Past Projects: Stud Welding Project

The Problem:

Stud welding is a relatively simple process that is used in construction of bridges. High Performance Steels (HPS) are widely used in the bridge decking for weathering applications. The most common of these used are HPS 70W and HPS 100W. Even though HPS 70W and HPS 100W are designed to be out in the weather, they will corrode over time. To overcome this failure that will occur, 403 Ferritic stainless steel was to be evaluated for bridge decking on Zn coated surfaces (hot dip galvanized, electro-galvanized). 

Background:

Stud welding is a process for joining a metal stud to a work piece. Stud welding guns hold the stud in place above the material to which it is to be joined. Electrical energy is used to heat the interface of the stud and the parent metal. The stud is then plunged into the parent metal to join them. This process uses a ceramic arc shield called a ferrule. The ferrule surrounds the stud to keep the molten metal contained and shield the arc.

Since arc stud welding time cycles are so short, heat input to the base metal is very small compared to the conventional arc welding. Because there is such a low heat input, the heat-affected zones (HAZ) are very small and minimal distortion occurs in the base metal where the stud is located. 

What we did:

The goal of this project was to examine the feasibility of using HPS 100W and 403 Ferritic as bridge decking. Repeatable parameters were established and optimized. The welds were evaluated for cracks, looked at for metallographic characterization, and hardness readings were taken. They were put through a series of destructive tests. An additional study was done to differentiate between solidification and hydrogen cracking through the introduction of carbon and hydrogen to the weld, and the results were evaluated. While evaluating the welds, obstacles were observed that could happen in the work field such as arc blow. Recommendations were made on how to prevent those obstacles and how to prevent cracking. 

Funding:

American Institute for Steel Construction, Chicago, IL: $75,000 / 1 year

Partners:

FWHA
http://www.fhwa.dot.gov/

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