Overview: Cold-formed fasteners (bolts, screws, nuts, washers) are typically made from plain carbon or low-alloy steels that are formed at room temperature without quenching or tempering. These steels must balance ease of forming with sufficient strength. Common low-cost grades include mild/low-carbon steels, free-machining alloys, boron-alloyed grades, and microalloyed HSLA steels. Below is a detailed comparison of their chemistry, mechanical properties, regional usage, applications, and trade-offs.

Steel Categories and Chemistry

• Low-Carbon (Mild) Steels (e.g. AISI 1008, 1010, EN S235JR):
  Carbon ≈ 0.05–0.10%; Manganese ≈ 0.3–0.6%; minimal S/P. These steels have very low cost and excellent ductility. In global markets they are ubiquitous (used wherever extremely cheap fasteners are needed).
• Medium-Carbon / Low-Alloy Steels (e.g. AISI 1018–1022, ASTM 1541):
  Carbon ≈ 0.15–0.33%; Mn ≈ 0.6–1.5%; may include Si ~0.1–0.3% or small alloying (e.g. 1541 has ~0.33%C, 1.4% Mn). These steels offer higher strength than low-carbon grades while still being cold-formable. They are common worldwide for medium-strength bolts and studs.
• Free-Machining Steels (e.g. AISI 1215, 1219, 12L14, 1117):
  Carbon ≈ 0.09–0.15%; high Sulfur and/or Phosphorus (≈0.25–0.35%) and sometimes Lead (~0.15–0.35% in 12L14) or Copper (AISI 1117 has ~0.20–0.40% Cu instead). These alloys are engineered for superb machinability. They are used globally (more in North America and Asia); in Europe lead-bearing grades are restricted, so lead-free versions (with more S/P or Cu) are used.
• Boron-Enhanced Steels (e.g. SAE 10B21, 20MnB5):
  Carbon ≈ 0.18–0.23%; Manganese ≈ 0.6–1.0%; Boron ≈ 0.0005–0.003%. The tiny boron addition greatly increases hardenability and as-formed strength. These steels are very popular in Asia (China/Japan) and increasingly worldwide for higher-strength fasteners because they form well and reach high strength without heat treating.
• High-Strength Low-Alloy (HSLA) Steels:
  Very low Carbon (~0.08–0.12%) with micro-alloying (Nb, V, Ti etc) and possibly controlled Si/Mn. They achieve moderate to high strength (yield ~300–550 MPa) through fine-grain structure rather than heat treatment. HSLA grades (often seen as CR260LA, CR420LA, etc. in Europe) are used for structural or automotive fasteners where extra strength is needed but complex heat treatment is to be avoided.

Mechanical Properties

• Low-Carbon Steels: Tensile ≈ 280–350 MPa; Yield ≈ 150–250 MPa; Elongation ≥30%; Hardness ≈ 70–90 HB. Very ductile, easy to deform/cold-heading.
• Medium-Carbon / Low-Alloy: Tensile ≈ 400–550 MPa; Yield ≈ 250–370 MPa; Elongation ≈ 15–20%; Hardness ≈ 110–160 HB. Higher strength with reasonable ductility.
• Free-Machining (1215/12L14): Tensile ≈ 500–600 MPa; Yield ≈ 400–450 MPa; Elongation ≈ 8–12%; Hardness ≈ 160–170 HB. Very high strength in the as-formed state (due to chemistry and cold work) but low ductility.
• Boron Steels: Tensile ≈ 600–650 MPa; Yield ≈ 400–550 MPa; Elongation often >20% (some grades show ~30%); Hardness ≈ 150–180 HB. High strength and unusually good ductility for that strength, making them excellent for cold heading into long, strong fasteners.
• HSLA Steels: Tensile ≈ 550–700 MPa; Yield ≈ 300–550 MPa; Elongation ≈ 15–20%; Hardness ≈ 130–180 HB. Very high yield strength with decent ductility; used where extra strength is needed without quench-and-temper.

(These values are approximate ranges for typical processed bars/wires; actual values depend on exact alloy and processing. For example, cold-drawn 1018 yields ~370 MPa and 15% elongation, whereas annealed 1022 might yield only ~205 MPa with 25% elongation.)

Regional Availability

• Asia: All above steels are produced, often in very high volumes. Boron steels (10B21, 20MnB5) are especially common in China, Japan, and South Korea. Free-machining grades (including leaded 12L14) are widely used (though regulations on lead are tightening). Various domestic standards (e.g. Japanese JIS, Chinese GB) correspond roughly to these carbon steel categories.
• Europe: Low-carbon and medium-carbon steels (EN S235JR, S355JR, DC04 sheet) are common. Free-machining steels are used, but lead-bearing grades are rare (lead-free variants like AISI 1144HC or AISI 1117 are used instead). Boron steels are available but less common than in Asia; instead, microalloyed HSLA steels (e.g. 340–550 MPa yield cold-rolled steels) are more often used for higher strength. Structural steels (EN10025 S235/S275) can also be cold-formed into basic fasteners.
• North America: Similar to Europe and Asia for 1010–1022. ASTM A36/A108 (≈S235/S355) steel rods and ASTM A576 (1215) are common. Leaded free-machining steels (12L14) are still sold (especially for turned screws), although environmental rules are reducing their use. Boron steels (SAE 10B21, ASTM A370/A146) are available but not as widely used as in Asia. HSLA and microalloyed rods (e.g. ASTM 1016, 4140 condition C) are available for stronger parts.

Applications and Suitability

• Low-Carbon Steels: Used for light-duty fasteners like small bolts, screws, rivets, and washers. Ideal where forming ease and cost are critical (e.g. furniture bolts, simple structural bolts, nails, brackets). Not suitable for high-stress connections.
• Medium-Carbon / Low-Alloy: Common in automotive, machinery, and construction fasteners (e.g. bolts of moderate strength like ASTM Grade 5 or ISO 8.8 equivalents, which in fact are quenched steels, but a lot of 8.8-equivalent performance can be approached with cold-worked 1045 or 1541). Also used for rivets, pins, and higher-load screws.
• Free-Machining Steels: Generally used when fasteners need machining (threads turned on lathes) rather than fully cold-formed. Typical uses include turned screws, set screws, and small machined parts. Their high as-formed strength is useful, but their brittleness means they are not well-suited to heavy cold heading.
• Boron Steels: Widely used for automotive and heavy-duty fasteners requiring high strength. Common in transmission gears, chassis bolts, large nuts, and structural components where cold heading or rolling is used. The excellent ductility helps form complex shapes without cracking.
• HSLA Steels: Used for sheet- or bar-formed fasteners in automotive and structural applications (e.g. subframe bolts, high-load screws) where extra yield strength allows thinner sections. Also used in spring washer springs (if not stainless), though springs often use more carbon or alloy.

Cost Considerations

All listed grades are considered low-cost relative to heat-treat or alloyed stainless steels:

• Least Expensive: Plain low-carbon steels (1008–1010) are cheapest due to minimal alloying and widespread production.
• Low to Moderate Cost: Medium-carbon (1018–1022) and simple low-alloy steels (1541) have slightly higher alloy content but are still low-cost commodity steels. Free-machining grades cost a bit more due to added S/P (and Pb or Cu), as well as scrap used, but still inexpensive.
• Moderate Cost: Boron steels add a trace element and sometimes more processing control, so they are a bit pricier than plain carbon steel, but still relatively cheap (boron is added in small parts per million). HSLA steels are generally the most expensive of these categories due to additional alloying and controlled processing, but they save cost overall by eliminating heat-treat steps.

Cost Rankings (approx): Low-carbon < Medium-carbon ≈ Free-machining < Boron < HSLA.

Advantages and Limitations

• Low-Carbon Steels: Advantages: Easiest to form/cold-head; very ductile; cheapest. Limitations: Lowest strength, very soft/hardness; may require larger shank for a given load; poor wear resistance; rust easily without coating.
• Medium-Carbon / Low-Alloy: Advantages: Balanced strength and ductility; still fairly formable; inexpensive. Limitations: Lower ductility than mild steel; formability limit when heavy upsetting; moderate corrosion resistance only.
• Free-Machining Steels: Advantages: Excellent machinability for screw-cutting; relatively high as-formed strength; moderate cost. Limitations: Very low ductility/toughness; prone to fracturing under impact or bending; heavy sulfur/phosphorus can reduce corrosion resistance; lead content (in 12L14) is environmentally restricted in some regions.
• Boron Steels: Advantages: High strength with surprisingly good ductility; good cold formability if chemistry controlled; inexpensive way to boost performance without quenching. Limitations: Must tightly control boron and carbon equivalence in steelmaking; weldability can be an issue if carbon is high (welding preheat may be needed on thick sections); still moderate rust resistance, so usually plated/painted.
• HSLA Steels: Advantages: Very high yield/strength with good toughness; can allow lighter weight parts; better toughness than quench-hardened steels of similar strength. Limitations: Higher alloy cost; more complex metallurgy; if severely cold-formed, may need annealing to avoid cracking; limited availability in bar stock sizes compared to plates/sheets.

Summary Comparison Table

Steel Type / Example Grades	Composition (approx.)	Tensile (MPa)	Elongation	Hardness (HB)	Regions	Typical Uses	Cost	Advantages / Limitations
Low-Carbon Steel (e.g. AISI 1008/1010, EN S235)	C ~0.05–0.10%; Mn ~0.3–0.6%	~280–350	≥30%	~70–90	Global	Light bolts, screws, nails, washers	Very Low	Pros: Very ductile/formable; lowest cost. Cons: Very low strength; soft; rusts easily.
Medium-Carbon / Low-Alloy (AISI 1018–1022, ASTM 1541)	C ~0.15–0.33%; Mn ~0.6–1.5%; (Si ~0.1–0.3)	~400–550	~15–20%	~110–160	Global	Automotive bolts; medium-load fasteners	Low	Pros: Higher strength, reasonable ductility. Cons: Less formable; limited cold heading upsets.
Free-Machining (AISI 1215, 12L14, 1117/1144)	C ~0.09–0.15%; S/P ~0.25–0.35%; Pb (0.15–0.35)% or Cu (~0.2–0.4%)	~500–600	~8–12%	~160–170	NA, Asia (Europe uses Pb-free)	Machined screws, turned fasteners	Low–Moderate	Pros: Excellent machinability; high as-formed strength. Cons: Very low ductility; brittle; lead use restricted.
Boron Steel (SAE 10B21, 20MnB5)	C ~0.18–0.23%; Mn ~0.6–1.0%; B ~0.001–0.003%	~600–650	~20–30%	~150–180	Asia (and worldwide)	High-strength bolts, automotive parts	Low–Med	Pros: High strength with good ductility and formability. Cons: Requires precise chemistry control; welded joints may need care.
Low-Alloy (e.g. 1541) >(ASTM A745)	C ~0.33%; Mn ~1.4%; Si ~0.15%	~600	~10–15%	~150–170	NA, Europe	Heavy bolts, rivets, pins	Moderate	Pros: Good strength, toughness. Cons: Higher cost; lower formability.
HSLA (microalloyed) (e.g. CR340LA, CR420LA)	C ~0.08–0.12%; Nb, V trace; Mn/Si controlled	~550–700	~15–20%	~130–180	Europe, Asia, NA	High-strength structural fasteners	Higher	Pros: Very high yield strength; good toughness. Cons: More expensive; processing sensitive.

Note: The above values are indicative ranges for cold-formed or cold-drawn steel products. Actual properties depend on processing (rolling, drawing, annealing state) and manufacturer specifications. Cost categories are relative; all listed steels are generally low-cost compared to quenched/tempered alloys.

Overall, plain low-carbon steels offer the lowest cost and easiest formability for very low-strength fasteners. Medium-carbon and low-alloy steels strike a balance for moderate strength. Free-machining steels give high strength for machined parts but at the expense of toughness. Boron steels combine high strength with good formability, making them popular for demanding fasteners. Microalloyed HSLA steels enable even higher yields (up to ~500 MPa) without heat treatment, useful in automotive and structural applications, though at somewhat higher material cost. Each grade’s suitability depends on required strength, form complexity, and environmental or cost constraints.