Phase composition and properties of spring steels 50KhFA and 65S2VA
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The decomposition of martensite in the process of tempering above 100° occurs with formation of alloyed cementite M3C in steels 50KhFA and 65S2VA.
In the process of tempering steel 50KhFA at temperatures <400°, cementite is enriched to a considerable extent by alloying elements-chromium (≤0.12%) and manganese (≤0.04%); vanadium remains in the α solid solution at tempering temperatures up to 600°.
Cementite in steel 65S2VA tempered at temperatures <400° is also partially enriched in chromium (≤0.01%) and manganese (≤0.02%); tungsten remains in solid solution. Cementite is enriched with tungsten at tempering temperatures >400°; at 500° cementite is enriched with as much as 0.10% W.
Chromium and vanadium in steel 50KhFA and silicon and tungsten in steel 65S2VA, which are tempered at 400 and 500° respectively, primarily harden the solid solution and increase its thermal stability.
Steel 65S2VA has the highest relaxation resistance at 20–200° only after tempering at temperatures ∼260–280° higher than the testing temperature. In this case the structure obtained after tempering is the most stable in stress relaxation tests at the temperature indicated.
KeywordsSilicon Chromium Manganese Solid Solution Thermal Stability
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