The primary purpose of this article is to describe general root causes of failure that are associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be common sources of failure-inducing defects in the bulk working of wrought products. The article addresses the types of flaws or defects that can be introduced during the steel forging process itself, including defects originating in the ingot-casting process. Defects found in nonferrous forgings—titanium, aluminum, and copper and copper alloys—also are covered.

Flow forming technology has emerged as a promising, economical metal forming technology due to its ability to provide high strength, high precision, thin walled tubes with excellent surface finish. This paper presents experimental observations of defects developed during flow forming of high strength SAE 4130 steel tubes. The major defects observed are fish scaling, premature burst, diametral growth, microcracks, and macrocracks. This paper analyzes the defects and arrives at the causative factors contributing to the various failure modes.

Cold-drawn type 303 stainless steel wire sections, 6.4 mm (0.25 in.) in diameter, failed during a forming operation. All of the wires failed at a gradual 90 deg bend. Investigation (visual inspection and 5.3x/71x/1187x SEM views) supported the conclusion that the wires cracked due to ductile overload. The forming stresses were sufficient to initiate surface ruptures, suggestive of having exceeded the forming limit. Recommendations included examining the forming process, including lubrication and workpiece fixturing.

The cold start advance solenoid sleeve was found leaking through the wall during troubleshooting complain of a diesel engine that failed to start in cold weather. The component was revealed to be a tubular product with a “bulb” section at one end and threads on the other. The manufacturing method used to create the bulb shape was hydroforming, using a 300 series stainless steel tube in the full-hard condition. The leak was attributed to a crack in the sleeve in the radius between the bulb area and the cylindrical portion of the sleeve. Fatigue cracks initiated at multiple sites near the OD of the sleeve were revealed by scanning electron microscopy of the broken-open crack. It was revealed by analysis that during the hydroforming process, heavy biaxial strains were imparted to the sleeve wall. It was interpreted that when combined with the heavy strains inherently present in the full-hard 300 series stainless steel, the hydroforming strains in the radius caused the microcracking. The root cause for this failure was identified to be omission of an intermediate stress relief or annealing treatment prior to hydroforming to the final shape.

Sheet forming failures divert resources from normal business activities and have significant bottom-line impact. This article focuses on the formation, causes, and limitations of four primary categories of sheet forming failures, namely necks, fractures/splits/cracks, wrinkles/loose metal, and springback/dimensional. It discusses the processes involved in analytical tools that aid in characterizing the state of a formed part. In addition, information on draw panel analysis and troubleshooting of sheet forming failures is also provided.

This article addresses the forms of corrosion that contribute directly to the failure of metal parts or that render them susceptible to failure by some other mechanism. It describes the mechanisms of corrosive attack for specific forms of corrosion such as galvanic corrosion, uniform corrosion, pitting and crevice corrosion, intergranular corrosion, and velocity-affected corrosion. The article contains a table that lists combinations of alloys and environments subjected to selective leaching and the elements removed by leaching.

Corrosion is the electrochemical reaction of a material and its environment. This article addresses those forms of corrosion that contribute directly to the failure of metal parts or that render them susceptible to failure by some other mechanism. Various forms of corrosion covered are galvanic corrosion, uniform corrosion, pitting, crevice corrosion, intergranular corrosion, selective leaching, and velocity-affected corrosion. In particular, mechanisms of corrosive attack for specific forms of corrosion, as well as evaluation and factors contributing to these forms, are described. These reviews of corrosion forms and mechanisms are intended to assist the reader in developing an understanding of the underlying principles of corrosion; acquiring such an understanding is the first step in recognizing and analyzing corrosion-related failures and in formulating preventive measures.

The A2 tool steel mandrel, part of a rolling tool used for mechanically joining two tubes was fractured after making five rolled joints. A 6.4 mm diam hole was drilled by EDM through the square end of the hardened mandrel due to difficulty was experienced in withdrawing the tool. The fracture progressed into the threaded section and formed a pyramid-shape fragment after it was initiated at approximately 45 deg through the hole in the square end. An irregular zone of untempered martensite with cracks radiating from the surface of the hole (result of melting around hole) was revealed by metallographic examination. A microstructure of fine tempered martensite containing some carbide particles was exhibited by the core material away from the hole. Brittle fracture characteristics with beach marks were exhibited by the fracture surfaces which is characteristic of a torsional fatigue fracture. As a corrective measure, the hole through the square end of the mandrel was incorporated into the design of the tool and was drilled and reamed before heat treatment and specified hardness of the threaded portion and square end of the mandrel was reduced.

An investigation was conducted to determine why 16 out of 139 pipe bends cracked during hot induction bending. The pipe conformed to API 5L X65 PSL2 line pipe standards and measured 1016 mm (40 in.) in diam with a wall thickness of 18.5 mm. A metallurgical cross section was removed along a crack on the extrados to document the crack morphology using optical microscopy. In addition to cracking, golden-yellow streaks were visible at the extrados, and the composition was examined using scanning electron microscopy with energy dispersive spectroscopy. Based on the results, investigators concluded the pipe was contaminated with copper at the mill were it was produced.