Virtual Gleeble tests

Physical thermomechanical testing is slow and expensive. A Gleeble machine grips a small specimen, resistively heats it along a programmed temperature-time path, deforms it if the test calls for it, and records dimensions, force and displacement throughout. Booking one, machining specimens and running a matrix of conditions takes weeks. Most of the time what you actually wanted was a first answer: does this grade soften in the HAZ at this cooling time, where does the dilatation curve bend, roughly what flow stress should I expect at 800 °C.

V-Gleeble replicates those experiments numerically. You describe the cycle in chat, the solver runs real phase-transformation physics against your prescribed thermal (and where applicable mechanical) schedule, and you get back the traces a machine would have produced — dilatation, phase fractions, hardness and, for deformation modes, flow stress.

It is worth being clear about what this is not. V-Gleeble computes one uniform specimen state stepping through the schedule you asked for; there is no temperature gradient across the specimen and no geometry. It is not a substitute for a physical test when you need certified data, and several of its predictions are known to be off in documented, specific ways. Those are listed at the end of this page and in known limits.

Running one#

Say what you want in plain language, naming the grade:

Run a V-Gleeble weld-HAZ cycle on 22MnB5 and check for HAZ softening.

Run Gleeble CCT dilatometry on DC04 at 0.1, 1, 10, 50 and 100 °C/s from 860 °C.

The agent replies with a vgleeble-params configuration card summarizing the test mode, material and parameters it understood. Nothing runs until you confirm it. See parameter blocks for how these cards work, and how the conversation works for the general pattern.

There is no default material. A bare "run a Gleeble test" gets a question back, not a run.

One phrase is genuinely ambiguous and the agent will ask about it. "CCT" can mean two different products here: a phase-boundary diagram (see CCT and TTT diagrams) or Gleeble-style dilatometry data. Say "CCT diagram" for the first and "Gleeble CCT" or "dilatometry" for the second.

The eight test modes#

The default mode is cct. Hyphens and underscores are both accepted (hot-tensile and hot_tensile are the same mode). An unrecognized mode is rejected before anything runs, with the supported list echoed back.

CCT dilatometry — cct#

Cools the specimen linearly from a start temperature to an end temperature, once per cooling rate in your list, starting from 100% austenite. Returns the dilatation-versus-temperature trace for every rate overlaid on one plot, the final phase fractions per rate as a grouped bar chart, and final hardness versus cooling rate on a log axis.

Reach for it when you want the measurement a dilatometer would produce — where the length change deviates, how sharp the martensite step is — rather than a boundary map.

Weld HAZ — haz#

The mode most people come here for. Heats from 20 °C at 300 °C/s to a peak temperature, holds 0.5 s at peak, then cools with an average rate of 300/dt8-5 °C/s through 800 °C and 500 °C down to 20 °C. dt85 is the cooling time from 800 °C to 500 °C in seconds — the standard weld-cooling descriptor.

Use it to compare grades or heat inputs for coarse-grained HAZ hardness and martensite fraction. Read the hardness caveat below before drawing conclusions on low-carbon grades.

Isothermal hold — isothermal#

Heats from 20 °C at 50 °C/s to the hold temperature and holds there for the requested time. There is no cooling segment. The cycle ends at temperature, so the reported final phase fractions are the phases present at the end of the hold, not a room-temperature microstructure.

Use it for isothermal transformation questions — how much ferrite and pearlite forms in 60 s at 700 °C.

Hot tensile — hot-tensile and hot compression — hot-compression#

Both run the same schedule, and only the test temperature, strain rate and maximum strain are yours to set. The specimen heats at 50 °C/s to the test temperature, soaks 5 s, deforms at the requested strain rate to the requested maximum true strain, holds 2 s at temperature, then cools at 20 °C/s back to 20 °C. The heating and cooling rates and the soak and hold durations are fixed.

Returns a flow-stress-versus-true-strain curve alongside phases and hardness. These are the two modes with the strictest material requirement — see below.

Satoh test — satoh#

Heats from 20 °C at 10 °C/s to the peak temperature, then cools at 5 °C/s back to 20 °C with the specimen axially restrained. Below the restraint temperature (set equal to the peak) the solver converts the thermal strain that would have occurred if the specimen were free into elastic stress, using a temperature-dependent modulus, and caps the accumulated stress at the yield stress read from the flow-stress table. Neither the heating nor the cooling rate is adjustable.

Use it for weld residual-stress reasoning: how much stress a restrained joint builds up as it cools, and where transformation plasticity relieves it.

Hot stamping — hot-stamping#

Takes no parameters at all. The cycle is fixed: austenitize at 950 °C reached in about 30 s, 300 s soak, 10 s transfer cooling at 5 °C/s (so the blank is at 900 °C when the die closes), then a 50 °C/s die quench to a 200 °C final temperature. Naming a temperature in your request changes nothing.

Use it as a standard press-hardening reference cycle for a boron grade.

Custom profile — custom#

Accepted, but read this before using it. The chat tool has no thermal_profile or mechanical_profile parameter, so a profile you describe cannot reach the solver. A custom run executes the solver's fixed default profile: 860 °C held for 5 s, then cooled to 20 °C over the following 5 s. If you need a specific schedule, express it through one of the parameterized modes instead.

Parameters, units and defaults#

The configuration card blocks obviously invalid submissions before they run: CCT needs at least one cooling rate and a start temperature above the end temperature; hot tensile and compression need a positive strain rate and positive maximum strain; HAZ needs a peak above 500 °C and a positive dt85; isothermal needs a positive hold temperature and hold time. The simulator panel's Configure tab caps a CCT sweep at 10 cooling rates.

The starting microstructure#

CCT, hot tensile, hot compression and hot stamping force 100% austenite as the starting state when you do not say otherwise. That is an imposed initial condition, not evidence that austenitization would actually have completed under your schedule.

HAZ, isothermal, Satoh and custom do not force austenite. If the starting state matters for those — and for HAZ softening questions it usually does — set it explicitly rather than relying on a default:

Run a V-Gleeble isothermal hold on EN13261 at 700 °C for 60 s, starting from 50% ferrite and 50% pearlite.

Accepted phase keys are case-insensitive and limited to ferrite, pearlite, bainite, martensite and austenite (the abbreviations fer, pear, bain, mart, aust also work). Keys outside that set are silently ignored. If the values do not sum to 1, they are renormalized. Those same five phases are what the solver tracks and reports throughout.

The deformation-table requirement#

This is the single most common disappointment on this simulator, so it is worth stating plainly.

Every mode needs a base material card and transformation kinetics. The three deformation modes — hot tensile, hot compression and Satoh — additionally need a reviewed bulk flow surface: a measured sigma(strain, strain rate, temperature) table for that grade. Thermal-only modes never load one. The full picture is in the capability matrix.

Seventeen grades ship with an exact per-grade table and run deformation modes with no caveat:

Three boron press-hardening grades have no exact table. 20MnB8, 25MnB5 and 29MnB7 run through an explicitly reviewed mapping onto a 16MnCr5 source table with strength scale factors of 1.05, 1.18 and 1.25 respectively. The result carries a warning naming the mapping and the scale factor. It is a reviewed surrogate, not measured data for that grade, and the run tells you so.

A custom chemistry cannot run a deformation mode at all. If your material's composition differs from its template's chemistry, the resolver returns an unavailable result rather than substituting something plausible:

No validated custom V-Gleeble bulk flow surface exists for [your material]; phase P1-P4 is not a compatible substitute.

The run then fails with Required material physics is unavailable for V-Gleeble <mode>, listing the missing capability. Nothing is silently approximated. A calculated phase flow-stress result is a different capability and cannot stand in for the bulk surface.

Thermal-only modes — CCT dilatometry, HAZ, isothermal, hot stamping and custom — do work with a custom chemistry. So if you have your own steel and want HAZ behavior, you can run it; if you want a hot flow curve, you cannot. See your own chemistry for how custom materials are created and what confirming one does and does not calculate.

Two more material rules. V-Gleeble cannot consume a raw material deck: a registry grade runs by its id and everything else runs through its chemistry, so launching a run from the workspace materials Simulate surface fails for a material with no stored composition. And the grades listed above are card-backed built-ins — check the material catalog for what your workspace actually has enabled, and workspace materials for saved custom grades.

What comes back#

Every run writes a versioned run folder to your session — see sessions, runs and artifacts.

For a CCT sweep you get three plots: cct_dilatometry.png (dilatation versus temperature for every rate, temperature axis inverted, each rate labeled with its final hardness), cct_phases.png (final phase fractions per rate) and cct_hardness.png (final hardness versus cooling rate on a log axis, each point annotated). The chat summary lists one line per rate with ferrite, bainite, martensite fractions and hardness.

For every other mode you get phases.png (phase fractions versus time with temperature overlaid) and hardness.png. A dilatation plot is added when the dilatation signal is non-trivial, and a flow-stress plot when any flow stress was computed. The chat summary reports step count, wall time, final phases above 0.1%, final hardness in HV and — when flow stress was computed — the maximum flow stress in MPa.

Every run also stores vgleeble_data.csv. For single-run modes it is the full trace: time, temperature, HV, flow stress, dilatation, strain, transformation dilatation and one column per present phase. For CCT it is one row per cooling rate. Alongside the plots, every run stores the exact resolved material card (mat_Steel.k) and a material_resolution.json manifest recording which physics was used — and for deformation modes, the exact bulk table that was resolved.

Each plot carries an annotation box naming the material and listing up to six composition elements in wt%. On single-run plots the box also gives the final phase fractions above 0.5% and the final hardness in HV; on the CCT plots it gives a per-rate table of ferrite, bainite and martensite fractions with hardness instead.

Limits worth knowing#

• A session is required. The material card and resolution manifest are mandatory uploads. If artifact persistence fails, the run is recorded as failed even though the physics completed.
• Flow stress is clamped, not extrapolated. Strain, strain rate and temperature outside the table's measured envelope return the boundary value rather than an error. Nothing warns you that you left the envelope.
• Flow stress is only evaluated while deformation is active. Outside the deformation window the reported value is zero.
• Satoh's stress trace is plotted against strain, not temperature. Satoh applies no mechanical strain, so its strain history is zero and the flow-stress figure is not the stress-versus-temperature chart you would expect from a Satoh test. Read the numbers from the CSV.
• Documented accuracy limits. HAZ hardness is over-predicted for low-carbon grades: at a 1350 °C peak and dt8-5 of 15 s the model gives 275 HV for DC04 and 277 HV for HC260LA where 150–200 HV and a mixed ferrite-bainite structure is expected, and 662 HV for EN13261 against an expected 450–550 HV. Hot compression at 1000 °C is systematically 50–100% high because the tables are scaled from room-temperature strength ratios and do not capture dynamic recrystallization. 22MnB5 hot-tensile flow stress at 800 °C is roughly 50% above published values. Isothermal holds and Satoh stresses validate well across the grades tested. Full detail is in how we validate and hardness validation.
• Hardness is bulk mixture hardness in HV, not the hardness of any individual phase.
• Access can be restricted. A workspace admin can disable the V-Gleeble simulator entirely, and a workspace viewer cannot run simulations — see workspaces and roles.

If a run does not behave the way you expect, common problems covers the usual causes, and unfamiliar terms are defined in the glossary.