Hydrogen Trapping in Quenched and Tempered 0.42C-0.30Ti Steel Containing Bimodally Dispersed TiC Particles

Abstract

The effect of tempering on hydrogen trapping in 0.42C-0.30Ti steel was studied by means of a hardness test, hydrogen thermal desorption spectrometry and high resolution transmission electron microscopy. In addition to the coarse undissolved TiC particles, fine TiC particles with a volume fraction up to 0.22 % precipitated during tempering at temperatures above 500°C. Coherent TiC square platelets with a diagonal length of about 2 nm and a thickness of less than 1 nm precipitated at 550 and 600°C, acting as reversible hydrogen traps. Tempering at 700°C caused the fine TiC particles to lose their coherency with the matrix, resulting in a very limited increase in reversibly trapped hydrogen content compared to the samples tempered below 500°C without TiC precipitation. On the other hand, the coarse undissolved TiC particles with an average diameter of 2 mm, acting as irreversible traps, greatly enhanced the irreversibly trapped hydrogen content when tempered at 500°C and were accompanied by a decrease in hydrogen desorption rate peak temperature. Comparison of both types of TiC particles with the same volume fraction indicated that the fine coherent TiC platelets were more effective in trapping hydrogen than the coarse incoherent undissolved TiC particles.KEY WORDS: hydrogen trapping; reversible and irreversible traps; titanium carbide; coherency; thermal desorption spectrometry; high resolution transmission electron microscopy.

Application potential of high performance steels for weight reduction and efficiency increase in commercial vehicles

“…This is due to the hydrogen trapping effect of microalloy precipitates (see Fig. 14) [12]. With increasing tempering temperature, the amount of microalloy precipitates increases and so does the hydrogen trapping potential.…”

Effect of Ti on Evolution of Microstructure and Hardness of Martensitic Fe–C–Mn Steel during Tempering

“…The heating up time to the tempering temperature is 138 s. The tempering temperature of 300°C is chosen to assure that all Ti atoms remain in solid solution and the tempering level of 550°C is chosen to assure that TiC nucleation and growth takes place during tempering. 8,9) All specimens are prepared by grinding and polishing to 1 μm diamond dispersion, followed by 5% nital etching or electro-polishing conducted in a solution of 8% perchloric, 10% butylcellosolve, 60% ethanol and 22% water. Electron probe micros-analysis (EPMA) is performed to verify that the specimens are indeed homogeneous in composition after the homogenization treatment, as determined with a spatial resolution of 1 μm.…”

“…This is estimated by comparing the Tifree and the Ti-containing steel during annealing at 300°C and by knowing that no TiC-precipitates were present after quenching and that no TiC-precipitates nucleate at 300°C. 8,9) The influence of TiC precipitates on the macroscopic hardness of martensite can be observed first after 30-60 minutes of annealing at 550°C, see Fig. 5(a).…”

“…................. (8) where Rn-1 is the radius in the previous time step tn-1 and Δt = (tn-tn-1). The equilibrium concentration of titanium in the matrix and in TiC at 550°C, and , are calculated using ThermoCalc.…”

“…7) Martensitic steel with medium carbon content and a small addition of Ti (around 0,04 wt%) is therefore an interesting candidate steel for making steels for fasteners that are stronger at higher temperatures. Furthermore are TiC-precipitates known to act as hydrogen traps [8][9][10] and improve the resistance to hydrogen-induced damage, a very desirable feature when creating a highstrength steel for the automotive industry.…”