Metal material guide
Alloy Steel
CNC Machining
CNC shafts, locating components and loaded parts, with steel grade, heat treatment and final machining planned as one route.
Confidential enquiries. NDA available.
- Specify
- 4140 by product specification or named alternative
- Review
- Bearing seat and Treatment zone
- Confirm
- Final condition and acceptance records
Start with the load and the final condition.
A steel part may need core toughness, a hard wear surface or a particular strength level. Specify those needs before choosing stock and deciding when to heat treat.
Shafts and drive components
Mark bearing seats, torque features and fatigue-sensitive transitions. Include the final material condition and the surfaces to be ground or finished.
Wear and locating parts
Separate surface-hardness needs from core properties. Define contact faces, case requirements if relevant and the test locations.
Tooling and fixtures
Identify locating features, clamping loads and corrosion protection. Use the drawing to distinguish wear-critical areas from general structural geometry.
Choose the grade and stock together.
Compare the Alloy Steel options below against the drawing and service conditions. Specify the complete supplier grade, condition and stock form; material examples do not establish current inventory or permit substitutions.
| Grade or stock | Why consider it | What to resolve |
|---|---|---|
| 4140 by product specification | General engineering parts with a specified alloy-steel strength and condition. | Name annealed, prehardened or quenched-and-tempered stock and the required final properties. |
| 4340 by product specification | Highly loaded parts where the design requires this nickel-chromium-molybdenum steel. | Confirm the section, treatment and testing requirements rather than substituting on a family name. |
| 8620 by product specification | Parts designed for an agreed case-hardening route. | Specify case depth, hardness, protected areas and machining after treatment. |
| 42CrMo4 by named standard | Drawings using an EN grade and a specified delivery condition. | Do not assume equivalence to a 4140 purchase specification without checking both standards. |
Selection examples are subject to material and drawing review. They are not an inventory list.
Already have a grade on the drawing?
Add it to your quotation checklist ↓Put heat treatment inside the machining plan.
An accurate pre-treatment part is not necessarily an accurate finished part. State the final condition for the dimensions and surfaces that drive assembly.
Stock hardness
Supply the ordered condition and any hardness limits. The tool path and finishing allowance depend on the material actually delivered.
Thermal movement
Identify long sections, keyways and asymmetric pockets. Discuss roughing, stress relief or treatment, then final sizing where the drawing requires it.
Bearing seats and ground faces
Mark the required fits and roughness, plus datum relationships. Identify any surfaces requiring grinding or protection during heat treatment.
Mark critical dimensions on the drawing. Achievable tolerances, wall thickness, part size and delivery are confirmed for the geometry, material, finish and quantity in the quotation.
Specify protection without losing the fit.
Black oxide or other conversion finish
State the exact requirement, corrosion expectations and any oil or seal condition. Do not treat a colour change as a defined corrosion performance.
Plating or coating
Define the coating, thickness acceptance, masked surfaces and final dimensions. Include relevant embrittlement-control requirements where applicable.
Ground or as-machined surfaces
Identify functional roughness and lay. Distinguish the final bearing or sliding surface from non-critical external faces.
Verify hardness and geometry in the agreed sequence.
Steel identity
Define grade, product specification and heat traceability. Keep material records connected to the delivered part lot.
Treatment evidence
Specify hardness method, location and limits. Add case-depth or other tests only when the drawing or purchase specification calls for them.
Final measurement
Identify dimensions to inspect after treatment and coating, including straightness, concentric features and bearing-seat relationships.
Three different checks.
The material record identifies the purchased stock. The inspection report checks the drawing. Application validation checks the part in service.
Review inspection requirements ↗Alloy Steel machining questions.
Answers to the decisions that affect the material, drawing and finished part.
Is 4140 always supplied hardened?
No. The delivery condition is part of the purchase specification. State the stock condition and final required hardness or properties on the RFQ.
Can I specify only a final hardness?
Hardness alone may not define the required grade, core properties, case depth or treatment route. Include the material standard and functional requirements.
Why leave material for machining after heat treatment?
Treatment can change shape or size. Where required, an agreed allowance and finishing step allow the functional surfaces to be produced in the final condition.
Are 4140 and 42CrMo4 automatically interchangeable?
They are often compared, but the complete standards and acceptance requirements must be checked. Substitution needs drawing-owner approval.
Does black oxide provide a complete corrosion specification?
No. State the environmental requirement and the coating or preservation scope. Colour alone does not define the protection needed.
How should a case-hardened component be quoted?
Include the grade, case-depth and hardness requirements, masked zones, final dimensions, quantity and test records. Identify any surfaces requiring finishing after treatment.
Prepare your enquiry
Define the steel grade and its final condition.
Send the CAD model and dimensioned drawing with quantities, service conditions and the requirements below. If the grade is undecided, describe the function and the constraints.
Your files stay confidential. NDA available.
Alloy Steel RFQ checklist
Material: [steel grade + product standard + delivery condition] Treatment: [final hardness, case depth if needed, masked zones] Features: [seats, keyways, datums, straightness] Final process: [grinding / machining after treatment] Protection: [coating, preservation, final-size requirements] Quantity and records: [lot size, heat traceability, test reports]
Material references & specification notes
Manufacturer information supports material selection. Use the datasheet for the exact grade, stock form and test conditions. It does not establish Prolean inventory, application approval or a guaranteed machining result.
Prepared October 2026. Final material and manufacturing requirements are agreed in the quotation.