20CrMo Heat Treatment Furnace

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Alloy structural steel 20CrMo is a kind of steel with high hardenability, no temper brittleness, good weldability, low tendency to form cold cracks, good machinability and cold strain plasticity.

1. Chemical Composition (℅)

C	Si	Cr	Mn	Mo
0.17～0.23	0.17～0.37	0.80～1.10	0.40～0.70	0.15～0.25

2. 20CrMo Purpose

It is used to manufacture high-pressure pipes and various fasteners that work in non-corrosive media and media containing nitrogen and hydrogen mixtures with a working temperature of less than 250°C, as well as higher-level carburized parts, such as gears, shafts, etc.

3. 20CrMo Heat Treatment Process

3.1 Normalizing

Normalizing treatment can eliminate excessive stress inside the gear. The purpose is to refine the grain, improve the structure, increase the toughness of the gear, improve the cutting performance of the material, and prepare for the final heat treatment.

3.2 20CrMo Carburizing Furnace

(1) Commonly used carburizing methods are: solid carburizing, liquid carburizing, and gas carburizing. Gas carburizing is most commonly used. The original state of the carburizing agent used can be gas or liquid such as kerosene. However, it is gaseous in the chemical heat treatment furnace. The penetrant used is required to be easily decomposed into active atoms, economical, easy to control, pollution-free, and the penetrating layer has good performance. Due to the low carbon content, high plasticity and toughness, poor hardness and mold resistance, gas surface carburizing heat treatment is used to obtain a lath-shaped martensite structure on the surface layer, that is, the high hardness can reach more than 58HRC, but the heart The part is still high plasticity and toughness, hardness is 33-45HRC, yield strength σs: ≥490 MPa elongation δ5 (%): ≥11.

(2) Carburizing temperature

Carburize gas, heat 900~920C, and calculate the holding time by 0.15~0.2mm/h, and the heating temperature should not exceed 920″C to avoid coarse grains. Carburizing is quenched and tempered, and the quenching is heated at 820~850C, and the temperature is kept warm. After oil cooling, low temperature tempering at 180°C.

(3) Carburizing medium

Methanol and kerosene

(4) Carburizing temperature and time

The carburizing temperature is above Ac3. Considering the diffusion rate of carbon in steel and other factors, the current widely used temperature for reproduction is 910^930°C. As the depth of the carburized layer increases, the diffusion coefficient of carbon in the steel increases exponentially, and the carburizing speed increases. Too high egg carburizing temperature will cause coarse grains, increased workpiece distortion, and reduced equipment life. The thickness of the infiltration layer is 0.8~1.2mm, and t=920°C can be selected. Holding time: 5 hours

(5) Carburizing process

After the furnace is installed, exhaust, the dripping amount is 35^65 drops/min, and the holding time is 160~180 drops/min. After the infiltration layer meets the requirements, it is cooled to 850±10C and pre-cooled for 30 minutes to prepare for quenching.

(7) 20CrMo carburizing furnace

Model	Temperature Uniform Size(W*H*L)	MAX Temperature	Ultimate Pressure	Temperature Uniformity	Loading Capacity
RVC-446	400*400*600mm	1500℃	20Pa	±5℃	200Kg
RVC-669	600*600*900mm	1500℃	20Pa	±5℃	500Kg
RVC-7710	700*700*1000mm	1500℃	20Pa	±5℃	700Kg
RVC-8812	800*800*1200mm	1500℃	20Pa	±5℃	1000Kg
RVC-9915	900*900*1500mm	1500℃	20Pa	±5℃	1200Kg
Remark: The working zone of equipment could be customized base on customer’s production.

3.3 20CrM Quenching Treatment

(1) The surface has high hardness, strength, wear resistance and contact fatigue resistance, and the core is still high in strength and toughness. It is required that the hardness of the heart tooth after quenching is 58-63HRC; the hardness of the tooth root is 33-45HRC; the other mechanical properties are: tensile strength σ b≥1000MPa; yield strength σs: ≥490 MPa elongation δ5 (%): ≥11

(2) Quenching temperature

Quenching temperature: 840 ± 10°C

Basis: 20CrMo is low carbon steel, heating temperature t=Ac3+30^50°C

(3) Quenching medium: oil cooling

(4) Holding time

20~ 30min

The holding time for the workpiece in the carburizing furnace is long enough without reheating for a long time.

(5) Organization after quenching:

After carburizing and quenching, the structure of the gear from the surface to the core is: martensite + carbide (a small amount) + retained austenite → martensite + retained austenite → martensite → low carbon martensite (heart Department).

(6) 20CrMo quenching furnace

Model	Temperature Uniform Size(W*H*L)	MAX. Temperature	Ultimate Pressure	Temperature Uniformity	Loading Capacity
VOGQ-446-2	400*400*600mm	1300℃	4*10-1Pa/6.7*10-3Pa	±5℃	200Kg
VOGQ-557-2	500*500*700mm	1300℃	4*10-1Pa/6.7*10-3Pa	±5℃	300Kg
VOGQ-669-2	600*600*900mm	1300℃	4*10-1Pa/6.7*10-3Pa	±5℃	500Kg
VOGQ-7710-2	700*700*1000mm	1300℃	4*10-1Pa/6.7*10-3Pa	±5℃	700Kg
VOGQ-8812-2	800*800*1200mm	1300℃	4*10-1Pa/6.7*10-3Pa	±5℃	1000Kg
VOGQ-9915-2	900*900*1500mm	1300℃	4*10-1Pa/6.7*10-3Pa	±5℃	1200Kg
Remark: The working zone of equipment could be customized base on customer’s production.

3.4 20CrMo Low Temperature Tempering

Tempering can reduce internal stress, stabilize structure and size, greatly improve toughness and obtain good comprehensive mechanical properties. Tensile strength σ b≥1000MPa; Yield strength σs: ≥885 Elongation 85(%): ≥11; Reduction of area ψ (%): ≥45; Impact energy Akv(J): ≥55; Impact toughness value akv (J/cm2): ≥69(7).

Fig 1 The overall process curve of heat treatment

Shanghai Geheng Vacuum Technology Co., Ltd. is a vacuum heat treatment furnace manufacturer with many years of experience in design, manufacturing and production. Mainly produce vacuum heat treatment furnace, vacuum sintering furnace, vacuum brazing furnace, New Energy And Environmental Protection Equipment and other vacuum equipments.Provide customized services, equipment work area can be based on customer output.