• PDF / 2,612,732 Bytes
• 11 Pages / 612 x 792 pts (letter) Page_size
• 3 Downloads / 264 Views

DOWNLOAD

REPORT

---

INTRODUCTION

THE HSLA-100 steel has a good combination of strength, toughness, and weldability. During the gas-metalarc welding (GMAW) of this steel, control of the geometry and microstructure is important in achieving defect-free, structurally sound, and reliable welds. Although several investigations have been undertaken on the welding of HSLA-100 steel in the past decade,[1–4] most of these studies have focused on the microstructural characterization of the weldment. In contrast, very little effort has been made to understand the evolution of weld metal macro-and microstructures from fundamental theories. During fusion welding, the interaction of the heat source and the material leads to rapid heating, melting, and vigorous circulation of the molten metal in the weld pool. The circulation helps to transport heat in the entire weld pool. As the heat source moves away from the molten region, solidification and subsequently a series of solid-state phase transformations occur. The heat transfer and fluid flow in the weld pool affects its shape and size, cooling rate, and the resulting microstructure. An accurate knowledge of the thermal cycle in the weld metal is a prerequisite for understanding its microstructure. The direct measurement of temperature profiles in the weld pool is difficult, and noncontact techniques for measuring weld pool surface temperatures are still evolving. Measurement of cooling rates in the interior of the weld pool remains both an exciting opportunity and a formidable

Z. YANG, Graduate Student, and T. DEBROY, Professor, are with the Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802. Manuscript submitted May 15, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS B

challenge in welding research. Mathematical modeling provides a recourse to address this problem. In recent years, calculations of fluid flow and heat transfer in the weld pool have provided detailed insight about the welding processes that could not have otherwise been obtained.[5–19] Significant progress has been made in understanding the development of weld pool shape and size,[6–12] cooling rate,[13,14] and concentration of volatile alloying elements from the weld pool.[15,16,17] Fairly recently, efforts have been made to use these calculations to advance our understanding of the development of weld metal microstructures[18,19] and inclusion characteristics.[20] The methodologies of heat transfer and fluid flow calculations are now well accepted, and reliable commercial computer programs for the solution of the equations of conservation of mass, energy, and momentum are now generally available to achieve high efficiency and accuracy of the numerical scheme. Previous experimental observations[21] and theoretical calculations[22,23] in gas-tungsten-arc (GTA) welding have indicated that, in many cases, the fluid flow in the weld pool is turbulent in nature. In GMAW, the high level of agitation[5] in the weld pool is aided not only by large mean velocities in a relatively sm