Glossary

A single answer from Phases mixes two vocabularies. One is metallurgy you may already know: austenite, dilatation, Ms, nugget diameter. The other belongs to the product: sessions, runs, capabilities, parameter cards. When a phrase in a result looks like it should mean something and does not, it is almost certainly in one of the two lists below.

Terms are alphabetical within each group. Product terms link to the page that covers them in full.

Metallurgical terms#

Ae1 — The equilibrium temperature below which austenite cannot exist. On slow cooling, the last austenite transforms to pearlite at Ae1. Phases reads the equilibrium boundaries from the material card's authored equilibrium curves; a chemistry you type is written into the card's composition curve, not into those boundaries, so editing carbon does not move Ae1. See known limits.

Ae3 — The equilibrium temperature above which the steel is fully austenitic. On cooling, ferrite starts to precipitate below Ae3. Same caveat as Ae1: it comes from the card, not from a calculation on your composition.

ASTM grain size — The standard number describing prior austenite grain size; a larger number means finer grains. It appears twice in Phases: as a kinetics factor authored on the material card, and as a required input for flow-stress prediction, which will not run without an explicit grain-size number. See the capability matrix.

Austenite — The face-centred-cubic high-temperature phase of steel. Every diffusional and martensitic transformation Phases models starts from austenite, which is why CCT sweeps impose a 100% austenite starting state.

Bainite — An intermediate transformation product formed between the pearlite and martensite ranges: fine ferrite plus carbides, harder than pearlite and tougher than untempered martensite. In the model bainite is allowed to consume all remaining austenite, which is one reason it competes strongly with pearlite at moderate cooling rates.

Bs (bainite start) — The temperature at which bainite begins to form on cooling. Phases takes it from the bainite critical-temperature curve on the material card; there is no explicit composition-corrected Bs formula in the current model, so it is not tuned per grade. See known limits.

CCT diagram — Continuous Cooling Transformation. Maps which microstructural phases form as steel cools continuously at a given rate. In Phases this is a sweep of several cooling rates plotted as transformation start and finish markers on a log-time versus temperature chart. See CCT and TTT.

Critical cooling rate — The slowest cooling rate that still suppresses diffusional transformation and gives the microstructure you want, usually full martensite. Phases does not solve for it directly; you bracket it by running a CCT sweep and reading where the ferrite, pearlite and bainite markers disappear. See find the critical cooling rate.

Dilatation — Length change during heating and cooling. Because phases differ in density, a transformation shows up as a departure from the straight thermal-expansion line. Phases computes it as a phase-weighted thermal term plus the volume change of the transformation itself.

Dilatometry — The experimental technique of measuring dilatation to detect transformation temperatures. The V-Gleeble CCT mode reproduces the dilatometry trace itself, which is a different output from the CCT diagram's phase-boundary map.

dt8/5 (Δt8/5) — The cooling time in seconds from 800 °C to 500 °C, the standard way welders characterise a weld thermal cycle. It is a direct input to the V-Gleeble HAZ mode: a smaller dt8/5 means a faster, harder cycle.

Faying surface — The sheet-to-sheet interface in a spot weld, where the nugget nucleates. It is one of the three contact interfaces the RSW solver models, along with the two electrode-to-sheet contacts.

Ferrite — The body-centred-cubic low-temperature phase, soft and formable. It dominates the room-temperature microstructure of the mild and HSLA grades in the catalog.

Flow stress — The true stress needed to keep a material deforming plastically at a given strain, strain rate and temperature. Phases has two separate flow-stress systems that are not interchangeable: per-phase flow-stress prediction from a material card, and the bulk flow-stress surface the V-Gleeble deformation modes require. See the capability matrix.

Gleeble — A physical thermomechanical simulator that subjects small specimens to precisely controlled heating, forces and cooling. "Virtual Gleeble" reproduces these tests numerically. See Virtual Gleeble.

HAZ (heat-affected zone) — The region beside a weld that was never molten but was hot enough to change microstructure. In the RSW post-processing Phases classifies each element by its peak temperature into nugget, upper HAZ, lower HAZ and base metal, and reports a diameter and phase composition for each zone; predicted hardness is added only when the model has cooled far enough by the end of the simulated time. See RSW validation.

HV (Vickers hardness) — The hardness scale Phases reports. The plots label it HV30, meaning Vickers hardness under a 30 kgf load. Every HV number Phases produces is a bulk rule-of-mixtures value computed from the phase fractions, the chemistry and the cooling rate — it is the hardness of the mixture, never the intrinsic hardness of one phase. See hardness validation.

Martensite — The hard, supersaturated phase formed by diffusionless shear when austenite is cooled below Ms. Phases models it with an athermal Koistinen–Marburger relation rather than a diffusional rate law, so the amount formed depends on how far below Ms you go, not on how long you hold there.

Ms (martensite start) — The temperature at which martensite begins to form on cooling. The material card stores a baseline Ms of 550 °C, shared across every grade, plus a composition-correction curve that shifts it per grade. That correction is real but partial: the shared baseline curve is what the martensite solver reads, so the effective Ms is not a per-chemistry calculation, and the Andrews correlation puts the true per-grade values across roughly 323–530 °C. See how we validate.

Nugget — The solidified molten zone that forms the actual joint in resistance spot welding. Its diameter is the primary quality metric, usually judged against a minimum of five times the square root of the thinner sheet thickness in millimetres. See resistance spot welding.

Pearlite — The lamellar ferrite-plus-cementite product of slow cooling through the eutectoid. Phases tracks it as its own phase, though the model cannot tune pearlite kinetics independently of bainite — a documented limitation. See known limits.

Phase fractions — The proportions of austenite, ferrite, pearlite, bainite and martensite in the microstructure, which set the mechanical properties. Phases reports them as fractions between 0 and 1 or as percentages, and they are the primary output of every thermal simulation.

Press-hardening / boron steel — Grades such as 22MnB5, austenitised then quenched in the die to form martensite, giving very high strength. Common in automotive safety structures. Boron's grain-boundary effect is not modelled explicitly; the boron grades work because one of them was the original calibration basis.

Quench rate versus quench medium — A cooling rate in °C/s is a number, not a model of water, oil or air. Phases will not relabel a rate as a quench medium unless you supply that mapping yourself, because the solver has no bath, no agitation and no part geometry.

RSW — Resistance Spot Welding. Joining sheet metal by passing current through electrodes clamped on the stack; resistive heating melts a nugget at the faying surface. See resistance spot welding.

Satoh test — A specimen is heated and then cooled while axially restrained, so thermal contraction that cannot happen as strain appears as stress instead. It is used to characterise weld residual stress, and it is one of the V-Gleeble test modes.

TTT diagram — Time-Temperature-Transformation. As above, but for isothermal holds rather than continuous cooling. Phases does not generate TTT diagrams: the request is accepted and answered with an explicit unsupported status. See CCT and TTT.

Phases product terms#

Artifact — Any file a run produced and stored: plots, animated GIFs, CSV data, the material card the run consumed, and the resolution manifest recording how that card was chosen. Artifacts live under the run's own storage prefix and are handed back as signed links, which expire — seven days for the plot links a simulation tool returns. See sessions, runs and artifacts.

Background task and replay — A long simulation keeps running on the server after you close the tab or lose your connection. When you come back, the client reconnects to the same task and replays the events it missed, so progress and results land in the conversation as if you had never left. The replay buffer lives in the backend process and keeps a finished task for ten minutes, so a reconnect much later returns nothing to replay. See common problems.

Base template — The verified catalog material card whose structure a custom chemistry is rendered onto. Your composition supplies the numbers; the template supplies the curve structure, the kinetics parameters and the schema the solver can read. A template that cannot represent every element you specified is rejected and the next candidate is tried. See your own chemistry.

Capability — What a simulator needs from a material before it will run. There are four: base card, transformation kinetics, phase flow stress, and bulk flow surface. Heat treatment and CCT need the first two; V-Gleeble deformation modes also need a bulk flow surface; RSW needs the first two only when microstructure tracking is enabled. If a capability cannot be resolved, the run fails with a typed message naming it rather than quietly substituting something else. See the capability matrix.

Confirmation gate — The stop Phases puts in front of any custom or changed chemistry. The tool creates nothing, tells you which catalog grade the chemistry is closest to, and asks whether to continue or adjust. Confirming stores a stable material definition plus a compatible base template — it does not calculate kinetics, flow stress or any physics, and it is not a calibration claim. See your own chemistry.

Distance badge (template match) — The good / moderate / high label shown beside a custom material. It measures how far your chemistry sits from the nearest catalog identity or template, and nothing else. It is not an accuracy score and not a calibration score; the simulator's own capability result is what tells you whether the physics is available. See your own chemistry.

Fenced parameter block — The mechanism behind the parameter cards. The agent emits a fenced code block with a specific tag and single-line JSON inside; the chat renders that block as an editable card instead of showing the code. The tags you will meet are phases-params, cct-params, rsw-params, vgleeble-params, material-params and flow-stress-params, plus rsw-results and flow-stress-results, which render finished output rather than an editable form. See parameter blocks.

Guest session — Using Phases without an account. An anonymous identity is created for you automatically and gets a limited number of messages per fixed window that starts with your first message — five per 24 hours unless the deployment is configured otherwise. Guests have no chat history sidebar, no materials workbench and no saved run browser. See guests and limits.

Material card — The LS-DYNA-format keyword file (.k) that carries everything the solver needs about a steel: chemistry, equilibrium curves, critical temperatures, kinetics parameters, thermal properties and the as-delivered phase fractions. Every run stores the exact card it consumed, as mat_Steel.k, alongside a material_resolution.json manifest recording how that card was resolved. See the material catalog.

Parameter card — The editable summary the agent shows before running a simulation: the parameters it understood, laid out as fields with a run button. You can correct any field before pressing run. For RSW the card is mandatory — the agent shows it first even when you have already stated every value. See how the conversation works.

Preserved-source kinetics — A named fallback, not a silent one. When a custom chemistry has no published kinetics model that applies to it, heat treatment, CCT and the V-Gleeble thermal modes will run using the verified template card's authored kinetics and report that choice as a warning. Those kinetics belong to the template, not to your chemistry, and must not be read as interpolated custom physics. See known limits.

Run — One execution of one simulator, with its own record, its own storage prefix and its own artifacts. A CCT sweep across five cooling rates is a single run, not five. See sessions, runs and artifacts.

Run version — The sequential number identifying a run within its session: run_001, run_002, and so on, which is also the folder name in storage. Versions are reserved before execution and are never reused, so a deleted run's number does not come back. This is what you cite when you say "inspect run 3". See reuse and share runs.

Session — One conversation and everything attached to it: the message history, the active material, and the numbered runs. The active material persists across turns within a session, which is why you can load a grade once and then run several simulations against it. See sessions, runs and artifacts.

Session material — A material that exists only inside the current conversation. Loading a catalog grade, or confirming a custom chemistry, produces one. It is shown in simulation output as the closest grade label followed by (custom) when a chemistry was applied. It disappears with the session unless you save it. See your own chemistry.

Workspace material — A material saved into a workspace library, with a name you chose, available to everyone in that workspace and loadable in future sessions. Saving requires a workspace and a member or admin role, and Phases refuses to save a material whose chemistry is identical to its unmodified base grade. Editing a loaded workspace material in chat forks it into a session material rather than changing the stored row. See workspace materials and workspaces and roles.

Where these terms come from#

If a term you need is missing, the fastest way to get an authoritative answer is to ask in the chat itself — the agent will not invent a capability it does not have, and it names its tools and their limits plainly. The full list of what it can call is in the tool reference, and the boundaries it will not cross are collected in known limits.