An Insight into the Defects-Driven Plasticity in Ductile Cast Irons

The microstructure and tensile behavior of two heavy section castings that had chemical compositions typical of GJS400 were investigated. Conventional metallography, fractography, and micro-Computer Tomography (μ-CT) were employed, enabling the quantification of the volume fractions of eutectic cells with degenerated Chunky Graphite (CHG), which was identified as the major defect in the castings. The Voce equation approach was exploited to evaluate the tensile behaviors of the defective castings for integrity assessment. The results demonstrated that the Defects-Driven Plasticity (DDP) phenomenon, which refers to an unexpected regular plastic behavior related to defects and metallurgical discontinuities, was consistent with the observed tensile behavior. This resulted in a linearity of Voce parameters in the Matrix Assessment Diagram (MAD), which contradicts the physical meaning of the Voce equation. The findings suggest that the defects, such as CHG, contribute to the linear distribution of Voce parameters in the MAD. Furthermore, it is reported that the linearity in the MAD of Voce parameters for a defective casting is equivalent to the existence of a pivotal point in the differential data of the tensile strain hardening data. This pivotal point was exploited to propose a new material quality index assessing the integrity of castings.

[1]  I. Riposan,et al.  Graphite Nodularity Evaluation in High-Si Ductile Cast Irons , 2022, Materials.

[2]  J. Bidulská,et al.  Effect of Austenitization Temperature on Hot Ductility of C-Mn-Al HSLA Steel , 2022, Materials.

[3]  G. Angella,et al.  The Correlation between Solidification Rates, Microstructure Integrity and Tensile Plastic Behaviour in 4.2 wt.% Silicon Strengthened Ductile Iron , 2022, Journal of Casting & Materials Engineering.

[4]  R. Bidulský,et al.  Overview of HSS Steel Grades Development and Study of Reheating Condition Effects on Austenite Grain Size Changes , 2021, Materials.

[5]  J. Rezende,et al.  Influence of Cooling and Strain Rates on the Hot Ductility of High Manganese Steels Within the System Fe–Mn–Al–C , 2020, steel research international.

[6]  G. Angella,et al.  Assessment of microstructure effects on tensile behaviour in silicon strengthened ductile irons produced through different cooling rates , 2020 .

[7]  F. Iacoviello,et al.  Relation between microstructural heterogeneities and damage mechanisms of a ferritic spheroidal graphite cast iron during tensile loading , 2020 .

[8]  G. Angella,et al.  Soundness Discrimination in Ferrite Ductile Irons Through Tensile Data Analysis , 2020, International Journal of Metalcasting.

[9]  M. Górny,et al.  The Role of Microstructure on Tensile Plastic Behavior of Ductile Iron GJS 400 Produced through Different Cooling Rates, Part I: Microstructure , 2019, Metals.

[10]  Donnini,et al.  The Role of Microstructure on the Tensile Plastic Behaviour of Ductile Iron GJS 400 Produced through Different Cooling Rates—Part II: Tensile Modelling , 2019, Metals.

[11]  W. Baer.  Chunky Graphite in Ferritic Spheroidal Graphite Cast Iron: Formation, Prevention, Characterization, Impact on Properties: An Overview , 2019, International Journal of Metalcasting.

[12]  M. Benedetti,et al.  Effect of graphite morphology on the fatigue and fracture resistance of ferritic ductile cast iron , 2019, Engineering Fracture Mechanics.

[13]  P. Mrvar,et al.  Effect of Si and Ni Addition on Graphite Morphology in Heavy-Section Spheroidal Graphite Iron Parts , 2018, Materials Science Forum.

[14]  B. Tonn,et al.  Degenerated Graphite Growth in Ductile Iron , 2018, Materials Science Forum.

[15]  André Ebel,et al.  Effects of high silicon contents on graphite morphology and room temperature mechanical properties of as-cast ferritic ductile cast irons. Part II – Mechanical properties , 2018 .

[16]  J. Lacaze,et al.  Effects of high silicon contents on graphite morphology and room temperature mechanical properties of as-cast ferritic ductile cast irons. Part I – Microstructure , 2018 .

[17]  C. Carollo,et al.  Fatigue strength improvement of heavy-section pearlitic ductile iron castings by in-mould inoculation treatment , 2017 .

[18]  P. Mrvar,et al.  Effect of inoculation on the formation of chunky graphite in ductile-iron castings , 2017 .

[19]  A. Bührig-Polaczek,et al.  Physico-chemical causes of the formation of chunky graphite in austenitic ductile iron , 2017 .

[20]  M. Gelfi,et al.  Fatigue design of heavy section ductile irons: Influence of chunky graphite , 2016 .

[21]  J. Lacaze,et al.  Chunky graphite formation in ductile cast irons: effect of silicon, carbon and rare earths , 2016 .

[22]  V. Cocco,et al.  Influence of the graphite elements morphology on the fatigue crack propagation mechanisms in a ferritic ductile cast iron , 2016 .

[23]  F. Berto,et al.  Mechanical and Fatigue Properties of Heavy Section Solution Strengthened Ferritic Ductile Iron Castings   , 2016 .

[24]  N. Shiraki,et al.  Relationship between Fatigue Limit and Defect Size in Spheroidal Graphite Cast Iron with Different Graphite Spheroidization Ratios and Microstructures , 2015 .

[25]  M. Arikan.  Hot Ductility Behavior of a Peritectic Steel during Continuous Casting , 2015 .

[26]  M. Endo,et al.  Effects of small defects, matrix structures and loading conditions on the fatigue strength of ductile cast irons , 2014 .

[27]  K. Jóźwiak,et al.  Cast Iron Casing Cracking Due to Chunky Graphite Formation , 2013, Journal of Failure Analysis and Prevention.

[28]  J. Lacaze,et al.  Statistical Analysis of the Influence of Some Trace Elements on Chunky Graphite Formation in Heavy Section Nodular Iron Castings , 2013, Metallurgical and Materials Transactions A.

[29]  Filippo Berto,et al.  Fatigue properties of ductile cast iron containing chunky graphite , 2012 .

[30]  K. Ravi-Chandar,et al.  Deformation and failure in nodular cast iron , 2012 .

[31]  Karl-Fredrik Nilsson,et al.  Analysis of ductile cast iron tensile tests to relate ductility variation to casting defects and material microstructure , 2009 .

[32]  C. H. Cáceres.  A rationale for the quality index of Al-Si-Mg casting alloys , 2000 .

[33]  Zdeněk P. Bažant,et al.  Mechanics of solid materials , 1992 .

[34]  C. M. Hansson,et al.  Cast iron technology , 1989 .

[35]  L. Feldkamp,et al.  Practical cone-beam algorithm , 1984 .

[36]  Sophia Blau,et al.  Introduction To Continuum Damage Mechanics , 2016 .

[37]  J. Lacaze,et al.  Experimental Evidence for Metallurgical Modification Associated to Chunky Graphite in Heavy-Section Ductile Iron Castings , 2012, International Journal of Metalcasting.

[38]  L. Björkegren,et al.  Chunky Graphite formation and influence on Mechanichal Properties in Ductile Cast Iron , 2005 .

[39]  U. F. Kocks,et al.  Physics and phenomenology of strain hardening: the FCC case , 2003 .