The Lehrer diagram often serves as a guide for selecting gas mixtures for nitriding alloy steels, but it is only accurate for ammonia gas nitriding processes when hydrogen is used as the diluting gas. This paper presents the results of a study showing that the use of pure nitrogen as a diluent has a marked effect on the phase boundary lines of the standard Lehrer diagram, essentially shifting them to the left. The paper also includes examples showing where the use of nitrogen is advantageous and where it is not.

Low pressure carbonitriding (LPCN) has the potential to improve the impact and fatigue strength of steel components through the enrichment of nitrogen and the effect of carburizing at higher temperatures. The work described in this paper investigates the influence of boron on the LPCN response of 20MnCr5 steel and the effect of niobium on that of 8620. LPCN treatments were developed to achieve a surface hardness of ~700 HV and case depth of 0.65-0.75 mm in four alloys: 20MnCr5, 20MnCr5 + B, 8620, and 8620 + Nb. The hardness and case microstructure of treated and quenched test samples are correlated with bending fatigue measured in Brugger fatigue specimens, which simulate the root of a gear tooth.

This paper reviews recent advances in the control of plasma ion nitriding processes and their effect on AR500 and 4140 steel and ductile and gray iron. The advanced discussed are primarily in the area of electrical power and gas flow control.

Controlled nitriding and ferritic nitrocarburizing can significantly improve the corrosion and wear resistance of carbon and low-alloy steels. The framework for maintaining these processes is based on standards, such as AMS 2759/10 and 2759/12A, that specify tolerances for control parameters. This work investigates the impact of admissible deviations in control parameters on the performance of treated alloy samples. The findings of the study demonstrate that although tolerances are allowed, precise control in specific furnace classes is necessary to consistently obtain superior results.

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.

This paper discusses the basic principles of multi-frequency eddy current testing and explains how it can be used on high-volume production lines to detect faulty heat-treated parts based on case depth, hardness patterns, tensile strength, carbon content, soft spots, and surface decarburization. It also presents examples showing how the method is used in high-speed inspection of cam shafts, screws, balls of various sizes and materials, distance pins, and complex bolts.