Ragnar,
Vagn Buckwald's book 'Iron, Steel and Cast Iron before Bessemer' (2008) includes metallography of iron and steel objects whose structure has been altered by modern museum annealing for conservation purposes, and (I think) a few objects which he interprets as having been altered by house fires etc - those conditions should be broadly similar to cremation, unless there is also an interaction between the iron and the cremated bone or burning body tissues.
All the best,
David



--------------------------------------------
On Fri, 5/6/15, David Starley <[log in to unmask]> wrote:

 Subject: Re: Questions about iron artefacts from cremation burials.
 To: [log in to unmask]
 Date: Friday, 5 June, 2015, 8:41
 
 Ragnar,Not from
 cremations, but from burials of the Saxon period in the UK.
 I examined spearheads from the site of Wasperton, some of
 which, appeared an metallographic analysis to have been
 deliberately annealed even when they contained hardenable
 steel (in a period when the heat treatment of edged weapons
 and tools was common practise). The picture is not entirely
 clear as some of the weapons were of such poor quality as to
 suggest they were not functional weapons, but made purely
 for deposition. However, some  clearly  incorporated steel, and
 thus might have been expected to have been quenched to
 harden the edge. My suggestion, for a society that had an
 understanding of quenching technology, was that the
 annealing was effectively a means of 'killing' a
 weapon, in much the same way as the deliberate bending also
 encountered. 
 
 I think
 for your period and region of interest, one could expect the
 tools / weapons to ordinarily incorporate a steel edge,
 which would be hardened by heat-treatment for use. Where
 quenched steel is present then a funeral pyre should reach
 sufficient temperatures to make microstuctural changes which
 could be easily identified in well preserved artefacts, or
 supeficially corroded ones. If entirely mineralised such
 identification would be problematic. 
 
 It might
 be worth considering whether the different preservation
 might also result from the use of different iron alloys, or
 combinations of alloys.
 Hope this
 helps David
 Starley PhD 
 75 Albert
 Rd.   Saltaire,
 Shipley,  
 W.Yorks  UK    
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    From: Ragnar Saage
 <[log in to unmask]>
  To:
 [log in to unmask] 
  Sent: Thursday, 4 June
 2015, 21:41
  Subject: Questions
 about iron artefacts from cremation burials.
    
 Hello! I figured there must be studies using
 metallographic analysis
 to distinguish iron
 artefacts that have gone through the funeral pyre
 before deposition from objects that
 haven't.
 
 Have these
 studies been successful?
 
 Is
 the distinction possible with heavily corroded artefacts?
 
 The burial site in question
 lies on the edge of a swamp and there are
 iron artefacts with minimum corrosion
 (supposedly cremated) and
 objects that are
 very heavily corroded (supposedly not cremated). The
 artefacts are spearheads, axes, knives, seaxes
 etc. from AD 10.-12.
 cc. Estonia.
 
 Any help would be greatly
 appreciated.
 
 Best
 wishes,
 
 Ragnar Saage
 University of Tartu
 Estonia