Abstract
Transformation induced plasticity (TRIP)-assisted annealed martensitic (TAM) steel combines higher tensile strength and elogangtion, and has been increasingly used but appears to bemore prone to hydrogen embrittlement (HE). In this paper, the hydrogen trapping behavior and HE of TRIP-assisted annealed martensitic steels with different vanadium additions had been investigated by means of hydrogen charging and slow strain rate tensile tests (SSRT), microstructral observartion, and thermal desorption mass spectroscope (TDS). Hydrogen charging test results indicates that apparent hydrogen diffusive index Da is 1.94 × 10−7/cm2·s−1 for 0.21wt.% vanadium steel, while the value is 8.05×10−7/cm2·s−1 for V-free steel. SSRT results show that the hydrogen induced ductility loss ID is 76.2% for 0.21wt.%V steel, compared with 86.5% for V-free steel. The trapping mechanism of the steel containing different V contents is analyzed by means of TDS and Transmission electron microscope (TEM) observations. It is found out that the steel containing 0.21wt.%V can create much more traps for hydrogen trapping compared with lower V steel, which is due to vanadium carbide (VC) precipitates acting as traps capturing hydrogen atoms.The relationship between hydrogen diffusion and hydrogentrapping mechanism is discussed in details.
Highlights
Modern advanced ultra-high strength steel (AHSS) had been widely used in various applications such as automotive, engineering, and machinery
Since no second peak temperature of up to 800 ◦ C is observed for all three steels, the temperature range indicating in the horizontal axis of Figure 5a is shortened to the 400 ◦ C range in order to clearly distinguish the three curves for different steels
Thermal desorption analysis (TDA) results show that the amount of desorption hydrogen during heating process are 7 ppm, 8.6 ppm, and 11.25 ppm, respectively, for the above three vanadium-added steels
Summary
Modern advanced ultra-high strength steel (AHSS) had been widely used in various applications such as automotive, engineering, and machinery. Hydrogen induced delayed fracture had always present a great challenging to the AHSS due to its inherent characteristic of high sensitivity to the hydrogen invasion and enrichment in metal matrix, when this kind of steel had been cold worked or serviced in a moist atmosphere. Extensive efforts had been done in order to address the problem challenged by hydrogen induced delayed fracture behavior. Extensive works showed that introduction of various kinds of hydrogen traps could effectively improve hydrogen induced delayed fracture behavior occurring in high strength steels [1,2,3,4,5,6,7]. Retained austenite in transformation induced plasticity (TRIP) steel [8] could play an effective role in improving the ductility of high strength steel due to the so-called TRIP effect. TiC had been well established as a Metals 2019, 9, 741; doi:10.3390/met9070741 www.mdpi.com/journal/metals
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