Fe2MoO4 as a Precursor Material for Mo Alloying in Steel (Part II): Up‐Scaling Test

The Mo yield when using three different alloying mixtures (MoO₃ +C; MoO₃ +C + FeO_x; and MoO₃+ C + CaO) was tested both in laboratory experiments (16 g and 0.5 kg scale) and industrial trials (3 ton scale). The alloying is based on in‐situ formation of compounds of Mo in the mixtures from molybdenite concentrate with industrial grade Fe₂O₃. Thermogravimetry (TGA) and X‐ray diffraction (XRD) analyses were performed to identify the reduction steps and final products of the alloying mixtures. At least two steps of mass change were discovered during the reduction of all tested mixtures by carbon. The Mo yield for MoO₃ + C mixture is 93% which was confirmed by both laboratory and industrial experiments. The Mo yield for MoO₃ + C + CaO mixture is around 92% during 16 g scale laboratory and 3 ton scale industrial tests. The best results were obtained in the case of the mixture which contained FeO_x, MoO₃ and C, resulting in the Mo yield up to 98% at all the experiment scale levels. It was found that the combination of both lower evaporation and fast reduction by carbon of the mixture along with further dissolution in steel are necessary to provide high Mo yield during steel alloying. The calculated mass balance of 3 ton trial heats showed that only a small part of initial Mo amount (8–13 ppm) has gone into slag.     

The Effect of Ladle Treatment on Inclusion Composition in Tool Steel Production

An in‐depth SEM‐investigation of the inclusion composition change in the ladle refining process during tool steel production was done. Plant trials were carried out at Uddeholm Tooling AB in Hagfors, Sweden. A series of samples was taken during ladle refining, from deslagging through vacuum treatment. The goal was evaluating the effects of the top slag and other process parameters on the inclusion composition during ladle refining. The main conclusion was that normal variations in the process have a large influence on inclusion composition. Furthermore, it was concluded that the MgO content in the top slag had a large influence on the inclusion composition throughout the whole ladle refining process. Also, the SiO₂ content in the ladle slag originating from the EAF‐slag, had a noticeable effect on the inclusions. The inclusions belonging to the system Al₂O₃‐CaO‐MgO‐SiO₂ showed a continuous composition change throughout the ladle refining process, from high Al₂O₃, via MgO‐spinel to finally complex types rich in CaO and Al₂O₃.     

An Experimental Study of Number Concentration Gradients of Inclusions during Deoxidation using Inductive and Gas Stirring

Concentration gradients of inclusions during inductive and gas stirring of AISI H13 tool steel in a ladle have been studied using a unique experimental technique at Uddeholm Tooling AB in Sweden. A specially designed sampling equipment, which allows five samples to be taken at the same time and at different depths was used. The aim was to experimentally quantify the existence of inclusion size population gradients in different positions of the steel melt. One experiment was carried out using induction stirring and one using gas stirring. The main findings from the induction stirring experiment was that i) concentration gradients of inclusions exist, ii) the number of inclusions decreases with stirring time in all positions, and iii) that the superficial positions show a more rapid decrease than the deeper ones. The main findings from the gas stirring experiment are that i) concentration gradients of inclusions exist, ii) the superficial positions are mostly affected by the gas plumes, and show a very pronounced decrease of the number of inclusions with stirring time, and iii) the deeper positions and also one of the superficial position (no “3”) shows no decreasing trend.     

A study of the sulfide capacities of iron-oxide containing slags

Sulfide capacities of iron-oxide containing slags in the “FeO”-Al₂O₃-SiO₂, “FeO”-CaO-SiO₂, “FeO”-MgO-SiO₂, and “FeO”-MnO-SiO₂ systems were experimentally determined using gas-slag equilibration technique. The experiments were conducted in a temperature range of 1673 to 1923 K. The experimental data were employed to optimize the model parameters of a sulfide capacity model developed earlier in the present laboratory. Based on these parameters, along with those obtained in previous works, an equation was suggested to predict the sulfide capacities of the “FeO”-Al₂O₃-CaO-MgO-MnO-SiO₂ slags. The results of model predictions show reasonable agreement with the experimental values of the six-component slags determined as a part of this work.     

Study of the Formation of Non‐metallic Inclusions by Ladle Glaze and the Effect of Slag on Inclusion Composition using Tracer Experiments

In the present work, BaO was used as tracer in the ladle slag to investigate the effect of slag on inclusion composition and the formation of non‐metallic inclusions by ladle glaze. Experiments were carried out at Uddeholm Tooling AB, Hagfors, Sweden. In the first heat of each series, about 20 mass% BaO was added to the ladle slag. In the next heat(s) using the same ladle, no BaO was added. BaO was detected in the inclusions. This observation showed strong evidence for the generation of non‐metallic inclusions by the ladle glaze. Even in the second and third heats, the fractions of BaO containing inclusions were still very high in all stages of the ladle treatment, indicating that ladle glaze was one of the major sources of inclusions. The sizes of the BaO containing inclusions were relatively big. The average size was 20 μm, while the biggest was around 100 μm. The increase of the fractions of BaO containing inclusions and their average content of BaO with the treatment stage suggested that the effect of slag on the composition of inclusions was a very slow process, due to the low solubility of Ba in the steel.     

Motion and Detachment Behaviors of Liquid Inclusion at Molten Steel–Slag Interfaces

Metallurgical and Materials Transactions B - The fundamental physics of particles adsorbed at the liquid interfaces has numerous applications in a wide field. In the current study, the motion and...     

Synthesis and Characterization of Fe2MoO4 as a Precursor Material for Mo Alloying in Steel

Iron molybdate (Fe₂MoO₄) has been studied as a new potential precursor for Mo additions in high alloy steel processing. Fe₂MoO₄ was synthesized by high temperature reactions between MoO₃, FeO_x and carbon by holding the mixture first for 23 hours at 873 K and then for 16 hours at 1373 K. The Fe₂MoO₄ syntheses were carried out with pure reagents as well as commercial grade materials supplied by steel industry. A thermodynamic analysis of the stabilities of the various phases in the Fe‐Mo‐O‐C quaternary was carried out. The synthesis processes, leading to the Fe₂MoO₄ formation from the precursors and further reduction by carbon were studied with the aid of thermogravimetric analysis (TGA), high‐temperature X‐ray diffraction (HT‐XRD) and evolved gas analysis by gas chromatography (GC). The maximum temperature in the case of all the experiments was 1373 K. It was found that the reactions between the precursor components start already above 873 K. The precursor mixture from commercial grade materials offers an economically advantageous process route with high Mo yield in steel.     

Effect of Top Slag Composition on Inclusion Characteristics during Vacuum Degassing of Tool Steel

The focus of the study was to investigate the effect of the chemical composition of the top slag on the inclusion chemical composition during vacuum treatment of a plastic mould tool steel. Sampling was done before and after vacuum degassing. The chemical composition of the inclusions was determined by using SEM combined with EDX. The results showed that several inclusion compositions were found before vacuum degassing, while only one main composition of inclusions was present after vacuum degassing. Furthermore, the composition of the top slag was found to have a great influence on the composition of the inclusions found in samples taken after vacuum degassing. The present study also shows that the vacuum degassing effectively reduces the number of inclusions in steel. Finally, the thermodynamic calculations of the activities using Wagner's equation were found to predict a lower oxygen activity value than the calculations made using the Thermo‐Calc software.