Free-cutting steel

Core application scenarios:
Standard parts and fasteners—such as bolts, nuts, screws, studs, pipe fittings, spring seats, and the like—are the primary components machined on automatic lathes.
Automotive components: crankshafts, connecting rods, electric motors, steering tie rods, gear‑type brakes, rack-and-pinion assemblies, and various small parts. (Note: For high‑fatigue‑load components such as main bearings, use leaded free‑cutting steel with caution.)
Mechanical and equipment components: machine tool leadscrews, smooth shafts, shafts (motor shafts, fan shafts, sewing machine shafts), valves, bushings, pins, and hydraulic press parts.
Electronics and Precision Instruments: instrument and meter components, watch parts, electronic terminal pins, office equipment (printer/fax machine components), and fiber-optic connectors.
Common grades: SUM24L, SUM23, 11SMnPb30, 12L14, SAE1215, 1117, SCM440HL SCM435HL, SCM415HL
Steel mills: Japan’s Daido, Japan’s JFE, Taiwan’s China Steel, Guizhou Steel, Jinan Iron & Steel…

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Free-cutting steel

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Product Description

Product Overview

Free‑cutting steel refers to a specialized structural steel in which sulfur (S), lead (Pb), calcium (Ca), and other machinability‑enhancing elements are deliberately added to significantly improve chip breaking, chip evacuation, tool wear, and surface finish. Its key characteristics include rapid machining, high surface quality, dimensional stability, and low cost, making it the preferred material for mass production of shafts, fasteners, precision hardware, and instrument‑turned components.

 

Mainstream Grade Classification (Most Common Selection)

Sulfur-containing free-machining steel (cost-effective, general-purpose grade; highest shipment volume)    
National Standard: Y15 / Y12 / Y20 / Y30
Japanese labels: SUM21 / SUM22 / SUM23
Features: Excellent chip breaking, no tool entanglement, high cutting speeds, and a smooth surface finish; weldability is moderate.
Applications: Standard pins, bolts and nuts, sleeves, and custom‑turned small parts.

 

Lead–sulfur composite free-machining steel (high‑shine, high‑precision, fast‑cutting flagship)
Japanese standard: SUM24L (the most classic)
Features: Exceptional lubrication and friction reduction, extended tool life, mirror‑smooth surface finish, and excellent dimensional consistency.
Applications: precision instrument components, hydraulic fittings, small shafts, and high-volume production on automatic lathes.

 

 

Calcium-based environmentally friendly free-machining steel (lead-free, low-sulfur, high-end alternative)
Features: Lead-free and environmentally friendly, solderable, with few surface defects, suitable for cleanroom environments and export control.
Applications: Automotive safety components, precision electronic parts; priority material selection under the EU RoHS directive.

 

Quenched and tempered free-cutting alloy steel (high-strength shafts)   
Such as 4140 free-machining alloy steel, CrMo free-machining bar stock.
Features: High strength and excellent wear resistance, while also delivering cutting efficiency.
Applications: motor shafts, gear shafts, and transmission pins

 

Typical specification form

Forms: hot-rolled round bars, cold-drawn bright round bars, hexagonal bars, and square bars.
Diameter: φ3–φ150mm, standard; non-standard custom lengths
Tolerances: Cold-drawn, h9/h10, high precision; hot-rolled, standard tolerances.
Delivery: Fixed lengths of 2.5 m / 3 m / 6 m, or random lengths.


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