Surface quality inspection
The surface quality of 304 stainless steel is mainly determined by the pickling process after heat treatment, if the surface oxide skin formed by the previous heat treatment process is thick, or the organization is not uniform, then pickling can not improve the surface finish and uniformity. Therefore, we should pay full attention to the heating of heat treatment or surface cleaning before heat treatment.
If the surface oxide thickness of the stainless steel plate is not uniform, the substrate metal surface finish below the thick place and the thin place is also different, and the dissolution of the surface oxide during pickling is different from the acid erosion of the substrate metal at the attachment site of the oxide, so the surface of the steel plate is not uniform. Therefore, in the heat treatment heating, it must be evenly formed oxide. To achieve this requirement, attention must be paid to the following issues:
If the stainless steel plate is attached to the surface of the workpiece when heating, the oxide thickness of the oil attachment part and the oxide thickness and composition of other parts are different, and carburizing will be produced. The carburized portion of the subcutaneous matrix metal will be severely eroded by acid. The oil droplets emitted by the heavy oil burner during the initial combustion, if attached to the workpiece, have a great impact. There is also an impact when the operator's fingerprint is attached to the workpiece. Therefore, the operator should not touch the stainless steel parts directly by hand, and do not make the workpiece stained with new oil. Clean gloves must be worn.
If there is lubricating oil attached to the surface of the workpiece during cold processing, it must be fully degreased in trichloroethylene degreasing agent and caustic soda solution and then cleaned with warm water, and then heat treatment.
If there is debris on the surface of the stainless steel plate, especially when organic matter or ash is attached to the workpiece, heating will of course have an effect on the oxide.
The difference in the atmosphere in the furnace is different in each part, and the formation of the oxide will also change, which is also the reason for the uneven pickling. Therefore, when heating, the atmosphere in each part of the furnace must be the same. For this reason, the cycle of atmosphere must also be taken into account.
In addition, the brick, asbestos, etc., which constitutes the bench used for heating the workpiece, if it contains water, when heating, the water will evaporate, and the atmosphere of the part directly in contact with the water vapor will differ from that of the other parts, and the formation of the oxide skin will of course be different. Therefore, objects in direct contact with the heating workpiece must be fully dried before they can be used. However, if placed at room temperature after drying, in the case of high humidity, water will still condense on the surface of the workpiece. Therefore, it is best to dry before use.
If the local parts of the stainless steel plate have residual oxide before heat treatment, the residual parts of the oxide after heating and the parts without oxide, there will be differences in the thickness and composition of the oxide, causing the surface to be uneven after pickling, so not only pay attention to the final heat treatment, but also pay full attention to the intermediate heat treatment and pickling.
There is a difference in the oxide produced by the stainless steel surface where the gas or oil flame is in direct contact with the place where it is not in contact. Therefore, the processing part must not be directly in contact with the flame port when heating.
The influence of different surface finish of stainless steel plate
If the surface finish is different, even if the same heating, the surface of the rough and fine oxide is not the same. For example, in the place where the local defect is cleaned and in the place where it is not cleaned, the condition of the formation of oxide skin is different, which causes the surface of the workpiece to be uneven after pickling.
In addition to the thermal conductivity of the metal, the total heat transfer coefficient depends on other factors. In most cases, the heat dissipation coefficient of the film layer, the rust and the surface condition of the metal. Stainless steel can keep the surface clean, so its heat transfer is better than other metals with higher thermal conductivity. Liaocheng Suntory Stainless Steel provides eight, stainless steel plate technical standards stainless steel plate corrosion resistance, bending processing performance and welding toughness, as well as welding parts of the stamping processing performance of excellent high-strength stainless steel plate and its manufacturing method. Specifically, the appropriate content of Si, Mn, P, S, Al, Ni, containing C:0.02% or less, N:0.02% or less, Cr:11% or more or less than 17%, And meet 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 stainless steel plate heating to 850~1250℃, Then the heat treatment is carried out at a cooling rate of more than 1℃/s. This can become a high-strength stainless steel plate containing 12% volume fraction with martensitic structure, high strength, corrosion resistance and bending performance above 730MPa, and excellent toughness in the welding heat affected zone. Using Mo, B, etc., can significantly improve the stamping machining performance of the welding part. Oxygen and gas flame can not cut stainless steel plate because stainless steel is not easy to be oxidized. 5CM thick stainless steel plate should be processed with special Cutting tools,
such as:
(1) large wattage Laser Cutting machine(laser cutting machine)
(2) hydraulic saw machine
(3) grinding disc
(4) human hand saw
(5)Wire Cutting machine(wire cutting machine).
(6) High-pressure water jet cutting (professional water knife cutting: Shanghai Xinwei)
(7) plasma arc cutting
