Use of the Aging Effect to Change the Local Properties of Structure Components

Abstract

Abstract. This research deals with processes leading to local strengthening effects in Advanced High Strength Steels (AHSS). Dual phase (DP), retained austenite (RA) -both hot and cold rolledand complex phase (CP) steels have been investigated to examine the effect of thermal and mechanical processing parameters on local properties. For this purpose, a method has been investigated to achieve local strengthening, namely local deformation and local heat treatment. Samples were locally deformed by bending and embossing processes. A local deformation with defined pre-strains leads to enhanced hardness and strengthening. A subsequent aging treatment leads to a further increase in mechanical properties. Local heat treatment was applied using a laser and an electron beam. Following local heat treatment with selected parameters, the microstructure of the surface and the cross section as well as the mechanical properties were evaluated by light optical, scanning as well as transmission electron microscopy, hardness measurement, tensile testing and thermal modelling. It can be stated that with partial heat treatment, local high strengthening can be produced. At lower heat treating temperatures, this effect could be attributed to bake hardening. With increased heat treating temperature, the initial microstructure near the surface is affected. A model can be improved, which defines the correlation between the influencing parameters and the local properties. The influence of over-aging in locally strengthen regions has been studied. For this investigation, parameters are stable to locally adjust the strengthening effect. Partial strengthening of AHSS by local deformation or local heat treatment can open up new fields of applications for locally using the strengthening effect to only influence relevant areas of interest, thus providing the potential for saving energy and designing the component's behaviour. Introduction:

Examining Failure Behaviour of Commercially Pure Titanium During Tensile Deformation and Hole Expansion Test

“…The material showed lowered fracture limit strain for AWJ (0.5) compared to EDM (0.8) after HET. The major-minor strain path at the hole edge is consistent with the uniaxial stress state behaviour on the forming limit diagram [20].…”

“…where df is final hole diameter and d0 is initial hole diameter. Generally, the forming limit diagram (FLD) is a plot of the major and minor strain evolution during sheet metal forming under different stress states [20]. The FLD provides information on the limit to which sheet metals are safely formed as well as predicting regions at which failure occurs.…”

Influence of the Hot Rolling Process on the Mechanical Behaviour of Martensitic Steel

“…the increase in strength is realized in the final heat treatment [4]. Previous own investigations [5,6] state the BH effect for multiphase steels to be much stronger than that one for conventional BH steels. Traditionally, the main objective in conventional thermomechanical controlled processing (TMCP) of multiphase steels has been to refine the final grain size through (1) refining prior austenite grains, (2) increasing grain boundary area per unit volume by changing the grain shape, e.g., pancaking, and (3) increasing boundaries [7].…”

“…For this study temperature intervals as well as the amounts of strains were varied (Table 2). The flat compression samples were deformed according to the experimental plan which was previously determined by the D-optimal design approach [9] introduced in [6]. In order to influence the shape and the size of the austenite grains before γ → α' transformation, austenite conditionings were conducted using three different deformation schedules.…”

Study of Bake Hardening Effect on Laser Welded Hot Rolled Ferrite‐Bainite Dual Phase Steels

“…These effects and changes in structure are well investigated, but the knowledge of the effects by tempering these parts is quite weak, especially for multiphase steels that show a strong BH effect, often stronger than that ones of BH steels 9–15. During the bake hardening process martensite tempering takes place.…”