The Shapes and Compositions of Non-Metallic Inclusions in Mild Steel Weld Metals (Report 3)

Abstract

In the 1st and 2nd reports, the authors analyzed chemically the non-metallic inclusions in weld metals and observed these shapes under optical and electron microscope. From these experiments, authors confirmed the mechanisum of the formation process of inclusion particles in molten weld metal.
In this report, inclusions were separated as residue from alcoholic iodine solution and analyzed these crystal formes using x-ray diffractometer. In the previous report, inclusions were analyzed using electron diffraction method but identification was difficult. The results of x-ray diffraction supplied the previous results and confirmed the relation between crystal forms, chemical compositions of inclusions and chemical compositions of weld metals.
Inclusions in weld metals were consist of the majority of amorphous and a part of crystal structure. 2MnO⋅SiO₂ was found in ilmenite type A, MnO-SiO₂ and 2MnO⋅SiO₂ was found in ilmenite type B and SiO₂ was found in low hydrogen type.
The chemical compositions of weld metals were as follows : ilmenite type A was Si poor, low hydrogen type was Si rich and ilmenite type B was most popular compositions of Mn and Si in weld metal. The chemical compositions of inclusions in all these weld metals were consist of MnO and SiO₂ but SiO2 contents in these inclusions were varied as follows : 33% in ilmenite type A, 46% in ilmenite type B and 49% in low hydrogen type. From these results and phase diagram of MnO-SiO₂ system or [O]-[Mn]-[Si] in molten steel (by Kdrber and Oelsen), the shapes of inclusion particles and the crystal forms of inclusions in weld metals could be estimated. These estimations were supported with the results of the experiments in this and previous reports.
Second experiment in this report, inclusions were separated and analyzed using x-ray diffractometer in the heat treated weld metals at 900°C and 1400°C. The crystal forms of inclusions in these weld metals were changed by means of heat treatments as follows : In the weld metals heated at higher temperature than the melting point of inclusions, inclusions were changed amorphous structure. On the other hand, in the weld metals heated at lower temperature than the melting point of inclusions, the crystal parts of inclusions were increased than the as-welded state.