What about forging cracks in the production of forgings
source: | date:2019-07-06 14:47:42 |
How does forging crack appear during forging production? This requires an analysis of the reasons for this situation.
(1) Forging cracks caused by steel ingot defects Most of the steel ingot defects may cause cracking when forged. The center crack of the 2Cr13 spindle forgings is shown in Figure 6-8. This is due to the narrow crystallization temperature range and large linear contraction coefficient when the 6t ingot solidifies. Insufficient condensation, large internal and external temperature difference, large axial tensile stress, cracking along the dendrite, the formation of steel ingot interaxial crystal crack, the crack further expanded during forging into a crack in the spindle forging.
(2) Sulfur in forged cracked steel caused by the extraction of harmful impurities along the crystal boundary in steel is often precipitated along the crystal boundary in the form of FeS, and its melting point is only 982 °C. At 1200 °C forging temperature, FeS on the crystal boundary will melt. It also surrounds the grains in the form of liquid films, destroying the binding between the grains and producing hot crispy, and slightly forging will crack.
(3) The mechanical properties of the second phase of forging crack steel caused by different phase(second phase) are often very different from those of the metal matrix, so that the additional stress caused by the deformation flow will cause the overall process plasticity to decline. Once the local stress exceeds the binding force between the heterophase and the matrix, the holes are separated and formed. For example, oxides, nitrides, carbides, borides, sulphides, silicates, and so on in steel. If these phases are dense. Chain distribution, especially in the weak junction along the grain boundary, high temperature forging will crack. Photo 6-10 shows the macroscopic morphology of the 20SiMn steel 87t ingot that causes forging cracking due to the precipitation of a small AlN along the crystal boundary. Its surface has been oxidized and presents a polyhedral columnar crystal. Microscopic analysis shows that forging cracking is related to the massive precipitation of small granular AlN along the primary grain boundary.
The response is:
1) Limit the amount of aluminum added to the steel, remove nitrogen from the steel, or inhibit AlN precipitation by adding titanium;
2) Adopt heat delivery steel ingots, supercooled phase change treatment process;
3) Increase heat transfer temperature(& GT; 900 °C) Direct heating forging;
4) Adequate homogenization annealing before forging, so that the grain boundary precipitation phase diffusion.
The above is the solution to forging crack.
Key words: forgings
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