JP2008179864A - METHOD FOR MANUFACTURING Ni-BASE ALLOY - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an Ni-base alloy by which an Ni-base alloy having high strength and nonmagnetism can be obtained with high manufacturability. <P>SOLUTION: An alloy containing, by weight, 30 to 45% Cr, 1.5 to 5.0% Al and the balance essentially Ni with inevitable impurities, is hot worked at ≥650°C and then subjected to heat treatment where a relationship between treatment temperature T(°C) and holding time t(h) satisfies equation [(T+273)×(20+logt)/1000=20.5 to 26.5] to regulate hardness to <600 HV. In the equation, T satisfies [650°C≤T≤(solid-solution temperature(°C) of α-phase)]. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a Ni-based alloy.

  Conventionally, Ni-based alloys are known as materials applied to various members that require high strength and non-magnetism.

  As a method for producing this type of Ni-based alloy, for example, in Patent Document 1, in weight percent, C: 0.1% or less, Si: 2.0% or less, Mn 2.0% or less, Cr: 30 to Ni-based alloy ingot containing 45% and Al: 1.5 to 5%, the balance of which is an inevitable impurity and Ni alloy composition is forged and rolled at a temperature of 1200 to 950 ° C, followed by solution heat treatment (1150 ° C. × 1 hour—water cooling) —A method of aging heat treatment (700 ° C. × 16 hours—air cooling) is disclosed.

JP 2002-69557 A

  According to a conventional Ni-based alloy manufacturing method, it is considered that a nonmagnetic Ni-based alloy having strength due to precipitation strengthening can be obtained.

  However, the conventional manufacturing methods have a problem that the manufacturability is low, for example, cracks are generated or corners are missing during the cooling process or movement during the manufacturing.

  The present invention has been made in view of the above problems, and the problem to be solved by the present invention is to provide a Ni-based alloy manufacturing method capable of obtaining a high-strength and non-magnetic Ni-based alloy with good manufacturability. It is to provide.

The manufacturing method of the Ni-based alloy according to the present invention is an alloy containing, by weight%, Cr: 30 to 45%, Al: 1.5 to 5.0%, with the balance being substantially made of Ni and inevitable impurities. After the hot working at a temperature of 650 ° C. or higher, the heat treatment is performed so that the relationship between the processing temperature T (° C.) and the holding time t (h) satisfies the following formula, thereby making the hardness less than 600 HV The gist.
(T + 273) × (20 + logt) /1000=20.5-26.5
However, 650 ° C. ≦ T ≦ α phase solution temperature (° C.)

  In this case, the alloy further contains 0.02 to 0.20% by weight% of one or more selected from B, Mg, and Ca (in the case of two or more, in total). Good to be.

Moreover, the manufacturing method of the Ni-based alloy according to the present invention includes, by weight%, Cr: 30 to 45%, Al and Mo in total: 1.5 to 5.0%, with the balance being substantially Ni. The alloy consisting of inevitable impurities is hot-worked at a temperature of 650 ° C. or higher, and then subjected to a heat treatment in which the relationship between the processing temperature T (° C.) and the holding time t (h) satisfies the following formula: Is less than 600 HV.
(T + 273) × (20 + logt) /1000=20.5-26.5
However, 650 ° C. ≦ T ≦ α phase solution temperature (° C.)

  In this case, the alloy further contains 0.02 to 0.20% by weight% of one or more selected from B, Mg, and Ca (in the case of two or more, in total). Good to be.

  In the Ni-based alloy manufacturing method according to the present invention, the alloy having the above chemical composition is hot-worked at a temperature of 650 ° C. or higher, and then the relationship between the processing temperature T (° C.) and the holding time t (h) is as described above. A heat treatment satisfying the formula is performed.

  That is, after the hot working, by performing a specific heat treatment between overaging and solid solution, the hardness decreases due to the spheroidization of the α phase (αCr) and the coarsening of the γ ′ phase. Therefore, the productivity of the Ni-based alloy can be improved. Further, the obtained Ni-based alloy has good strength and nonmagnetic properties.

  At this time, when the alloy composition to be used contains a specific proportion of Mo, the strength and corrosion resistance can be improved. Moreover, when a specific ratio of B, Mg, and Ca is included in the alloy composition, hot workability can be improved.

  Hereinafter, a method for producing a Ni-based alloy according to an embodiment of the present invention (hereinafter sometimes referred to as “the present production method”) will be described in detail. In this manufacturing method, an alloy having a specific chemical composition is hot-worked and then heat-treated under specific conditions. Hereinafter, the reason for limiting each condition will be described.

  Alloys (first alloy and second alloy) used in this production method contain the following elements, with the balance being substantially made of Ni and inevitable impurities. In addition, the unit of the component ratio mentioned below is weight%.

(First alloy)
Cr: 30 to 45%
Cr is a main element that forms an α phase (αCr), and high strength can be obtained by the composite precipitation of the α phase with the γ ′ phase. Cr also contributes to improving the corrosion resistance of the alloy. In order to obtain the effect, the lower limit of the Cr content is set to 30% or more. The lower limit of the Cr content is preferably 31% or more, and more preferably 32% or more.

  On the other hand, when Cr content becomes excessive, the tendency for hot workability to fall is seen. Therefore, the upper limit of the Cr content is 45% or less. The upper limit of the Cr content is preferably 44% or less, and more preferably 43% or less.

Al: 1.5-5.0%
Al is an important element that forms the γ ′ phase. Further, Al contributes to the improvement of high temperature corrosion resistance. In order to obtain the effect, the lower limit of the Al content is set to 1.5% or more. The lower limit of the Al content is preferably 1.7% or more, and more preferably 2.0% or more.

  On the other hand, when the Al content is excessive, the hot workability tends to be reduced. Therefore, the upper limit of the Al content is 5.0% or less. The upper limit of the Al content is preferably 4.7% or less, more preferably 4.5% or less.

  In addition to the elements described above, the first alloy may further contain the following elements as necessary.

One or more selected from B, Mg and Ca (in the case of two or more, in total): 0.02 to 0.20%
B contributes to the improvement of hot workability and helps to prevent a decrease in high-temperature strength and toughness. B is also effective in increasing the high temperature creep strength. However, excessive addition reduces hot workability.

  Mg and Ca are elements having a deoxidation and desulfurization action and contribute to increasing the cleanliness of the alloy. Mg and Ca contribute to increasing the strength by segregating at the grain boundaries. However, excessive addition reduces hot workability.

  Therefore, from these viewpoints, the lower limit of the content of the above elements (in the case of two or more elements) is set to 0.02% or more. The lower limit of the content of the above elements (in the case of two or more elements) is preferably 0.025% or more, and more preferably 0.030% or more.

  On the other hand, the upper limit of the content of the above elements (in the case of two or more elements) is set to 0.20% or less. The upper limit of the content of the above elements (in the case of two or more elements) is preferably 0.17% or less, more preferably 0.15% or less.

(Second alloy)
The second alloy is that the first alloy is defined as Al: 1.5-5.0%, whereas Al and Mo: 1.5-5.0% only. It is different. Therefore, since other points are the same as those of the first alloy, they are omitted, and different points will be mainly described.

Al and Mo: 1.5 to 5.0%
Al is an important element that forms the γ ′ phase. Further, Al contributes to the improvement of high temperature corrosion resistance. However, when the Al content is excessive, the hot workability tends to decrease.

  On the other hand, Mo not only increases the strength of the alloy by solid solution strengthening, but also improves the corrosion resistance. However, when the Mo content is excessive, the hot workability tends to decrease.

  From these viewpoints, the lower limit of the content of Al and Mo (the sum of the Al content and the Mo content) is set to 1.5% or more. The lower limit of the content of Al and Mo is preferably 1.7% or more, and more preferably 2.0% or more.

  On the other hand, the upper limit of the content of Al and Mo is set to 5.0% or less. The upper limit of the content of Al and Mo is preferably 4.7% or less, more preferably 4.5% or less. Fe, Si, C and the like which are supposed to be mixed from the melting furnace are not particularly limited.

  The first alloy and the second alloy are prepared by, for example, melting the alloy having the above-described chemical composition in a melting furnace such as an electric furnace or a high-frequency induction furnace and casting the alloy into an alloy ingot. It ’s fine.

  In this manufacturing method, an alloy having the above chemical composition is hot-worked.

  Examples of the hot working method include hot forging and hot rolling. An optimal method can be appropriately selected so that a necessary shape can be obtained. In the present manufacturing method, these may be performed either alone or both. Further, when both are performed, the order is not particularly limited. Preferably, the order is hot forging and hot rolling.

  In this production method, the lower limit of the temperature when performing the hot working is set to 650 ° C. or more from the viewpoint of ensuring good hot workability. The temperature is preferably 675 ° C. or higher, more preferably 700 ° C. or higher.

  On the other hand, the upper limit of the temperature at the time of performing the hot working is not particularly limited. Preferably, it is 1300 ° C. or lower, more preferably 1250 ° C. or lower, from the viewpoint of preventing coarsening of crystal grains.

  The temperature at which the hot working is performed may be selected in consideration of a processing temperature T selected at the time of heat treatment to be described later. Preferably, a temperature higher than the processing temperature T selected at the time of the heat treatment described later is selected from the viewpoint of cost reduction and good hot workability.

  Here, in the present manufacturing method, after the hot working, heat treatment is performed in which the relationship between the processing temperature T (° C.) and the holding time t (h) satisfies the following formula. Thereby, the hardness of the obtained Ni-based alloy becomes less than 600 HV.

(T + 273) × (20 + logt) /1000=20.5-26.5

  However, the lower limit of the treatment temperature T (° C.) is 650 ° C. or higher. This is because if the lower limit of the treatment temperature is less than 650 ° C., the hardness of the Ni-based alloy becomes difficult to be less than 600 HV, and the productivity is lowered.

  The lower limit of the treatment temperature T (° C.) is preferably 680 ° C. or higher, more preferably 690 ° C. or higher, and still more preferably 700 ° C. or higher.

  On the other hand, the upper limit of the treatment temperature T (° C.) is a temperature equal to or lower than the solid solution temperature of the α phase. This is because if the upper limit of the treatment temperature is higher than the solid solution temperature of the α phase, the hardness of the Ni-based alloy is hardly made less than 600 HV, and the productivity is lowered.

  The upper limit of the treatment temperature T (° C.) is preferably a temperature lower than the solid solution temperature of the α phase. Specifically, the upper limit of the treatment temperature T (° C.) is preferably less than 1200 ° C., more preferably 1150 ° C. or less, and even more preferably 1100 ° C. or less.

  In the heat treatment in this manufacturing method, if the treatment temperature T (° C.) is determined, the range of the holding time t (h) during the heat treatment can be obtained from the above formula. Note that the base of the log function is 10.

  The heat treatment method during the heat treatment is not particularly limited as long as the heat treatment can be performed at a treatment temperature and a holding time that satisfy the above conditions. Specifically, as the heat treatment method, for example, after performing the hot treatment, an appropriate cooling method such as natural heat dissipation, water cooling, oil cooling, gas cooling, or the like is used, and the range of the treatment temperature in the flow. A method of performing the heat treatment after the temperature is lowered to a temperature can be exemplified. According to this method, since it is not necessary to perform heating again, energy efficiency is good and it contributes to cost reduction.

  In addition, after the hot working, the temperature is lowered in the same manner as described above, and after one temperature is lowered below the lower limit of the processing temperature, heating means such as a heating furnace, energization, and induction heating are then performed again. A method of performing the heat treatment as a temperature within the range of the above processing temperature can be employed.

  In addition, if the temperature during the hot working is lower than the processing temperature, after the hot working, the temperature is raised to a temperature within the processing temperature range using the heating means, A method of performing the heat treatment can also be employed.

  Although the basic steps of this production method are as described above, steps such as a solution treatment and an aging treatment may be added as necessary.

  In this case, the solution treatment is preferably performed between the hot working and the heat treatment. Examples of the solution treatment include a method of heating to a temperature equal to or higher than the optimum solution temperature according to the composition of the alloy, and then maintaining the temperature for a certain time and cooling.

  The lower limit of the temperature during the solution treatment is preferably 1060 ° C. or higher, more preferably 1080 ° C. or higher, and even more preferably 1100 ° C. or higher, from the viewpoint of the solid solution of the α phase and the γ ′ phase. On the other hand, the upper limit of the temperature during the solution treatment is preferably 1300 ° C. or less, more preferably 1275 ° C. or less, and even more preferably 1250 ° C. or less, from the viewpoint of preventing crystal grain coarsening.

  The time for the solution treatment is not particularly limited. It can be varied according to the dimensions of the material. Preferably, it may be selected from a range of 0.1 to 10 hours.

  Further, the aging treatment can be performed after the heat treatment or after plasticity or machining by applying heat treatment, and is not particularly limited.

  The lower limit of the temperature during the aging treatment is preferably 350 ° C. or higher, more preferably 375 ° C. or higher, and still more preferably 400 ° C. or higher from the viewpoint of precipitation of α phase and γ ′ phase. On the other hand, the upper limit of the temperature during the aging treatment is preferably 600 ° C. or less, more preferably 625 ° C. or less, from the viewpoint of preventing the α phase (αCr) from being spheroidized or preventing the γ ′ phase from becoming coarse. Even more preferably, it is 650 ° C. or lower.

  The time for the aging treatment is not particularly limited. From the viewpoint of precipitation of α phase and γ ′ phase, it is preferable to select from the range of 0.1 to 100 hours.

  The hardness of the Ni-based alloy obtained by this manufacturing method is less than 600 HV. The hardness of the Ni-based alloy varies depending on the heat treatment conditions. The hardness referred to in the present application is the Vickers hardness of the Ni-based alloy material itself (measured in accordance with JIS Z 2244) and is affected by work hardening by cold working and various surface treatments. Measured from no part.

  The upper limit of the hardness of the obtained Ni-based alloy is preferably 595 HV or less, more preferably 590 HV or less, and even more preferably 585 HV or less, from the viewpoint of balance between strength and toughness.

  On the other hand, the lower limit of the hardness of the obtained Ni-based alloy is preferably 300 HV or higher, more preferably 305 HV or higher, and still more preferably 310 HV, from the viewpoint of cold workability, balance between strength and toughness. It is good to be above.

  Further, the crystal grain size (after the heat treatment) of the Ni-based alloy obtained by the present production method varies depending on the hardness and the like.

  The upper limit of the crystal grain size of the obtained Ni-based alloy is preferably 1000 μm or less, more preferably 700 μm or less, and even more preferably 500 μm or less, from the viewpoints of workability and strength.

  On the other hand, the lower limit of the crystal grain size of the obtained Ni-based alloy is preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably, from the viewpoint of easily obtaining a hardness of less than 600 HV. Is preferably 0.1 μm or more.

  The crystal grain size is a value measured by an image analyzer after preparing a sample for tissue observation.

  Moreover, the Ni-based alloy obtained by this manufacturing method is nonmagnetic.

  The magnetic permeability μ of the obtained Ni-based alloy is preferably 1.05 or less, more preferably 1.01 or less, and even more preferably from the viewpoint of not affecting the generated magnetic field. It is good that it is 005 or less.

  The magnetic permeability is a value measured using a VSM (Vibrating Sample Magnetometer) under conditions of an external magnetic field of 100 Oe and room temperature.

  The manufacturing method has been described above. The use of the Ni-based alloy obtained by this production method is not particularly limited, and can be applied to various uses that require high strength and non-magnetism.

  Specifically, for example, a powder molding die, a resin molding die, a metal molding die, a chemical molding die, a food molding die, a kneading machine, an extruder, a screw such as an injection molding machine, Automotive parts (bolts, nuts, valves, cooling water systems, oil systems, electrical systems, mechanical systems, etc.), electronic parts (housing, bolts, nuts, etc.), medical parts (bolts, nuts, bushes, mortars, etc.) It can be illustrated.

  Hereinafter, the present invention will be described more specifically with reference to examples.

  First, using a high-frequency vacuum induction furnace, alloys having chemical components shown in Table 1 (the solution temperature of the α phase was 1185 ° C.) were melted to cast 150 kg of alloy ingots.

  Next, each of the obtained alloy ingots was hot forged at 1200 ° C. to produce round bars each having a diameter of 16 mm.

  Next, each of the obtained round bars was naturally radiated as it was, adjusted to each processing temperature described in Table 2 and Table 3, and then held at each processing temperature for each holding time described in Table 2 and Table 3. A heat treatment was performed.

  Here, alloy no. And the numbers of the examples and comparative examples correspond to each other. In other words, the numbers corresponding to the examples and the comparative examples use alloys having the same chemical composition.

  However, with respect to the examples, the processing temperature and the holding time are subjected to heat treatment that satisfies the above-described conditional expression. However, for the comparative example, the processing temperature and the holding time satisfy the above-described conditional expression. There is no heat treatment. Moreover, about Comparative Examples 1-4, 15 and 16, the round bar of diameter 150mm was cooled with the cooling rate of Table 1 at the said hot forging process.

  Next, the hardness, Charpy impact characteristics, and magnetic permeability were measured as follows using each of the round bars that had undergone the predetermined heat treatment. The productivity was evaluated with a round bar having a diameter of 150 mm in the hot forging process.

<Hardness>
Each round bar that has undergone the above prescribed heat treatment is cut in a direction perpendicular to its axial direction, and the hardness of the part separated by a distance of half the radius in the radial direction from the center of the cut surface is the Vickers hardness. Using a meter, five points were measured according to JIS Z 2244. In addition, the measured average value of 5 points | pieces was made into the hardness of each round bar.

<Charpy impact value>
In accordance with JIS Z 2242, Charpy impact values were measured using 10 mmR notch test pieces (10 mm square bars) collected from each round bar that had undergone the above predetermined heat treatment. The average value of the three Charpy impact values measured for each round bar was taken as the Charpy impact value for each round bar.

<Permeability>
Each round bar subjected to the predetermined heat treatment was cut into a 5 mm square, and the magnetic permeability was measured using a VSM (Vibrating Sample Magnetometer) under conditions of an external magnetic field of 100 Oe and room temperature.

<Manufacturability>
When the above round bars were manufactured, cracks did not occur during the cooling process or movement, and when the corners were not chipped, it was judged that the manufacturability was good. On the other hand, when cracking occurred during the cooling process or movement, or when corners were chipped, it was judged that the productivity was poor. In Tables 2 and 3, the case where the manufacturability is good is indicated as “◯”, and the case where the manufacturability is inferior is indicated as “x”.

  Table 1 shows a list of each alloy composition. Tables 2 and 3 summarize the heat treatment conditions, the measurement results, and the evaluation results of manufacturability.

  When Tables 1 to 3 are evaluated relative to each other, the following can be understood.

  That is, it can be seen that even if the alloys have the same chemical composition, the obtained hardness differs depending on whether or not a specific heat treatment is performed. FIG. 1 shows the relationship between the value of (T + 273) × (20 + logt) / 1000 and the Vickers hardness (HV). 1 also shows that there is a high correlation between specific heat treatment conditions and hardness. Moreover, it turns out that the superiority and inferiority of manufacturability are actually divided in the case where hardness is less than 600HV and the case where it is 600HV or more.

  Moreover, about Comparative Examples 1-4, 15 and 16, the crack generate | occur | produced when it cooled with the cooling rate of Table 3 to the round bar of diameter 150mm at the hot forging process. In another comparative example, when a round bar having a diameter of 150 mm was naturally radiated in the hot forging process, cracks and chips were generated.

  Therefore, it can be seen from these facts that the productivity of the alloy can be improved by setting the hardness of the alloy to less than 600 HV by a specific heat treatment.

  Further, as can be seen by comparing the Charpy impact value and the permeability value, it can be seen that in the comparative example, it is difficult to obtain a sufficient strength even if a nonmagnetic alloy can be obtained. On the other hand, in an Example, the high intensity | strength (high toughness) and nonmagnetic alloy can be obtained.

  Therefore, it can be said that according to the method for producing a Ni-based alloy according to the present invention, a Ni-based alloy having high strength and nonmagnetic properties can be obtained with good manufacturability.

  As mentioned above, although the manufacturing method of the Ni base alloy which concerns on this invention was demonstrated, this invention is not limited to the said embodiment and Example at all, and various modification | change is within the range which does not deviate from the summary of this invention. Is possible.

It is the figure which showed the relationship between the value of (T + 273) * (20 + logt) / 1000, and Vickers hardness (HV).

Claims (4)

An alloy containing Cr: 30 to 45% and Al: 1.5 to 5.0% by weight and the balance being substantially made of Ni and inevitable impurities was hot worked at a temperature of 650 ° C. or higher. Then, the manufacturing method of the Ni base alloy which makes hardness less than 600 HV by performing the heat processing with which the relationship between processing temperature T (degreeC) and holding time t (h) satisfy | fills a following formula.
(T + 273) × (20 + logt) /1000=20.5-26.5
However, 650 ° C. ≦ T ≦ α phase solution temperature (° C.)   2. The alloy according to claim 1, further comprising 0.02 to 0.20% by weight percent of one or more selected from B, Mg, and Ca (a total of two or more types). The manufacturing method of Ni-based alloy of description. An alloy containing, by weight%, Cr: 30 to 45%, Al and Mo in total: 1.5 to 5.0%, with the balance being substantially made of Ni and unavoidable impurities at a temperature of 650 ° C. or higher. A method of manufacturing a Ni-based alloy having a hardness of less than 600 HV by performing a heat treatment in which the relationship between the processing temperature T (° C.) and the holding time t (h) satisfies the following formula after hot working.
(T + 273) × (20 + logt) /1000=20.5-26.5
However, 650 ° C. ≦ T ≦ α phase solution temperature (° C.)   The alloy further contains 0.02 to 0.20% by weight percent of one or more selected from B, Mg and Ca (in the case of two or more, in total). The manufacturing method of Ni-based alloy of description.

Images