Reasons for the increased hardness value of L360NCS after heat treatment.

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Our factory carries out heat treatment on the pipes L360NCS used for highly acidic natural gas, with a controlled temperature of 300 degrees; the rate of temperature increase is less than 120 degrees per hour. The thickness of these pipes is 8.8 millimeters, and they are held at this temperature for one hour. The temperature decreases at a rate of less than 100 degrees per hour, with the final temperature remaining within 620 degrees plus or minus 20 degrees. Hardness tests were conducted on the welds, the base material, and the heat-affected zone before and after heat treatment. It was found that, after heat treatment, the hardness of the base material decreased slightly, while the hardness of the welds and the heat-affected zone increased. Although these values remained within the specified ranges, it was still puzzling.