Ni-base heat resisting super alloys have been used for conponents of welded stuructures. However, most of Ni-base alloys are unweldable. And there are many reports on the weld cracking of such alloys.
It is said that René 62 is weldable, in addition, it possesses favourable elevated temperature properties. Fundamental properties (including weldability) were investigated on Rene 62 and the following results were obtained.
(1) Precipitating phases in René 62 are γ' phase {Ni
3 (Al, Ti, Nb)} and Laves phase {(Fe, Cr)
2 (Mo, Nb, Ti)}, and age hardening is caused by precipitation and growth of γ' phase.
(2) Short time tensile strength of aged Rene 62 is approx. 100 kg/mm
2 at room temperature and approx. 80 kg/mm
2 at 750°C.
(3) As the result of bead-on-plate test on solution-treated René 62, the H.A.Z., where maximum heated temperature is in the region of 850-900°C, is hardened by fine precipitation of γ' phase. However, hardening is not so large as that in high strength steels.
(4) Welding of 7 mm thick Rene was made by Tig method. No weld cracking was observed, and the joint efficiency was very good.
(5) In Ni-Al-Nb alloys shown in Table 2, Nb promotes the precipitation of γ' phase.
(6) When AI content of René 62 is increased to 4.15%, weld cracking is formed in bead-on-plate test on as-cast materials. Decrease in ductility of matrix and decrease in γ' phase dissolved range at elevated temperature by increasing Al content are considered to increase the weld crack sensibility.
(7) Therefore, in Rene 62, a low level of Al content is considered to be one of the important factors for good weldability.
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