Iron-chromium-carbon-vanadium white cast irons: The microstructure and properties

Abstract

The as-cast microstructure of Fe-Cr-C-V white irons consists of M7C3 and vanadium rich M6C5 carbides in austenitic matrix. Vanadium changed the microstructure parameters of phase present in the structure of these alloys, including volume fraction, size and mophology. The degree of martensitic transformation is also dependent on the content of vanadium in the alloy. The volume fraction of the carbide phase, carbide size and distribution has an important influence on the wear resistance of Fe-Cr-C-V white irons under low-stress abrasion conditions. However, the dynamic fracture toughness of Fe-Cr-C-V irons is mainly determined by the properties of the matrix. The austenite is more effective in this respect than martensite. Since the austenite in these alloys contained very fine M23C6 carbide particles, higher fracture toughness was attributed to a strengthening of the austenite during fracture. Besides, the secondary carbides which precipitate in the matrix regions also influence the abrasion behavior. By increasing the matrix strength through a dispersion hardening effect, the fine secondary carbides can increase the mechanical support of the carbides. Deformation and appropriate strain hardening have occurred in the retained austenite of Fe-Cr-C-V alloys under repeated impact loading. The particles of precipitated M23C6 secondary carbides disturb dislocations movement and contribute to increase the effects of strain hardening in Fe-Cr-C-V white irons.

Mikrostruktura Fe-Cr-C-V belih gvožđa u livenom stanju se sastoji od M7C3 karbida i M6C5 karbida bogatih vanadijumom u austenitnoj metalnoj osnovi. Vanadijum menja mikrostrukturne parametre faza prisutnih u strukturi ovih legura, uključujući zapreminski udeo, veličinu i morfologiju. Stepen martenzitne transformacije, takođe, zavisi od sadržaja vanadijuma u leguri. Zapreminski udeo karbidne faze, veličina karbida i raspodela ima značajan uticaj na otpornost na habanje abrazijom Fe-Cr-C-V belih livenih gvožđa u uslovima malih naprezanja. Međutim, žilavost Fe-Cr-C-V gvožđa je uglavnom određena svojstvima metalne osnove. Austenit je mnogo efektniji od martenzita. Budući da austenit u ovim legurama sadrži vrlo fine čestice M23C6 karbida, veća žilavost je povezana sa ojačavanjem austenita u toku loma. Pored toga, sekundarni karbidi, istaloženi u regionima metalne osnove, takođe, utiču na ponašanje pri habanju abrazijom. Povećavajući čvrstoću metalne osnove kroz efekat disperznog ojačavanja, fini sekundarni karbidi povećavaju mehaničku podršku eutektičkim karbidima. U uslovima ponovljenih udarnih opterećenja u zaostalom austenitu Fe-Cr-C-V belih gvožđa javlja se deformacija i deformaciono ojačavanje. Čestice istaloženih M23C6 sekundarnih karbida ometaju kretanje dislokacija i doprinose pojačanju efekta deformacionog ojačavanja.