Delayed Fracture Using CSRT and Hydrogen Trapping Characteristics of V-bearing High-strength Steel

Abstract

The delayed fracture characteristics of V-bearing steel were evaluated using conventional strain rate test (CSRT) and the hydrogen absorption and desorption behaviors were studied with the specimens hydrogen-charged and then exposed to air of 30°C for up to 2.5 months. CSRT was carried out at two test sites, and nearly the same delayed fracture resistance was obtained for the V-bearing steel. The fracture appearance changed from quasicleavage to intergranular with increasing hydrogen content. The hydrogen content of the boundary between fracture appearances was approximately 4 mass ppm. The hydrogen introduced into the V-bearing steel was composed of a diffusible one which decreased in concentration in 24 h when exposed to air of 30°C, and two types (weakly and strongly) of trapped ones. The strongly trapped hydrogen remained in the specimen after 2.5 months of exposure in air. By analyzing the thermal desorption profiles with Gaussian function, the peak temperatures of these hydrogen types were 100°C, 167°C and 198°C, corresponding to diffusible, weakly and strongly trapped hydrogen, respectively. The hydrogen-charged specimens of more than 4 mass ppm were fractured in the intergranular mode. After exposure in air and the hydrogen content became less than 4 mass ppm, the fracture mode changed to quasicleavage. After recharging the hydrogen to more than 4 mass ppm, the fracture mode became intergranular again.KEY WORDS: conventional strain rate test (CSRT); delayed fracture; V-bearing steel; hydrogen embrittlement; hydrogen trapping; thermal desorption analysis; diffusible hydrogen.

Electrochemical Hydrogen Permeation Test under Controlled Temperature and Humidity after Outdoor Exposure at Beijing, Chongqing and Okinawa

“…The critical hydrogen content for delayed fracture (hydrogen embrittlement) (H C ) has been regarded as one of the determining factors for delayed fracture of high strength steels. [1][2][3] H C and the relationship between fracture stress and diffusible hydrogen content have been examined by using constant load test, [1][2][3][4] slow strain rate test (SSRT), [5][6][7][8][9] conventional strain rate test (CSRT) [10][11][12][13] of tensile specimens charged with hydrogen in conjunction with hydrogen content measurement by means of thermal desorption analysis (TDA).…”

Reduction of Delayed Fracture Susceptibility of Tempered Martensitic Steel through Increased Si Content and Surface Softening

“…Various ways of improving the microstructures have been proposed: strengthening grain boundaries by adding boron, 8,9) trapping hydrogen by adding vanadium [10][11][12] and stabilizing dislocation structures through high-temperature tempering. 13) While boron reduces tempering embrittlement caused by phosphorus or sulfur segregating near grain boundaries, 14) there are inconsistent reports regarding the effect of boron on hydrogen-induced intergranular fracture.…”

Comparison of Constant Load, SSRT and CSRT Methods for Hydrogen Embrittlement Evaluation Using Round Bar Specimens of High Strength Steels

“…In contrast, CSRT [13][14][15][16] is performed under a high strain rate similar to ordinary tensile testing rate which makes the stress-induced diffusion negligible. Therefore, hydrogen content at the crack initiation site of hydrogen embrittlement in the vicinity of the notch root is equivalent to the average hydrogen content in the specimen.…”

“…Recently, susceptibility to delayed fracture is evaluated by Slow Strain Rate Test (SSRT) [6][7][8][9][10][11][12] and Conventional Strain Rate Test (CSRT) [13][14][15][16] which can complete the delayed fracture test in a shorter time than CLT. The relationship between H C and fracture stress can be obtained by SSRT and CSRT.…”