Abstract
This study focuses on the impact of solidification on the inclusion morphologies in different sizes of production-scale electro-slag remelting (ESR) and electro-slag remelting under a protected pressure-controlled atmosphere, (PESR), ingots, in a common martensitic stainless steel grade. The investigation has been carried out to increase the knowledge of the solidification and change in inclusion morphologies during ESR and PESR remelting. In order to optimize process routes for different steel grades, it is important to define the advantages of different processes. A comparison is made between an electrode, ESR, and PESR ingots with different production-scale ingot sizes, from 400 mm square to 1050 mm in diameter. The electrode and two of the smallest ingots are from the same electrode charge. The samples are taken from both the electrode, ingots, and rolled/forged material. The solidification structure, dendrite arm spacing, chemical analyzes, and inclusion number on ingots and/or forged/rolled material are studied. The results show that the larger the ingot and the further towards the center of the ingot, the larger inclusions are found. As long as an ingot solidifies with a columnar dendritic structure (DS), the increase in inclusion number and size with ingot diameter is approximately linear. However, at the ingot size (1050 mm in diameter in this study) when the center of the ingot converts to solidification in the equiaxial mode (EQ), the increase in number and size of the inclusions is much higher. The transition between a dendritic and an equiaxial solidification in the center of the ingots in this steel grade takes place in the region between the ingot diameters of 800 and 1050 mm.
Highlights
Uddeholms AB specializes in producing tool steels
The current study focuses on the solidification process and the oxide inclusions in a production-scale electrode, relative to electro-slag remelted (ESR) and pressure-controlled atmosphere (PESR) ingots of different sizes in a stainless martensitic steel
The material studied was from one ingot-cast consumable electrode 300 × 300 mm2, one ESR remelted ingot 400 × 400 mm2, and three PESR remelted ingots 500, 800, and 1500 mm in diameter
Summary
The material studied was from one ingot-cast consumable electrode 300 × 300 mm2(denoted as the CE-300 sample), one ESR remelted ingot 400 × 400 mm (denoted as the ESR-400 sample), and three PESR remelted ingots 500, 800, and 1500 mm in diameter (denoted below as the PESR-500, -800, and -1050 samples, respectively). The material studied was from one ingot-cast consumable electrode 300 × 300 mm. The electrode, the ESR-400, and the PESR-500 were cast from the same initial steel charge. The difference between the ESR and PESR process is that the ESR here represents a multiple-electrode remelting process (involving electrode changes), which is performed in a moving mould, in an open furnace under an air atmosphere, using a continuous aluminum deoxidation. The PESR process is a single-electrode remelting process using a static mould and an inert pressure-controlled atmosphere. A typical composition of martensitic stainless steel used in this study is as follows: C. In the ESR and PESR trials, a common process slag was used containing about one-third each of CaO, CaF2 , and Al2 O3 , and including ≈3% MgO and ≈1% SiO2
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