JP2017137534A - Nickel-based alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel-based alloy capable of providing a constant high temperature hardness in short time and a nickel-based alloy excellent in high temperature strength in a temperature range of 900°C or more compared to conventional nickel-based alloy.SOLUTION: There is provided a nickel-based alloy containing, by wt.%, 0.01 to 0.05% C, 0.1 to 0.5% Si, 0.1 to 0.5% Mn, 0.001 to 0.01% B, 20.0 to 23.5% Cr, 0.7 to 1.3% Nb, 2.0 to 3.2% Ti, 1.2 to 2.2% Al, 50 to 53% Ni, 0.3 to 1.0% Cu, 1.5 to 3.0% Mo, 1.0 to 2.0% W and the balance Fe with inevitable impurities. There is also provided a nickel-based alloy having sum of the Ti content and the Al content of 4.0% or more.SELECTED DRAWING: None

Description

  The present invention relates to an automotive engine component, particularly a nickel-base alloy used in a high temperature atmosphere such as an exhaust valve.

  In recent years, there has been remarkable progress in improving the fuel efficiency of automobiles. For example, the automobile engine has been made smaller and lighter than before, and the shortage of output is combined with a turbocharger to compensate for the shortage of output. Turbo is becoming mainstream.

  As materials used for such automobile engine parts, for example, in Patent Document 1, 0.01 to 0.1% C, 0 to 0.5% Si, 0 to 0.5% Mn, and 23% in weight percent are used. More than 25% Cr, 0.5 to 1.5% Nb, 2.0 to 3.0% Ti, 1.0 to 2.0% Al, more than 45% to 50% Ni, 0 A nickel-base alloy composed of 0.1 to 1.2% Cu, 0.3 to 2.0% W, etc. is disclosed. The nickel-base alloy is described as being useful as a heat-resistant alloy for valves because it has excellent high-temperature tensile strength at 900 ° C. and high hardness even after prolonged aging treatment at 800 ° C. .

Patent Document 2 discloses that 40 to 49% Ni, 1.2 to 1.8% Al, 2.0 to 3.0% Ti, 0.9 to 7.8% Nb, 1% or less by weight. A nickel-base alloy composed of Mo or the like is disclosed. The nickel-base alloy is described as being useful as a diesel engine component (particularly an exhaust valve component) because of its excellent corrosion resistance and wear resistance.

Japanese Patent Laid-Open No. 4-191344 JP-T-2004-512428

However, it is explained that the nickel-base alloy of Patent Document 1 maintains a certain high hardness (for example, HRC38-39 on the Rockwell C scale) even after an aging treatment of 300 hours in an atmosphere of 800 ° C. However, there is a problem that the aging treatment time required until the high hardness is obtained is relatively long.

Similarly, it is described that the nickel base alloy of Patent Document 2 can also obtain high hardness (for example, HRC27 to 28 on the Rockwell C scale) by performing an aging treatment in the vicinity of 800 ° C. There was a problem that the aging treatment time required until the hardness was obtained was relatively long.

Furthermore, as described above, the exhaust gas temperature of the automobile engine may reach around 900 to 1000 ° C. with the miniaturization and weight reduction of the automobile engine. In the nickel-base alloys described in Patent Documents 1 and 2, the high temperature strength is high. In addition, there is a problem that the high temperature creep characteristics are insufficient.

  Accordingly, an object of the present invention is to provide a nickel-base alloy that is superior in high-temperature strength in a temperature range of 900 ° C. or higher as compared with conventional nickel-base alloys.

  In order to solve the above-described problems, the nickel-base alloy according to the present invention is 0.01 to 0.05% C, 0.1 to 0.5% Si, 0.1 to 0.5% by weight. Mn, 0.001 to 0.01% B, 20.0 to 23.5% Cr, 0.7 to 1.3% Nb, 2.0 to 3.2% Ti, 1.2 to 2.2% Nickel containing Al, 50-53% Ni, 0.3-1.0% Cu, 1.5-3.0% Mo, 1.0-2.0% W, the balance being Fe and inevitable impurities A base alloy was used.

The nickel-base alloy according to claim 2 is a nickel-base alloy in which the sum of the Ti content and the Al content is 4.0% by weight or more.

The nickel base alloy according to the present invention has an effect that the tensile strength in a high temperature atmosphere of 900 ° C. or higher is improved as compared with the above-described conventional nickel base alloy. Further, the nickel-base alloy according to claim 2 can have excellent high temperature creep characteristics. Therefore, the nickel-base alloy according to the present invention is suitable for an automobile exhaust valve part that is exposed to a high temperature atmosphere of 900 ° C. or higher for a long time.

An example of an embodiment of the present invention will be described. The components constituting the nickel-base alloy according to the present invention and the reasons for limiting the component ranges will be described in detail below.

The C (carbon) content is 0.01 to 0.05% by weight. C combines with Ti, Nb and Cr to form carbides and improves high temperature strength. In order to obtain such an effect, at least 0.01% by weight or more must be added. However, when added excessively, a large amount of MC carbide is generated to reduce hot workability, so the upper limit was made 0.05% by weight.

The content of Si (silicon) is 0.1 to 0.5% by weight. Si is added as a deoxidizing element. Moreover, the addition of an appropriate amount improves the oxidation resistance. However, if added excessively, ductility is lowered, so the upper limit was made 0.5 wt%.

The content of Mn (manganese) is 0.1 to 0.5% by weight. Mn is also added as a deoxidizing element in the same manner as Si. However, if added excessively, the high temperature strength is lowered, so the upper limit was made 0.5% by weight.

The content of B (boron) is 0.001 to 0.01% by weight. B enhances the crystal grain boundary to increase the creep strength and has the effect of improving hot workability. For this reason, addition of 0.001% by weight or more is necessary. However, if added excessively, a low melting point compound is formed at the grain boundary and hot workability is impaired, so the upper limit was made 0.01 wt%.

The content of Cr (chromium) is 20.0 to 23.5% by weight. Cr is an essential element for improving oxidation resistance and corrosion resistance. Further, when added to some extent, an acicular structure grows and an improvement in creep resistance is recognized. However, when excessively added, the acicular structure becomes coarse and causes performance deterioration, so the content was made 20.0 to 23.5% by weight.

The content of Nb (niobium) is 0.7 to 1.3% by weight. Nb precipitates an intermetallic compound phase such as Ni ₃ (Al, Ti, Nb) and improves high-temperature strength. Moreover, it combines with C to produce carbide NbC, which contributes to improvement in high temperature hardness and strength. However, if added excessively, the material becomes brittle, so the content was made 0.7 to 1.3% by weight.

The content of Ti (titanium) is 2.0 to 3.2% by weight. Ti combines with Ni to form an intermetallic compound γ ′ phase and strengthens the austenite phase. Increasing the amount of Ti increases the amount of γ ′ phase, which is a strengthening phase, and improves the high-temperature strength. However, if added excessively, the embrittlement phase precipitates and the hot formability of the material is impaired, so the range of addition was limited to 2.0 to 3.2 wt%.

The content of Al (aluminum) is 1.2 to 2.2% by weight. Al is an important element that combines with Ni to form an intermetallic compound γ ′ phase and strengthens the austenite phase. Increasing the amount of Al increases the amount of γ ′ phase, which is a strengthening phase, and improves the high-temperature strength. However, if added excessively, the strengthening phase becomes unstable, leading to the precipitation of the embrittlement phase. For this reason, since the hot formability of a raw material is inhibited, the addition range was limited to 1.2 to 2.2% by weight.

The content of Ni (nickel) is 50 to 53% by weight. Ni is indispensable for forming an austenite base that is a matrix. Further, a γ 'phase that is a precipitation strengthening phase is formed, and the high temperature strength is improved. In order to dissolve the strengthening element, a certain amount is necessary, and the lower limit of the addition amount is set to 50% by weight or more. However, when excessively added, the cost of the alloy increases, and the resistance to sulfidation corrosion deteriorates, so the upper limit was made 53 wt%.

The content of Cu (copper) is 0.3 to 1.0% by weight. Cu is added for the purpose of improving sulfide corrosion. When excessively added, hot embrittlement occurs, so the content was limited to 0.3 to 1.0% by weight.

The content of Mo (molybdenum) is 1.5 to 3.0% by weight. Mo is an element that improves high-temperature strength and high-temperature creep characteristics by solid solution strengthening in a temperature range in which a precipitation strengthening phase that achieves hot strength is dissolved. If the content is less than 1.5% by weight, the effect of improving the high-temperature strength and high-temperature creep properties is not manifested. If the content exceeds 3.0% by weight, the hot workability is detrimental, so the content is limited. .

The content of W (tungsten) is 1.0 to 2.0% by weight. W is an element that improves high-temperature strength and high-temperature creep characteristics by solid solution strengthening in a temperature range in which a precipitation strengthening phase that achieves hot strength is dissolved. If the content is less than 1.0% by weight, the effect of improving the high-temperature strength and the high-temperature creep property is not manifested, and if the content exceeds 2.0% by weight, the hot workability is harmful. Limited.

  A tensile test at a high temperature was performed using a nickel-based alloy according to the present invention (hereinafter referred to as the present invention material) and a conventional nickel-based alloy (hereinafter referred to as a conventional material), and the test results will be described. In this test, the steel of the present invention and the conventional material were both melted in a vacuum melting furnace to produce a steel ingot, subjected to solution treatment at 1050 ° C. for 1 hour, and then water-cooled. About the test piece, the column-shaped test piece of diameter 16mm and height 15mm was produced from the steel ingot, and the aging treatment was performed.

Regarding the aging treatment conditions, the aging temperature was 750 ° C., and the aging time was 4 hours. Table 1 shows the chemical compositions of the inventive material and the conventional material of this example.

  The test piece used was manufactured by cutting from a rolled material having a diameter of 16 mm prepared from the steel ingot so that the parallel part had a diameter of 6 mm and a length of 25 mm. The test conditions were as follows: the test piece was kept soaked for 20 minutes in a total of three atmospheres: room temperature, 800 ° C., and 900 ° C., followed by a tensile test at a tensile speed of 2 mm / min. Strength: unit MPa), 0.2% proof stress (unit: MPa), elongation (unit:%), and drawing (unit:%) were measured. Tables 2 to 4 show various properties such as the tensile strength at room temperature, 800 ° C. and 900 ° C. of the material of the present invention and the conventional material.

    As shown in Table 2, the tensile strength and the 0.2% proof stress of the present invention materials were slightly lower than those of the conventional materials as shown in Table 2. However, with regard to elongation and drawing, the inventive material showed a value about 4 to 8 times that of the conventional material.

Next, as shown in Table 3, the tensile strength at 800 ° C. of the conventional material is 669 MPa, while the material of the present invention is 689 MPa, and the material of the present invention has a tensile strength equal to or higher than that of the conventional material. .

Moreover, about 0.2% yield strength, this invention material was 645 MPa, while the conventional material was 590 MPa. From this, it was found that the tensile strength and 0.2% proof stress of the material of the present invention at 800 ° C. have the same or better properties than the conventional material.

Also, as shown in Table 4, the tensile strength at 900 ° C. was 336 MPa for the conventional material, whereas it was 394 MPa for the material of the present invention. Furthermore, regarding the 0.2% proof stress, the material of the present invention was 394 MPa, whereas the conventional material was 261 MPa. Therefore, it was found that the material of the present invention exhibits excellent tensile strength and 0.2% proof stress in a high temperature atmosphere up to 800 to 900 ° C. as compared with the conventional material.

Next, a creep test at a high temperature was performed using the material of the present invention and the conventional material shown in Table 1, and the time until the test piece broke was measured. The results will be described. The test piece used was a solution treatment of the steel ingot described above at 1050 ° C., followed by aging treatment at 750 ° C. for 4 hours, and a test piece was prepared after cooling.

The test piece was manufactured so that the parallel part had a diameter of 6.4 mm. The creep test was performed in a state where 70 MPa was applied to the test piece in a high temperature atmosphere of 900 ° C., and the time until the test piece broke was measured. Table 5 shows the time (break time) until the specimens made of the present invention and the conventional specimens creep rupture, the elongation (unit:%) of the specimen and the drawing (unit:%).

As shown in Table 5, the creep rupture time of the inventive material and the conventional material was that the conventional material broke in 160 hours, whereas the inventive material had a rupture time of 206 hours, approximately 1. Three times the creep characteristics were obtained. Similarly, the elongation of the test piece and the drawing were 28%, while the elongation of the material of the present invention was 36%. The diaphragm is 59% of the conventional material, whereas the invention material is 32%. From the above results, it was found that the material of the present invention has excellent creep characteristics in a high temperature atmosphere as compared with the conventional material.

Claims (2)

  % By weight, 0.01-0.05% C, 0.1-0.5% Si, 0.1-0.5% Mn, 0.001-0.01% B, 20.0-23. 5% Cr, 0.7 to 1.3% Nb, 2.0 to 3.2% Ti, 1.2 to 2.2% Al, 50 to 53% Ni, 0.3 to 1.0% Cu, A nickel-base alloy containing 1.5 to 3.0% Mo and 1.0 to 2.0% W, the balance being Fe and inevitable impurities.   2. The nickel-base alloy according to claim 1, wherein the sum of the Ti content and the Al content is 4.0% or more by weight.