August 2024 Volume 6

MATERIALS

After the NDT techniques, there is a review of review of the basic techniques and equipment used in failure analyses. (Note, these are explained more in-depth in the “Failure Analysis of Metal Prob lems”). The technique discussion focuses on analysis of fracture surface and subsequent metallographic anal ysis. Fracture Surface Analysis can also be considered an NDT tech nique and includes:

2. The sections through the origin are used to determine if the fracture initiated from a defect such as porosity or inclusions. 3. Secondary cracking and grain boundary voiding in the bulk material adjacent to the fracture can provide additional clues to the fracture mode. 4. Local regions of high temperature exposure can be observed. Temperature estimates can be made provided the time and temperature exposure is sufficient to produce measurable changes in the microstructure. Once the viewer is armed with the tools and techniques, the course then dives into the examples which apply the tools and techniques. The examples include: 1. Closed Die: a crack in a stainless steel flange 2. Open-Die: a forging burst in a large alloy steel cylinder 3. Rolled-Ring: a forging lap in a carbon steel ring. Along with the examples applying the techniques in conducting the failure analysis, they also present the typical outputs of a failure analysis. This includes: • Failure mode – initiation and propagation modes – linkage to stress states, ductile or brittle fracture modes, failure sequence. • Initiation location – possible geometric stress concentrations, manufacturing defects, material defects. • Environmental distress modes – oxidation and/or corrosion attack. • Semi-quantitative analysis of material with comparison to base line – is the material composition? • Microstructure evaluation – was the material processed correctly, is there evidence of over-temperature exposure? • Temperature estimates may be performed depending on mate rial and time/temperature exposure. Consult your materials engineer. Conclusion We’ll say it again. The Forging Industry Association (FIA) recognizes that providing a wide range of high-quality training courses is one of its top services to its members. And the FIA staff regularly reviews its training offerings and find ways to improve and keep them fresh. This is evidenced by the 70+ online training courses in their Forging University library, the addition of the general metals failure analysis course to that library, and this latest addition of forging specific supplement with case studies.

1. Examination of the fracture surface is performed using binoc ular scope with up to 100x magnification and/or with the scan ning electron microscope (SEM) up to 10,000x magnification. 2. Surface features can help identify cause as well as initiation and propagation modes and direction. 3. Semi-quantitative analysis of the surfaces can be performed to detect the presence of contaminants. 4. Cracks in components can be broken open to reveal the frac ture surfaces. 5. Preserving information on fracture surfaces is important. Therefore: a. Do not try to put fractured parts back together! b. Keep fracture surfaces in the as-found condition as much as possible – do not touch the surfaces!

Metallographic Analysis is a destructive inspection technique, and typically done to look further at the material in suspected failure initiation locations(s) and/or an area that didn’t fail for comparison. Details that metallographic analysis are looking for include: 1. Metallographic sections of the component are used to determine if the initial microstructure is proper, that is, if the material was processed properly.

FIA MAGAZINE | AUGUST 2024 35