Details:
Ferritic low-temperature steel
Ferrite low-temperature steel general obvious toughness-brittle transition temperature, when the temperature is reduced to a critical (or interval) will be a sudden decrease of toughness. The appended drawings says carbon 0.2% carbon steel impact value and the relationship between temperature, the temperature change in-20 ℃ or so. Therefore, the ferrite steel in the transition temperature below should not be used, generally need to join Mn, Ni etc alloy elements, reduce the gap impurities, fine grains, control the size of the second phase in steel, shape and distribution etc, make ferritic steel toughness-brittle transition temperature decrease (see the strengthening of the metal). Ferrite low-temperature steel is divided into three categories according to the composition
(1) low carbon manganese steel
Low carbon manganese steel (C0.05 ~ 0.28%, Mn0.6 ~ 2%). Make Mn/C we 10, reduce oxygen, nitrogen, and sulfur and phosphorus and other harmful impurities, some still add a little aluminum, niobium, titanium, vanadium elements to fine grains. This kind of steel minimum temperature 60 ℃ use for-to the left.
(2) the low alloy steel
Low alloy steel. Main have low nickel steel (Ni2 ~ 4%), manganese nickel MuGang (Mn0.6 ~ 1.5%, Ni0.2 ~ 1.0%, Mo0.4 ~ 0.6%, 0.25% or C), nickel chrome MuGang (Ni0.7 ~ 3.0%, Cr0.4 ~ 2.0%, Mo0.2 ~ 0.6%, 0.25% or C). These kinds of strength higher than that of low carbon steel, use the lowest temperature up to-110 ℃ or so. China has developed several section of the nickel with low alloy steel temperature such as 09 Mn2V, etc.
(3) (high) alloy steel
(high) alloy steel. Main 6% Ni steel, steel, 36% 9% Ni Ni steel, of which 9% Ni steel is the cryogenic are widely used in steel. This kind of high nickel steel using temperature can be low to-196 ℃.
Austenitic low-temperature steel
Austenitic steel with high low temperature of low temperature toughness, generally not toughness-brittle transition temperature. According to the alloy component is different, can be divided into three series:
(1) Fe-Cr-Ni department
Fe-Cr-Ni department. Mainly for the 18-8 type cr-ni stainless steel acid. This steel low temperature toughness, corrosion resistance and technology were well, already different degree applied in all kinds of cryogenic (150 ~ 269 ℃) technology.
(2) the Fe-Cr-Ni-Mn and Fe-Cr-Ni-Mn-N department
Fe-Cr-Ni-Mn and Fe-Cr-Ni-Mn-N department. This kind of steel to replace some nickel manganese, nitrogen to stable austenitic. Nitrogen and the strengthening function, make steel with high toughness and very low magnetic conductance and stable austenitic organization, applicable to ultra-low temperature for no magnets (namely material magnetic conductance small). Such as 0 Cr21Ni6Mn9N and 0 Cr16Ni22Mn9Mo2 in-269 ℃ and without magnetic structure parts.
(3) Fe-Mn-Al department austenitic low temperature without magnets
Fe-Mn-Al department austenitic low temperature without magnets. China's development is the saving nickel chrome, new kinds, such as 15 Mn26Al4, such as part of the nickel chrome instead of austenitic steel, used to-196 ℃ the following extremely low temperature area. If better of this steel chemical resistance ability, still can expand their application scope.
Using range
Low-temperature steel in liquefied petroleum gas (LPG) in cryogenic self-tightening separation equipment, the vast majority of the lowest temperature 110 ℃ for-use, individual equipment for-150 ℃, respectively the low alloy steels, 3 ~ 6% nickel steel or 9% nickel steel. In air separation equipment, the minimum temperature of 196 ℃-use commonly 9% nickel steel or austenitic steel at low temperature. Working temperature 253 ℃ for-the liquid hydrogen production, storage and transportation equipment, working temperature 269 ℃ for-the YeHai equipment, shall be made in the structure of the organization of the stability of the austenite low-temperature steel. And some special equipment such as superconducting magnets or HTS motors, appropriate is used in the temperature of a stable work except the austenitic organization, but also to keep a very low magnetic conductance (μ) or lower than 1.01) of steel. Some high low temperature toughness of iron and nickel ni-based high-temperature alloy as A-286, Inconel718, InconelX-750, it is also used in need of high strength of low temperature equipment.
