Can 1045 steel be induction hardened?

1045 is the classic induction-hardening steel because it has just enough carbon, 0.43-0.50%, to form 55-60 HRC martensite, and no alloying to make it harden deeply. An induction coil heats only the surface layer, for a few seconds, to roughly 900-1000 °C (1650-1830 °F), hotter than a furnace would use because the time is so short, and a water or polymer spray quenches it immediately. Only the heated layer transforms. The core stays in whatever condition it arrived in, cold-drawn, normalized or quenched and tempered, so the part ends up with a hard, wear-resistant skin, a tough core, and compressive residual stress at the surface that raises fatigue strength. Because the heating is local and fast, distortion is far lower than with furnace hardening, and a single diameter, a journal, a gear tooth or a pin end can be hardened while the rest of the part stays machinable.

Case depth is set mostly by frequency and power. High frequency, about 100-400 kHz, gives shallow cases of roughly 0.5-1.5 mm (0.020-0.060") for small pins and gear teeth; 10-30 kHz suits 1.5-3 mm (0.060-0.120") on typical shafts; 1-10 kHz reaches 3-6 mm (0.12-0.25") and deeper on large rolls and axles. Parts are scan hardened (the coil travels along a shaft) or single-shot hardened (the whole zone at once), then tempered at 150-200 °C (300-400 °F) in a furnace or by a second, low-power induction pass, which brings the surface to about 52-58 HRC and removes the risk of delayed cracking. The prior microstructure matters: normalized or quenched-and-tempered 1045 responds quickly and evenly, while coarse or spheroidized structures need more time at temperature and can leave soft spots. Induction-hardened, chrome-plated 1045 bar is the standard material for hydraulic cylinder rods.

Geometry is where induction hardening goes wrong. Sharp shoulders, keyways, cross holes and thread roots concentrate both the heat and the quench, and 1045 in a water quench cracks at them. Chamfer and radius hole edges, keep keyways and cross holes out of the hardened zone or plug them, stop the pattern short of sharp shoulders or use a fillet-hardening coil where fatigue in the fillet matters, and avoid ending a hardened zone in a highly stressed section, because the transition from hard case to soft core is a fatigue weak spot. After hardening, the surface can only be ground: leave 0.1-0.3 mm (0.004-0.012") on the diameter for finish grinding, and expect long shafts to need straightening. Where a stronger core or deeper, more even hardening is needed, 4140 pre-hard is the usual step up.