steel of the present invention was set to 105 compared with the comparative steel.
It can be seen that if the temperature is 0 to 1150 ° C. and the processing rate is 20% or more, fine grains with a crystal grain size of 3.0 can be obtained.

[0025]

As described above, according to the present invention, it is possible to provide a 9 to 12% Cr heat-resistant steel excellent in high-temperature strength and toughness, and in particular, a gas turbine disk or a gas turbine which is an important component constituting a gas turbine. And / or used for compressor disc material to obtain beneficial effects.

[Brief description of the drawings]

FIG. 1 shows the effect of the forging heating temperature and the working ratio on the grain size of the steel of the present invention.

FIG. 2 shows the effect of forging heating temperature and working ratio on the grain size of comparative steel.

 ──────────────────────────────────────────────────の Continued on the front page F term (reference) 3G002 AA02 AA11 AA13 AB00 4K032 AA02 AA05 AA12 AA13 AA16 AA19 AA20 AA21 AA22 AA24 AA31 AA36 AA37 CA02 CB01 CF01 CF02

Claims (5)

[Claims] C. 0.10 to 0.16 V: 0.10 to 0.30 Si: ≦ 0.10 Nb: 0.02 to 0.10 Mn: ≦ 0. 20 N: 0.01 to 0.07 Ni: 1.6 to 2.8 B <0.0010 Cr: 9.0 to 12.0 Mo: 0.5 to 1.7 or W: 0.1 to 2 And 9 to 12% Cr-based heat-resistant steel excellent in high-temperature strength and toughness, which is composed of one or two kinds and the balance of Fe and unavoidable impurities. 2. The composition according to claim 1, wherein Ni ≦ 6000 × B.
2% Cr heat resistant steel. 3. The grain size (ASTM No.) is 3.0.
The 9 to 12% Cr heat-resistant steel excellent in high-temperature strength and toughness according to claim 1 or 2, characterized by being finer grains. 4. A gas turbine for a gas turbine, comprising the 9 to 12% Cr heat-resistant steel excellent in high-temperature strength and toughness according to any one of claims 1 to 3. Disc and / or compressor disc material. 5. A material is adjusted under the condition of the chemical composition according to claim 1 or 2, and a final forging heating temperature using the material is 1050 to 1150 ° C., and a material surface temperature at the end of forging. Forging at 700 to 900 ° C and a working ratio of 20% or more, then performing quenching heat treatment at a quenching temperature of 1030 to 1090 ° C, and then performing one or more tempering heat treatments at a tempering temperature of 500 to 650 ° C. The grain size (AST
M No. ) A method for producing a 9 to 12% Cr heat-resistant steel excellent in high-temperature strength and toughness, which is finer than 3.0.