There are 3 main options for treating cranks and as far as I can remember Alfa chose tuftriding. Here is an explanation of the processes, hot cyanide non the less!:
Tuftriding was a process used by some OEM's on special high-performance crankshafts, primarily to avoid the stresses imposed by induction hardening. In Tuftriding, the crankshaft is immersed in hot cyanide compounds, creating a tough, resistant surface that improves fatigue resistance. The hard layer in a Tuftrided crank is usually very shallow, only penetrating around .005. One drawback of Tuftriding is the potential for warpage of the crank.
Nitriding is a chemical hardening process in which the part is heated in a furnace, the oxygen is vacuumed out, and nitrogen is introduced which penetrates the entire surface. The depth of hardness is dependent upon the time the crankshaft is exposed to the gas. Typically, a nitrided crankshaft will have a hardness depth of about .010 - .030. Nitriding is a low heat process compared to Tuftriding, but it shares the advantage of avoiding the introduction of localized stress zones as in induction hardening.
In most cases, a stock OEM steel forged crankshaft can be welded and/or ground then installed without concern. The induction hardening process has a significant depth, and on non welded journals will remain after being ground.
Tuftrided crankshafts can be welded and ground without concern. However, the shallow depth of the hardness would be lost after the grind. Therefore, it is recommended to have the crankshaft hardened again.