To obtain good performance organization of forgings, in addition to need to make sure that the good quality of raw material outside, still need to have proper forging process and heat treatment process.
Forging process generally have the following process composition, namely next makings, heating, cooling, after forming, forged pickling (corrosion) and forging after heat treatment. Forming process including free forging, forging, trimming and correction; Free forging including upsetting, pull long, punch, bending and reverse, etc.; Die forging pulled long, including rolling, forging, eventually gets squeezed forging and the heading, etc.
From the above process to see, forging process of forging process and influence on the performance of the organization, and finally boils down to the influence of thermodynamics.
The so-called thermodynamic factors is refers to deformation temperature, deformation speed, the cooling speed and stress state and so on.
Choose reasonable thermodynamic factors can be improved through the following a few the raw material of the organization:
1. The broken columnar crystal, improve macro segregation, the as-cast organization into forging state organization, and in the right temperature and stress conditions, welding and internal pore, improve the density of material;
2. Bubble after forging, form the fibre, further through the rolling, extrusion, forging, make forgings get reasonable distribution of fiber direction;
3. Control the size of the grain and the homogeneous degree;
4. Improve out-of-phase (such as: ledebrite steel alloy of carbide) distribution;
5. Make the organization get deformation strengthen or deformation, phase strengthening, etc.
Due to the improvement of the organization, forgings plasticity, impact toughness, weak intensity and lasting performance has improved, and then through the components of the final heat treatment can get parts required hardness, strength and the plastic and good comprehensive performance and organization.
The following specific discussion on thermodynamics factors forgings influence on the performance of the organization.
1. The influence of the temperature of deformation
Forging heating is not only to ensure that has good forging of plastic deformation resistance and low, but also for the organization and performance after forging also has very big effect. For the steel is concerned, because the heat of forging average temperature is the final heat treatment temperature than parts high, so high temperature grain size and then the organization of forgings quality change can bring certain effect. Without proper heating temperature is always give forgings defects caused.
If the temperature too high and heating heating time is too long, can cause the decarburization, overheating, burning (especially high alloy steel and steel with Si most easily decarburization), such as: alloy steel and cause overheating fracture, and martensite stainless steel appear δ ferrite, austenitic stainless steel appear ferrite, 9 Cr18 bearing steel carbide crystal line along the non-infarct-related separation, heat resistant alloy appear coarse grains, titanium alloy appear β organization coarsening, etc. And permeability of the carbon steel forging overheating, makes carburizing appeared after the thick martensite and mesh carbide. The above all sorts of organizations that forgings defects of mechanical properties especially the toughness and fatigue performance decline.
Forging heating temperature of α + β titanium alloy organization and influence on the performance of the special obvious. Forging temperature α + β titanium alloy of β grain size and influence on the performance of the machine room temperature, if the heating temperature is too low, not only easy cause uneven deformation, heat resistant alloy and aluminum alloy after quench heating easy appear coarse grain or grain uneven thickness phenomenon, make YaGongXiGang form bands organization, and in the forging when still can cause various forms of crack.
2. Deformation degree and the influence of the deformation styles
Ingot of a kind of special effects than forging is the mechanical property of main factors. Forging the porosity, than ingot non-metal inclusions and toughness influence, toughness began to have certain increase, and then gradually reduce, its reason is due to the result of the organization formed fibers. A fibre steel continue to deformation, as the fiber distribution changed, transverse and longitudinal performance change with it. Steel fiber direction along the original of the transverse and longitudinal compression performance index changed. Hot extrusion of aluminum alloy bars toughness has very obvious directional, longitudinal and transverse toughness toughness maximum minimum. If die forging the transverse lateral flow or when, the horizontal toughness can be improved.
Use appropriate forging process, can make the metal parts of the biggest stress along the fiber distribution orientation. Streamline uniform for the appearance of the forging distribution, can make the forging the mechanical properties of the fatigue properties and especially stress corrosion resistance performance improved.
Final forming process of deformation degree is the effect of the important factors of forgings grain, for this with no change of grain heterogeneous materials is even more so. When the final process of deformation in critical deformation area, forging grains special bulky, its mechanical performance decline. Generally speaking, deformation degree than critical deformation, can obtain fine grain. But, deformation degree caused by excessive of structural phenomenon, will make the aluminum alloy forgings produce bulky grain; Some high temperature alloy forgings for deformation degree is too great, make the grain boundary carbide broken, may also appear bulky grain.
The heading of deformation and pull out way (one-way heading out the dui, jozabad, double cross heading out) and large enough deformation degree can achieve purpose as follows:
(1) refined and uniform HSS, chromium 12 steel, 3 Cr2W8V steel of carbide, improving the use performance;
(2) eliminate aluminum alloy, titanium alloy organization and performance in the direction, improve the uniformity of the organization and performance.
3. The influence of deformation speed
Generally speaking, improve the deformation will speed the ductility is reduced, even if the metal plastic drop, increase the deformation resistance.
Deformation rate will affect forging permeability. In the large deformation degree, the smaller the deforming velocity, the forging permeability more better, more beneficial to the grains will be refined and recrystallization, which is also beneficial to the improvement of process plastic.
4. The effect of heating speed
For the section size and the thermal conductivity of the poor blank, if heating speed too fast, holding time too short, often make temperature distribution uneven, cause thermal stress, and make blank produce craze. Such as: high alloy steel, high alloy steel, high temperature alloy steel ingot casting and forging by heating often happened not cracking. Blank temperature differentials, still can cause deformation and uneven organization, to generate additional stress, modelling internal craze, etc.
5. The effect of the cooling speed
The cooling speed improper, often make forging produce hot stress, organization and second phase separation of stress. Martensite stainless steel, ledebrite steel (HSS and chromium 12 steel), if the cooling rate after forging too fast, usually because martensite organization transformation cause organization stress, cause forging surface cracking. But, there are some materials after forging
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