Growth of bainitic ferrite and carbon partitioning during the early stages of bainite transformation in a 2 mass% silicon steel studied by in situ neutron diffraction, TEM and APT

In situ neutron diffraction, transmission electron microscopy (TEM) and atom probe tomography (APT) have been used to study the early stages of bainite transformation in a 2 mass% Si nano-bainitic steel. It was observed that carbon redistribution between the bainitic ferrite and retained austenite at the early stages of the bainite transformation at low isothermal holding occurred in the following sequence: (i) formation of bainitic ferrite nuclei within carbon-depleted regions immediately after the beginning of isothermal treatment; (ii) carbon partitioning immediately after the formation of bainitic ferrite nuclei but substantial carbon diffusion only after 33 min of bainite isothermal holding; (iii) formation of the carbon-enriched remaining austenite in the vicinity of bainitic laths at the beginning of the transformation; (iv) segregation of carbon to the dislocations near the austenite/ferrite interface; and (v) homogeneous redistribution of carbon within the remaining austenite with the progress of the transformation and with the formation of bainitic ferrite colonies. Bainitic ferrite nucleated at internal defects or bainite/austenite interfaces as well as at the prior austenite grain boundary. Bainitic ferrite has been observed in the form of an individual layer, a colony of layers and a layer with sideplates at the early stages of transformation.

Microstructure and texture evolution during tensile deformation of symmetric/asymmetric-rolled low carbon microalloyed steel

The deformation and fracture mechanisms of a low carbon microalloyed steel processed by asymmetric rolling (AsR) and symmetric rolling (SR) were compared by microstructural and texture evolutions during uniaxial tensile deformation. A realistic microstructure-based micromechanical modeling was involved as well. AsR provides more effective grain refinement and beneficial shear textures, leading to higher ductility and extraordinary strain hardening with improved yield and ultimate tensile stresses as well as promoting the occurrence of ductile fracture. This was verified and further explained by means of the different fracture modes during quasi-static uniaxial deformation, the preferred void nucleation sites and crack propagation behavior, and the change in the dislocation density based on the kernel average misorientation (KAM) distribution. The equivalent strain/stress partitioning during tensile deformation of AsR and SR specimens was modeled based on a two-dimensional (2D) representative volume element (RVE) approach. The trend of strain/stress partitioning in the ferrite matrix agrees well with the experimental results.

Metabolite profiling reveals distinct changes in carbon and nitrogen metabolism in phosphate-deficient barley plants (Hordeum vulgare L.)

Plants modify metabolic processes for adaptation to low phosphate (P) conditions. Whilst transcriptomic analyses show that P deficiency changes hundreds of genes related to various metabolic processes, there is limited information available for global metabolite changes of P-deficient plants, especially for cereals. As changes in metabolites are the ultimate ‘readout’ of changes in gene expression, we profiled polar metabolites from both shoots and roots of P-deficient barley (Hordeum vulgare) using gas chromatography–mass spectrometry (GC-MS). The results showed that mildly P-deficient plants accumulated di- and trisaccharides (sucrose, maltose, raffinose and 6-kestose), especially in shoots. Severe P deficiency increased the levels of metabolites related to ammonium metabolism in addition to di- and trisaccharides, but reduced the levels of phosphorylated intermediates (glucose-6-P, fructose-6-P, inositol-1-P and glycerol-3-P) and organic acids (α-ketoglutarate, succinate, fumarate and malate). The results revealed that P-deficient plants modify carbohydrate metabolism initially to reduce P consumption, and salvage P from small P-containing metabolites when P deficiency is severe, which consequently reduced levels of organic acids in the tricarboxylic acid (TCA) cycle. The extent of the effect of severe P deficiency on ammonium metabolism was also revealed by liquid chromatography–mass spectrometry (LC-MS) quantitative analysis of free amino acids. A sharp increase in the concentrations of glutamine and asparagine was observed in both shoots and roots of severely P-deficient plants. Based on these data, a strategy for improving the ability of cereals to adapt to low P environments is proposed that involves alteration in partitioning of carbohydrates into organic acids and amino acids to enable more efficient utilization of carbon in P-deficient plants.