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冷轧不 锈钢工艺流程及特点 Process and characteristics of cold-rolled stainless steel

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【摘要】:
所谓冷 轧不锈钢板带生产,不是单纯的“冷轧”。在冷轧前还要退火、酸洗、修磨等,冷轧后还要平整、矫直、剪切、垛板等,所以实 际上是从热轧卷开始直到生产出冷轧成品的全过程。   由于不 锈钢的特性和对产品质量的特殊要求,冷轧生 产工艺具有下列特点:   ①不锈钢 是一种高合金钢,轧制变形抗力较大。为了进行高效率、高精度的轧制,应采用刚性大的轧机,一般采用多辊冷轧机。   ②带钢在 可逆式轧机上冷轧时,缠绕在卷取机
  所谓冷 轧不锈钢板带生产,不是单纯的“冷轧”。在冷轧前还要退火、酸洗、修磨等,冷轧后还要平整、矫直、剪切、垛板等,所以实 际上是从热轧卷开始直到生产出冷轧成品的全过程。
 
  由于不 锈钢的特性和对产品质量的特殊要求,冷轧生 产工艺具有下列特点:
 
  ①不锈钢 是一种高合金钢,轧制变形抗力较大。为了进行高效率、高精度的轧制,应采用刚性大的轧机,一般采用多辊冷轧机。
 
  ②带钢在 可逆式轧机上冷轧时,缠绕在 卷取机上的头尾部分得不到压下,被切掉成为废品。为改变 这种状况以提高成材率,带钢两 端在轧前都要焊接引带;另外,如果热 轧卷重量太小时,为提高 轧制效率和成材率,钢卷还 需预先并卷焊接;在连续 退火和酸洗机组上,由于是连续作业,钢带头 尾连接也需要焊接。所以,焊接是 不锈钢生产不可缺少的环节。但是,不锈钢 的焊接不同于普通钢,比一般钢难焊得多;特别是 有些焊缝还需经受压下,对焊接 质量的要求也严格得多。因此,特殊的 焊接工艺也是不锈钢冷轧带钢生产的一个特点。
 
  ③不锈钢生产过程中,原料(热轧卷)要退火,冷轧过 程中要中间退火,最终成品还要退火,故退火 是生产中的重要环节。而不锈钢的种类很多,各种钢的属性不同,热处理的目的、方法和 要求都不同于一般,有一套 独特的工艺制度。
 
  ④冷轧不 锈钢是一种高级钢材产品,对表面 质量的要求十分严格,不仅不 允许残留前工序带来的冶金缺陷,而且不 允许有冷轧加工过程造成的明显缺陷。为此,生产过 程中采取了一系列消除和防护的措施。例如:为消除 热轧的氧化铁皮,热轧带 钢要喷丸处理和酸洗;为消除 坯料带来的缺陷和冷轧、热处理后造成的缺陷,带钢往 往要在修磨机组上修磨;为保证 冷轧后的表面质量,对轧辊 的研磨有非常严格的要求;为了防 止生产过程中擦划伤,要求各 机组的钢卷卷紧、卷齐,而且冷 轧前后的许多机组卷取时都要在钢卷的层间垫上工艺纸;另外,在容易 产生擦划伤的操作和设备上也采取了一些特殊防护措施;为了得到良好的、均匀的表面光泽,成品退火后还要酸洗,有特殊 要求的光亮板还要进行保护气氛退火;为保护成品的表面,有的产 品表面还要覆膜等等。总之,冷轧不锈钢的生产,是一个 精工细作的工艺过程,这是其 他钢种不可比拟的。
 
  ⑤不锈钢 的精整也不同于普通钢,有一些特殊要求,例如:平整工 序既要改善板形,还采用光洁度很高(麻面板除外)的轧辊,生产出光滑的2B钢板,对于铁 素体钢还要通过控制平整的压下量(或延伸率)来改善 钢板的成形加工性能,这实际 上是一种调质轧制。不锈钢由于钢质较硬,同时对 平整度要求严格,必须用 强力矫直机矫直,而且不 同厚度的产品往往需用不同的矫直方法。不锈钢 冷轧产品通常以成卷和切板两种方式交货,有的还需要分条交货。因此,现代化 的不锈钢冷轧厂要分别设置纵切和横切机组。
 
  ⑥冷轧不 锈的生产是多机组联合作业,工序平 衡和工序管理十分重要,必须有 一个强有力的生产调度系统,才能保 证持续地优质生产。另外,冷轧不 锈钢厂的设备是比较复杂的,机组多,高、精、尖设备多,涉及到机、电、仪表自动化、热工等 各个方面的技术,搞好设 备管理是提高生产水平和产品质量的根本保证。
 
  冷轧不锈钢工艺流程
 
  不锈钢 带的生产工艺与一般冷轧带钢生产工艺的区别在于不锈钢板带在冷轧前必须先经退火和在生产过程中必须随时保持带钢表面的洁净,以提高 成品率和抗腐蚀性能。
 
  不锈钢 带的生产工艺流程大致如下:热轧带钢(坯料)一退火,碱、酸洗一 检查修磨一冷轧一退火,碱、酸洗一 平整一抛光一剪切一检查分类一包装一入库。
 
  铁素体 钢和马氏体钢的退火时间较长,目的是 便于再结晶和溶解碳化物。通常在罩式炉中退火,退火温度约800℃,保温2~6h。铁素体 钢要在空气中迅速冷却,以防脆化。马氏体 钢不允许快速冷却,以免引 起过大的内应力及硬化裂纹。奥氏体 钢在连续炉中加热温度为1000~1100℃,在水中 或空气中迅速冷却。
 
  退火后 的带钢先经抛丸处理,打碎表面氧化铁皮,经刷洗后进入酸洗槽,彻底清 除氧化铁皮和使表面钝化。一般用 硝酸或硫酸进行酸洗。硝酸溶液温度为20~55℃,硫酸溶液温度为50~70℃。
 
  不锈钢 带坯的退火和酸洗一般在退火酸洗机组中进行。
 
  酸洗后 的带钢经检查后,在带式 修磨机上整修表面缺陷,然后送冷轧机轧制。不锈钢属于难变形钢,冷轧时 容易产生加工硬化,特别是 多道次低压缩率轧制时更为明显。不锈钢 带一般在四辊轧机和多辊轧机上轧制,如采用偏八辊轧机(MKW轧机)和二十辊轧机等。对于较 易轧制的奥氏体钢,每道次压缩率不超过25%,每轧程 的总压缩率不超过75%。对于碳 含量较高的马氏体钢,每道次压缩率为15%,每轧程 总压缩率不大于50%。
 
  一个轧程完成后,需经中间退火酸洗,消除冷轧加工硬化(再结晶退火)。对于奥氏体钢,加热温度为1050~1080℃。对于铁 素体和马氏体钢,加热温度为800℃左右。加热后在水、空气或蒸汽中淬冷。在热处 理过程中产生的铁皮在盐浴炉中氧化和疏松,以利酸洗。
 
  酸洗后 需对带钢表面进行检查,并在修 磨机上清除缺陷。成品不 锈钢带进行光亮退火,即在无 氧化气氛中作最后一次再结晶退火。通常采 用分解氨做保护气体。
 
  经过光亮退火后,一般不 再进行研磨和抛光,以保持 已获得的带钢表面粗糙度。平整的 目的在于改善带钢表面质量,同时也 可改善带钢的板形和消除屈服平台。平整时 的压缩率一般不超过2%。为了获 得极其光洁的带钢表面,在平整 过程中轧辊应经常抛光。
 
  为了提 高不锈钢带的抗腐蚀性能,对于某 些特殊品种的不锈钢带还要进行研磨和抛光。一般采用湿式研磨(用油和乳化液),研磨时 要防止由于不锈钢导热性能差而产生的灼斑或裂纹。抛光工 序由抛光和擦净两部分组成。一般用 乳化液做抛光剂。为防止带钢表面划伤,整个工 艺过程中所有与带钢接触的辊子表面必须十分光洁,或采用包胶辊。卷取时,必须在 每层间垫上纸带。成品收 集更需要每层间垫纸,以保护 表面不致相互擦伤。
 
The so - called cold - rolled stainless steel strip production, is not a simple "cold - rolled". Before cold rolling, annealing, pickling, grinding, etc., and after cold rolling, leveling, straightening, cutting, pilling, etc., so in fact from the hot rolling roll until the production of cold rolling products.
 
 
Due to the characteristics of stainless steel and the special requirements for product quality, the cold-rolling process has the following characteristics:
 
 
Stainless steel is a kind of high alloy steel with high deformation resistance. In order to carry out high efficiency and high precision rolling, a large rigid rolling mill should be adopted.
 
 
In the cold rolling process of a reversible mill, the end and end of the end of the string are cut off and become waste. In order to change this condition and improve the rate of finished product, both ends of strip steel should be welded with the lead band before rolling. In addition, if the weight of the hot rolled coil is too small, in order to improve the rolling efficiency and the finished material rate, the steel coil shall be prerolled and welded. In the continuous annealing and pickling unit, the steel head and tail connection also need to be welded because of continuous operation. Therefore, welding is an indispensable link in stainless steel production. However, the welding of stainless steel is different from that of ordinary steel. In particular, some welds still need to undergo pressure, and the quality of welding is much more strict. Therefore, special welding technology is also a feature of stainless steel cold-rolled strip steel production.
 
 
In the process of production of stainless steel, the raw material (hot rolled coil) should be annealed, the intermediate annealed during cold rolling and the final product annealed. Therefore, annealing is an important link in production. There are many kinds of stainless steel, different properties of steel, different purposes, methods and requirements of heat treatment are different from the general, a set of unique process system.
 
 
(4) cold-rolled stainless steel is a kind of advanced steel products, the surface quality requirement is very strict, not only does not allow residue before process of metallurgical defects, and there is no obvious defects caused by cold rolling process. Therefore, a series of elimination and protection measures have been taken in the production process. For example, in order to eliminate hot rolled oxidized iron sheet, hot rolled strip steel needs shot blasting and pickling. In order to eliminate the defects caused by the blank and the defects caused by cold rolling and heat treatment, the strip steel is often to be ground on the grinding machine. In order to ensure the surface quality after cold rolling, there are very strict requirements for roll grinding. In order to prevent scratches and scratches in the production process, it is required that the steel coils of each unit be tightly wound and even coiled, and many units before and after cold rolling should be filled with process paper between layers of steel coils. In addition, some special protective measures have been taken on the operation and equipment which are prone to scratch. In order to get a good, even surface gloss, the finished products after annealing must be pickling, there are special requirements of the bright plate to protect the atmosphere annealing; To protect the finished surface, some of the product surface also covered with film and so on. In a word, the production of cold-rolled stainless steel is an elaborate process, which is incomparable to other kinds of steel.
 
 
(5) the finishing of stainless steel is different from ordinary steel, there are some special requirements, such as: flat process should not only improve the strip shape, and also the finish is very high, with the exception of pits plate roll, produce smooth 2 b plates, for ferritic steel and by controlling the reduction of the flat (or elongation) to improve the forming performance of the steel plate, it is actually a conditioning rolling. Stainless steel is hard in quality and strict in flatness. It must be straightened by a strong straightener. Stainless steel cold-rolled products are usually rolled and cut in two ways, some of which require separate delivery. Therefore, the modern stainless steel cold rolling mill should set up longitudinal cutting and cross cutting units respectively.
 
 
The production of cold rolling non-rust is a joint operation of multiple units. Process balance and process management are very important. A strong production scheduling system is needed to ensure continuous high-quality production. In addition, cold-rolled stainless steel factory equipment is relatively complex, units, high, fine, sharp equipment, involved in machine, electric, instrument automation, thermal, and other aspects of technology, better improve the level of production and equipment management is the fundamental guarantee of product quality.
 
 
Cold rolled stainless steel process flow
 
 
Stainless steel belt production technology and the difference between general cold-rolled strip steel production technology of stainless steel strip in front of the cold rolled, must first after the annealing and in the process of production must keep the strip surface is clean, in order to improve the yield and corrosion resistance.
 
 
Stainless steel belt production process is roughly as follows: hot rolled steel strip (blank) an annealing, alkali, acid pickling a check grinding, cold rolled annealed, alkali, acid pickling a smooth, polished shear a check classification, packaging warehousing.
 
 
Ferritic steel and martensite steel have a long annealing time, with the aim of facilitating recrystallization and dissolution of carbides. Usually in the bell type annealing furnace, annealing temperature of about 800 ℃, insulation 2 ~ 6 h. Ferrite steel should be cooled rapidly in the air to prevent embrittlement. Martensite steel is not allowed to cool quickly to avoid excessive internal stress and hardening cracks. Austenitic steel in the continuous furnace heating temperature is 1000 ~ 1100 ℃, rapid cooling in the water or air.
 
 
After annealing, the strip is processed by shot blasting, and the surface oxidized iron sheet is broken. After brushing, it enters the pickling tank, and completely removes the oxidized iron sheet and passivates the surface. Generally, it is pickling with nitric acid or sulfuric acid. Nitrate solution temperature is 20 ~ 55 ℃, the sulfuric acid solution temperature is 50 ~ 70 ℃.
 
 
Annealing and pickling of stainless steel strips are generally carried out in annealing pickling unit.
 
 
After the pickling strip is inspected, the surface defects are repaired on the belt mill and then rolled by the cold mill. Stainless steel is hard to deformation of steel, cold rolling process hardening is easy to occur, especially in the multi-pass low compression rate rolling more obvious. Stainless steel bands are generally rolled on four-high and multi-high rolling mills, such as partial eight-high rolling mill (MKW rolling mill) and 20-high rolling mill. For easier rolling austenitic steel, the compression rate per pass shall not exceed 25% and the total compression rate per roll shall not exceed 75%. For martensite steel with high carbon content, the compression rate per pass is 15%, and the total compression rate per roll is not more than 50%.
 
 
After the completion of a rolling process, the intermediate annealing pickling is required to eliminate cold rolling hardening (recrystallization annealing). For austenitic steel, the heating temperature is 1050 ~ 1080 ℃. For ferrite and martensite steel, the heating temperature is 800 ℃ or so. Quench in water, air or steam after heating. During the heat treatment process, the iron sheet is oxidized and loose in the salt bath furnace to facilitate pickling.
 
 
The surface of strip steel shall be inspected after pickling and defects shall be removed on the grinding machine. The finished stainless steel band is bright annealed, that is, the last recrystallization annealing is performed in the atmosphere without oxidation. Ammonia is usually decomposed as a protective gas.
 
 
After bright annealing, grinding and polishing are generally not carried out to maintain the obtained surface roughness of strip steel. The purpose of leveling is to improve the surface quality of strip steel, but also to improve the shape of strip steel plate and eliminate the yield platform. The compression rate during leveling is generally no more than 2%. In order to obtain extremely smooth surface of strip steel, roll should be polished frequently during leveling.
 
 
In order to improve the corrosion resistance of stainless steel belts, some special types of stainless steel belts have to be ground and polished. Generally, wet grinding (oil and emulsifying liquid) is used to prevent burning spots or cracks caused by poor thermal conductivity of stainless steel. The polishing process consists of two parts: polishing and cleaning. Emulsion is usually used as a polish. In order to prevent the surface of strip steel from scratch, the surface of all rollers in contact with strip steel must be very smooth, or rubber roller should be used. Paper tape must be padded between each layer when rewinding. The collection of finished products requires interlayer paper to protect the surface from abrasion.

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