Three Functions of Solution Treatments
Posted: 08/21/2017 09:53:04 Hits: 26
Why do stainless steel pipes and pipe fittings need to have solution treatments?
We often soften austenitic stainless steel by the solution treatment; generally, stainless steel pipes and pipe fittings are heated from 950 to 1150℃; after some heat preservation time, carbide and various alloying elements are fully and evenly dissolved in austenite and then are quickly hardened and cooled; there is no enough time for carbon and other alloying elements to precipitate; in this way, the pure austenite structure is obtained, which is known as the solution treatment.
Three functions of solution treatments
1. Make organization and composition of steel pipes uniform, which is particularly important for raw materials; because rolling temperatures and cooling rates of wire rods' each section are different, the structure becomes inconsistent.
At high temperatures, the atom is more active and the sigma phase dissolves; the chemical composition tends to be uniform and the uniform homogeneous structure is obtained after rapid cooling.
2. Eliminate the work hardening in order to facilitate the cold working.
Through the solution treatment, the crooked lattice recovers; extended and broken grains will crystalize again; internal stress will be eliminated; tensile strength of steel pipes will decrease and elongation will increase.
3. Restore inherent corrosion resistance of stainless steel.
The cold working can cause precipitation of carbide and lattice defects, which will make corrosion resistance of stainless steel poor. Corrosion resistance of steel pipes is restored to the best condition after the solution treatment.
For stainless steel pipes, the three elements of the solution treatments are temperature, heat preservation time and cooling velocity. The solution temperature is mainly determined by chemical composition.
In general, the solution temperature should be increased accordingly for the stainless steel pipes made of various kinds of alloy and high content of alloy, especially for stainless steel pipes made of steel with high content of manganese, molybdenum, nickel and silicon. Only by improving the solution temperature, can these alloys be dissolved and the effect of softening be reached.
Stainless steel is rustless and corrosion resistant because of the formation of chromium-rich oxidation film or passivation film on its surface. Stainless steel's properties of being rustless and corrosion resistant are relative.
The experiment shows that when steel is in atmospheres, water or oxidizing media like nitric acid, corrosion resistance of steel will increase due to the increasing of the steel's chromium content. When chromium content gets to a certain percentage, corrosion resistance of steel will mutate, that is, changing from being easy to rust to antirust and from being easily corroded to corrosion resistant.
We often soften austenitic stainless steel by the solution treatment; generally, stainless steel pipes and pipe fittings are heated from 950 to 1150℃; after some heat preservation time, carbide and various alloying elements are fully and evenly dissolved in austenite and then are quickly hardened and cooled; there is no enough time for carbon and other alloying elements to precipitate; in this way, the pure austenite structure is obtained, which is known as the solution treatment.
Three functions of solution treatments
1. Make organization and composition of steel pipes uniform, which is particularly important for raw materials; because rolling temperatures and cooling rates of wire rods' each section are different, the structure becomes inconsistent.
At high temperatures, the atom is more active and the sigma phase dissolves; the chemical composition tends to be uniform and the uniform homogeneous structure is obtained after rapid cooling.
2. Eliminate the work hardening in order to facilitate the cold working.
Through the solution treatment, the crooked lattice recovers; extended and broken grains will crystalize again; internal stress will be eliminated; tensile strength of steel pipes will decrease and elongation will increase.
3. Restore inherent corrosion resistance of stainless steel.
The cold working can cause precipitation of carbide and lattice defects, which will make corrosion resistance of stainless steel poor. Corrosion resistance of steel pipes is restored to the best condition after the solution treatment.
For stainless steel pipes, the three elements of the solution treatments are temperature, heat preservation time and cooling velocity. The solution temperature is mainly determined by chemical composition.
In general, the solution temperature should be increased accordingly for the stainless steel pipes made of various kinds of alloy and high content of alloy, especially for stainless steel pipes made of steel with high content of manganese, molybdenum, nickel and silicon. Only by improving the solution temperature, can these alloys be dissolved and the effect of softening be reached.
Stainless steel is rustless and corrosion resistant because of the formation of chromium-rich oxidation film or passivation film on its surface. Stainless steel's properties of being rustless and corrosion resistant are relative.
The experiment shows that when steel is in atmospheres, water or oxidizing media like nitric acid, corrosion resistance of steel will increase due to the increasing of the steel's chromium content. When chromium content gets to a certain percentage, corrosion resistance of steel will mutate, that is, changing from being easy to rust to antirust and from being easily corroded to corrosion resistant.
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