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:
Yield strength of highly dislocated metals is known to be directly proportional to thesquare root of dislocation density (ρ), so called Bailey-Hirsch relationship. In general, themicrostructure of heavily cold worked iron is characterized by cellar tangled dislocations. On theother hand, the dislocation substructure of martensite is characterized by randomly distributeddislocations although it has almost same or higher dislocation density in comparison with heavilycold worked iron. In this paper, yielding behavior of ultra low carbon martensite (Fe-18%Ni alloy)was discussed in connection with microstructural change during cold working. Originally, theelastic proportional limit and 0.2% proof stress is low in as-quenched martensite in spite of its highdislocation density. Small amount of cold rolling results in the decrease of dislocation density from6.8x1015/m-2 to 3.4x1015/m-2 but both the elastic proportional limit and 0.2% proof stress aremarkedly increased by contraries. 0.2% proof stress of cold-rolled martensite could be plotted onthe extended line of the Bailey-Hirsch equation obtained in cold-rolled iron. It was also confirmedthat small amount of cold rolling causes a clear microstructural change from randomly distributeddislocations to cellar tangled dislocations. Martensite contains two types of dislocations;statistically stored dislocation (SS-dislocation) and geometrically necessary dislocation(GN-dislocation). In the early deformation stage, SS-dislocations easily disappear through thedislocation interaction and movement to grain boundaries or surface. This process produces aplastic strain and lowers the elastic proportional limit and 0.2% proof stress in the ultra low carbonmartensite
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/14/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.539-543.228.pdf
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