6135
Chromium-Vanadium High-Toughness Tool Steel
Overview
6135 is a low-medium carbon chromium-vanadium forging steel used in Taiwan's hand tool industry, with carbon 0.32–0.38%, chromium 0.50–0.90%, and vanadium 0.10–0.15%. It is positioned as the sister grade to 6140 — sharing the same Cr-V design and ultra-low sulfur control, but with carbon shifted approximately 0.06% lower to gain higher toughness and impact absorption. When the design priority for a hand tool shifts from "hardness" to "fracture resistance," 6135 becomes the rational alternative to 6140: large wrench bodies, impact-resistant forged claws, and long-handle tool shafts under bending load are its typical applications.
Double Steel has specialized in bar steel for over 30 years. 6135 is a permanent stock item sourced from Fengxing, CSC, and Weizhi mills, with a mill certificate (MTC) provided for every shipment.
Chemical Composition (Mill Specification)
| Element | Spec Range (%) |
|---|---|
| C (Carbon) | 0.32 – 0.38 |
| Si (Silicon) | 0.15 – 0.35 |
| Mn (Manganese) | 0.50 – 0.90 |
| P (Phosphorus) | ≤ 0.035 |
| S (Sulfur) | ≤ 0.004 |
| Ni (Nickel) | ≤ 0.25 |
| Cr (Chromium) | 0.50 – 0.90 |
| V (Vanadium) | 0.10 – 0.15 |
| Cu (Copper) | ≤ 0.035 |
6135 is not a JIS G 4053 or SAE J404 standard grade — it is a mill specification for the hand tool industry. It shares the same Cr, V, and sulfur/phosphorus control ranges as 6140; the only difference is carbon content.
6135 vs 6140 Composition Comparison
Selection guide: when the design hardness target is HRC 40+ and hardness is the primary performance criterion, select 6140. When the part must withstand significant impact loading, fracture toughness is the primary concern, or the Q+T target hardness falls in the HRC 35–42 range, select 6135.
| Element | 6135 | 6140 | Significance |
|---|---|---|---|
| C (Carbon) | 0.32 – 0.38% | 0.38 – 0.43% | 6140 has a higher hardness ceiling; 6135 has greater toughness margin |
| Cr (Chromium) | 0.50 – 0.90% | 0.50 – 0.90% | Identical |
| V (Vanadium) | 0.10 – 0.15% | 0.10 – 0.15% | Identical |
| S (Sulfur) | ≤ 0.004% | ≤ 0.004% | Identical (hand tool forging grade) |
Mechanical Properties After Heat Treatment (Reference)
| Condition | Tensile (MPa) | Yield (MPa) | Elongation (%) | Hardness |
|---|---|---|---|---|
| Normalizing | ≈ 600–700 | ≈ 350–450 | ≥ 19 | ≈ HB 160–200 |
| Q+T (Tempered at 500–600°C) | ≈ 850–1000 | ≈ 700–850 | ≥ 14 | ≈ HRC 26–32 |
| Q+T (Tempered at 400–500°C) | ≈ 1000–1200 | ≈ 850–1050 | ≥ 12 | ≈ HRC 32–38 |
| Q+T (Tempered at 250–350°C) | ≈ 1200–1400 | ≈ 1050–1250 | ≥ 10 | ≈ HRC 38–44 |
Values above are reference figures. Finished hand tools typically target HRC 34–42 — lower than the equivalent 6140 range. This hardness range corresponds to higher elongation and impact values, suitable for parts under dynamic loading.
Forging & Heat Treatment Characteristics
Forging Temperature Window
Recommended hot forging temperature for 6135 is 1050–1200°C, with a finish-forging temperature no lower than 850°C — identical to 6140. The lower carbon content gives slightly greater process latitude at forging temperature, making it more forgiving on automated forging lines. Post-forge air-cool microstructure uniformity is also marginally better than 6140.
Q+T Path and Hardness Trade-off
Austenitizing temperature for 6135 is 840–870°C with oil quench; tempering temperature is adjusted to the target hardness. Compared to 6140, 6135 achieves approximately HRC 3–5 lower hardness at the same tempering temperature, but with significantly higher Charpy V-notch impact values. In practice, 6135 is used where finished hardness is HRC 34–42. If design requirements exceed HRC 44, select 6140 directly — forcing 6135 to higher hardness sacrifices its toughness advantage.
Shared Value of Vanadium and Low Sulfur
Vanadium microalloying inhibits grain coarsening and retards temper softening; S ≤0.004% minimizes MnS inclusions. Both mechanisms are equally effective in 6135 and 6140 — the only difference is the base hardness range determined by carbon content. For tools where the primary failure mode is fracture rather than wear (e.g., impact sockets, impact driver bits), 6135's toughness combination can be even more critical than 6140's.
Nitriding and Induction Hardening
Where a finished part requires localized high surface hardness, 6135's lower base hardness makes it an excellent candidate for nitriding (surface HV 550+) or induction hardening of specific working surfaces (ratchet teeth, engagement faces) to HRC 50+ while retaining a tough core. This "hard shell, tough core" design leverages 6135's low-carbon base material advantage.
Machining Notes
Machinability
6135 in the normalized condition has hardness approximately HB 160–200, giving better machinability than 6140 and S45C. It is well suited for hand tool parts requiring extensive machining — e.g., complex threaded bodies or keyway-containing tool shanks. Lower carbon content translates to better tool life and easier dimensional tolerance control during finish machining.
Advantage in Large Cross-Section Forgings
Lower carbon content makes 6135's core properties more stable in large cross-section forgings — as section size increases, hardenability limitations and core toughness degradation become more pronounced. 6135's low-carbon design advantage grows progressively in this regime. For hand tool forgings with cross-section diameters exceeding 50 mm (heavy wrenches, long-handle tools), 6135 is specified more frequently than 6140.
Surface Treatment Compatibility
Common surface treatments — chrome plating, nickel plating, black oxide, and shot blasting — are all compatible, identical to 6140. Due to its lower hardness, 6135 has lower hydrogen embrittlement susceptibility, making post-plating bake-out requirements less stringent and the plating line process more manageable.
International Standard Equivalents
| Standard | Equivalent Grade | Correspondence |
|---|---|---|
| Mill specification | 6135 | Reference standard |
| AISI/SAE (USA) | 6135 (J404) | Near equivalent (lower Cr minimum; narrower V range; stricter S control) |
| JIS (Japan) | SCr435 / SCM435 | Reference only (Cr-series; no vanadium) |
| DIN / EN (Germany/Europe) | 34Cr4 (1.7033) / 34CrMo4 (1.7220) | Reference only (Cr Q+T steel; no V microalloying) |
| GB (China) | 35CrV | Near equivalent (same Cr-V design concept; composition range varies) |
6135 has no single exact equivalent in any international standard system. Its design logic is "6140 with reduced carbon" — any Cr-V medium-carbon Q+T steel grade can serve as a near-reference, but none overlap exactly on composition range, sulfur/phosphorus cleanliness, or V content. The same verification checklist as 6140 applies: confirm Cr content, V content, and sulfur/phosphorus cleanliness level when specifying substitutes.
Typical Applications
Large-Section Hand Tool Forgings
Large adjustable wrenches, long-handle pipe wrenches, and large open-end wrenches — tools with larger cross-sections under higher bending loads. 6135's lower carbon gives better core toughness than 6140, reducing fracture risk under high-torque application.
Impact Tools
Impact wrench sockets, impact driver bits, and power tool torque transmission components — these tools experience repeated impact rather than steady torque. 6135's toughness characteristics deliver superior service life in this class of application compared to 6140.
Forged Claws and Connectors
Connecting pins, latches, shackles, and hooks for construction equipment — dynamic load forgings where 6135's Q+T hardness of HRC 34–40 combined with good toughness balances wear resistance and impact resistance.
Mechanical Components (Medium-Load Q+T Parts)
When SCM440 strength is excessive but S45C is insufficient, 6135 fills the gap — particularly for structural parts that must remain machinable after Q+T, or large cross-section applications where core toughness is a primary design constraint.
Supply Specifications
| Form | Size Range | Source |
|---|---|---|
| Hot-rolled round bar | Ø 13 – 100 mm | Fengxing, Weizhi |
| Hot-rolled round bar | Ø 13 – 42 mm | CSC |
| Hot-rolled coil (wire rod) | Ø 5.5 – 42 mm | Common for tool forging |
| Ground bar | Ø 6 – 100 mm | — |
Length 5–12 m; cut-to-length available on request. Large hand tool forgings and Q+T structural parts typically use straight bar; small tool heads are supplied as coil/wire rod. Every shipment includes a mill certificate (MTC) with full chemistry and heat number traceability.
Material Selection Guide
6135 is the toughness-first option in hand tool forging steel — it is complementary to, not a replacement for, 6140. When the primary failure mode is fracture rather than wear, or when section size is large and core toughness degradation becomes the bottleneck, 6135 provides a better answer than 6140.
6140
Finished hardness HRC 42+; wear resistance is the primary criterion
If the tool must reach HRC 42+ in finished hardness, 6135's carbon content cannot support it — select 6140 directly. 6140 is the primary material for hand tool forgings.
SCM440
General structural parts; not hand-tool-specific applications
SCM440 is more broadly specified for mechanical structural components — Mo enhances hardenability for larger sections. For non-tool applications with larger cross-sections, SCM440's wider available size range is an advantage.
S45C
Standard Q+T parts; cost-sensitive; no toughness requirement
S45C contains no Cr or V, making it less expensive but inferior to 6135 in fatigue and impact performance. Suitable for static-load general structural parts where toughness is not a design requirement.
For technical consultation, sample quotations, or mill certificate review, contact the Double Steel sales team via the inquiry form below or LINE customer service.