Why does stainless steel also rust?
Why does stainless steel also rust? When stainless steel tubal surface appears Brown rusty spot (dot) when, people feels amazed greatly: Think " stainless steel is rustless, rusting is not stainless steel, the likelihood is steel appeared character problem " . Actually, this is a kind of when lack understanding to stainless steel one-sided wrong view. Stainless steel also can rust below certain condition.
The capacity that stainless steel has counteractive air to oxidize -- do not become rusty namely quality, the ability that in also having the medium that containing acerbity, alkaline, salt at the same time, corrodes therefore -- be able to bear or endure namely corrode sex. But its fight the size that corrodes ability is chemistry of therewith steel qualitative itself composition, add protect condition, use condition and environmental medium type and of the change. Be like 304 steel tube, in the air of dry cleanness, have fight rustily ability admirably absolutely, but move it littoral area, in the sea fog that contains many salt portion, can rust very quickly; And 316 steel tube are behaved good. Accordingly, not be a kind of any stainless steel, fall in any environments can anti-corrosive, rustless.
Stainless steel is to rely on its surface to form a paper-thin and what stabilize compactly stably is rich chromic oxidation film (defend film) , prevent oxygen atomic to continue infiltration, continue to oxidize, and obtain fight rustily ability. Once have some kind of reason, this kind of film sufferred be destroyed ceaselessly, atom of the oxygen in air or liquid is met the iron in ceaseless infiltration or metal is atomic ceaselessly analyse leaves come out, form loose ferric oxide, metallic surface also gets ceaselessly rustily. The form that film of this kind of surface is destroyed is very much, see more in daily life have a few kinds as follows:
Surface of 1. stainless steel retains the attachment that accumulating the dust that contains other tantalum or alien metal grain, in humid air, the condenser water between attachment and stainless steel, become both a small cell repeatedly, caused electrochemistry reaction, diaphragm is destroyed, say call electrochemistry is corroded.
Conglutinate of surface of 2. stainless steel has machine content juice (the dish that be like melon, water in which noodles have been boiled, phlegmy etc) , below circumstance of oxygen having water, make organic acid, long an organic acid is right of metallic surface corrode.
Conglutinate of surface of 3. stainless steel contains acerbity, alkaline, salt kind material (if decorate splash of the buck of wall, limewater) , cause isolated corrosion.
4. is in the air that has pollution (if contain the air of nitrogen of carbon of a large number of sulfide, oxidation, oxidation) , treat condenser water, form place of fluid of vitriolic, nitric acid, acetic acid, cause chemistry to corrode.
Small stick person
To ensure metallic surface is permanent and shining, not by rustily, we suggest:
1) often must undertake to decorating stainless steel surface cleanness is swabbed, purify attachment, eliminate cause got-up outside element.
2) seaside area should use 316 material qualitative stainless steel, 316 material can resist seawater is corroded character.
Some stainless steel are in charge of chemical composition to cannot accord with corresponding state level on 3) market, short of 304 material ask character. Because this also can be caused,rust, this chooses to have the product of credit manufacturer seriously with respect to need user.
Note 1:
316 material qualitative stainless steel (18Cr-12Ni-2.5Mo) , because add Mo, reason its are able to bear or endure corrode sex, be able to bear or endure sex of atmospheric corrosion t and high temperature strength are particularly good, can use below the condition of exacting cruel; Machine sclerotic sex to actor or actress (without magnetism) .
Apply at the manufacturing device such as equipment, chemical, dye, papermaking, oxalic acid, fertilizer is being used in seawater; Illuminate picture, lever of establishment of food industry, foreland, rope, CD, bolt, nut
Note 2:
304 material are qualitative (18Cr-8Ni) , regard a kind of utility as extensive steel, have be able to bear or endure goodly corrode sex, hear resistance, microtherm intensity and physical characteristic; Punch, bend it is good to wait for hot-working sex, without phenomenon of heat treatment sclerosis (without magnetism, use Wen Chong - 800 ℃ of 196 ℃ ～ ) .
Apply at domestic articles for use (1, crock of 2 kinds of tableware, ambry, indoor cop, water heater, boiler, bath) , car a replacement (windscreen rain is brushed, muffler, mould) , medical treatment appliance, building materials, chemical, food industry, agriculture, shipping component
