0001]The present invention relates to an austenitic heat resistant alloy, more particularly NiCrFe alloy. BACKGROUND [0002]Conventionally, equipment such thermal power boilers, chemical plants, operating in a high temperature environment (e.g., 400 ~ 800 ° C.), further contact with the process fluid containing the sulfides and / or chlorides. Therefore, the materials used in these facilities, it is required creep strength and corrosion resistance at high temperatures. [0003] 　Material used in such equipment, for example, SUS304H, SUS316H, SUS321H, and 18-8 stainless steel such as SUS347H, there is NiCrFe alloys typified by Alloy800H defined as NCF800H in JIS standard. [0004] 　NiCrFe alloy is excellent in comparison to corrosion resistance and high temperature strength 18-8 stainless steel. NiCrFe alloy addition is excellent in economy as compared to the Ni-base alloy represented by Alloy617. Therefore, NiCrFe alloys are widely used in the site of harsh environments. [0005] 　Such NiCrFe alloys used in harsh environments, JP 2013-227644 (Patent Document 1), JP-A-6-264169 (Patent Document 2), JP 2002-256398 (Patent Document 3), and it has been proposed in JP-a 8-13104 (Patent Document 4). [0006] 　Patent Document 1 austenitic heat resistant alloys disclosed in, in mass%, C: less than 0.02%, Si: 2% or less, Mn: 2% or less, Cr: 20% or more and less than 28%, Ni: 35% 50% or less beyond, W: 2.0 ~ 7.0%, Mo: less than 2.5% (including 0%), Nb: less than 2.5% (including 0%), Ti: 3. below 0% (including 0%), Al: 0.3% or less, P: 0.04% or less, S: 0.01% or less and N: 0.05% or less, the balance being Fe and impurities consists, furthermore, f1 = (1/2) W + Mo is 1.0 ~ 5.0, f2 = (1/2) W + Mo + Nb + 2Ti 2.0 to 8.0 and f3 = Nb + 2Ti is 0.5-5.0 it is. [0007] 　It disclosed in Patent Document 2 heat and corrosion resistant alloy, in weight%, nickel 55 to 65%, chromium 19 to 25%, aluminum 1 to 4.5%, yttrium from 0.045 to 0.3%, titanium 0.15 to 1%, carbon from 0.005 to 0.5%, silicon 0.1 to 1.5%, 1% manganese less, magnesium, at least one element selected from the group consisting of calcium and cerium total 0.005%, magnesium and total less than 0.5% calcium, cerium less than 1%, boron from 0.0001 to 0.1%, 0.5% zirconium less, nitrogen 0.0001 to 0.2 percent, cobalt 10% or less and the balance being iron and incidental impurities. [0008] 　Disclosed austenitic alloy in Patent Document 3, by mass%, C: 0.01 ~ 0.1%, Mn: 0.05 ~ 2%, Cr: 19 ~ 26%, Ni: 10-35% contained, the content of Si satisfies the equation 0.01