WO2013136506A1 - Co-cr-mo-based alloy, and method for producing co-cr-mo-based alloy - Google Patents

Abstract

A Co-Cr-Mo-based alloy which is produced by heating a Co-Cr-Mo-based alloy containing 22 to 33 mass% inclusive of Cr and 3 to 7 mass% inclusive of Mo at a temperature of 1000˚C or higher, subjecting the heated alloy to a hot working at a height ratio of 50% or more and then gradually cooling the resultant product so that massive transformation of the product can occur, and which has a crystal structure that is an ε-phase having an HCP structure, a 0.2% proof stress of 600 MPa or more at room temperature and a 0.2% proof stress of 450 MPa or more at 600˚C, can exhibit improved strength regardless of whether the alloy is subjected to precipitation strengthening or not, and can have excellent strength properties in a medium temperature range; and a method for producing the Co-Cr-Mo-based alloy.

Description

Co-Cr-Mo alloy and method for producing Co-Cr-Mo alloy

The present invention relates to a Co—Cr—Mo alloy and a method for producing a Co—Cr—Mo alloy.

Co-based alloys such as Co—Cr—Mo are excellent in corrosion resistance, mechanical properties, and biocompatibility, and have a high record of use as biomaterials such as artificial knees and hip joints. Recently, application and practical application to general industries such as molds, injection molding cylinders for resin products containing glass fibers, and turbine disk materials and friction stir welding (FSW) tool materials that require heat resistance. Is also expected. For example, in the case of an FSW for an Al alloy, there are concerns about problems such as reactivity, but since a Co-based alloy exhibits excellent corrosion resistance against Al (see, for example, Non-Patent Document 1), an FSW for an Al alloy is used. It is considered that a Co-based alloy is suitable.

Co-based alloys such as Co—Cr—Mo are known as main constituent phases of γ phase of FCC structure, ε phase of HCP structure, and σ phase which is an intermetallic compound, but from the viewpoint of workability. In most cases, the main constituent phase is a γ phase in practical use (see, for example, Non-Patent Document 2). Further, precipitation strengthening by fine dispersion of carbide is generally used for increasing the strength of the γ phase, and recently precipitation strengthening by a γ ′ phase (intermetallic compound) has been reported (for example, Patent Documents 1 and 2). Non-Patent Documents 3 to 5).

JP 2004-35974 A JP 2011-62731 A

However, precipitation strengthening using a carbide or intermetallic compound phase in the γ phase has a problem that ductility is reduced and embrittlement is caused. In consideration of application to members that require heat resistance in the so-called medium temperature range of 500 ° C to 800 ° C, such as turbine disks, heat-resistant springs, aluminum die-casting sleeves, and FSW tools, the γ phase is the main component. The Co-based alloy used as a constituent phase also has a problem that high strength characteristics cannot be maintained in an intermediate temperature range.

The present invention has been made by paying attention to such a problem, and can increase the strength regardless of precipitation strengthening, and can provide a Co—Cr—Mo alloy and a Co— An object of the present invention is to provide a method for producing a Cr—Mo alloy.

In order to achieve the above object, the Co—Cr—Mo alloy according to the present invention contains Cr in an amount of 22% by mass to 33% by mass, Mo in an amount of 3% by mass to 7% by mass, and has a main crystal structure. It is characterized by being the ε phase of the HCP structure.

In the Co—Cr—Mo alloy according to the present invention, the stacking fault energy of the HCP structure is low in the middle temperature range of 500 ° C. to 800 ° C., so that stacking faults are easily formed on the bottom surface of the HCP structure. Slip and cross-slip activities can be suppressed. For this reason, the ε phase of the HCP structure can be increased in strength, and high strength characteristics can be maintained particularly in the middle temperature range. As described above, the Co—Cr—Mo alloy according to the present invention can be strengthened regardless of precipitation strengthening by utilizing the temperature dependence of stacking fault energy, and the strength characteristics in the middle temperature range can be achieved. Are better. In a specific example, the Co—Cr—Mo alloy according to the present invention can provide a 0.2% yield strength at room temperature of 600 MPa or more and a 0.2% yield strength at 600 ° C. of 450 MPa or more.

The Co—Cr—Mo alloy according to the present invention may contain 5% by mass or less of Si. In this case, by adding Si, the temperature at which the stacking fault energy of the ε phase of the HCP structure becomes zero can be shifted to the high temperature side, so that the strength characteristics at a higher temperature can be improved. Moreover, by adding Si, formation of the σ phase of the intermetallic compound can be suppressed to a lower temperature side, and the ε phase of the HCP structure can be stabilized to a higher temperature using the main phase. Si is preferably contained in an amount of 1% by mass to 5% by mass.

The method for producing a Co—Cr—Mo alloy according to the present invention comprises a Co—Cr—Mo alloy containing Cr in an amount of 22% by mass to 33% by mass and Mo in an amount of 3% by mass to 7% by mass at 1000 ° C. After heating as described above and performing hot working with a height ratio of 50% or more, it is gradually cooled so as to undergo massive transformation. According to the method for producing a Co—Cr—Mo alloy according to the present invention, the Co—Cr—Mo alloy according to the present invention can be produced.

According to the present invention, there are provided a Co—Cr—Mo alloy and a method for producing a Co—Cr—Mo alloy that can achieve high strength regardless of precipitation strengthening and have excellent strength characteristics in a middle temperature range. be able to.

(A) EBSD image, (b) XRD profile of Co-27 (mass%) Cr-5 (mass%) Mo alloy of an example of the present invention. Temperature of 0.2% proof stress (0.2% proof stress) of Co-27Cr-5Mo alloy (CCMε), Co-33Cr-5Mo-1.3Nγ alloy, and Co forged alloy “Haynes 188” of the embodiment of the present invention It is a graph which shows dependence. It is a graph which shows the temperature dependence of the stacking fault energy (Stacking fault energy) when changing Si addition amount (mass%) of the Co-27Cr-5Mo alloy of the Example of this invention. It is a graph which shows the influence of the addition element which acts on HCP-> FCC phase transformation temperature (Ms) of Co (citation from Sims CT, Stoloff NS, Hagel WC, “Superalloy II”). It is a state diagram when changing Si addition amount (mass%) of the Co-27Cr-5Mo alloy of the Example of this invention.

In order to obtain a ε single-phase structure after melting a Co-27 (mass%) Cr-5 (mass%) Mo alloy by high frequency induction melting and subjecting it to homogenization heat treatment at 1250 ° C. for 6 hours, 1100 A constant temperature forging with a compression rate of 70% or more was performed at 0 ° C., and the furnace was cooled to room temperature. FIG. 1 shows the microstructure (EBSD image) and XRD profile of the Co-27Cr-5Mo alloy thus produced. As shown in FIG. 1, it was confirmed that the structure of the ε phase having an average crystal grain size of 42 μm as the main phase can be obtained by promoting the ε transformation (massive transformation) while suppressing the generation of the σ phase.

FIG. 2 shows the temperature dependence of 0.2% yield strength (“CCMε” in FIG. 2) obtained by a tensile test on the manufactured Co-27Cr-5Mo alloy. FIG. 2 shows the same Co—Cr—Mo based alloy Co-33Cr-5Mo-1.3Nγ alloy having a γ phase as a main phase, and a Co forged alloy already put into practical use as a heat-resistant Co-based alloy. The results of the strength characteristics of “Haynes 188” are also shown. As shown in FIG. 2, it was confirmed that even in the same Co—Cr—Mo-based alloy, the ε phase showed significantly higher strength characteristics than the γ phase. It was also confirmed that CCMε in the ε phase exhibits higher strength characteristics than a heat-resistant Co-based alloy (Haynes 188) that has been put into practical use.

Further, as shown in FIG. 2, it was confirmed that CCMε in the ε phase kept high strength up to 700 ° C. This is considered to be due to the following reason. That is, the deformation mechanism of the Co—Cr—Mo alloy having the ε phase as the main phase is dominated by the activities of the bottom surface <a> slip and the column surface <a> slip at room temperature. On the other hand, as the temperature increases, stacking faults are generated on the bottom surface of the HCP, and the movement of decomposition dislocations is active on the bottom surface. Therefore, cross-slip to the column surface and column surface <a> Cross slip to the bottom of the dislocation is suppressed. For this reason, high strength is maintained in a temperature range of 700 ° C. or lower. This deformation mechanism can be explained by the relationship with the temperature dependence of the stacking fault energy of the HCP phase and FCC phase of the Co—Cr—Mo alloy.

FIG. 3 shows the temperature dependence of stacking fault energy when the Si addition amount (mass%) is changed in the Co-27 mass% Cr-5 mass% Mo alloy. As shown in FIG. 3, in the Co-27Cr-5Mo-0Si alloy to which Si is not added, that is, CCMε shown in FIG. 2, the stacking fault energy of HCP decreases with increasing temperature, and is almost 0 at around 820 ° C. It was confirmed that the stacking fault energy of FCC increases at higher temperatures. This means that as the temperature increases to around 820 ° C., the HCP phase is structurally destabilized and above about 820 ° C., the γ phase is stabilized as an equilibrium phase.

As shown in FIG. 2 and FIG. 3, in CCMε, high strength is maintained up to 700 ° C., so that the temperature at which stacking fault energy becomes 0 (820 ° C.) to 120 ° C. or lower (700 ° C.). It can be seen that high strength can be maintained. From this, it is possible to further improve the high-temperature strength characteristics by shifting the temperature at which the stacking fault energy of the HCP phase to 0 is shifted to a higher temperature side and alloying so as to stabilize the HCP phase to a high temperature. it is conceivable that. In the example shown in FIG. 2, it is considered that the temperature (700 ° C. to 750 ° C.) at which the strength of CCMε greatly decreases can be shifted to a higher temperature side.

FIG. 4 is a graph showing the influence of additive elements on the HCP → FCC phase transformation temperature (Ms) of Co. In FIG. 4, the vertical axis indicates the solubility limit of the additive element (Solubility limit in FCC Co), and the horizontal axis indicates the temperature at which Ms changes per 1 at% of the additive element (Change in HCP to FCC transformation by 1.0% addition). ). FIG. 4 shows that the higher the temperature from 0 to minus, the more effective the FCC crystal is stabilized. Conversely, the higher the temperature from 0 to plus, the more stable the HCP crystal. As shown in FIG. 4, there are Cr, Mo, Si, and W as elements that stabilize HCP. Further, the formation of the σ phase of the intermetallic compound is suppressed as much as possible, and the HCP phase is stabilized to a high temperature as the main phase. Shows that Si is promising.

FIG. 5 shows a phase diagram of the Co-27Cr-5Mo alloy when the Si addition amount (mass%) is changed. As shown in FIG. 5, it can be seen that the addition of Si can suppress the formation of the σ phase to the low temperature side, and can further strongly stabilize the HCP. Moreover, as shown in FIG. 3, the temperature at which the stacking fault energy of the HCP phase becomes 0 is shifted to the high temperature side by adding Si, and can be shifted to the high temperature side by about 80 ° C. by adding 5 wt% Si. Recognize. Furthermore, since Si can suppress the formation of the σ phase, which is a brittle metal compound phase, the HCP phase can be strongly stabilized. Thus, the high temperature strength can be increased by adding Si to the Co—Cr—Mo alloy at 5 wt% or less.

The Co—Cr—Mo alloy according to the present invention is excellent in heat resistance and strength characteristics in a medium temperature range of 500 ° C. to 800 ° C., and therefore has a mold, an injection molding cylinder for resin products including glass fibers, and has heat resistance characteristics. It can be used as a material for required turbine disks, heat-resistant springs, aluminum die-casting sleeves, and friction stir welding (FSW) tools.

Claims (4)

1. A Co—Cr—Mo alloy containing Cr in an amount of 22% by mass to 33% by mass, Mo in an amount of 3% by mass to 7% by mass, and the main crystal structure being an ε phase of an HCP structure.
2. The Co-Cr-Mo alloy according to claim 1, wherein the 0.2% yield strength at room temperature is 600 MPa or more, and the 0.2% yield strength at 600 ° C is 450 MPa or more.
3. 3. The Co—Cr—Mo based alloy according to claim 1 or 2, characterized by containing 5% by mass or less of Si.
4. A Co—Cr—Mo alloy containing 22 mass% to 33 mass% of Cr and 3 mass% to 7 mass% of Mo is heated to 1000 ° C. or more, and hot working with a height ratio of 50% or more. And a slow cooling so as to cause a massive transformation, a method for producing a Co—Cr—Mo alloy.
   
   

Images