Effect of Non-Metallic Inclusion from the Continuous Casting Process on the Multi-Stage Forging Process and the Tensile Strength of the Bolt: A Case Study

The paper presents the influence of non-metallic inclusions on the multi-stage forging process and the mechanical properties of the dodecagon socket bolt used in the automotive industry. The detected metallurgical defect was so large that it directly influenced the mechanical properties of the bolt and resulted in failure to meet the requirements of the mechanical property class. In order to assess the defect, an X-ray examination and metallographic examination of the defective bolt were performed, showing exogenous non-metallic inclusion. The size of the defect on the cross section was 0.531 mm in width and 1.523 mm in length; the defect was continuous along the entire axis of the bolt. In analysis, a finite element method (FEM) simulation of the multi-stage forging process was designed, taking into account a non-metallic inclusion parallel to the sample axis, reflecting the studied case. The process of defect propagation due to material upset in the head area was analyzed. The final forging stage in shaping the dodecagonal socket and filling the flange area was particularly studied. The effect of the defect was observed to significantly reduce the effective cross-section as a result of the expansion of the defect perpendicular to the axis of the bolt. The mechanical properties of products with and without the defect were analyzed. In the first step, the hardness test confirmed that the required value for the mechanical class 8.8 of both bolt types was obtained. In the second step, the bolts were subjected to a static tensile test. The bolts without the defect gave a positive result, while all 10 bolts with the defect gave a negative result, achieving a tensile strength below the requirements. Tensile strength tests were confirmed by metallographic tests and FEM simulation with perpendicular inclusion spread in the area of the head. The bolts were damaged directly under the bolt head, which is inconsistent with the requirements of ISO 898-1. It has been shown that non-metallic inclusions with orientation in accordance with the axis of the bolt can directly cause loss of functionality and these defects should be detected even before assembling in the machine element.

• Tomasz Dubiel
• Tadeusz Balawender
• Mirosław Osetek

• continuous casting
• multi-stage forging
• non-metallic inclusion
• upset bolt head

[1] S. Louhenkilpi, „Continuous Casting of Steel”, in Treatise on Process Metallurgy, vol. 3, S. Seetharaman, Ed. Elsevier, 2014, pp. 373-434.
[2] T. Emi, „Improving steelmaking and steel properties” in Fundamentals of Metallurgy, S. Seetharaman, Ed. Woodhead Publishing, 2005, pp. 503-554.
[3] J. Campbell, „The fracture of liquids”, in The Mechanisms of Metallurgical Failure, J. Campbell, Ed. Butterworth-Heinemann, 2020, pp. 1-165.
[4] S. Sridhar, H.Y. Sohn, „The kinetics of metallurgical reactions” in Fundamentals of Metallurgy, S. Seetharaman, Ed. Woodhead Publishing, 2005, pp. 270–349.
[5] U. Zerbst, M. Madia, C. Klinger, D. Bettge, T. Murakami, „Defects as a root cause of fatigue failure of metallic components. II: Non-metallic inclusions,” Eng. Fail. Anal., vol. 98, pp. 228–239, Apr. 2019.
[6] R.K. Pandey, „Failure of diesel engine crankshafts,” Eng. Fail. Anal., vol. 10, pp.165–175, Apr. 2003.
[7] M.E. Stevenson, J.L. McDougall, R.D. Bowman, R. L. Herman, „Failure analysis of a high-speed pinion shaft,” J Fail. Anal. and Preven., vol. 5, pp. 48–54, Apr. 2005.
[8] C. Baldizzone, A. Gruttadauria, C. Mapelli, D. Mombelli, „Investigation of Failure in a Crankpin of a Motorcycle Engine,” J Fail. Anal. and Preven., vol. 12, pp. 123–129, Apr. 2012.
[9] A.I.Z. Farahat, A. Hamid, N. Gomaa, „Failure analysis of train vehicles engagement arm,” J. Fail. Anal. Prev., vol. 15 pp.576–582, Oct. 2015.
[10] K.P. Balan, „Failure analysis of a wire rope,” ASME Int, Pract. Fail. Anal., vol. 3, pp. 71–74, March 2002.
[11] AR. Jo, M.S. Jeong, S.K. Lee, Y.H. Moon, S.K. Hwang, „Multi-Stage Cold Forging Process for Manufacturing a High-Strength One-Body Input Shaft,” Materials, vol. 14, pp. 532-546, Jan. 2021.
[12] JS. Choi, HC. Lee, YT. Im, „A study on chevron crack formation and evolution in a cold extrusion,” J. Mech. Sci. Technol., vol. 24, pp. 1885–1890, Oct. 2010.
[13] V. Singh, R. Khan, B. Bandi, G.G. Roy, P. Srirangam, „Effect of non-metallic inclusions (NMI) on crack formation in forged steel. Mater,” Today Proc., vol. 41, pp. 1096-1102, 2021.
[14] Z. Li, D. Wu, J.X. Liu, „Analysis of cracking phenomenon occurring during cold forging of ML25Mn Steel,” Key Eng. Mater., vol. 324–325, pp. 643–646, Nov. 2006.
[15] S.H. Hosseini, M. Sedighi, J. Mosayebnezhad, „Numerical and experimental investigation of central cavity formation in aluminum during forward extrusion proces,” J. Mech. Sci. Technol., vol. 30, pp. 1951–1956, May 2016.
[16] ISO 898-1:2013 – „Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1: Bolts, screws and studs with specified property classes — Coarse thread and fine pitch thread”.
[17] EN 10263-2:2017 – „Steel rod, bars and wire for cold heading and cold extrusion. General technical delivery conditions”.
[18] D. Krewerth, T. Lippmann, A. Weidner, H. Biermann „Influence of non-metallic inclusions on fatigue life in the very high cycle fatigue regime,” Int. J. Fatigue, vol. 84, pp. 40–52, March 2016.
[19] U. Zerbst, S. Beretta, G. Köhler, A. Lawton, M. Vormwald, H.Th. Beier, C. Klinger, I. Černý, J. Rudlin, T. Heckel, D. Klingbeil, „Safe life and damage tolerance aspects of railway axles – A review,” Eng. Fract. Mech., vol. 98, pp. 214-271, Jan. 2013