Study of restoration by welding of pearlitic ductile cast iron
Introduction
Ductile cast iron is an important cast material to the designer which combines the advantages of cast iron, such as cheapness, ease of machining, low melting temperature, good fluidity, good wear resistance properties, high damping capacity, excellent heat resistance properties and those of steel, such as high strength, ductility, toughness, hot workability and hardenability [1], [2], [3]. Therefore, such material can economically replace steel in a very wide variety of applications.
The poor weldability of ductile cast iron can be attributed to two factors, the formation of martensite in the heat affected zone (HAZ), and the development of hard, brittle iron carbide in the zone of partial fusion [4], [5], [6]. Most of the welding performed on cast iron is repair welding. It is either the repair of discontinuities produced during the casting process or those developed in the cast component itself while in service [7]. Despite this, the welding of this material has always been proven difficult and continues to require specialised knowledge and techniques [8].
The aim of this work is to restore the surface or to improve the surface properties of iron casting damaged by spalling or wear. This can be achieved by welding repair and/or hardfacing.
Section snippets
Experimental work
Pearlitic ductile cast iron base metal test plates 20×20×60 mm were machined from Y-blocks casting and prepared for welding by employing the manual shield metal arc welding (SMAW). The chemical composition is given in Table 1. The specimens were surfaced, single pass bead on-plate welds were deposited on the flat position using manual SMAW process, the level of preheat was 200°C for 1 h, the interpass temperature should be not less than 200°C. After the welding was performed, the specimens were
Results and discussion
The microstructure of the as-received ductile iron plate is shown in Fig. 1. The structure consists of graphite nodules surrounded by ferrite rings and the darker lamellar structure in the matrix is pearlite. This typical structure is described as a bull's eye pattern. Fig. 2 shows the optical micrographs of the weld metal and HAZ of the specimens surfaced by using different filler materials. The various phases detected in both the melt region (MR) and HAZ are listed in Table 4. It is clear
Conclusions
- 1.
The problems associated with welds with pure Ni, Ni–Fe alloy, Ni–Cu alloy and stainless steel are also present to various extent in welds made with ferritic steel filler metal.
- 2.
Preheating to 300°C appears as the best option when welding by ferritic steel filler metal. This is reflected in narrow MR, discontinuous carbide areas and bainitic HAZ.
- 3.
Higher heat input allows smaller MR and pearlitic HAZ.
- 4.
PWHT slightly reduces the maximum hardness of the HAZ.
- 5.
Multipass welding exhibits a smaller MR and
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