Quantitative Test and Engineering Application of Wear Resistance of a Kind of Mine-Filled Composite Pipeline

Wear resistance is one of the most important performance indicators of filling pipelines, but there are few studies on its quantitative test and life prediction. In this paper, an experimental device and its application method for testing the wear resistance of the pipeline are proposed, and the device is used to test the wear resistance of the self-developed lining composite pipeline, the traditional 16 Mn steel pipeline and the ordinary carbon structural steel pipeline. The results show that the wear resistance of the composite lining material is 12.35 times of that of 16 Mn steel and 7.32 times of that of ordinary carbon structural steel. The wear resistance mechanism is analyzed from the perspective of the material composition of the composite liner, mainly because the composite liner material uses fused alumina grain sand, silicon carbide and other extremely wear-resistant materials with high hardness as aggregate, and the aggregates are spherical or nearly spherical particles, with smooth surface and small friction resistance. Finally, through a comparison engineering application of a certain iron ore concentrate transportation. Compared with the traditional 16 Mn steel pipeline, the composite lined pipeline has been used for more than 5 years without any problems, while the traditional 16 Mn steel pipeline is worn through within 1 year. Engineering application shows that the composite lined pipeline has good wear resistance, and it also confirms the reliability of the detection method proposed in this paper.

Study on MnS Inclusion Aggregation along Continuous Casting Slab Thickness of Medium Carbon Structural Steel

Precipitation of MnS inclusions in steel affects the mechanical properties of the material significantly. The evolution of MnS inclusions along the continuous casting slab thickness and its influencing factors has not been clearly established and comprehensively studied. In this paper, solidification macrostructure, sulfur segregation and MnS inclusions in the continuous casting slab of medium carbon structural steel 45# were studied by various methods, including the metallographic observations, elemental analysis, scanning electron microscope (SEM) with Energy Dispersive Spectrometer (EDS) observation, automatic particle analysis, and thermodynamic calculations. The 2D/3D morphologies of MnS inclusions suggest that the sulfides turn from globular to rodlike, and further to dendritic shape along the slab thickness progressively. Furthermore, it was found that MnS inclusions are remarkably aggregated in the columnar crystals and the equiaxed crystals mixed zone, where the sulfides have the largest average diameter of 6.35 μm and the second maximum area fraction of 0.025% along the slab thickness. In order to reveal the mechanism of this phenomenon, the precipitation temperature of MnS inclusion in the 45# steel was clarified by thermodynamic calculation and experimental observation, and the quantitative relationships among the distribution of sulfur content, secondary dendrite arm spacing (SDAS), and precipitation area fraction of MnS inclusions were discussed. Moreover, the inclusion size was numerically predicted to compare with the measured value. The results indicate that the large SDAS, high sulfur content and low cooling rate accounting for the large-size aggregated MnS inclusions in the mixed zone. Unfortunately, the dendritic MnS inclusions, even if the average diameter exceeds 52 μm, can act as the nucleation sites for ferrites, and the distribution of the sulfides promotes uneven microstructure in the steel.

Dilatometric Analysis of the Austenite Decomposition in Undeformed and Deformed Low-Carbon Structural Steel

This paper aims to analyze the effect of deformation on the phase transformation kinetics of low-carbon structural steel. The steel used for the investigation was subjected to two different dilatometric analyses using a DIL 805A/D device. The first analysis was to determine the phase transformation kinetics without deformation of austenite before cooling. Then, the analysis under deformation conditions was conducted to investigate the deformation effect on the transformation kinetics. Microscopic studies by light microscopy were performed. The essential part of the research was hardness analysis for different cooling rates and the creation of continuous-cooling-transformation (CCT) and deformation continuous-cooling-transformation (DCCT) diagrams. It was found that the deformation of the samples before cooling increases a diffusion rate in the austenite resulting in the corresponding increase of ferritic, pearlitic, and bainitic start temperatures, as well as shifting the austenite transformation product regions to a longer time. The increase of the transformation area and a decrease in grain size are observed for the deformed samples.

Effect of Oxide Particles on Microstructure and Mechanical Properties of the 45 Carbon Structural Steel

Striking difference in density between the oxide and the steel results in difficulty in preparing oxide dispersion strengthened steel with large size parts or materials. In this research, Al2O3 and TiO2 particles were initially milled with the 20 steel, and then the mixture was heated to a molten state to form a master alloy, which was used as a raw material for further preparation of the object steel. It was found that homogeneous distribution of the oxide particles was obtained in the mass production of the steel. Moreover, the obtained 45 carbon structural steel presents fine microstructures, together with improved mechanical properties, especially the impact ductility. This should be attributable to the transformation from the introduced micro-size oxide particles to the nano ones, which act as heterogeneous nucleants that play an important role in grain refinement and dispersion strengthening for the steel, during the remelting of the master alloy.