Jominy Hardenability: How Deep the Hardness Reaches

Maximum hardness is set almost entirely by CARBON CONTENT: a 0.40 percent carbon steel will not exceed a certain hardness however it is quenched. HARDENABILITY is set by the alloying elements and determines how far below the surface that hardness extends. Two steels of identical carbon content reach nearly the same surface hardness and behave completely differently at the core of a thick section, and a shop substituting one for the other because 'the carbon is the same' produces a part that tests correctly at the surface and is soft where it is loaded. The Jominy end-quench curve is how hardenability is expressed: hardness against distance from a quenched end. A real bar of a given diameter, quenched at a given severity, cools at its centre like a particular position along that bar, and that EQUIVALENT JOMINY DISTANCE is the bridge between a quench and a hardness. Higher severity and smaller diameter both move the equivalent position closer to the quenched end, where the hardness is higher. The equivalence is a chart lookup rather than a formula, so it is entered here along with the hardness the steel's own curve gives at that distance -- both come from the steel's data and the applicable severity chart, and inventing a correlation for them would be worse than asking for them. THE SEVERITY LEVER HAS A COST THAT IS EASY TO IGNORE. Moving from oil to water may make the core hardness on a marginal steel, and it roughly triples the distortion and the quench-cracking risk on any part with section changes, sharp corners or holes. On many parts that is not an acceptable trade, and the answer is a more hardenable steel rather than a more severe quench -- which is a purchasing decision made before the part is cut rather than a process decision made at the tank. This evaluates entered hardenability data. It does not supply a Jominy curve for any steel, compute the equivalent Jominy distance from a diameter and a severity (that is the Lamont chart lookup this asks for), predict distortion or cracking risk, address tempering, which follows and reduces the hardness, model the hardness at any other location in the section, or select a steel or a quench. The steel supplier's Jominy data, the applicable hardenability charts, and the metallurgist govern.

the Jominy end-quench curve read at an equivalent Jominy distance; the equivalence between a bar diameter at a quench severity and a position on the Jominy bar is a CHART lookup rather than a closed form, so the distance and the hardness there are entered.

Steel hardenability as ASTM A255 expresses it, with the Lamont-type severity charts as the equivalence. Hardness is set by CARBON and hardenability by ALLOYING -- they are different properties. This asks how DEEP hardness reaches; `quench-severity` asks whether agitation helps, through the Biot number.

An entered chart reading and its comparisons.

Estimate. AHJ and licensed professional govern.

Field names used by the API: jominy_distance_sixteenths, hardness_at_distance_hrc, required_core_hardness_hrc, alt_jominy_distance_sixteenths, alt_hardness_hrc, surface_hardness_hrc, jominy_distance_in, hardness_margin_hrc, alt_jominy_distance_in, alt_margin_hrc, core_to_surface_drop_hrc

• The equivalence is a chart lookup not a closed form, so the distance is enteredthe applicable severity charts
• The Jominy curve is entered it is a property of the specific steel and heatthe steel supplier's data
• Tempering follows and reduces hardness and is not modelled herethe heat treatment specification