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ORIGINAL ARTICLE

Comparison of Cold and Hot Forged EN8 Flats: Spring Back Effect, Surface Hardness and Microstructural Features Rupinder Singh1

•

Bibandeep Singh1 • S. S. Banwait1

Received: 27 March 2020 / Accepted: 24 August 2020  The Indian Institute of Metals - IIM 2020

Abstract This paper reports the comparison of cold and hot forged EN8 flats for spring back effect, surface hardness and microstructural features as a case study of an industrial component ‘U-Fork’ (a subpart of tractor’s threepoint hitch’s lift rod). The industrial component/benchmark has been selected as a common agricultural automobile component used under cyclic loading conditions. For this comparative study, surface hardness and surface roughness (Ra) of the material have been analyzed by using microVickers hardness and 3D rendered images, Ra profiles, amplitude distribution function, respectively, whereas microstructure and its features (grain size number, average grain diameter, porosity, etc.) have been characterized using energy-dispersive X-ray spectroscopy and scanning electron microscope. The result of the case study reveals that hot forging has increased the dimensional accuracy by 11.15%, overcoming the spring back effect. Also, a significant reduction in porosity (54.28%) and increment in surface hardness (15.66%) are observed for hot forged EN8 flats in comparison to cold forged components. Keywords EN8  Hot forging  Cold forging  Microstructure  Spring back  Grain size

& Rupinder Singh [email protected] Bibandeep Singh [email protected] S. S. Banwait [email protected] 1

Department of Mechanical Engineering, National Institute of Technical Teachers Training and Research, Chandigarh, India

1 Introduction The EN8 engineering steel is an unalloyed medium carbon (C) steel, with a C content of 0.36–0.44% and manganese (Mn) ranging from 0.6 to 1.0%, making it stronger than low C steel with improved machining and wear resistance properties [1]. Due to these features, EN8 steel is extensively used in general engineering and automotive trades for the manufacturing of bolts, gears, studs and U-Fork, automobile axles, crankshafts, respectively [2]. Based upon the C percentage, forging of EN8 material should be performed at or above its re-crystallization temperature (hot forging) but commercially in many industries (like hand tools, automobile ancillary components, etc.), parts are being manufactured by cold forging. One of the reasons for this may be that in cold forging, no post finishing operations are required [3]. In a typical cold forging process, the components are annealed before forging [4–7]. It has been widely reported that cold forging results in material saving as one gets near a net-shaped product, offers a good level of surface finish and dimensional stability [8–11]. For commercial operations, high production rates and better die life are other significant advantages of cold forging [12–15]. On the other hand, hot forging has less spring back effect, better stress relieving capabilities. During fo