Effect of hydrogen on tensile properties of ferritic-pearlitic carbon steels

Effect of hydrogen on tensile properties of ferritic-pearlitic carbon steels was investigated. Tensile tests were conducted in air at room temperature using virgin and 10%-30% pre-strained specimens of the following carbon steels : IF (0.002 mass% C), S15C (0.17mass%C) and S45C (0.43 mass% C). Volume fraction of pearlite of these steels varied from 0% to 54.7% with increasing carbon content. The specimens were charged with hydrogen by immersing in a 20 mass% NH₄SCN aqueous solution at 313 K for 48 h. The results of the current study were combined with results for SGP⁽⁴⁾ (0.078 mass%C) and STPG 370⁽⁵⁾ (0.19 mass%C) from previous studies. Hydrogen content increased with pre-strain and volume fraction of pearlite. The tensile strength was not changed by increasing hydrogen. In contrast, the reduction of area decreased with increasing hydrogen content. At the same hydrogen content, the relative reduction of area, φ_H/φ (where φ is reduction of area of uncharged specimen and φ_H is that of hydrogen-precharged specimen), was higher for low carbon steels (IF and SGP) than for others (S15C, STPG370, and S45C). The difference in the φ_H/φ value between these steels was caused by a difference in fracture morphology. That is, voids were formed in IF and SGP steels, whereas pearlite cracks were formed in S 15 C, STPG 370, and S45C steels. From these results, guidelines for the application of carbon steels in hydrogen environments were proposed.