PRODUCT CATEGORIES

Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Heat Treatment of Steel for Carburizing Plastic Mould

Steel for carburizing plastic molds is mainly used for cold extrusion molding plastic molds. In order to facilitate cold extrusion molding, this type of steel must have high plasticity and low deformation resistance in the annealed state. Therefore, low or ultra-low carbon content is required for this type of steel. In order to improve the wear resistance of the mold, This type of steel is generally carburized and quenched and tempered after cold extrusion, and the surface hardness can reach 58-62HRC. There are special steel grades for this kind of steel abroad, such as 8416 in Sweden, P2 and P4 in the United States and so on. Industrial pure iron (such as DT1 and DT2), 20, 20Cr, 12CrNi3A and 12Cr2Ni4A steel are often used in China.

1. LJ Steel

Chemical Composition:Table 1 is the chemical composition of LJ steel.

C	Mn	Si	Cr	Ni	Mo	V
≤0. 08	≤0.3	≤0.2	3.6～4.2	0.3～0.7	0.2～0.6	0.08～0.15

Table 1 Chemical Composition of LJ steel (mass fraction/%)

The steel contains very low carbon content, so it has excellent plasticity and low deformation resistance. The main added element in steel is chromium, and the auxiliary added elements are nickel, molybdenum, vanadium, etc. The main function of alloying elements is to improve the hardenability and carburizing ability, increase the hardness and wear resistance of the carburized layer, and the strength and toughness of the core.

Process Performance: LJ steel has good forgeability and heat treatment processability.

Forging process: heating temperature of 1230℃, initial forging temperature of 1200℃, final forging temperature of 900CC.

Annealing process: heating at 880℃, holding for 2h, slowly cooling with the furnace to 650℃ (cooling rate of about 40℃/h), and then air cooling. , Annealing hardness 100~105HBW, cold extrusion molding can be carried out smoothly.

Solid carburizing process: heating 930℃×(6~8)h, after infiltration, oil quenching at 850～870℃, and then 200~220℃× 2h low temperature tempering, after heat treatment, the surface hardness is 58~60HRC, the core hardness is 27~29HRC, and the heat treatment deformation is small. The carburizing speed of U steel is fast, and the depth of the carburizing layer is twice as deep as that of 20 steel.

Practical application:The cold formability of LJ steel is similar to that of industrial pure iron, and the mold cavity formed by cold extrusion has a clear, smooth and high precision. LJ steel is mainly used to replace precision plastic molds of 10, 20 steel and industrial pure iron. Due to the deep carburizing and hardening layer and the high hardness of the matrix, there will be no cavity surface collapse and inner wall biting, and the use effect is good.

2. 12CrNi3A Steel

Chemical Composition:12CrNi3A steel is a traditional medium hardenability alloy carburizing steel, and its composition is shown in Table 2.

The steel has a low carbon content, and nickel and chromium alloy elements are added to improve the hardenability of the steel and the strength and toughness of the carburized layer, especially nickel, which significantly increases the plastic toughness of the steel while producing solid solution strengthening. Compared with other cold-formed plastic mold steels, the cold formability of this steel is moderate.

C	Si	Mn	Cr	Ni	P、S
0.09～0.16	0.17～0.37	0.30～0.60	0.60～0.90	2.75～3.25	≤0.025

Table 2 The chemical composition of 12CrNi3A steel (mass fraction/%)

Process Performance:

Forging process: forging heating temperature is 1200℃, initial forging temperature is 1150℃, final forging temperature is greater than 850℃, slow cooling after forging, and softening annealing must be performed.

Annealing process: heating at 740~760℃, after 4~6h heat preservation Slowly cool to 600°C at a rate of 5~10°C/h, and then cool to room temperature. The hardness after annealing is less than 160HBW, suitable for cold extrusion molding.

Normalizing process: 870~900°C heating and heat preservation for 3~4h After air cooling, the hardness after normalizing is less than or equal to 229HBW, and the workability is good.

When 12CrNi3A steel adopts the gas carburizing process, the heating temperature is 900~920℃ for 6~7h, and a carburized layer of 0.9~1.0mm can be obtained. After carburizing, it is pre-cooled to 800~850℃ for direct oil quenching or air cooling and quenching. The hardness of the back surface layer can reach 56~62HRC, the hardness of the core is 250~380HBW, and the deformation is small.

Practical application:12CrNi3A steel is mainly used for cold-extrusion forming of shallow-cavity plastic molds with complex shapes. It can also be used to make large and medium-sized plastic molds for cutting and forming. In order to improve the machinability, the mold blanks must be normalized.