Metallographic Techniques in Failure Analysis

METALLOGRAPHIC EXAMINATION is one of the most important procedures used by metallurgists in failure analysis. Development of powerful electron metallographic instruments, such as the scanning electron microscope, has not diminished the importance of light microscopy. Basically, the light microscope is used to
assess the nature of the microstructure and its influence on the failure mechanism. The purpose in using the light microscope may be twofold. One purpose may be to determine the relationship between the microstructure and the crack path (in failures involving fracture) and/or the nature of corrosion or wear damage. The second purpose is to determine whether processing or service conditions have produced undesirable microstructural conditions that have contributed to the failure, such as abnormalities due to material quality, fabrication, heat treatment, and service conditions. Examples are given in this
article to demonstrate such analytical work.

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Metallographic Examination of Heavily Eroded Structural Steel from World Trade Center Buildings 1, 2 and 7

Steel samples from Buildings 1, 2 and 7 of the World Trade Center were collected during the Federal Emergency Management Agency forensic investigation shortly after the September 11, 2001 incident. Macroscopically, the steel samples supplied exhibited severe “erosion” with plate thickness varying from 12.7mm to a total loss of metal in many areas. Also, some localized plastic deformation was observed. A determination of the cause of this unexpected erosion and an estimate of the maximum temperature that this steel likely experienced are the subjects of this paper.

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Metallographic Assesment of the Thermal Exposure to the Three Mile Island Unit 2 Reactor Lower Head

The accident at Three Mile Island Unit No.2 (TMI-2) on March 28, 1979 was the worst nuclear accident in US history. One of the tasks of the international TMI-2 Vessel Investigation Project (VIP) was to assess the integrity of the vessel. By January 1990, it was possible electrochemically to machine coupons from the lower head by using a specially designed tool.

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Influence of Thermal Exposure on the Microstructure of the Lower Head of the Three Mile Island Unit 2 Reactor

Influence of Thermal Exposure on the Microstructure of the Lower Head of the Three Mile Island Unit 2 Reactor

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Identifying the Cause of Tool and Die Failure

Steels used for tools and dies differ from most other steels in several aspects. First they are used in the manufacture of other products by a variety of forming processes. Second, tools and dies are generally used at higher hardnesses than most other steel products; 58 to 68 Rockwell C is a typical range. Dies for plastic molding or hot working are usually used at lower hardnesses, typically from 30 to 55 Rockwell C.

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Fractography

Fracture Modes

Transgranular: Cracking across grains without preference for grain boundaries

Intergranular: Cracking between grains, the crack propagates in the grain boundaries

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Failures of Tools and Dies

FAILURE MECHANISMS in tool and die materials that are very important to nearly all manufacturing processes are discussed in this article. A wide variety of tool steel compositions are used. Properties and selection of tool steels are described in the Section "Tool Materials" in Volume 3 of the 9th Edition of Metals Handbook; microstructures and metallographic techniques for tool steels are detailed in the article "Tool Steels" in Volume 9 of the 9th Edition of Metals Handbook. This article is primarily devoted to failures of tool steels used in cold-working and hot-working applications.

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resourcesThe articles and presentations that can be down-loaded from this web site are based upon work done by GFV while employed at Bethlehem Steel (1967-1983), Carpenter Technology (1983-1996), Buehler Ltd. (1996-2009) and Struers (2009-Present) and from the authors consulting work for companies such as, Latrobe Steel, Scot Forge, etc., and from his litigation work. GFV's bylined articles appearing in various issues of the ASM Handbook series have been listed here courtesy of ASM International, Materials Park, Ohio.

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