6Cr4W3Mo2VNb steel, namely 65Nb steel, is a common matrix steel, which is jointly developed by Huazhong Institute of Technology [SCALE STEEL]and Daye Steel Plant.65Nb steel is made of high speed steel W6Mo5Cr4V2 with composition adjustment and a small amount of Nb added.
CHEMICAL COMPOSITION（%）（GB/T 1299-2014）
C 0.60~0.70 Cr 3.80~4.40
Si ≤0.40 W 2.50~3.50
Mn ≤0.40 Mo 1.80~2.50
P ≤0.030 V 0.80~1.20
S ≤0.030 Nb 0.20~0.35
① Isothermal Annealing
Annealing process of 65NB steel: heating at 860±10℃, holding for 3~4h;The furnace was cooled to 740±10℃ and held for 5~6h.The furnace is cooled to below 500℃ and the furnace is cooled.After annealing, the hardness is less [SCALE STEEL]than 241Hbs, and the structure is spherical pearlite.The hardenability of steel is higher, Ø 50 mm sample in air hardening, Ø 80 mm can be hardening in the oil.
② Quenching Specification
SCHEMES I II III
REQUESTS GOOD TOUGHNESS GOOD WEAR RESISTANCE NORMAL
PRE-HEATING TEM℃ 840 840 840
QUENCHING TEM℃ 1080~
COOLING METHODS OIL COOLING TO 20~60℃，
OR 150~200℃ AND THEN AIR COOLING
HRC ≥61 ≥61 ≥61
③Tempering Specification：Tempered Tem540~580℃，Twice，1~2h per Time，Harness≥56HRC。
Temperature’s Relationship with Hardness(Tempering)
Quenching Tem→ 1080℃ 1120℃ 1160℃
Tempering Tem↓ HardnessHRC↓
200℃ 61.3 61.4 61.5
300℃ 58.0 58.5 59.0
400℃ 58.0 59.0 59.5
450℃ 59.4 59.9 60.3
500℃ 60.1 61.4 61.8
520℃ 60.1 62.3 62.6
540℃ 60.2 62.2 62.5
560℃ 58.5 60.4 61.5
580℃ 58.3 60.3 60.5
600℃ 55.5 57.0 58.5
④ Surface Strengthening (Nitriding)
In order to further improve the wear resistance, the 65NB steel mold can be treated with gas soft nitriding or ion nitriding surface strengthening treatment.
Gas soft nitride can be at 520~530℃, [SCALE STEEL]2.5~3.5h, using methanol and ammonia (methanol and ammonia ratio is 1:1).
Ion nitriding can be done at 500~540℃, with ammonia as nitriding medium, and the time is 30~60min.
The basic composition of 65NB steel is similar to that of HSS, and the compressive yield strength is slightly lower than that of HSS, but the bending strength, especially the toughness, is much higher than that of HSS.Because there is no excess carbide and niobium is added into the steel, it plays the role of refining grain.Therefore, [SCALE STEEL]it has high toughness and fatigue strength.Compared with the steel without niobium, the bending strength, impact toughness and fracture toughness are increased by 25%, more than doubled and 20% respectively.
65 nb is a strong combination of steel grade, suitable for making complicated shape, large impact load or cold work mould size is larger, often used to replace T10, Cr12MoV, W6Mo5Cr4V2 make Allen for the multi-station cold heading [SCALE STEEL]machine, punch, philips light punch, bolt trimming die, cold heading bolt top die, steel plate spring punch punch, bolt pressure Angle of intensive, flat round head die, ring cold die, etc.