Masters Theses

Date of Award

12-2005

Degree Type

Thesis

Degree Name

Master of Science

Major

Materials Science and Engineering

Major Professor

Carl D. Lundin

Committee Members

David C. Joy, Hahn Choo

Abstract

The objective of the program is to determine the suitability of ASTM A923 “Standard Test methods for Detecting Detrimental Intermetallic Phase in Wrought Duplex Austenitic-Ferritic Stainless Steels” for 25 Cr Cast Super Duplex Stainless Steels (ASTM A890-5A).

Different tests were carried out on the materials procured from various steel foundries as stated in the ASTM A923. The foundries were designated as Foundry A, B, C and D. All the materials were foundry solution annealed. Materials from Foundry D were solution heat treated at The University of Tennessee also and then they were subjected to heat treatment schedule which was derived from the testing of wrought DSS to establish the A923 specification. This was possible because the material from the same heat was sufficient for conducting the full scope of heat treatment. This was done prior to carrying out various other tests.

Charpy samples were machined. The Ferrite content was measured in all the Charpy samples using Feritscope® and ASTM E562 Manual Point Count Method. After the ferrite content was measured the samples were sent to AMC-Vulcan, Inc. in Alabama to conduct the Charpy impact test based on ASTM A923 Test Method B. This was followed by etch testing and corrosion analysis based on ASTM A923 Test Methods A and C respectively at University of Tennessee. Hardness testing using Rockwell B and C was also carried out on these samples. A correlation was derived between all the three test methods and the best method for evaluating the presence of intermetallic in the material was determined. The ferrite content was correlated with the toughness values.

Microstructural analysis was carried out on the etch test samples using Scanning Electron Microscopy in order to determine if intermetallic phases were present. The fracture surfaces from Charpy test specimens were also observed under SEM in order to determine the presence of any cracks and whether it was a brittle or a ductile fracture. A correlation was carried out between the ferrite content, hardness values and the type of fracture. SEM was also carried out on the corrosion samples in order to see the difference on the surface after corrosion analysis has been carried out. Energy Dispersive Spectroscopy was carried out on the material acquired from Foundry D in order to determine the variation in the amount of the chemical composition of various elements when the material is subjected to different heat treatment schedules.

X-Ray analysis was also carried out in order to verify whether it is possible to identify the different phases present in the material. Volume percentage of ferrite was also calculated from X-Ray diffraction and compared with the Feritscope® and ASTM E562 Manual Point Count data in order to determine whether X-Ray Diffraction is a suitable method for carrying out qualitative analysis of different phases present.

From the various tests that were conducted, it was concluded that since ASTM A923 Methods adequately identifies the presence of intermetallic phases in A890 – 5A grade Cast Super Duplex Stainless Steel A890 – 5A can be directly included in ASTM A923. Correlation was determined between all the ASTM A923 Test Methods A, B and C and Test Method B were identified as the best method for detecting the presence of detrimental intermetallic phases. The micrographs from the A890-4A grade (now in ASTM A923) were identified as applicable for the A890-5A grade to compare and detect the presence of intermetallic phases. Using these micrographs one can verify whether an A890-5A sample has an unaffected, affected or a possibly affected structure. It was also observed that when compared to the A890-4A grade A890-5A grade is more sensitive to heat treatment. From the ferrite and hardness measurement a correlation was developed between toughness, volume percentage ferrite and hardness of the material. From SEM and EDS the type of intermetallic phase present and its chemical composition was determined. The best method for calculating volume percentage ferrite was determined between the Feritscope®, ASTM E562 Manual Point Count and X-Ray Diffraction. The test data will be submitted to ASTM to support the adoption of the ASTM A890-5A Cast Super Duplex in the A923 specification.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS