# Heat Treatment and Temper Conditions for CNC Alloys

> Temper conditions for CNC alloys: steel quench-and-temper hardness by temperature, 6061-O to T651, 7075-T73 and 17-4PH H900 to H1150 with NACE limits.

https://www.sinbo-machining.com/wiki/reference/heat-treatment-conditions/

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## On This Page

- Carbon and alloy steel — heat-treatment processes and typical hardness
- What Hardness Should I Expect from Annealed Versus Normalized 1045 Steel?
- What Hardness Is 4140 Supplied at in the Pre-Hardened Condition?
- How Hard Is Steel Immediately After Quenching, Before Tempering?
- What Does Quenching and Tempering Mean and Why Is It Specified?
- How Much Stronger Is 6061-T6 Compared with 6061-O?
- Is 6061-T651 Stronger Than 6061-T6?
- What Is the T73 Temper and When Should I Choose It?
- What Is the Strongest Standard Aging Condition for 17-4PH?
- Which 17-4PH Condition Offers the Highest Toughness?
- Can 17-4PH Be Used in NACE Sour-Gas Service?
- How to Use These Numbers
- Frequently Asked Questions
- Standards & Sources
- Related Pages
- Download This Table

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# Heat Treatment and Temper Conditions for CNC Alloys

Temper conditions for CNC alloys: steel quench-and-temper hardness by temperature, 6061-O to T651, 7075-T73 and 17-4PH H900 to H1150 with NACE limits.

## Carbon and alloy steel — heat-treatment processes and typical hardness

| Process | What it does | Typical hardness | Typical application | Governing standard |
| --- | --- | --- | --- | --- |
| Annealing | Heat above or near the critical temperature, then cool very slowly in the furnace to soften and relieve stress | 160–217 HB (grade-dependent) | Machining stock, cold forming, stress relief before re-hardening | GB/T 16923; ASTM A29; SAE J412 |
| Normalizing | Heat 30–50 °C above Ac3/Acm, then cool in still air to refine grain and homogenize the structure | 187–300 HB (grade-dependent) | Large forgings, structural parts where quenching risks distortion | GB/T 16923; ASTM A29 |
| Quenching + tempering | Austenitize, quench to martensite in water or oil, then reheat below Ac1 to relieve stress and tune hardness | 24–57 HRC (depends on tempering temperature) | Finished engineering parts: shafts, gears, fasteners | GB/T 16924; ASTM A29 |
| Quench and high temper (Q&T) | Quench followed by high-temperature tempering at 500–650 °C, producing tempered sorbite with the best strength-toughness balance | 28–34 HRC (common supply band) | Connecting rods, bolts, gears, shafts under alternating load | GB/T 16924; GB/T 7232 |

> **How to read this table.** Typical values move with grade, section size and furnace practice; design to the governing specification and the mill test report. Quench and temper (Q&T) on drawings means quenching followed by high-temperature tempering at about 500–650 °C — a combined designation, not a separate process. Untempered as-quenched martensite is brittle and is not used in service.

## What Hardness Should I Expect from Annealed Versus Normalized 1045 Steel?

Annealed 1045 sits at about 160–200 HB (163 HB typical hot-rolled), while normalized 1045 reaches about 187 HB with 640 MPa tensile — normalization trades some machinability for a stronger, more uniform structure.

| Condition | Tensile (MPa) | Yield (MPa) | Elongation (%) | Hardness | Source |
| --- | --- | --- | --- | --- | --- |
| Hot-rolled / annealed | 565 (typical hot-rolled) | 310 | 16 | 163 HB; annealed band 160–200 HB | S21 / S22 / S5 |
| Normalized | 640 | 410 | 22 | 187 HB | S6 / S5 |
| Quenched and tempered | — | — | — | 220–290 HB | S5 |
| As-quenched (water, surface) | — | — | — | 55–60 HRC | S5 |
| Flame / induction hardened (surface) | — | — | — | 55–58 HRC, case depth 1.5–5 mm | S5 |

## What Hardness Is 4140 Supplied at in the Pre-Hardened Condition?

Pre-hardened 4140 arrives at 28–34 HRC; the standard heat treatment tempered at 540 °C lands at 28–32 HRC and 1,000–1,100 MPa tensile. Chromium and molybdenum give 4140 far better hardenability than 1045, so it keeps its tempered hardness in larger sections — verify big bars on the mill test report, because hardness falls with section size.

| Condition / tempering temperature | Tensile (MPa) | Yield (MPa) | Elongation (%) | Hardness | Source |
| --- | --- | --- | --- | --- | --- |
| Annealed | ~655 | ~415 | 25 | 197–217 HB | S4 |
| Normalized | ~1,020 | ~650 | 17 | 250–300 HB | S4 |
| As-quenched (oil) | — | — | — | 55–60 HRC | S4 |
| Q&T at 205 °C | ~2,000 | ~1,600 | 8 | 52–57 HRC | S4 |
| Q&T at 315 °C | ~1,700 | ~1,450 | 10 | 45–50 HRC | S4 |
| Q&T at 425 °C | ~1,400 | ~1,250 | 12 | 38–42 HRC | S4 |
| Q&T at 540 °C (standard HT) | 1,000–1,100 | 850–950 | 18 | 28–32 HRC | S4 |
| Q&T at 650 °C (high ductility) | ~850 | ~700 | 22 | 24–28 HRC | S4 |
| Pre-hardened as-supplied | — | — | — | 28–34 HRC | S4 |

## How Hard Is Steel Immediately After Quenching, Before Tempering?

Both 1045 (water quench) and 4140 (oil quench) reach about 55–60 HRC as-quenched — but that untempered martensite is too brittle for service, so every quenched part is tempered back to its working hardness before use.

| Steel | Quench medium | As-quenched (HRC) | Tempered service hardness | Note |
| --- | --- | --- | --- | --- |
| 1045 | Water | 55–60 | 220–290 HB (Q&T) | Shallow-hardening carbon steel; the core softens in large sections |
| 4140 | Oil | 55–60 | 28–32 HRC (tempered at 540 °C) | Cr-Mo alloy with deep hardening; pick it for bigger sections |

## What Does Quenching and Tempering Mean and Why Is It Specified?

Quenching and tempering means quench to martensite, then reheat below the critical temperature; quench and high temper (500–650 °C) produces tempered sorbite — typically 28–32 HRC — the best strength-toughness balance for shafts and gears. Tempering always trades hardness for toughness: the same 4140 that leaves the quench at 55–60 HRC spans 52–57 HRC down to 24–28 HRC as the tempering temperature rises from 205 °C to 650 °C.

| Steel | Q&T supply band | After quench only | Why temper |
| --- | --- | --- | --- |
| 1045 | 220–290 HB | 55–60 HRC (water) | Untempered martensite cracks in service; tempering buys toughness back at a controlled hardness cost |
| 4140 | 28–34 HRC pre-hard | 55–60 HRC (oil) | High tempering at 500–650 °C forms tempered sorbite — the condition shafts and gears are specified in |

## How Much Stronger Is 6061-T6 Compared with 6061-O?

6061-T6 reaches 310 MPa (45 ksi) tensile against 125 MPa (18 ksi) for 6061-O — about 2.5× — with yield 276 vs 55 MPa and hardness 95 vs 30 HB; heat treatment, not alloying, produces the whole difference. Standard minimums sit beside the typicals: 6061-T6 sheet and plate must reach 290 MPa (42 ksi) tensile and 240 MPa (35 ksi) yield, while 310/276 MPa are typical values.

| Alloy and temper | Tensile, MPa (ksi) | Yield, MPa (ksi) | Elongation (%) | Hardness (HB) | Source |
| --- | --- | --- | --- | --- | --- |
| 6061-O | 125 (18) | 55 (8) | 25–27 | 30 | S7 / S8 |
| 6061-T4 / T451 | 240 (35) | 145 (21) | 22 | 65 | S7 / S8 |
| 6061-T6 / T651 | 310 (45) | 276 (40) | 12–15 | 95 | S7 / S8 |

## Is 6061-T651 Stronger Than 6061-T6?

No — both are 310 MPa (45 ksi) tensile and 276 MPa yield. T651 adds 1–3% permanent stretching after quenching to relieve quench stress, so it holds tighter dimensions during machining; that is why plate and panel work starts from T651 stock.

| Temper | Process | Mechanical difference | Governing standard | Source |
| --- | --- | --- | --- | --- |
| O | Fully annealed — heated and slowly cooled to the softest state | Lowest strength, highest formability | ISO 2107; ASTM B209/B221 | S14 / S19 / S7 |
| T4 | Solution heat-treated, then naturally aged at room temperature | Moderate strength, still formable | ISO 2107; ASTM B209/B221 | S14 / S15 / S7 |
| T6 | Solution heat-treated, then artificially aged to peak strength | Highest strength for the alloy | ISO 2107; ASTM B209/B221 | S14 / S15 / S7 |
| T651 | T6 plus 1–3% stretching for stress relief before aging | Strength equal to T6; better dimensional stability in machining | ISO 2107; ASTM B209/B221 | S14 / S7 / S24 |
| T73 | Solution heat-treated, then overaged in a two-step aging treatment | Lower strength than T6; much better stress-corrosion resistance; mainly 7xxx series | AMS 4078; ASTM B209; GB/T 3880 | S9 / S2 |

## What Is the T73 Temper and When Should I Choose It?

T73 is an overaged two-step temper chosen for stress-corrosion resistance in aerospace parts. 7075-T73 strength comes in two published bases kept as separate rows — the ASM Handbook typical 505 MPa and the ASTM B209 plate specification 460–475 MPa — and the two are never averaged. 6061 is not supplied in T73, which is why 7075 carries the numbers.

| Applicable basis | Tensile (MPa) | Yield (MPa) | Elongation (%) | Hardness | Source |
| --- | --- | --- | --- | --- | --- |
| 7075-T73 — ASM Handbook typical (bar / forging reference) | 505 | 435 | 13 | — | S1 / S2 |
| 7075-T73 — ASTM B209 / AMS 4078 plate, by thickness (spec) | 460–475 | 385–390 | 5–8 | 126–140 HB | S9 |
| 7075-T6 — typical, for comparison | 572 (83 ksi) | 503 (73 ksi) | — | — | S7 |

## What Is the Strongest Standard Aging Condition for 17-4PH?

H900, aged at 482 °C (900 °F) for 1 hour, gives a minimum 1,310 MPa (190 ksi) tensile, 1,170 MPa (170 ksi) yield and at least 40 HRC — the highest-strength, lowest-toughness end of the three standard conditions. All values are bar specification minimums per ASTM A564 / AMS 5643.

| Condition | Aging temperature / time | Tensile min, MPa (ksi) | Yield min, MPa (ksi) | Elongation min (%) | Hardness | Charpy V-notch (ft-lb) | Source |
| --- | --- | --- | --- | --- | --- | --- | --- |
| H900 | 482 °C (900 °F) / 1 h | 1,310 (190) | 1,170 (170) | 10 | ≥40 HRC (typical 44) | 10–15 (low) | S3 / S23 |
| H1025 | 552 °C (1,025 °F) / 4 h | 1,070 (155) | 1,000 (145) | 12 | ≥35 HRC (typical 38) | 35–45 (moderate) | S3 / S23 |
| H1150 | 621 °C (1,150 °F) / 4 h | 930 (135) | 725 (105) | 16 | 28–33 HRC (typical 33) | 60–80 (high) | S3 / S23 |

## Which 17-4PH Condition Offers the Highest Toughness?

H1150, aged at 621 °C, keeps 930 MPa (135 ksi) minimum tensile with 16% elongation and 28–33 HRC — the highest Charpy toughness of the three. From H900 to H1150, tensile falls about 30% and yield about 38% while elongation rises from 10% to 16%: the higher aging temperature coarsens the copper-rich precipitates and trades strength for toughness. Charpy values are longitudinal representative bands and move with product form and orientation.

| Condition | Charpy V-notch (ft-lb) | Elongation (%) | Hardness | Best for |
| --- | --- | --- | --- | --- |
| H900 | 10–15 (low) | 10 | ≥40 HRC | Highest-strength parts with no impact or cryogenic exposure |
| H1025 | 35–45 (moderate) | 12 | ≥35 HRC | The general-purpose balance condition |
| H1150 | 60–80 (high) | 16 | 28–33 HRC | Impact- and cryogenic-facing parts; also the NACE-compliant choice |

## Can 17-4PH Be Used in NACE Sour-Gas Service?

Only H1150 — or H1025 with per-heat verification that actual hardness stays at or below 33 HRC — qualifies under NACE MR0175 / ISO 15156-3; H900 at a 40 HRC minimum does not qualify. The rule is hardness-driven: sour service caps hardness at 33 HRC.

| Condition | Spec hardness | NACE MR0175 status | Note |
| --- | --- | --- | --- |
| H900 | ≥40 HRC (typical 44) | Not qualified | Exceeds the 33 HRC sour-service cap by a wide margin |
| H1025 | ≥35 HRC (typical 38) | Conditional | Only with per-heat verification that actual hardness stays at or below 33 HRC |
| H1150 | 28–33 HRC (typical 33) | Compliant | The standard pick for sour service |

## How to Use These Numbers

- Values marked min are specification minimums from the governing standard (ASTM / AMS); unmarked values are typical and move with product form, section size and furnace practice — design to the governing specification and the mill test report.
- Steel hardness falls with section size (the mass effect): 4140 pre-hard 28–34 HRC applies to the supplied bar size, so verify large sections on the mill test report rather than assuming the catalogue value.
- Representative heat-treatment parameters: 6061 solution treatment 530 °C water quench, T6 artificial aging 160 °C for about 18 h or 177 °C for about 8 h, annealing to O at 413 °C; 7075-T73 two-step aging 110 °C for 8 h plus 175 °C for 8 h, after solution treatment at 475 °C for 90 min and 3 days natural aging.
- 17-4PH conditions are one solution-treated parent (Condition A after cooling from about 1040 °C) aged at different temperatures — the H number is the aging temperature in °F. Bar uses ASTM A564/A564M, plate and sheet ASTM A693, aerospace parts AMS 5643/5604; the Chinese counterpart 05Cr17Ni4Cu4Nb sits in GB/T 1220.
- Quenched-but-untempered martensite (55–60 HRC in both anchor steels) is a machining and grinding hazard, not a delivery condition — order steel in the annealed, normalized or quenched-and-tempered state and let the heat treater do the rest.

## Frequently Asked Questions

### What hardness should I expect from annealed versus normalized 1045 steel?

Annealed 1045 is about 160–200 HB (163 HB typical), while normalized 1045 reaches about 187 HB with 640 MPa tensile.

### What hardness is 4140 supplied in the pre-hardened, quenched-and-tempered state?

Pre-hardened 4140 is typically 28–34 HRC; standard HT tempered at 540 °C lands at 28–32 HRC and 1,000–1,100 MPa tensile.

### How hard is steel immediately after quenching, before tempering?

Both 1045 (water quench) and 4140 (oil quench) reach about 55–60 HRC as-quenched, but untempered martensite is too brittle for service.

### What does quenching and tempering mean and why is it specified?

Quench plus high-temperature tempering at 500–650 °C to form tempered sorbite, typically 28–32 HRC — the best strength-toughness balance for shafts and gears.

### How much stronger is 6061-T6 compared with 6061-O?

6061-T6 reaches 310 MPa (45 ksi) tensile versus 125 MPa (18 ksi) for 6061-O — about 2.5× the strength.

### Is 6061-T651 stronger than 6061-T6?

No — both are 310 MPa (45 ksi) tensile and 276 MPa yield; T651 adds 1–3% stretching for stress relief, so it holds tighter dimensions in machining.

### What is the T73 temper and when should I choose it?

An overaged two-step temper: 7075-T73 gives 505 MPa tensile per ASM Handbook (460–475 MPa for plate per ASTM B209), chosen for stress-corrosion resistance.

### What is the strongest standard aging condition for 17-4PH?

H900, aged at 482 °C for 1 hour: minimum 1,310 MPa (190 ksi) tensile and at least 40 HRC — with the lowest toughness of the three.

### Which 17-4PH condition offers the highest toughness for impact or cryogenic parts?

H1150, aged at 621 °C: 930 MPa (135 ksi) tensile with 16% elongation and 28–33 HRC, the highest Charpy toughness of the three.

### Can 17-4PH be used in NACE sour-gas service?

Only H1150, or heat-verified H1025 at maximum 33 HRC, qualifies under NACE MR0175; H900 at a 40 HRC minimum does not qualify.

## Standards & Sources

- S1 — ASM Metals Handbook, Vol. 2 (Properties and Selection: Nonferrous Alloys), 10th edition: 7075-T73 typical values
- S2 — Peer-reviewed study of AA7075 forgings (PMC): T73 aging sequence and the ASM benchmark values
- S3 — JN Alloys, 17-4PH heat treatment: H900 / H1025 / H1150 condition data (cross-checked against ASTM A564 minimums)
- S4 — Nifty Alloys, 4140 steel heat treatment: tempering chart by temperature
- S5 — steelstandart grade data for 1045: annealed, Q&T and as-quenched hardness
- S6 — Published mill sheet, 1045 medium-tensile carbon steel bar, normalized properties
- S7 — Tech Steel, 6061 (UNS A96061) properties: temper-by-temper typicals and the 7075-T6 comparison
- S8 — Weltstahl, Aluminum 6061 data sheet: mechanical-property typicals
- S9 — 7075-T73 / T7351 sheet and plate data: mechanical properties by thickness (ASTM B209 basis)
- S14 — ISO 2107, aluminum temper designations (GB/T 16475 is the Chinese counterpart); S15 — AZoM aluminum classifications; S19 — GB/T 16475; S24 — aluminum temper guide (T651 stretching practice)
- S21 / S22 — 1045 annealed-condition data (The World Material; SAE 1045 mill data); S23 — Alloy 17-4PH quick-facts sheet: hardness and Charpy bands
- Governing standards carry the load-bearing minimums: ASTM A564/A564M, ASTM A693, ASTM B209/B221, AMS 4078/5643/5604, ISO 2107, SAE J412, GB/T 16923, GB/T 16924, GB/T 7232, GB/T 1220, NACE MR0175 / ISO 15156-3
- MatWeb was excluded (robots.txt blocks automated access); distributor data sheets carry only typical-value columns, while spec minimums cite the ASTM / AMS / GB originals

## Related Pages

- [/wiki/reference/hardness-conversion/](/wiki/reference/hardness-conversion/) — Sibling quick table: convert between HB, HRC and HV hardness scales
- [/wiki/reference/cutting-parameters/](/wiki/reference/cutting-parameters/) — Sibling quick table: cutting speeds and feeds to run once the heat-treatment condition is fixed
- [/wiki/reference/material-density/](/wiki/reference/material-density/) — Sibling quick table: density for weight and material cost estimates

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