Effect of microstructure on fatigue behaviour of advanced high strength ductile cast iron produced by quenching and partitioning process

Abstract

The fatigue behaviour of high strength ductile cast iron produced by a quenching and partitioning process (Q&P) is evaluated. The Q&P process is receiving increased attention as a new way to produce ultra-high strength steels with multiphase microstructures composed of a martensite matrix and substantial amounts of carbon-stabilized retained austenite. Currently, the mechanical properties arising from applying the Q&P process in ductile cast irons have not been investigated. Thermal treatments consisted of heating the material to 880°C for a 2 hour soaking time followed by quenching in oil at 140°C and 170°C, intermediate temperatures between Ms and Mf allowing the formation of a controlled amount of athermal martensite. The material was reheated to 300°C and 375°C (the partition treatment) for different times between 15 and 120 minutes and subsequently air-cooled to room temperature. Microstructural evolution and carbon partitioning was investigated by in situ synchrotron X-ray diffraction. With a microstructure composed of tempered martensite, bainitic ferrite and carbon-enriched stabilized austenite, a new class of properties was obtained, with an enhanced strength when compared to ADI (austempered ductile iron) while still maintaining reasonable elongation. Fatigue testing was undertaken using polished plain bend bars (no stress concentration features) assessed under four-point bending. Uninterrupted tests at varying loads show that the higher partitioning temperature is beneficial for fatigue life. Fracture initiation sites are primarily from pores and a number of decohered graphite nodules. A strong influence of the microstructure on subsequent fatigue crack growth is observed from interrupted testing with replica records and SEM examination of tested samples, with cracks exhibiting significant tortuosity, at times even appearing to grow approximately parallel to the tensile axis. Using these results, the effects of the Q&P treatment, particularly the role of the partitioning time and temperature, on the fatigue properties of ductile cast iron are assessed.

Effect of plasma nitriding on high‐cycle fatigue properties and fracture behaviors of GJS700 nodular cast iron under cyclic bending loading

“…A literature review was performed on studies about the improvement in HCF lifetimes of cast irons. The first category of these methods is the heat treatment effect, which was presented by Melado et al, 5 Toktas et al, 6 Salman et al, 7 Tayanc et al, 8 Verdu et al, 9 Lin and Chang, 10 Bartosiewicz et al, 11 Kogoh et al, 12 and Borsato et al 13,14 For the surface treatment, details of studies are described in the following sentences.…”

A preliminary mechanical design evaluation of the Wikispeed car: for light-weighting implications

“…Traditionally, low-density materials such as aluminium, steel, magnesium and composite materials have been prominently used in the automobile industry to replace ferrous alloys (Barton and Fieldhouse, 2018). Higher strength, ductility is provided by ferrous alloys at a lower cost when compared to low density alloys (Melado et al, 2017). High strength to weight ratio is provided by ultra-high strength cast alloyssuch materials properties produce structural components for passenger car vehicles (especially for the production of thinner wall section thus decreasing the overall weight of the component) (Mohrbacher, 2013).…”

Çift Fazlı (α + M) Küresel Grafitli Dökme Demirlerde Martenzit Hacim Oranı-Mekanik Özellikler-Dislokasyon Yoğunluğu Arasındaki İlişkilerin İncelenmesi

“…Küresel grafitli dökme demirler (KGDD) düşük üretim maliyetleri, yüksek dayanım ve süneklik kombinasyonları, işlenebilirlik kabiliyetleri, çeliklere göre düşük yoğunlukları, düşük üretim maliyetleri gibi avantajlarıyla ilgi çekici konumdadırlar [1][2][3]. Çift fazlı küresel grafitli dökme demirlerin (ÇF-KGDD) kontrol edilebilir farklı dayanım ve süneklik seçenekleri sunmaları, son yıllarda araştırmacıların dikkatini çekmiştir [4][5][6][7].…”