The research presented in this series of articles is a summary of inclusion characterisation techniques in routine to support the process improvement needs of internal customers of ArcelorMittal Global R&D, East Chicago. This paper highlights the use of characterisation techniques including total oxygen analysis, cathodoluminescence microscope on remelt buttons and clogging materials, and pulse discrimination analysis to study steelmaking and casting issues that affect productivity and quality of steel at ArcelorMittal USA. Use of cathodoluminescence microscope for examination of remelt buttons to correlate the nature of inclusions to castability for Ca treated steel grades is explained. Example results of application of total oxygen analysis and pulse discrimination analysis on Ti stabilised ultra low carbon, advanced high strength steels and transformation induced plasticity steels are shown. Formation of spinel inclusions and their impact on castability for desulphurised non-Ca treated versus Ca treated grades is also discussed.

Improving steelmaking and casting processes to adapt to the requirements of internal and external customers involves continuous monitoring and evaluation of existing and development of new steel refining practices. Internal quality control of semifinished products requires tools that can correlate product defects to process anomalies. This article focuses on use of techniques such as measurement of complete steel and slag chemistry, inclusion analysis, process analysis and thermodynamics to assess the influence of process conditions on product properties. Examples from both long and flat products, including low carbon aluminium killed steels, medium carbon aluminium killed steels, advanced high strength steels and free machining steels, are presented to explain the benefit of using these tools to understand the process conditions necessary for clean steelmaking and thus improve product quality.

The reheating of high aluminum content transformation‐induced plasticity (TRIP) and light‐weight steels in a nitrogen‐rich atmosphere has been shown to cause development of subsurface aluminum nitride precipitates in addition to internal and external oxides. It is important to understand how these nitrides and oxides form and their consequences for the quality of steel products. This study looks at model iron‐aluminum (up to 8 wt.% aluminum) alloys and uses confocal laser scanning microscopy, XRD, SEM‐EDS, and TEM to study the effect of various conditions on the growth and development of these precipitates in a subsurface oxygen‐depleted region. It was found that nitrides formed when bulk aluminum content was below 8 wt.% when oxygen was sufficiently depleted due to the internal oxidation. In the samples containing 1 wt.% aluminum, the depth of the internal oxide and nitride zones were in agreement with the model proposed by Meijering. Increasing aluminum content to 3 and 5 wt.% had the effects of modifying the surface‐oxide scale composition and increasing its continuity, which gradually decreased the internal precipitation zones with increasing aluminum content. In samples containing 8 wt.% aluminum, a thick continuous oxide sale formed and completely prevented nitrogen and oxygen penetration into the bulk of the sample, thus preventing the formation of any internal precipitates.

The slab reheating process of binary iron-aluminum alloys and an industrial TRIP steel grade has been investigated in both dry and wet atmospheres. The presence of water vapor has a significant effect on the overall scale growth and internal corrosion depth. Heating rate greatly influences the porosity of the surface oxide layer with the surface getting more porous at faster heating rates. Nitride formation could be suppressed in the presence of water vapor, leading to a reduction of internal corrosion depth and a better formability of the final material. Experimental results were compared to thermodynamic predictions and critically discussed.

No abstract