The effect of explosive welding parameters on metallurgical and mechanical interfacial features of Inconel 625/plain carbon steel bimetal plate
Introduction
Inconel 625 as a nickel based superalloy is featured in development of strategic industries where a harsh environment makes the application of materials possessing superior characteristics inevitable. Inconel 625 owes such a constructive role to its hot strength and great corrosion resistance [1]. Despite the excellent properties of Inconel 625, high production costs have restricted the individual application of this alloy. Consequently, cladding and welding procedures are applied to lay Inconel superalloy on an appropriate economical substrate. Though fusion welding and cladding processes are inexpensive, available and flexible, the deterioration of corrosion resistance and mechanical properties of Inconel 625 due to intense heat input [2], [3], intermetallic compounds development [2], hot cracking [4], [5], dilution [2] and segregation [3], [4], [5], [6], [7] during fusion cladding has persuaded industries to extend their cladding methods into solid state procedures.
Explosive cladding/welding is a potential solid state method to fabricate Inconel 625-substrate bimetal plates for industries needing superalloy characteristics. The whole procedure of explosive cladding can be summarized in the following steps. As Fig. 1 depicts the parallel setup for explosive cladding of plates, the cladding plate (flyer plate) lies on the substrate (parent plate) with a uniform predetermined air gap called stand-off distance (d). Also, a uniform thickness of proper explosive by a known detonation velocity (VD) will be laid on the flyer plate. The mass ratio of the explosive to the flyer plate is called the load ratio (R) which plays an important role in explosive cladding procedures. By detonating the explosive, the flyer plate accelerates towards the parent plate through great pressure which is released by the explosion. The flyer plate collides with the parent plate obliquely by a collision angle of β and impact velocity of VF (Fig. 1). As a result of intense oblique impact, the contaminant surface layer of plates will be removed through the formation of a jet. Higher load ratios and/or longer stand-off distances yield higher impact velocities at a fixed detonation velocity, and therefore increase the possibility of a jet formation. A pure metallic contact surface issuing from the jet formation phenomenon besides great impact pressure bringing the gap between the free surface of the plates to an atomic distances results in metallic bonding between the flyer and parent plates [8].
Like all other cladding methods, the explosive welded interface, where joining materials meet, plays an important role in eventual characteristics of the cladded plate. Intermetallic compounds formation, interfacial structure, local melting and adhesion strength are all metallurgical and mechanical interfacial features that dominate the overall behavior of the explosive welded plate. As a result, for each case of explosive welding, the effect of welding parameters on interfacial features and consequently overall properties must be investigated to evaluate how we can reach a specific characteristic or avoid an undesired feature in final cladded plate through controlling the welding parameters. The present study aims to relate the most important explosive welding parameters including load ratio and standoff distance to interfacial features of Inconel 625/plain carbon steel bimetal plate such as shear strength, hardness variation across the interface, local melting at interface, interfacial structure and localization of plastic deformation in the vicinity of interface.
Section snippets
Experimental procedure
In all fabricated samples, Inconel 625 plate with the dimensions of 150×100×3 mm3 was clad on ASTM A517 low carbon steel plate with the dimensions of 130×80×20 mm3. The chemical compositions of the materials measured by a quantometer are listed in Table 1. Also, both plates were chosen in annealed condition to avoid the likely effect of material texture on the results. In order to remove coarse contaminants from the contact surfaces, the plates were grinded with emery papers up to a 600 grade.
Interfacial morphology
In explosive welding, due to nonuniform velocity of the explosion along the weld seam, the interface usually does not possess a uniform structure [11]. Clearly, this feature is more significant near the detonation zone where explosion is more unstable. Anyhow, by considering the main shape of interface along the weld line as a dominant interfacial structure, it is concluded that linearity and waviness are two possible interfacial forms in explosive welded plates. Various studies are carried out
Conclusion
The present study suggests the dependency of metallurgical and mechanical interfacial characteristics of explosive cladded Inconel 625/plain carbon steel bimetal plates on explosive welding parameters. It is seen that the interfacial structure is mostly linear at low impact energies, and increasing the impact energy through raising load ratio and standoff distance shifts this structure to a wavy interface. This wavy structure will be spoiled locally at excessive impact energies.
According to the
Acknowledgments
The authors would like to acknowledge and extend their heartfelt gratitude to Nicole Kurtz who has made the completion of this paper possible.
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