Nitriding is a surface hardening treatment used on steel components to improve their resistance to corrosion, fatigue, and wear. Iron nitrides at the nitrided steel surface form a compound layer known for its high hardness but also for its brittle nature. It is not uncommon for this layer to chip or break away during metallurgical sample preparation, making it difficult to accurately characterize the microstructure of the nitrided load. This paper presents the results of several studies that assess the effect of cutting and polishing operations along with polishing pressure, the use of foils, and Ni plating. A best practice procedure has been developed to prevent damage to nitrided samples and minimize uncertainty when evaluating part quality.

Microstructural examination of a nitrided part is the most commonly used method for evaluating nitriding material and process performance. Microstructural evaluation also helps to validate that the process ran as intended and produced the desired nitrided case characteristics. However, sample preparation is often complicated by the partial or complete breakaway of the compound layer and may affect the accuracy of the conclusions made. A set of experiments was performed to evaluate the effect of two saw cutting methods, the use of metal foil for sample mounting, and the use of Ni plating before cutting. Microstructures of 12 experimental conditions were analyzed. Recommendations were made for the nitrided sample preparation best practice to analyze compound layer uniformity and thickness.

The focus of this investigation was on examining the effect of cryogenic treatment on the microstructure and mechanical properties of Austempered Ductile Cast Iron (ADI) with an upper bainitic (ausferritic) microstructure. The investigation also examined the effect of cryogenic treatment on the fracture toughness of the material. Compact tension and cylindrical tensile specimens were prepared from ductile cast iron as per ASTM standards and were austempered in the upper bainitic temperature range of 371 °C to 400°C and were cryogenically processed. The mechanical properties and fracture toughness of these materials were evaluated and compared with non-cryogenically treated samples.

An investigation was carried out to examine the influence of cryogenic processing on the microstructure and mechanical properties of Austempered Ductile Cast Iron (ADI). ADI has emerged as a major engineering material in recent years because of its many attractive properties. These include high yield strength with good ductility, good fatigue strength, fracture toughness and wear resistance. In this investigation, compact tension and cylindrical tensile specimens were prepared from ductile cast iron as per ASTM standards and were austempered at a lower bainitic temperature of 288°C (550°F). These specimens were then cryogenically processed. The mechanical properties and fracture toughness of these samples were evaluated and compared with the noncryogenically treated samples. The influence of cryogenic heat treatment on the microstructure of these samples was also examined. Test results show that the cryogenic processing can improve the mechanical properties without compromising the fracture resistance of the material.