Influence of welding interpass temperature on Charpy V-notch impact energy of coarse-grain heat-affected zone of AISI 4130 steel pipe

Abstract

Increasing the welding interpass temperature (IT) can reduce the welding time and cost of welding but may degrade the quality of the welded joint. The objective of the present study was to analyze the effects of the IT on microstructure and Charpy V-notch (CVN) impact energy of coarse-grain heat-affected zone (CGHAZ) of an AISI 4130 steel welded pipe. The welding was computationally simulated using finite element method. The CGHAZ was physically simulated and evaluated via optical and scanning electron microscopy, electron backscatter diffraction analysis, Vickers microhardness, and CVN impact. The numeric model had an accuracy of 97.5% (difference in the simulated and measured maximum temperatures), with a simulated cooling rate equal to the measured value. An increase in IT changed the microstructure from bainite (B) and martensite (IT 315 °C) to B, ferrite with aligned martensite–austenite–carbide (AC), and pro-eutectoid ferrite (FP) (IT 400 °C), followed by ferrite AC, FP, ferrite with non-aligned martensite-austenite-carbide, and ferrite–carbide aggregate (IT 475 and 550 °C). These changes in microstructure significantly impacted the effective grain size and grain boundary character distribution, which directly influenced CVN impact energy of the CGHAZ. IT = 315 °C exhibited the highest CVN impact energy (89 J), and ITs ≥ 400 °C did not satisfy the ASME 31.3 code. Therefore, indiscriminately increasing the IT is unsuitable method for reducing the welding cost for AISI 4130 steel pipes.