JP4781767B2 - Manufacturing method of structure for high temperature - Google Patents

Description

The present invention relates to a high-temperature structure. In particular, the present invention relates to a structure for high temperature having high creep deformation resistance in an intermediate temperature and low stress region (use temperature range: about 450 to 550 ° C., use stress range: about 10 kg / mm ² or less).

  Conventionally, examples of heat-resistant steel used for a steam turbine for thermal power generation include low alloy steel (CrMoV steel, 2.25CrMo steel, CrMo steel) and high Cr steel (9Cr steel, 12Cr steel (Patent Literature 1, Patent Literature). 2))) has been used exclusively.

Among these, low alloy steel has high temperature strength between carbon steel and high Cr steel, and also has excellent impact characteristics and weldability, as well as excellent manufacturability and cost competitiveness for large forged and cast steel materials. . For this reason, it has been preferably used as a turbine structural member, particularly in an intermediate temperature range of about 450 to 550 ° C. Conventionally, low alloy steels for turbine structural members have been subjected to appropriate tempering heat treatment so as to satisfy predetermined strength characteristics after being formed into a near net shape material by forging, rolling or casting. For example, a rotor material that requires tensile strength characteristics is manufactured by quenching and tempering by rapid cooling, and thick plates, main valves, and cast members are subjected to normalizing and tempering by air cooling.
JP-A-60-165359 JP-A-62-103345

When the low-alloy steel thick plate or forged steel product produced by the above method is used as a partition plate for adjusting the steam flow of the steam turbine, the intended medium temperature and low stress region (operating temperature range: about 450 to 550) ° C., using stress range: for large creep strain amount at about 10 kg / mm ² or less), over time I had creep in the axial direction is generated, as a result, that the problem of contact between the partition plate and the rotor is caused there were.

  In order to solve the above-described problems, an object of the present invention is to provide a high-temperature structure in which creep deformation is reduced in a medium temperature and low stress region.

The present invention is a method for producing a Atsushi Ko structural material, and 0.05 to 0.17 wt% C, and 1.00 to 2.50 wt% of Cr, from 0.45 to 1.10 mass A low-alloy steel containing% Mo is heated to 800 to 1000 ° C. and then cooled to at least 600 ° C. at a cooling rate of 40 ° C./hour or less. Including . Upper SL low alloy steel, and C 0.05 to 0.15 wt%, and 2.00 to 2.50 wt% of Cr, and 0.90 to 1.10 wt% of Mo, 0.30 to It is a 2.25% Cr 1% Mo steel composed of 0.60% by mass of Mn, 0-0.50% by mass of Si, and the balance, the balance of Fe and inevitable impurity elements . The high-temperature structure preferably has a ferrite / pearlite / bainite structure in which the area ratio of the bainite phase is 0 to 40%.

  The structure for high temperature of the present invention has its metal structure controlled by heat treatment, and can reduce creep deformation in a medium temperature and low stress region. By using such a structure for a steam turbine member, it is possible to prevent contact and seizure between the stationary part and the moving part, prevent misalignment of the fitting part, and also preferably used as a member of a gas turbine, a boiler, etc. be able to.

The present invention uses a low alloy steel containing 0.05 to 0.17% by mass of C, 1.00 to 2.50% by mass of Cr, and 0.45 to 1.10% by mass of Mo. The balance of the low alloy steel substantially contains Fe as a basic component and usually contains an inevitable impurity element. As the low alloy steel, 2.25% Cr 1% Mo steel excellent in high temperature strength and toughness in a medium temperature range (450 to 550 ° C.) is used .

  2.25% Cr 1% Mo steel is preferably 0.05 to 0.15% by mass of C, 2.00 to 2.50% by mass of Cr, and 0.90 to 1.10% by mass of Mo. And 0.30 to 0.60% by mass of Mn, 0 to 0.50% by mass of Si, and the balance, and the balance usually consists essentially of Fe and inevitable impurity elements. The inevitable impurity element varies depending on the raw materials used, but for example, 0.035% by mass or less of P, 0.035% by mass or less of S, 0.4% by mass or less of Cu, 0.4% by mass or less of Ni, 0 0.03 mass% or less of V, 0.02 mass% or less of Nb, or the like.

2. After forming 25% Cr1% Mo steel by forging, rolling and casting, annealing is performed to obtain a desired structure. The annealing treatment is held at a temperature of 800 to 1000 ° C. for a time corresponding to the plate thickness (for example, 1 hour per 25 mm). Here, when the treatment temperature is less than 800 ° C., the austenite single phase is not obtained, and the previous structure cannot be sufficiently destroyed, so that a homogeneous desired structure cannot be obtained. Moreover, when it exceeds 1000 degreeC, the coarsening of a crystal grain will arise and it will have a bad influence on an impact characteristic. Since the austenite single phase is obtained in a relatively short time and there is no concern about the coarsening of crystal grains, the annealing temperature is particularly preferably around 925 ° C. The atmosphere for the heat treatment can be an air atmosphere.

  Such an annealing process can be performed in a furnace set to a predetermined temperature, and since apparatuses and procedures that can be used are known to those skilled in the art, description thereof is omitted here.

  Next, as a cooling condition for the annealing treatment, the average cooling rate up to 600 ° C. is cooled to at least 600 ° C. at a cooling rate of 10 ° C./min or less. This is because if the average cooling rate up to 600 ° C. is 10 ° C./min or less, it intersects with the precipitation nose of ferrite and a part of the ferrite / pearlite structure that is the object of this embodiment can be generated. Further, in order to increase the amount of ferrite / pearlite structure produced, the slower the cooling rate is, the more preferable it is, more preferably 200 ° C./hour or less, which is a cooling rate equivalent to furnace cooling, particularly preferably in the examples described later. If the cooling rate is controlled and gradually cooled below 40 ° C./hour (0.67 ° C./min) as shown in FIG. The total amount of ferrite / pearlite structure can be reduced. This is because the cooling rate is slowed to suppress the precipitation of the bainite phase during cooling as much as possible, and the cooling rate can be industrially implemented with mass production equipment. In addition, there may be a period in which the cooling rate is 0 ° C./min during the slow cooling from the annealing temperature to 600 ° C. or less. In other words, there may be a period during which the temperature is kept constant without lowering the temperature over a predetermined time.

  In order to achieve slow cooling at a predetermined cooling rate, cooling can be performed while adjusting the temperature in the furnace.

  To cool to at least 600 ° C. at a cooling rate of 10 ° C./min or less, once cool to 600 ° C. at a cooling rate of 10 ° C./min. Considering temperature fluctuations due to latitude, etc., it may be cooled at a cooling rate of 10 ° C./min or more. From the viewpoint of production efficiency, it is preferable to cool to 600 ° C. or less at a cooling rate of 10 ° C./min or less and then air cool.

The reason why it is important to control the cooling rate of such annealing is that the precipitation of the bainite phase during cooling can be suppressed as much as possible, and the area ratio of the ferrite / pearlite structure can be increased. Fine needle-like M ₂ C type carbides are precipitated in the ferrite phase, and this is the medium temperature and low stress range (usage temperature range: about 450 to 550 ° C., use stress range: about 10 kg / day), which is the use condition of the steel of the present invention. Contributes to creep strengthening at ² mm or less. Therefore, it is preferable that the ferrite / pearlite structure has a higher creep deformation resistance than the bainite structure, and the area ratio of the bainite phase is as low as possible.

The structure for high temperature according to the present embodiment controls the cooling rate of the annealing treatment as described above, and the medium temperature and low stress region (use temperature range: about 450 to 550 ° C., use stress range: the use condition of the steel of the present invention). It is characterized by being controlled so as to have a tissue form suitable for use at about 10 kg / mm ² or less).

The structure for high temperature obtained according to the present embodiment has a ferrite / pearlite structure that is not easily deformed in an intermediate temperature and low stress region. In the high-temperature structure of the present invention, having a ferrite / pearlite structure means that 60% or more of the total metal structure is occupied by the ferrite / pearlite structure and the area ratio of the bainite phase is 40% or less. The area ratio of the bainite phase is calculated by image processing at an observation magnification of 100 times. Conventional high-temperature structures obtained by normalizing and tempering treatments have a bainite single-phase structure, and have high hardness and tensile strength, but medium temperature and low stress range (operating temperature range: about 450 to 550 ° C, operating stress range) : About 10 kg / mm ² or less), the high temperature structure according to the present embodiment has a ferrite / pearlite structure, so that the medium temperature low stress region (operating temperature range: about 450 to 550 ° C., use stress range: about 10 kg / mm ² or less) and has high creep deformation resistance.

The high-temperature structure according to the present invention can be preferably used as a member for a steam turbine. Examples of the steam turbine member include a steam turbine partition plate, a steam turbine casing, a steam turbine valve box, and a steam turbine main steam pipe. By applying the steam turbine partition plate to the steam turbine partition plate, it is possible to prevent the steam turbine partition plate from coming into contact with the rotor due to creeping over time. Further, by applying to the steam turbine casing, it is possible to prevent contact with the rotating part due to creep deformation of the steam turbine casing. Moreover, by applying to a steam turbine valve box, seizure of the sliding part due to creep deformation of the steam turbine valve box over time can be prevented. Furthermore, by applying to the steam turbine main steam pipe, it is possible to prevent misalignment of the fitting portion due to creep deformation of the steam turbine main steam pipe over time.

In FIG. 1, the conceptual diagram of the partition plate 1 for steam turbines which applied the structure concerning this invention, and the steam turbine 10 provided with the same is shown. In the steam turbine 10, the partition plate 1 is attached to the casing 2, and the rotor blade 3 is attached to the rotor 4. The partition plate 1 for a steam turbine is a member for adjusting a steam flow and sending it to a moving blade, and is a structure in which a stationary blade is coupled by an outer ring and an inner ring. A steam turbine for conventional thermal power is used in a medium temperature and low stress region (operating temperature range: about 450 to 550 ° C., operating stress range: about 10 kg / mm ² or less). And according to the partition plate for steam turbines to which the structure concerning this invention is applied, it has high creep tolerance, without producing a creep collapse deformation | transformation over about 300,000 hours time on these conditions.

  Moreover, the structure for high temperature concerning this invention can be used as a member for gas turbines, and a gas turbine outer casing is mentioned as a member for gas turbines, for example. By applying to the gas turbine outer casing, it is possible to prevent the gas turbine outer casing from coming into contact with the rotating part due to creep deformation over time. Furthermore, the high temperature structure according to the present invention can be applied to boiler piping. Then, by applying to boiler piping, creep deformation of the boiler piping over time can be prevented.

Examples and Comparative Examples A 150 mm thick plate of 2.25% Cr1% Mo steel (ASTM A387Gr22 steel) having the chemical composition shown in Table 1 was subjected to heat treatment under the conditions shown in Table 2, and the structure and creep characteristics were investigated. . The air cooling material conventionally used is a comparative steel, and the cooling rate is 40 ° C./hour (0.67 ° C./min) or less until the cooling rate is 600 ° C., and then the air is cooled by opening the furnace. The test material of the fast surface layer is Invention Steel-1, the test material of the central part having a slow cooling rate is Invention Steel-2, and the cooling rate is up to 500 ° C. at 40 ° C./hour (0.67 ° C./min) or less. The surface layer part of what was cooled in the furnace and then air-cooled by opening the furnace was designated as invention steel-3.

  Table 3 shows the structure observation results. The air-cooled material of the comparative steel exhibits a bainite single-phase structure, and in the steel of the present invention, the area ratio of the bainite phase decreases and the ratio of ferrite / pearlite structure increases. Bainitic phase in the order of the surface layer portion of the test material (invention steel 1), the central portion (invention steel 2), and the surface layer portion (invention steel 3) of the test material that opened the furnace at 500 ° C. It is considered that the area ratio of the bainite phase generally depends on the cooling rate. In order to make the bainite phase as close to zero as possible, it is preferable that the cooling rate is 40 ° C./hour (0.67 ° C./min) or less and the furnace is opened at 500 ° C. or less.

FIG. 2 shows the results of the creep test results arranged according to the Larson Miller Parameter (LMP) of the minimum creep speed. The Larson Miller parameter is expressed by the following formula.
LMP = (273 + T) × (20−log A) / 1000
(In the formula, T is temperature (unit: ° C.), and A is the minimum creep rate (unit: mm / mm / Hr).)
From the above equation, LMP increases as the minimum creep speed decreases, and FIG. 2 indicates that the creep deformation speed decreases (creep strain decreases) toward the right side. The creep deformation rate of the comparative steel is small in the high stress region where the stress is 20 kg / mm ² or more, but the order is reversed in the low stress region below that, particularly 10 kg / mm ² or less, and the creep deformation rate of the steel of the present invention is higher. small. That is, the ferrite / pearlite structure has a smaller creep deformation rate and is more advantageous in the low stress region of 10 kg / mm ² or less than the bainite structure. Among the steels of the present invention, the creep rate changes corresponding to the area ratio of the bainite phase, and a tendency that the creep deformation rate tends to be smaller as the area ratio of the bainite phase is smaller.

FIG. 3 shows a comparison of the amount of partition plate collapse by three-dimensional creep analysis using the creep data. Here, the relative fall amount taken on the vertical axis indicates the relative fall amount when the fall amount after 300,000 hours of operation of the comparative steel is 1.
FIG. 4 shows the amount of falling of the partition plate (creep falling amount). The partition plate has a structure in which the outer ring is fixed to the passenger compartment, and creep deformation occurs downstream in the steam flow direction. The amount of deformation of the inner ring of the partition plate in the downstream direction is the creep collapse amount. In the actual measurement, the amount of collapse on the downstream side of the inner ring inner peripheral end was measured using the downstream root as a reference point before deformation.
It was found that the steel according to the present invention has a smaller creep collapse amount than that of the comparative steel, and in particular, little change with time. And the relative fall amount of the present invention steel after 300,000 hours of operation is greatly reduced to about 15% to 46% of the relative fall amount of the comparative steel, and if it is reduced to this level, the plant design life The contact between the rotor and the partition plate can be reliably avoided, and there is no hindrance to the actual continuous operation of the steam turbine. Therefore, the steam turbine to which the partition plate of the present invention is applied is very reliable.

  FIG. 5 shows the relationship between the amount of relative collapse after 300,000 hours of operation and the amount of precipitation of the bainite phase. As the area ratio of the bainite phase increases, the relative collapse amount tends to increase. To achieve a relative collapse amount of half that of the reference steel, which is a guideline, the area ratio of the bainite phase is 40% or less (including zero). It was found that it should be controlled. If the relative fall amount of half of the comparative steel that is a guideline can be achieved, contact between the rotor and the partition plate within the plant design life can be avoided, and stable operation of the steam turbine becomes possible.

  From the above, it was demonstrated that the relative collapse amount can be greatly reduced by controlling the cooling rate of the annealing treatment of 2.25% Cr1% Mo steel and controlling the area ratio of the bainite phase to 40% or less. .

It is a conceptual diagram of the partition plate for steam turbines which applied the structure concerning this invention. It is the rearrangement result by the Larson Miller parameter of the minimum creep speed of the comparative steel and the steel of the present invention. It is a figure which shows the relative fall amount comparison of the partition plate of the comparative steel and this invention steel by the three-dimensional creep analysis using creep data. It is a figure which shows the amount of creep collapse of a partition plate. It is a figure which shows the correlation with the amount of relative collapse and the area ratio of a bainite phase.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Partition plate 2 Casing 3 Rotor blade 4 Rotor 10 Steam turbine

Claims (2)

0.05 to 0.15 mass% C, 2.00 to 2.50 mass% Cr, 0.90 to 1.10 mass% Mo, and 0.30 to 0.60 mass% Mn If, and 0 to 0.50 wt% Si, Ri Do from the rest, said residue portion, a 2.25% Cr1% Mo steel Ru Fe and inevitable impurity elements Toka Rana, after heating to 800 to 1000 ° C. The manufacturing method of the structure for high temperature including the process characterized by performing the annealing process formed by cooling to at least 600 degrees C or less with the cooling rate of 40 degrees C / hour or less. The method for producing a high-temperature structure according to claim 1 , wherein the high-temperature structure has a ferrite and pearlite structure having an area ratio of 40% or less of a bainite phase.

Images