Steel 4145 · heat-treated state
Steel 4145 Q&T
Properties of the Q&T condition, compared with the other 4145 tempers.
Default oilfield/heavy-shaft condition: ~110 ksi minimum yield with usable toughness through thick sections.
What is 4145 Q&T?
4145 Q&T is 4145 heat treated to Q&T — default oilfield/heavy-shaft condition: ~110 ksi minimum yield with usable toughness through thick sections. 4145 Q&T has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 90% of steel grades. Elongation at break is 16% and the elastic modulus is 205 GPa (29.7 Msi). 4145 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 — 900 MPa (131 ksi), better than 90% of steel grades
Limitations
- Limited formability — 20/100, worse than 80% of steel grades
4145 Q&T properties
Typical room-temperature values for 4145 Q&T — 12 properties are specific to this condition; the rest are grade-level values shared by every 4145 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
4145 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).
Mechanical17
4145 Q&T has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 90% of steel grades. Elongation at break is 16% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4145 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).
Electrical2
4145 Q&T has an electrical resistivity of 2.2×10⁻⁷ Ω·m.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of 4145 Q&T takes about 29 MJ of energy and emits 2.3 kg of CO₂ — less than 53% of steel grades. Typical recycled content is 30%.
Manufacturability7
4145 Q&T's machinability is fair (45/100, worse than 65% of steel grades); weldability poor (30/100); formability poor (20/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 4145 tempers and conditions
4145 is also supplied in 11 other conditions. The full side-by-side table is on the 4145 overview.
- HRDefaultCheapest stock form for parts that will be heat treated after rough machining.520 MPa yield · 235 HB
- Q&T-36-40HRCPick for wear-critical, non-sour parts; toughness and machinability drop sharply and hydrogen-cracking risk rises.1,120 MPa yield · 38 HRC
- Q&T-32-36HRCPick when higher yield and wear resistance are needed and impact loading is moderate.1,000 MPa yield · 34 HRC
- Q&TDefault oilfield/heavy-shaft condition: ~110 ksi minimum yield with usable toughness through thick sections.900 MPa yield · 33 HRC
- Q&T-28-32HRCPick for shafts, mandrels and tool bodies needing a balance of strength, toughness and machinability.860 MPa yield · 30 HRC
- CDPick for small-diameter bar needing good straightness, size tolerance and a bright turned/drawn surface.700 MPa yield · 248 HB
- Q&T-22HRCPick for H2S / sour well components where sulphide stress cracking must be avoided.700 MPa yield · 21 HRC
- NormalizedPick for uniform fine-grain structure in forgings before machining or final Q&T.675 MPa yield · 32 HRC
- AnnealedPick when the part will be rough-machined or cold-worked before final heat treatment.435 MPa yield · 207 HB
Working with 4145 Q&T
Is 4145 easy to machine?
Machine best at 200–280 HB (annealed/N+T); at 30–37 HRC use rigid setups, carbide/coated inserts, ~80–120 m/min and heavy positive feeds to avoid work hardening.
Can 4145 be welded?
Poor weldability — preheat 300–350 °C, low-hydrogen consumables or matching 4145 filler, interpass control, and immediate 600–650 °C PWHT; avoid welding parts above 32 HRC in sour service.
Can 4145 be formed, bent or molded?
A hot-work grade: forge 1100–1200 °C, finish above 900 °C, then normalize or Q&T; cold forming is limited to mild straightening.
What surface finishes work on 4145?
No inherent corrosion resistance — use black oxide, phosphate + oil, zinc/nickel plating (bake at 190–220 °C to de-embrittle) or hard chrome; grinds and polishes well for seal surfaces.
4145 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 |
|---|---|---|
| C4145H band: 0.42–0.49 | 0.43 – 0.48 | 0.45 |
| Mn4145H band: 0.70–1.05 | 0.75 – 1 | 0.88 |
| Si | 0.15 – 0.35 | 0.25 |
| Cr4145H band: 0.75–1.20 | 0.8 – 1.1 | 0.95 |
| Mo4145H band: 0.13–0.28 | 0.15 – 0.25 | 0.2 |
| P | ≤ 0.04 | — |
| Smax; ≤0.015 typical for oilfield/HIC service | ≤ 0.04 | — |
| Fe | balance | — |
4145 Q&T — frequently asked
What is 4145 Q&T used for?
4145 Q&T is typically used for oilfield drill collars, downhole tool bodies and subs, heavy shafting, mandrels and stabilizers, forged couplings and flanges and wear-resistant machine spindles. In short: premium Cr-Mo forging bar.
What is the yield strength of 4145 Q&T?
4145 Q&T has a typical yield strength of 900 MPa (131 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 90% of steel grades. Strength varies by condition: see the 12 listed tempers.
Is 4145 Q&T easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machine best at 200–280 HB (annealed/N+T); at 30–37 HRC use rigid setups, carbide/coated inserts, ~80–120 m/min and heavy positive feeds to avoid work hardening.
Can 4145 Q&T be welded?
Not readily — weldability is rated poor (30/100). Poor weldability — preheat 300–350 °C, low-hydrogen consumables or matching 4145 filler, interpass control, and immediate 600–650 °C PWHT; avoid welding parts above 32 HRC in sour service.
What surface finishes work on 4145 Q&T?
No inherent corrosion resistance — use black oxide, phosphate + oil, zinc/nickel plating (bake at 190–220 °C to de-embrittle) or hard chrome; grinds and polishes well for seal surfaces.
Can 4145 Q&T be formed, bent or molded?
A hot-work grade: forge 1100–1200 °C, finish above 900 °C, then normalize or Q&T; cold forming is limited to mild straightening.
What is the maximum service temperature of 4145 Q&T?
4145 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 4145-HR and 4145-IH?
HR is the default condition — cheapest stock form for parts that will be heat treated after rough machining. IH: pick for journals, pins and wear surfaces needing a hard skin over a tough Q&T core. Yield strength is 520 MPa in HR versus 900 MPa in IH.
Can FabDigit make parts in 4145 Q&T?
Yes — 4145 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)
- SAE J1268 — Hardenability Bands for Alloy H-Steels (4145H) — SAE International (2019)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- API Spec 7-1 — Rotary Drill Stem Elements (drill collar 285–341 HB) — American Petroleum Institute (2016)
- GB/T 3077 — (45CrMo) — SAC / (2015)
- NACE MR0175 / ISO 15156-2 — Materials for H2S-containing environments — NACE/ISO (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating — ASM International (1991)
- Machinery's Handbook (machinability ratings) — Industrial Press (2020)
- 45CrMo — Mysteel / 1688 (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.