What this page is, and what it refuses to be
It is a clock. You bring a schedule — a soak rate, a floor, however many cycles, however long the tempers run — and it adds them up, tells you when to light the oven and shows you which part of the day is doing the damage to your afternoon.
It is not a source of heat treat data and it will not become one. There is no table of steels behind it, no default that describes any particular alloy, and no verdict on whether what you typed is sensible. The numbers that go in the boxes live on the manufacturer data sheet for the steel you have, and the difference between two steels that look identical on the shelf can be the difference between a blade and a wall hanger. If you do not know which steel it is, there is no schedule to build.
Why the soak scales with thickness and nothing else does
Soak time is about getting the middle of the piece to the same condition as the outside, so it tracks the distance heat has to travel — the controlling section. That is why schedules quote it per inch, and why they put a floor under it: on a very thin section the rate produces a time so short it stops being meaningful.
Everything else in the schedule is indifferent to how thick the piece is. The oven takes the same time to recover whether it has a paring knife or a cleaver in it. A two hour temper is two hours. So on thin stock the soak is a rounding error against the tempers, and the schedule for a whole day is set almost entirely by things that have nothing to do with the piece.
The practical consequence, which the table on the page makes visible: batching by thickness saves you almost nothing. Batching by schedule — everything that shares the same cycle structure going in together — saves you a whole day per load you avoid.
The cool-down between tempers, counted once fewer than you think
| Temper cycles | Cool-downs counted | Why |
|---|---|---|
| 1 | 0 | Nothing follows it, so the piece cools on your bench and not on the clock |
| 2 | 1 | Between the two |
| 3 | 2 | Between the first and second, and between the second and third |
This is the classic off-by-one and it costs a whole cool-down every time it is got wrong. The page counts cycles minus one, and prints zero rather than a stray line when there is only one cycle.
What the quench does to the clock
Almost nothing, which is why there is no field for it. The transfer and the quench itself happen in seconds and disappear into the rounding on a schedule measured in hours. What the quench does to the rest of the day is different: it is the one irreversible step, it is the one with fire in the room, and it is the step where the piece either survives or does not. The clock is indifferent to all of that.
The tank is worth a thought that is not on this page. A quench takes heat out of the steel and puts it into the medium, and a tank that is too small for the load coming into it gets hot enough to change what it does. That is a heat capacity question with an answer, but the answer depends on the medium, and the medium is another thing this page will not name.
Questions people ask
What soak rate should I put in?
The one on the data sheet for your steel, and nothing else. This page holds no soak figures for any steel and the number sitting in the box by default exists purely so the arithmetic has something to render — it does not describe any alloy and it is not a starting point. Soak rates differ substantially between steels that look identical, and the output on this page always attributes the figure back to you for exactly that reason.
Why does the soak barely change the total?
Because on thin stock it is a small part of a schedule dominated by fixed times. The oven equalise happens once per cycle regardless of what is in it, and a temper cycle is however long it is whether the piece is a tenth of an inch or half an inch. Double the section and the soak doubles, but the total moves by only that difference. The table on the page shows the effect at half, double and four times your section.
Should the cool-down after the last temper be counted?
No, and the page does not count it. A cool-down is only on the clock when something has to happen after it — the piece has to be back at room temperature before the next cycle can start. After the final cycle the piece cools on the bench while you do something else, so it costs no schedule time. With one temper cycle the cool-down field contributes nothing at all and the output says so rather than printing an empty line.
Does this tell me whether my heat treat worked?
No, and nothing that is only arithmetic can. Whether a schedule produced what you wanted is settled by testing the pieces — and by which steel it actually was, which is the input everything else depends on. A schedule run perfectly on the wrong data sheet is a schedule run wrong. This page adds up the clock for the schedule you brought and takes no view on the schedule itself.
Can I run several loads through and just multiply?
That is what the loads field does, and it assumes they run one after another in the same oven with no overlap. If you have two ovens, or you can start the second load equalising while the first is tempering, the real elapsed time is shorter than the figure here — but by how much depends on your oven and your bench space, so the page takes the conservative reading rather than guessing at an overlap you may not have.