Tool Steel Delivery Conditions: Annealed, Pre-Hardened, QT, and ESR

When you place a tool steel order, the grade is only half the specification. You also specify the delivery condition, which determines the state the bar or block arrives in, the amount of machining and heat treatment required, and the cost between the raw material and a finished tool. Choose the wrong condition and you either pay for purity the job never needed or accept a distortion risk you could have designed out. This guide covers the four conditions most often quoted and when each is the right call.

Recocido

Annealed is the default delivery condition for most tool steel grades. The mill heats the steel, holds it, and slowly cools it in the furnace, usually as a spheroidizing anneal that gathers the carbon into rounded carbide particles within a soft ferrite matrix. The result is the softest state the grade can hold.

The reason to buy annealed material is machinability. Soft steel cuts fast, maintains tolerance through roughing, and lets the toolmaker cut a die or punch to close to the final geometry without the cutter fighting back. It also carries no locked-in stress from rolling or forging, so the block behaves predictably on the machine. The tradeoff is that annealed steel has no working hardness. After machining, the toolmaker hardens and tempers the part in-house to achieve the wear resistance required by the application, which means either owning or outsourcing that step and accepting the small dimensional movement it entails.

Pre-Hardened

Pre-hardened steel arrives already heat-treated to a moderate working hardness, typically around 28-35 HRC, or roughly 300 HB. P20 and 4140 are common examples, widely used for mold bases, holder blocks, and general machine parts.

The advantage of pre-hardening is that it eliminates the need for a heat-treatment step after machining. Hardening a fully machined die or mold is exactly where distortion, warping, and cracking do their damage, and on a complex cavity that risk is expensive. A pre-hard block is machined straight to final dimension and put into service with no further thermal processing, so the geometry that comes off the machine is the geometry you keep. The cost is tool wear, since cutting hardened steel is slower and harder on inserts than cutting an annealed block. For applications that do not require extreme hardness, the trade-off is usually worth it.

QT (Quenched and Tempered)

QT stands for quenched and tempered, and it describes the full hardening sequence rather than a machinability grade. Pre-hardened delivery is a commercial form of QT intended for easy machining, but plates and blocks are also sold in the QT condition purely for out-of-the-mill structural strength and toughness.

Quenching heats the steel to its austenitizing temperature and cools it fast in water, oil, air, or salt, which traps the structure as martensite. Martensite is very hard but brittle and full of internal stress, so it is never usable on its own. Tempering follows immediately, reheating the steel to a lower temperature to restore toughness and dimensional stability at the cost of a slight loss of peak hardness. A part delivered as QT has already been through this cycle and arrives with a balanced combination of yield strength and notch toughness.

ESR (Electroslag Remelting)

ESR is not a heat treatment. It is a secondary melting process that buys metallurgical cleanliness, and it is priced accordingly.

A casting ingot serves as a consumable electrode that melts drop by drop in a bath of reactive molten slag within a water-cooled copper mold. As each droplet passes through the slag, sulfur and non-metallic oxide inclusions are stripped out, and because the mold pulls heat in a direction, the refined steel solidifies from the bottom up. That controlled solidification removes the center porosity, pipe, and segregation found in conventional ingots, leaving steel that is clean, uniform in every direction, and highly resistant to fatigue and cracking. Because the process is slow and costly, ESR is reserved for the most demanding dies, bearings, and aerospace tooling, where an unexpected failure is not acceptable.

For a full breakdown of the process and when the premium is justified, see our dedicated guide to ESR tool steel.

How to choose a delivery condition

The condition follows from where you want the heat-treatment risk to fall. If you need maximum hardness and want to control the hardening yourself, order the part annealed and cut it to a soft condition. If the part does not require extreme hardness and you want to skip post-machining heat treatment and its associated distortion risk, order pre-hard or QT. If the tool runs under heavy fatigue or in a safety-critical role, ESR earns its premium; for general tooling it does not.

Grade, condition, and section size are quoted together, so specifying the condition up front avoids re-quoting and keeps lead time predictable.

Aobo Steel supplies its core cold-work and hot-work grades in annealed, pre-hardened, and ESR conditions, with QT available on plate and block on request. If you are unsure which condition best fits your process, send the grade and the finished-part requirement, and we will confirm the correct delivery state before quoting.