141 Introduction

High-performance steels (HPS) were developed through a cooperative research program between the US Navy, the Federal Highway Administration (FHWA), and the American Iron and Steel Institute (AISI). At the time of this writing, two grades of HPS are available and have successfully been used in bridge construction. Their ASTM designations are HPS50W and HPS70W (the equivalent metric designations are HPS345W and HPS485W, respectively). A primary objective of developing HPS is to take advantage of the higher strength offered by high-strength steels without compromising on weldability. Conventional high-strength steels have a relatively high carbon content (approximately 19% by weight), and so special attention is needed to obtain high quality welds. This typically requires preheating of the welded parts, controlling the interpass temperature, controlling the energy input during passes, using special electrodes, careful handling of the welding consumables, and if necessary applying postweld treatment such as controlled cooling and feathering of the welds. When all operations are performed correctly and all prescribed procedures are followed carefully, one can often obtain good quality welds in conventional high-strength steels. Unfortunately, while these conditions can usually be met in a controlled environment such as in a shop, difficulties may arise when such welding has to be done on the field. This is particularly the case for bridge construction, when welding under less than optimal condition is often the norm. HPS have a carbon content that is very comparable to low carbon steel, and they can be welded under a variety of conditions without requiring the rather time consuming and often expensive pre- and postweld treatments. In addition, it has been demonstrated experimentally that HPS exhibit good toughness and satisfactory ductility values for use as an effective construction material.

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