The effect of sulfide type on the fracture behavior of HY180 steel

In this paper are discussed the effects of sulfide type on the fracture toughness of HY180 steel. Manganese was added to one heat and the sulfides in this heat were MnS. Lanthanum additions but no manganese additions were made to the second heat and the sulfur was gettered in this heat as particles of La2O2S. Neither lanthanum nor manganese additions was made to the other two heats. These two heats were modified by small titanium additions. The sulfur in these two heats was gettered as particles of Ti2CS. After the usual heat treatment for HY180 steel the fracture toughness of the heat in which the sulfur was gettered as MnS was 256 MPa rootm. The fracture toughness of the heat in which the sulfur was gettered as La2O2S was 344 MPa rootm. The fracture toughness of this heat was greater than the fracture toughness of the heat in which the sulfur is gettered as MnS because the particles of La2O2S are larger and more widely spaced than the particles of MnS. The fracture toughness of the two titanium modified heats were 478 MPa rootm- and over 550 MPa rootm. Void generation studies indicate that void generation is more difficult at particles of Ti2CS than at particles of MnS or La2O2S. The improved fracture toughness of the heats in which the sulfur is gettered as Ti2CS is attributed to the particles of (TiCS)-C-2 having greater resistance to void generation than particles of MnS or La2O2S. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.