Influence of Preheating on Lamellar Gray Cast Iron for Surface Layer Welding applications with Plasma-Transferred Arc Powder and Metal Inert Gas Welding Processes with Duplex Steel as Filler Material

U Reisgen,E Gonzalez Olivares,T Engler,M Oechsner,R Sharma,B Heider,E Zokoll,G Andersohn,J Ellermeier

doi:10.1007/s11666-020-01014-9

Abstract

The good capacity of gray cast iron for the manufacture of complex geometry components is widely recognized, but its low resistance to corrosion and low weldability complicate the use of this material for some industrial applications. The corrosion resistance can be improved by metallic surface layers using welding processes with low percentages of dilution between the filler and base material. However, the welding processes impose very high heat load on the base material, which in the case of cast iron could promote the formation of hard and brittle microstructures, facilitating the formation of cracks. This work deals with weld beads of duplex steel on lamellar gray cast iron made either by plasma-transferred arc powder (PTA-P) or by metal inert gas (MIG) using the cold metal transfer (CMT) technology, with emphasis on achieving low dilution, hardness and imperfections (internal porosities). Preheating was used to reduce the hardness in the heat-affected zone, while different levels of helium were added in the shielding gas to study its effect on the geometry and hardness of the weld beads. The results showed that the PTA-P process resulted in lower values of dilution and hardness because of a low cooling rate compared to that of the MIG-CMT process. In addition, it was observed that preheating the base material reduced the hardness of the heat-affected zone but increased the dilution of the weld bead.

Highlights

For geometrically complex, flow-optimated components like pump casings, casting is the production method of choice
These changes in the partially melted zone (PMZ) and the heat-affected zone (HAZ) are visible in Fig. 10, where a large change in the HAZ is observed for 400 °C preheating temperature
The bead width obtained by the plasma-transferred arc powder (PTA-P) process was influenced significantly just when the amount of helium increased in the shielding gas; this is due to the increase in the arc energy, as it happened with the metal inert gas (MIG)-cold metal transfer (CMT) process

Summary

Introduction

Flow-optimated components like pump casings, casting is the production method of choice. Cavitation and abrasive materials can make higher alloyed base materials necessary, resulting in reduced castability, and in higher production costs because expensive alloys are present in areas without exposition to the medium (Ref 1-3). Through the surface layer located in the areas affected by corrosion, cavitation and abrasion, it is possible to reduce costs, increasing the effectiveness and life of the component [4,5,6,7,8,9,10,11]. A cast iron alloy is defined as an iron–carbon-based alloy containing more than 2.06 wt.% carbon. By adding alloying elements like manganese, it is possible to modify the geometrical form of those depositions resulting in different mechanical–technological properties. While heat treatments can change the metal matrix as well as the properties of the cast iron, the

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