Heat treatment is the operation that turns a finished-looking quote into a money-loser the day the parts come back from the furnace. The part is machined, the price is set — then it ships to the heat treater, sits in a batch for a day, comes back hardened and distorted, and now needs a second machining pass to bring it back into tolerance. Heat treatment cost does not behave like a surface coating bolted onto the end of the job. It is a bulk metallurgical process that changes the part all the way through, it is priced by weight and furnace load rather than by area, it almost always rides between two machining operations rather than after them, and it carries a distortion risk that costs you again on the bench. Quote it as a flat add-on and you will misprice the small lots, miss the second op entirely, and eat the scrap when a part warps past correction.

This guide breaks a heat-treatment line item into the inputs you can actually estimate — process type, part weight and furnace load, lot minimums, hardness and case-depth spec, and the post-treat machining the process forces — and shows how to price hardening, annealing, and stress relief into a quote you can defend.

Why heat treatment is priced unlike machining or coating

Machining cost scales with spindle time. Surface coating scales with area. Heat treatment scales with neither — it scales with mass and furnace load. A heat treater runs a furnace at temperature for a fixed cycle, and that cycle costs the same energy whether the basket holds 5 kg of parts or 50 kg. So they price by weight, floored by a minimum lot charge, with surcharges for the more demanding processes and atmospheres.

That makes the cost behave in ways that surprise estimators coming from a machining mindset. A heavy, simple block costs more to treat than a light, intricate part, because the furnace charges for the kilogram, not the complexity. A single prototype can cost the same to treat as twenty parts, because the minimum lot charge covers the furnace cycle regardless of how full the basket is. And the most expensive part of the whole exercise is often not the furnace invoice at all — it is the second machining operation the process forces you to plan, grind, or hold tighter on. Quote heat treatment as a percentage of machining cost and you get all three of those wrong.

The cost drivers of a heat-treatment line item

Five inputs set the heat-treatment cost on a part. Estimate each and the line item builds itself.

• Process type — stress relief, annealing/normalizing, through-hardening (quench and temper), or case-hardening (carburizing, nitriding, induction). Each has a different cycle, atmosphere, and price band.
• Part weight and furnace load — total kilograms in the batch, since the treater prices by mass against a minimum.
• Lot minimum — the floor charge per furnace run, which dominates on small quantities and prototypes.
• Spec severity — target hardness (HRC), case depth, and any certification or test-coupon requirement, which push toward longer cycles and controlled atmospheres.
• Post-treat machining — grinding, finish-turning, or straightening needed because the process distorted the part or left scale and a hard skin.

Add the per-kilo furnace charge for the batch, compare against the lot minimum and take the higher, then add the post-treat machining as its own burdened hours. That last term is the one flat add-ons forget, and it is frequently the largest.

A process-and-cost map for the common treatments

The treatments a job shop quotes most often sit in distinct cost bands. Treat these as typical, approximate ranges to calibrate against your own heat treater's price list — material, mass, atmosphere, and certification all move them.

Process	What it does	Distortion / scale risk	Relative cost band
Stress relief	Removes residual stress after machining/welding	Low — but can move thin parts	Lowest
Annealing / normalizing	Softens for machining, refines grain	Low–moderate, plus scale	Low
Through-hardening (quench + temper)	Hardens the whole section to a target HRC	High — quench distortion likely	Moderate
Carburizing (case-harden)	Hard wear case over a tough core	High — long cycle + quench	Higher
Nitriding	Hard case at lower temp, minimal distortion	Low distortion, premium process	Highest per cycle

The estimating trap is reading "harden" on a drawing and quoting a single generic furnace charge. A part that calls out a controlled case depth and a tempered core is a different cost — and a different lead time — from one that needs only a stress relieve after welding. Read the callout, not the word, the same way you would read a finish spec.

Weight, furnace load, and the lot minimum

The heat treater prices the basket, not the part. For a quote you do not need a gram-accurate weight; a reasonable estimate of part mass times quantity is enough, because the per-kilo rate is modest and on small lots the minimum governs anyway.

A workable formula for the batch:

1. Estimate the weight of one part in kilograms (volume × material density is close enough for quoting).
2. Multiply by quantity to get the batch weight.
3. Multiply batch weight by the treater's per-kilo rate for that process.
4. Add any surcharge for atmosphere, certification, or test coupons.
5. Compare the total to the lot minimum and take the higher of the two.
6. Add the post-treat machining hours separately — this is part of your cost, not the treater's invoice.

Step 5 is the one hand-built quotes skip, and it is the one that loses money on prototypes. A typical lot minimum runs anywhere from €80 to €200 depending on process and shop. Spread across the batch, the per-part cost swings hard with quantity:

Batch size	Lot minimum	Heat-treat cost per part
1	€120	€120.00
5	€120	€24.00
25	€120	€4.80
100	€120	€1.20 (or per-kilo rate, if higher)

A single hardened prototype quoted with the hundred-off treatment cost loses you the difference on every order. This is the same batch-divide discipline that governs setup and programming in how to price CNC machined parts — a fixed cost spread over quantity — and it applies just as hard to an outsourced furnace run as it does to an in-house setup.

Distortion, scale, and the second machining operation

Here is the cost that flat add-ons miss entirely. Hardening processes that involve a quench move the part. A through-hardened shaft bows, a carburized gear grows and warps, a flat plate cups. That distortion is exactly why the standard route for a precision hardened part is rough machine → heat treat → finish machine, not machine-then-harden. The hard, distorted part comes back and has to be ground or hard-turned back into tolerance — and grinding a 60 HRC surface is slow, expensive work, not the same operation you ran before the furnace.

This is why heat treatment cannot be costed as a single end-of-job line. It splits the part's routing into two machining phases with the furnace in the middle, and each phase carries its own setup, its own cycle time, and its own burdened rate. Building that multi-step routing correctly is the whole subject of quoting multi-step operations with work plans — the heat-treat job is the textbook case where skipping the second op turns a profitable quote into a loss.

The drawing tells you how much that second op will cost before you ever quote it. A tight tolerance or a fine finish callout on a hardened feature means grinding, not turning; a high hardness on a thin section means distortion and straightening. Reading those callouts the way G&D&T and tolerances for estimators lays out is what separates a heat-treat quote that holds from one that bleeds on the surface grinder.

Outsourced treatment: markup and lead time

For nearly every small and mid-size shop, heat treatment is sent out. That changes two things in the quote. First, the furnace charge is a vendor invoice, not a burdened hour — and you should mark it up like any bought-in service, not pass it through at cost, because you carry the handling, the freight both ways, the quality risk, and the cash-flow gap. Decide that markup deliberately; the difference between margin and markup, and how to apply each, is laid out in margin vs markup in manufacturing pricing.

Second, outsourced heat treatment adds calendar days — typically two to five working days plus transit, more for carburizing or anything requiring metallurgical certification — and that has to land in your promised lead time, not just your price. A part that machines in a day but waits a week at the heat treater, then comes back for a grinding op, is a two-week part. Manufacturing lead-time estimation covers how to fold outside-process queue time into the date you quote, so the furnace step does not quietly turn an on-time job late.

Whichever way you go, the heat-treatment cost — and the second machining op it forces — belongs as its own line on the quote, not buried in a finishing percentage. A clear line item is part of what makes a quote readable and defendable, which is the whole point of a consistent manufacturing quote template.

From drawing to a heat-treat-inclusive quote

The slow, error-prone part of quoting hardened parts is the reading: catching the heat-treat callout, distinguishing a stress relieve from a controlled case depth, spotting the tolerance that forces a post-treat grind, estimating the part weight, and remembering to route the second machining op at all — every one of those before you reach the treater's price list. Under deadline pressure that reading gets shortcut, and the heat-treat line becomes a round-number guess that ignores the most expensive part of the job.

QuoteBuddy reads the technical drawing and surfaces the inputs a heat-treatment line needs — material, hardness and case-depth callouts, tolerances on treated features, and geometry it can weigh — so the estimator works from a complete picture instead of a hurried scan. The cost engine then builds heat treatment as its own line, by process, weight, lot minimum, and your vendor markup, and prompts the post-treat machining the spec implies, the same way every time, so two estimators quoting the same part land on the same number.

Start a 30-day trial and run a few real hardened drawings through the process — from upload to a complete, itemised quote. See whether the cost it builds matches what you would have quoted by feel, and where the missing second op was quietly costing you on every hardened job.