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Manufacturing SOP Example: Batch Annealing (SOP-HT-014)

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Batch Annealing — Stress Relief, Furnace #3

Standard Operating Procedure

SOP-HT-014

Rev. C

Effective

2026-05-01

Material

AISI 4140

Owner

Process Eng.

Class

Controlled

1.0 — Purpose & Scope

This procedure defines the controlled stress-relief annealing of AISI 4140 steel components in Furnace #3. It applies to production lots up to 250 kg. Operators must hold current Level 2 thermal-process certification before performing this procedure independently. Deviations are dispositioned per §4.0.

2.0 — Equipment & Pre-checks

Ref	Check	Acceptance	By
2.1	Furnace empty and interior free of debris/scale	Visual — pass	OP
2.2	Thermocouple TC-3 calibration current	≤ 30 days	OP
2.3	Inert atmosphere (N₂) supply pressure	2.5–4.0 bar	OP
2.4	Chart recorder / data logger online	Confirmed	OP

3.0 — Procedure

Step	Action	Parameter / Tolerance	By
3.1	Load components on rack; maintain part-to-part spacing for even heat	25–40 mm	OP
3.2	Purge chamber and establish inert atmosphere before ramp	≥ 3 vol. exchanges	OP
3.3	Ramp to soak temperature under inert atmosphere	730 ± 14 °C	OP
3.4	Hold at soak; record chart every 15 min	90 ± 5 min	OP / QA
3.5	Controlled furnace cool, lid closed — do not force-cool	≤ 55 °C / hr	OP
3.6	Unload below handling temperature	≤ 60 °C	OP
3.7	Verify hardness on coupon from the same lot	22–28 HRC	QA

4.0 — Deviations & Disposition

Any soak excursion beyond ±14 °C, a cooling rate above 55 °C/hr, or a hardness result outside 22–28 HRC shall be recorded as a non-conformance and routed to the Material Review Board (MRB) before lot release. No affected lot proceeds to the next operation without written MRB disposition.

5.0 — Records & Traceability

Attach the furnace chart (Form QF-22), hardness log, and lot traveler to the batch record. Retain per the QMS-04 retention schedule. The completed record must show operator and QA sign-offs at each indicated step and a unique lot identifier traceable to incoming material certification.

6.0 — Revision History

Rev	Change	Date	By
A	Initial release	2025-09	Eng.
B	Added inert-purge step 3.2; tightened soak band	2026-01	Eng.
C	Added MRB deviation route; cooling-rate cap	2026-05	Eng.

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