Precipitation hardening stainless steel:
Add different types and quantities of strengthening elements based on the chemical composition of stainless steel. Through the precipitation hardening process, different types and quantities of carbides, nitrides, carbonitrides and intermetallic compounds are precipitated, which not only improves the strength of the steel but also maintains sufficient toughness. A type of high-strength stainless steel, referred to as PH steel.
Precipitation hardening stainless steel is divided into three types：
- Martensitic
- Semi-austenitic
- Austenitic
Introduction：
Precipitation hardening stainless steel, a type of stainless steel with high strength, high toughness and high corrosion resistance obtained by adding hardening elements alone or in combination to various stainless steels
Classification:
According to the content of the main alloying elements in the steel and the added hardening elements, it is divided into four categories:
- Martensitic precipitation hardening stainless steels generally contain 0.1% less carbon. Strengthening by adding hardening elements (copper, aluminum, titanium and aluminum, etc.) to make up for the lack of strength. The chromium content is generally higher than 17%, and an appropriate amount of nickel is added to improve corrosion resistance;
- Maraging stainless steel, the carbon content is not more than 0.03% to ensure the toughness, corrosion resistance, weldability and workability of the martensitic matrix, and the chromium content is not more than 12% to ensure corrosion resistance. In addition, the alloying element cobalt is added to further improve the heat treatment effect of the steel;
- Semi-austenitic, that is, transitional precipitation-hardening stainless steel, containing not less than 12% chromium. This type of steel with low carbon content and aluminum as its main precipitation hardening element has better comprehensive properties than martensitic precipitation hardening stainless steel;
- Austenitic precipitation hardening stainless steel is a stainless steel with stable austenite structure in both quenched state and aging state. It contains high nickel (higher than 25%) and manganese, and contains more than 13% chromium to ensure good corrosion resistance. Titanium, aluminum, vanadium or phosphorus are usually added as precipitation hardening elements, and trace amounts of boron, vanadium, nitrogen and other elements are added to obtain excellent comprehensive properties.
Characteristic:
Precipitation hardening stainless steel has comprehensive properties such as high strength, high toughness, high corrosion resistance, high oxidation resistance and excellent formability and weldability.
Typical grade:
- 0Cr17Ni4Cu4Nb
The steel is a martensitic precipitation hardening stainless steel, the Ms point is about 150°C, and the Mf point is below 30°C. Whether the martensitic transformation is complete or not is affected by the composition and cooling method. The copper in the steel is dispersed in the matrix in the form of very fine and dispersed ε phase to improve the strength. In H900 treatment, σb=1310MPa, σ0.2=1170MPa, δ5=10%, ψ=40%. The steel has good corrosion resistance, the corrosion resistance is better than that of general martensitic stainless steel, and it is similar to general austenitic stainless steel. It has good cutting properties, can be welded without preheating and can be partially annealed after welding. It is mainly used in the manufacture of corrosion-resistant and high-strength components such as jet engine compressor casings and large steam turbine final stage blades.
- 0Cr17Ni7Al
This grade is a semi-austenitic precipitation hardening stainless steel. It is a steel that is hardened by adding aluminum to the unstable austenitic steel of 0Cr17Ni7, and then undergoing martensitic transformation and precipitation of NiAl compounds. After RH950 treatment, σb=1580MPa, σ0.2=1470MPa, δ5=6%. The steel has good corrosion resistance in oxidizing acids, but poor corrosion resistance in non-oxidizing acids such as sulfuric acid and hydrochloric acid. The acid resistance after A or A1750 treatment is the best. On the other hand, the acid resistance after treatment with TH, RH, and CH deteriorated. The steel can be welded using the same welding process as austenitic stainless steel. If an electrode with the same composition as the base metal is used for welding, a large amount of delta ferrite will appear in the weld, resulting in a decrease in the toughness of the weld, so the electrode can be appropriately reduced in chromium or increased in nickel. Inert gas protection should be used during welding to prevent oxidation of aluminum in the electrode. In order to obtain good welding efficiency, the solution annealed weldments should be solution treated first, and then adjusted and aged. This type of steel is mainly used to manufacture aircraft shells, structural parts, pressure vessels and components of missiles, jet engine parts, springs, diaphragms, bellows, antennas, fasteners, measuring instruments, etc.
- 0Cr15Ni25Ti2MoVB
The steel is an austenitic precipitation hardening stainless steel, that is, an iron-nickel-based superalloy. Steel is not only in the solid solution state, but also in the aging state is a stable austenite structure. – Generally, the formation of intermetallic compounds in the steel achieves increased strength and improved high temperature performance. In the aging state σb=1035MPa, σ0.2=690MPa, δ=25%, ψ=40%. The steel has good high temperature strength, and the operating temperature can reach 600-700 °C. The high temperature yield strength below 650°C is similar to room temperature. Good low temperature toughness, but there are disadvantages such as low room temperature strength and poor welding performance.
Application:
It is widely used in cutting-edge industries and civil industries, such as typical precipitation hardening stainless steel 17-4P, which can be used to make structures that require corrosion resistance, wear resistance and high strength below 370 °C
