Heat treating the ductile cast iron produced austempered ductile iron (ADI), which has outstanding mechanical properties that can be varied over a wide range by varying the heat treatment parameters. In the present work a series of test were conducted and the effects of austempering temperature and times onto the material properties was investigated. The machinability of ADI was evaluated by comparing tool life, tool wear rate, cutting forces, and surface finish produced on a job as general criteria. Machinability tests were carried out following ISO 3685: 1993 (E) standard “Tool Life Testing with Single Point Turning Tools”. The cutting force data used in the analyses were gathered by a tool breakage detection system that detects the variations of the cutting forces measured by a three-dimensional force dynamometer. Six pairs of ductile iron specimens, austempered at 300, 350 and 400 °C for 1 and 2 h were tested. The cutting tools used in the tests were coated carbide inserts, ISO SNMG 120408 (K10), clamped on tool holders CSBNR 2525 M12. No cutting fluid was used during the turning operations. During the experiments cutting forces, flank wear and surface roughness values were measured throughout the tool life and the machining performance of ADI having different structures were compared.

The effects of austempering temperature and time onto the machinability of austempered ductile iron

Successful casting of three groups of austenitic ductile irons was achieved covering a carbon equivalent (CE) range from 3.51% to 5.04%. The three groups implied the change of C, Si or Ni contents to control the CE%. In case of using Ni element to vary CE%, austenitic ductile iron could be obtained starting from 13.5% up to 34.7% Ni. Generally, the microstructure consisted of graphite nodules embedded in austenitic matrix. Nodule characteristics were affected by the variation of CE%. Nodularity was almost 100% for all tested specimens. Slight decrease in hardness and tensile strength (σu) was observed with increasing the CE%. 0.2% proof stress (σ0.2) showed almost a constant value with increasing CE%. Tensile elongation was mainly increased with increasing CE% with different degrees owing to the alloying element (C, Si or Ni).

C, Si and Ni as alloying elements to vary carbon equivalent of austenitic ductile cast iron: Microstructure and mechanical properties

Tribological behaviour of shot peened Cu–Ni austempered ductile iron

Tribological behavior of shot peened/austempered AISI 5160 steel

An investigation was carried out to examine the influence of austempering temperature on microstructural parameters and the wear behaviour of austempered ductile iron. Ductile iron was austenitised at 900 °C for 30 min and austempered for 2 h at 260, 280, 300, 320, 350, 380 and 400 °C. Resulting microstructures were characterised through optical microscopy and X-ray diffraction. Wear test was carried out using a pin-on-disc machine with sliding speed of 289 m min−1. Coarse ausferrite microstructure exhibited higher wear rate than fine ausferrite microstructure. At high austempering temperature large amounts of austenite was instrumental in improving the wear resistance through formation of deformation induced martensite. Study of the wear surface under scanning electron microscope showed that, under dry sliding condition, wear occurred mainly due to adhesion and delamination. Wear rate was found to be dependent on the yield strength, austenite content and its carbon content.

Study of wear behaviour of austempered ductile iron

Microstructure, tensile, impact, hardness, fractography and wear characteristics were investigated for: (1) Austempered ductile iron (ADI); and (2) low alloyed ductile iron. Comparison has been made between the properties of these two types and that of conventional ductile iron. Detailed analysis, of the fracture mode for the 3 types of ductile iron, which failed under tensile and impact testing, were presented using the SEM. The wear properties were determined using pin-on-ring machine, under dry sliding conditions. The variation of mass loss and coefficient of friction with sliding distance, at different loads and speeds were presented and discussed. The wear mechanisms were investigated by means of subsurface observations. Microhardness test was used to study the change in the matrix strength with distance from the worn surface due to plastic deformation.

A. Refaey

Papers

Effect of microstructure on properties of ADI and low alloyed ductile iron