Low carbon steel (e.g., 1020) is usually used for case hardening,
because you usually want a very ductile core inside the hard, brittle
outer surface. That way any cracks in the brittle surface do not
propogate through the whole part. The quench gives the greatest
hardness to the steel that is highest in carbon and nearest the
surface.

The link below shows EN1A has .15% (max) carbon and is similar to 1215.
It also has .07% phosphorus which acts like carbon to some extent.
With ~.2% carbon-equivalent it should work well.

links:
http://www.gulfstreamsteel.com/Excel%20spec%20files/comparison%20of%20USA%20standards%20(chemistry).xl s
http://yarchive.net/metal/case_hardening.html

David