Precipitation-hardenable stainless

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. 

Table 3.12. Examples of Precipitation Hardening Stainless Steels...

ASTM A747 Precipitation hardening stainless SEW 410 G5121... 

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. 

In some cases testing may be needed to identify a suitable material. For example, low concentrations of CO2 (250 ppm) in anhydrous hydrazine accelerate the decomposition of hydrazine in stainless steel. Long-term storage tests of hydrazine propellants in 17-7 PH stainless steel and AM350 precipitation-hardened stainless steel at 50°C for about three years showed no pressure rise or hydrazine decomposition253. 

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. 

Precipitation hardening stainless steels must never be used in the as-purchased annealed condition. They are not only soft and weak, but they lack toughness and will fail prematurely. 

Figure 4-8. Precipitation hardening stainless steels are the strongest group of stainless steels.

Precipitation hardening stainless steels are those alloys ending with the sufBx PH (i.e., precipitation hardening), for example, 17 PH (17Cr-4Ni-4Cu) (UNS S17400). They are hardenable by heat treatment. They are most often used for springs, valve stems, the internals of rotating equipment. 

The martensitic and precipitation-hardening stainless steels are more susceptible to hydrogen embrittlement than are the austenitic alloys. The susceptibility of these stainless steels is sensitive to microstructure and strength level. Figure 22 shows the resistance to cracking for a martensitic (type 410) stainless steel and some precipitation-hardening stainless steels in an H2S-saturated solution [174]. The low resistance of type 410 stainless steel is typical for most... 

R. R. Gaugh, Sulfide stress cracking of precipitation-hardening stainless steels. 

Ferritic stainless steel, precipitation-hardening stainless steel, chromium, brass, bronze, copper... 

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