Comparative Machinability of Bloom Cast Free Cutting Steels 970520
The relative machinability of four low carbon, resulfurized, rephosphorized free cutting steels (1215, 12L14, 1214+0.1wt%Bi & 1214+0.2wt%Bi) were evaluated using a modified ASTM E618 machine form tool wear test.
The chemical, mechanical and micro-structural characteristics of these four steels are compared and correlated to the machining performance.
The 1215 consistently survived 8 hours machining at 77.4m/min (meters/minute)[(254sfpm (surface feet per minute)] and 4 of 6 tests passed 8 hours at 85.3m/min (280sfpm). The 12L14 survived 8 hours at 85.3m/min (280sfpm), but consistently failed the test at 95.1m/min (312sfpm). The 1214+0.1wt%Bi consistently survived 8 hours at 95.1m/min (312sfpm), but failed at 111m/min (364sfpm). The 1214+0.2wt%Bi also survived 8 hours at 95.1m/min (312sfpm) and one of six tests passed 8 hours at 111m/min (364sfpm).
At each test speed the rough form tool and finish form tool generated surface roughness (Ra) was monitored. The Ra of the rough form tool generated surface was highest for 1215 and smoothest for 1214+0.2wt%Bi. The Ra of the finish form tool generated surface was found to be the smoothest for the 1215.