NMI in electrical steels are known to have a very complex chemical makeup and history of formation, and exert a large influence on the handling of this steel in secondary metallurgy and casting. We ...have developed routines to analyse the non-metallic inclusion contents of non grain-oriented electrical steels by automated FEG-SEM analysis. We automatically analyze NMI of sizes down to 0.08 μm2 in a steel that has significant amount of alloyed Si (2.3 wt%) by employing a matrix spectrum subtraction routine that leaves only the signal of the NMI itself to be quantified. We describe data reduction procedures for the NMI populations that consist out of duplexing oxides, sulfides, and nitrides. The chemical complexity can be represented and understood in terms of using a multicomponent projection technique, and based on the analysis of the particles it is possible to calculate quantitatively the amount of elements contained in the NMI assemblage of a steel sample. We find that this mass balance gives results in good to excellent agreement with bulk steel analyses for elements that are dominantly inclusion bound, such as Ca, if the complete inclusion size range above 0.08 μm2 is taken into account. Based on these data analysis methods, we compare the NMI development in two heats through the secondary metallurgy process. Although the same steel composition was alloyed, the NMI developed vastly different depending on the details of treatment on the ladle furnace.
Currently, the available evaluation methods for determining the chip breakability in the industry are mainly based on subjective visual assessment of the chip formation by an operator during ...machining or on chips that were collected after the tests. However, in many cases, these methods cannot give us accurate quantitative differences for evaluation of the chip breakability of similar steel grades and similar sets of machining parameters. Thus, more sensitive methods are required to obtain more detailed information. In this study, a new method for the objective assessment of chip breakability based on quantitative determination of the weight distribution of chips (WDC) was tested and applied during machining of stainless steels without Ca treatment (316L) and with Ca treatment (316L + Ca). The obtained results show great consistencies and the reliability of this method. By using the WDC method, significant quantitative differences were obtained by the evaluation of chips, which were collected during the machining process of these two similar grades of steel at various cutting parameters, while, visually, these chips look very similar. More specifically, it was found that the Ca treatment of steel can improve the chip breakability of 316L + Ca steel in 80% of cutting trials, since a fraction of small light chips (Type I) from this steel increased and a fraction of large heavy chips (Type III) decreased accordingly. Moreover, the WDCs that were obtained at different cutting parameters were determined and compared in this study. The obtained results can be used for the optimization of chip breakability of each steel at different cutting parameters. The positive effect of Ca treatment of stainless steel was discussed in this study based on consideration of the modification of different non-metallic inclusions and their effect on the chip breakability during machining.
This paper deals with the examination of the impact of steel cast speed on the occurrence of the non-metallic inclusions due to the investigation of the individual samples taken at different steel ...cast speeds. The aim of this paper was to identify and describe the relation between the non-metallic inclusions occurring in the metal and the cast speed variations at the continuous casting machine. The non-metallic inclusions within this investigation were identified by the method (AES) based on the atomic emission spectroscopy that evaluates the occurrence of the determined elements in the metal. This method applies the principle of the light emitting acquired by the high-voltage spark supply. The investigation of the impact of both the technological production parameters, and the casting on the cleanliness of the given absorption quality of steel leads to their optimization, as well as, to total minimization of occurrence of the non-metallic inclusions in the steel volume were studied.
Using correlation-regression analysis, the effects of structure and chemical composition on
KC
V impact strength anisotropy and difference in critical brittleness temperatures for longitudinal and ...transverse specimens of ferrite-pearlite and high-strength (ferrite + bainite) steels after thermomechanical rolling are studied. The significant effect of pearlite content and sulfide inclusions on impact strength anisotropy and difference in critical brittleness temperatures for longitudinal and transverse specimens of ferrite-pearlite steels is demonstrated. For high strength ferrite-bainite steels prepared using thermomechanical rolling technology the effect of carbon and sulfur on degree of embrittlement for transverse specimens is considered that also depends on the content of titanium carbonitride and Al
2
O
3
-based aluminum oxides.
Ultra-long cycle fatigue fracture origins in high strength steels are mostly at non-metallic inclusions due to the influence of the trapped hydrogen. In the vicinity of a non-metallic inclusion at ...the fracture origin, an optically dark area (ODA) is often observed inside a fish-eye mark, which represents the particular morphology associated with mechanism of failure at an early stage: hydrogen assisted fatigue. From an analysis of several features involved in this mechanism of failure, as the development of the ODA, the threshold for pure fatigue propagation, as a function of crack length and inclusion size, an expression was deduced to estimate the internal fatigue limit, that is, the stress level below which fracture produced by cracks initiated from an internal inclusion is not found after 10
10 cycles:
σ
e
Int
=256
ΔK
th
R
i
max
where Δ
K
th is the pure fatigue crack propagation threshold as a function of crack length estimated with the following expression:
ΔK
th
=4×10
−3(H
V
+120)(3R
i
max
)
1/3
If
ΔK
th
≤10
MPa
m
1/2
Otherwise
ΔK
th
=10
MPa
m
1/2
R
i
max is the maximum radius of the non-metallic inclusions from which the crack initiates, in μm, and
H
V is the Vickers hardness, in kgf mm
−2. The internal fatigue limit was estimated for several steels and compared with experimental results obtained from the literature for internal fatigue lives in the range of 10
8–10
10 cycles. Differences between the estimated internal fatigue limit and the experimental one ranged from 4 to −29%.
The results of studying the effect of microcrystalline complex alloys with alkaline earth metals (AEM) on the quality indicators of 17G1S-U pipe steel have been considered. It has been shown that the ...treatment of steel with these alloys reduces both the maximum score of non-metallic inclusions (NI) and the mean level of contavmination for the main types of inclusions including corrosive-active ones (CANI). Alongside with this, fine calcium, strontium and barium oxysulfides with a reduced oxygen content are formed in the metal. The complex alloys with alkali-earth metals contribute to obtaining a more homogeneous and refined metal structure, an increase in the cold resistance and corrosion resistance of steel.
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