Effect of Annealing Procedures on Alloy 625 Mechanical and Microestructural Properties

Monday, June 23, 2008 - 3:30 PM

Effect of Annealing Procedures on Alloy 625 Mechanical and Microestructural Properties

O. Covarrubias, O. Elizarraras, Frisa Aerospace SA de CV, Santa Catarina, Mexico

The effect of annealing procedures on Alloy 625 is evaluated when forged rings were exposed to different heat treatment conditions. Samples of these rings were analyzed by mechanical testing and microstructural evaluation, including optical microscopy and SEM techniques to define relationships between reported properties and microestructural characteristics.Several seamless rings were forged and rolled under controlled parameters. These rings were then segmented to evaluate initial alloy properties and microstructural characteristics. Other segments from each ring were annealed under selected parameters to determine the effect of time and temperature on alloy characteristics. After annealing heat-treatment, segments were tested to evaluate microstructural, hardness and tensile properties.

After mechanical testing, two behaviors for Alloy 625 are observed: 1) the higher the annealing temperature, the lower the mechanical properties obtained, and 2) at one selected temperature above 900ºC, as soaking time is increased, mechanical properties as hardness and tensile decrease.

From the point of view of microstructure, Alloy 625 grain size tends to coarse when annealing temperature is increased above 950ºC for more than 100 minutes, and as mentioned, mechanical characteristics are negatively affected. When this alloy is exposed to a selected annealing temperature below 950ºC, grain size do not coarse, but mechanical properties are decreased.

This behavior can be explained by development of fine precipitates into grains during heating and cooling operations performed on forging and rolling procedures. After annealing heat treatment at temperatures above 900 it was observed these precipitates present coalescense, decreasing mechanical properties without affect grain size.

Summary: This document summarizes main results generated when alloy 625 rings are exposed to different anneal conditions: effects on microstructure and mechanical properties are reported.