Fracture toughness of hydrogen charged as-quenched ultra-high-strength steels at low temperatures

Abstract

The effect of hydrogen on the fracture and impact toughness of ultra-high-strength steels at sub-zero temperatures in the transition temperature region has been investigated with arctic applications in mind. Two types of as-quenched microstructure were studied, i.e. autotempered martensite and a mixture of martensite and bainite, both having yield strengths close to 1000 MPa. These were charged with hydrogen using passive cathodic protection and then tested in both the charged and uncharged condition at sub-zero temperatures. Hydrogen contents were measured with meltextraction. Fractography, kernel average misorientation measurements and cohesive zone modelling were used to analyse the results considering the degree and the active mechanisms of hydrogen embrittlement. It is shown that hydrogen embrittlement is present at sub-zero temperatures, causing an increase in fracture toughness reference temperature T 0 and a small decrease in deformation capability. The relationship between the T 0 and the impact toughness transition temperature T 28J , which, in the case of ultra-high-strength steel, deviates from that observed for lower strength steels, is proposed to be affected by the hydrogen content.

Mechanical properties and microstructural evaluation of the heat-affected zone in ultra-high strength steels

“…: gas metal arc welding (GMAW) [21,22], laser welding (LW) [23][24][25], laser gas-metal-arc hybrid welding [26], and tungsten inert gas welding [27]. The main issues related to these weldments were cold cracking [28], reduction in the joint's strength [29], ductility [24], and fracture toughness [30][31][32].…”

Hydrogen embrittlement analysis in a CrMoV steel by means of sent specimens

“…The best technique to evaluate hydrogen embrittlement in structural steels and to obtain industrial solutions as a function of service conditions has yet to be established. Some authors use slow strain rate tension tests in different hydrogen environments [8][9][10], permeation tests [11][12][13], fracture toughness tests [14][15][16], fatigue crack propagation tests [17][18][19] or small punch tests [20][21][22]. According to previous research, the presence of a crack in the specimen [23,24] and the decrease in the displacement test rate are important variables that increase the embrittlement of steels.…”

Effects of heat input on the mechanical properties of butt-welded high and ultra-high strength steels

“…These methods are exemplified by the laser welding (LW) of S960 grade [19][20][21], the gas metal arc welding (GMAW) [22,23], laser gas-metal-arc hybrid welding [24], and tungsten inert gas welding [25]. Several issues associated with the welded HSS/UHSS are reported in the literature including cold cracking [26], reduction in the load carrying capacity [16], lower fracture toughness [27][28][29] and lack of ductility [18].…”