Steel Nitralloy 135 QT28-32
Hardness band · default condition
QT28-32 = q&T to 28–32 HRC
The stocked default: quenched and tempered above the nitriding temperature so the core is dimensionally stable during gas nitriding.
Values for the QT28-32 condition
Other Nitralloy 135 tempers and conditions
Nitralloy 135 is listed in 9 conditions; see the grade overview at Nitralloy 135.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Choose for deep machining, cold sawing or subsequent full heat treatment by the user. | 500 | 760 | 22 | 220 HB | — |
Hot rolled | Mill delivery condition for oversize stock that the user will anneal or Q&T themselves. | 580 | 900 | 16 | 27 HRC | 7.8 % IACS |
Normalized | Homogenised structure for forgings before final quench and temper; not a service condition for nitriding. | 620 | 930 | 18 | 28 HRC | 7.8 % IACS |
Cold drawn | Small-diameter bar with good size tolerance and straightness for screw-machine work prior to heat treatment. | 650 | 830 | 12 | 22 HRC | 7.8 % IACS |
Q&T to 24–28 HRC | Pick when core toughness and easier finish machining outrank core strength (large shafts, thick sections). | 690 | 860 | 19 | 26 HRC | — |
Q&T plus stress relief after rough machining | Specify for precision parts (spindles, extruder screws) to minimise distortion during the long nitriding cycle. | 800 | 950 | 17 | 30 HRC | 7.8 % IACS |
QT28-32DefaultThis page Q&T to 28–32 HRC | The stocked default: quenched and tempered above the nitriding temperature so the core is dimensionally stable during gas nitriding. | 815 | 965 | 17 | 31 HRC | — |
Q&T + gas nitrided | The functional end condition: extremely hard, wear- and scuff-resistant surface with high fatigue strength on a tough Q&T core. | 815 | 965 | 14 | 67 HRC | — |
Q&T to 32–36 HRC | Use when the nitrided case must be supported by a strong core (small gears, high-load screws, thin sections). | 950 | 1,100 | 15 | 34 HRC | — |
What is Nitralloy 135 QT28-32?
Nitralloy 135 QT28-32 is Nitralloy 135 heat treated to QT28-32 — the stocked default: quenched and tempered above the nitriding temperature so the core is dimensionally stable during gas nitriding. Nitralloy 135 QT28-32 has a yield strength of 815 MPa (118 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 87% of steel grades. Elongation at break is 17% and the elastic modulus is 210 GPa (30.5 Msi). Nitralloy 135 QT28-32 has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,425°C (2,597 °F).
Advantages
- High service temperature — 500°C (932 °F), better than 90% of steel grades
- High strength — 815 MPa (118 ksi), better than 87% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Difficult to weld — 15/100, worse than 91% of steel grades
- Limited formability — 15/100, worse than 87% of steel grades
- Difficult to machine — 35/100, worse than 84% of steel grades
- Poor heat conductor — 34 W/m·K (19.6 BTU/hr·ft·°F), worse than 77% of steel grades
Nitralloy 135 QT28-32 properties
Typical room-temperature values for Nitralloy 135 QT28-32; 12 are specific to this condition. Other listed values are Nitralloy 135 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
Nitralloy 135 QT28-32 has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
Nitralloy 135 QT28-32 has a yield strength of 815 MPa (118 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 87% of steel grades. Elongation at break is 17% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
Nitralloy 135 QT28-32 is rated for continuous service to 500°C (932 °F). It conducts heat at 34 W/m·K (19.6 BTU/hr·ft·°F), worse than 77% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
Nitralloy 135 QT28-32 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of Nitralloy 135 QT28-32 takes about 32 MJ of energy and emits 2.3 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 30%.
Manufacturability8
Nitralloy 135 QT28-32's machinability is fair (35/100, worse than 84% of steel grades); weldability poor (15/100); formability poor (15/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Nitralloy 135 QT28-32
Is Nitralloy 135 easy to machine?
Rough and finish machine in the Q&T (28–32 HRC) condition with carbide tooling and rigid setups; leave 0.03–0.08 mm for post-nitride grinding since the nitrided case can only be ground or lapped.
Can Nitralloy 135 be welded?
Effectively non-weldable in service parts — the ~1 % Al plus Cr-Mo content promotes cracking and destroys the nitriding response; if unavoidable, use high preheat, matching Cr-Mo filler and full re-heat-treatment.
Can Nitralloy 135 be formed, bent or molded?
Hot forge at 1050–1150 °C with slow cooling and immediate anneal; cold forming is impractical in any hardened condition.
What surface finishes work on Nitralloy 135?
Nitride at 500–530 °C after stress relief; strip the brittle white layer by lapping/polishing where fatigue matters, then oil, black-oxide or phosphate for rust protection (the steel itself has no corrosion resistance).
Nitralloy 135 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CNitralloy 135 Modified is narrower, 0.38–0.43 | 0.35 – 0.45 | 0.4 |
| Mn | 0.4 – 0.7 | 0.55 |
| Si | 0.2 – 0.4 | 0.3 |
| Cr | 1.4 – 1.8 | 1.6 |
| AlNitride former responsible for the very high case hardness | 0.85 – 1.3 | 1.05 |
| MoNitralloy 135 Modified (135M) raises Mo to 0.30–0.45 | 0.15 – 0.25 | 0.2 |
| Niresidual | ≤ 0.3 | — |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
Nitralloy 135 QT28-32 — frequently asked
What is Nitralloy 135 QT28-32 used for?
Nitralloy 135 QT28-32 is typically used for aircraft gears, precision shafts, cam followers and gauge components. In short: classic US Nitralloy grade; maximum gas-nitrided case hardness; aerospace precision nitriding steel.
What is the yield strength of Nitralloy 135 QT28-32?
Nitralloy 135 QT28-32 has a typical yield strength of 815 MPa (118 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 87% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is Nitralloy 135 QT28-32 easy to machine?
Not especially — machinability is rated fair (35/100, worse than 84% of steel grades). Rough and finish machine in the Q&T (28–32 HRC) condition with carbide tooling and rigid setups; leave 0.03–0.08 mm for post-nitride grinding since the nitrided case can only be ground or lapped.
Can Nitralloy 135 QT28-32 be welded?
Not readily — weldability is rated poor (15/100). Effectively non-weldable in service parts — the ~1 % Al plus Cr-Mo content promotes cracking and destroys the nitriding response; if unavoidable, use high preheat, matching Cr-Mo filler and full re-heat-treatment.
What surface finishes work on Nitralloy 135 QT28-32?
Nitride at 500–530 °C after stress relief; strip the brittle white layer by lapping/polishing where fatigue matters, then oil, black-oxide or phosphate for rust protection (the steel itself has no corrosion resistance).
Can Nitralloy 135 QT28-32 be formed, bent or molded?
Hot forge at 1050–1150 °C with slow cooling and immediate anneal; cold forming is impractical in any hardened condition.
What is the maximum service temperature of Nitralloy 135 QT28-32?
Nitralloy 135 QT28-32 is rated for continuous use to about 500°C (932 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Nitralloy 135 QT28-32 and Nitralloy 135-A?
QT28-32 is the default condition — the stocked default: quenched and tempered above the nitriding temperature so the core is dimensionally stable during gas nitriding. A: choose for deep machining, cold sawing or subsequent full heat treatment by the user. Yield strength is 815 MPa in QT28-32 versus 500 MPa in A.
Sources
- SAE J412 / SAE J404 — Nitriding steels (Nitralloy types) — SAE International (2018)
- EN 10085 — Nitriding steels (34CrAlMo5-10, 1.8507) — CEN (2001)
- GB/T 3077 (38CrMoAl) — SAC (2015)
- ASM Handbook Vol.4 — Heat Treating (Nitriding) — ASM International (1991)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- Nitriding steel bar datasheets (Böhler/voestalpine, Ovako, Baosteel 38CrMoAl) — various producers (2023)
- Mysteel / 1688 38CrMoAl (2026)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.