Just extracted two broken M10 bolts in block

[JohnMc]

Cannot believe it actually worked. One of the bolts was 12.9 hardness.
Heated bolts with Mapp/Oxy torch until as hot as I could get it (parts were red hot). Let cool down by itself to hopefully remove tempering from bolts.
Used a center punch with 2 pound hammer to make indentation. (probably overkill).
Drilled almost all the way through the center of bolts with 1/8 inch left hand drill bit with drill in reverse.
Then used a 1/4 inch left hand drill bit with drill in reverse and in just a short time the bolt start unscrewing and came out.
No damage.
Found all this stuff out on the internet. So many sites just said do not use Easyouts - as they break off and then you have a high tempered piece of steel that is a bugger to get out.

1970 Fiat 124 Spider -

[sgkent]

the heating removed the temper. Another solution is to soak with penetrating oil for awhile Manifold bolts, nuts and studs sometimes are so tight they will snap with a wrench but with penetrating oil and a couple hours they almost come off hand tight.