Surface Hardening of Ferritic Spheroidal Graphite Cast Iron by Friction Stir Processing

Abstract

A ferrite-based spheroidal graphite cast iron (FCD450) is difficult to harden using a conventional surface hardening method, because the carbon content in the matrix is very low. In order to solve this problem, the friction stir processing (FSP) was used in this study as a new hardening method for cast irons. The authors have clarified in a previous study that the pearlite-based cast iron, such as FC300 and FCD700, can be hardened using the friction stir processing and that there are several advantages, such as a higher hardness and no required post surface machining. In this study, it was clarified that a Vickers hardness of about 700 HV is obtained due to the formation of fine martensite even in the ferrite-based spheroidal graphite cast irons, although the optimal process range is much narrower than that of the pearlite-based cast iron due to the requirement of both the heat input for diffusion of the carbon into the matrix and the high cooling rate for the martensitic transformation.

The Effect of Hardening Techniques on Wear Resistance and Fatigue Life of Ductile Cast Iron

“…The fully matrix transformed into acicular ferrite, Fe3C and martensite with retained austenite aggregates, significant increase of microhardness was achieved up to 1000 HV reference to base metal of 215 HV, and an improvement in erosion wear resistance [26]. Ferritic cast iron FCD450 Vickers hardness of (200 HV as base to about 700 HV) was obtained due formation of fine martensite [27] and was applied to flake cast iron (FC300) and nodular cast iron (FCD700) with pearlitic matrices resulted in fine martensite structure formation, and increased hardness to 700 HV for both cast irons compared to base irons ( 170-210HV) and (200-230 HV) respectively [28].…”

Friction Stir Processing of Cast Iron Using Cermet Tool

“…Recently, a new processing technique, friction stir processing (FSP), was applied to the surface hardening of cast iron [1,2]. FSP is based on the technique of friction stir welding (FSW).…”

“…For steel materials, conventional FSW tool for light alloy is easily damaged under high process temperature and high pressure. Therefore, FSW tool made by material with good high-temperature strength [1,2,[7][8][9][10] and the columnar tool without a pin [1,2] were researched. In the case of FSP by using this columnar tool without a pin, although friction stir (FS) zone becomes depthless, hardening is occurred in heat-affected zone (HAZ) after passing the tool.…”

“…As a FSW tool material for high-melting-point materials, PCBN [7,10], W or W-Re alloy [9], Ir alloy, Ni-based alloy, Co-based alloy, Si 3 N 4 and WC-Co cemented carbide [1,2,8] have been researched. However, expensive price of these materials is a problem for practical application.…”