Quenching and tempering
Last updated 2026-10-02 · route revision 5
The shop does not release a quench without a temper: straight from the bath a part is brittle and stressed, and tempering relieves it and brings the hardness down to working level. It is one operation pair, so it is written up together.
Austenitising
Heating is done in the КЭП-1 and КЭП-2 chamber furnaces, two thermocouples each, held to ±10 °C. Tool grades go in with a preheat so nothing cracks on the way up; 9KhS and Kh12MF get a two-stage preheat, and Kh12MF sits at 850 °C before it goes on to the working temperature.
| Grade | Austenitising, °C | Quenchant | Hardness |
|---|---|---|---|
| 45 | 820–840 | polymer–water | 45–50 HRC |
| 40Kh | 840–860 | oil I-20A | 48–52 HRC |
| 40KhN | 820–840 | oil I-20A | 48–53 HRC |
| 65G | 810–830 | oil I-20A | 55–60 HRC |
| U8 | 780–800 | water | 58–62 HRC |
| 9KhS | 840–860 | oil I-20A | 60–63 HRC |
| ShKh15 | 830–850 | oil I-20A | 61–65 HRC |
| Kh12MF | 1020–1040 | oil or air | 58–62 HRC |
Quenchants
Oil I-20A is held at 40–60 °C and stirred - cold oil pulls heat too fast and cracks parts. For distortion-prone 45 we use an 8–12 % polymer–water bath and check the concentration with a refractometer once a shift. Water is kept only for carbon U8 in a heavy section.
Tempering
Tempering is set no later than four hours after the quench, or tool grades pick up cracks from sitting hardened. We step around the 250–400 °C window, where many structural steels lose impact toughness to temper embrittlement.
| Band | Temperature, °C | Time | Result |
|---|---|---|---|
| low | 150–250 | 1.5–2 h | stress relief, hardness down by 1–3 HRC |
| medium | 350–450 | 1.5–2.5 h | springiness, 42–48 HRC on spring grades |
| high | 550–650 | 2–3 h | improvement, a tough core at 28–34 HRC |
Base tempering time grows with the section: we add an hour for every 25 mm. The high temper runs in the dedicated ПО-1 furnace held to ±5 °C, because here a steady temperature matters more than a high ceiling.
Quench-and-temper takes 2–4 working days, depending on furnace load and batch size. Related: allowances and prep, how we measure hardness, why distortion happens.