Hydrogen embrittlement of dual-phase steels
- PDF / 2,342,308 Bytes
- 6 Pages / 594 x 774 pts Page_size
- 46 Downloads / 245 Views
H Y D R O G E N in steels often leads to embrittlement, that is, loss of ductility and strength; 1 3 it appears to be immaterial whether the hydrogen is deliberately introduced by cathodic charging, is the result of a plating operation or is from a reactive corrosive environment. Hydrogen embrittlement can be either irrevrsible where, after a large amount of hydrogen has been introduced into the steel, permanent cracks are produced, or reversible, where if the hydrogen is removed from the steel by heating no permanent damage has occurred. 4 It is the reversible hydrogen embrittlement, which often leads to intergranular fracture, that is the subject of the present investigation. For quenched and tempered martensitic steels to be susceptible to hydrogen embrittlement, their yield strengths must be greater than about 1035 MPa (150 ksi). 5 The dual-phase, ferrite plus martensite, steels that are first finding applications have a yield stress of about 345 MPa (50 ksi) and a tensile strength of about 655 MPa (95 ksi).6-8 Thus, from a consideration of strength alone, these dual-phase steels would not be expected to be susceptible to hydrogen embrittlement. However, these dual-phase steels have a structure consisting of 15 to 20 vol. pct high carbon martensite (0.5 to 0.6 pct C) with a tensile strength in excess of 2070 MPa (300 ksi), in a ductile ferrite matrix. 7 Embrittlement of hydrogen charged mixed ferrite plus martensite structures has not been previously investigated; the possibility that hydrogen may interact with the high carbon martensite regions lead to this study. To study the influence of hydrogen on the ductility of ferrite plus martensite structures, two dual-phase steels which have similar tensile properties but different chemical compositions and thermal histories were chosen. In addition to investigating the properties of the steels in the as-received condition, the influence of both tempering, which will modify the properties of the martensitic component, and cold-work on subsequent hydrogen embrittlement was studied. R. G. DAVIES, Senior Staff Scientist, is with Ford Motor Company, Rm 2046, Scientific Lab., P.O. Box 2053, Dearborn, MI 48121. Manuscript submitted November 21, 1980.
Experimental Procedure Two types of dual-phase steels were studied; 1) a vanadium containing steel that was air cooled from the intercritical ~ + 7 region and 2) a lower alloy steel that was water quenched from an intercritical temperature and tempered at about 260 ~ for a few minutes; the composition of these steels is given in Table I. The steels were in the form of sheets 0.8 mm (0.031 in.) thick. Both standard tensile specimens with a gage 50 mm (2 in.) long by 12.5 mm (0.5 in.) wide,and double-notched samples, which had a 90 degree notch, a notch root radius of 150/~ (0.006 in.) and a width between the notches of 12.5 mm (0.5 in.), were utilized. All testing was done in an Instron tensile machine with a crosshead rate of 0.042 m m / s (0.1 in./min.) for the tensile specimens; for the notched samples the crosshead rate w
Data Loading...
