Bright Annealing Technology of Thin Wall Stainless Steel

1. Elimination of work hardening to obtain a satisfactory metallographic arrangementLight annealing furnace is mainly used for stainless steel products in the maintenance atmosphere of heat treatment. When the performance requirements are not used together, the request for the metallographic arrangement after the light annealing is different, and the technology of the light heat treatment is also different. 300 series austenitic stainless steel typical heat treatment technology is solution treatment. During the heating process, the carbides are dissolved into the austenite and heated to 1050-1,150 °C. For a short time so that all the carbides are dissolved in the austenite and then rapidly cooled to below 350 °C. To obtain a supersaturated solid solution one-way austenitic arrangements. The key to this heat treatment technique is rapid cooling, which requires the cooling rate to reach 55 °C / s and rapidly pass through the carbide remelt temperature zone (550-850 °C). Insulation time to try to be short, otherwise coarse grains, affecting the appearance of finish.

400 series ferritic stainless steel heating temperature is relatively low (about 900?), and more use of slow cooling to obtain annealing softening arrangements. Martensitic stainless steel annealing

method used, but also the choice of sub-quenching and tempering method of treatment.

From the above we can see that 300 series and 400 series stainless steel in the heat treatment system vary greatly, in order to obtain qualified metallographic arrangements, to request light annealing furnace cooling section equipment has great conditioning. Therefore, the modern leading light annealing furnace, the cooling section is usually used in the selection of strong convection cooling, set up three cooling sections, can regulate air flow alone. Along the width of the strip is divided into three sections, the air flow diversion conditioning strip width direction of the cooling rate, the control plate stainless steel cold-rolled strip heat treatment is another crucial question is the request of the entire strip width, length. The arrangement is very uniform. Muffle light annealing furnace selection of large-scale muffle tube, muffle tube from outside the uniform arrangement of heated air spiral around, the strip uniform heating. But to ensure that the strip along the length of the uniform arrangement, we must adhere to the strip in the furnace speed unchanged. Therefore, before and after the modern vertical light heat treatment furnace can be equipped with a fine adjustment of the roller tension adjustment equipment. Not only does it make the import and export speed of steel strip satisfied with the heat treatment speed request, it is not influenced by the empty set or full set of the looper quantity, and it is necessary to establish and finely adjust the tension of the strip steel according to the plate shape condition of the strip steel, request.

2. Obtain the appearance of non-oxidative lightBright annealing, is the H2 maintenance atmosphere on the strip heat treatment. To reach the request of the BA board, it is necessary to very strictly control the furnace maintenance atmosphere, try to avoid oxidation. H2 maintenance atmosphere oxidation is how the attack? The main alloy components of stainless steel are Fe, Cr, Ni, Mn, Ti, Si and so on. In the annealing temperature range, oxidation of Fe and Ni is not the primary question. However, the oxidation intervals of Cr, Mn, Si and Ti are just within the heating temperature range. It is the oxidation of these alloying elements that affect the strip's apparent brightness. In particular, the oxidation of chromium strip appearance of chromium, will reduce the corrosion resistance of stainless steel. When Cr content is 17% ~ 18% and Ti content is 0.5%, it is necessary to lower the dew point of H2 below -60? to avoid the oxidation of Cr and Ti in the heating range of 800? ~ 1150?.

In addition, how to maintain the purity of the gas in the furnace is also questionable. In this regard, the muffle seal is good, and will not attack such as electric heating furnace pollution of the maintenance atmosphere, providing a more purely environmental space. In addition, vertical furnace strip entrances and exits are located at the bottom of the furnace, the furnace pressure is stable, so compared with the horizontal furnace, the risk of air entering much smaller. But bright annealing furnace import and export of sealing boxes, strip delivery section, the tension conditioning roller and top guide roller box should be guaranteed to reach the parts per million (ppM level) of the sealing request, so that oxygen, water vapor can not enter the maintenance of gas can not escape.

A worker from a steel pipe company, which is located in China.