Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/056—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 10% but less than 20%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%

Definitions

• the present invention relates to a Ni-based super alloy.
• Ni-based super alloys NCF751, NCF80A, and the like have been widely known.
• Such a kind of Ni-based super alloys have used for exhaust valve of automobile engines and the like where high-temperature strength is required.
• Reference 1 discloses a Ni-based super alloy for exhaust valves comprising, by mass %, C: 0.01 to 0.15%, Si: 2.0% or less, Mn: 2.5% or less, Cr: 15 to 25%, Mo+1/2W: 0.5 to 5.0%, Nb+Ta: 0.3 to 3.0%, Ti: 1.5 to 3.5%, Al: 0.5 to 2.5%, B: 0.001 to 0.02%, Fe: 5% or less, and the balance of substantially Ni.
• Reference 2 discloses a Ni-based super alloy for exhaust valves comprising, by mass %, C: 0.16 to 0.54%, Si: 0.5% or less, Mn: 1.0% or less, Co: 2.0 to 8.0%, Fe: 12% or less, Cr: 17.0 to 23.5%, and one or two of Mo and W in the range of 2.0 ⁇ Mo+1/2W ⁇ 5.5, which further containing Al: 1.0 to 2.0%, Ti: 2.5 to 5.0% (provided that 5.0 ⁇ 1.8Al+Ti ⁇ 4C ⁇ 6.0), and one or two of B: 0.001 to 0.020% and Zr: 0.005 to 0.15%, and the balance of substantially Ni excluding impurities.
• exhaust gas temperature of the conventional engines for automobiles are mainly around 800° C.
• Ni-based super alloy which has excellent high-temperature strength
• alloys containing Co in an amount of 12 to 14% such as WASPALOY and UDIMET520.
• an advantage of some aspects of the invention is to provide a relatively inexpensive Ni-based super alloy excellent in high temperature mechanical properties and grindability.
• the present inventors have made eager investigation to examine the problem. As a result, it has been found that the foregoing objects can be achieved by the following Ni-based super alloys. With this finding, the present invention is accomplished.
• the present invention is mainly directed to the following items:
• a Ni-based super alloy comprising, by mass %: C: 0.01 to 0.15%; Si: 1% or less; Mn: 1% or less; P: 0.02% or less; S: 0.01% or less; Co: less than 0.10%; Cr: 16 to 22%; Mo: 4 to 10%; W: 5% or less; Al: 1.2 to 2.5%; Ti: 2.4 to 4%; B: 0.001 to 0.05%; Zr: 0.01 to 0.5%; Fe: 1% or less; and a balance of Ni and inevitable impurities.
• Ni-based super alloy according to item 1 or 2 which further comprises at least one selected from the group consisting of: Nb: 0.1 to 3%; and Ta: 0.1 to 3%.
• Ni-based super alloy according to any one of items 1 to 3, which further comprises at least one selected from the group consisting of: Ca: 0.001 to 0.03%; Mg: 0.001 to 0.03%; and REM: 0.001 to 0.1%.
• Ni-based super alloy according to any one of items 1 to 4, which further comprises: Cu: 0.01 to 2%.
• Ni-based super alloy according to any one of items 1 to 5, which further comprises: V: 0.05 to 1%.
• the Ni-based super alloy according to the invention has contents of specific ingredients in specific ranges. Therefore, the Ni-based super alloy according to the invention is excellent in mechanical properties such as tensile strength and fatigue strength even at a high temperature of 900° C.
• the balance is Ni except for inevitable impurities such as oxide, sulfide, etc.
• the content of Co is particularly limited to less than 0.10%. Therefore, it is excellent in grindability and the material costs become inexpensive as compared with WASPALOY and UDIMET520.
• the Ni-based super alloy according to the invention is used as a material for engine valves, it is easy to improve engine performance. Furthermore, the life of grindstone to be used at grinding of products is lengthened and also surface accuracy of the products can be improved.
• Ni-based super alloy according to the invention is also useful for turbine disks, blades, and the like, for example.
• the contents of the specific ingredients fall within the ranges defined in the above and the balance comprises Ni and inevitable impurities.
• the reasons for defining the kinds of the specific ingredients and contents thereof are as follows. In this connection, the unit of the following contents is mass %.
• C is an element which forms MC carbides in combination with Ti, Nb, and Ta and M 23 C 6 and M 6 C carbides in combination with Cr, Mo, and W, and contributes to prevent coarsening of grains and strengthening the grain boundary.
• the content of C is suitably 0.01% or more, preferably 0.03% or more.
• the content of C when the content of C increases, the carbides increases and, for example, it becomes difficult to form a valve shape and toughness and ductility tend to lower. Therefore, the content of C is suitably 0.15% or less, preferably 0.10% or less.
• the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• Si is an element which acts as a deoxidizer at dissolution and refining and may be incorporated according to need. Moreover, Si also contributes to improvement of oxidation resistance.
• the content of Si increases, toughness and workability tend to lower. Therefore, the content of Si is suitably 1% or less.
• the minimal amount present in the alloy is at least 1/10 of the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• Mn is an element which mainly acts as a deoxidizer and may be incorporated according to need.
• the content of Mn is suitably 1% or less.
• the minimal amount present in the alloy is at least 1/10 of the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• P is an element which lowers hot workability. Since Ni is lowered in the present alloy, the range of temperature where hot working is possible is relatively narrow and hence it is desirable to secure hot workability as far as possible. Therefore, the content of P is suitably 0.02% or less.
• the minimal amount present in the alloy is at least 1/10 of the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is 1.1 times the highest amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• S is an element which lowers hot workability. Therefore, the content of S is suitably 0.01% or less.
• the minimal amount present in the alloy is at least 1/10 of the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is 1.1 times the highest amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• Co is a main element which lowers grindability. Moreover, it is also a main element which increases the material costs. Therefore, the content of Co is suitably less than 0.10%.
• the minimal amount present in the alloy is at least 1/10 of the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is 1.1 times the highest amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• Cr is an element which is necessary to improve the high temperature oxidation resistance and the corrosion resistance.
• the content of Cr is suitably 16% or more.
• the content of Cr when the content of Cr increases, the ⁇ -phase precipitates, so that toughness and high-temperature strength lower. Therefore, the content of Cr is suitably 22% or less.
• the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• Mo is an element which enhances high-temperature strength mainly through solid solution strengthening of the matrix.
• the content of Mo is suitably 4% or more to enhance strength at 900° C.
• the content of Mo is suitably 10% or less, preferably 7% or less.
• the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is 1.1 times the highest amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• W is an element which enhances high-temperature strength mainly through solid solution strengthening of the matrix and may be incorporated according to need.
• the content of W is suitably 5% or less, preferably 3% or less.
• the minimal amount present in the alloy is at least 1/10 of the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• the above contents of Mo and W is preferably selected so that Mo+1/2W falls within the range of 4 to 10%, more preferably within the range of 4 to 7%. This is because the resulting alloy is excellent in high-temperature strength and hot workability.
• the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is 1.1 times the highest amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• Al is an important element for forming the ⁇ ′-phase which is effective for enhancing high-temperature strength in combination with Ni.
• the content of Al is suitably 1.2% or more.
• the content of Al is suitably 2.5% or less, preferably 2.0% or less.
• the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• Ti is an element for forming the ⁇ ′-phase in combination with Ni.
• the content of Ti is suitably 2.4% or more.
• the content of Ti increases, the ⁇ -phase (Ni 3 Ti) is apt to precipitate and thus there is observed a tendency that high-temperature strength and toughness deteriorate and hot workability lowers. Therefore, the content of Ti is suitably 4% or less, preferably 3.5% or less.
• the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• B is an element which contributes to the improvement of hot workability. Moreover, it is an element which segregates at grain boundary and is effective for strengthening the grain boundary and improving strength properties. In order to obtain the effects, the content of B is suitably 0.001% or more.
• the content of B is suitably 0.05% or less.
• the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is 1.1 times the highest amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• Zr is an element which contributes to the improvement of hot workability. Moreover, it is an element which segregates at grain boundary and is effective for strengthening the grain boundary itself and suppressing the formation of denuded zone of ⁇ ′ in the vicinity of grain boundary to enhance strength at high temperature. In order to obtain the effects, the content of Zr is suitably 0.01% or more.
• the content of Zr is suitably 0.5% or less.
• the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• Fe is an element which lowers high-temperature strength and thus is desirably reduced as far as possible. Therefore, the content of Fe is suitably 1% or less.
• the minimal amount present in the alloy is at least 1/10 of the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• the present alloy may further contain one or more elements selected from the following elements in addition to the aforementioned constitutional elements.
• the reasons for specifying the contents of these elements are as follows.
• Nb is an element which strengthens the ⁇ ′-phase in combination with Ni together with Al.
• the content of Nb is suitably 0.1% or more.
• the content of Nb is suitably 3% or less, preferably 2% or less.
• Ta is an element which strengthens the ⁇ ′-phase in combination with Ni together with Al.
• the content of Ta is suitably 0.1% or more.
• the content of Ta is suitably 3% or less, preferably 2% or less.
• the minimal amount present in the alloy is at least 1/10 of the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is 1.1 times the highest amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• Ca, Mg, and REM are elements effective for improving hot workability.
• the contents of Ca, Mg, and REM are suitably 0.001% or more.
• the content of Ca is suitably 0.03%,or less.
• the content of Mg is suitably 0.03% or less.
• the content of REM is suitably 0.1% or less.
• the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is 1.1 times the highest amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• Cu is an effective element for improving oxidation resistance.
• the content of Cu is suitably 0.01% or more.
• the content of Cu is suitably 2% or less.
• the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1.
• the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• V is an element which contributes to solid solution strengthening of the matrix. Moreover, it has effects of forming MC carbides and stabilizing the carbides. In order to obtain the effects, the content of V is suitably 0.05% or more.
• the content of V is suitably 1% or less.
• the minimal amount present in the alloy is at least 1/10 of the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the minimal amount present in the alloy is the smallest non-zero amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is 1.1 times the highest amount used in the examples of the developed alloys as summarized in Table 1. According to a further embodiment, the maximum amount present in the alloy is the maximum amount used in the examples of the developed alloys as summarized in Table 1.
• the resulting alloy ingot may be subjected to solution treatment, aging treatment, or the like according to need.
• the temperature for the above aging treatment there can be specifically exemplified, for example, a temperature of 500 to 1000° C., preferably 600 to 900° C.
• the applications of the present alloy as described in the above are not particularly limited.
• applications of the present alloy there may be specifically exemplified engine valves, turbine disks, blades, heat-resistant springs, engine shafts, valves for ships, volts, and the like.
• each round bar was water-cooled to perform solution treatment and, after held at 750° C. for 4 hours, it was air-cooled to perform aging treatment, thereby each test material being formed.
• a grinding test was carried out on each test material after aging.
• the piece was tested by a method of 5-paths grinding with a grindstone having an outer diameter of 600 mm at a grinding speed of 700 m/minute, a feeding speed of 30 mm/second, and a radial depth of 0.2 mm per path.
• the abraded amount of the grindstone with each test piece was represented by a ratio to the abraded amount with the test piece according to Comparative Example 1, the amount being assigned as 100.
• the ratio was regarded as an index indicating the grindability.
• Tables 1 and 2 shows chemical compositions of the Ni-based super alloys according to Examples and Comparative Examples and Table 3 shows test results of the Ni-based super alloys according to Examples and Comparative Examples.
• Example 3 Comparative 0.04 0.06 0.07 0.004 0.005 0.04 15.48 0.08 — 0.08 1.18 2.32 — — 7.26 Bal. Nb: 1.03
• Example 4 Comparative 0.05 0.08 0.05 0.002 0.003 1.02 19.43 0.06 — 0.06 1.43 2.26 — — 1.53 Bal. —
• Example 5 Comparative 0.04 0.06 0.07 0.004 0.005 0.04 15.48 0.08 — 0.08 1.18 2.32 — — 7.26 Bal. Nb: 1.03
• Example 4 Comparative 0.05 0.08 0.05 0.002 0.003 1.02 19.43 0.06 — 0.06 1.43 2.26 — — 1.53 Bal. —
• Example 5 Comparative 0.04 0.06 0.07 0.004 0.005 0.04 15.48 0.08 — 0.08 1.18 2.32 — — 7.26 Bal. Nb: 1.03
• Example 4 Comparative 0.05 0.08 0.05 0.002 0.003 1.02 19.43 0.06 — 0.06 1.43 2.26 — — 1.5
• the Ni-based super alloys according to Comparative Examples 1 and 2 particularly have an extremely high Co content. Therefore, it is found that they are poor in grindability. Moreover, since they contain a large amount of expensive Co, the material costs thereof are relatively high.
• the Ni-based super alloys according to Comparative Examples 3 to 5 has a reduced Co content but the contents of ⁇ ′-phase-forming elements such as Al and Ti are low. Furthermore, the Ni-based super alloys according to Comparative Examples 4 and 5 has an extremely low contents of solid solution strengthening elements such as Mo and W and the content of Fe decreasing high-temperature strength is extremely high. For these reasons, it is found that the Ni-based super alloys according to Comparative Examples 3 to 5 are poor in mechanical properties at high temperature.
• the contents of the specific ingredients fall within specific ranges. Therefore, the Ni-based super alloys according to Examples 1 to 15 are excellent in mechanical properties such as tensile strength and fatigue strength even at such a high temperature of 900° C.
• the content of Co is particularly limited to less than 0.10%. Therefore, they are not only excellent in grindability but also inexpensive in material costs.
• Ni-based super alloys are used as materials for engine valves, it may be easy to improve engine performance. Furthermore, the life of grindstone to be used at grinding of products is lengthened and also surface processing accuracy of the products can be improved.

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