INFLUENCE OF ALLOYING ELEMENTS ON THE TOUGHNESS OF LOW ALLOY MARTENSITIC HIGH STRENGTH STEELS
Final technical rept. Jul 1967-Sep 1968
TRW INC CLEVELAND OH
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The study examined the effects of various elements on the notch bend fracture toughness and Charpy impact behavior of a 0.35C, 3Ni, Cr-Mo-V martensitic steel having a room temperature yield strength of approximately 160- 180 ksi. A classical approach was used in the design of alloys which permitted a direct evaluation of single element effects rather than interactions. The elements C, Mn, Si, Cr, and Mo raised both the notch bend fracture mode transition temperature and the Charpy V-notch transition temperature 100 fibrosity criterion. In amounts above that required for deoxidation and grain refinement aluminum degraded the transition temperature and toughness slightly. A minimum toughness occurred at a vanadium content of 0.1. Over the entire range of compositions examined 1.26 - 6.23 nickel decreased the transition temperature and improved toughness at the lower test temperatures. Charpy shelf energy, C sub v max, and fracture toughness K sub max at 75F, did not correlate well with work hardening exponent n. Good agreement was obtained however when these parameters were plotted versus true fracture strain. At - 321F, toughness was essentially fracture strain independent suggesting that a critical strain criterion based on fracture strain is valid only when fracture is fibrous. A comparison was made of measured K sub 1c calculated from tensile data. The results indicated that the increased contribution on non-ductile fracture which accompanies increases in strength andor decreases in test temperature in low alloy steels can lead to large errors in the predicted toughness.
- Metallurgy and Metallography