Small-diameter
thick-walled seamless pipes are steel pipes with a small ratio of outer diameter to wall thickness. How should such steel pipes be heat treated?
1. The repaired parts need to be normalized during the heat treatment process. The normalizing is a heat treatment process of heating the small-diameter thick-walled tubes of
seamless steel tubes to 45 ° C above Ac3, and after cooling for a suitable time, in a static air. Structural parts requiring mechanical properties require quenching after normalizing to meet mechanical performance requirements. Medium and high alloy steels and large forgings require high temperature tempering after normalizing to eliminate the internal stress generated during normalizing.
2. Annealing treatment of small-diameter thick-walled tubes of seamless steel tubes is a heat treatment process in which metals and alloys are heated to a suitable temperature for a certain period of time and then slowly cooled. After annealing, the sub-eutectoid steel is ferrite plus flaky pearlite; the eutectoid steel or hypereutectoid steel is granular pearlite. In summary, the annealed tissue is a tissue that is close to equilibrium.
4. Over-eutectoid steel normalizing heating knife Acm or more, so that the original mesh-like cementite is dissolved into austenite, and then cooled at a faster rate to inhibit the precipitation of cementite in the austenite grain boundary , which can eliminate the network carbide and improve the structure of the hypereutectoid steel. Welded parts require normalizing of the weld strength to improve the weld structure and ensure weld strength.
5. Some seamless steel pipe small-diameter thick-walled pipes produce partial martensite transformation during forging to form hard tissue. In order to eliminate this kind of bad organization, when it is normalized, it is heated and kept at a temperature of about 20 °C higher than the normal normalizing temperature for normalizing. The normalizing process is relatively simple, which is beneficial to the use of forging waste heat normalizing, which can save energy and shorten the production cycle. Normalized processes and improper handling also produce tissue defects, similar to annealing, and the remedies are basically the same.
