Hydrogen Embrittlement Susceptibility Evaluation of Tempered Martensitic Steels Showing Different Fracture Surface Morphologies

Abstract

The effects of the crosshead speed, hydrogen content and temperature on fracture strength and fracture surface morphology were investigated using a tempered martensitic steel containing 1.67 mass% of Si (H-Si) and one containing 0.21 mass% of Si (L-Si). When L-Si specimens were charged with a small amount of hydrogen, fracture surfaces showed a transition from quasi-cleavage (QC) to intergranular-like (IG-like) to intergranular (IG) at room temperature. In contrast, when H-Si specimens were charged with a small amount of hydrogen, fracture surfaces showed a transition from QC to IG-like at room temperature. This transition in the fracture surface morphology can be explained by the magnitude relationship between intergranular and transgranular strengths under hydrogen charging. At a temperature of − 196°C, hydrogen did not lower the fracture strength nor did it change the fracture surface morphology. Hence, hydrogen embrittlement at room temperature was presumably caused by hydrogen accumulation and lattice defect formation during stress application as well as by hydrogen trapped before stress was applied. Fracture strength decreased and converged to a constant value (lower critical stress) with decreasing crosshead speed. The crosshead speed for obtaining lower critical stress decreased as the fracture surface changed from IG to IG-like to QC. Therefore, the crosshead speed for obtaining lower critical stress should not be treated as a constant but should be determined experimentally for each type of fracture surface.

Effect of Hydrogen on Spot-Welded Tensile Properties in Automotive Ultrahigh-Strength TRIP-Aided Martensitic Steel Sheet

“…This is because the steels with the tensile strength of 1 200 MPa or less are not susceptible for hydrogen (Figs. 10,11). The TS-H = 1 126 MPa of the base metal specimen for the TM steel with hydrogen charging and the TS-W = 1 450 MPa of the welded specimen for the TM steel showed the similar strength as those of the HS1 steel (Fig.…”

“…In the tempered martensitic steels with a tensile strength of 1 470 MPa grade with changing the additive amount of Si, occurring the quasi-cleavage and the intergranular fractures due to hydrogen, the effects of the strain rate, the hydrogen concentration and the temperature on the fracture strength and the fracture morphology of the round bar notched specimen have been investigated. 11) In addition, in the evaluation of the side collision of automobiles, the effect of the heat affected zone (HAZ) softening on the strength and the elongation of the spot-welded tensile specimens is considered since the flange of the B pillar on the side of the car body may occur the in-plate tensile deformation mode. 12) However, the sufficient research has not been conducted on the hydrogen embrittlement resistance of the spot-welded TM steels.…”

“…embrittlement and the spot-welding than the TS-WH = 811 MPa of the welded specimen of the HS1 steel after hydrogen charging (Figs. 10,11). When the TM steel and the HS1 steel are charged with hydrogen, the hydrogen is mainly trapped at the prior austenite grain boundaries and the lath boundaries, 19) on dislocations, 20) in retained austenite, or at the retained austenite/martensite boundaries 21) whereas it is considered that the hydrogen was mainly trapped at the martensite/cementite boundaries 22) in addition to the prior austenite grain boundaries, lath boundaries, and dislocations in the HS1 steel in the same way as the TM steel.…”

Crack Initiation and Propagation Behavior of Hydrogen-induced Quasi-cleavage Fracture in X80 Pipeline Steel with Stress Concentration

“…Fracture often occurs in the elastic region of the load-displacement curve as the load increases for notched high-strength steels charged with hydrogen. 16,17) In contrast, the results for the X80 specimens showed that they did not fracture suddenly but rather under plastic deformation as the load was increased as indicated in Figs. 5 and 6.…”

A fast fracture approach to assess hydrogen embrittlement (HE) susceptibility and mechanism(s) of high strength martensitic steels

“…Thus, understanding the hydrogen (H) induced fracture mechanism(s) of these materials is challenging in spite of the availability of extensive literature on their susceptibility [1,[9][10][11][12][13][14]. In general, the susceptibility of a Q & T steel to HE could be related to the mechanical properties such as yield strength, toughness, hardness etc.…”