Direct metal laser sintering (DMLS) is an established technology in metal additive manufacturing. This complex manufacturing process yields unique as-built material properties that influence mechanical performance and vary with different machine parameters. Part porosity and residual stresses, which lead to part failures, and grain structure, as it relates to mechanical properties and anisotropy of DMLS parts, require investigation for different print settings. This work presents results for density, residual stress, and microstructural inspections on designed test artifacts for the benchmarking of 3D metal printers. Results from printing artifacts on two separate DMLS printer models with default parameters show highly dense parts for both printers, with relative densities above 99.5%. Characterization of residual stress through cantilevered deflection specimens indicates similar resulting thermal stresses developed in both build processes, with deflection averages of 32.48% and 28.09% for the respective machines. Additionally, properties of the test artifact printed after adjusting default machine parameters for equal energy density are characterized.

The transient behavior of boiling phenomena during quenching of an AISI 304 stainless steel, conical-end, cylindrical probe in flowing water at 60 °C was studied. Two free-stream velocities (0.2 and 0.6 m/s) and two initial probe temperatures (850 and 950 °C) were investigated. From high-speed video recordings, undulations of the liquid vapor interface that appear periodically and propagate in the direction of the flow stream were observed during the vapor film stage. After the collapse of the vapor film, a wetting front is formed which consists of many small bubbles that coalesce rapidly in a small area while fewer and larger bubbles nucleate and grow below it. The initial temperature has a marginal effect on the size and half-life of the large bubbles. However, the water flow rate produces larger values of maximum diameter and half-life time for water flowing at 0.2 m/s than their equivalents for 0.6 m/s.

Two stainless steel parts used in automotive engines are carburized in the course of their production to achieve desired properties. To reduce costs and improve product quality, the gas carburizing process that had been used was replaced by low-pressure vacuum carburizing. The two parts are similar in composition except that one contains 0.25 wt% Mo and the other 0.4 wt% Mo. Both also contain around 17 wt% Cr and thus naturally form a Cr 2 O 3 passivation layer that provides corrosion resistance but also acts as a barrier to carbon. As a result, the parts are etched in a pickling solution prior to carburizing. In the initial assessment of the new carburizing and pretreatment process, engineers observed differences in the pitting and oxide regeneration behaviors of the two stainless steels. The paper describes how the engineers determined the cause of the pitting and the extent to which it could be controlled. Because of the tradeoffs involved, the engineers decided to make both parts from the same material and optimize process parameters accordingly.

Austenitic stainless steels are carburized or nitrided (i.e., surface hardened) at low temperatures in order to maintain their superior corrosion resistance. Treatment temperature must be low enough to prevent precipitation in the diffusion zone, yet high enough to allow sufficient diffusion depths to meet design specifications. At these temperatures, prior machining processes can have a significant effect not only on diffusion, but also the surface hardness and corrosion resistance achieved. This paper presents practical examples showing how cutting, grinding, honing, and polishing processes influence the results of low temperature surface hardening treatments for stainless steel parts. It also discusses the influence of surface deformation and finish.

Gas nitriding is proving to be a viable low temperature case hardening process for stainless steels used in numerous applications. In this study, a comparison between austenitic (grade 304) and martensitic (grade 401) stainless steels shows how pre-oxidation temperature affects the thickness and porosity of the compound layer produced as well as hardness and nitriding diffusion depth. The results indicate that austenitic stainless steel would be the best choice for a part requiring wear resistance and strength, and that a standard rolled martensitic stainless steel would suffice if only a wear resistant surface is needed.