AMS 2745
Induction Hardening of Steel Parts
Induction hardening — localized austenitizing by electromagnetic induction followed by quenching and tempering — of carbon, alloy and martensitic stainless steel parts, including process qualification and control of hardened pattern, case depth and surface hardness.
What AMS 2745 specifies
AMS 2745 governs surface or local hardening of steel parts by induction heating: a coil at high frequency (roughly 1–10 kHz for deep cases, 100–450 kHz for shallow ones) austenitizes the selected zone in seconds, a spray or immersion quench (water, polymer or oil) forms martensite in that zone, and the part is tempered. It applies to medium- and high-carbon steels (1045, 1050, 1141, 4140, 4340, 52100) and to hardenable stainless. Because an induction setup cannot be surveyed with furnace pyrometry, the sheet relies on qualification: a first article or coupon is sectioned to show hardened-pattern location, surface hardness, effective case depth by hardness traverse (per SAE J423, with the threshold set by carbon content) and freedom from cracks, after which power, frequency, coil, scan speed, quench concentration, temperature and flow are frozen for production. Requirements also cover tempering after hardening, transition (soft) zone location, prior microstructure, and magnetic-particle inspection where specified.
Tests and the drawing call-out
Tests the document imposes
- Surface hardness per ASTM E18 (HRC, or HR15N / HR30N on shallow cases) at drawing locations
- Effective case depth by hardness traverse on a sectioned qualification part or coupon per SAE J423 (threshold set by carbon content, for example 45 HRC for 0.43–0.52 % C)
- Hardened-pattern location and transition zone by macro-etch (nital) of the cross-section
- Magnetic particle inspection per ASTM E1444 for quench cracks when specified
- Microstructure check for prior condition and for overheating / grain coarsening when specified
- Process-parameter record (power, frequency, time, scan speed, quench) against the qualified setup
How to cite it
Drawing call-out
INDUCTION HARDEN PER AMS 2745, 1045, SURFACE 55–62 HRC, EFFECTIVE CASE DEPTH 0.060–0.090 IN TO 45 HRC IN ZONE SHOWN; TEMPER; MAGNETIC PARTICLE INSPECT PER ASTM E1444Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to AMS 2745
| Treatment | Role | Cost |
|---|---|---|
Induction hardening uses an alternating magnetic field to austenitize selected steel surfaces, followed immediately by quenching. | Governing | $$ |
AMS 2745 — frequently asked
Which steels respond to induction hardening?
Steels with at least about 0.35–0.40 % carbon so the austenitized skin forms hard martensite: 1045 and 1050 reach 55–62 HRC, 4140 and 4340 about 55–60 HRC, 52100 60–65 HRC; low-carbon steel must be carburized first. Prior structure matters — a quenched-and-tempered or normalized core dissolves its carbon fast enough for a seconds-long heat, coarse spheroidised or ferrite–pearlite structures may not.
How is case depth specified?
As effective depth to the SAE J423 threshold hardness for the steel's carbon content (40 HRC for 0.33–0.42 % C, 45 HRC for 0.43–0.52 % C, 50 HRC above 0.53 % C) measured on a traverse; typical depths are 0.030–0.150 in (0.75–4 mm), set mainly by frequency and heating time. State the depth range, the location and whether it applies after grinding.
Why temper after induction hardening?
As-quenched martensite above 60 HRC is brittle and carries high residual stress; a temper at 300–400 °F (150–205 °C) for 1–2 h, or an induction temper, restores enough toughness to stop cracking while keeping most of the hardness. Tempering also stabilises the compressive residual stress that gives induction-hardened shafts their fatigue benefit.
What are the design limits?
Sharp corners, keyways and holes inside the hardened zone concentrate current and crack; the transition zone between hard and soft must sit away from stress raisers and should be shown on the drawing. Distortion is small compared with furnace hardening because the core stays cold, but long shafts may still need straightening or grind stock.
AMS 2745 is copyrighted by SAE International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗