Heat treatment method for austenitic stainless steel bowl 5

Due to its high nickel content and austenitic single-phase structure at room temperature, it has high corrosion resistance with CR13 stainless steel, high plasticity and toughness at low temperature, room temperature and high temperature, as well as good cold work forming and weldability. However, the strength at room temperature is low, the intergranular corrosion and stress corrosion tendency are large, and the machinability is poor.

Austenite has no phase change when heated, so it cannot be strengthened by heat treatment. Heat treatment can only be carried out to improve the corrosion resistance of steel:

1) Solution treatment; The aim is to make the carbide sufficiently dissolved and retained in the austenite at room temperature, so that the single-phase austenite structure is obtained at room temperature, so that the steel has the highest corrosion resistance.

The heating temperature of solution treatment is generally high, between 1050-1100C, and the carbon content is appropriately adjusted. Due to the poor thermal conductivity of 18-8 stainless steel, it is not only necessary to be preheated and then quenched, but also has a long holding time during solution treatment (quenching heating). Special attention should be paid to preventing carburization during solution treatment.

Because the carburization will increase the intergranular corrosion tendency of 18-8 steel. The cooling medium is generally clean water. The solution treated microstructure is generally single-phase austenite, but stainless steels containing titanium, niobium, and molybdenum, especially when castings, also contain a small amount of ferrite.

The hardness after solution treatment is generally about 135hbs.

2) stress reduction annealing; In order to eliminate the residual stress after cold working, the treatment is carried out at a lower temperature. Generally, it is heated to 250-425C, and 300-350C is often used. For steels that do not contain titanium or niobium, it should not exceed 450C to avoid precipitation of chromium carbide and intergranular corrosion.

In order to eliminate the residual stress after welding and eliminate the susceptibility of the steel to stress corrosion, the treatment is generally carried out at a higher temperature. The heating temperature is generally not lower than 850C. Cooling method, for steel containing titanium or niobium, it can be cooled directly in air; For steels that do not contain titanium or niobium, they should be water-cooled to 500C and then cooled in air.

3) stabilization; In order to prevent the reduction of intergranular corrosion resistance of austenitic stainless steels such as titanium and niobium due to the reduction of TIC and NBC during welding or solution treatment, the stainless steel should be heated to a certain temperature (at which the chromium carbide is completely dissolved in the austenite, while the TIC and NBC are only partially dissolved) and then cooled slowly. During the cooling process, the carbon in the steel is fully combined with titanium and niobium to precipitate stable Tic and NBC without precipitating chromium carbides, thereby eliminating the intergranular corrosion tendency of 18-8 austenitic stainless steel, which is called stabilization.

18-8 stainless steel stabilized annealing, generally heated to 850-880C, kept warm for 2-6h, and then air-cooled or furnace-cooled.

Abstract]:According to the standard (JB T4730-2005) on the ultrasonic testing and quality classification of austenitic stainless steel butt welds, this paper explores the instrument adjustment before testing, and proposes a simple and practical method as a supplement.

Author Affilications]: Ningbo Special Equipment Inspection and Testing Center;

Body Snapshot]:

1 Introduction Due to the coarse and directional grain of austenitic welds, and the serious ultrasonic scattering and attenuation, it is generally considered that ultrasonic detection cannot be used. When the 4730 standard was revised in 2005, "Ultrasonic Testing and Quality Classification of Austenitic Stainless Steel Butt Welds" was added to Part 3 "Ultrasonic Testing", which provided a standard specification for the inspection of stainless steel welds in pressure equipment and played a guiding role in daily testing.

You make centrifuges, and the cylinder on the outside of my previous centrifuge was called a drum. Austenitic stainless steel should be annealed for stress relief after welding, and the annealing temperature should generally not exceed 400 degrees, otherwise it will produce sensitization and reduce corrosion resistance.

Whether the welding deformation of austenitic stainless steel can be shaped by low-temperature tempering.

No, hardening through heat treatment can only play a role when it is organized (such as martensitic stainless steel), the austenitic stainless steel matrix is all austenite, heat treatment will not cause changes in the structure, and the hardness will not change, and improper heat treatment temperature will also cause impurities to precipitate in the austenite grain boundaries to cause intergranular corrosion, reducing the grain boundary adhesion of the material, so austenitic stainless steel is generally not heat treated.

Increasing the hardness can be done through surface carburizing or nitriding, and grain refinement can also be achieved through deformation heat treatment, note that the deformation heat treatment here is not a general heat treatment, it is pre-deformed and then short-term heating and quenching to form fine grains.

1. Both austenitic and ferritic stainless steels can be heat treated.

2. Austenite is a laminar microstructure of steel, usually a non-magnetic solid solution with a small amount of carbon in -Fe, also known as Vostenite iron or -Fe. The name austenite comes from the British metallurgist William Chandler Roberts-Austen. Austenite has good plasticity, low strength, certain toughness, and no ferromagnetism.

3. Ferrite is an interstitial solid solution of carbon dissolved in -Fe, which is often represented by the symbol F. It has a body-centered cubic lattice, and its carbon-dissolving capacity is very low, and it can only dissolve carbon at room temperature, and the maximum carbon-dissolving capacity at 727 is. It is called ferrite or solid solution, denoted by or f, and is commonly used in phase diagram annotations, and f is commonly used in literature.

The austenite of the sub-eutectic component is precipitated by pre-eutectic to form ferrite.

Heat treatment is possible! The common heat treatment process of austenitic stainless steel is: austenitic stainless steel generally adopts solution treatment, that is, the steel is heated to 1050 1150, and then water cooled to obtain a single-phase austenitic structure.

There is no generally accepted consensus on the heat treatment process for ferritic stainless steels, but the most commonly used is annealing and softening. Someone has studied the heat treatment of ferritic stainless steel. The results of the study show that:

When the ferritic stainless steel solution treatment was treated, there was no obvious change in the structure below 900 °C, and its hardness changed slowly with the increase of temperature. Around 900, recrystallization occurs, and the hardness is significantly reduced; After heat treatment, the precipitate increases, the hardness increases, and the corrosion resistance is seriously reduced, that is, there is obvious 475 brittleness.

Yes. Austenite is called solution treatment, and ferrite is called annealing and softening treatment.

First of all, ferritic or austenitic stainless steel has no structural change when heating, heat preservation and cooling, so that there is no need for heat treatment, and it is also very important that it will appear after heat treatment"Sensitization"phenomenon, the sensitivity to stress corrosion increases, the anti-rust effect decreases, and it is easy to be damaged under the condition of stress, and the gains must not be compensated, of course, heat treatment is not done.

As for the solution treatment, it is very well understood, of course, there are alloying elements in stainless steel, and the content of alloying elements is quite high, which cannot be dissolved at room temperature, and the solution treatment is heated to the austenite, so that these alloying elements are well dissolved, and when cooled, these alloying elements will not precipitate, which is called supersaturation and dissolved into the matrix of ferrite or austenite, so that the overall performance is consistent, of course, the mechanical properties will decline, so we also need a treatment, Aging treatment, so that these oversaturated alloying elements in alloy carbides, alloy compounds and other forms of precipitation, the lost mechanical properties back, and better than the mechanical properties before the solution treatment, and the performance is still very uniform, there is no damage breakthrough point.

The reason why heat treatment changes the properties of steel is that the internal structure of the steel is changed by different heating, heat preservation and cooling methods, so as to obtain the desired properties. If there is no structural change during reheat treatment, the steel cannot be heat treated.

If stainless steel is composed of a single ferrite or austenite, there will be no structural change during heating, heat preservation and cooling, and of course, the performance will not change significantly, so it cannot be heat treated.

The difference between quenching treatment and solution treatment: both are heated and insulated and cooled quickly, but the strength, hardness and wear resistance increase after quenching, while the strength, hardness and wear resistance decrease after solution treatment. After solution treatment, the strength, hardness and wear resistance can be increased.

Stainless steel solution treatment is also a type of steel heat treatment process.

Solution treatment: It refers to the heat treatment process in which the alloy is heated to a high temperature single-phase zone and maintained at a constant temperature, so that the excess phase is fully dissolved into the solid solution and then quickly cooled to obtain a supersaturated solid solution.

The solubility of carbon in austenitic stainless steels has a great influence on temperature. When the chromium content drops below the corrosion resistance limit, there is a grain boundary poor chromium, which will produce intergranular corrosion, and can become a powder in severe cases. Therefore, austenitic stainless steels with intergranular corrosion tendency should be treated with solution heat treatment or stabilization.

Solution heat treatment: the austenitic stainless steel is heated to about 1100, so that the carbide phase is completely or basically dissolved, the carbon is dissolved in the austenite, and then quickly cooled to room temperature to make the carbon reach a supersaturated state. This heat treatment method is solution heat treatment.

Rapid cooling in solution heat treatment seems to be similar to the quenching of ordinary steel, but the 'quenching' at this time is different from the quenching of ordinary steel, the former is a softening treatment, and the latter is hardening. The latter also uses different heating temperatures to obtain different hardnesses, but it is less than 1100.

Stainless steel will change the metallographic structure after high temperature heat treatment. Heat treatment is a metal thermal processing process that heats, insulates and cools metal materials in a certain medium, and controls their properties by changing the metallographic structure on the surface or inside the material. Only the metallographic structure of the material is changed, while the chemical composition is not changed.

The solution treatment of austenitic stainless steel and the quenching treatment of steel have different purposes of heat treatment due to the different structures obtained.

The solution treatment of stainless steel is to obtain single-phase austenite structure, and the purpose is to improve the toughness of stainless steel; The quenching treatment of steel is to obtain martensitic structure, and the purpose is to improve the hardness of steel.

The working principle of tungsten argon arc welding is adopted, which uses the arc between the tungsten rod and the weldment of the non-melting electrode as the heat source to make the stainless steel plate self-fuse to form a weld. The electric plates and arc zone and the melted stainless steel are protected by argon gas, which isolates them from the air. Since argon is an inert gas, it does not react chemically with the metal and does not melt into the metal, so it can avoid the oxidation of the weld metal and the burning of alloying elements.

Make the welding process simple and easy to control. To this end, we have designed our own electronic control equipment to make the welded surface smooth and clean, without secondary processing, as long as polishing, you can achieve bright and traceless, and you can't find the weld. Argon protection is used in welding, it has low thermal conductivity, does not absorb heat at high temperatures, so the heat loss is small, and its working voltage is only 8-15 volts.

Without preheating, austenitic stainless steel has good weldability.

If possible, it is best to carry out post-welding treatment. In general, the weldability of stainless steel is poor, and heat treatment should be carried out, especially martensitic and ferritic stainless steel, and the correct pre-welding preheating and post-welding treatment are necessary conditions to ensure the welding quality.

Welding: also known as welding, bonding, is a manufacturing process and technology that joins metals or other thermoplastic materials such as plastics by heating, high temperature or high pressure. Welding achieves the purpose of bonding through the following three ways:

1. Heat the workpiece to be joined to partially melt it to form a molten pool, and the molten pool will be joined after cooling and solidifying, and the melt filler can be added to assist if necessary;

2. Separate heating of the solder with a low melting point, without melting the workpiece itself, connecting the workpiece by the capillary action of the solder (such as soldering and hard welding);

3. At a temperature equal to or lower than the melting point of the workpiece, supplemented by high pressure, superimposed extrusion or vibration, etc., the two workpieces can penetrate and bond with each other (such as forging welding and solid-state welding).

According to the specific welding process, welding can be subdivided into gas welding, resistance welding, arc welding, induction welding and laser welding and other special welding.

There are many types of energy** used in welding, including gas flames, arcs, lasers, electron beams, friction, and ultrasonics. In addition to being used in factories, welding can also be performed in a variety of environments, such as in the field, underwater, and in space. Welding can be dangerous to the operator wherever it is, so proper precautions must be taken when performing welding.

The possible injuries to the human body caused by welding include burns, electric shock, vision damage, inhalation of toxic gases, excessive ultraviolet radiation, etc.

Without preheating, austenitic stainless steel has good weldability. Whether you want post-treatment, it depends on the welding situation, unimportant parts, the deformation is not large, generally do not require post-processing, the cost of post-processing is not low. However, if the welding process is not up to standard, resulting in serious deformation of the weldment, it is necessary to carry out correction and post-heat treatment to relieve stress.