CN1036666C - heat-resistant steel - Google Patents

Abstract

The present invention proposes a heat-resistant steel containing (by weight) 0.05-0.2% C, less than 0.5% Si, less than 0.6% Mn, 8-13% Cr, and 1.5-3% Mo , 2-3% Ni, 0.05-0.3% V, 0.02-0.2% Nb and/or Ta, 0.02-0.1% N, and the balance is basically iron. Since the gas turbine of the present invention is composed of various parts such as impellers, blades, shafts, etc. made of such alloys, it is possible for the gas turbine structure to have high creep rupture strength and pendulum impact value.

Description

heat-resistant steel

The present invention relates to a novel heat-resistant steel; more particularly, the present invention relates to a novel gas turbine in which said heat-resistant steel is used.

At present, the impellers of gas turbines are made of Cr-Mo-V steel.

From the standpoint of energy conservation, there has recently been a need to improve the thermal efficiency of gas turbines. The most feasible way to improve the thermal efficiency of gas turbines is to increase the temperature and pressure of the gas used. By increasing the temperature of the gas used from 1100°C to 1300°C and increasing the compression ratio from 10 to 15, the thermal efficiency is expected to increase by 3%.

However, since conventional Cr-Mo-V steels are not strong enough at such high temperatures and compression ratios, high-strength steels are required. Creep rupture strength has the greatest impact on high temperature performance, so it is a critical condition for strength. Austenitic steels, Ni-based alloys, Co-based alloys, and martensitic steels are known to be structural steels with higher creep rupture strength than Cr-Mo-V steels. However, Ni-based alloys and Co-based alloys are undesirable in hot workability, machinability, vibration damping, and the like. Austenitic steel is also undesirable due to its low high temperature strength at temperatures of 400-450°C and from the point of view of the entire gas turbine system. On the other hand, martensitic steels are well used for other constituent parts and have sufficient high temperature strength. Typical martensitic steels are disclosed in Japanese Patent Application Laid-Open Nos. 58-110661 and 60-135054 and Japanese Patent Publication No. 46-2739. However, these materials cannot achieve high creep rupture strength at a temperature of 400-450°C, and in addition, the toughness becomes lower after a long time of high-temperature heating, so they cannot be used as turbine impellers, and as a result, improvements in the thermal efficiency of gas turbines cannot be achieved. From the above, it is evident that if a material having only high strength is used to solve the high temperature and high pressure problem of a gas turbine, it is impossible to increase the temperature of the gas. In short, as the strength increases, the toughness decreases.

Therefore, an object of the present invention is to provide a heat-resistant steel that not only has high-temperature strength but also has high toughness after being heated at a high temperature for a long time.

Another object of the present invention is to provide a gas turbine with high thermal efficiency.

To achieve the above object, according to the first aspect of the present invention, a heat-resistant steel is provided, which contains 0.05-0.2% (weight) of C, less than 0.5% (weight) of Si, less than 0.6% (weight) ) of Mn, 8-13% (weight) of Cr, 1.5-3% (weight) of Mo, 2-3% (weight) of Ni, 0.05-0.3% (weight) of V, the total amount is 0.02-0.2 % by weight of Nb and/or Ta, 0.02-0.1% by weight of N, the above-mentioned ratio of Mn to Ni (Mn/Ni) is less than 0.11, and the balance is basically iron.

According to the second aspect of the present invention, there is provided a heat-resistant steel containing 0.07-0.15% by weight of C, 0.01-0.1% by weight of Si, 0.1-0.4% by weight of Mn, 11 - 12.5% by weight of Cr, 2.2-3.0% by weight of Ni, 1.8-2.5% by weight of Mo, a total of 0.04-0.08% by weight of Nb and/or Ta, 0.15-0.25% (weight) of V, 0.04-0.08% (weight) of N, the above-mentioned ratio of Mn to Ni (Mn/Ni) is 0.04-0.10, the balance is basically iron, and the above-mentioned heat-resistant steel has complete tempering body structure.

In addition, the steel of the present invention may also contain at least one substance selected from the group consisting of less than 1% by weight of W, less than 0.5% by weight of Co, less than 0.5% by weight of Cu, less than Less than 0.01% (weight) of B, less than 0.5% (weight) of Ti, less than 0.3% (weight) of Al, less than 0.1% (weight) of Zr, less than 0.1% (weight) of Hf, less Less than 0.01% by weight of Ca, less than 0.01% by weight of Mg, less than 0.01% by weight of Y and less than 0.01% by weight of rare earth elements.

The composition of the steel of the present invention should be adjusted such that the Cr equivalent calculated by the following equation is less than 10, and it is preferable to ensure that the ?-ferrite phase is practically not contained in the steel.

Cr equivalent = -40C-2Nn-4Ni-30N

  +6Si+Cr+4Mo+11V

  +5Nb+2.5Ta (In the above equation, use the weight percentage content of the corresponding elements in the alloy to calculate.)

According to a third aspect of the present invention, there is provided a gas turbine impeller, the impeller has a plurality of grooves on its outer circumference for inserting blades, the center of which is the thickest, and has a plurality of grooves on its outer circumference for bolts to pass through. The through hole for connecting multiple impellers is characterized in that the impeller is made of martensitic steel having the following properties, that is, after heating at 500°C for 103 hours, the creep rupture strength at 450°C and 10 ⁵ -h is high At 490 kPa, 25°C, the V-notch pendulum impact strength value is higher than 0.49 kPa-m, and has a complete tempered martensitic structure; or is made of heat-resistant steel with the above-mentioned composition herein.

A plurality of turbine impellers are connected by bolts at their outer circumferences, and spacers are installed between the impellers, and these spacers are characterized in that they are made of martensitic steel with the above-mentioned properties or heat-resistant steel with the above-mentioned composition.

According to a fourth aspect of the present invention, there are provided the following components (a), (b) and (c), characterized in that each component is made of a martensitic steel having the above composition:

(a) the cylindrical isolation chamber through which the turbine wheel is bolted to the compressor wheel;

(b) At least one set of bolts connecting multiple turbine wheels and another set of bolts connecting multiple compressor wheels;

(c) Compressor impeller, the outer circumference of which has a plurality of grooves for inserting blades, and a plurality of through holes for bolts to pass through to connect multiple impellers, and the center and the part with through holes thickest.

According to a fifth aspect of the present invention, there is provided a gas turbine, comprising a turbine end shaft, a plurality of turbine impellers connected to the shaft by turbine combination bolts with spacers in the middle, and turbine blades embedded in each turbine impeller, The turbine combination bolt is connected to the isolation chamber of the turbine impeller, and the compressor combination bolts are used to connect multiple compressor impellers in the isolation chamber, the compressor blade embedded in each compressor impeller and the first-stage impeller connected to the compressor impeller as a whole Compressor end shafts, characterized in that at least the turbine wheel is made of martensitic steel having the properties of having a 450°C, 105 ⁵ -h creep rupture strength higher than 490 after heating at 500°C for ¹⁰³ hours kPa and 25°C, the V-type pendulum notched impact strength value is higher than 0.49 kPa-m, and has a fully tempered martensite structure. The martensitic steel consists in particular of a heat-resistant steel having the composition described above.

When the above-mentioned martensitic steel is used for the impeller of a gas turbine according to the present invention, the ratio (t/D) of the thickness (t) of the central portion of the impeller to its diameter (D) is limited to 0.15-0.3 so that the weight of the impeller can be reduced. In particular, by limiting the t/D ratio to 0.18-0.22, the distance between the individual impellers can be shortened, which can improve thermal efficiency.

1 is a sectional view showing a rotating portion of a gas turbine according to an embodiment of the present invention;

Fig. 2 is a graph showing the relationship between impact value after embrittlement and Mn/Ni ratio;

The graph in Fig. 3 is similar to that in Fig. 2, but shows the relationship between the impact value after embrittlement and the Mn content;

The graph of Fig. 4 is similar to Fig. 2, but represents the relationship between the impact value after embrittlement and the Ni content;

Fig. 5 is a graph showing the relationship between creep rupture strength and Ni content;

Figure 6 is a cross-sectional view of a turbine wheel according to one embodiment of the present invention;

Figure 7 is a schematic illustration of yet another preferred embodiment of the present invention, partially in section showing the rotating portion of the gas turbine.

The reason for limiting the composition range of the material of the present invention will be described below.

In order to obtain high tensile strength and high proof stress, C needs to be at least 0.05% by weight. However, if excessive C is added, the metal structure will become unstable when the steel is exposed to high temperature for a long time, so that the 10 ⁵ -h creep rupture strength will be reduced, so the C content must be less than 0.20% by weight, preferably The carbon content range is 0.07-0.15% (weight), preferably 0.10-0.14% (weight).

When the steel is melted, Si is added as a deoxidizer, and Mn is added as a deoxidizer and desulfurizer. Even if the addition of these two elements is small, they are also effective. Si is a δ ferrite former, adding a large amount of Si will lead to the formation of δ ferrite, reducing fatigue strength and toughness, so the Si content must be less than 0.5% by weight. Sometimes carbon vacuum deoxidation method, electroslag smelting method, etc. are used. At this time, Si does not need to be added, so it is best not to add Si.

In particular, from the viewpoint of embrittlement, the Si content is preferably less than 0.2% by weight, and even if Si is not added, 0.01 to 0.1% by weight of Si impurities are still contained.

Since Mn promotes embrittlement after heating, its content must be less than 0.6% by weight. In particular, Mn is effective as a desulfurizing agent, so the content of Mn is preferably in the range of 0.1-0.4% by weight so as not to cause heat embrittlement. The content range of Mn is preferably 0.1-0.25% by weight. In addition, the total amount of Si+Mn is preferably less than 0.3% by weight in order to prevent embrittlement.

Cr enhances corrosion resistance and high temperature strength, however, if added in excess of 13% by weight, Cr will result in the formation of a delta ferrite structure. If the Cr content is less than 8% by weight, sufficient corrosion resistance and high temperature strength cannot be obtained. Therefore, the content range of Cr is limited to 8-13% by weight, especially, the content of Cr should preferably be 11-12.5% by weight.

Mo can improve the creep rupture strength due to its solid solution strengthening and precipitation strengthening effects, and it also has the effect of preventing embrittlement. If the Mo content is less than 1.5% by weight, sufficient creep rupture strength cannot be obtained. More than 3.0% by weight, Mo leads to the formation of delta ferrite. Therefore, the Mo content is limited within the range of 1.5-3.0% by weight, preferably within the range of 1.8-2.5% by weight. In addition, when the Ni content exceeds 2.1% by weight, the effect of Mo is also that the higher the content, the higher the creep rupture strength, especially when the Mo content is higher than 2.0% by weight. obvious.

V and Nb precipitate carbides, thus bringing about the effects of enhancing high-temperature strength and improving toughness. If the contents of V and Nb are lower than 0.1% by weight and 0.02% by weight, respectively, sufficient effects cannot be obtained, however, if the contents of V and Nb are higher than 0.3% by weight and 0.2% by weight, respectively , will result in the formation of delta ferrite with a tendency to reduce toughness. Therefore, the preferable range of the V content is 0.15-0.25% by weight, and the preferable range of the Nb content is 0.04-0.08% by weight. Ta can be added to replace Nb in exactly the same amount, or Nb and Ta can be added in combination.

Ni can enhance the toughness after being heated at high temperature for a long time, and also has the effect of preventing the formation of delta ferrite. If the Ni content is less than 2.0% by weight, no sufficient effect can be obtained, but if it is more than 3% by weight, the long-term creep rupture strength will be lowered. The preferred range of Ni content is 2.2%-3.0% by weight, preferably more than 2.5% by weight.

Ni has the effect of preventing heating embrittlement, but Mn destroys this effect. The present inventors found that there is a close correlation among these elements, that is, found that when the Mn/Ni ratio is less than 0.11, heating embrittlement is significantly prevented. In particular, the ratio should be less than 0.10, preferably 0.04-0.10.

N is effective in improving creep rupture strength and preventing the formation of delta ferrite, but if the N content is less than 0.02% by weight, sufficient effects cannot be obtained. If the N content exceeds 0.1% by weight, toughness will be lowered. Superior properties can be achieved when the N content ranges from 0.04 to 0.08% by weight.

In the heat-resistant steel of the present invention, Co is effective in enhancing the strength of the steel, but it promotes embrittlement, therefore, the content of Co should be less than 0.5% by weight. Since W contributes similarly to Mo in increasing strength, its content may be less than 1% by weight. In addition, the high temperature strength can be improved by adding the following elements: less than 0.01% by weight of B, less than 0.3% by weight of Al. Less than 0.5% by weight of Ti, less than 0.1% by weight of Zr, less than 0.1% by weight of Hf, less than 0.01% by weight of Ca, less than 0.01% by weight of Mg, Less than 0.01% by weight of Y, less than 0.01% by weight of rare earth elements and less than 0.5% by weight of Cu.

With regard to the heat treatment of the material of the present invention, it is uniformly heated at a temperature sufficient to completely transform the material into austenite (minimum 900°C, maximum 1150°C), followed by quenching to obtain a martensitic structure. The martensitic structure is obtained by quenching or hardening the material at a rate higher than 100°C/h, heating it and keeping it at a temperature of 450-600°C (primary tempering), then heating it and keeping it Secondary tempering is carried out at 550-650°C. When hardening, it is best to stop quenching at a temperature slightly above the martensite formation point to prevent quenching cracks. Specifically, it is preferable to stop quenching at a temperature higher than 150°C. Hardening is best done with oil hardening or water spray hardening. A tempering is started from the temperature at which the quenching was stopped.

More than one of the aforementioned isolation chambers, turbine spacers, turbine combination bolts, compressor combination bolts and at least the final stage impeller of the compressor wheel may be made of heat-resistant steel composed of 0.05-0.2% (weight) C, less than 0.5% (weight) Si, less than 0.1% (weight) Mn, 8-13% (weight) Cr, less than 3% (weight) Ni, 1.5-3% (weight) of Mo, 0.05-0.3% (weight) of V, 0.02-0.2% (weight) of Nb, 0.02-0.1% (weight) of N, the balance is basically iron, and the heat-resistant steel has all Tempered martensitic structure. By constituting all these parts with this heat-resistant steel, the temperature of the gas can be further increased to improve thermal efficiency. Especially when at least one part is made of heat-resistant steel composed of heat-resistant steel containing 0.05-0.2% by weight of C, less In 0.5% (weight) of Si, less than 0.6% (weight) of Mn, 8-13% (weight) of Cr, 2-3% (weight) of Ni, 1.5-3% (weight) of Mo, 0.05 -0.3% (weight) of V, 0.02-0.2% (weight) of Nb, 0.02-0.1% (weight) of N, wherein the Mn/Ni ratio is less than 0.11, preferably 0.04-0.10, and the balance is basically Iron, the heat-resistant steel has a fully tempered martensitic structure.

In addition, although martensitic steels with 450°C, ¹⁰⁵ -h creep rupture strength higher than 392 kPa and 20°C, V-notch impact strength values higher than 0.49 kPa-m were adopted as materials for these parts , but in its particularly preferred composition, after heating at 500°C for 103 hours, it has a 450°C, 10 ⁵ -h creep rupture strength above 490 kPa and a 20°C, V above 0.49 kPa-m Type notched pendulum impact strength values.

This material may further contain at least one element selected from the group consisting of less than 1% by weight of W, less than 0.5% by weight of Co, less than 0.5% by weight of Cu, less than 0.01% (weight) of B, less than 0.5% (weight) of Ti, less than 0.3% (weight) of Al, less than 0.1% (weight) of Zr, less than 0.1% (weight) of Hf, less than 0.01% Ca, less than 0.01% by weight of Mg, less than 0.01% by weight of Y and less than 0.01% by weight of rare earth elements.

In the compressor impeller, the above-mentioned heat-resistant steel can be used to make at least the final stage or all stages. However, due to the low temperature of the gas in the region from the first stage to the middle stage, another low-alloy steel can be used. For the impellers in this area, the impellers from the intermediate stage to the final stage are made of the above-mentioned heat-resistant steel. For example, Ni-Cr-Mo-V steel with the following composition and properties can be used to make the impeller from the first stage upstream of the air flow to the intermediate stage, and the Ni-Cr-Mo-V steel contains 0.15-0.30% (weight ) of C, less than 0.5% (weight) of Si, less than 0.6% (weight) of Mn, 1-2% (weight) of Cr, 2.0-4.0% (weight) of Ni, 0.5-1% (weight) ) of Mo, 0.05-0.2% (weight) of V, and the balance is basically iron. The tensile strength of the Ni-Cr-Mo-V steel at room temperature is higher than 784 kPa, and the V-notch impact value at room temperature is high At 1.96 kPa-m, it is possible to use Cr-Mo-V steel having the following composition and properties as the impeller from the intermediate stage onwards but except the final stage, the Cr-Mo-V steel containing 0.2-0.4% (weight ) of C, 0.1-0.5% (weight) of Si, 0.5-1.5% (weight) of Mn, 0.5-1.5% (weight) of Cr, less than 0.5% (weight) of Ni, 1.0-2.0% (weight) ) of No, 0.1-0.3% (weight) of V, the balance is basically iron, the tensile strength of the Cr-Mo-V steel at room temperature is higher than 784 kPa, the elongation is higher than 18%, and the section is reduced rate above 50%.

The above-mentioned Cr-Mo-V steel can also be used as compressor end shafts and turbine end shafts.

The compressor impeller of the present invention is an oblate ring, and there are a plurality of holes for inserting combination bolts on its outside, preferably the ratio (t/D) of the minimum thickness (t) of the impeller to the diameter (D) is limited to 0.05 -0.10.

The isolation chamber of the present invention is cylindrical, and two ends are equipped with flanges, which are respectively connected with the compressor impeller and the turbine impeller with bolts. Preferably, the ratio of its minimum thickness (t) to maximum internal diameter (D) is limited to 0.05-0.10.

For the gas turbine of the present invention, it is preferable that the ratio (l/D) of the interval (l) between the individual impellers of the turbine to the diameter (D) of the turbine impeller is limited to 0.15-0.25.

For example, where the compressor impeller assembly includes 17 stages, the 1st to 12th stage impellers can be made of the above-mentioned Ni-Cr-Mo-V steel, and the 13th to 16th stage impellers can be made of the above-mentioned Cr-Mo-V steel, the 17th stage impeller can be made of martensitic steel as mentioned above.

In a compressor wheel assembly, the first stage impeller is more rigid than the following stage impeller, and the last stage impeller is more rigid than the preceding stage impeller. Also, the impellers are tapered in thickness from the first stage to the last stage, thereby reducing the stress generated by high speed rotation.

Each blade of the compressor is preferably made of martensitic steel of the following composition, which contains 0.05-0.2% by weight of C, less than 0.5% by weight of Si, less than In 1% (weight) of Mn, 10-13% (weight) of Cr, and the balance is iron; (weight) Ni martensitic steel.

For the annular shroud, which is in sliding contact with the outer end of the turbine blade, a Ni-based casting alloy may be used in its part corresponding to the first stage, said alloy containing 0.05-0.2% by weight of C, less than 2% (weight) of Si, less than 2 (weight) of Mn, 17-27% (weight) of Cr, less than 5% (weight) of Co, 5-15% (weight) of Mo, 10-30% (weight) of Fe, less than 5% (weight) of W, less than 0.02% (weight) of B, and the balance is mainly Ni; in its part corresponding to other grades, Fe-based casting alloys are used, which alloys contain 0.3-0.6% (weight) of C, less than 2% (weight) of Si, less than 2% (weight) of Mn, 20-27% (weight) of Cr, 20-30% (weight) of Ni, 0.1-0.5% by weight of Nb, 0.1-0.5% by weight of Ti, and the balance mainly being Fe. These alloys form a ring structure composed of many unit parts.

For the diaphragm of the fixed turbine nozzle, the part corresponding to the turbine nozzle of the first stage is made of Cr-Ni steel containing less than 0.05% by weight of C, less than 1% by weight of Si, less than 2% (weight) of Mn, 16-22% (weight) of Cr, 8-15% (weight) of Ni, the balance is basically iron; parts corresponding to other turbine nozzles use high C- Made of Ni alloy.

Each turbine blade is made of a Ni-based cast alloy containing 0.07-0.25% by weight of C, less than 1% by weight of Si, less than 1% by weight of Mn, 12-20% ( Cr of 5-15% by weight, Co of 5-15% by weight, Mo of 1.0-5.0% by weight, W of 1.0-5.0% by weight, B of 0.005-0.03% by weight, 2.0-7.0% by weight Ti, 3.0-7.0% (weight) of Al, and at least one element from the following group: less than 1.5% (weight) of Nb, 0.01-0.5 (weight) of Zr, 0.01-0.5% (weight) Hf and 0.01-0.5% (weight) of V, the balance is basically Ni, the alloy has a structure in which the r' phase and the r" phase are precipitated in the austenite phase matrix. Co Based cast alloys containing 0.20-0.60% by weight of C, less than 2% by weight of Si, less than 2% by weight of Mn, 25-35% by weight of Cr, 5-15% by weight of Ni, 3-10% by weight of W, 0.003-0.03% by weight of B, the balance being substantially Co, the alloy has a structure in which eutectic carbonization and secondary carbides contained in the austenite phase matrix; or made of Co-based casting alloys further containing at least one element selected from the following elements in addition to the above-mentioned components: 0.1-0.3% (by weight) of Ti, 0.1 - 0.5% (by weight) of Nb and 0.1-0.3% (by weight) of Zr, the alloy has a structure in which eutectic carbides and secondary carbides are contained in the matrix of the defectite phase. The above two The alloy is subjected to an aging treatment after solution heat treatment to form the above-mentioned precipitates, thereby enhancing the strength of the alloy.

In addition, in order to prevent turbine blades from being corroded by high-temperature combustion gases, Al, Cr or Al+Cr diffusion coatings can be coated on turbine blades. The thickness of the coating is preferably 30-150um, and the coating is coated on the blade exposed to the gas.

A plurality of combustion chambers are arranged around the turbine, and each combustion chamber has a duplex structure consisting of an outer cylinder and an inner cylinder. The inner cylinder is made of a solution heat-treated Ni-based alloy containing 0.05-0.2% by weight of C, less than 2% by weight of Si, less than 2% by weight of Mn, 20-25 % (weight) of Cr, 0.5-5% (weight) of Co, 5-15% (weight) of Mo, 10-30% (weight) of Fe, less than 5% (weight) of W, less than 0.02 % (by weight) of B, the balance being essentially Ni, the alloy has a fully austenitic structure. The above-mentioned Ni-based alloy plate is plastically processed to have a thickness of 2-5mm, and an inner cylinder is formed by welding, and crescent-shaped air holes for supplying air are provided on the entire periphery of the cylinder.

The present invention will be clarified by the description of the following examples. Example 1

Another 20 kg of the sample with the composition (percentage by weight) shown in Table 1 was melted, cast into an ingot, heated to 1150° C., and forged at this temperature to obtain the test material. After these materials were heated at 1150°C for 2 hours, they were blown to cool until the temperature dropped to 150°C, then the cooling was stopped, then they were heated from this temperature to 580°C and kept at this temperature for 2 hours, and then tempered for the first time, then Air cooling was performed, then it was heated to 605°C and held at this temperature for 5 hours, a second tempering was performed, followed by furnace cooling.

Test pieces for creep rupture test, tensile test and V-notch pendulum impact test were obtained from these heat-treated materials and then subjected to experiments. The impact test was carried out on an brittle material obtained by heating the above-mentioned heat-treated material at 500°C for 1000 hours. According to the Larson-Miller parameters, this embrittled material has the same conditions as the material embrittled by heating at 450°C for ¹⁰⁵ hours.

Table 1 Number Composition (weight%) C Si mn Cr Ni Mo V Nb N Mn/Ni Fe 1 0.12 0.01 0.24 11.5 2.75 2.0 0.20 0.07 0.05 0.08 margin 2 0.12 0.25 0.71 11.5 2.83 1.8 0.32 - 0.03 0.25 " 3 0.10 0.02 0.38 11.8 2.09 2.0 0.29 0.05 0.07 0.18 " 4 0.10 0.09 0.71 12.0 2.41 1.9 0.29 0.04 0.06 0.30 " 5 0.08 0.15 0.82 11.9 1.62 2.5 0.27 0.06 0.07 0.51 " 6 0.09 0.09 0.84 11.8 2.10 2.3 0.35 0.05 0.07 0.40 " 7 0.09 0.05 0.20 11.0 1.71 1.9 0.20 0.05 0.06 0.12 " 8 0.10 0.04 0.15 10.9 2.51 2.4 0.19 0.06 0.06 0.06 "

Table 2 Number Tensile strength (kPa) 0.2% proof stress (kPa) Elongation (%) Section reduction rate (%) 450°C breaking strength (kPa) Impact value at 25°C (kPa-m) Before embrittlement After embrittlement 1 1105.4 918.3 20.9 63.8 534.1 1.12 0.93 2 1128.0 921.2 19.8 60.0 411.6 1.02 0.33 3 1097.6 914.3 19.6 60.1 540.0 0.99 0.35 4 1112.3 974.1 19.5 59.9 530.2 0.96 0.28 5 1084.9 910.4 19.5 59.7 541.0 0.84 0.21 6 1094.7 917.3 19.8 60.2 532.1 0.74 0.24 7 1092.7 957.5 22.6 62.3 568.4 0.76 0.43 8 1116.2 933.9 24.8 61.1 569.4 1.04 0.86

See Table 1, wherein samples 1 and 8 are materials of the present invention, and samples 2-7 are comparative materials (sample 2 corresponds to M152 steel currently used as impeller material).

Table 2 shows the mechanical properties of these samples. It has been confirmed that the materials of the present invention (samples 1 and 8) meet the 450°C, 10 ⁵ -h creep rupture strength (>490 kPa) and 25°C required as high-temperature and high-pressure gas turbine materials after embrittlement treatment. V-notch impact strength value (above 0.49 kPa-m). In contrast, it is equivalent to M152 (sample 2), which is currently used as a material for gas turbines. Because of its 450°C; 10 ⁵ -h creep rupture strength is 411.6 kPa, 25°C, V-notch pendulum type The impact strength value after embrittlement treatment is 0.33 kPa-m, which cannot meet the mechanical properties required as a high-temperature and high-pressure gas turbine material. In addition, in samples 3-7, the content of Si+Mn is 0.4% to about 1% by weight, and the Mn/Ni ratio is higher than 0.12. required creep rupture strength values, but these steel samples could not meet this requirement due to their embrittled V-notch pendulum impact strength values below 0.42 kPa-m.

Fig. 2 is a graph showing the relationship between the impact value after embrittlement and the Mn/Ni ratio. As shown in the figure, when the ratio (Mn/Ni) is higher than 0.12, no significant improvement occurs, but when the ratio is lower At 0.11, the embrittlement performance improves significantly to above 0.49 kPa-m, and when the ratio is below 0.10, to 0.74 kPa-m. Mn is indispensable as a deoxidizer and desulfurizer, so the addition of Mn should be less than 0.6% (weight).

Figure 3 is a graph similar to Figure 2 but showing the impact value after embrittlement as a function of Mn content. As shown in the figure, when the Ni content is less than 2.1% by weight, the reduction of the Mn content has little effect, but when the Ni content exceeds 2.1% by weight; the reduction of the Mn content has a significant effect. Especially when the Ni content is higher than 2.4% by weight, a better effect can be obtained.

In addition, when the Mn content is close to 0.7% by weight, no matter how much the Ni content is; there is no improvement in the impact value, but if the Mn content is lower than 0.6% by weight and the Ni content is higher than 2.4% by weight, then the Mn content The lower the value, the higher the shock value.

Figure 4 is a graph similar to Figure 2 but showing the impact value after embrittlement as a function of Ni content. As shown in the figure, when the Mn content is higher than 0.7 wt%, the Ni content increases; the embrittlement performance is only slightly improved, but when the Mn content is less than 0.7 wt%, the Ni content increases Significantly improved the embrittlement performance. Especially when the Mn content is 0.15-0.4% (weight), if the Ni content is higher than 2.2% (weight), the improvement of embrittlement performance is particularly obvious, that is, if the Ni content is higher than 2.4% (weight), the impact value It can be higher than 0.74 kPa-m, and if the Ni content is higher than 2.5% by weight, the impact value can be higher than 0.86 kPa-m.

Fig. 5 is a graph showing the relationship between the breaking strength at 450°C x 10 ⁵ -h and the Ni content. As shown in the figure, the Ni content up to about 2.5% by weight does not substantially affect the creep rupture strength, but when it exceeds 3.0% by weight, the strength decreases to less than 490 kPa, so the desired strength cannot be obtained . It is also noted that the lower the Mn content, the higher the strength obtained, and the Mn content in the range of 0.15-0.25% by weight achieves the most significant strength-increasing effect, thus providing high strength.

Fig. 6 is a schematic sectional view showing a gas turbine impeller according to the present invention. Table 3 shows the chemical composition (weight percent) of the impeller.

table 3 no C Si mn Cr Ni 9 0.12 0.04 0.20 11.1 2.70 Mo Nb V N Mn/Ni Fe 2.05 0.07 0.20 0.05 0.07 margin

The smelting of steel is carried out by adding carbon and vacuum deoxidation. After forging, heat the forged steel at 1050°C for two hours and quench it in oil at 150°C, then heat the quenched steel from 150°C to 520°C and keep it for 5 hours for the first tempering, then Cool in air, then heat at 590°C for 5 hours for a second tempering, and cool in the furnace. When these heat treatments were completed, the steel was machined into the shape shown in Fig. 6, whereby the resulting impeller had an outer diameter of 1000 mm and a thickness of 200 mm. The diameter of the center hole 11 is 65 mm, and the hole for inserting the combination bolt is arranged on the 12 part, and the turbine blade is embedded on the 13 part.

This impeller has excellent properties, namely, after the aforementioned embrittlement, its impact value is 0.98 kPa-m, and its creep rupture strength at 450°C for 10 ⁵ -h is 541.0 kPa. Example 2

Fig. 1 is a sectional view of a rotating portion of a gas turbine in an embodiment of the present invention, which uses the above-mentioned impeller. The rotating part shown includes turbine end shaft 1, turbine blade 2; turbine combination bolt 3, turbine spacer 4, isolation chamber 5, compressor wheel 6, compressor blade 7, compressor combination bolt 8, compressor end shaft 9 , Turbine wheel 10 and center hole 11. The gas turbine of the present invention has seventeen stages of compressor wheels 6 and two stages of turbine blades 2 . Turbine blades can be tertiary and both structures can use the steel of the invention.

The materials shown in Table 4 were made into large castings equal to the actual size by electroslag remelting, followed by forging and heat treatment. Forging was performed in the temperature range of 850 to 1100°C, and heat treatment was performed under the conditions shown in Table 4. Table 4 is the chemical composition of the samples expressed in weight percent. As for the microstructure of these materials, samples Nos.6 to 9 are all tempered martensite structures; samples 10 to 11 are all tempered bainite structures, and sample No.6 is used for the isolation chamber and the final stage of compression For the impeller, the former has a thickness of 60mm, a width of 500mm, and a length of 1000mm, while the latter has a diameter of 1000mm and a thickness of 180mm. No. 7 samples were used for turbine impellers, each with a diameter of 1000 mm and a thickness of 180 mm. Sample No. 8 is used for positioning pieces, with an outer diameter of 1000mm, an inner diameter of 400mm, and a thickness of 100mm. Sample No. 9 is for combination bolts of turbine and compressor, each with a diameter of 40mm and a length of 500mm. Sometimes sample No. 9 is also used to make bolts connecting the isolation chamber and the compressor impeller. Specimen Nos. 10 and 11 were forged turbine end shafts and compressor end shafts respectively, each having a diameter of 250 mm and a length of 300 mm. Also, steel sample No. 0 is used for the compressor impeller 6 of the thirteenth to sixteenth stages, and steel sample No. 11 is used for the compressor impeller 6 of the first to twelfth stages, and all compressors are manufactured Make the impeller of turbine and compressor have the same size during impeller 6. Except for steel sample No.9, all test parts use the central part of the sample, and its direction should be perpendicular to the axial direction (longitudinal direction) of each sample. In this example, the test parts were taken in the longitudinal direction of the sample.

Table 5 indicates the results of the room temperature tensile strength test, the V-notch pendulum impact test at 20°C and the creep rupture test of the steel samples shown in Table 4. The creep rupture strength at 450°C and 10 ⁵ -h was measured by the commonly used Larson-Miller method.

According to No. 6 to No. 9 steel (12Cr steel) of the present invention, the creep fracture strength at 450°C and 10 ⁵ -h is greater than 499.8 kPa, and the V-notch pendulum impact value at 20°C is greater than 0.69 kPa-m. Therefore, it can be confirmed that No. 6 to No. 9 steels have sufficient strength as materials for high-temperature gas turbines.

In addition, the low-alloy steel Nos, 11 and 12 used for end shafts have low creep rupture strength at 450°C, but the tensile strength exceeds 842.8 kPa, and the V-notch pendulum impact value at 20°C is greater than 0.69 kPa-m . This confirms that steel Nos. 10 and 11 fully meet the strength necessary for the end shaft (tensile strength ≥ 793.8 kPa, V-notch pendulum impact value of 0.49 kPa-m at 20°C).

The gas turbine of the present invention composed of the above materials can make the compression ratio reach 14.7, the allowable temperature is higher than 350°C, the compression efficiency is greater than 86%, and the gas temperature at the inlet of the first stage nozzle is about 1200°C, thus making the thermal efficiency greater than 32%. (LHV).

Under these conditions, the temperature of the isolation chamber and the final stage compressor wheel can reach up to 450°C. The thickness of the former is preferably 25 to 30 mm, and the thickness of the latter is preferably 40 to 70 mm. The turbine and compressor wheels each have a central through hole, and a residual compression square is left along the central through hole of each turbine wheel.

In addition, the above-mentioned heat-resistant steel shown in Table 3 is used for the turbine spacer 4, the isolation chamber 5 and the compressor impeller 6 of the final stage, and other components can also be made of the above-mentioned similar steel. The obtained structure can make the compression ratio reach 14.7, the allowable temperature is higher than 350°C, the compression efficiency is greater than 86%, and the gas temperature at the inlet of the first stage nozzle is 1200°C. As a result, not only can a thermal efficiency greater than 32% be obtained, but also the above As mentioned above, it can also have high creep rupture strength and impact value after heat embrittlement, so a more reliable gas turbine can be obtained.

Table 4 Example Type of steel Composition (%) heat treatment C Si mn Cr Ni Mo V Nb N Fe 6 isolation room 0.10 0.04 0.70 11.56 1.98 1.98 0.20 0.08 0.06 Bal. 1050℃×5hOQ550℃×15hAC600℃×15hAC 7 (turbine impeller) 0.10 0.05 0.65 11.49 1.70 2.04 0.19 0.08 0.06 " 1050℃×8hOQ550℃×20hAC600℃×20hAC 8 positioning pieces 0.09 0.07 0.59 11.57 2.31 2.22 0.18 0.09 0.06 " 1050℃×3hOQ550℃×10hAC600℃×10hAC 9 combination bolts 0.10 0.03 0.69 11.94 1.86 2.25 0.21 0.15 0.05 " 1050℃×1hOQ550℃×2hAC600℃×2hAC 10cr-Mo-V steel 0.26 0.25 0.79 1.09 0.41 1.25 0.23 - - " 975℃×8hWQ665℃×25hAC665℃×25hAC 11Ni-cr-Mo-V steel 0.20 0.21 0.36 1.51 2.78 0.62 0.10 - - " 840℃×8hWQ635℃×25hAC635℃×25hAC

table 5 Types of Example Steel Tensile strength (kPa) 0.02% proof stress (kPa) Elongation (%) rate of reduction in area(%) Shock value vE ₂₀ (kPa-m) 10 ⁵ -h creep rupture strength (kPa) 6 1097.6 777.1 19.8 60.1 0.85 500.8 7 1094.7 779.1 20.1 59.3 0.81 512.5 8 1120.1 795.8 19.5 62.5 0.71 502.7 9 1133.9 809.5 22.3 63.4 0.85 516.5 10 846.7 - 26.7 60.0 0.74 345.0 11 850.6 755.6 26.9 69.1 1.78 225.4 Example 3

Fig. 7 shows another preferred solution, wherein the gas turbine impeller is made of the heat-resistant steel of the present invention, and particularly shows the cross-section of the rotating part of the gas turbine. In this embodiment, a two-stage turbine wheel 10 is provided. The turbine wheel 10 has a central hole 11 at the inlet side of the flowing gas. All turbine wheels in this embodiment were made of the heat resistant steels shown in Table 3. In addition, in this embodiment, the heat-resistant steel shown in Table 3 is also used for the final-stage compressor impeller 6 on the outlet side of the flowing gas, the isolation chamber 5, the turbine spacer 4, the turbine combination bolt 3 and the compressor Combination bolt 8. The alloys shown in Table 6 were used for other components, namely turbine blade 2, turbine nozzle 14, liner 17 of combustor 15, compressor blade 7, compressor nozzle 16, diaphragm 18 and shroud 19. In particular the turbine nozzle 14 and the turbine blade 2 are cast. The compressor of this embodiment has seventeen stages of compressor impellers, and is configured in the same manner as in Embodiment 2. In this embodiment, the turbine end shaft 1 and the compressor end shaft 9 are manufactured in the same manner as in the second embodiment.

Table 6 C Si mn Cr Ni co Fe Mo B W Ti other turbine blade 0.15 0.11 0.12 15.00 Bal. 9.02 - 3.15 0.015 3.55 4.11 Zr 0.05, Al 5.00 turbine nozzle 0.43 0.75 0.66 29.16 10.18 Bal. - - 0.010 7.11 0.23 Nb 0.21, Zr 0.15 combustion chamber lining 0.07 0.83 0.75 22.13 Bal. 1.57 18.47 9.12 0.008 0.78 - - Compressor blades and nozzles 0.11 0.41 0.61 12.07 0.31 - margin - - - - - Guards (1) 0.08 0.87 0.75 22.16 Bal. 1.89 18.93 9.61 0.005 0.85 - - Guards (2) 0.41 0.65 1.00 23.55 25.63 - margin - - - 0.25 Nb 0.33 Baffle 0.025 0.81 1.79 19.85 11.00 - " - - - - -

The turbine blades, turbine nozzles, shrouds (1) and baffles indicated in Table 6 are used in the first stage upstream of the gas flow inside the gas turbine, and the shrouds (2) are used in the second stage.

In this embodiment, the ratio (t/D) of the minimum thickness (t) to the outer diameter (D) of the final compressor impeller 6 is 0.08, the (t/D) ratio of the isolation chamber 5 is 0.04 and each turbine The ratio (t/D) of the maximum thickness (t) of the central part of the impeller to its diameter (D) is 0.19 in the first stage and 0.205 in the second stage, and the gap between the impellers (l) and its diameter ( D) The ratio (l/D) was 0.21. There is a gap between each turbine wheel. Each turbine wheel has a number of equally spaced holes throughout its circumference for the insertion of bolts to couple the wheels.

Said device can make compression ratio up to 14.7, allowable temperature is higher than 350°C, compression efficiency is greater than 86%, and the gas temperature at the nozzle inlet of the first stage of turbine is 1200°C, thus providing thermal efficiency greater than 32%. Furthermore, the above-mentioned heat-resistant steels having high creep rupture strength and less embrittlement after heating can be used as turbine impellers, isolation chambers, spacers, final-stage compressor impellers and combination bolts. In addition, since each turbine blade is made of an alloy having a high high-temperature strength, an alloy having a high temperature and a high temperature toughness is used for a turbine nozzle, and an alloy having a high temperature and a high fatigue resistance is used for Lining the combustor makes it possible to obtain a well-balanced and completely reliable gas turbine.

According to the present invention, heat-resistant steel (gas temperature: higher than 1200° C., compression ratio: 15) whose creep rupture strength and impact value meet the requirements of high-temperature and high-pressure gas turbine impellers after heating embrittlement can be obtained. The finished gas turbine can bring excellent results, such as extremely high thermal efficiency.

Claims (2)

1. A heat-resistant steel with excellent resistance to high temperature brittleness, characterized in that it contains (weight) 0.05-0.2% of C, less than 0.5% of Si, less than 0.33% of Mn, 8-13% of Cr, 1.5% -3% Mo, higher than 2.1% but lower than 3% Ni, 0.05-3.% V, 0.02-0.2% Nb, 0.02-0.1% N, the ratio of Mn to Ni (Mn/Ni ) is lower than 0.11, and the balance is basically iron. 2. A heat-resistant steel with excellent resistance to high temperature brittleness, characterized in that it contains (weight) 0.05-0.2% of C, less than 0.5% of Si, less than 0.33% of Mn, 8-13% of Cr, 1.5% -3% Mo, more than 2.1% but less than 3% Ni, 0.05-0.3% V, 0.02-0.2% Nb, 0.02-0.1% N, less than 1% W, the Mn and Ni The ratio (Mn/Ni) is lower than 0.11, and the balance is basically iron.

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