Thermophysical Properties of Pipe Steel in the Liquid State

Abstract

The temperature dependences of the kinematic viscosity and surface tension of liquid pipe steel with different modes of melt preparation were investigated. A transition zone was found on the temperature dependences of the thermophysical properties, which separates the regions with different activation energies of viscous flow and surface tension. At the heating stage in the transition zone, the thermal decomposition of clusters based on cementite Fe3C occurs. As a result of the decomposition, free carbon atoms appear which tend to give a uniform distribution in liquid iron with increasing temperature. At a low content of alloying elements and impurities, a high-temperature melt should have a large-scale cluster structure, which provides a more uniform distribution of chemical elements. The melt after vacuum degassing has a narrow transition zone near 1920 K, in contrast to the wide transition zone of the melt without vacuum degassing. The wider transition zone is shifted to high-temperature and this shift is associated with the thermal decomposition of carbides and oxides. Studies have shown that heating liquid pipe steel above the temperature of the liquid–liquid structural transition makes it possible to obtain a more homogeneous structure with a more uniform distribution of alloying and impurity elements in the melt. The sharp drop in surface tension at temperatures above 1920 K in the melt without vacuum degassing is associated with the diffusion of free S and O atoms, which are released after thermal decomposition of sulfides and oxides.

The Effect of Nickel on the Viscosity of Iron-Based Multicomponent Melts

“…Aluminum oxide Al 2 O 3 and aluminum nitride AlN have a melting point above 2300 K. An increase in kinematic viscosity at temperatures above 1900 K can be associated with the decomposition of high-temperature clusters based on cementite and silicon oxides. A similar increase in viscosity in the high-temperature region was observed in liquid pipe steel [31]. The growth of the viscosity in the hightemperature region in Figure 4 corresponds to the beginning of LLST.…”

“…As the temperature rises, the structure of the melt should become more disordered, and various atoms and clusters tend to have a more chaotic distribution. A more uniform arrangement of atoms and clusters corresponds to a larger-scale structure of the multicomponent melt [31]. Clusters can be joined by Ni, Nb, Mo atoms, as well as free Fe and Si atoms, which form a cloud around B-containing clusters.…”

The Effect of Trace Oxygen Addition on the Interface Behavior of Low-Alloy Steel

“…According to Brooks, only around 50 ppm of oxygen can reduce the surface tension of pure iron by 50% [16]. In the case of more complex systems, i.e., binary, ternary, quaternary systems, and Fe-based alloys, oxygen also affects the surface tension, lowering it [10,[17][18][19][20][21][22]. It is also worth noting that for polycomponent steels, the interface wetting is challenging to simulate, and therefore accurate data are obtained mostly experimentally [10].…”