20 # steel

C4 steel (00 cr14ni14si4) is a kind of ideal type of nitric acid resistant high silicon low carbon stainless steel, 85 national corrosion material during the period of a major breakthrough.

With high purity aluminum, high silicon cast iron as well as ordinary stainless steel,

C4 steel has the following advantages:

A, no blade corrosion after welding, and has better ability to resist corrosion holes and good ability to resist stress corrosion;

Second, C4 gangsu good toughness, increased the safety and reliability, to avoid the pure titanium in fuming nitric acid firing and explosion danger;

Three, C4 steel is far better than the high purity aluminum corrosion resistance, and has compared the mechanical properties of high silicon cast iron in the way of the welded joint with parent metal mechanical properties and corrosion resistance.

C4 steel used for the indirect method (magnesium nitrate method) in nitric acid unit of the pipe, valve, condenser, pumps, etc. Use effect is very good. C4 steel quality as: 00 cr14ni14si4 ultra-low carbon austenitic stainless steel, with excellent intercrystalline and stress corrosion resistance.

Nitric acid is an important chemical raw material, it is widely used many departments of national economy. Nitric acid production and use of nitric acid, nitric acid corrosion problems. Nitric acid is a strong oxidizing acid, even the dilute nitric acid has a strong oxidizing. Easily in the stainless steel in dilute nitric acid passivation, thus has good corrosion resistance. Almost all of the stainless steel in dilute nitric acid have good corrosion resistant ability. The 18-8 Cr - Ni austenitic stainless steel, such as 0 cr19ni9, 00 cr19ni11, 0 cr18ni11ti (or 1 cr18ni9ti) has both excellent dilute nitric acid resistance, and good mechanical, processing and forming, welding and other comprehensive performance, so in 65% or less of dilute HNO3, this are dosage the biggest, the most widely application scope of stainless steel. At the same time, do not contain Mo of duplex stainless steel, such as 00 cr25ni6ti, 00 cr25ni6n have also made very good use effect.

This century since the 70 s level of nitric acid stainless steel, mainly refers to contain 0.015% or less C, Si 0.10% or less, B 10 PPM or less, P 0.02% or less, Mo 0.2% or less of 00 cr19ni11 and C 0.02% or less, Si 0.20% or less, P 0.020% or less, Mo 00 cr25ni20 steel of 0.2% or less. In dilute HNO3 65% or less, they are not only resistant to intergranular corrosion of sensitized state significantly improve the performance of intergranular corrosion (see), and general corrosion resistance performance has improved significantly. For example, in the boiling 65% HNO3, nitrate level 18-8 steel solid solution state corrosion rate is only 0.06 0.14 mm/a, sensitization state is only 0.30 mm/a.

With the increase of the concentration of nitric acid, especially when the concentration in azeotropic concentration above 68.4%, average 18-8 steel can not meet the requirements. When the concentration of 85% or less, often can choose Cr25Ni20 stainless steel. But no matter how high concentration, due to nitric acid peroxidation and containing Cr passivation of stainless steel itself, only 18-8 Cr25Ni20 steel and steel corrosion will severely. As a result, high Si Cr - Ni stainless steel, such as containing Si ~ 4% 0 cr13sinbre, 1 cr17ni11si4a1ti, 00 cr14ni14si4 (Ti), 00 cr17ni14si4 (Ti, Nb), 00 cr20ni24si4ti etc. Often used in the temperature of 80 ℃ or less of fuming nitric acid and nitric acid. High temperature, you may need to choose Si content to ~ 6% of stainless steel, such as 00 cr17ni17si6.