More than 125 presentations of original, unpublished work will be delivered when the ASM Heat Treating Society convenes for its 29th conference and exhibition in Columbus, Ohio, October 24-26. The information exchanged in these sessions – as researchers and practitioners share their latest discoveries, theories, and advancements – will have a significant impact on design and manufacturing innovation as well as the fortunes of industry.
One example of the cutting-edge work that will be unveiled is an investigation on the effect of heat treating on additively manufactured medical implants. Additive techniques offer unprecedented design flexibility for dental and orthopedic implants, but the intense heating and cooling spikes associated with direct metal laser sintering can leave the microstructure of titanium – a good bio-material but a poor thermal conductor – in a less than optimum state. To quantify the potential for improvement, researchers evaluated several heat treat processes and measured changes in hardness, residual stress, and corrosion. The promising findings will be shared in a Thursday morning session.
Caption: Optical metallography reveals microstructural differences between the build and deposition planes as well as pores near the surface of an as-printed titanium test sample. Structural mismatch is a source of residual stress, while pores can lead to fatigue fracture and corrosion.
Caption: X-ray diffraction results indicate that heat treating as-printed titanium parts (blue trace) reduces the ratio of α to β phase precipitates as seen in the narrowing of α peaks and the development of β peaks (green, orange, and red traces). This seems to correlate with measured improvements in corrosion resistance because micro-galvanic reactions stemming from phase differences cause pitting in α precipitates, a likely pathway for corrosion.
Another significant accomplishment that will be reported is a new method to predict the quenched and tempered hardness of complex steels based on chemistry data. Two researchers, building on prior attempts to calculate hardness as a function of chemistry, have developed a hybrid model that works for mixed microstructure alloys containing less than 0.5wt%Cr. As Cr levels increase, however, other alloying elements such as Mo and V become more influential, compounding the complexity of the problem. The researchers will describe the new method and its limitations on Tuesday morning.
Caption: A corrective variation on an earlier method for calculating tempered hardness in complex steels based on chemistry shows considerable improvement when measured and calculated data plots are compared side by side.
Caption: Hardness profiles for a 95 mm bar of SAE 4142 steel quenched in water and tempered at 1100°F as calculated from chemistry data using a recently developed method.
The results of several cross-sector efforts will also be presented, including a paper submitted by a group examining the role of vanadium in induction hardened shafts. Vanadium microalloying is common in carbon steel shafts because it increases load capacity. Induction hardening offers additional benefits, but the presence of vanadium adds uncertainty to the process. Seeking clarity, researchers have obtained evidence that, under certain conditions, vanadium carbonitride precipitates formed during induction reduce austenite in the case/core region but not the case. Retained austenite, characterized by compositional gradients and undissolved carbides, is believed to limit case depth and hardenability.
Caption: Cross-sectional images of 1045 steel shafts in various induction hardened conditions reveal distinct differences in case, core, and case/core regions that correspond with the presence of vanadium and its effect on microstructure formation.
Caption: A high volume fraction of martensite (M) revealed by SEM imaging is believed to be the result of a large amount of austenite formed with the help of vanadium during induction hardening of 1045 steel.
