Surface quality inspection of 304 stainless steel plate

　　The surface quality of 304 stainless steel is mainly determined by the pickling process after heat treatment. If the surface oxide layer formed by the previous heat treatment process is thick or the structure is uneven, pickling cannot improve the surface smoothness and uniformity. Therefore, full attention should be paid to the heating of heat treatment or surface cleaning before heat treatment.

　　If the thickness of the oxide skin on the surface of stainless steel plate is uneven, the surface smoothness of the base metal below the thick and thin areas is also different, and the dissolution of the oxide skin on the surface during acid washing is different from the degree of acid erosion of the base metal at the attachment area of the oxide skin, so the surface of the steel plate is uneven. Therefore, during heat treatment and heating, it is necessary to uniformly form oxide skin. To achieve this requirement, attention must be paid to the following issues:

　　If oil adheres to the surface of the stainless steel plate during heating, the thickness and composition of the oxide skin on the oil adhered area will be different from those on other parts, and carburization will occur. The carburized part of the oxidized subcutaneous matrix metal will be severely corroded by acid. The oil droplets sprayed by the heavy oil burner during initial combustion, if attached to the workpiece, have a significant impact. When the operator's fingerprint is attached to the workpiece, it can also have an impact. So, operators should not directly touch stainless steel parts with their hands and do not let the workpiece get new oil stains. Clean gloves must be worn for operation.

　　If there is lubricating oil attached to the workpiece surface during cold processing, it must be fully degreased in Trichloroethylene degreaser and caustic soda solution, and then cleaned with warm water, and then heat treated.

　　If there are impurities on the surface of stainless steel plates, especially organic matter or ash adhering to the workpiece, heating will naturally affect the oxide skin.

　　The difference in atmosphere inside the stainless steel plate furnace varies in different parts, and the formation of oxide skin may also change, which is also the reason for uneven pickling. So, during heating, the atmosphere in all parts of the furnace must be the same. To this end, it is also necessary to consider the circulation of atmosphere.

　　Furthermore, if the bricks, asbestos, and other materials used to form the heating workpieces contain moisture, the moisture will evaporate during heating, and the atmosphere of the parts that are directly in contact with the water vapor will differ from other parts, resulting in a different formation of oxide skin. Therefore, objects that come into direct contact with heated workpieces must be thoroughly dried before use. However, if placed at room temperature after drying, even in high humidity conditions, water will still condense on the surface of the workpiece. So, it is best to dry before use.

　　If there is residual oxide skin on the parts of the stainless steel plate before heat treatment, there may be differences in the thickness and composition of the oxide skin between the parts with and without oxide skin after heating, resulting in uneven surface after pickling. Therefore, not only should the final heat treatment be paid attention to, but also intermediate heat treatment and pickling should be fully paid attention to.

　　There is a difference in the oxide scale generated on the surface of stainless steel that is directly in contact with the flame of gas or oil, and on areas that are not in contact. Therefore, during heating, it is necessary to ensure that the processed parts do not directly come into contact with the flame opening.

　　The Influence of Different Surface Finishes on Stainless Steel Plates

　　If the surface finish is different, even if heated the same, the oxide skin on the rough and fine parts of the surface will not be the same. For example, the formation of oxide scales varies between areas where local defects have been cleaned and areas where they have not been cleaned,

　　If the surface finish is different, even if heated the same, the oxide skin on the rough and fine parts of the surface will not be the same. For example, in areas where local defects have been cleaned and areas where they have not been cleaned, the formation of oxide skin is different, resulting in uneven surface of the workpiece after acid cleaning.

　　The total Heat transfer coefficient of a metal depends on other factors besides its thermal conductivity. In most cases, the heat dissipation coefficient of the film layer, rust scale, and surface condition of the metal. Stainless steel can maintain a clean surface, so its heat transfer performance is better than other metals with higher thermal conductivity. Liaocheng Suntory Stainless Steel Co., Ltd. provides eight technical standards for stainless steel plates. Stainless steel plates are high strength stainless steel plates with excellent corrosion resistance, bending processing performance, toughness of welding parts, and stamping processing performance of welding parts and their manufacturing methods. Specifically, stainless steel plates containing C: 0.02% or less, N: 0.02% or less, and Cr: 11% or more but less than 17%, with an appropriate content of Si, Mn, P, S, Al, Ni, and meeting the requirements of 12 ≤ Cr Mo 1.5Si ≤ 17, 1 ≤ Ni 30 (C N) 0.5 (Mn Cu) ≤ 4, Cr 0.5 (Ni Cu) 3.3Mo ≥ 16.0, 0.006 ≤ C N ≤ 0.030, are heated to 850-1250 ℃, and then subjected to heat treatment with a cooling rate of more than 1 ℃/s. In this way, it can become a high-strength stainless steel plate with Martensite structure containing more than 12% volume fraction, high strength, corrosion resistance and bending processing performance above 730MPa, and excellent toughness of welding heat affected zone. Reusing materials containing Mo, B, etc. can significantly improve the stamping performance of welded parts. The flame of oxygen and gas cannot cut stainless steel plates because stainless steel is not easily oxidized. 5CM thick stainless steel plate shall be processed with special cutting tools, such as: (1) Laser Cutting machine with large wattage (2) Hydraulic saw (3) Grinding disc (4) Hand saw (5) Wire Cutting machine. (6) High pressure water jet cutting (professional water jet cutting: Shanghai Xinwei) (7) Plasma arc cutting