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PH Stainless Steel

PH Stainless Steel


Precipitation hardening stainless steel refers to adding different types and quantities of strengthening elements on the basis of the chemical composition of stainless steel, and precipitating different types and quantities of carbides, nitrides, carbonitrides and intermetallic compounds through the precipitation hardening process. , a type of high-strength stainless steel that not only improves the strength of steel but maintains sufficient toughness, referred to as PH steel. Precipitation hardening stainless steel can be divided into three categories: martensitic, semi-austenitic and austenitic according to the metallographic structure of its matrix.

Overview

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 grades

(1)0Cr17Ni4Cu4Nb steel

This steel is a martensitic precipitation hardening stainless steel with an Ms point of approximately 150°C and an Mf point 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 extremely fine and dispersed ε phase, thereby improving the strength. During H900 treatment, σb=1310MPa, σ0.2=1170MPa, δ5=10%, ψ=40%. This steel has good corrosion resistance, which is better than that of general martensitic stainless steel and similar to that of general austenitic stainless steel. It has good cutting performance, can be welded without preheating and does not require local annealing after welding. It is mainly used to manufacture corrosion-resistant and high-strength components such as jet engine compressor casings and large turbine final blades.

(2)0Cr17Ni7Al steel

This grade is a semi-austenitic precipitation hardening stainless steel. It is a steel type that adds aluminum to 0Cr17Ni7, an unstable austenitic steel, and then hardens it through 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. Acid resistance is best after treatment with A or A1750. The acid resistance becomes worse after treatment with TH, RH, and CH. This steel can be welded using the same welding process as austenitic stainless steel. If a welding rod 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. Therefore, the chromium can be appropriately reduced or nickel increased in the welding rod. Inert gas protection should be used during welding to prevent oxidation of the aluminum in the electrode. In order to obtain good welding efficiency, it is best to perform solution treatment on weldments after solution annealing, and then adjust and age them. This type of steel is mainly used to manufacture aircraft casings, structural parts, missile pressure vessels and components, jet engine parts, springs, diaphragms, bellows, antennas, fasteners, measuring instruments, etc.

(3)0Cr15Ni25Ti2MoVB steel

The steel is an austenitic precipitation-hardened stainless steel, an iron-nickel-based high-temperature alloy. Steel has a stable austenite structure not only in the solid solution state but also in the aging state. - Generally, intermetallic compounds are formed in steel to increase strength and improve high-temperature properties. In the aging state σb=1035MPa, σ0.2=690MPa, δ=25%, ψ=40%. This steel has good high-temperature strength and can be used at temperatures up to 600-700°C. The high temperature yield strength below 650℃ is almost the same as room temperature. It has good low-temperature toughness, but has shortcomings such as low room temperature strength and poor welding performance.


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