Erzsébet Czopyk Jan 2, 2016:

to form a question is also important - help the others giving all sources and as much context as possible

Lucia Valentino (asker) Jan 2, 2016:

Esatto, è questo il testo di partenza.

Erzsébet Czopyk Jan 2, 2016:

is that your text? (I guess) Confirmation of the segregation of boron to grain boundaries and its presence in the carbides was obtained by autoradiography.114 Das et al. compared a grade 91 steel and a boron-containing variant.117 In addition to a uniform grain size across the HAZ for the boron-containing steel and a smaller trough in the hardness profile, they claimed that the consequent reduction in the ‘metallurgical notch’ contributed to the avoidance of type IV failure.

http://www.twi-global.com/technical-knowledge/published-pape...

Erzsébet Czopyk Jan 2, 2016:

Alloy development

Boron
In view of the severe degradation in creep rupture strength that welding introduces in currently available steels, it is desirable to develop steels in which such degradation is much diminished. One approach to improving the creep rupture strength of the type IV region is to modify the parent steel composition. The most promising step towards the elimination of poor cross-weld creep strength has been the addition of boron as an alloying element, shown to improve creep strength in general for 9%Cr steels; low concentrations are present in coded steel grade 92, for example (the specified range is 0•001–0•006 wt-%).111 Higher concentrations have been shown to enhance the creep strength, with the TAF steels developed in the late 1990s by Fujita at NIMS (0•04%B) still being unsurpassed.112,113 Boron is reported to combine with M23C6 precipitates and prevent their coarsening and the onset of tertiary creep.114 Abe explained that theoretically, boron will segregate to grain boundaries during austenitising at 1100°C.115,116 During tempering at ~800°C, boron at the boundaries is incorporated into the precipitating carbides, giving M23(C,B)6 precipitates.

Lucia Valentino (asker) Jan 2, 2016:

Correggo: mi servirebbe sarebe il significato di "a smaller trough in the hardness profile", a differennz di quanto ho riportato nel titolo