Microstructures and hardness of as-quenched martensites (0.1-0.5%C)
Artikel i vetenskaplig tidskrift, 2011

Four commercial steels with carbon contents in the range 0.1-0.5 wt.% have been examined in the as-quenched condition using electron microscopy, X-ray diffraction and atom probe tomography. The austenite had been deformed 0%, 10% and 30% prior to brine quenching. No influence of this deformation was evident on the martensite hardness or in any of the microstructure measurements. Increasing carbon content showed a well-known marked effect on the hardness but resulted in little refinement in the grain structure of the martensite. All crystal structures were cubic; no evidence of tetragonality was seen even at the highest carbon level but some systematic changes in grain boundary misorientations existed. The content of carbon in true interstitial solid solution deduced from X-ray line shifts was small (similar to 0.02 wt.%), and was independent of the total carbon content in the steel. Atom probe tomography showed that carbon was almost completely segregated to lath boundaries and dislocations but with an increasing density of segregates in the higher carbon steels. Calculations of diffusion distances confirmed that the segregation patterns were compatible with autotempering of the martensite during quenching. Analysis of different possible contributions to strength leads to the conclusion that segregated carbon atoms at defects behave similarly to carbon in true solid solution and that this is the largest single factor controlling the strength of as-quenched martensite. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

iron

Steel

Electron microscopy

field-ion microscopy (AP-FIM)

steel

Martensite

Microstructure

Atom-probe

Författare

B. Hutchinson

Swerea KIMAB

J. Hagstrom

Swerea KIMAB

Oskar Karlsson

Swerea KIMAB

D. Lindell

Swerea KIMAB

M. Tornberg

Swerea KIMAB

F. Lindberg

Swerea KIMAB

Mattias Thuvander

Chalmers, Teknisk fysik, Mikroskopi och mikroanalys

Acta Materialia

1359-6454 (ISSN)

Vol. 59 5845-5858

Ämneskategorier

Materialteknik

DOI

10.1016/j.actamat.2011.05.061