Study of the fatigue behaviour of synthetic nodular cast irons at low and high frequency cyclic loading

Alan Vaško,Eva Tillová,Juraj Belan,M Vasko,A Sapietová,M Sága,L Jakubovičová,P Kopas,M Blatnická,V Baniari,O Štalmach,M Handrik

doi:10.1051/matecconf/201815707014

Abstract

The paper presents the results of low and high frequency fatigue tests carried out on nodular cast iron. The specimens of synthetic nodular cast irons from three different melts were studied in the high cycle fatigue region (from 105 to 108 cycles) using fatigue experimental equipments for low and high frequency cyclic loading. Low frequency fatigue tests were carried out at frequency f ≈ 120 Hz using the fatigue experimental machine Zwick/Roell Amsler 150HFP 5100. High frequency fatigue tests were carried out at frequency f ≈ 20 kHz using the ultrasonic fatigue testing device KAUP-ZU. Both of them were carried out at sinusoidal cyclic push-pull loading (stress ratio R = -1) at ambient temperature (T ≈ 20 °C). The relationship σa = f (N) and fatigue strengths were determined experimentally; mechanical properties, microstructures and fracture surfaces were investigated.

Highlights

The majority of service interruptions and cracks at the present time is caused by fatigue processes, degradation of materials properties in long time service and influence of external environment
The transition from the traditional use of pig iron to synthetic nodular cast iron prepared from steel scrap requires the regulation of chemical composition of melt
Three different melts of nodular cast iron were chosen for experiments and the specimens from them were used for metallographic analysis, mechanical tests, fatigue tests and microfractographic analysis

Summary

Introduction

The majority of service interruptions and cracks at the present time is caused by fatigue processes, degradation of materials properties in long time service and influence of external environment. The paper deals with the study of the fatigue behaviour of synthetic nodular cast irons at low and high frequency cyclic loading. Nodular cast iron is a group of cast structural materials with a wide application in engineering practice (especially in the automotive industry). It combines high tensile strength and plasticity with high fatigue strength. The production of nodular cast iron has been from an economic point of view orientated to synthetic melts where a part of more expensive pig iron in a metal charge is substituted for cheaper steel scrap. The transition from the traditional use of pig iron to synthetic nodular cast iron prepared from steel scrap requires the regulation of chemical composition of melt. Addition of metallurgical SiC to a nodular cast iron melt shows specific advantages in comparison with other Si and C carriers what has been described as a special pre-inoculating effect [4,5,6,7]

Experimental material and methods

Metallographic analysis

Mechanical tests

Fatigue tests

Microfractographic analysis

Conclusions