Improving the Mechanical Strength of Ductile Cast Iron Welded Joints Using Different Heat Treatments.

Eva S.V. Marques,António B. Pereira,F.J.G. Silva,Olga C. Paiva

doi:10.3390/ma12142263

Eva S.V. Marques, António B. Pereira + Show 2 more

Open Access

https://doi.org/10.3390/ma12142263

Copy DOI

Journal: Materials	Publication Date: Jul 14, 2019
Citations: 12	License type: CC BY 4.0

Affiliation: Polytechnic Institute of Porto

Abstract

The main advantage of welding cast iron is to recover parts by repairing defects induced by casting processes (porosities, etc.), before they enter their working cycle, as well as repair cracks or fractures when already in service. This method contributes to decreased foundry industrial waste and avoids the additional energy costs of their immediate recycling. Therefore, it is necessary to have a welded joint with similar or better characteristics than the parent material. The major problem of welding cast iron is that this material has a very high content of carbon in comparison to steel (≈3%). Therefore, when it is heated by the very high temperatures from arc welding and during its process of solidification, very hard and brittle phases originate, known as ledeburite and martensite, and appear in the partially melted zone and in the heat-affected zone. Eventually, this problem can be solved by implementing heat treatments such as preheat or post weld heat treatments under specific parameters. Therefore, in this study, the aim is to collect data about the effects of heat treatments performed at different temperatures on welded joints of high strength ductile cast iron (SiboDur® 450), and to evaluate the effects of heat treatments performed at diverse temperatures on welded joints of this type of material, using Shield Metal Arc Welding and nickel electrodes. Mechanical strength, hardness, and microstructure were analyzed, showing that the best mechanical strength in the joint (380 MPa) was obtained using two passes of E C Ni-Cl (ISO EN 1071:2015) filler metal and post weld heat treatments (PWHT) of 400 °C for two hours.

Highlights

Cast iron is a class of Fe-C alloys with higher C content than steels and, depending on the alloying elements and the microstructure formed during solidification, it is classified as lamellar /grey cast iron, nodular/ductile cast irons or white cast iron
Since the aim of this work is to achieve a UTS value of 360 MPa, which corresponds to an 80% mechanical strength of the parent material, tensile tests are of utmost importance, due to the fact it is the first stage to exclude or accept the sets of experimental samples
Similar to ledeburite and cementite, martensite has harmful made, and how the hardness values were calculated for each area: partially melted zone (PMZ), heat-affected zone (HAZ), filler metal (FM), and MB

Summary

Introduction

Cast iron is a class of Fe-C alloys with higher C content than steels and, depending on the alloying elements and the microstructure formed during solidification, it is classified as lamellar /grey cast iron, nodular/ductile cast irons or white cast iron. Some of these cast irons can still be subjected to specific heat treatments, which give rise to other classes of cast iron, such as malleable or austempered ductile iron (ADI) [1]. DCIs have a great number of advantages as compared with other cast irons and common steels, such as obtaining complex shapes through casting and foundry processes and have lower specific weights allowing casting of thinner-walled parts while maintaining superior mechanical properties (ductility and fracture toughness) [3,4].

Objectives

Methods

Results

Discussion

Conclusion