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Abstract
The mechanical behavior of a wear-resistant CrMoV-alloyed martensitic steel in quenched and tempered conditions has been investigated and correlated with the microstructure. The steel has a combination of ultra-high tensile strength of 2065 MPa and total elongation of 7.4 pct in the as-quenched condition. The strength and ductility of the steel change initially during tempering and thereafter remain quite stable during tempering at either 450 °C or 550 °C. A good combination of yield strength and total elongation is achieved after tempering at 550 °C for 2 to 8 hours (about 1300 MPa and 14 pct). The evolution of the mechanical properties can be mainly related to an initial condition with high density of dislocations (in the order of 1015) and carbon in solid solution, while quite early during tempering, dislocations will start to annihilate and carbide precipitates form. On the other hand, there is a negligible evolution of the effective grain size during tempering. Modeling of the individual strengthening mechanisms and the overall yield strength is in good agreement with the tensile test results, in particular for the tempered samples. Finally, the relatively low yield strength of the fresh martensite, significantly lower than for the tempered conditions, is discussed in relation to the two available theories.
Highlights
WEAR-RESISTANT steels with excellent combination of strength/hardness and toughness have wide applications, for example tipper bodies, which usually suffer frequent loading and unloading of heavy and sharp rocks, steel scrap, concrete with rebars, etc
Evolution of effective grain size The evolution of the martensitic microstructure is firstly studied by electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI)
MC Becker/Doering time-dep. ortho-equilibrium grain boundary and subgrain boundary auto planar sharp interface + size correction results indicate that the effective grain sizes of the investigated three samples are constant within the experimental error margin, i.e., 1.56 ± 0.24 lm for the as-quenched sample, 1.50 ± 0.26 lm for the 2-hour tempered sample and 1.63 ± 0.20 lm for the 5-hour tempered sample at 550 deg
Summary
WEAR-RESISTANT steels with excellent combination of strength/hardness and toughness have wide applications, for example tipper bodies, which usually suffer frequent loading and unloading of heavy and sharp rocks, steel scrap, concrete with rebars, etc. The steels need to have a high resistance towards dent formation and abrasion to increase the lifetime of the product These property requirements are generally met by combining a martensitic microstructure and precipitation-hardening, which generates a combination of ultra-high strength/hardness and good toughness.[1,2] The diffusionless nature of the martensitic transformation leads to a martensitic microstructure that is defect-rich, with high supersaturation of alloying elements and a hierarchic microstructure consisting of packets, blocks, sub-blocks, and laths.[3,4,5,6,7,8,9,10,11] The. METALLURGICAL AND MATERIALS TRANSACTIONS A martensitic microstructure is not so ductile and a tempering treatment is required subsequently to the quench-hardening. Yield strength modeling attempts to elucidate the contribution of different microstructural parameters to the yield strength
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