Machinerys mentions steel with low manganese can be very brittle and at
about 4 - 5.5% manganese is so brittle it can be pulverised with a
hammer. Raising the manganese levels further increases the ductility
upto 12% (Hadfield steel) which does have extremely good wear
properties. Looks like one should be careful with the manganese additions.

wrote:

I am not an expert by any means, but googled and found this.

Metallurgical Factors Affecting Transition Temperature

Changes in transition temperature of over 55°C (100°F) can be
produced by changes in the chemical composition or microstructure of
mild steel. The largest changes in transition temperature result from
changes in the amount of carbon and manganese. This transition
temperature is lowered about 5.5°C (10°F) for each increase of 0.1
percent manganese. Increasing the carbon content also has a pronounced
effect on the maximum energy and the shape of the energy
transition-tempera lure curves.

The Mn/C ratio should be at least 3/1 for satisfactory notch toughness.
A maximum decrease of about 55°C (100°F) in transition temperature
appears possible by going to higher Mn/C ratios.

Note this article is talking Manganese not Moly to lower the transition
temperature. Also note if you do some googling that the transition
temperature for mild steel is much higher than -40 F. One of the
causes of the Titanic disaster was that the rivets were made of steel
which failed at approximently plus 32 degrees F . Not minus 32 F.
Similar failure occurred during WWII.

The high strength Kryptonite bike lock will shatter when cooled with a
can of stuff used for cooling electronics ( troubleshooting ) and hit
with a hammer.

You can make a alloy with a lot of manganese which has high wear
qualities. I think it is also high strength, so I don't think that
adding too much manganese is a problem.


Dan