IN ITALIA. 23/11/2018, Università degli Studi di Modena

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1 23/11/2018, Università degli Studi di Modena Ottimizzazione del processo di tempra dell acciaio attraverso la simulazione Andrea Giuseppe Pisa (ARGO srl) IN ITALIA

2 Introduction to heat treatments (HT) WHAT Industrial processes to increment mechanical properties (Hardness, UTS, Toughness, ) of metallic parts. Non-optimized process conditions lead to distortions, part cracking, inadequate or inhomogeneous properties. Commonly, industrial parts are not intentionally designed to withstand HT induced mechanical stresses. With Code_Aster we can design the HT for each component. Among HTs, quenching is famous for bringing many issues

3 Quenching of steels Hardness increase treatment. WHAT HOW Martensite(Ms) is an hard phase formed by the rapid cooling of the austenite phase (hot phase) of iron, when carbon atoms do not have time to rearrange in equilibrium room temperature microstructures. ISSUES We have to be sure that the HT is homogeneously done avoiding stresses that lead to permanent deformations (stress>yield). Quenching simulation requires a dedicated model

4 Quenching Simulation model Quenching is a multi-scale and multi-physics problem. Stress/strain behaviour is the sum of 2 phenomena Cooling rate TEMPERATURE EVOLUTION Thermal dilatation induced stress (expansion/contraction) PHASE TRANSFORMATIONS Phase transformations induced stress STRESS/STRAIN

5 What Code_Aster offers for steel quenching META_ACIER is used to model the transformations kinetics and the related metallurgical behavior. Master degree Politecnico di Torino (2015) Simulazione Numerica dello Stadio di Tempra con Diversi Mezzi Tempranti su Acciai Basso Legati Mediante Software Open Source Mario Questino, rel. Prof. Ugues co-rel. Andrea G. Pisa, Andrea Colosimo Detailed material properties need to be included Properties that usually are difficult to find (mainly by literature)

6 Material properties 42CrMo4 Code_Aster was calibrated to model 42CrMo4 steel CCT DIAGRAM (literature) VOLUME CHANGES (experimental)

7 Relation between temperature and metallurgy Material properties are of main importance for quench simulations However the first step to get an accurate quenching simulation is the detailed modeling of the cooling rate. Cooling rate is the driving force of the metallurgical transformations. How we model the cooling? Cooling is mainly modeled with Heat Exchange (or Transfer) Coefficient - HEC

8 Introducing Heat Exchange Coefficient (HEC or h) WHY HEC? Part surface temperature during cooling is heterogeneous, Heat transfer has strongly non-linear behavior! We need to set non-linear boundary conditions in Code_Aster How?

9 Measuring h(t) h average values only for comparison Accurate simulations need accurate boundary conditions (h) Accurate h (T) [W/m 2 C] values are gathered experimentally Thermocouple REF. Simulazione numerica del trattamento termico di un particolare in acciaio forgiato. Andrea Giuseppe Pisa, rel. Daniele Ugues, Giovanni Maizza We calculate h(t) from the thermal evolution at the center of a small pure copper sphere, knowing its surface extension, volume and thermal properties.

10 h(t) values for quenching oils real issue 3000 OIL 40 C OIL 60 C OIL 40 C OIL 60 C h TEMPERATURE [ C]

11 Heat transfer coefficient inside Code_Aster THER_NON_LINE Heat exchange (ECHANGE) subroutines of Code_Aster can only handle a h coefficient function of time h(inst), but we need to model h(t surface )! The heat exchange is defined as a non linear thermal flux (FLUX_NL) acting on the quenching surface depending by its temperature (TEMP).

12 Oil quenching example Temperature distribution ΔT ~100 C ΔT >300 C

13 Case study - Quench oil degradation effects Usually oil quenching baths are only refilled when the level is too low, however such oils get degraded by working conditions losing their properties. OLD degraded NEW

14 Results of oil degradation on a 42CrMo4 demo gear NEW OIL OLD DEGRADED OIL MARTENSITE FRACTION NEW OIL OLD DEGRADED OIL BAINITE FRACTION Ref. Simulazione Numerica dello Stadio di Tempra con Diversi Mezzi Tempranti su Acciai Basso Legati Mediante Software Open Source Mario Questino

15 Comments Martensite fraction is lower when using degraded quenching oil As a consequence there is an higher fraction of bainite phase with old oil Wear on the gear tooth with lower martensite will be more severe Accurate cooling simulation with experimental HEC importance has been demonstrated. This is a real example of how simulations and Code_Aster can help to solve real industrial issues in HT sector.

16 Future works - Orientation influence Influence of the cooling direction on final stresses in: Immersion quenching (orientation) Gas quenching (flow direction) The future will be the coupling of a HEC, calculated by CFD software, with Code_Aster to simulate the real influence of quenching orientation in terms of distortions and phase distribution. We have already performed HEC simulations of gas quenching in vacuum furnaces

17 Future developments CFD coupling (Code_Saturne) Vacuum furnace simulation with code_saturne Simulazione numerica di un processo di tempra in vuoto con software open source. Andrea Macaluso, rel. Prof. Ugues co-rel. Andrea Pisa Thermocouple Simulation Heat Flux

18 THANK YOU FOR YOUR ATTENTION ANY QUESTION? Contacts: