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.

Strengthening Mechanism and Carbide Precipitation Behavior of Nb-Mo Microalloy Medium Mn Steel

This study investigates the strengthening mechanism and carbide precipitation behavior of medium Mn steel with Nb-Mo microalloy after cyclic quenching and austenite reverse transformation treatment. The results show that the Nb/Mo element not only precipitates (Nb,Mo)C in the grains, hindering the movement of dislocations and increases the strength, but also segregates at the austenite/ferrite grain boundary, thus delaying the transformation from austenite to ferrite. In addition, a large amount of nano-scale cementite is retained after cyclic quenching and austenite reverse transformation, which has a positive effect on the proportion of retained austenite in medium Mn steel. Moreover, the carbides with small size and low Mn content are dissolved, and the decomposed C and Mn content are beneficial to the nucleation of austenite during the intercritical annealing process at a temperature of 690 °C.

Tailoring the Austenite Fraction of a Cu and Ni Containing Medium-Mn Steel via Warm Rolling

Developing medium-Mn steels (MMnS) demands a better understanding of the microstructure evolution during thermo-mechanical treatments (TMTs). This study demonstrates the relationship among processing, microstructure, and mechanical properties of a warm-rolled medium-Mn steel (MMnS) containing 1.5 wt. % Cu and 1.5 wt. % Ni. After short-time warm rolling (WR) in an intercritical temperature range, a significant quantity (40.6 vol.%) of austenite was reverted and retained after air cooling. The microstructure and tensile properties of the WR specimens were compared with two typical process routes, namely hot rolling+ cold rolling+ annealing+ tempering (CRAT) and warm rolling+ annealing+ tempering (WRAT). The WR specimen exhibited comparable tensile properties with the CRAT specimens (967 MPa yield strength, 1155 MPa tensile strength, 23% total elongation), with a remarkably shortened process route, which was derived from the dislocation accumulation and austenite reversion during rolling. The WR route stands out among the traditional CRAT and the extended WRAT routes for its excellent tensile properties and compact processing route.

A Scale-up Study on Chemical Segregation and the Effects on Tensile Properties in Two Medium Mn Steel Castings

Two ingots weighing 400 g and 5 kg with nominal compositions of Fe–8Mn–4Al–2Si–0.5C–0.07V–0.05Sn were produced to investigate the effect of processing variables on microstructure development. The larger casting has a cooling rate more representative of commercial production and provides an understanding of the potential challenges arising from casting-related segregation during efforts to scale up medium Mn steels, while the smaller casting has a high cooling rate and different segregation pattern. Sections from both ingots were homogenized at 1250 $$^{\circ} $$ ∘ C for various times to study the degree of chemical homogeneity and $$\delta $$ δ -ferrite dissolution. Within 2 hours, the Mn segregation range (max–min) decreased from 8.0 to 1.7 wt pct in the 400 g ingot and from 6.2 to 1.5 wt pct in the 5 kg ingot. Some $$\delta $$ δ -ferrite also remained untransformed after 2 hours in both ingots but with the 5 kg ingot showing nearly three times more than the 400 g ingot. Micress modeling was carried out, and good agreement was seen between predicted and measured segregation levels and distribution. After thermomechanical processing, it was found that the coarse untransformed $$\delta $$ δ -ferrite in the 5 kg ingot turned into coarse $$\delta $$ δ -ferrite stringers in the finished product, resulting in a slight decrease in yield strength. Nevertheless, rolled strips from both ingots showed $$>900$$ > 900 MPa yield strength, $$>1100$$ > 1100 MPa tensile strength, and $$>40$$ > 40 pct elongation with $$<10$$ < 10 pct difference in strength and no change in ductility when compared to a fully homogenized sample.

Critical Redistribution of Nitrogen in the Austenitic Cr-Mn Steel under Severe Plastic Deformation

A narrow temperature range of changes in the mechanism and kinetics of structural-phase transformations during mechanical alloying under deformation in rotating Bridgman anvils was determined by the methods of Mössbauer spectroscopy, electron microscopy, and mechanical tests in the high-nitrogen chromium-manganese steel FeMn22Cr18N0.83. The experimentally established temperature region is characterized by a change in the direction of nitrogen redistribution—from an increase in the N content in the metal matrix during cold deformation to a decrease with an increase in the temperature and degree of severe plastic deformation. The change in the direction of nitrogen redistribution is due to the acceleration of the decomposition of a nitrogen-supersaturated solid solution of austenite with the formation of secondary nanocrystalline nitrides. The presence of a transition region for the mechanism of structural-phase transitions is manifested in the abnormal behavior of the mechanical properties of steel.