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Metal Processing Module

Simulate Metallurgical Phase Transformations in Mechanical Components

When a material like steel or cast iron undergoes cooling from an elevated temperature, metallurgical phase transformations may occur. The Metal Processing Module is an add-on product to the COMSOL Multiphysics® simulation software that can be used to study how these phase transformations affect the mechanical and thermal properties of the materials. The module includes functionality for modeling phase transformations that are deliberate (such as in steel quenching and carburization) and introduced inadvertently (in additive manufacturing and welding, for example), as well as functionality for annealing. The built-in multiphysics capabilities can help improve the performance of a component by optimizing the phase composition.

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A metal spur gear model with a small slice shown.
A bevel gear model shown in orange and purple.

Steel Quenching

Steel quenching is a heat treatment process where steel parts that have been heated to a fully austenitic state are rapidly cooled. Steel quenching is also a multiphysics process, as it involves a combination of austenite decomposition, heat transfer, and structural analysis. The Metal Processing Module provides specialized features and functionality to facilitate the model setup for this multiphysics process.

After running the analysis, phase compositions and the influence of cooling rate on the final distortions and residual stresses during the quenching of a component can be examined. These results provide insight into the efficacy of a certain quenchant and how the physical geometry of a component affects the attainable phase composition in its interior.

Carburization

The process of carburization involves heating a steel component and exposing it to a carbon-rich environment, such as carbon monoxide. Diffusion of carbon from the surrounding environment occurs through the boundary and into the material by means of a time-dependent diffusion process. Running carburization analyses helps ensure that the process is carried out correctly. Carburization followed by quenching can produce compressive stresses at the surface of a component, which helps reduce the risk of fatigue.

A model of a spur gear shown with a slice missing, revealing the inside of the gear.
Three spur gear segments showing the equivalent plastic strain, annealing condition, and temperature.

Annealing

Modeling the heating of steel that has undergone plastic deformation is often necessary. When exposed to sufficiently high temperatures, steel loses its previous work hardening, and this effect should be included in the computational model. The Metal Processing Module, combined with the Nonlinear Structural Materials Module, provides annealing modeling capabilities. These capabilities allow for the specification of an annealing temperature; at or above this temperature, the prior work hardening of the steel is eliminated by a reset of the plastic hardening variables.

This modeling capability is particularly valuable in scenarios involving thermal cycling, such as multipass welding. In these situations, the residual stress state of the material is significantly influenced by its plastic history.

Features and Functionality in the Metal Processing Module

Model metallurgical phase transformations and related phenomena.

A close-up view of the Phase Transformation settings and a 2D plot of the austenite phase fraction.

Metal Phase Transformations

The Metal Phase Transformation interface is used for studying metallurgical phase transformations that occur in a material like steel during heating or cooling. The Metallurgical phase feature can be used to define the initial phase fraction and material properties; the Phase transformation feature can be used to define the source phase, destination phase, and phase transformation model.

For diffusion-controlled phase transformations, such as when austenite decomposes into ferrite, five types of phase transformation models are provided: Leblond–Devaux; Johnson–Mehl– Avrami–Kolmogorov; Kirkaldy–Venugopalan, simplified; Microstructure based; and Hyperbolic rate.

For modeling displacive (diffusionless) martensitic phase transformations, the Koistinen–Marburger model is available.

These phase transformation models can be defined using, for example, TTT diagram data. Phase transformation data is defined for each model separately and can be imported from the software JMatPro®.

In addition to the provided phase transformation models, they can also be user defined.

A close-up view of the Model Builder with three physics nodes highlighted and a spur gear model in the Graphics window.

Steel Quenching

A predefined Steel Quenching multiphysics interface is available that automatically sets up a steel quenching simulation. It adds an Austenite Decomposition interface as well as a Solid Mechanics interface and a Heat Transfer in Solids interface. Multiphysics couplings are automatically set up to account for phase transformation strains and latent heat for the individual metallurgical phases.

When combined with the Nonlinear Structural Materials Module, the Metal Processing Module can be used to make detailed computations of stresses and strains during quenching. Plastic strains of individual metallurgical phases are included, and a plastic recovery option and a nonlinear weighting scheme can be used to model the effective initial yield stress of the compound material. The volume reference temperature and thermal expansion coefficient are used to compute a thermal strain tensor in each phase. Transformation-induced plasticity (TRIP) effects can also be analyzed when inelastic straining of the material results from stresses that are below the yield stress and would not cause plastic flow in a classical plasticity sense.

A close-up view of the Model Builder with the Metal Phase Transformation node highlighted and the results of a round bar in the Graphics window.

Phase and Compound Material Properties

The Metal Phase Transformation and Austenite Decomposition interfaces can compute effective material properties based on the material properties of the individual metallurgical phases. These effective properties can be utilized transparently by other interfaces, such as Heat Transfer in Solids and Solid Mechanics. Material properties are defined for each metallurgical phase separately and can be imported from the software JMatPro®.

A close-up view of the Model Builder with the Parameter Estimation node highlighted and a TTT diagram in the Graphics window.

Calibrate Phase Transformation Models

When defining phase transformation models to use in a simulation, an experimental calibration may be necessary for a given phase transformation. Common phase transformation diagrams can be computed to facilitate calibration against experimental data, such as continuous cooling transformation (CCT) and time–temperature-transformation (TTT) diagrams. Note that the Optimization Module is required for calibration against TTT data.

A close-up view of the Model Builder with the Austenite Decomposition node highlighted and the stress of a spur gear model in the Graphics window.

Austenite Decomposition

The Austenite Decomposition interface is a specialized version of the Metal Phase Transformation interface and is used for modeling austenite decomposition during the rapid cooling of steel from an austenitic state. The interface automatically includes the metallurgical phases — austenite, ferrite, pearlite, bainite, and martensite — as well as phase transformations that may occur during the quenching process.

A close-up view of the Model Builder with the Carbon Concentration result node selected and a steel gear shown in the Graphics window.

Carburization

The Carburization interface is used to model carburization processes during heat treatment. This interface can be used to define the carbon concentration of the surrounding environment, specify the way in which carbon can move across the surface, and define how carbon is able to diffuse internally in the component.

A close-up view of the Model Builder with the Phase Transformation Latent Heat node highlighted and the temperature of a round bar in the Graphics window.

Heat Transfer with Phase Transformations

The Heat Transfer with Phase Transformations multiphysics interface can be used to model metallurgical phase transformations during thermal loading. The Metal Processing Module is equipped to model heat transport using the full heat equation in the analysis. A multiphysics coupling is automatically set up to account for latent heat. The thermal conductivity, density, and specific heat capacity can be temperature dependent and can even depend on the current phase composition. For example, the thermal conductivity of austenite is different from that of ferrite and as the phase fractions evolve, so will the thermal conductivity of the compound material.

A close-up view of the Model Builder with the Alpha–Beta Phase Transformation interface highlighted and a titanium plate model in the Graphics window.

Phase Transformation in Titanium Alloys

The Alpha–Beta Phase Transformation interface is a specialized version of the Metal Phase Transformation interface and is used for modeling the formation and dissolution of different alpha phases during heating and cooling of a heat treatable alpha–beta titanium alloy. The interface automatically includes the metallurgical phases — beta, Widmanstätten alpha, and alpha martensite — and it includes the phase transformations for the formation and dissolution of the alpha phases.

A close-up view of the Steel Composition settings and a bevel gear in the Graphics window.

Microstructure Based Phase Transformations

The Microstructure based phase transformation model can be used to model austenite decomposition based on microstructural and chemical information. This capability reduces the need for time consuming experimental work to calibrate phase transformation models.

The Steel Composition node is used to specify the chemical composition, Fe—C diagram, and austenite grain size of the steel before selecting a model formulation for use with the Microstructure based phase transformation model.

Extended Modeling with the Metal Processing Module

As with the other products in the product suite, when the Metal Processing Module is added to COMSOL Multiphysics®, the features and functionality are fully integrated into the modeling workflow and ready to be used with any other added modules. For instance, the Metal Processing Module can be combined with the:

  • Nonlinear Structural Materials Module to make detailed studies of residual stresses and strains in quenching simulations
  • Heat Transfer Module to combine the effects of thermal radiation that may be relevant in a quenching situation
  • AC/DC Module to perform induction hardening simulations where the calculated temperature field from an induction heating simulation is being used as the input to a quenching simulation
A close-up view of the stress on a circular metal bar.
A close-up view of the temperature and electromagnetic fields of a steel billet model.

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