Metal Strength Chart: Tensile, Yield, Hardness & Density for CNC Materials

A metal strength chart compares yield strength, tensile strength, hardness, and density across the alloys that appear most on CNC purchase orders. This guide covers eight grades in bar stock form at room temperature: Al 6061-T6, Al 7075-T6, SS 304, SS 316L, 4140 alloy steel (quenched and tempered), 1045 carbon steel (as-rolled), brass C360 (half-hard), and Ti-6Al-4V (annealed). Every value is tied to a product specification (ASTM or AMS), and the testing methods behind those numbers (ASTM E8/E8M-25 for tension, ASTM E18-25 for Rockwell hardness) are noted alongside the data.

Yield strength, not tensile strength, is the design limit for most machined parts. A bracket that deforms past its yield point loses dimensional accuracy and fails functionally, even without fracturing. The data here is structured around that principle: yield strength occupies the first column, and each row includes a strength-to-weight ratio for mass-sensitive comparisons.

Scope: bar stock, room temperature, published typical values. Cast, forged, and elevated-temperature conditions are not covered.

1. CNC Metal Strength, Hardness and Density Reference Table

All values are published typical properties for bar stock at room temperature (10 to 38°C per ASTM E8/E8M-25, 10 to 35°C per ASTM E18-25). Hardness uses the Rockwell scale appropriate to each material: HRC for hardened steels and titanium, HRBW (tungsten carbide ball indenter per ASTM E18-25) for softer alloys. “Typical” means representative of the grade and condition shown, not a guaranteed minimum. Request the supplier’s mill test report when your design operates near a strength class boundary.

Material (Condition)	Yield (MPa)	Tensile (MPa)	Hardness	Density (g/cm³)	Yield/Density	Spec
Al 6061-T6 (extruded bar)	276	310	60 HRBW	2.70	102	ASTM B221-21
Al 7075-T6 (extruded bar)	503	572	87 HRBW	2.81	179	ASTM B221-21
SS 304 (annealed bar)	215	505	92 HRBW	8.00	27	ASTM A276-25
SS 316L (annealed bar)	170	485	79 HRBW	8.00	21	ASTM A276-25
4140 Q&T (25 mm bar)	655	850	25 HRC	7.85	83	ASTM A29-23
1045 as-rolled (bar)	310	565	84 HRBW	7.85	39	ASTM A29-23
Brass C360 (half-hard rod)	140	340	78 HRBW	8.50	16	ASTM B16-24
Ti-6Al-4V (annealed bar)	880	950	36 HRC	4.43	199	AMS 4928

The Yield/Density column (MPa·cm³/g) is the comparison metric for weight-sensitive parts. Ti-6Al-4V at 199 is 2.4 times the ratio of 4140 steel at 83, which explains titanium’s dominance in aerospace brackets despite 5 to 10 times the material cost. 7075-T6 at 179 sits close behind titanium and machines 4 to 5 times faster, making it the default when corrosion and temperature requirements allow aluminum.

Hardness scale matters. 60 HRBW (6061-T6) and 25 HRC (4140 Q&T) cannot be compared by number. HRBW uses a tungsten carbide ball at 100 kgf; HRC uses a 120° diamond cone at 150 kgf. Cross-scale conversion requires ASTM E140 tables and remains approximate.

SS 316L shows lower yield (170 MPa) than 304 (215 MPa) despite better corrosion resistance. The molybdenum addition in 316L improves pitting resistance but does not raise strength. If both corrosion resistance and higher yield are needed, cold-worked 316 or a precipitation-hardened grade like 17-4 PH is the direction.

4140 Q&T properties depend on bar diameter. The 655 MPa yield shown is for 25 mm bar. A 75 mm bar quenched and tempered to the same process will show lower yield because the core does not cool fast enough to fully transform. The 4140 vs 1018 vs 1045 comparison covers how section size and heat treatment interact for these three grades.

2. How to Read This Chart: Yield Strength vs Tensile Strength

A CNC bracket loaded to 80% of its tensile strength has already yielded, bent, and lost its mating dimensions. The part has failed functionally without breaking.

Yield strength marks the stress where permanent deformation begins. ASTM E8/E8M-25 determines this value using the 0.2% offset method: a line parallel to the elastic portion of the stress-strain curve is drawn at 0.2% strain, and the intersection with the curve is reported as yield strength. The standard presents 0.2% as the common offset, not a universal mandate. Some aerospace specs require 0.02%.

Tensile strength (maximum stress before fracture) governs two specific cases: fasteners under tensile preload where bolt yield causes clamp loss, and structures where fracture, not deformation, is the failure mode. For brackets, housings, shafts, and fixtures, yield is the governing number.

The design formula: Allowable stress = Yield strength / Safety factor. A 6061-T6 bracket with 276 MPa yield and a safety factor of 2.5 gives 110 MPa allowable working stress. Typical factors: 2 to 3 for well-characterized static loads, 3 to 5 for dynamic or uncertain loading, higher where codes (ASME, FAA) apply.

For parts where applied stress must stay below yield at the most loaded feature, the tight tolerance machining guide explains how to assign tolerances that reflect real functional requirements.

2.1. Elastic Modulus and Deflection

Strength and stiffness are different properties. Aluminum alloys (6061, 7075) share an elastic modulus of about 69 GPa. Steel alloys cluster around 193 to 200 GPa. Ti-6Al-4V sits at 114 GPa.

A geometrically identical bracket in aluminum deflects roughly 2.9 times more than one in steel under the same load. When deflection, not yield, is the failure criterion (long unsupported spans, precision stages), increasing the aluminum cross-section to compensate can partially cancel the weight saving.

2.2. How the Data Was Generated

Yield and tensile values come from uniaxial tension testing per ASTM E8/E8M-25. A machined coupon (12.5 mm diameter round bar, 5D gauge length for E8M) is pulled to fracture. Strain rate during yield measurement: 0.015 ± 0.006 mm/mm/min (Control Method B).

ASTM E8/E8M-25 Section 4.2 states that tensile test results from a standard coupon do not represent the finished CNC part. The coupon captures one location, one cross-section, and one surface state. Geometry, residual stress, and surface condition in the final part all differ.

Hardness values follow ASTM E18-25. The test applies a 10 kgf preliminary force, then the full test force (100 kgf for HRBW, 150 kgf for HRC), held for 2 to 6 seconds, then released. The residual indentation depth converts to a hardness number. Reporting precision: 0.1 Rockwell unit per ASTM E29.

3. Metal Density Chart: Weight Comparison for CNC Materials

Density sets the finished part weight, the raw material cost per piece, and the shipping weight. The same eight materials from Section 1, sorted lightest to heaviest:

Material	Density (g/cm³)	Density (lb/in³)	Relative Weight (Steel = 1.00)
Al 6061-T6	2.70	0.098	0.34
Al 7075-T6	2.81	0.102	0.36
Ti-6Al-4V	4.43	0.160	0.56
4140 steel	7.85	0.284	1.00
1045 steel	7.85	0.284	1.00
SS 304	8.00	0.289	1.02
SS 316L	8.00	0.289	1.02
Brass C360	8.50	0.307	1.08

A 6061-T6 part weighs 34% of the same geometry in steel. Ti-6Al-4V weighs 56%. These ratios hold regardless of shape because density is a bulk property.

3.1. Strength-to-Weight Ratio

Yield/Density from Section 1, sorted: Ti-6Al-4V 199, 7075-T6 179, 6061-T6 102, 4140 Q&T 83, 1045 39, SS 304 27, SS 316L 21, C360 16.

7075-T6 reaches 90% of titanium’s strength-to-weight ratio at roughly one-fifth the material cost and one-quarter the machining time. For structural brackets not exposed to seawater or temperatures above 120°C, 7075-T6 is the economically correct choice over titanium. The aluminum heat sink material comparison covers the narrower case where thermal conductivity, not strength, drives aluminum grade selection.

3.2. Quick Weight Estimate

Weight (grams) = Volume (cm³) × Density (g/cm³). A 50 × 50 × 20 mm solid block (50 cm³): 6061-T6 = 135 g, 4140 steel = 393 g, Ti-6Al-4V = 222 g, C360 = 425 g. Raw billet weight sets the material cost baseline and affects freight for offshore sourcing.

4. Metal Hardness Chart: HRC, HRB and Rockwell Scale for Machined Parts

Hardness on a CNC drawing appears as a Rockwell number: HRC for hardened steels and titanium, HRBW for aluminum, brass, and annealed stainless. The two scales use different indenters and different forces. A part at 60 HRBW machines with standard carbide; a part at 60 HRC requires CBN or grinding.

4.1. Rockwell Scale Selection per ASTM E18-25

Scale	Indenter	Total Test Force	Typical Materials
HRBW	WC ball, 1.588 mm	100 kgf (981 N)	Aluminum, brass, copper, soft steel, annealed stainless
HRC	120° diamond cone, 0.200 mm tip	150 kgf (1471 N)	Q&T steel, hardened tool steel, titanium
HRA	120° diamond cone, 0.200 mm tip	60 kgf (589 N)	Thin steel, shallow case-hardened layers

All three scales start with a 10 kgf (98 N) preliminary force. ASTM E18-25 designates HRBW (not HRB) when a tungsten carbide ball is used. Older reports showing HRB or HRBS (steel ball) are not directly comparable.

4.2. Hardness Values for the Eight CNC Metals

HRBW scale: 6061-T6 at 60 (machines with uncoated carbide), 7075-T6 at 87 (sharper edge geometry reduces built-up edge), C360 at 78 (free-cutting, highest machinability on this list), 1045 as-rolled at 84 (straightforward), 316L annealed at 79 (softer than 304 but gummier chip control), 304 annealed at 92 (near top of HRBW range, work hardens during cutting).

HRC scale: 4140 Q&T at 25 (carbide insert grades P20/P30 at moderate speeds), Ti-6Al-4V annealed at 36 (low thermal conductivity traps heat at the tool tip, needs high-pressure coolant).

Comparing 92 HRBW (304) to 25 HRC (4140 Q&T) by number alone would suggest 304 is harder. The scales differ. Approximate Vickers conversion per ASTM E140: 92 HRBW converts to about 195 HV, 25 HRC converts to about 253 HV. The 4140 Q&T is harder.

4.3. Curvature Correction for CNC Turned Parts

ASTM E18-25 Section 6.4 and Appendix A6: testing on a convex cylindrical surface underreads true hardness. On a 10 mm diameter bar at 25 HRC measured, the correction is 1.5 to 2.0 HRC units. On 25 mm bar, below 1.0 unit. Testing on diameters smaller than Table A6.1 minimum is not permitted. For small-diameter CNC pins, test a flat witness coupon processed with the parts.

ASTM E18-25 Section 6.1 requires the test face to be smooth, free of oxide scale, and free of machining-induced cold work or overheating. A rough-turned or grinding-burned surface gives unreliable readings. The surface roughness Ra chart maps what each CNC process delivers.

4.4. Hardness-to-Tensile Conversion

ASTM E18-25 Section 8.1: no universally accurate method exists for converting between Rockwell scales or from Rockwell to tensile strength. ASTM E140 provides approximate tables for specific material families (carbon steel, austenitic stainless, nickel alloys, brass, copper). Applying the carbon steel table to Ti-6Al-4V or 304 stainless produces misleading numbers.

When reporting a converted value, ASTM E18-25 Section 9.3 requires both the converted and original measurement: for example 253 HV (25 HRC). The ISO 286 fits reference covers how tolerance class selection on mating surfaces interacts with hardness and wear expectations.

5. Steel vs Aluminum vs Titanium: Selecting the Right Family

5.1. Steel

1045 as-rolled delivers 310 MPa yield at the lowest raw material cost on this list. Machine bases, brackets, shafts, and fixtures where weight does not matter start here. When 310 MPa is not enough, 4140 Q&T reaches 655 MPa yield at 25 mm section. Gears, drive shafts, and high-load tooling use this grade.

Steel’s limitation is weight: 7.85 g/cm³ is 2.9 times 6061-T6. For moving parts (robot arms, drone frames, EV structural components), that mass penalty drives acceleration loads upward. Corrosion is the second constraint. Uncoated carbon steel rusts in ambient air. SS 304 and 316L solve corrosion but trade away strength and machinability. Cast iron is an alternative where damping and compressive strength matter more than tensile performance.

5.2. Aluminum

6061-T6 is the production default for non-ferrous CNC parts. Its 276 MPa yield handles moderate structural loads at 2.70 g/cm³, and machinability allows cutting speeds 4 to 5 times faster than steel. A 6061-T6 bracket that meets the stress requirement will almost always be cheaper to machine than the same bracket in 4140, even if the aluminum billet costs more per kilogram.

7075-T6 at 503 MPa yield fills the gap between 6061 and steel. It machines slightly slower than 6061 and cannot be reliably welded, but for a single-piece structural component needing more strength without steel’s weight, 7075-T6 is the step up.

Aluminum’s limitation is stiffness: elastic modulus of 69 GPa versus 200 GPa for steel means 2.9 times more deflection under the same load. Temperature is the second boundary: yield drops above roughly 120 to 150°C. Anodizing adds corrosion and wear resistance but changes dimensions (50% inward, 50% outward per MIL-PRF-8625F). Mask features requiring tight tolerance control.

5.3. Titanium

Ti-6Al-4V at 880 MPa yield and 4.43 g/cm³ delivers the highest strength-to-weight ratio on this list (199 MPa·cm³/g). It resists corrosion in seawater, body fluids, and most chemical environments. It is biocompatible for implant applications under ASTM F136.

Titanium is justified when at least one condition holds: yield above 500 MPa with low mass is required simultaneously; the corrosion environment defeats both anodized aluminum and coated steel; the part is a medical implant; or the service temperature sits between 150°C and 400°C.

If none of those conditions apply, 7075-T6 meets most structural requirements at one-fifth the material cost and one-quarter the machining time.

Titanium’s machining difficulty comes from low thermal conductivity (6.7 W/m·K versus 167 W/m·K for 6061-T6). Cutting speeds for Ti-6Al-4V run 30 to 60 m/min versus 250 to 500 m/min for 6061-T6. Sharp tools, rigid setups, and high-pressure coolant are required.

5.4. Relative Machining Cost

Material	Relative Cost (6061-T6 = 1.0×)	Main Cost Driver
Al 6061-T6	1.0×	Baseline
Brass C360	0.8 to 1.0×	Free-cutting, minimal burr
Al 7075-T6	1.2 to 1.5×	Slightly lower speeds, more tool wear
1045 as-rolled	1.5 to 2.0×	Lower speeds, harder on tools
4140 Q&T	2.0 to 3.0×	Harder material, insert wear
SS 304 annealed	2.5 to 4.0×	Work hardening, poor chip breaking
SS 316L annealed	2.5 to 4.0×	Gummy chips, built-up edge
Ti-6Al-4V	5.0 to 10.0×	Low cutting speed, rapid tool wear

These multipliers reflect cutting speed and tool life differences for the same part geometry. They do not include raw material cost. For production volumes above a few hundred parts, the machining cost multiplier dominates per-piece cost more than material price.

6.Frequently Asked Questions

What is the strongest metal for CNC machined parts?

Among common CNC bar stock, Ti-6Al-4V annealed reaches 880 MPa yield and 4140 Q&T reaches 655 MPa at 25 mm section. Maraging steels exceed 1,700 MPa tensile but are rarely practical for general CNC work due to extreme tool wear. A part needing 300 MPa yield does not benefit from specifying 880 MPa titanium.

When should I use yield strength versus tensile strength for design?

Yield strength for any part that must hold shape under load: brackets, housings, shafts, fixtures. Tensile strength for parts where fracture is the failure mode: bolts under preload, safety-critical structures. For fatigue-loaded parts under cyclic stress, the relevant parameter is the fatigue endurance limit, which must be measured directly for non-ferrous metals.

Is 7075-T6 aluminum strong enough to replace steel?

7075-T6 at 503 MPa yield exceeds annealed 304 stainless (215 MPa) and as-rolled 1045 (310 MPa). For static loads below 120°C without severe corrosion, 7075-T6 can replace these steels at one-third the weight. It cannot replace 4140 Q&T (655 MPa) in high-load applications, and it cannot be welded by conventional methods.

Why does the table show HRBW for some metals and HRC for others?

Each Rockwell scale covers a different hardness range. HRBW (tungsten carbide ball, 100 kgf) applies to softer metals: aluminum, brass, annealed stainless. HRC (120° diamond cone, 150 kgf) applies to hardened steels and titanium. ASTM E18-25 defines the scale assignments. Testing soft aluminum on HRC gives meaningless results. Cross-scale comparison requires ASTM E140 conversion tables and is approximate.

Related Resources

Related Capability: CNC Machining for aluminum, steel, stainless, titanium, and brass from prototype through production.

Related Material Guide: Materials & Properties covers grade-level data and alloy selection beyond the eight metals in this chart. Related Standards Reference: Tolerances & Standards collects ISO 2768, ISO 286, GD&T, and surface finish references used alongside strength data on CNC drawings