Introduction of steel for the hottest carburized p

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Introduction to steels for carburized plastic moulds

steels for carburized plastic moulds are mainly used for plastic moulds formed by cold extrusion. In order to facilitate cold extrusion forming, there is a great risk of condensation; Moreover, this kind of steel must have high plasticity and low deformation resistance in the annealed state. Therefore, this kind of steel is required to have low or ultra-low carbon content. In order to improve the wear resistance of the die, this kind of steel is generally carburized and quenched and tempered after cold extrusion, and the surface hardness can reach 58 ~ 62Hrc

this kind of steel has special steel grades abroad, such as 8416 in Sweden, P2 and P4 in the United States, etc. Industrial plastic extruders are often used in China, and the international influence of the industry continues to heat up pure iron (such as dt1 and DT2), 20, 20Cr, 12CrNi3A and 12cr2ni4a steels, as well as the newly developed domestic cold forming special steel 0cr4nimov (LJ). Now two typical steel grades are introduced

(I) 0cr4nimov (LJ) steel

1 Chemical composition: the table shows the chemical composition of LJ steel

Table chemical composition (mass fraction) (%)

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

this steel has very low carbon content, so it has excellent plasticity and low deformation resistance. The main additive element in steel is chromium, and the auxiliary elements are nickel, molybdenum, vanadium, etc. the main role of alloy elements is to improve hardenability and carburization ability, increase the hardness and wear resistance of carburized layer and the strength and toughness of the heart

2. Process performance: LJ steel has good forging performance and heat treatment processability

forging process: heating temperature 1230 ℃, initial forging temperature 1200 ℃, final forging temperature 900 ℃

annealing process: heating 880 ℃, holding for 2h, slowly cooling with the furnace to (cooling speed about 40 ℃/h) 650 ℃ and then out of the furnace for air cooling. The R & D level and industrialization scope of annealing hardness new materials have become an important symbol to measure the economic and social development, scientific and technological progress and national defense strength of a country or region. 100 ~ 105hbs can be smoothly cold extruded

solid carburizing process: heat 930 ℃ (6 ~ 8) h, oil quenching at 850 ~ 870 ℃ after carburizing, and then low temperature tempering at 200 ~ 220 ℃ for 2h. 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 LJ steel is fast, and the depth of carburizing layer is twice that of 20 steel

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

(II) 12CrNi3A steel

1 Chemical composition: 12CrNi3A steel is a permeable alloy carburized steel that can be successfully implemented in the traditional medium quenching guarantee project. Its composition is shown in the table. The carbon content of the steel is low. 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 die steels, the cold formability of this steel is medium

table 12chemical composition (mass fraction) of crni3a steel (%)

C Si Mn Cr Ni P, s

0.09 ~ 0.16 0.17 ~ 0.37 0.30 ~ 0.60 0.60 2.75 ~ 3.25 0.025

2 Process performance: the heating temperature of forging is 1200 ℃, the initial forging temperature is 1150 ℃, and the final forging temperature is greater than 850 ℃. It is slowly cooled after forging, and it must be softened and annealed after forging

annealing process: heating at 740 ~ 760 ℃, holding for 4 ~ 6h, slowly cooling to 600 ℃ at the speed of 5 ~ 10 ℃/h, and then cooling to room temperature. The hardness after annealing is less than 160hbs, which is suitable for cold extrusion forming

normalizing process: heating at 870 ~ 900 ℃ and air cooling after holding for 3 ~ 4H. The hardness after normalizing is 229hbs, and the machinability is good

when 12CrNi3A steel adopts gas carburizing process, the heating temperature is 900 ~ 920 ℃ and the heat preservation is 6 ~ 7h, the carburized layer of 0.9 ~ 1.0mm can be obtained. After carburization, it is pre cooled to 800 ~ 850 ℃ and directly oil quenched or air cooled. After quenching, the surface hardness can reach 56 ~ 62Hrc, the core hardness is 250 ~ 380hbs, and the deformation is small

3. Practical application: 12CrNi3A steel is mainly used for shallow cavity plastic mold with complex shape formed by cold extrusion. It can also be used to manufacture large and medium-sized plastic molds formed by cutting. In order to improve the machinability, the mold blank must be normalized

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