3.0L GTV6 and tempering steels

["Reid, Warren" <Warren.Reid@xxxxxxxxxxxxxxxxxxx>]

Re Ben Dixons query on 3.0L GTV6s

Ben I believe that quite a few FI 3.0 litre V6 engines got imported into
this country (possibly from the UK or US). Consequently there are a few 3.0
L GTV6s around here in Australia. I know Hugh Harrison here in Melbourne has
installed quite a few. He currently has a Quad Cam 3.3L one in his workshop
right at this very moment (apart from his own race car). He also does Twin
Spark conversions for Alfettas and 105 series (I believe).

Bruce Giller was asking about tempering steel. 
Generally, steel tempering temperatures are anything below about 700C
(1300F) or a soft Cherry red colour. Above that temperature you start to
normalise the steel which produces a change (increase) in the grain size of
the material. With tempering there is no change to the grain structure of
the material, however even at relatively low temperatures subtle things
start to happen. 
	- 100C, precipitation of carbides
	- 250C, retained Austenite begins to decompose (this is about the
straw or wheat colour you refer to)
	- 350C, Cementite begins to form (bluish colour)
	- > 500C, Cementite particles begin to grow in size, and produce a
spheroidized structure.

The time at temperature also makes a difference as all these reactions take
time. Typically tempering temperatures are done for an hour or more to allow
these stages to take place. Substantial softening begins to take place above
about 400C. Usually tempering is a heat treatment applied to alloy steels
after some form of quenching takes place. An alloy steel could be very hard
after a quenching process, however it is also likely to be extremely
brittle. The tempering process softens the steel slightly but greatly
improves its toughness (ie non-brittleness). Care must also be taken with
the type of steel being tempered and the tempering temperature, as some
temperatures (250 - 350 C) can make certain steels (high carbon and alloyed)
very brittle due to the formation of thin films of cementite along grain
boundaries. Other precautions also need to be taken as to the way in which
the steel is heated and the atmosphere surrounding it as decarburization of
the steel can also occur

Following tempering it is necessary to let the steel cool slowly (usually
left in the oven to cool at the same rate as the oven after its turned off).

Warren Reid
Melbourne Australia

68 1750 GTV 
86 Spider Veloce (Euro Spec)
84 Alfetta GCL
(also thinking about a GTV6 - 3.0L?)

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