ISSN:
1662-9752
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
The effect of boron on microstructure and creep deformation behavior has beeninvestigated for a tempered martensitic 9Cr-3WVNb steel with emphasis on the role of boron freefrom boron nitrides. Creep tests were carried out at 650oC for up to about 3 x 104 h, usingspecimens of 10 mm in gauge diameter and 50 mm in gauge length. The addition of boron incombination with no nitrogen addition effectively reduces the coarsening rate of M23C6 carbides byan enrichment of boron in M23C6 particles in the vicinity of prior austenite grain boundaries duringcreep at 650oC. This stabilizes martensitic microstructure during creep and retards the onset ofacceleration creep, resulting in a decrease in minimum creep rate and an increase in creep life.Excess addition of boron and nitrogen causes the formation of boron nitrides during normalizing at1050-1150oC, which reduces dissolved boron and nitrogen. The dissolved boron enriches inM23C6 carbides, while the dissolved nitrogen causes the precipitation of fine MX carbonitrides.The variation of creep rates in transient region and of the onset time of acceleration creep withvarious combinations of boron and nitrogen contents can be explained by the dissolved boron andnitrogen concentrations after normalizing into account
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/15/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.539-543.2982.pdf
