Evolution of Al 2 O 3 inclusions by magnesium treatment in H13 hot work die steel

The modification mechanism of cerium (Ce) on oxides and multilayer carbontrides in H13 steel is investigated by industrial trials and thermodynamic calculations. The morphology, composition, and size of inclusions are analyzed by scanning electron microscopy and energy dispersive spectroscopy. The main inclusions in H13 steel without Ce content in the molten steel are MgAl2O4 spinel inclusions and multilayer carbonitrides. The carbonitrides have a multilayer structure in which MgAl2O4 acts as the nucleation core and the second layer is (Ti, V)(C, N). As the cerium content in molten steel increases from 0 to 0.03 wt%, the MgAl2O4 is effectively modified into cerium oxide (Ce–O) and cerium oxy‐sulfide (Ce–O–S), and the evolutionary process is as follows: MgAl2O4 → CeAlO3 → Ce–O and Ce–O–S. Likewise, the structure of multilayer carbonitrides in the H13 steel also changed. The MgAl2O4 and CeAlO3 act as heterogeneous nucleation cores of multilayer carbonitrides. However, Ce–O and Ce–O–S can effectively inhibit the heterogeneous nucleation of carbonitrides. The number density of large‐size carbontrides is remarkably reduced with increasing Ce content. A prediction model of optimum Ce content in molten steel is built, which has remarkable agreement with the experimental observations.

Section: Resultsmentioning

confidence: 99%

Effect of Cerium on the Behavior of Inclusions in H13 Steel

Huang

Cheng

et al. 2018

“…These inclusions generally are angular and have high hardness, which results in cracking defects of steel easily and should be avoided in steel. [5][6][7] Calcium treatment is commonly used to modify alumina inclusions to various types of calcium aluminum inclusion. The modification of alumina and spinel inclusions to a lower melting-point state by calcium is alternative to minimize their detriments to steel and maximizing inclusion removal during liquid steel refining.…”

Section: Introductionmentioning

confidence: 99%

Evolution of Calcium Aluminate Inclusions by Cerium Treatment in Al‐Killed Steel during Ruhrstahl–Heraeus Refining Process

Geng

Shi

2020

The effect of cerium addition during Ruhrstahl–Heraeus (RH) refining process on liquid calcium aluminum inclusion in Al‐killed steel is studied based on plant trials and thermodynamic calculation. Before cerium addition, liquid calcium aluminum inclusion surrounded by an outer CaS layer are observed. Cerium modified liquid calcium aluminum inclusion to CeAlO3 + CaS + CaO–Al2O3 complex inclusion. The modification process of liquid calcium aluminum inclusion by cerium is different from that of solid Al2O3 or MgO·Al2O3 inclusion and can be concluded as following. Cerium added into molten steel reacts first with liquid calcium aluminum inclusion in molten steel. Then the solid CeAlO3 and CaO, as reaction product, are surrounded by liquid calcium aluminum. At the same time, CaO reacts with dissolved sulfur, resulting in the generation of CaS inclusions.

“…Huang et al discovered that the addition of elemental Ce effectively inhibits the heterogeneous nucleation of primary carbides in industrial H13 steel, and the number density of primary carbontrides is remarkably decreased with increasing Ce content. Li et al reported that the addition of elemental Mg in H13 steel converts Al 2 O 3 into MgAl 2 O 4 , and the MgAl 2 O 4 particle acts as a more effective heterogeneous nuclei and provides more nucleation sites than the Al 2 O 3 inclusion, resulting in a more uniform distribution of primary carbides . Xie et al discovered that Ti‐rich carbonitride precipitates first and that V‐rich carbide precipitates at the end of solidification in Ti–H13 steel .…”

Section: Introductionmentioning

confidence: 99%

Precipitation Behavior of Large Primary Carbides in Cast H13 Steel

Huang

Cheng

et al. 2019

The large primary carbides precipitated during solidification can significantly reduce the performance of H13 steel. To better inhibit the formation of primary carbides, it is necessary to obtain the precipitation mechanism of primary carbides in H13 steel. First, an electronic probe microanalyzer (EPMA) is used to analyze the microsegregation of alloying elements in the last-to-solidify region. The enrichment of elemental V, Mo, Cr, and C in the last-to-solidify region is the main reason for the formation of primary carbides. The number density, size, and morphology of the carbides in a two-dimensional (2D) observation are obtained through an automatic inclusion analysis system. A non-aqueous electrolysis method is used to show the three-dimensional (3D) morphology of the primary carbides. There is a large difference between the 2D and 3D primary carbide observation. Finally, the precipitation mechanism and process of carbides during solidification are calculated with the Thermo-Calc thermodynamic software, and the calculated results are in keeping with the experimental observation.