Induction Heat Treatment of Sheet-Bulk Metal-Formed Parts Assisted by Water-Air Spray Cooling

• Published in: Steel research international Vol. 87; no. 9; pp. 1220 - 1227
• Main Authors: Besserer, Hans-Bernward, Dalinger, Andrej, Rodman, Dmytro, Nürnberger, Florian, Hildenbrand, Philipp, Merklein, Marion, Maier, Hans Jürgen
• Format: Journal Article
• Language: English
• Published: Weinheim Blackwell Publishing Ltd 01.09.2016; Wiley Subscription Services, Inc
• Subjects: Alloys; Cold working; Compressive properties; Crack initiation; DP600; Fatigue failure; Fatigue life; Forming; induction heat treatment; orbital forming; Residual stress; Sheet metal; water-air spray cooling; Workpieces
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.201500404

In order to produce components with massive secondary functional elements from sheet metal bulk forming operations, termed sheet‐bulk metal forming, can be applied. Owing to high, three‐dimensional stress and strain states present during sheet‐bulk metal forming, ductile damage occurs in the form of micro‐voids. Depending on the material flow properties, tensile residual stresses can also be present in the components' formed functional elements. During service, the components are subjected to cyclic loading via these functional elements, and tensile residual stresses exert an unfavorable influence on crack initiation and crack growth, and therefore on the fatigue life. Following the forming process, temperature and microstructurally related compressive residual stresses can be induced by local heat treating of the surface. These residual stresses can counteract potential crack initiation on the surface or in the subsurface regions. In the present study, the adjustability of the residual stress state is investigated using a workpiece manufactured by orbital cold‐forming, which possesses an accumulation of material in its edge region. Based on residual stress measurements in the workpiece's edge region using x‐ray diffractometry, it is possible to verify the compressive residual stresses adjusted by varying the cooling conditions. By cold bulk forming processes applied to sheet metal, components with massive secondary functional elements can be produced. Due to this three‐dimensional cold‐forming operations unfavorable tensile residual stresses can remain in the components’ surface area. By induction heat treating and subsequent water–air spray cooling, it is possible to induce compressive residual stress and improve mechanical properties of the workpieces.