1、Hot rolled stainless steel plate

A hot rolled stainless steel plate is a stainless steel plate manufactured with hot rolling technology. It is a thin sheet if the thickness is not greater than 3mm, and it is a thick plate if greater than 3mm. They are used to make corrosion-resistant parts, containers and equipments for the industry of chemistry, petroleum, mechanics, and ship manufacturing, etc. with the category and product numbers as follows:

     1．Austenite section steel

(1)1Cr17Mn6Ni15N；(2)1Cr18Mn8Ni5N；(3)1Cr18Ni9；(4)1Cr18Ni9Si3；(5)0Cr18Ni9；
(6)00Cr19Ni10；(7)0Cr19Ni9N；(8)0Cr19Ni10NbN；(9)00Cr18Ni10N；(10)1Cr18Ni12；
（11) 0Cr23Ni13；(12)0Cr25Ni20；(13) 0Cr17Ni12Mo2；(14) 00Cr17Ni14Mo2；
(15) 0Cr17Ni12Mo2N；(16) 00Cr17Ni13Mo2N；(17) 1Cr18Ni12Mo2Ti；(18) 0Cr18Ni12Mo2Ti；
(19) 1Cr18Ni12Mo3Ti；(20) 0Cr18Ni12Mo3Ti；(21) 0Cr18Ni12Mo2Cu2；
(22) 00Cr18Ni14Mo2Cu2；(23) 0Cr19Ni13Mo3；(24) 00Cr19Ni13Mo3；(25) 0Cr18Ni16Mo5；
(26) 1Cr18Ni9Ti；(27) 0Cr18Ni10Ti；(28) 0Cr18Ni11Nb；(29) 0Cr18Ni13Si4

    2．Austenite--ferrite section steel

（30）0Cr26Ni5Mo2；（31）00Cr18Ni5Mo3Si2；

    3．Ferrite section steel

（32）0Cr13Al；(33) 00Cr12；(34)1Cr15；(35)1Cr17；(36)1Cr17Mo；(37)00Cr17Mo；
(38)00Cr18Mo2；(39)00Cr30Mo2；(40)00Cr27Mo

    4．Martensite section steel

（41）1Cr12；（42）0Cr13；（43）；1Cr13；（44）2Cr13；（45）3Cr13；（46）4Cr13；
（47）3Cr16；（48）7Cr17

    5．Precipitation hardening section steel

（49）0Cr17Ni7Al

2、Cold rolled stainless steel plate

   A cold rolled stainless steel plate is a stainless plate manufactured with cold rolling technology. It is a thin sheet if the thickness is not greater than 3mm, and a thick plate if greater than 3mm. They are used to make corrosion-resistant components, pipes and containers for petroleum and chemical industry, medical devices, and ship equipments, etc. with the category and product numbers as follows:

    1．Austenite section steel
    (1) 2Cr13Mn9Ni4(2) 1Cr17Ni7(3) 1Cr17Ni8, and others are the same as in the section of hot rolling (29 categories).

    2．Austenite--ferrite section steel
(1) 1Cr18Ni11Si4AlTi (2) 1Cr21Ni5Ti, and others are the same as in the section of hot rolling (2 categories).

    3．Ferrite section steel
00Cr17, and others are the same as in the section of hot rolling (9 categories).

   4．Martensite section steel
1Cr17Ni2, and others are the same as in the section of hot rolling (8 categories).

   5.Precipitation hardening section steel：the same as in the section of hot rolling.

3、Introduction to Ferrite, Austenite, and Martensite steel

As we all know that solid state metal and alloy are all crystals, that is to say, the atoms inside the metal or alloy are arranged in a pattern. Normally there are 3 modes of arrangement, namely: body centered cubic lattice structure, face centered cubic lattice structure, and hexagonal closely-packed lattice structure. Metals are composed of poly-crystals; the poly-crystal structure is formed during the metal crystallization process. Iron in iron-carbon alloy has two lattice structures：it is α—iron with body centered cubic lattice structure under 910℃，and Υ—iron with face centered cubic lattice structure above 910℃。If carbon atoms push their way into the lattice of iron atoms without damaging the original iron lattice structure，a matter called solid solution will be formed. It is called ferrite steel if carbon is dissolved into α—iron to form a solid solution, with a extremely low carbon-dissolving capacity and a maximum solubility not exceeding 0.02%, while it is called austenite steel if carbon is dissolved into Υ - iron to form a solid solution, with a relatively higher carbon-dissolving capacity and a maximum solubility up to 2%. Austenite steel is the high temperature phase of the iron-carbon alloy.

At high temperatures, steel is in the form of austenite, while turns into an unstable super-cooled austenite when super-cooled to below 727℃. If it is super-cooled to below 230℃ at a extremely large cooling speed, the carbon atoms inside of the austenite would have no chance for diffusing, therefore, the austenite will be directly turned into an α solid solution super-saturated with carbon, which is called martensite. Due to the super-saturation of carbon, the strength and hardness of martensite are increased, while the plasticity is decreased, and the brittleness is increased.

Stainless steel becomes corrosion resistant due to chromium. Experiments have shown that the corrosion resistant ability of steel will not be enhanced significantly unless it’s chromium content exceeds 12%, therefore, usually chromium content in stainless steel should not be lower than 12%. Increased chromium content will also affect the structure of steel. If chromium content is high while carbon content is low, chromium will help iron and carbon be equilibrated. In the diagram, the Υphase region will diminish, or even disappear. This type of stainless steel is of a structure of ferrite, and there will be no phase change when heated, therefore, it’s called ferrite stainless steel.

When chromium content is relatively low (but still higher than 12%), and carbon content is relatively high, the alloy is extremely easily turned into martensite when the temperature of the alloy drops from a high temperature, therefore, this type of steel is called martensite stainless steel.

Nickel can extend the Υ phase region, so that steel will have a structure of austenite. If nickel content is so high that steel would have a structure of austenite even at room temperatures, then this type of steel is called austenite stainless steel.

4、A rough correlation between steel numbers in Japan and China of the commonly used stainless steel

2．The suffix NO．1 at the back of steel numbers stands for that it undergoes heat treatment, acid rinsing, or similar treatments after hot rolling; NO．2 means that undergoes heat treatment, acid rinsing, or related treatments after cold rolling; NO．2B means that it undergoes heat treatment, acid rinsing, or similar treatment after cold rolling, and finally it undergoes cold rolling to get a certain degree of finish. Example: 304NO．1 stainless steel plate stands for hot rolled stainless steel plate with a steel number of 304. Another example: 321-2B means cold rolled stainless steel with a steel number of 321, the surface is required to undergo heat treatment, acid rinsing, or similar treatment after cold rolling, and finally it undergoes cold rolling to get a certain degree of finish.

5、Application of stainless steel in different areas

1．During the period of approximately 40 years from 1960 to 1999, the production volume of stainless steel in western countries increased rapidly from 2,150,000 tons to 17,280,000 tons, a increase of about 8 folds, with averaged annual growth rate of about 5．5%. Stainless steel is mainly used for the industry of kitchen, electrical appliance, transportation, architecture, and construction, etc. It’s mainly used for wash bowl and electrical or gas water heater in the field of kitchen equipments, and for roller of fully automatic laundry machines in the field of electrical appliance. The demand of stainless steel is expected to increase further from an environmental protection point of view for the benefits of energy saving and recycling.

In the field of transportation, it’s mainly used for the exhaust system of vehicles and automobiles, and the stainless steel used for the exhaust system of every unit of vehicle is around 20 - 30 kg. The annual demand worldwide of it for this purpose is about 1,000,000 tons, which is the greatest application area of stainless steel.

In the field of architecture, the demand increases rapidly recently, e.g., around 5,000 tons of stainless steel exterior decoration materials were used for the protection apparatus for the subway stations in Singapore. Another example is that the stainless steel used for architecture has increased by about 4 folds since 1980 inJapan, which is mainly used for roof, interior and exterior building decoration material, and structural material. In the 1980’s, paint-free roof materials of the type of 304 used in the coastal area of Japan were replaced by pre-painted stainless steel for the sake of anti-rust. Highly corrosion resistant ferrite stainless steel with a high Cr content exceeding 20% was developed and used as roof material in the 1990’s, in the mean time, all kinds of surface finish machining technology were developed for the sake of aesthetics.

In the field of construction, stainless steel is used for the water-drawing tower of dams in Japan. In cold areas of Europe and America, salt is sprayed over the surface of express ways and bridges to prevent ice forming, which will speed up the corrosion of steel bars, therefore, stainless steel bars have to be used. In the recent three years, stainless steel bars have been used for road construction in North America in approximately 40 construction projects, with a consumption volume of 200 – 1,000 tons for every project. In the future, demands of stainless steel in the markets of this field will increase for sure.
   
2．The key to expand the application of stainless steel in future lies in environmental protection, longer service lifetime, and the popularization of IT.

In the aspect of environmental protection: firstly, from the atmospheric protection point of view, the demand of heat-resistant, high-temperature corrosion-resistant stainless steel will increase, which can be used to make the dioxin-suppressing high-temperature garbage burning equipment, LNG power generating devices, and coal-consuming highly efficient power generating devices. Furthermore, stainless steel will also be used to make the shell for the batteries for the fuel battery powered automobiles which is estimated to be put into practice at the beginning of the 21st century. From the water protection point of view, demand of stainless steel with excellent corrosion-resistant property will also increase, which can be used for water treatment equipments such as water supplying and draining equipments.

With respect to longer service lifetime: the use of stainless steel is increasing for the existing facilities in Europe such as bridge, express way, and tunnel, and it’s estimated that this trend will be widespread all over the world. Furthermore, the lifetime of ordinary household buildings in Japan are especially short, merely around 20-30 years; therefore, the treatment of used materials becomes a big problem. Recently, buildings with a target lifetime of 100 years have been built; the demand of such materials with excellent durability will increase. Long lifetime materials will decrease the amount of construction and architecture waste materials, however, in the mean time, from the earth environmental protection point of view, it is necessary to research on novel methods in the designing stages to decrease the maintenance cost.

With respect to the popularization of IT: functional materials for hardware of instruments play important roles in the development and popularization of IT. Demand of high-precision, quality functional materials is huge, e.g., stainless steel is used to make components of cell phones and microcomputers due to its excellent properties such as high strength, good elasticity, and being non-magnetic, etc.., which extended the application field of stainless steel. Furthermore, stainless steel with good degree of cleanness and durability also plays important roles in the field of equipments to manufacture semiconductors and all kinds of base plates.

Stainless steel has excellent properties which many other metal materials don’t, and it’s also a recyclable material with excellent durability; therefore, it will be widely used in different kinds of fields with the development of new technology in the future.