Surface quality inspection of stainless steel sheet

 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, pickling can not improve the surface finish and uniformity. Therefore, full attention should be paid to the heating of heat treatment or surface cleaning before heat treatment. If the stainless steel sheet surface oxide thickness is not uniform, thick and thin place below the base metal surface finish is also different, surface and pickling surface oxide dissolution and the base metal oxide adhesion part of the acid erosion is different, so the surface of the steel plate is not uniform. Therefore, during heat treatment, it is necessary to uniformly form oxide crust. To achieve this requirement, attention must be paid to the following issues:

1, stainless steel sheet if the workpiece surface is attached to oil when heated, the thickness of the oxide skin of the oil attachment part and the thickness and composition of the oxide skin of other parts are different, and will produce carburization. The carburized portion of the oxidized subcutaneous matrix metal will be severely attacked by acid. The oil droplets emitted by the heavy oil burner during initial combustion, if attached to the workpiece, have a great impact. It also affects when the operator's fingerprint is attached to the workpiece. Therefore, do not use your hands to directly touch the stainless steel parts, do not make the workpiece with new oil. Must wear clean gloves to operate. The surface of the workpiece, such as cold processing attached lubricating oil, must be fully degreased in trichloroethylene degreaser, caustic soda solution after cleaning with warm water, and then heat treatment.

2, stainless steel sheet if there are sundries on the surface, especially organic matter or ash attached to the workpiece, heating will of course have an effect on the oxide scale.



3, the difference of the atmosphere in the stainless steel sheet furnace atmosphere in different parts of the furnace, the formation of the oxide scale will also change, which is also the cause of the uneven pickling. Therefore, when heating, the atmosphere in each part of the furnace must be the same. To this end, the circulation of atmosphere must also be considered. Also, the bricks and asbestos used for heating the workpiece, if it contains water, when heating, the water will evaporate, the atmosphere of the part directly in contact with the water vapor will produce differences with other parts, and the formation of the oxide scale will of course be different. Therefore, the object in direct contact with the heating workpiece must be fully dried to use. 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.

4, stainless steel sheet if handled locally before heat treatment with residual scale, scale after heating the remaining parts and not the part of the scale, there will be differences in thickness and composition of scale, cause after pickling surface uneven, so not only should pay attention to the final heat treatment, but also to fully pay attention to the intermediate heat treatment and pickling.

5, gas or oil flame direct contact of stainless steel surface and no contact place produced by the oxide scale is different. Therefore, it is necessary to keep the processing part away from the flame port during heating.

6, stainless steel sheet surface finish at the same time

If the surface finish is different, even if the same heating, the rough and fine surface of the oxide scale will be different. For example, in the place where the local defects have been cleaned and the place where they have not been cleaned, the condition of the oxide scale is different, which causes the uneven surface of the workpiece after pickling.

 

Comments

Post a Comment

Popular posts from this blog

POSCO Has Sought Import Assistance From Mexico

Image
It is understood that POSCO, South Korea's largest steelmaker, has sought import assistance from Mexico after failing to persuade the United States to lift its steel quota restrictions. According to the Korean steel giant, the company has asked the Mexican government to continue raising its import quota for cold-rolled steel sheets for automobiles over the next five years. Specifically, POSCO requires import quotas to increase from 547,500 tons this year to 585,000 tons next year, 606,000 tons in 2021, 633,000 tons in 2022 and 677,000 tons in 2023. In addition, Hyundai Steel, a Korean steelmaker, has made similar requests. The Mexican government is expected to respond within this year. The move follows Washington's announcement to lift a year-long steel and aluminum tariff on Mexico and Canada while maintaining quota restrictions on South Korean steel. To avoid imposing a 25% steel tariff from the United States, South Korea must keep its shipments below 70% of its annu...
Read more

Wanatiara Persada Rail Plant: $600 Million to be Operational by the end of the year

Image
Recently, Arif S. Tiammar, senior adviser to PT Wanatiara Persada, said that the company's refinery in Obi Island, North Maluku Province, has progressed 93%, the plant has a production capacity of 260,000 tons, nickel content of 15%. He said the nickel-iron refinery has four processing facilities and the first production line is now in operation, with the subsequent third expected to be operational in 12 months. Operationally, the refinery produces 2 million tons of ore per year. At the same time, the nickel mine at the iron refinery will be supplied by a mine owned by pt wanatiara persada, which has a production and operation mining licence (IUP OP). However, without too many reserves, ARIF said it would enter mining supplies from other mines. In terms of investment, the railway plant costs up to $600 million. According to PT Wanatiara Persada,'s Aneka Tambang Tbk railway plant aims to become one of three rail plants to operate in 2019. In addition to the Wanatiar...
Read more

Steel Export Tax Rebate May be cut to 9% or Cancelled

Image
  According to relevant reports, the Asian steel market has been talking about the possibility of China cutting the steel export tax rebate from the current 13% to 9%, or abolishing it altogether. Since the end of January, the industry has revealed more and more details. A dealer said that this may be in line with the direction of the central government's policy of reducing steel production capacity. Reducing the export tax rebate will force steel mills to rely more on the domestic market rather than increase production to meet the overseas market. Analysts believe that whether it is down or canceled, the impact is not small, all steel prices are bound to rise. This means that the domestic steel mills will no longer be the main players in the overseas market, and the export market will empty the supply gap, which will boost the spot price. This is indeed good news for global steel mills, because China's steel products are no longer the cheapest, which greatly reduces the pres...
Read more