A synchrotron transmission X-ray microscopy study on precipitate evolution during solid-state thermal cycling of a stainless steel

During additive manufacturing of stainless steels, sub-micron sized oxide (i.e., MnSiO3, SiO2, and CrMn2O4) non-oxide sulfide, in particular MnS, possibly carbides, phosphides nitrides) precipitates form during solidification. But do they evolve the subsequent solid-state thermal cycling (SSTC) until end printing process? A recent study on subjecting thin-film lamellae extracted from an additively manufactured steel to heating-cooling treatments inside a transmission electron microscope (TEM) confirmed that precipitate composition can indeed SSTC. However, could not provide any conclusive evidence volume fraction, density, size evolution. In this work, we have quantified these changes using novel experimental procedure combining (i) micropillar extraction steel, (ii) them different SSTC (including annealing) TEM, (iii) performing synchrotron X-ray microscopy identify precipitates, (iv) machine learning model segment quantify size. Comparing quantities before after each SSTC/annealing sequence reveals new oxides nucleated rapid with high maximum temperature. slow temperature annealing, dissolve because oxygen evaporation TEM. empirical relationship correlating sizes cooling rates is proposed. It good agreement data collected conventional casting, directed energy deposition, powder bed fusion processes.