jominy-test

name	jominy-test
description	Jominy end-quench hardenability test — ASTM A255/E18 procedure, specimen geometry, hardness traverse, H-band steels, ideal critical diameter DI, Grossmann multiplying factors, Jominy distance to DI conversion, SAE H-band steel selection, alloy effect on hardenability, case study.
metadata	{"priority":7,"promptSignals":{"phrases":["Jominy test","end quench test","hardenability test","Jominy hardenability","ideal critical diameter","ASTM A255 hardenability"],"minScore":3}}

Jominy End-Quench Hardenability Test — Complete Skill

Purpose and Principle

Hardenability: ease with which a steel transforms to martensite upon quenching; NOT the same as hardness High hardenability → martensite forms at slow cooling rates (thick sections, mild quench) → consistent through-hardening

Jominy test principle: Austenitize standard specimen → quench one end with water jet → measure hardness traverse → position-dependent cooling rate maps to CCT diagram

Critical use cases:

• Select steel grade for required hardness at a given section depth
• Verify incoming material meets H-band specification (SAE H-steels)
• Design heat treatment: quench media + section size from DI value

Test Procedure (ASTM A255 / SAE J406)

Specimen Preparation

Specimen geometry: Round bar: 25 mm (1 inch) diameter × 100 mm (4 inch) long End face: machined square (flat, perpendicular to axis); no burrs One end step: 25 mm diameter shoulder to locate in quench fixture

Austenitizing: Temperature: per alloy → typically 860°C for 1020; 870°C for 4140; 855°C for 8620 Hold time: 30 minutes minimum at temperature (after thermal soak) Furnace atmosphere: protective (endothermic or Ar) to prevent decarburization → decarb falsifies surface hardness

Transfer time: max 5 seconds from furnace to quench fixture (ASTM A255) Specimen mounted in Jominy fixture: end face directly under water jet

Quench Parameters

Water jet: Temperature: 24 ± 3°C (75 ± 5°F) Orifice diameter: 12.5 mm (0.5 inch) Free jet height (orifice to specimen end): 63.5 mm (2.5 inch) Flow: 0.25 gallons/minute (ASTM A255) → produces standardized cooling rate at end face

Quench duration: until specimen is cold (≥ 10 minutes typical; end face reaches ambient T) Sides of specimen: NOT quenched; air cools during test; slower than end face

Hardness Measurement

Flat ground on specimen: two diametrically opposite flats, 0.38 mm deep × 100 mm long, ground after quench Hardness traverse: Readings at J1.5, J3, J5, J7, J10, J13, J16, J19, J22, J25, J32, J38, J51, J64 mm from quenched end (J notation: J + distance in mm; US also uses J + fraction inches: 1/16" = J1/16", 2/16" = J2/16", etc.)

Hardness scale: Rockwell C (HRC); all readings on same ground flat Minimum HRC resolution: ±0.5 HRC; replicate reading within ±1 HRC

Jominy Hardenability Curve

Interpretation

Quenched end (J0): fastest cooling; approaches full martensite → maximum hardness Remote from quench: increasingly pearlitic + bainitic → softer Inflection point: where bainite becomes dominant; position varies by steel

Typical Jominy curves: 1020 (low carbon, low hardenability): drops rapidly from 50 HRC to 20 HRC by J3 4140 (medium alloy): starts 55 HRC; stays above 40 HRC to J15; gradual decline 4340 (high alloy): starts 57 HRC; stays above 52 HRC to J50+; very flat curve

Cooling rate correlation: J end face = 350°C/s (very fast; essentially water quench rate) J5 ≈ 35°C/s; J10 ≈ 14°C/s; J20 ≈ 7°C/s; J50 ≈ 2°C/s (approximate rates) These rates correlate to specific CCT curve positions → hardness from % martensite

H-Band Steels (SAE H-Steels)

H-band specification: guaranteed hardenability range (max and min Jominy curve) H-band width: typically ±5–8 HRC at critical J positions Chemistry: composition specified with tighter limits than standard grades to control hardenability scatter

Designation: e.g., 4140H, 8620H, 4340H (H suffix = H-band)

H-band examples at J10 (from SAE J1268):

Steel	J10 min HRC	J10 max HRC
1045H	22	42
4140H	38	54
4340H	50	60
8620H	25	43
9310H	30	47

Application: critical drivetrain gears, aerospace components where lot-to-lot property consistency is mandatory; mill cert must include Jominy data

Ideal Critical Diameter (DI) and Grossmann Method

DI Definition

DI: diameter of round bar that, when quenched in an ideal quench (H = ∞), produces 50% martensite at center Ideal quench: instantaneous surface temperature drop to quench temperature; infinite cooling rate at surface; H = ∞

DI from Jominy curve: J distance corresponding to 50% martensite hardness on Jominy curve = J_crit DI = f(J_crit) from chart: DI [mm] ≈ 4 × J_crit [mm] (rough approximation; use actual chart from ASTM A255 Annex)

More precisely (from Jominy-DI chart, ASTM A255 Figure A1): J_crit [1/16 inch] → DI [inch]; then convert to mm

Grossmann Multiplying Factors

Composition-based DI calculation: DI = DI_base × f_C × f_Mn × f_Si × f_Ni × f_Cr × f_Mo × f_V

Base DI (carbon content and grain size, from chart): DI_base = f(C%, grain size); typical DI_base for ASTM grain size 7 (average): 0.20% C → DI_base ≈ 9 mm; 0.40% C → DI_base ≈ 11 mm; 0.60% C → DI_base ≈ 13 mm

Grossmann multiplying factors (f_x):

Element	Percent	Factor f_x
Mn	0.50%	1.26
Mn	1.00%	1.59
Mn	1.50%	2.01
Si	0.25%	1.07
Si	0.50%	1.15
Ni	0.50%	1.09
Ni	1.00%	1.19
Ni	3.50%	1.71
Cr	0.25%	1.11
Cr	0.50%	1.24
Cr	1.00%	1.56
Mo	0.15%	1.37
Mo	0.25%	1.64
Mo	0.50%	2.60
V	0.05%	1.15

Example (4140: 0.40C, 1.00Mn, 0.28Si, 0.10Ni, 1.00Cr, 0.20Mo): DI = 11 × 1.59 × 1.06 × 1.04 × 1.56 × 1.56 ≈ 70 mm (approximately; match to tables for accuracy)

Real Quench Critical Diameter (D)

D vs. DI relationship: D = DI × f(H) [D = actual bar diameter hardening to 50% martensite at center; H = Grossmann quench severity] Quench severities: H = 0.2 (still oil) → 0.35 (agitated oil) → 0.7 (still water) → 1.0 (agitated water) → 2.0 (brine)

Conversion chart (Grossmann): DI = 70 mm, H = 1.0 (agitated water) → D ≈ 55 mm (read from chart; bar ≤ 55 mm diameter fully hardening)

Polymer quench (PAG): H ≈ 0.5–0.8 depending on concentration; intermediate between oil and water

Application to Section Design

Given: section diameter D_actual and required core hardness:

1. From required core hardness → required martensite % → find minimum DI (from Jominy chart)
2. From H (quench severity) → DI_required = D_actual / f(H)
3. Select steel with DI ≥ DI_required → use Grossmann factors to calculate DI and verify

Alloy Effects on Hardenability

Carbon: increases base DI; also directly affects max achievable hardness (H_max ≈ 20 + 60 × C%) Manganese: most effective per % added; inexpensive; common in structural steels Chromium: significant effect; also improves tempering resistance (Cr carbides) Molybdenum: very powerful per %; prevents temper embrittlement; expensive Nickel: moderate effect; improves low-temperature toughness; expensive Vanadium: grain refiner (reduces DI_base) + moderate hardenability multiplier; net usually slightly positive Boron: extraordinary effect in concentrations of 0.001–0.003% (1–30 ppm); f_B = 1.5–3.5 Boron effect only works when steel is aluminum killed (Al ties up nitrogen that would deactivate B)

Common Errors in Jominy Testing

Decarburization: falsely low hardness at surface (J0); prevent by protective atmosphere Slow transfer: partial transformation before quench; lower J0 hardness Non-standard water: temperature, flow, orifice size affect cooling rate → shifts curve Grinding damage: surface overheating → temper → falsely low reading; use light grinding passes

Standards

Standard	Scope
ASTM A255	Standard test methods for Jominy end-quench hardenability
SAE J406	Methods for determining hardenability of steel
SAE J1268	H-band steel composition and hardenability limits
ASTM E18	Rockwell hardness test
ISO 642	Hardenability by Jominy method
AMS 2759	Heat treatment of steel (references Jominy requirements)

Output

Provide: steel grade and composition (C, Mn, Si, Cr, Mo, Ni, V [wt%]), Jominy curve (HRC vs. J distance [mm] at key positions: J1.5, J5, J10, J25, J50), H-band specification (SAE grade, min/max HRC at J10), DI calculation (DI_base from carbon content + grain size; multiplying factors product; final DI [mm]), actual quench severity H (quench medium), critical bar diameter D for 50% martensite at center [mm], core hardness estimate at section diameter of interest [HRC], comparison to H-band max and min bounds, grain size effect on DI (ASTM grain size 5 vs. 7 vs. 9), and applicable standard (ASTM A255, SAE J406, ISO 642).