Structural changes during hot deformation after multiple compression tests in high alloy steel

Sammanfattning

The focus of this thesis is to acquire a deeper knowledge about how high alloy stainless steel will behave during one and more compressions with varying strains, as well as multiple temperatures. This study will examine if abnormal grain growth can occur during the forging process when producing bars, as well as investigating how so-called necklace structures can form depending on different strains and temperatures. A brief investigation will also be performed on how the precipitation of precipitates will change due to recrystallization and how temperature will impact these results. The primary material used in this thesis is Sanicro 28, however the initial test was performed using Sanicro 41. A Gleeble 3500 system was used to compress the samples, where single compression experiments were performed using strains from 0.02-0.50. Multiple compressions were performed on a single sample to investigate how the material will behave due to accumulated strain, as well as how the structure will change due to multiple recrystallizations. The results show no evidence of abnormal grain growth due to different strains. In order to produce a necklace structure a significant amount of accumulated strain is needed. However, if the strain or temperature is too high to form a necklace structure the matrix will just recrystallize without forming necklaces. The results also indicates that precipitation can occur in large quantities instantly during dynamic recrystallization.