Zanardi Fonderie S.p.A. INFORMATIONAL SHEET ON AUSTEMPERED DUCTILE IRON - PROPERTY WEAR RESISTANCE -

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1 Scope The aim of this document is to familiarize the designer with the Wear behaviour of Austempered Ductile Iron and Isothermed Ductile Iron. It is an informative document, not to be referred as a standard. The data in this document are taken from Zanardi research database, international standards and technical papers. Disclaimer The content of this informational sheet has to be considered for information only. The real component design shall be based only upon international standards and/or contractual agreements. References 1. ZANARDI STANDARD 101: ISO 17804:2005 Founding Ausferritic Spheroidal Graphite Cast irons Classification 3. ISO 1083:2004 Founding Spheroidal graphite cast irons 4. ZANARDI Database 5. ASTM G Standard Test Method for Pin Abrasion Testing 6. EN12513: 2010 (DRAFT) 7. ISO Calculation of load capacity of spur and helical gears Part 5: Strength and quality of materials 8. MATWEB.COM The Online Materials Database 9. G. Straffelini, Università delgi Studi di Trento Attrito e Usura 10. G. Straffelini, C. Giuliari Comportamento a Strisciamento - Rotolamento delle ghise ADI, IDI e acciaio 42CrMo4 QT + Ni 11. L. Maines, G. Straffelini, A. Molinari, A. Bassetti, Università delgi Studi di Trento Comportamento ad Usura delle Ghise Austemperate per Applicazioni motoristiche 12. M. Hatate, T. Shiota, N. Takahashi, K. Shimizu, Influences of graphite shapes on wear characteristics of austempered cast iron 00 Emesso nuova edizione, modificato titolo VEN Rev Descrizione Data Firma Zanardi Fonderie Spa Italy Ed.01 Rev All rights reserved Pag. 1/15

2 Summary Scope... 1 Disclaimer... 1 References...1 Summary...2 Material notes...2 Examples of microstructure and static fracture behaviour... 3 Contact fatigue wear... 4 Material notes Austempered Ductile Iron (ADI) is produced by heat-treating an alloyed ductile iron, casted with a special preconditioning of the metal bath. The matrix structure consists predominantly of ferrite and austenite. The matrix is called ausferritic and gives to the new material unique mechanical properties. Isothermed Ductile Iron (IDI) is produced by heat-treating an unalloyed ductile iron, casted with a special preconditioning of the metal bath. The matrix structure of the grade IDI consists predominantly of ferrite and pearlite, distributed differently from the usual shapes of the as cast grades. The new matrix is called perferritic and gives to the new material unique mechanical properties. The grade IDI is subject of a patent application by Zanardi Fonderie SpA. Nitrided 42CrMo4 Q&T Steel is considered for benchmarking and is produced by hot rolling. Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 2/15

3 Zanardi Fonderie S.p.A. Examples of microstructure and static fracture behavior FRACTURE SURFACE 500 x 42CrMo4 + Ni ADI ADI800-8 IDI GS MICROSTRUCTURE 100 x Figure 1 Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 3/15

4 Examples of microstructure of considered abrasion resistant materials Ni-Cr-HC Class I A (Ni-Hard) ADI WR2 EN-GJN-HB555 Martensite + Ledeburite + Carbides Acicular ausferrite + 50% retained austenite 12% Cr Class II A ADI WR1 EN-GJN-HB510 Martensite + Carbides Acicular ausferrite + 30% retained austenite 25%Cr Class III A JS/HBW400 (ADI 1400) Martensite + Ledeburite + Carbides Fine acicular ausferrite (10% austenite) QT 33MnCrB5 JS/HBW450 (ADI 1600) Bainite JS/800-2 (GS 800) JS/ (ADI 1000) Acicular ausferrite (50% austenite) Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 4/15

5 General concepts on Wear Some general concepts on contact between surfaces and the consequent wear phenomenon will be shown below. Taken from reference [9]. In mechanics, many different wear processes may occur, depending on the contact mode. As regard the most typical ADI applications, we can identify the following wear processes: 1) Sliding wear (fig 1a) 2) Rolling wear, (fig 1b) 3) Sliding-rolling contact (fig 1c) 4) Fretting (fig 1d) 5) Abrasion (fig 1e) V c V c1 = V c2 V c1 > V c2 Fig. 1a Fig. 1b Fig. 1c V c V c Fig. 1d Fig. 1e In each process it is possible to find different wear mechanisms, dependently on the : 1) Adhesive wear 2) Tribo-oxidative wear 3) Abrasive wear 4) Surface fatigue In table 1 we associate wear processes to predominant wear mechanisms and the ADI application field in which it is possible to find them Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 5/15

6 Wear Process Wear mechanism Field application Sliding wear Adhesion Tribo-oxidation Abrasion Positioning gears Crankshaft connection rods Rolling wear Surface fatigue Rollers or contact to rollers surface Very high speed gears Sliding-rolling contact Surface fatigue Adhesion Tribo-oxidation Gears Pulleys Fretting Adhesion Tribo-oxidation Connection by friction Positioning Lever Vibrating contacts Abrasive Wear Abrasion (High load contact) Heart moving machines Undercarriage applications Mining Concrete mixers Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 6/15

7 ADI behavior in case of high load Abrasive Wear Abrasion wear process occurs when a surface is in contact with another surface characterized on the presence of very highly hard particles. In practice, this happens when a part works on sand/stony grounds or into concrete or other abrasive means. ADI is a well known wear resistant material. The abrasive wear resistance of a given material mainly depends on its hardness. Differently, with ADI this property depends on its hardness and especially on its particular microstructure. The content of this chapter is based on experimental figures collected in Zanardi Fonderie S.p.A. by a Pin on Disk test filed [4] and other similar research works [10], [11], [12], [13] and the results are shown in fig 2, as follows: Relative Abrasion Resistance vs Hardness Resistenza relativa all'usura vs Durezza 110% [1] REF TO ASTM532-93a [2] REF TO EN12513: 2010 (Draft) 12% Cr Class II A [1] EN-GJN-555 (XCr11) [2] 100% Ni-Cr-HC Class I A [1] (Ni-Hard) EN-GJN-510 [2] 90% ADI WR2 Wr [%] ADI WR1 80% JS/HBW400 (ADI 1400) JS/HBW450 (ADI 1600) 33MnCrB5 (Q&T) 70% JS/ (ADI 1000) 25%Cr Class III A HARDOX % HRC 66HRC Hardness [HBW] Figure 2, values of relative Wear rate are referred to Ni-Cr HC Class 1A (62.5 HRc) taken as 100% Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 7/15

8 ADI when compared to a given material with the same hardness level show a higher wear resistance to abrasion (e.g see in figure 2 the comparison with Hardox 400 HB). This behavior is due to the P.I.T.R.A.M. effect (Pressure Induced Transformation of Retained Austenite to Martensite) or sometimes called also S.I.T.R.A.M. effect (Stess Induced Transformation of Retained Austenite to Martensite) promoted by the application of mechanical stress. This structural change takes place locally, at a microscopic level, and produces a marked increment of hardness and therefore an improved abrasion resistance. PITRAM effect does not affect the surface hardness, so it is not possible to see the work hardening on the part because of the microscopic transformation. There would only be an increase of the part or, in our test s case, the specimen duration. The high load contact with an abrasive material produces on the abraded surface high local stresses and this is the main reason why ADI is successfully applied when this wear process occurs. In addition to the traditional ADI grades, as in reference [1], and other typical wear resistant materials as abrasion-resistant cast iron and several steels, an innovative class of materials (included into the ZND 102 Company Standard) is considered: ADI WR (Wear Resistant ADI): two grades of this material have recently been developed at Zanardi Fonderie enhancing this PITRAM effect and consequently with the double aim to produce an as-cast machinable material with a good toughness after austempering heat treatment. Therefore, ADI WR are directly in competition with: traditional abrasion-resistant white cast iron (unalloyed or low alloyed - nickelchromium based - high chromium based). ADIs WR offer an improved toughness, better impact properties and a machinable as-cast matrix due to the absence of ascast simple or complex carbides. some steels, ADIs WR offer adequate toughness and impact properties in several applications. Even if the experience with this materials is limited, the first results from the application field are promising, competing favorably with the majority of traditional materials for wear application. Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 8/15

9 Relative Abrasion Resistance Resistenza relativa all'usura abrasiva 107% 100% 100% [1] REF TO ASTM532-93a [2] REF TO EN12513: 2010 (Draft) 88% 87% 80% 79% 80% 77% 76% 71% Wr [%] 60% 62% 40% 20% 0% Ni-Cr-HC Class I A L2 (Ni-Hard) [1] EN-GJN-HB510 [2] 12% Cr Class II A L2 [1] EN-GJN-HB500 (XCr11) [2] ADI WR2 ADI WR1 33MnCrB5 (Q&T) Material Materiale JS/HBW450 (ADI 1600) JS/HBW400 (ADI 1400) 25%Cr Class III A JS/ (ADI 1000) HARDOX 400 Figure 3 The picture above shows the ranking of the materials tested during the Zanardi research activity. It has been assumed the conventional abrasive wear resistance of 100% for the reference material Ni-Cr-HC Class IA (695 HBW 62.5 HRC). Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 9/15

10 Un-notched Impact Resistance Vs Hardness Resistenza all'impatto Vs Durezza MnCrB5 (Q&T) 140 JS/ (ADI 1000) 120 K +23 C [J] HARDOX 400 JS/HBW400 (ADI 1400) JS/HBW450 (ADI 1600) 20 ADI WR1 12% Cr Class II A Ni-Cr-HC Class I A 25%Cr Class III A ADI WR2 (Ni-Hard) Hardness [HBW] (63 HRC) (66 HRC) Un-notched Impact Resistance vs Hardness Resistenza all'impatto vs Durezza 35 [1] REF TO ASTM532-93a [2] REF TO EN12513: 2010 (Draft) 30 JS/HBW450 (ADI 1600) 25 K +23 C [J] ADI WR1 10 ADI WR2 5 25%Cr Class III A 12% Cr Class II A [1] EN-GJN-555 (XCr11) [2] Ni-Cr-HC Class I A [1] (Ni-Hard) EN-GJN-510 [2] Hardness [HBW] 63HRC 66HRC Figure 4 The picture shows the hardness (HBW) and the un-notched impact resistance at room temperature for the different materials. The highest Cr-Hard and Ni-Cr-Hard grades have high hardness but low impact properties. Impact resistance is frequently required in the application field (e.g. stone crushers). ADI WR1 and ADI WR2 show better impact resistance than Cr-Hard and Ni-Hard cast irons. Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 10/15

11 ADI and IDI behavior in case of sliding-rolling contact Sliding-rolling contact is a wear process that typically occurs on gears. In fact on the primitive diameter there would be theoretically a pure rolling contact or line contact between two teeth flanks. Actually when two teeth meshes the dynamic of the contact starts with : - a pure sliding (fig 4a), - pure rolling contact on the primitive diameter (fig 4b) - and again sliding when the contact is going to be finished (fig 4c). Once more, due to the deformation that on any material occurs, the contact zone can not be a line but it should be an area thus we have to consider a sliding contact in the areas close to the theoretical contact point. This wear mechanism is reasonably similar to a disk to disk contact that turn at a different velocity, as shown in fig 5. Figure 4 Figure 5 Figure 6, theoretical line contact Figure 7, actual contact area The content of this chapter is based on experimental figures coming from Disk on Disk test filed in dry conditions [10]. The aim of the following paragraphs is to compare the behavior of ADI and IDI when sliding-rolling contact wear occurs with a 42CrMo4 QT Nitrided, that is typically used on gears. Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 11/15

12 Nitrided steel behavior Nitrided steel is characterized of its typical surface white layer induced by Nitriding treatment. This is a very hard layer and gives to the material a very good wear resistance due to its surface hardness, limited to the white layer duration. In fact, as shown, in figure 8, its thickness is limited to some tenths of millimeter ( mm). This layer can be also reduced in case of grinding operations in order to restore the geometrical requirements. Figure 8 Nitrided steel shows the following wear mechanism: - during the contact the bulk material, under the nitrided layer, is deformed. The nitrided layer, is less deformable than the substrate thus during the contact will be fractured. - Fractures on nitrided layer during the process will detach small particles of nitrided layer. - These particles acts on the surface as an abrasive material (fig 9) Figure 9 Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 12/15

13 ADI and IDI behavior ADI thanks to its production process shows an homogeneous structure through out the section of the considered component. For this reason the component will not have any sudden wear of its performances during its predicted life. ADIs have shown very good wear performances, even better than Nitrided steel. Grade JS/ have shown the best performances in case of sliding-rolling contact, in terms of lower wear rate and lower friction coefficient than nitrided steel. IDI have shown an higher wear rate than ADI but it could be enough for some low stressed application. ADI and IDI show the following wear behavior: - during the contact the material on surface starts to be deformed as much as the contact pressure is high. - After few meters of contact a very hard layer begins to forms on the contact surface. This layer is called Mechanically Mixed Layer. (Fig 10-12) - The wear mechanism appeared as a combination of adhesion and tribo-oxidation and it acts on the Mechanically Mixed Layer. It was not proved but it is reasonable to say that the deformation process into the Ausferritic matrix has induced the martensitic transformation of retained Austenite, previously called PITRAM effect. For this reason the hardness of the MML in ADI grade is higher than in IDI, that has not an Ausferritic matrix. - Due to the homogeneity of ADI and IDI Mechanically Mixed Layer is continuously renewed by the substrate material - Nodules are part of the substrate structure and during its deformation are taken out to the surface. Since they are on surface they work as a solid lubricant, reducing the friction coefficient (fig. 14) IDI JS/ JS/ Figure 10 Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 13/15

14 HV vs Hertzian Pressure Mechanically Mixed Layer = MML HV p [MPa] JS/ JS CrMo4+ Ni IDI Figure 11, Mechanically Mixed Layer Figure 12, Surface Hardness of MML 1,40E-03 Wear Rate ranking 4,00E-01 Friction coefficient ranking 1,20E-03 Nitrided Steel 3,50E-01 Nitrided Steel 1,00E-03 3,00E-01 Wr [mm3/m] 8,00E-04 6,00E-04 ADI JS/ IDI µ 2,50E-01 2,00E-01 1,50E-01 ADI JS/ ADI JS/ IDI 4,00E-04 ADI JS/ ,00E-01 2,00E-04 5,00E-02 0,00E ,00E Figure 13, Wear resistance comparison Figure 14, friction coefficient comparison The aim of Wear resistance comparison, shown in figure 13, is to give a semiquantitative suggestion to Designer on which are the opportunities offered by ADI. Since the wear rate measurements is based on the loss of weight of the sample during the test, is only possible to state that ADI has a similar resistance than Nitrided steel in case of sliding-rolling contact. Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 14/15

15 ADI and IDI behavior with other wear processes Since the experience is limited to Abrasion wear and Sliding-rolling contact is only possible to make some reasonable considerations on the ADI and IDI behavior for each wear process based on the presence of known wear mechanism. The following table gives a suggestion of which ADI should be most suitable for each wear process. Of course, these suggestions must be adapted to the real application Design process. Wear Process Wear mechanism ADI and IDI Behavior Sliding wear Adhesive wear Tribo-oxidation Abrasion Due to the presence of abrasive wear mechanism, the principal driver would be the hardness of the considered material. For this reason, ADI grades under the grade JS/ could not be suitable in case of Sliding wear and fretting process. Higher hardness grades, included ADI WR Rolling wear Sliding-rolling contact Abrasion Surface fatigue Surface fatigue Adhesive wear Tribo-oxidation Abrasive wear (High load contact) could be applicable. ADI low grades and IDI have shown good wear properties in case of rolling wear or rolling contact, in dry conditions. In fact this mechanism seems to be the promoter of Mechanically Mixed Layer in those materials. For this reason, ADI grades and IDI under the grade JS/ can be suitable when Rolling wear, Sliding-rolling contact and rolling contact occurs. Higher hardness grades, included ADI WR could not be suitable in this case. Due to the presence of high load abrasive wear mechanism, in this case there are two principal drivers: hardness and microstructure. For this reason, ADI grades and IDI under the grade JS/ could not be suitable in case of Sliding wear process. Higher hardness grades, especially ADI WR are suggested in case of Abrasive wear process. In any case the ADI grade should be chosen taking into account also the other properties required on the specific application and that can be reached by ADI (e.g. fatigue resistance, impact resistance, etc.). Zanardi Fonderie Spa Italy Ed.00 Rev All rights reserved Pag. 15/15