A Newly Developed Ti-Oxide Bearing Steel Having High HAZ Toughness

Abstract

A study was carried out on the transformation characteristic of a newly developed Ti-O steel in comparison with that of ordinary steels. The microstructure of the weld heat affected zone (HAZ) in the Ti-O steel is characterized by the formation of intragranular ferrite plate (IFP), or so-called acicular ferrite, which was found to start from titanium sesquioxide (Ti2O3) particles dispersed in the matrix of the steel. The welding thermal cycle simulation test on the Ti-O steel showed that IFP development takes place over a wide range of conditions such as heating temperature and chemical composition. The high stability of Ti2O3 particles at high temperature explains the effect of the former condition. The effect of the latter can be well understood from the distribution of Ti2O3 particles, which is irrelevant to the microsegregation of alloying elements such as manganese and niobium. IFP formation restricts development of ferrite side plate, refines the effective grain size, and improves HAZ toughness. Various experimental results suggested that the Ti2O3 particle has an IFP formation function through the manganese sulfide (MnS) attached on it.

Evolution of Size, Composition, and Morphology of Primary and Secondary Inclusions in Si/Mn and Si/Mn/Ti Deoxidized Steels.

“…[1][2][3][4][5][6][7][8][9][10] To date there has been no practical application for the utilization of inclusions as catalysts to the grain refinement in the interior part of steel plates. Yet, utilization of inclusions in steel plates is recently drawing much attention [11][12][13][14][15][16][17] because acicular ferrite microstructures nucleated from inclusions are known to present an optimized combination of mechanical properties.…”

Progress in thermomechanical control of steel plates and their commercialization

“…Examples of application of TMCP steel for building constructions in Japan (modified after [7] Peak temperature (°C) Figure 24. Change in Charpy-V-notch transition temperature of simulated HAZ with peak temperature [66].…”

“…The plates of offshore structures developed use titanium oxide, which is stable even at high temperatures [65]. Figure 24 [66] shows the simulated HAZ toughness, represented by the ductile to brittle transition temperature, of TiO steel in comparison with that of a TiN steel, which does not contain titanium oxide. The toughness of the former is excellent, because titanium oxide particles are stable even in the high-temperature region close to the weld metal and function as effective nucleation sites for the intragranular ferrite transformation.…”

Weldability Evaluation of Api 5l X52 Steel and Heat-Affected Zone (Haz) Simulation Using Gleeble

“…The BM and SCHAZ regions also exhibited a slight decrease in toughness that was not observed in the ICHAZ, FGHAZ, and CGHAZ regions when tested at a lower temperature of -40 o C The maintenance of good toughness for the HAZ regions at low temperatures can be partially attributed to the formation of retained austenite in the HAZ microstructures, which has been shown to have a beneficial effect on toughness. These toughness values of different simulated samples are validated by following reference paper [10,12]. The effect of retained austenite has been attributed to acting as a sink for elements deleterious to fracture toughness such as carbon, and in disrupting the crystallographic alignment of the martensite packets.…”