Creep Rupture Strength of Incoloy (32Ni-20Cr Steel)

Abstract

It is a well known fact that austenitic stainless steels such as 18 Cr-8 Ni type or high Ni base alloys Inconel (70 Ni-15 Cr alloy). They are quite useful materials as the chemical plant fabricated materials used in a high temperature or corrosion atmosphere service.Incoloy (32 Ni-15 Cr-45 Fe) is also a useful material as intermediate between the two above mentioned materials. But its high temperature properties, especially creep rupture data are not accurately defined as yet.We have made high temperature creep rupture tests on domestic Incoloy mother plates and weld joints, and attempted to clarify their high temperature characteristics which has so far been left ambiguous.The results can be summarized as follows.1) The high temperature creep rupture strength on the mother plates increases as the grain size grows to the grain number 3-4 by the solution heat treatment.2) The creep rupture strength on the weld joints {mother plate: coarse-grained material, welding rod: Inco weld-A rod (70 Ni-15 Cr)} is more or less superior to that of the coarse grained mother plate.3) We dwelt upon the relation which exists among the optional temperature, stress and creep rate. The results are formal that a fine-grained material behavior is superior to a coarse-grained one below 720°C and vice versa above 720°C, and generally speaking any fine-grained material tends to decrease its strength in comparison to any coarse-grained materials as the temperature increases.4) The high temperature creep rupture strength level of Incoloy is almost identical with those of AISI 304, 310, 330 type or Inconel, which are generally considered to be heat resistant alloys.