An assessment of cleanliness techniques for low alloyed steel grades

Abstract

In order to find a method to characterize the inclusion distribution of high-cleanliness materials, complementary techniques were tested, such as high-frequency (80 MHz) ultrasonic testing, X-ray tomography or Extreme Value Analysis (EVA). The micro-cleanliness was also characterized by standard methods based on observations of polished surfaces by light optical or scanning electronic microscopy. The combination of all these techniques, enhanced by metiS software, allows us to determine the complete 3D distribution of oxides or to estimate the probability of largest inclusion size by modelling virtual samples. At the end, fatigue testing was performed in order to try to link fatigue results to previous characterization outcomes.

Electrode manufacture for the remelting processes

“…The extent to which they are an issue in alloy use depends widely on the alloy, the application and the property concerned. Studies [2,[6][7][8][29][30][31][34][35][36][37][44][45][46]49] of the inclusion populations in remelted alloys have indicated that a general characteristic is the infrequent occurrence of large inclusions (>50 µm), but the population of small inclusions (<2 µm) may be as large as, or larger than, that in the original electrode (Figure 5).…”

“…In almost all of the published data on inclusion populations before and after ESR, a salient feature is the absence of large inclusions in the ESR ingot [49]. It is likely that this finding does not imply a complete absence of large inclusions but instead is an indication that the population is sufficiently sparse that there is only a small probability that an inclusion might be found in a finished part located in a stress zone large enough for it to initiate a failure [49].…”

“…In almost all of the published data on inclusion populations before and after ESR, a salient feature is the absence of large inclusions in the ESR ingot [49]. It is likely that this finding does not imply a complete absence of large inclusions but instead is an indication that the population is sufficiently sparse that there is only a small probability that an inclusion might be found in a finished part located in a stress zone large enough for it to initiate a failure [49]. For most applications, the population of very small inclusions has no effect on properties and the inclusion-related property improvements observed are the result of the considerable reduction in the small number of larger inclusions.…”

“…Since the metal is usually subject to considerable composition changes in ladle processing and during casting, it would seem valuable to consider the oxygen content of the solid electrode as quality variable indicative of the electrode manufacturing process conforming to a standard practice. Assessment of the quality with respect to inclusions in the remelted product is thus seen to introduce a troublesome gap between the minimum size of inclusion detectable by ultrasonic testing methods and the inclusion sizes reasonably measurable by metallographic methods [49]. The minimum inclusion size detectable by ultrasonic testing is ill-defined since in most cases, the feature detected is not the inclusion but instead is a crack associated with it which has developed during mechanical working.…”

Impact of Solidification on Inclusion Morphology in ESR and PESR Remelted Martensitic Stainless Steel Ingots

“…The sample areas in laboratory-scale trials are usually about 100 mm 2 . According to Franceschini et al [28], an analyzed surface of 5000 mm 2 is suitable for evaluating the cleanliness for remelting processed samples, to compare with air samples where 1000 mm 2 is sufficient.…”