An experimental study was made of the changes in the stress-rupture life, ductility, hardness, and microstructure of S-816 and Inconel 550 specimens that had been exposed to varying amounts and conditions of thermal fatigue.

An investigation of overheating HS-31 alloy to temperatures of 1,650 degrees, 1,800 degrees, 1,900 degrees, and 2,000 degrees F during the course of rupture tests 1,500 degrees F was carried out. The overheating was applied periodically for 2 minutes in most of the tests. The intent was to develop basic information on the effect of overheats on creep- rapture properties in order to assist in the evaluation of damage from overheats during gas- turbine operation.

The rupture-test characteristics at 1350 degrees F of two wrought alloys in the solution-treated and aged condition, NR-82 (6059 modified-low carbon) and NR-84 (N-155 modified-low carbon), and three precision-cast alloys in aged condition, NR-71 (X-40), NR-87 (Co-Cr-Ni base-9Mo) and NR-90 (Co-Cr-Ni base-5Mo, 5W) are reported. The properties are shown to compare favorably with those of the strongeest similar alloys previously investigated. A correlation of NACA and OSRD data is presented, showing the variation of ruture strengths with temperature for the alloys between 1350 degrees and 2000 degrees F.

Physical properties at room temperature and rupture test characteristics at 1200 degrees F were used as criterions to evaluate the effects of systematic variations of solution treatments, aging treatments, and hot-cold-work on the properties of bar stock from one heat of low-carbon N-155 alloy. On the basis of the yield strength for 0.02-percent offset at room temperature and rupture properties at 1200 degrees F, standard-type treatments that are best for the alloy could be set up. Trends found for the effects of various treatments should apply to other alloys of the same type.

Use of careful control over processing conditions in this investigation has shown that it is possible to correlate stress-rupture properties of forged alloys of the low-carbon N-155 alloy type at 1200 degrees F with systematic variations in chemical composition and that a wide range in properties can be obtained by such variations. However, no alloy was obtained which had properties which were outstanding compared with those of the standard basic analysis of low-carbon N-155 alloy.