Stainless Steel 7Cr17MoV QT55-57
Hardness band · default condition
GB 7Cr17MoV
QT55-57 = q&T 55–57 HRC
Default finished-blade condition for Chinese folders and outdoor knives: best balance of edge holding and chip resistance.
Values for the QT55-57 condition
Other 7Cr17MoV tempers and conditions
7Cr17MoV is listed in 7 conditions; see the grade overview at 7Cr17MoV.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Mill-supply condition for blanking, stamping and machining before hardening. | 420 | 740 | 20 | 210 HB | — |
Cold Rolled + Annealed strip | The standard 0.8–4 mm knife-blank strip form sold by Chinese mills. | 420 | 730 | 20 | 17 HRC | 3.1 % IACS |
Hot Rolled + Annealed | Thicker plate/bar stock for large blades and tooling, softened for sawing and milling. | 430 | 760 | 18 | 20 HRC | 3.1 % IACS |
Q&T 50–52 HRC | Tougher setting for large choppers, machetes and tools where chipping matters more than edge life. | 1,500 | 1,700 | 7 | 51 HRC | — |
Q&T 53–55 HRC | Common kitchen-knife hardness: easy to re-sharpen, good toughness, moderate edge retention. | 1,620 | 1,850 | 5 | 54 HRC | — |
QT55-57DefaultThis page Q&T 55–57 HRC | Default finished-blade condition for Chinese folders and outdoor knives: best balance of edge holding and chip resistance. | 1,700 | 1,950 | 4 | 56 HRC | — |
Q&T + Cryo 57–59 HRC | Sub-zero treated maximum-hardness setting for razor-type edges; noticeably more brittle and prone to edge chipping. | 1,780 | 2,050 | 2.5 | 58 HRC | — |
What is 7Cr17MoV QT55-57?
7Cr17MoV QT55-57 is 7Cr17MoV heat treated to QT55-57 — default finished-blade condition for Chinese folders and outdoor knives: best balance of edge holding and chip resistance. 7Cr17MoV QT55-57 has a yield strength of 1,700 MPa (247 ksi) and a tensile strength of 1,950 MPa (283 ksi) — stronger than 100% of stainless steel grades. Elongation at break is 4% and the elastic modulus is 200 GPa (29 Msi). 7Cr17MoV QT55-57 has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 65% of stainless steel grades. It melts at 1,370°C (2,498 °F).
Advantages
- High strength — 1,700 MPa (247 ksi), better than 100% of stainless steel grades
- Polishes to a fine finish — 82/100, better than 95% of stainless steel grades
- Low embodied carbon — 3.2 kg CO₂/kg, better than 95% of stainless steel grades
- High electrical conductivity — 2.9 % IACS, better than 87% of stainless steel grades
- Conducts heat well — 24 W/m·K (13.9 BTU/hr·ft·°F), better than 81% of stainless steel grades
Limitations
- Limited ductility — 4%, worse than 100% of stainless steel grades
- Low fracture toughness — 22 MPa·√m (20 ksi·√in), worse than 100% of stainless steel grades
- Difficult to machine — 8/100, worse than 100% of stainless steel grades
- Limited formability — 5/100, worse than 99% of stainless steel grades
- Difficult to weld — 15/100, worse than 98% of stainless steel grades
7Cr17MoV QT55-57 properties
Typical room-temperature values for 7Cr17MoV QT55-57; 13 are specific to this condition. Other listed values are 7Cr17MoV reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
7Cr17MoV QT55-57 has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 65% of stainless steel grades. It melts at 1,370°C (2,498 °F).
Mechanical15
7Cr17MoV QT55-57 has a yield strength of 1,700 MPa (247 ksi) and a tensile strength of 1,950 MPa (283 ksi) — stronger than 100% of stainless steel grades. Elongation at break is 4% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
7Cr17MoV QT55-57 is rated for continuous service to 400°C (752 °F). It conducts heat at 24 W/m·K (13.9 BTU/hr·ft·°F), better than 81% of stainless steel grades. Thermal expansion is 10.2 µm/m·K (5.67 µin/in·°F).
Electrical3
7Cr17MoV QT55-57 conducts electricity at 2.9 % IACS, better than 87% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (55/100), worse than 71% of stainless steel grades.
Sustainability4
Producing a kilogram of 7Cr17MoV QT55-57 takes about 48 MJ of energy and emits 3.2 kg of CO₂ — less than 85% of stainless steel grades. Typical recycled content is 45%.
Manufacturability7
7Cr17MoV QT55-57's machinability is not recommended (8/100, worse than 100% of stainless steel grades); weldability poor (15/100); formability not recommended (5/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 7Cr17MoV QT55-57
Is 7Cr17MoV easy to machine?
Machine, drill and blank only in the annealed state with sharp carbide tooling and rigid setups; after hardening it is grind/EDM/laser only, and grinding must be wet to avoid burning the edge.
Can 7Cr17MoV be welded?
Essentially not a welding grade — high carbon martensite cracks; if a tang must be joined, preheat 250–300 °C, use austenitic 309/310 filler and temper immediately after.
Can 7Cr17MoV be formed, bent or molded?
Blank, punch and profile in the annealed condition (bend radii ≥2t); harden at 1030–1070 °C, quench in oil or forced gas, optional −70 °C cryo, then temper 150–200 °C (avoid 400–550 °C temper embrittlement/corrosion loss).
What surface finishes work on 7Cr17MoV?
Takes a fine satin or mirror polish; passivate in nitric or citric acid after grinding, and PVD/black-oxide or stonewash finishes are common on knife blades — do not anodize.
7Cr17MoV 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 |
|---|---|---|
| Chigh carbon for martensite hardness + Cr carbides | 0.6 – 0.75 | 0.7 |
| Si | ≤ 1 | 0.4 |
| Mn | ≤ 1 | 0.5 |
| Pimpurity limit | ≤ 0.04 | — |
| Simpurity limit | ≤ 0.03 | — |
| Crprovides stainless passivity | 16 – 18 | 17 |
| Mopitting resistance and temper strength | 0.3 – 0.75 | 0.5 |
| Vgrain refinement, fine carbides for edge retention | 0.07 – 0.3 | 0.15 |
| Niresidual | ≤ 0.6 | — |
| Fe | balance | — |
7Cr17MoV QT55-57 — frequently asked
What is 7Cr17MoV QT55-57 used for?
7Cr17MoV QT55-57 is typically used for pocket knives, kitchen cutlery and outdoor blades. In short: 440A-class blade steel; better edge holding than 7Cr17; grind-only after hardening.
What is the yield strength of 7Cr17MoV QT55-57?
7Cr17MoV QT55-57 has a typical yield strength of 1,700 MPa (247 ksi) and a tensile strength of 1,950 MPa (283 ksi) — stronger than 100% of stainless steel grades. Strength varies by condition: see the 7 listed tempers.
Is 7Cr17MoV QT55-57 easy to machine?
Not especially — machinability is rated not recommended (8/100, worse than 100% of stainless steel grades). Machine, drill and blank only in the annealed state with sharp carbide tooling and rigid setups; after hardening it is grind/EDM/laser only, and grinding must be wet to avoid burning the edge.
Can 7Cr17MoV QT55-57 be welded?
Not readily — weldability is rated poor (15/100). Essentially not a welding grade — high carbon martensite cracks; if a tang must be joined, preheat 250–300 °C, use austenitic 309/310 filler and temper immediately after.
What surface finishes work on 7Cr17MoV QT55-57?
Takes a fine satin or mirror polish; passivate in nitric or citric acid after grinding, and PVD/black-oxide or stonewash finishes are common on knife blades — do not anodize.
Can 7Cr17MoV QT55-57 be formed, bent or molded?
Blank, punch and profile in the annealed condition (bend radii ≥2t); harden at 1030–1070 °C, quench in oil or forced gas, optional −70 °C cryo, then temper 150–200 °C (avoid 400–550 °C temper embrittlement/corrosion loss).
What is the maximum service temperature of 7Cr17MoV QT55-57?
7Cr17MoV QT55-57 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 7Cr17MoV QT55-57 and 7Cr17MoV-A?
QT55-57 is the default condition — default finished-blade condition for Chinese folders and outdoor knives: best balance of edge holding and chip resistance. A: mill-supply condition for blanking, stamping and machining before hardening. Yield strength is 1,700 MPa in QT55-57 versus 420 MPa in A.
Sources
- GB/T 1220 (martensitic 7Cr17 family) (2007)
- ASTM A276/A276M — Stainless Steel Bars and Shapes (Type 440A) — ASTM International (2017)
- ASM Specialty Handbook: Stainless Steels — ASM International (1994)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating (martensitic stainless steels) — ASM International (1991)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.