Microstructures and Crack Formation in Hot Compression Test of Ultrahigh Carbon Steel

Abstract

Experimental works were carried out to investigate microstructure and crack formation during compression tests of 1.9wt%Cultrahigh carbon steel according to temperature and strain rate. As-received ultrahigh carbon steel is composed of precipitated cementites and pearlite matrix. In addition, numerous voids were observed in the matrix of as-received material. The compression tests at 800oC showed that the voids within the matrix are closed with increase of reduction ratio. On the other hand, when the reduction ratio increased numerous micro-cracks were newly formed in the bulky cementites and at the interfaces between hard cementite and soft matrix. It was also observed that because the volume fraction of cementite is reduced when temperature increased, volume fraction of newly formed micro-crack significantly decreased. Cast microstructures were observed after compression test at 1130oC due to local melting. From experimental results and microstructure anlayses, it was concluded that the forging temperature should be controlled at the temperature of more than 900oC and less than 1130oC.