# Research on Friction Welded Connections of B500SP Reinforcement Bars with 1.4301 (AISI 304) and 1.4021 (AISI 420) Stainless Steel Bars

## TL;DR

This paper studies friction welding of stainless steel bars with reinforcement bars, finding that high yield strength alone does not ensure connection quality.

## Contribution

The study evaluates the performance of friction-welded connections using different stainless steel types with reinforcement bars.

## Key findings

- Martensitic stainless steel meets yield strength requirements but connection quality is critical.
- Austenitic 1.4301 steel performed better than martensitic 1.4021 despite lower yield strength.
- Incorrect steel selection can lead to significant financial and safety risks in foundation pile manufacturing.

## Abstract

Steel and prestressed concrete traction poles can be fixed to reinforced concrete pile foundations using typical bolted connections. The stainless steel fastening screw is connected to the ordinary steel foundation pile reinforcement by friction welding under specific friction welding process parameters. From the perspective of the structural strength of the connection between the traction pole and the foundation pile, regarding the transfer of tensile and shear forces through a single anchor bolt, the yield strength of stainless steel bolts should be Re,min ≥ 345 MPa for M30 anchors, Re,min ≥ 310 MPa for M36 anchors and Re,min ≥ 300 MPa for M42 anchors. This requirement is reliably met by martensitic stainless steels, while other stainless steels have yield strengths below the required minimum. What truly determines the foundation pile’s load capacity is not the satisfactory mechanical strength of the stainless steel (here, the parameters are met), but the quality of the friction-welded end connection between the reinforcement and the threaded bars. Incorrect selection of the type of prestressing steel in the analyzed connection can have enormous consequences for foundation pile manufacturers. Annual production of foundation piles amounts to thousands of units, and an incorrect decision made by the pile designer at the design stage can result in significant financial losses and a high risk to human life. This article presents the results of studies on friction-welded connections of M30, M36, and M42 threaded bars made of austenitic 1.4301 (AISI 304) and martensitic 1.4021 (AISI 420) stainless steel with B500SP reinforcement bars. The tests yielded negative results for 1.4021 (AISI 420) steel, despite its yield strength exceeding Re ≥ 360 MPa.