Development and microstructure characterization of BG110E high-strength expansion pipe

The BG110E high-strength expansion pipe was developed using medium manganese steel and subjected to a two-phase zone heat treatment process.Mechanical properties and microstructure analysis results have proven that the BG110E expansion pipe exhibits uniform elongation of more than 19%.Moreover,after undergoing expan-sion deformation,its strength,toughness,and plasticity are found to meet the stringent requirements of the P110 pipe.The microstructure of this high-strength expansion pipe,which has a strength of 110 ksi(1 ksi=6.895 MPa),consists of tempered martensite,ferrite,retained austenite,and granular bainite.The propotion of retained austenite reaches up to 12%,ensuring high plasticity and the occurrence of the transformation-induced plasticity effect during the deformation process.Consequently,it enhances the coordinated deformation ability between different phases,which significantly improves the internal yield pressure of the BG110E high-strength expansion pipe in turn.

Mechanical Properties and ITZ Microstructure of Recycled Aggregate Concrete Using Carbonated Recycled Coarse Aggregate

The effect of carbonation treatment and mixing method on the mechanical properties and interfacial transition zone（ITZ） properties of recycled aggregate concrete（RAC） was investigated. Properties of recycled concrete aggregate（RCA） were tested firstly. Then, five types of concretes were made and slump of fresh concrete was measured immediately after mixing. Compressive strength and splitting tensile strength of hardened concrete were measured at 28 d. Meanwhile, the microstructure of RAC was analyzed by backscattered electron（BSE） image. It was found that the water absorption ratio of carbonated recycled concrete aggregate（CRCA） was much lower when compared to the untreated RCA. Comparatively, the apparent density of CRCA was not significantly modified. The concrete strength results indicate that the mix CRAC-2 prepared with CRCA by adopting two-stage mixing approach shows the highest compressive strength value compared to the other mixes. The microstructural analysis demonstrate that the mix CRAC-2 has a much denser old ITZ than the untreated RAC because of the chemical reaction between CO2 and the hydration products of RCA. This study confirms that the ITZ microstructure of RAC can be efficiently modified by carbonation treatment of RCA and encourages broadening the application of construction and demolition wastes.

Precipitation Softening and Precipitate Free Zones of V_(55)Ti_(30)Ni_(15) Alloys During Heat Treatment

The microstructure, hardness, and precipitate free zones（PFZ） of V55Ti30Ni15 alloys during heat treatment have been investigated in this study. The microstructure resulting from different heat treatment conditions has a great influence on hardness. The microstructure resulting from different heat treatment conditions has a great influence on hardness. Fine Ni Ti particles precipitate from the supersaturated V-matrix solid solution at 750 °C, increase in quantity until 800 °C, and then dissolve back into the V-matrix at 850 °C. The resultant hardness decreases with temperature until 800 °C, and then increases from 800 to 850 °C. The microstructure containing small Ni Ti precipitates resulting from the treatment of 18 h at800 °C has a good soft condition for workability. PFZ formed at the grain boundary of V-matrix during heat treatment was observed. Vacancies depletion in V-matrix maybe led to the formation of PFZ.