Microstructures and properties of carbidic austempered ductile Iron containing Fe3C particles and superfine ausferrite. (15th January 2020)

• Record Type: Journal Article
• Authors: Penghui, Yang; Hanguang, Fu; Guolu, Li; Jinhai, Liu; Xuebo, Zhao
• Is Part Of: Materials & design. Volume 186(2020)
• Publication Date: 2020-01-15
• Subjects: CADI -- Super-high temperature pretreatment -- Superfine ausferrite -- Precipitates -- Impact toughness; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2019.108363
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: A new type heat treatment process comprising super-high temperature pretreatment and austempering treatment (S&A treatment) was used to process carbidic austempered ductile iron (CADI). The results showed that the netlike eutectic carbides were significantly reduced after super-high temperature pretreatment. Due to the increase in supercooling during super-high temperature pretreatment cooling, the inter-laminar spacing of pearlite was reduced from 300 nm to 100 nm. When the ductile iron with superfine pearlite was reheated, a large amount of Fe3 C particles were retained inside the prior austenite grains. After austempering, a superfine ausferrite matrix with a length of 1–3 μm and a thickness of 50 nm was obtained. The main reason for this refinement is the increased number of nucleation-sites for the austenite grains and the retardation-effect of Cr on their growth. TEM results indicated that a possible orientation relationship between bainitic ferrite with a cubic lattice and precipitated Fe3 C particles with a orthorhombic lattice is (01 1 ¯ )α-Fe //(210)Fe3C, and their boundaries are coherent boundaries. The CADI obtained by S&A treatment has an impact toughness 120% higher than the traditional CADI without sacrificing hardness, and has excellent wear resistance under high wear load. Graphical abstract: Unlabelled Image Highlights: The impact toughness of CADI is significantly improved by super-high temperature pretreatment and austempering treatment. The CADI obtained by S&A treatment has excellent wear resistance under high wear load. With the rise of reheating temperature, the pearlite decreases gradually, and the precipitated particles are retained. A superfine ausferrite matrix with a length of 1-3 μm and a thickness of 50 ± 10 nm is obtained. The boundaries between bainitic ferrite and precipitated particles are coherent boundaries.