H. T. Ma

Eutectoid Magnetite in Wüstite Under Conditions of Compressive Stress and Cooling

During hot rolling, the existence of a wüstite layer is favored from the standpoint of improved descaling performance. In this work, the mutual effect of external compressive stress and cooling on the phase transformation of oxide scales formed on steel was investigated. Optical microscopy images showed that a fast cooling rate of about 80xa0°C/min promoted the formation of magnetite/Fe eutectoid. When applying a compressive stress, growth of the magnetite/Fe eutectoid was increased. It was inferred that the promoting effect of fast cooling rate on the diffusion is advantageous to the growth of magnetite/Fe eutectoid. The increase of system chemical potential by the compressive stress also promoted the growth of magnetite/Fe eutectoid.

Effect of compressive stresses on oxidation kinetics and oxide scale failure of pure nickel at 973 K

Abstract The effect of a compressive stress on the oxidation kinetics and oxide scale failure of pure nickel was investigated. Compressive samples were subjected to stresses of 10 and 20 MPa, and the oxidation behaviour was studied at a temperature of 973 K. This study was performed mainly by comparisons of oxidation kinetics, surface morphology and cross-section of the oxidised samples. The results showed that applying a compressive stress induced an increase in the oxidation rate, and changes of the surface morphology. Compared with the samples without any applying stress, the oxide scale failure for the samples subjected to applying stresses was changed. This was related to the effect of compressive stresses on the vacancy diffusion.

The Oxide-Scale Growth and Failure on an Fe–16Cr Alloy in the Presence of Compressive Stress

The high temperature oxidation behavior of an Fe–16Cr binary alloy, oxidized under different compressive stresses in air at 900xa0°C, was investigated. Surface and cross-sectional micrographs, observed by scanning electron microscopy, indicated that the resulting morphology of the thermally grown oxide scale depended on the compressive stress. Results showed that oxide scales were infact below 5xa0MPa stress after 10xa0h of oxidation. Delamination developed at the outer/inner oxide scale interface in the case of compressive stress above 5xa0MPa. Growth kinetics measurements revealed that the rate of oxide-scale growth increased by the compressive stress.

Effect of Compressive Stress on the High-Temperature Oxidation Behavior of a Fe-20Ni Alloy in Air

The oxidation behavior of Fe-20Ni alloy under compressive stress in air was studied at 800, 900 °C. The results examined by using scanning electron microscope (SEM) and X-ray diffraction (XRD) indicates that the oxide scales were consisted of an external scale and a subscale which has an intragranular scale (above 5 h at 800 °C and 900 °C) and an intergranular scale. Compared with the unstressed specimen, the growth kinetics of external scale was accelerated by an applied compressive stress. Besides, the compressive stress induced an increase in the growths of intragranular scale and intergranular scale formed on the specimens oxidized at 900 °C. However, the effect of compressive stress on the growth of intergranular scale and intragranular scale was not obvious in the case of 800°C. In addition, cracks developed in the subscale for the specimens oxidized under 2.5 MPa compressive stress when the oxidation time exceeded 20 h.

The Fabrication of W-Cu Modified Layers on the Surface of the Continuous Casting Machine Mould Copper Plate by Infiltration

In this paper, a new method named infiltration was applied to fabricate W-Cu surface modified layers of copper mould firstly in order to promote the life span of the continuous casting machine (CCM) mould. Our efforts concentrated on fabricating the W-Cu modified layers on the surface of mould copper plate by presintering and infiltration under inert gases. The W particle size and sintering temperature of W skeleton were adjusted to gain homogeneous microstructure of W-Cu modified layers. The results show that homogeneous microstructure of W-Cu modified layers can be obtained with the method of presintering and infiltration. For the excellent microstructure of W-Cu modified layers, the suitable tungsten particle size is 300 meshes and the optimal presintering temperature is about 1300°C. W-Cu modified layers have good bonding strength with copper substrate.