Steel 4145
AISI/SAE 4145 · UNS G41450 · JIS SCM445 · GB 45CrMo
4145 (G41450, SCM445) is a chromium-molybdenum alloy steel with about 0.45 % carbon — higher than 4140 — so it hardens deeper and holds higher strength in heavy sections.
Values for the HR condition
4145 tempers and conditions
4145 is supplied in 12 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
Compare all 12 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
full anneal, soft machining condition | Pick when the part will be rough-machined or cold-worked before final heat treatment. | 435 | 725 | 22 | 207 HB | — |
HRDefault Hot rolled | Cheapest stock form for parts that will be heat treated after rough machining. | 520 | 830 | 18 | 22 HRC | 7.8 % IACS |
Normalized and tempered | Pick for large forgings/heavy sections where oil quenching risks cracking but moderate strength is needed. | 620 | 900 | 18 | 26 HRC | 7.8 % IACS |
austenitized ~870 °C, air cooled | Pick for uniform fine-grain structure in forgings before machining or final Q&T. | 675 | 1,030 | 16 | 32 HRC | — |
Cold rolled | Rarely stocked; use for thin flat product needing tight thickness and a smooth surface before hardening. | 700 | 850 | 10 | 24 HRC | 7.8 % IACS |
Cold drawn | Pick for small-diameter bar needing good straightness, size tolerance and a bright turned/drawn surface. | 700 | 830 | 12 | 23 HRC | 7.8 % IACS |
high-temper sour-service condition (NACE MR0175) | Pick for H2S / sour well components where sulphide stress cracking must be avoided. | 700 | 830 | 20 | 21 HRC | — |
general machinery / shaft condition | Pick for shafts, mandrels and tool bodies needing a balance of strength, toughness and machinability. | 860 | 1,000 | 17 | 30 HRC | 7.8 % IACS |
Quenched and tempered | Default oilfield/heavy-shaft condition: ~110 ksi minimum yield with usable toughness through thick sections. | 900 | 1,080 | 16 | 33 HRC | — |
Induction hardened | Pick for journals, pins and wear surfaces needing a hard skin over a tough Q&T core. | 900 | 1,080 | 14 | 55 HRC | 7.5 % IACS |
high-strength Q&T condition | Pick when higher yield and wear resistance are needed and impact loading is moderate. | 1,000 | 1,140 | 15 | 34 HRC | 7.8 % IACS |
maximum practical bulk hardness | Pick for wear-critical, non-sour parts; toughness and machinability drop sharply and hydrogen-cracking risk rises. | 1,120 | 1,250 | 13 | 38 HRC | — |
What is 4145?
4145 (G41450, SCM445) is a chromium-molybdenum alloy steel with about 0.45 % carbon — higher than 4140 — so it hardens deeper and holds higher strength in heavy sections. It is supplied as hot-rolled, cold-drawn, annealed, normalized, induction-hardened and quenched-and-tempered bar in fixed hardness bands from 22 HRC up to 36–40 HRC for drill collars, subs and heavy shafting. The extra carbon costs weldability and cold formability: preheat and PWHT are mandatory, cold work is limited to straightening, and there is no inherent corrosion resistance. Use 4140 where welding or forming is required. 4145 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). 4145 has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 67% of steel grades. Elongation at break is 18% and the elastic modulus is 205 GPa (29.7 Msi).
What is 4145 used for?
- Oilfield drill collars
- Downhole tool bodies and subs
- Heavy shafting
- Mandrels and stabilizers
- Forged couplings and flanges
- Wear-resistant machine spindles
4145 properties
Typical room-temperature values for 4145-HR; bars are the position among steel grades.
Physical3
4145 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 has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 67% of steel grades. Elongation at break is 18% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4145 is rated for continuous service to 400°C (752 °F). It conducts heat at 43 W/m·K (24.8 BTU/hr·ft·°F), better than 51% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
4145 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of 4145 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's machinability is fair (50/100, worse than 53% of steel grades); weldability fair (35/100); formability poor (25/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 4145 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 4145
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.
Manufacturability
The process limits FabDigit applies to 4145. Every 4145 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better50 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair25 / 100 |
|---|---|
| Weldability | Better35 / 100 |
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 4145 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G41450
- GB (China)
- 45CrMo
- JIS
- SCM445
How much does 4145 cost?
4145 is a standard-cost steel ($$), cheaper than about 61% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
4145 — frequently asked
What is 4145 used for?
4145 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?
4145 has a typical yield strength of 520 MPa (75.4 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 67% of steel grades. Strength varies by condition: see the 12 listed tempers.
Is 4145 easy to machine?
Reasonably — machinability is rated fair (50/100, worse than 53% 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 be welded?
With care — weldability is rated fair (35/100). 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?
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 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?
4145 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.
How much does 4145 cost?
4145 is a standard-cost steel ($$), cheaper than about 61% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in 4145?
Yes — 4145 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. 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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.