Joint part
Provided is joint part capable of suppressing diffusion of carbon and nitrogen contained in the steel member to the TiAl-based alloy member and suppressing formation of voids, titanium carbide or a nitride due to diffusion of carbon and nitrogen contained in the steel member, and thereby suppressing decrease in the brazing strength. A joint part comprises a steel member containing alloy elements including C and Cr, a TiAl-based alloy member, and a Ni-based brazing filler metal via which the steel member and the TiAl-based alloy member are joined to each other, wherein the steel member has a carbide and a nitride each forming a bond with at least one of the alloy elements at least on a side of a boundary with the Ni-based brazing filler metal, and diffusion of C and N to the Ni-based brazing filler metal adjacent to the TiAl-based alloy member is suppressed by the carbide and the nitride. The joint part may be a turbine body 1 comprising a turbine wheel 2 and a shaft 3 , and a structural steel material of the shaft 3 is structural steel material containing 0.30 to 0.45 wt % of C and 0.85 to 1.25 wt % of Cr, or a martensitic stainless steel material containing at most 15 wt % of C and 11.5 to 13 wt % of Cr.
1. A joint part comprising:
a steel member turbine shaft containing alloy elements including C and Cr,
a turbine wheel comprising a TiAl-based alloy member, and
a Ni-based brazing filler metal via which the turbine shaft and the turbine wheel are joined to each other,
wherein the turbine shaft has a carbide and a nitride each forming a bond with at least one of the alloy elements at least on a side of a boundary with the Ni-based brazing filler metal, and diffusion of C and N to the Ni-based brazing filler metal adjacent to the turbine wheel is suppressed by the carbide and the nitride under a high temperature of from 900° C. to 1,000° C.,
wherein the steel member turbine shaft comprises a structural steel material containing 0.30 to 0.45 wt % of C and greater than 1.0 up to 1.25 wt % of Cr, and
wherein a spec value at which a minimum strength for resisting a centrifugal stress is equal to or more than 1.0 and equal to or less than 1.15, the spec value being obtained b dividing 0.2% proof stress of the turbine shaft after thermal treatment by a strength of the turbine wheel.
2. The joint part according to claim 1 ,
wherein the turbine shaft has a carbide and a nitride having a carbon and a nitrogen, respectively, bonded to at least one of the alloy elements including Cr at least on a side of a boundary with the Ni-based brazing filler metal in the structural steel material.
3. The joint part according to claim 2 , wherein the nitrogen is mixed in during production of the steel member.
4. The joint part of claim 1 , wherein the steel member turbine shaft comprises a structural steel material containing 0.30 to 0.35 wt % of C.
5. The joint part of claim 1 , wherein the steel member turbine shaft comprises a structural steel material containing 0.44 to 0.45 wt % of C.