Properties of 4Cr3Mo2NiVNb (HD) Steel- SCALE STEEL.

4Cr3Mo2NiVNB steel code name is HD steel, is a kind of air-cooled hardening martensitic hot work die steel, is based on Sweden Udholm QRO-80 steel, by the Huazhong University of Science and Technology and other units[SCALE STEEL] independently developed new hot work die steel.  

CHEMICAL COMPOSITION（%）
C 0.35～0.45 Cr 2.50～3.00
Si ≤0.35 Mo 1.80～2.20
Mn ≤0.40 Ni 0.80～1.20
P ≤0.030 V 1.00～1.40
S ≤0.030 Nb 0.10～0.25

Citical Point  
AC1 =789℃, AC3 =910℃, MS =363℃  
 
Hot Forming
➣ HD Steel Forging Process Specification  
ITEMS STEEL INGOT BILLET
HEATING TEM℃ 1140～1180 1120～1160
FORGING TEM(BEGINNING)℃ 1080～1140 1060～1120
FORGING TEM(END)℃ ≥900 ≥850
COOLING METHOD[SCALE STEEL] SAND OR PIT SLOW COOLING SAND OR PIT SLOW COOLING

Preliminary Heat Treatment  
Isothermal annealing of forging material: < 500℃ into furnace with furnace temperature rise, heating temperature 830 ~ 850℃, holding time (H) 1+1min/mm, isothermal temperature 730±10℃, holding time (H) 2+1min/mm, with furnace [SCALE STEEL]cold to < 500℃ air cooling (HB≤250).  
 
Quenching Specification  
Quenching temperature is 1130±10℃, oil cold.  
➣ The Relationship Between Quenching Temperature And Hardness And Grain Size Of Hd Steel  
QUCHENING TEM/℃ HARDNESSHRC GRAIN SIZE/CLASS
1050 50.5 --
1100 53.5 11
1130 53.5 10
1160 56.0 8～9
1180 56.0 7～8
1200 56.5 7～8

➣ HD Stee’s Hardness Levels on Different Tempered Tem:
Tempered Tem/℃ HRC
HD Steel 3Cr2W8VSteel
300 52.5 51.0
400 52.0 51.0
500 52.5 51.4
530 53.5 52.3
560 54.0 51.5
590 53.8 51.8
620[SCALE STEEL] 51.2 50.0
650 47.0 46.0
700 41.0 34.0

Mechanical Properties（Comparing with 3Cr2W8V Steel）

➣ HD Steel’s Mechanical Property under Different Room Tem:
Heat Treatments 1130℃ Quenching
650℃ Tempering 1130℃ Quenching
700℃ Tempering 
HD 3Cr2W8V HD 3Cr2W8V
σ0.2/MPa 1633 1463 1165 952
ψ（%） 32.4 41.8 45.7 41.9
αk/(J/cm2) 38.8 -- 48.8 --

➣ HD Steel’s Mechanical Property under Different Tem:
Test Tem 650℃ 700℃
HD 3Cr2W8V HD 3Cr2W8V
σ0.2/MPa[SCALE STEEL] 536.9 414 405.3 235
ψ（%） 66.1 49.1 69.3 85.4
αk/(J/cm2) 56/54 -- 75/40 62/38

Note: The denominator in αk value is hardness value (HRC).  
 
Performance Characteristics:
On the basis of 4Cr3Mo3V steel, the toughness and thermal stability of 4Cr3Mo2NiVNb (HD) steel at room temperature and high temperature were improved by reducing the content of Mo and V and adding[SCALE STEEL] the mass fraction of 1%Ni and 0.15%Nb. The hardness of 4Cr3Mo3V steel at 700℃ could still maintain 40HRC.  Under the same conditions of hardness, HD steel has 50% higher fracture toughness than 3Cr2W8V steel, 70% higher tensile strength at 700℃, 1 times higher cold and hot fatigue resistance and 50% higher hot wear resistance, respectively.  
 
Applications  
HD steel comprehensive performance is good, suitable for making heating temperature about 700 ℃, using strict hot-work mold, such as ferrous and non-ferrous materials of hot extrusion die, such as hot fine[SCALE STEEL] forging die, in the steel tube hot extrusion convex die, the bottom of the copper alloy tube extrusion die and punch needle, hot extrusion convex die and concave die bearing ring, valve end of extrusion die and mold USES,  The service life of 3Cr2W8V steel is significantly improved.