Stainless steels precipitation-hardening alloys

Stainless steels are the most widely used alloys for heat and corrosion resistance and low temperature toughness. Wrought stainless steels are named for their metallurgical structure martensitic, ferritic, austenitic, duplex, and precipitation hardening. Cast stainless steels groups are heat resistant and corrosion resistant. 

Intergranular hydrogen cracking in a precipitation-hardening martensitic stainless steel has been suppressed by the addition of palladium. Heat treatment of the alloy produces submicrometer-sized PdAl precipitates that act as reversible traps and are thought to reduce the amount of hydrogen at prior austenite grain boundaries [134]. 

Hardness of Precipitation-Hardening Austenitic Stainless Steels Machinability Rating of Wrought Coppers and Copper Alloys Hardness of Wrought Aluminum Alloys Hardness of Wrought Titanium Alloys at Room Temperature... 

There are three t) es of precipitation-hardenable (pH) stainless steels martensitic, austenitic, and semiaustenitic. The relationship between these alloys is shown in Figure 5.1. The semiaustenitic steels are supplied as an... 

The austenitic stainless steels resist hydrogen effects, but martensitic and precipitation-hardening alloys may be susceptible to both hydrogen stress cracking and chloride stress cracking. 

The enhanced strength and corrosion properties of duplex stainless steels depend on maintaining equal amounts of the austenite and ferrite phases. The welding thermal cycle can dismpt this balance therefore, proper weld-parameter and filler metal selection is essential. Precipitation-hardened stainless steels derive their additional strength from alloy precipitates in an austenitic or martensitic stainless steel matrix. To obtain weld properties neat those of the base metal, these steels are heat treated after welding. 

Austenitic stainless steels are the most corrosion-resistant of the three groups. These steels contain 16 to 26 percent chromium and 6 to 22 percent nickel. Carbon is kept low (0.08 percent maximum) to minimize carbide precipitation. These alloys can be work-hardened, but heat treatment will not cause hardening. Tensile strength in the annealed condition is about 585 MPa (85,000 Ibf/in"), but workhardening can increase this to 2,000 MPa (300,000 Ibf/in"). Austenitic stainless steels are tough and ducdile. 

The precipitation-hardening stainless steels are proprietary grades hardened by both the martensitic transformation and precipitation hardening. These contain higher amounts of chromium (16-17% ) and nickel (4- 7%) than (he 12% chromium ferritic alloys. These steels are normally used at lower temperatures than the 12% chromium ferritic superalloys. 

For the pressure of 825 bar forgings of high strength ferritic-martensitic material have to be used. These steels are normally not suitable for welding. Because of special corrosion requirements and in order to avoid the use of liners, a martensitic precipitation-hardening stainless chromium steel was used for the cylinder and the covers. The clamps were made of a low alloy high strength steel. 

---