mungosforge

It's my understanding that ductile iron can be surfaced hardened by torching the surface to 900c and then hitting it with a spray quench. You might check out : http://www.ductile.org/didata/Section7/7intro.htm#Surface Hardening There also are apparently some interesting effects on work hardening the surface. Actually some of the stuff I'm running across indicates that ductile iron work hardens far better than grey iron: http://books.google.com/books?id=NbgtnLo7jhwC&pg=PA77&lpg=PA77&dq=work+hardening+ductile+iron&source=bl&ots=IjP6Pk7M_D&sig=KIQcvUPMIEJjrVAu7Q41IC1_k0c&hl=en&sa=X&ei=KttJUc7xL5fI4APmzIG4BQ&ved=0CD8Q6AEwAQ#v=onepage&q=work%20hardening%20ductile%20iron&f=false This also from the Ductile.org website: The presence of stable, carbon enriched austenite also accounts for another inadequately understood property of ADI. While thermodynamically stable, the enriched austenite can undergo a strain-induced transformation when exposed to high, normal forces. This transformation, which gives ADI its remarkable wear resistance, is more than mere "work hardening". In addition to a significant increase in flow stress and hardness (typical in most metallic materials), this strain induced transformation also produces a localized increase in volume and creates high compressive stresses in the "transformed" areas. These compressive stresses inhibit crack formation and growth and produce significant improvements in the fatigue properties of ADI when it is machined after heat treatment or subjected to surface treatments such as shot peening, grinding or rolling