631 stainless steel belongs to semi-austenitic precipitation hardening stainless steel, which is a stainless steel with unstable austenite. 631 stainless steel is a solid solution state, also known as 17-7PH stainless steel. It is an austenitic structure at room temperature. After 631, it is 0Cr17Ni7Al in my country. 631 is a semi-austenitic precipitation hardening stainless steel, which is a stainless steel with unstable austenite. , this steel is in solid solution state, and it is austenite structure at room temperature. After cold working, cold treatment or heating to about 750 degrees for adjustment, austenite can be transformed into martensite, and then aging treatment can be formed on the martensite matrix. Precipitation of the second phase strengthens the steel. The role of Al is to form a precipitation hardening phase with other elements such as (Ni3Al). During the aging process, the cooling cannot be carried out rapidly, otherwise it is difficult to achieve the strengthening effect.

Chemical composition of 631 stainless steel

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Mechanical properties of 631 stainless steel

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Physical properties of 631 stainless steel

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Heat Treatment of 631 Stainless Steel

631 stainless steel is a precipitation hardening alloy that requires heat treatment to achieve maximum strength and hardness. Heat treatment consists of two steps: annealing and aging. Annealing is to increase ductility, and aging is to increase strength and hardness. Heat treatment parameters:

1) Solid solution, rapid cooling at 1000~1100°C;

2) Aging at 565°C, after solution treatment, keep at 760±15°C for 90 minutes, cool to below 15°C within 1 hour, keep for 30 minutes, then heat to 565±10°C for 90 minutes, and air-cool;

3) Aging at 510°C, after solution treatment, keep at 955±10°C for 10 minutes, air-cool to room temperature within 24 hours, cool to -73±6°C, keep for 8 hours, then heat to 510±10°C for 60 minutes, and air-cool.

It should be noted that the specific heat treatment process parameters (such as temperature, time and cooling method, etc.) will vary according to the specific stainless steel alloy composition and required properties, so sufficient physical property testing and design are required before heat treatment.

Corrosion resistance of 631 stainless steel

631 stainless steel is a high-strength low-carbon ferritic stainless steel with good corrosion resistance. Its corrosion resistance is mainly reflected in the following aspects:

Oxidation resistance: 631 stainless steel contains high chromium and aluminum elements, which can form dense chromium oxide and aluminum oxide films to effectively prevent the intrusion of oxygen, thereby improving the oxidation resistance of stainless steel.

Acid resistance: The chromium element in 631 stainless steel can combine with the oxygen in the acid medium to form a dense chromium oxide film to prevent further erosion of the acid medium, so it has good acid resistance.

Alkali resistance: The aluminum element in 631 stainless steel can form a dense aluminum oxide film in alkaline media, thereby improving the alkali resistance of stainless steel.

Salt corrosion resistance: 631 stainless steel has a high chromium content, which can form a solid chromium oxide film, making it have high salt corrosion resistance, and is suitable for use in salt corrosion environments such as seawater.

Processing of 631 stainless steel

Stainless steel 631 has the characteristics of high strength and toughness, so it can be used as a hard material suitable for mechanical equipment. Satisfactory machining results require rigid mounting and sharp cutting tools. The alloy can be machined in the annealed or aged condition.

Welding of 631 stainless steel

631 stainless steel is a high-strength, corrosion-resistant stainless steel material commonly used in the chemical, marine, and aerospace industries.

Welding of 631 stainless steel can use a variety of methods, such as gas tungsten arc welding (GTAW), gas metal arc welding (GMAW) and resistance welding. Preheating and post-weld heat treatment are recommended to avoid cracks and improve the mechanical properties of the weld.

631 stainless steel needs to be preheated before welding to reduce welding stress and risk of cold cracking. The preheating temperature is generally 100°C to 150°C. When welding, it is necessary to maintain an appropriate welding speed and welding current to avoid welding defects caused by overheating or excessive welding speed.

After the welding is completed, the welded joint needs to be post-treated, such as removing oxides, sanding, polishing, etc. This improves the surface quality and corrosion resistance of the weld.

The use of 631 stainless steel

Stainless steel is an alloy material with corrosion resistance, which is made of mixed alloys of iron, chromium, nickel and other elements. Among them, stainless steel 631 is a kind of stainless steel with high mechanical strength, which is widely used in the following fields:

Aerospace field: Stainless steel 631 has high strength and good corrosion resistance, and is often used in the manufacture of various parts of aerospace equipment, such as aircraft seat rods, bolts, springs, etc.

Chemical industry: The high temperature resistance and corrosion resistance of stainless steel 631 make it suitable for the manufacture of various chemical equipment, such as reactors, pipelines, storage tanks, etc.

Automobile industry: Stainless steel 631 is often used in the manufacture of automotive engine parts, such as cylinder heads, intake valves, exhaust valves, etc. Its high temperature strength and heat resistance allow the engine to work in high temperature environments.

Food processing industry: Stainless steel 631 meets hygienic standards and will not produce any pollutants to food, so it is widely used in the manufacture of food processing equipment, such as food storage tanks, food delivery pipelines, etc.

Pharmaceutical field: The chemical stability and corrosion resistance of stainless steel 631 make it an ideal material for pharmaceutical equipment manufacturing, such as pharmaceutical storage tanks, pipelines, etc.

In conclusion, stainless steel 631 plays an important role in many fields, and its high strength, temperature resistance and corrosion resistance make it an ideal structural ma