Phase composition, structure, and properties of steel R9M4K8

Autor: I. K. Kupalova
Rok vydání: 1979
Předmět:
Zdroj: Metal Science and Heat Treatment. 21:493-498
ISSN: 1573-8973
0026-0673
DOI: 10.1007/bf00703654
Popis: 1. The retained austenite in quenched steel R9M4K8 has a smaller lattice constant, which increases during tempering. This is evidently due to elastic compression of the austenite lattice during the martensitic transformation and the subsequent reduction of elastic deformation of austenite during tempering resulting from stress relaxation. 2. No stable cementite is observed in quenched steel R9M4K8. It appears after tempering for 1 h at 350–600°. This may indicate a substantial change in the properties of carbides of the cementite type formed in the presence of high-carbon martensite and austenite in the elastically compressed condition. The higher strength and toughness of quenched steel R9M4K8 in comparison with other high-speed steels are evidently due to the absence of cementite. 3. Intermetallic phases of the Laves type are observed in the steel in all structural conditions. 4. Special carbides of the MC (VC) and M2C (Mo2C) types are precipitated during tempering of steel R9M4K8. Highly dispersed M6C carbides are observed after tempering at temperatures above 650°, and thus M6C is a weakening phase. 5. After the optimal heat treatment (quenching from 1220°, austenite grain size grade 10–11, triple tempering at 560° for 1 h), ensuring the maximum hardness, strength, and toughness of steel R9M4K8, the structure consists of highly alloyed (∼7.3% alloying elements) twin-dislocation martensite, excess carbides (not dissloved during quenching) of the M6C and MC types, intermetallic phase of the Laves type (∼8.7%), and dispersed special carbides of the MC and M2C types with a size of order 50 A and M3C in the form of platelets with a length of 1000–5000 A and thickness 100–700 A (∼5.0% in all).
Databáze: OpenAIRE
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