If oil is attached to the surface of the workpiece during heating, the thickness and composition of the oxide skin on the oil-attached part is different from that of the other parts, and carburization will occur. The part of the base metal under the oxide skin that is carburized will be seriously eroded by acid. The oil droplets ejected from the heavy oil burner* when it first burns will also have a significant impact if they adhere to the workpiece. The operator’s fingerprints will also be affected when they are attached to the workpiece. Therefore, the bath operator should not touch the stainless steel parts directly with his hands and should not make the workpiece stained with new oil. Must wear clean gloves to operate.
Workpiece surface such as cold processing attached lubricants, etc., must be fully degreased in trichloroethylene degreaser, caustic soda solution and then cleaned with warm water, and then heat treatment.
Spiral steel pipe if the surface has debris, especially organic matter or ash attached to the workpiece, heating will of course have an impact on the oxide skin.
Large diameter spiral steel pipe furnace atmosphere differences in the furnace atmosphere in the various local differences in the formation of oxide skin a will also change, which is also the cause of uneven after pickling. Therefore, when heating, the atmosphere in all parts of the furnace must be the same. For this reason, the circulation of the atmosphere must also be considered.
Also, if the bricks and asbestos used to form the table used to heat the workpiece contain moisture, when heating, the moisture has to evaporate, the part directly in contact with water vapor and other parts of the atmosphere will be different, and the formation of oxide skin will of course be different. Therefore, objects in direct contact with the heated workpiece must be fully dried before use. However, after drying, if left at room temperature, moisture will still coalesce on the surface of the workpiece in the case of high humidity. Therefore, it is * better to dry before use.
Spiral steel pipe if the local part of the treated part has residual oxide before heat treatment, after heating the part with oxide residue and the part without oxide, there will be differences in the thickness and composition of the oxide, causing uneven surface after pickling, so we should not only pay attention to the * final heat treatment, but also pay sufficient attention to the intermediate heat treatment and pickling.