Titanium Carbosulfide Research Articles

Structural and phase inhomogeneity of cast corrosion-resistant steels of the austenitic class

1. The kinetic dependence of the amount of nontransformed ferrite on the speed of crystallization is nonmonotonic; this has to do with the thermal conditions and liquation phenomena in the forming of large ingots of austenitic corrosion-resistant steels. 2. In steels type Kh18N10T microliquation of nickel is direct, of chromium inverse. The maximal chemical inhomogeneity of sulfur, nickel, and titanium found in steel ingots is due to dendritic liquation, interphase redistribution, and chemical interaction between these elements. 3. Intergranular fracture of titanium-containing corrosion-resistant steels can be initiated by titanium carbosulfides which embrittle the austenitic matrix both in temperature ranges near the solidus and at normal temperature.

A comparison of the fracture behavior of two commercially produced heats of HY180 steel differing in sulfide type

The mechanical properties of two heats of HY180 steel are compared after aging at 425 °C or 510 °C. The two heats of material appear very similar microstructurally, except most of the sulfides in one are believed to be titanium carbosulfides, while the sulfides in the other heat appear to be manganese sulfides. At both aging temperatures, the crack tip opening displacement at fracture (δIC) of the heat containing the titanium carbosulfides is over twice that of the heat containing the manganese sulfides. Measurements of the void volume fracture as a function of strain indicate that the titanium carbosulfide particles are much more resistant to void nucleation than are the manganese sulfide particles. The unusually high toughness of the heat containing the titanium carbosulfides is attributed to this increased resistance to void nucleation.

Sulfide Stability, Void Nucleation and the Toughness of Ultra High Strength Steels

The upper shelf fracture toughness of ultra high strength steels is dependent on both the microstructure, which is determined by composition and heat treatment, and on the inclusions present in the steel. The inclusions In ultra high strength steels are typically oxides and sulfides [1]. In most ultra high strength steels the sulfides are manganese sulfides, although depending on the composition of the steel and the melt practice used, other sulfides are found, such as chromium sulfide, calcium sulfide and lanthanum oxy-sulfide [2]. If the inclusions can be regarded as pre-existing voids then the inclusion volume fraction and spacing appear to be sufficient to characterize the inclusion population from the standpoint of fracture toughness [3,4]. The purpose of this paper is to discuss results which show sulfur can be gettered as particles which are much more resistant to void nucleation than manganese sulfides and that this increased resistance to void nucleation can result in vastly improved upper shelf fracture toughness. In particular, when HY180 steel contains manganese sulfides the fracture toughness is about 250 MPa but when the sulfur is gettered as particles containing titanium, carbon and sulfur the fracture toughness of HY180 steel will approach 550 MPa . These particles, believed to be titanium carbosulfides, are much more resistant to void nucleation than manganese sulfides and this increased resistance to void nucleation appears to be the reason for the improved fracture toughness.

Sulfides and carbides in 18-8 type steels

1. Crystallization of corrosion-resistant 18-8 type steels with additions of titanium ceases with eutectic transformation. First from the liquid there is separation of titanium carbosulfide eutectic, and then at a lower temperature titanium carbide eutectic forms. 2. In 18-8 type steels even with a small carbon and sulfur content a considerable amount of eutectic forms as a result of dendrite liquation of sulfur and carbon. In ingots and castings during cooling after solidification carbides and carbosulfides hardly separate from austenite. These inclusions may only precipitate after high-temperature heating of the steel (to 1200–1340°C), with which a considerable amount of eutectic titanium carbides and carbosulfides dissolves in austenite. 3. In industrial 18-8 type steels complex sulfides (Mn, Ti) and (Fe, Ti) are not observed.