On the increase of intrinsic workability and hot working temperature range of M42 ledeburitic super high speed steel in as-cast and wrought states

In order to remain competitive to powder metallurgy and spray forming, further improvements of a classical production route are needed and desired. This paper describes the means by which the intrinsic hot deformability may be improved and the temperature range of the safe hot working extended for AISI M42 super high speed steel, one of the most challenging materials with respect to hot deformability. A special hot compression procedure is described to determine appropriate soaking temperatures of as-cast and semi-wrought states. Moreover, conventional hot compression tests in the extended temperature range (850–1150 °C) and strain rates range 0.001–5 s−1 were carried out. The complex behaviour of carbides is discussed, which depends on the soaking temperature and time, deformation temperature and strain rate. Deformation conditions for improved crushing of initial eutectic carbides networks during the first stages of hot working are identified. Apparent activation energies for hot working in two temperature ranges and constants of the hyperbolic sine function are determined. The microstructure and respective carbides are characterised by field emission scanning electron microscope, optical microscopy, X-ray diffraction and the results compared to equilibrium thermodynamic calculations using ThermoCalc.This work was supported by the Slovenian Research Agency (ARRS) under programme grants P2-0344 and P2-0268

Antibacterial activity of endophytic fungi isolated from conifer needles

Fungi, in particular endophytes are a promising source of new antimicrobial compounds. The aim of this study was to screen the extracts of conifer needle fungal endophytes for antimicrobial activity and taxonomically place fungi producing ones to determined active metabolites. Seventy three strains of endophytic fungi were isolated from plant samples, mainly from needles of conifers, and cultured. Extracts of cultured endophytic strains were tested for antimicrobial properties using a microdilution assay. Their activity was compared to that of the antibiotic ampicillin. Samples that exhibited antimicrobial properties were further examined. Genomic DNA from five active fungal strains was isolated and species-specific DNA regions (ITS regions) were amplified and sequenced allowing us to determine the identity of the samples. Active endophytic fungi were two strains of Lophodermium pinastri, two strains of Lophodermium seditiosum and one of Phoma herbarum. All of these strains are known as parasitic and can be treated as endophytes only according to the lack of symptoms in their host tissue. This work demonstrates an interesting bottom-up approach to the discovery of new antimicrobial compounds. Key words: Endophyte, antibiotic, parasitic, Lophodermium, antimicrobial, Phoma