Analysis of Precipitates in Welded Joint of TP347H Stainless Steel

The precipitates in welded joint heat affected zone (HAZ) and base metal of TP347H stainless steel were observed and analyzed by SEM, TEM and EPMA. The results show that precipitate of NbC can be observed in welded joint HAZ in as-welded, and more NbC precipitate in high temperature service. The size of primary NbC in base metal ranges from tens of nanometers to hundreds of nanometers, but only tens of nanometers of the precipitated NbC. The fine precipitate of NbC is mainly distributed in the crystal, however, continuous distribution of NbC is also observed on the grain boundary of the service joint. Cr carbide precipitates at the grain boundary, and some of particles distribute continuously on the grain boundary after service. The fine NbC precipitated in the crystal strengthens the matrix, and the continuous distribution of Nb and Cr carbides on the grain boundary reduces the interfacial bonding strength, then both of which result decrease of the material plasticity.

Microalloying Additions to Commodity C-Mn Structural Steels: Fundamental Strengthening Mechanisms Leading to Improvements in Mechanical Properties, Alloy Optimization, Reduced Alloy Costs and Robustness of Hot Rolling Processing

Niobium in steels can be used as substitutional solid solute or as precipitates. In solution, Nb exerts a solute drag effect delaying but usually not interrupting static recrystallization during hot rolling and increasing hardenability during post rolling cooling. Fine precipitates generated during rolling/cooling can interrupt recrystallization in finishing and precipitate in the ferrite matrix increasing strength. As a relatively fine precipitate Nb can also inhibit austenite grain growth during reheating.This paper highlights the idea that micro-additions of Nb, up to 0.02%, to ordinary commodity C-Mn structural steels can improve their strength. Industry trial results are presented giving evidence that mechanical properties can be improved, and a leaner/optimized chemistry may be used by adding these micro-quantities of Nb to otherwise ordinary commodity C-Mn steels.Microstructural analysis of a C-Mn vs. a leaner/optimized C-Mn-micro Nb steel along with austenite evolution modeling using MicroSim-PM©helped identifying which type of metallurgical mechanisms are in-play resulting in higher strengths. This alternative composition has led to lower costs, lower CE, improved microstructure and a more stable process.

Mechanical and Erosion Behaviour of Ti47Al-3W/TI2ALC Composites by Reactive Arc-Melting

Ti-50Al alloy and Ti-47Al-3W alloy and its composites have been prepared by reactive arc melting technique using elemental powders. Composites have been reinforced using 3.5, 10 and 18 vol% of Ti2AlC in the matrix of TiAl with and without addition of W and C. By the addition of tungsten and carbon to TiAl alloy, we have produced composites that are reinforced randomly by reacted rod like Ti2AlC particles with fine precipitate of Ti2AlC particles and B2 particles. Compared to Ti-50Al alloys, the Ti-47Al-3W alloy and its composites have superior mechanical properties like bending strength, hardness, fracture toughness and erosion. Ti-47Al-3W/3.5 vol% Ti2AlC has excellent erosion resistance because of the dispersion of fine Ti2AlC and B2 particles in the matrix.

The Preparation of III-V Semiconductors in Aqueous Solution

Indium arsenide colloids have been prepared by passing arsine through an aqueous solution of the metal nitrate. Similar experiments with gallium solutions produced an extremely fine precipitate which has been tentatively identified as amorphous gallium arsenide. Attempts to precipitate aluminium arsenide from aqueous solutions or mixed organic solvent systems were unsuccessful. The materials were characterised by transmission electron microscopy, X-ray powder diffraction and and optical absorption spectroscopy.