4140 Alloy Steel Round Bar Suppliers
127 vetted U.S. suppliers · 30 states
4140 round bar is the workhorse alloy steel for shafting, axles, fasteners, and machinery components — through-hardenable and machinable in both annealed and heat-treated condition. Below is our live count of vetted U.S. suppliers with state distribution and a one-click RFQ flow.
Geographic distribution
Where these suppliers are
Top 8 states by vetted-supplier density. 40 more across 22 additional states — listed below the chart.
Also covered
North Carolina (5) · Connecticut (4) · Arizona (3) · Missouri (3) · Washington (2) · Minnesota (2) · New Hampshire (2) · Massachusetts (2) · Georgia (2) · New Jersey (2) · Iowa (2) · Virginia (1) · Alabama (1) · Wyoming (1) · Maryland (1) · Kansas (1) · New Mexico (1) · Wisconsin (1) · Utah (1) · Indiana (1) · Tennessee (1) · Oklahoma (1)
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What 4140 alloy steel round bar is
4140 is a chromium-molybdenum low-alloy steel — moderate carbon (~0.40%), through-hardenable, with excellent machinability in the annealed condition and high strength after heat treatment. Round bar is supplied annealed (HRB ~95), normalized, or quenched-and-tempered (Q&T) to a Brinell range. ASTM A322 and A29 cover hot-rolled bar; cold-finished, ground-and-polished (G&P), and turned-ground-and-polished (TG&P) are available for tighter tolerance and better surface. Common forms: round bar from 0.25" through 12" diameter, longer specialty up through 24".
What to look for in a supplier
Decide on the heat-treat condition you need: annealed (for buyers who'll heat-treat after machining), normalized (for higher strength as-shipped), or Q&T to a Brinell range (190-220, 220-260, 285-331 BHN are common). Surface and tolerance: hot-rolled is cheapest and roughest; cold-finished tightens tolerance; G&P/TG&P gives precision shafting surface ready for press-fit work. Ask about end-condition and length — most stockists supply 12-20 ft lengths and cut-to-length on demand. For pre-hardened bar, confirm the Brinell range was hardness-tested per heat lot.
FAQ
Common questions
What's the difference between 4140 and 4340?
Both are low-alloy chromium-molybdenum steels. 4340 adds nickel (~1.8%), giving higher strength, deeper hardenability, and better toughness — at significant cost premium. Use 4340 for large cross-sections where through-hardening is needed (landing gear, large shafts, aerospace structural). Use 4140 for everything else.
What's the difference between 4140 and 4140 PH (pre-hard)?
4140 PH (also called 4140 HT) is supplied pre-hardened to a specific Brinell range (typically 285-331 BHN), ready for machining without further heat treatment. Standard 4140 is supplied annealed (~190 BHN) and needs heat treatment after machining to reach final strength. Pre-hard saves a heat-treat step but is harder to machine.
What surface finish does 4140 round bar come in?
Hot-rolled is the rough mill-finish (scale, draft). Cold-finished cleans up the surface and tightens diameter tolerance. Ground-and-polished (G&P) gives a precision shaft surface. Turned-ground-and-polished (TG&P) is the highest finish for precision shafting work.
What sizes are stocked vs. mill-order?
Most stocking distributors carry round bar from 0.25" through 8" in increments of 1/16" up to 1", then 1/8" steps. Above 8" diameter, large cross-sections, or specialty lengths typically run mill-order with 4-8 week lead time.
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