1978 Volume 64 Issue 7 Pages 851-859
Four kinds of ferrite-pearlite steels (JIS S10C, S20C, S40C and S55C steel) have been fractured by static tension in the temperature range from 77K to 300K.
The evaluation of fracture behavior has been made by fracture toughness KC. critical crack opening displacement (COD) ΦC, electron fractographic and metallographic observations. They have had good correlation with acoustic emission (AE) characteristics such as total count, root mean square (RMS) volt and waveforms. The load for calculating fracture toughness was determined from the condition of AE where the count rate was close to zero and the occurence of large RMS volt was ceased. KC and ΦC values were monotonically decreased with the lowering of testing temperatures; the values in S10C steels were the highest, followed by those of S40C steels, S20C steels and S55C steels in order.
The generation characteristics in AE agreed with the transitional fracture behavior under the changes of testing temperature and were classified into three groups; I) cleavage crack type, II) stable crack growth type, and III) mixed type of I) and II). The AE total count remained constant to KIC up to 40MPa·m1/2, independent of carbon content, and they turned to linear relationship to KC.
AE characteristics were dependent on the volume fraction ratio of ferrite and pearlite, and reached to maximum when the ratio was close to 1.
