Microstructure and abrasive wear resistance of an alloyed ductile iron subjected to deep cryogenic and austempering treatments

doi:10.1016/j.jmst.2017.08.003

Abstract

Abstract:

To further improve the mechanical performance of a new alloyed austempered ductile iron (ADI), deep cryogenic treatment (DCT) has been adopted to investigate the effect of DCT time on the microstructure and mechanical behaviors of the alloyed ADI Fe-3.55C-1.97Si-3.79Ni-0.71Cu-0.92Mo-0.64Cr-0.36Mn-0.30 V (in wt.%). With increasing the DCT time, more austenite transformed to martensite and very fine carbides precipitated in martensite in the extended period of DCT. The amount of austenite decreased in alloyed ductile irons, while that of martensite and carbide precipitation increased. The alloyed ADI after DCT for 6 h had the highest hardness and compressive strength, which can be attributed to the formation of more plate-like martensite and the finely precipitated carbides. There was a gradual decrease in hardness and compressive strength with increasing the DCT time to 12 h because of the dissolution of M₃C carbide. After tempering, there was a decrease in mechanical properties compared to the direct DCT sample, which was caused by the occurrence of Ostwald ripening of precipitated carbides. The optimum wear resistance was achieved for the alloyed ADI after DCT for 6 h. The wear mechanism of the alloyed ADI in associating with DCT is mainly consisted of micro-cutting wear and some plastic deformation wear.

Key words: Alloyed ductile iron, Austempering, Deep cryogenic treatment (DCT), Microstructure, Mechanical properties

Cui Junjun, Chen Liqing. Microstructure and abrasive wear resistance of an alloyed ductile iron subjected to deep cryogenic and austempering treatments[J]. J. Mater. Sci. Technol., 2017, 33(12): 1549-1554.

Figures/Tables 10

Table 1 Processes of the austempered alloyed ductile iron with cryogenic deep treatment.

Samples	Treatment processes
DCT-00	Austempering + untreated
DCT-04	Austempering + deep cryogenic treatment at -196 °C for 4 h
DCT-06	Austempering + deep cryogenic treatment at -196 °C for 6 h
DCT-12	Austempering + deep cryogenic treatment at -196 °C for 12 h
DCT-04T	Austempering + deep cryogenic treatment at -196 °C for 4 h +tempering at 450 °C for 2 h

Fig. 1. Optical microstructure of the alloyed ductile iron at isothermally quenched state (DCT-00).

Fig. 2. XRD pattern of the austempered alloyed bainitic ductile iron.

Fig. 3. Optical microstructures of the austempered alloyed ductile iron after deep cryogenic treatment: (a) DCT-04, (b) DCT-06, (c) DCT-12, (d) DCT-04T.

Fig. 4. XRD profiles of austempered alloyed ductile iron with deep cryogenic treatment at different holding time.

Fig. 5. XRD pattern of the austempered alloyed ductile iron with DCT-04T treatment.

Fig. 6. TEM images of martensite (a) and carbide precipitation (b) of austempered alloyed ductile iron after DCT-04T treatment.

Table 2 Hardness and compressive strength of the alloyed ADI after various processes of DCT.

Samples	Hardness (HRC)	Compressive strength (MPa)
DCT-00	62.9	3000
DCT-04	64.4	2870
DCT-06	66.0	3140
DCT-12	65.8	3040
DCT-04T	63.9	2770

Table 3 Wear resistance of the alloyed ADI after various processes of DCT.

Samples	Weight loss (g)	Wear resistance (g^-1)
DCT-04	0.7322	1.3657
DCT-06	0.5936	1.6846
DCT-12	0.6172	1.6202
DCT-04T	0.7939	1.2596

Fig. 7. Worn surface morphologies of the alloyed ADI after various processes of DCT. (a) DCT-04, (b) DCT-06, (c) DCT-12, (d) DCT-04T.

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