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Hot extrusion die and medium, small machine forging die steel and heat treatment. |
1. Working conditions and performance requirements of hot extrusion dies and medium and small machine forging dies.
When the hot extrusion dies, the stress, bending stress and stripping stress are affected. By impact load is smaller than hammer forging die, but the time is longer than hammer forging die in contact with the hot metal, high working temperature is hammer forging die, extruding different metal temperature is different also, up to 800 a, 85090. The thermal stress caused by quenching and quenching is also greater than that of hammer forging. The main failure mode of hot extrusion dies is the excessive plastic deformation of the cavity, the fatigue damage, thermal wear and surface oxidation corrosion caused by repeated heating and cooling.
The working conditions of forging die of medium and small machine are similar to that of hot extrusion die. Therefore, the failure mode of the forging die of medium and small machine is similar to that of hot extrusion die. Therefore, it is required that hot extrusion die and medium and small machine forging die have higher heat resistance fatigue, thermal stability and good wear resistance, as well as high temperature strength and toughness.
2. Hot extrusion die and medium and small machine forging steel.
Commonly used in the hot extrusion mould and, minicomputers forging die steel for tungsten steel and chrome steel, chrome and key, tungsten aluminium chromium and platinum tungsten is a new type of steel and steel matrix, etc.
(1) tungsten steel are representative of this kind of steel material for the traditional 3 cr2w8v steel, due to its thermal fatigue resistance is poorer, the hot extrusion die applications will reduce gradually, but the application in die mold is more, so in the die-casting die steel for its detail.
(2) the typical steel type of the chromium heat making mold steel is 4Cr5MoSiV,4Cr5MoSiV1 and 4Cr5 W2VSi. The first two are equivalent to the American H11 and H13 steel, and 4Cr5W2VSi is developed from 4Cr5MoSiV steel. W 2 2% instead of 2 Mo=1%O. All three types of carbon have a mass fraction of about 5%, which belongs to the medium carbon steel.
The common property of this kind of steel is that the amount of chromium is high, and it has a high hardenability, such as 4Cr5MoSiV1 steel with a thickness of 150mm. And this kind of steel of supercooled austenite between 400 a 400 ℃ has high stability, long heat preservation and do not change, which is suitable for hierarchical quenching. The heat resistance is good, because chromium and silicon improve the oxidation resistance of steel, so the chromium steel is better suited to the working conditions of quenching and quenching. (3) high tempering stability, such as 4 cr5mosiv, 4 cr5w2vsi steel quenching hardness at about 1070 ℃ and 1200 ℃ respectively reaches the maximum when quenching. And tempering, the hardness with the tempering temperature and almost remain the same, and in 500 a 550 ℃ in the secondary hardening peak, then drops rapidly. (4) and department of tungsten steel are compared, have higher toughness, but lack of high temperature strength, heat resistance is a bit poor, working temperature is generally not more than 6501 (5) types and volume of this kind of carbide steel contains roughly the same. Therefore overheating sensitivity are similar. It has a high thermal plasticity, small deformation resistance, and small forging, but the forging temperature range is narrow, and the forging temperature must be strictly controlled.
(3) chromium key steel and cr tungsten key steel include 4Cr3Mo3SiV(H10), 3Cr3Mo3VNb(HM3), 3Cr3Mo3W2V(HMI), 5Cr4W5Mo2V(RM2), 4Cr3Mo3 W4 VNb(GR), etc.
The properties and application of some steel are briefly introduced.
1)3Cr3 Mo3 VNb(HM3) steel: this steel is characterized by low carbon content and a small number of keys. Therefore, it has high heat resistance fatigue and toughness, good tempering stability and excellent performance of other processes. It is suitable for the forming die, roll forging die and small hammer forging die of strong water cooling, and its working life is obviously higher than that of 5CrNiMo,4Cr5W2VSi and 3Cr2W8V steel.
2) 5Cr4W5Mo2V (RM2) steel: the quality fraction of the steel carbon is about 0.5%, the total mass fraction of the alloy element is 12%, and the use state contains more carbon, which is mainly M6C. Therefore, the steel has a high tempering resistance and thermal stability, and the thermal stability at the hardness of 50HRC can reach 700cC, which is good for anti-wear. Suitable for small section hot extrusion, high speed forging die and roll forging die.
3) 4Cr3Mo2W4VTiNb (GR) steel: this steel is a small amount of ni in the tungsten key system, and obtains high tempering stability and high thermal intensity. Its thermal fatigue, thermal stability, wear resistance and high temperature are obviously higher than 3Cr2W8V steel. The steel by 1160 a 1200 ℃ oil quenching, 630 a 600 ℃ tempering 2 times, each time the processing of lh, the hardness can be up to 50 a 55 HRC, tensile strength of up to 188 ompa, impact toughness of 17 j/cm2. The steel has a good hardenability and cold and heat processability. It is suitable for hot forging die, such as heat seal, fine forging and high speed forging.
(4) the substrate steel substrate can have multiple steel in steel and cold work die steel and hot-work die steel, such as 6 w8cr4vti (LM1), 6 cr5mo3w2vsiti (LM2) and 6 cr4mo3ni2wv (CG - 2), etc., with 5 cr4mo3simnvai (012 a1) steel is mainly used for hot extrusion mould, such as bearing heat extrusion punch, heat transmission rod badge and so on, its service life than the traditional steel are 3 cr2w8v has greatly improved.
3. Material selection for hot extrusion dies and medium and small machine forging dies.
Choose the hot extrusion mould processing materials, mainly according to be squeezed and the extrusion temperature to determine the kinds of metal, moreover also should consider to factors such as extrusion ratio, extrusion speed and lubrication condition, in order to improve the service life of mould. Table 3 shows the selection of processing materials for hot extrusion dies. The material selection of the forging mould of medium and small machine is mainly concerned with the type and production batch of forging materials, and the influence of mold size, deformation speed and lubrication condition on die life is also considered.
4. Heat treatment of hot extrusion die and medium and small machine forging die.
The manufacturing process of this kind of mould is generally: the blanking * forging, pre-heat treatment * mechanical processing forming, quenching, tempering and finishing.
The following analyses the process characteristics of each thermal process.
(1), small machine in hot extrusion die forging process and forging die steel for high alloy steel, so die blanks need to the good forging, especially aluminized steel, to pay attention to the control of forging heating temperature and holding time, in order to avoid serious decarburization lead to premature failure of the mold.
(2) prepare heat treatment.
1) annealing. The annealing process of the die in hot extrusion die is mainly to choose the annealing temperature correctly, maintain the sufficient heat preservation time, and cool it with the appropriate cooling rate. In addition, in order to ensure good abrasion resistance, need to keep a certain amount of carbide after quenching, due to the shape of the carbide has a great influence on toughness of steel, therefore should also pay attention to the carbide shape after annealing. They generally want to get round and small carbides.
2) high temperature adjustment. In order to improve the mechanical properties (especially the fracture toughness) of the forging, the pretreatment of the blank is often used in the method of forging. This kind of heat treatment method is to heat the die blanks after forging to the high temperature quenching, and then the high temperature tempering. By this treatment, the carbide can be distributed evenly, and the shape is round and small, which not only improves the performance of steel, but also shortens the pretreatment cycle. Quenching heating temperature can be determined according to different types of steel. For example, 3Cr3Mo3 W2V steel is 120090, which is similar to conventional quenching temperature. High temperature tempering temperature generally between 700 - a - 750 ℃.
3) positive fire after forging. After the forging, it is obvious that the mould with the crystal chain carbide should be eliminated and then the spheroidized annealing. The direct annealing of this chain carbide is difficult to eliminate.
(3) the quenching and tempering for commonly used hot extrusion die steel die steel and the medium and small machine, selecting quenching temperature, the main consideration is the size of the austenite grain size and impact toughness of high and low, then consider the working conditions of the mold, the structure shape, the failure forms of performance requirements.
For the selection of the thermal insulation time, the main consideration is to complete the transformation of the organization, so that the carbon and alloy elements can be fully dissolved, so as to ensure high tempering resistance and thermal hardness. Quenching thermal insulation time coefficient general salt bath furnace takes 0.5 1 min/mm, the smaller the size the larger the coefficient.
Hot extrusion die steel and medium and small machine forging die steel belong to high alloy steel, the hardenability is good, the quenching cooling can be used oil cold, also can adopt air cooling. The mould with small deformation can also adopt isothermal quenching or step quenching.
The correct process of tempering is very important to the failure mode of the mould. The principle of choosing tempering temperature is to improve the hardness of the mold as far as possible without affecting the anti-brittle ability of the mold, which needs to determine the tempering parameters according to the specific failure mode of the mold.
Tempering after quenching mould should be implemented as soon as possible, especially complex shape mould, when the surface temperature is below 80 ℃, tempering was performed. In order to avoid the occurrence of residual stress, it should be carried out slowly in tempering heating and cooling.
The tempering time can be calculated at 3min/mm, but not less than 2h. The second tempering temperature was 10 to 20CC lower than the first time.
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