01
Parts move after the furnace
A 4140 shaft comes back 0.08 mm out of round and the bore no longer matches the bearing. Distortion was never budgeted for, so the finishing cut has to be redone or the part is scrapped.
Steel Heat Treatment
Heat Treatment Steel
Hardness, toughness and machinability come from the thermal cycle, not the alloy alone. We machine steel parts to final geometry, then specify the thermal cycle that holds the tolerances your drawing calls for.
1018 / 1045 / 4140 / 4340±0.005 mmCase and through hardeningStress relief before finishingHardness reports on request
15 yearsSteel part production since 2011
127High-precision CNC machines
±0.005 mmAchievable tolerance
99.99%Qualification rate
Where it goes wrong
Problems you have probably paid for already
Most failures trace back to a step that was skipped, not to a bad alloy.
02
Hard where it should be tough
Quench and no temper leaves a 58 HRC surface with almost no impact resistance. The first assembly knock cracks a corner, and the whole batch is suspect.
03
Soft core under a hard skin
A case depth of 0.3 mm on a part that wears 0.5 mm per year just delays the failure. The specification looked fine on paper and was wrong for the load.
04
Scale and decarb on the surface
Furnace atmosphere was not controlled, so the outer 0.05 mm lost carbon. Threads gall, mating faces do not seat, and the hardness reading at the skin is misleading.
How we run it
Plan the thermal cycle around the machining sequence
The order of operations decides whether the final dimensions survive the furnace.
Sequence first
Rough, stress relieve, then finish
For any steel part that will be hardened, we rough machine leaving 0.3–0.5 mm on critical faces, send it for stress relief, then take the finishing cuts after the part has stopped moving. This costs one extra setup and saves the whole batch when a thin wall or a long shaft would otherwise warp.
On 1045 and 4140 parts with tight bore-to-bore relationships, we hold the finishing operation until after quench and temper. The material arrives at the finishing stage at its final hardness, so the dimensions we measure are the dimensions the customer receives.
- 1Rough stock0.3–0.5 mm left on faces that will be heat treated
- 2Stress reliefRemoves residual stress from roughing before the finishing cut
- 3Finish after temperFinal dimensions cut at final hardness, not before
Process selection
Pick the cycle from the load, not from habit
Annealing softens a part so it can be machined, formed or straightened. Normalizing does the same job with air cooling and leaves a more uniform grain structure, which suits weldments and large castings where you want predictable machining across the whole part.
Quenching raises hardness fast, and tempering trades some of that hardness back for toughness. Tool steel and 4340 parts usually land between 28 and 45 HRC after tempering. Below that range the part wears; above it, notch sensitivity climbs and thin sections become brittle.
- 1Soften to cutAnnealing and normalizing for machinability and straightness
- 2Harden for wearQuench plus temper for surfaces that slide, roll or clamp
- 3Case for edgesCarburizing or nitriding when only the outer layer must resist wear
Selection guide
Which cycle fits which part
A starting point for common steel grades. Final spec depends on section size and load.
| Process | Typical steel | Result you get |
|---|---|---|
| Annealing | 1018, 1045 | Low hardness, easy to machine and straighten |
| Normalizing | A36, 4130 weldments | Uniform grain, predictable machining |
| Quench + temper | 4140, 4340, 1045 | 28–45 HRC with usable toughness |
| Carburizing | 1018, 8620-type | Hard skin over a soft, tough core |
| Nitriding | 4140, tool steel | Thin hard layer, minimal distortion |
| Stress relief | Any pre-hardened part | Stable dimensions after finishing cuts |
What we do
Machining services that feed the thermal cycle
One shop for the geometry and the preparation steps that come before and after treatment.
01
5 Axis CNC Machining
Complex steel geometry in one setup, which keeps datums consistent before hardening.
02
CNC Milling & Turning
Shafts, housings, plates and bushings in 1018 through 4340 and tool steel.
03
Rapid Prototyping
One-off steel parts for fit checks before you commit to a hardened batch.
04
Sheet Metal Fabrication
Brackets and panels that need normalizing after welding to stay flat.
05
Part Surface Finishing
Black oxide, plating, bead blasting and polishing after the final heat cycle.
06
Custom 3D Printing
Jigs and fixtures for holding hardened parts during inspection and assembly.
Scope
Steel grades and shop limits
What we machine in-house and what we can hold after treatment.
| Item | Range | Notes |
|---|---|---|
| Steel grades | 1018, 1045, 4130, 4140, 4340, A36, tool steel | Others on request |
| Max part size | 4,000 mm | 4,000 × 400 × 150 mm travel |
| Tolerance | ±0.005 mm | ±0.0002 in |
| Surface finish | Ra 0.2–3.2 μm | Depending on process and feature |
| Order size | 1 to 10,000+ parts | No minimum order quantity |
| Inspection | 100% before shipment | Reports on request |
Why GreatLight
Numbers we work to
Fifteen years of steel work, three plants and a fixed set of limits we hold to.
15Y
Steel since 2011
Fifteen years of machining heat-treated steel parts across aerospace, automotive and industrial machinery.
127
CNC machines
16 simultaneous 5-axis centers, 16 mill-turn centers and 27 three-axis machines under one roof.
±0.005
Millimeters
Tolerance we hold on finished steel parts, including bores machined after quench and temper.
12 h
Quote turnaround
Quotation and free DFM analysis within 12 hours of receiving a drawing.
99.99%
Qualification rate
Raw material check, in-process monitoring and final inspection on every order.
3–5 d
Typical shipping
Parts ship in 3–5 days once production starts, with late-delivery risk below 2%.
7,600 m²Manufacturing space
150Technicians
3Wholly-owned plants
ISO 9001Plus IATF 16949, ISO 13485, ISO 27001
What the work looks like
Industry requirements and what we deliver
Automotive and EV
Steering and drivetrain parts machined in 4140, hardened and tempered for fatigue life.
- 28–45 HRC
- ±0.005 mm
- 100% inspection
Industrial machinery
Long shafts and rolls turned from 1045 and stress relieved between roughing and finishing.
- 4,000 mm max
- Ø400 mm rotary table
- Straightness held
Tooling and fixtures
Tool steel inserts and wear plates ground after quench to keep mating faces flat.
- Tool steel
- Ra 0.2–0.8 μm
- Hardness report
Medical and electronics
Stainless and alloy steel components that need clean surfaces after the final thermal step.
- ISO 13485
- No minimum order
- NDA on request
FAQs
Questions engineers ask before releasing a steel part
Should I machine before or after heat treatment?
Both, in the right order. Rough machine first, leave stock, then treat, then finish. Hardened steel above 45 HRC is difficult to cut with normal tooling and the extra grinding or EDM time usually costs more than the second setup.
If the part must be finished in the soft state, tell us at quoting. We will add a stress relief step and adjust the stock allowance so the finished dimensions still land inside tolerance.
What hardness can you machine after treatment?
We routinely finish parts up to about 45 HRC with carbide tooling. Above that, we plan for grinding or EDM on the critical features instead of turning and milling.
Anything above 50 HRC needs a different process plan. Send the drawing and we will say which features can be cut and which cannot.
How much distortion should I expect?
It depends on section thickness, quench severity and how much material was removed before treatment. Thin walls and long unsupported shafts move the most.
We reduce it by leaving uniform stock, controlling the quench, and finishing after tempering. On parts where distortion is a known risk, we measure after treatment and correct in the finishing setup.
Case hardening or through hardening?
Through hardening suits parts that must be hard all the way through, such as pins, dies and wear plates. Case hardening suits parts that need a hard surface over a tough core, such as gears and shafts that see impact.
Give us the load and the wear mode and we will suggest a case depth. A depth that is too shallow wears through quickly; one that is too deep defeats the purpose of a tough core.
Which steel grades do you machine most?
1018, 1045, 4130, 4140, 4340 and A36, plus tool steel for wear parts. These cover most brackets, shafts, housings and dies we see.
If your drawing calls for a grade outside this list, tell us the required hardness and the service temperature. We will confirm whether we can machine it and what the lead time looks like.
Can you supply parts with a hardness report?
Yes. Inspection reports, including hardness readings and dimensional data, are available on request. We also keep raw material certificates when the order calls for traceability.
Every order goes through raw material check, in-process monitoring and final inspection before shipment. Ask for the report format you need at the quoting stage.
What is the smallest order you accept?
One piece. There is no minimum order quantity, so a single prototype and a 10,000-part run go through the same process plan.
For a first article we often recommend machining to near-final geometry and treating one piece, so you can check the hardness and the fit before the full batch is released.
How do you keep drawings confidential?
Uploads are handled as confidential. We can sign an NDA before you send the files if your project requires it.
If the part is sensitive, we also restrict who inside the shop sees the drawing and keep the inspection data on the same controlled basis.
Send your steel part for a process review
Tell us the grade, the required hardness and where it wears. We will come back with a machining sequence and a quote.
12-hour quote100% inspectionNo minimum order±0.005 mmNDA available
