An ejector pin is a precision wear part, and its heat treatment determines how it behaves in the mold. There are two fundamental options: nitrided pins and through-hardened nitrided pins. Choosing between them is a matter of matching the hardness profile to the ejection job.
Nitrided Ejector Pins: Hard Surface, Tough Core
Nitrided pins are made from AISI H13 (1.2344) tool steel, hardened and then nitride-treated on the surface. The result is a distinct two-zone hardness profile: a surface hardness of 65–75 Rc for wear resistance against the mold and the plastic, and a core hardness of 39–43 Rc for toughness and resistance to bending. The head is annealed to 30–35 Rc so it can flex slightly under load without cracking, and the working finish is held to 8–10 RMS with a maximum 1/32 in. radius on the tip.
Nitrided pins are the standard choice for general ejection duty: clean wear resistance, good dimensional stability, and a cost profile that makes them the default for most mold builds.
Through-Hardened Nitrided Pins: For Slender, High-Load Pins
Through-hardened pins take a different approach: the entire pin is hardened through, then nitrided on the surface. The result is a surface hardness of 65–74 Rc with a core hardness of 50–55 Rc — a significantly harder core than the standard nitrided pin. That extra core hardness resists bending and peening in slender pins, thin ejectors, and pins that take heavy ejection loads on a small diameter.
The trade-off is toughness: a harder core is stiffer and less forgiving under side loading or misalignment. Through-hard pins belong where the pin is the weakest link in the ejection system — long, small-diameter pins and pins ejecting stiff, high-shrinkage materials.
Ordering by Spec, Not Guesswork
Ejector pins are ordered by catalog number plus overall length. A typical nitrided parallel pin is specified by its body diameter, overall length, and body style (parallel or shoulder). Shoulder versions add the shoulder diameter to the spec. Some sizes are standard stock; others are made-to-order — always confirm availability before scheduling a build around a non-standard length.
A Practical Rule of Thumb
Start with nitrided pins for standard cores and cavities. Step up to through-hardened pins when the pin is long relative to its diameter, when ejection loads are high, or when you are seeing bending and peening rather than surface wear. When you see surface wear only, the fix is usually better ejection geometry or a harder surface — not a harder core.
Tooling Components stocks both nitrided and through-hardened ejector pins in inch and metric sizes. Call 814-438-7657 or visit www.toolingcomponent.com.