| High-resistance electrothermic alloy is a core electric heating material which is widely applied in industry and household and has a large market. A certain company is a main enterprise which earliest engaged in producing High-resistance electrothermic alloy. This thesis studied evolution rules of microstructure and mechanical properties of this enterprise's Cr20Ni80 during manufacturing course and provides references to control quality and improve service life of the product.To investigate specific improvement of Cr20Ni80 ingot after ESR (electroslag remelting), cross section's macrostructure, inclusions, mechanical properties of ingots were comparatively studied before and after ESR. The results showed that the range of columnar crystal zone on big end and small end and fine grain zone on small end reduced after ESR. The columnar crystal zone is two thirds of the radius in the big end and the crystal grain are coarse in the small end after ESR. SEM analysis showed that there are 5 types of inclusions in the ingot and not new inclusion after ESR. By analyzing the amount and size of inclusions in the ingot before remelting, it was found that the main mechanism for inclusion segregation in lower part of the ingot is the catching of large inclusions by showering crystallites during floatation. Area ratio of inclusions of the ingot decreases 48.3%, distribution of inclusion is more homogeneous, plasticity improves 8?9 times, toughness improves 5?6 times after ESR.The ingot was forged to billet of 80×80 after ESR. Sampling from sections of billet corresponding to big end, middle-big, middle-small, small end of the ingot and conducting tensile test and impact test. Sampling from edge, middle from center to edge, center sections of the billet and conducting grain size grade assessment and microstructure observation. Discover:(l) On cross section, recrystallization is very complete from edge to center of the billet, grain size number increases from 8.5 to 6.7 corresponding to big end to small end of the ingot. (2) From the two aspects of the yield ratio and elongation, the section of billet corresponding to middle-small of the ingot has the best plasticity. (3) The impact energy of the billet increases from big-end to middle but decreases from middle to small-end corresponding to the ingot.Sampling from wire rod after hot-rolling(?8.0mm),solution treatment,drawing(?5.7mm, ?2.3mm and ?1.0mm) and solution treatment on cross and longitudinal section.to observe microstructure. Find recrystallization is complete after hot rolling. Grain size grow up after solution treatment. On cross section, grains crush severely, on longitudinal section, grains were stretched along drawing direction, both section have a number of twins and slip bands in grains. Sampling from wire rod after each working procedure and conducting mechanical property test. Find the section of middle of wire rod has the best plasticity. After drawing to ?5.7mm the mechanical properties of wire rod are uniform, the average extension rate is 12%,the average yield strength is 1045MPa, and become 53.5% and 239MPa after solution treatment.After drawing to ?2.3mm, the average extension rate is 7.5%, the average yield strength is 443MPa, and become 43% and 185MPa after solution treatment. After drawing to ?1.0mm, the wire has barely plasticity, and the yield strength ratio is 0.43 after solution treatment. |
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