HeatWeldForming - combined thermomechanical property improvement of welding seams
Final Report Abstract
The characteristics of the heat input during the fusion welding process lead to different peak temperatures and temperature gradients and different cooling rates in the joining zone. This leads to the formation of the so-called heat-affected zone (HAZ), which is characterized by an inhomogeneous microstructure and thus altered mechanical-technological properties compared to the base material. The aim of the research project is to achieve homogeneous mechanical-technological properties in the entire joining zone, which are similar to those of the base material. This is achieved by combining the individual processes of preheating, welding, forming and postheating in an inline process sequence in order to achieve a targeted microstructure adjustment in the weld seam area and the heataffected zone. In this project it could be shown that the extension of the process chain (welding/rolling) by an additional pre-heating/post-heating device is beneficial. With the material S235JR, the metadynamic/static recrystallization can be stimulated by the additional post-heating, and a homogeneous microstructure with mechanical-technological properties similar to those of the base material is created in the area of the heat input. However, the chosen method of a plasma arc for post-heating does not achieve complete penetration of the material due to the process speed, so that complete recrystallization can only be observed up to a penetration depth of 1,5 mm. The additional post-heating proves to be disadvantageous for the material S700MC. This highstrength fine-grained structural steel obtains its properties from its fine-grained microstructure in combination with the introduction of dislocations, which are introduced by a targeted thermo-mechanical treatment. In this case, the additional post-heating leads to a reduction of dislocations and to a recrystallized grain structure. It turns out that an optically comparable microstructure, similar to the base material, can be achieved by recrystallization in the area of the post heat treatment, but in this case the material parameters for strength and hardness are greatly undercut, which is an exclusion criterion. By eliminating the post-heating step, it is possible to incorporate targeted hardening and obtain mechanical-technological properties similar to those of the base material in the joining zone of the S700MC. This is achieved by preheating the semi-finished sheet metal parts to be joined to approx. 180°C using an acetylene torch. The additional preheating of the sheet metal leads to a higher inlet temperature into the rollers, whereby the seam is quenched on contact with the cold roller bodies, which results in a significantly higher hardness on the surface. Hot rolling as a subsequent process step for homogenization reduces this effect and also allows the hardening of the weld metal and the control of the recrystallization behavior , thus enabling a further convergence to the base material properties.
Publications
-
The Benefit of the Process Combination of Wire Arc Additive Manufacturing (WAAM) and Forming—A Numerical and Experimental Study. Metals, 12(6), 988.
Sydow, Benjamin; Jhanji, Avantika; Hälsig, André; Buhl, Johannes & Härtel, Sebastian
-
Influence of the Initial Microstructure on the Mechanical Behavior During Forming for Inline Manufacturing Process Routes. Lecture Notes in Mechanical Engineering, 513-524. Springer Nature Switzerland.
Jhanji, Avantika; Sydow, Benjamin; Adams, Tom-Eric; Habisch, Stefan & Härtel, Sebastian
-
Temperature Control During the Process Combination Welding and Rolling for Enabling Full Recrystallization with Homogenized Grain Size Distribution. Lecture Notes in Mechanical Engineering, 192-202. Springer Nature Switzerland.
Sydow, Benjamin & Härtel, Sebastian
