A hardness value at one location does not fully describe how deeply a steel may harden during quenching. BVM introduces Jominy testing and hardenability for buyers of engineering steel, using public technical references checked on 22 October 2026.
What hardenability describes
Cambridge describes hardenability as the ability to harden through martensitic transformation under specified conditions. Illinois notes that cooling rate changes with distance from the surface when a thick section is quenched.
BVM recommends asking separately where hardness was measured and how hardening capability through depth was assessed.
Reading a Jominy curve
Illinois describes heating a cylindrical specimen to the austenitic condition, cooling one end with a water jet, preparing the surface and measuring hardness along its length. Plotting hardness against distance produces the hardenability curve.
Identify the distance axis, hardness scale and test conditions. The curve represents the response at locations experiencing different cooling rates, rather than a single hardness reading.
State the method in the documents
The public ASTM A255-26 overview, marked updated 14 October 2026, covers end-quench testing and calculation from chemical composition. It calls for supplier–purchaser agreement on the method and identification of that method in the material report.
BVM recommends checking whether a supplied result was tested or calculated, which document edition applies and which batch it represents. This article uses the public overview, not the full standard.
Questions for a purchasing enquiry
BVM suggests preparing the grade, specification, dimensions and delivery condition; the required assessment method and acceptance criteria supplied by engineering; and batch identification with supporting documents.
These are purchasing suggestions. Do not independently convert a distance on a Jominy specimen into the hardened depth of an actual component or adopt acceptance limits from a reference graph. Engineering should confirm applicability to the material, geometry and heat-treatment process.
Related reading: HB, HRC and HV.
Sources: Cambridge and Illinois, no publication date displayed; ASTM A255-26 public overview, updated 14 October 2026. Checked 22 October 2026. Cover: AI-created BVM illustration with the authentic logo, not an actual test or steel batch photograph.
