Stabilisation and Microstructural Modification of Stainless Steel Converter Slag by Addition of an Alumina Rich By-Product

Abstract

This work aimed to assess the possibility of stabilising argon oxygen decarburisation (AOD) stainless steel slag with CaO/SiO 2 * 1.6, by using a secondary alumina by-product (*75 wt% Al 2 O 3 , referred herein as SA, found under the name ''ValoxyÒ'') and reduced levels of B 2 O 3 . Two groups of samples were synthesised: one reference group with AOD slag and 0.26, 0.16, 0.10 and 0.05 wt% of B 2 O 3 and one with equivalent compositions but to which 5 wt% of SA is added. Experimentally, the slags were produced in a platinum crucible in a resistance furnace, heated with 5°C/min until 1,640°C, equilibrated for 1 h, followed by slow cooling to room temperature. The mineralogical composition was analysed by QXRD whereas the micro-hardness was measured through a Vickers indentation test. The microchemistry and morphology were analysed by EPMA-WDS. Analysis indicated that AOD was successfully stabilised by 5 wt% SA and 0.10 wt% B 2 O 3 , whereas for 0.05 wt% B 2 O 3 , volumetric expansion occurred over time. In terms of mineralogy, the use of SA promoted the formation of spinel instead of gehlenite. Electron microscopy revealed a more dense morphology in the samples with SA when compared to the reference ones. Elemental maps indicated that Cr predominantly participates in the spinel phase. Vickers tests showed a slight increase in hardness in the samples with SA. In conclusion, the addition of SA resulted in substantially different microstructures that appear to be promising in terms of chemical and mechanical stability. However, in terms of volumes the required addition levels for effective stabilisation are substantial compared to B 2 O 3 additions.

A Review of Circular Economy Prospects for Stainless Steelmaking Slags

“…Another instability problem comes from hydration of free lime (CaO free ) and periclase (MgO free ) which are typically present in basic slags (AODS, LFS). Conventional "hot modification" of slag can be performed during slag tapping/pouring or in the slag pot by adding a "stabilizer" (borate, MgO, Al 2 O 3 ) which prevents the dust-forming β-C 2 S to γ-C 2 S transition [36][37][38][39][40][41].…”

Investigation on Stabilization of Ladle Furnace Slag with Different Additives

“…An alternative stabilization mechanism to boron is the addition of alumina and red mud obtained from aluminium industry [23] as these additions also avoid the disintegration of slag by formation of the stable C2AS (di-calcium alumino silicate) compound. Addition of alumina reduces slag basicity by changing the slag chemistry subsequently avoiding the formation of C2S by moving the system out of the C2S stable region in the CaO-SiO2-Al2O3 phase diagram.…”

Ladle metallurgy stainless steel slag as a raw material in Ordinary Portland Cement production: a possibility for industrial symbiosis

“…The AOD slag can also be considered since its characteristics resemble LM slag. Unlike current industrial practice, the new process does not involve the addition of any stabilising agents (such as boron compounds) to prevent the pulverisation of the slag (Iacobescu et al, 2014). Quite the contrary, this transformation is exploited as it delivers a very fine slag with no need for milling.…”