Steel 4135 · heat-treated state
Steel 4135 Q&T
Properties of the Q&T condition, compared with the other 4135 tempers.
Standard delivery condition for shafts, bolts and gears needing ~1000 MPa strength with good toughness.
What is 4135 Q&T?
4135 Q&T is 4135 heat treated to Q&T — standard delivery condition for shafts, bolts and gears needing ~1000 MPa strength with good toughness. 4135 Q&T has a yield strength of 850 MPa (123 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 88% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi). 4135 Q&T has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F). HR is the default condition FabDigit quotes; Q&T is available on request or by drawing note.
Advantages
- High strength — 850 MPa (123 ksi), better than 88% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
4135 Q&T properties
Typical room-temperature values for 4135 Q&T — 15 properties are specific to this condition; the rest are grade-level values shared by every 4135 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
4135 Q&T has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F).
Mechanical15
4135 Q&T has a yield strength of 850 MPa (123 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 88% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4135 Q&T is rated for continuous service to 400°C (752 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
4135 Q&T conducts electricity at 7.8 % IACS, worse than 58% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 4135 Q&T takes about 34 MJ of energy and emits 2.3 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 25%.
Manufacturability7
4135 Q&T's machinability is fair (47/100, worse than 58% of steel grades); weldability fair (35/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 4135 tempers and conditions
4135 is also supplied in 8 other conditions. The full side-by-side table is on the 4135 overview.
- HRDefaultDefault stock condition for bar and plate that will be machined and then heat treated by the user.460 MPa yield · 200 HB
- Q&T 34-38 HRCUse for highly loaded shafts, torsion parts and tool holders where ~1150 MPa is needed and toughness can be traded down.1,010 MPa yield · 36 HRC
- Q&TStandard delivery condition for shafts, bolts and gears needing ~1000 MPa strength with good toughness.850 MPa yield · 31 HRC
- Q&T 28-32 HRCSpecified where a controlled hardness band is required (NACE-limited hardware, high-strength fasteners).820 MPa yield · 30 HRC
- CDChoose for close-tolerance bright bar with raised yield strength and good surface, machined without further heat treatment.680 MPa yield · 230 HB
- NormalizedUniform fine-grain structure with higher strength than annealed; common for tube and forgings before machining.570 MPa yield · 24 HRC
- AnnealedPick for maximum machinability, cold forming or before further heat treatment.390 MPa yield · 175 HB
Working with 4135 Q&T
Is 4135 easy to machine?
Machines well at 180–230 HB with carbide at 120–200 m/min; above 34 HRC use coated carbide/CBN, rigid setups and reduced feed, and prefer rough-machining before final temper.
Can 4135 be welded?
Weldable with low-hydrogen E80xx/ER80S-D2 filler but requires 200–320 °C preheat, controlled interpass and post-weld temper/stress relief at 600–650 °C to avoid HAZ cracking.
Can 4135 be formed, bent or molded?
Cold form only in annealed condition with generous radii; hot forge at 1150–1200 °C finishing above 900 °C, then normalize or anneal before machining.
What surface finishes work on 4135?
Not anodizable — protect with zinc, zinc-nickel or hard chrome plating, phosphate/oil or black oxide; bake after plating to relieve hydrogen; gas nitriding gives a hard wear surface without distortion.
4135 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 |
|---|---|---|
| CSAE J404 / ASTM A29 | 0.33 – 0.38 | 0.35 |
| Mn | 0.7 – 0.9 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| Cr | 0.8 – 1.1 | 0.95 |
| Mo | 0.15 – 0.25 | 0.2 |
| P | ≤ 0.04 | — |
| Smax; 4135H/resulfurized variants differ | ≤ 0.04 | — |
| Fe | balance | — |
4135 Q&T — frequently asked
What is 4135 Q&T used for?
4135 Q&T is typically used for industrial drive and axle shafts, high-strength bolts and studs, gears and pinions, high-pressure cylinder and aerospace tube, hydraulic piston rods and tool holders and machine spindles. In short: workhorse Cr-Mo bar.
What is the yield strength of 4135 Q&T?
4135 Q&T has a typical yield strength of 850 MPa (123 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 88% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 4135 Q&T easy to machine?
Reasonably — machinability is rated fair (47/100, worse than 58% of steel grades). Machines well at 180–230 HB with carbide at 120–200 m/min; above 34 HRC use coated carbide/CBN, rigid setups and reduced feed, and prefer rough-machining before final temper.
Can 4135 Q&T be welded?
With care — weldability is rated fair (35/100). Weldable with low-hydrogen E80xx/ER80S-D2 filler but requires 200–320 °C preheat, controlled interpass and post-weld temper/stress relief at 600–650 °C to avoid HAZ cracking.
What surface finishes work on 4135 Q&T?
Not anodizable — protect with zinc, zinc-nickel or hard chrome plating, phosphate/oil or black oxide; bake after plating to relieve hydrogen; gas nitriding gives a hard wear surface without distortion.
Can 4135 Q&T be formed, bent or molded?
Cold form only in annealed condition with generous radii; hot forge at 1150–1200 °C finishing above 900 °C, then normalize or anneal before machining.
What is the maximum service temperature of 4135 Q&T?
4135 Q&T is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4135-HR and 4135-CD?
HR is the default condition — default stock condition for bar and plate that will be machined and then heat treated by the user. CD: choose for close-tolerance bright bar with raised yield strength and good surface, machined without further heat treatment. Yield strength is 460 MPa in HR versus 680 MPa in CD.
Can FabDigit make parts in 4135 Q&T?
Yes — 4135 Q&T is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- GB/T 3077 — (35CrMo) — SAC (2015)
- EN 10083-3 — Quenched and tempered steels (34CrMo4) — CEN (2006)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating — ASM International (1991)
- Machinery's Handbook, 31st ed. — Industrial Press (2020)
- 35CrMo — Mysteel (2025)
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.