Stainless steels are known as high-alloy steels. They contain about 4-30% of chromium. They are further divided into martensitic, austenitic, and ferritic steels. Another group of stainless steels are known as precipitation-hardened steels. They are a combination of austenitic and martensitic steels.
Grade 17-4 stainless steel is the most widely used steel of the precipitation hardening grade steels. It has high toughness, strength, and corrosion resistance.
The following table shows the chemical composition of grade 17-4 stainless steel.
||15.0 - 17.5
||3.0 - 5.0
||3.0 - 5.0
|Niobium, Nb (Columbium, Cb)
|Nb + Ta
||0.15 - 0.45
The physical properties of grade 17-4 stainless steel are given in the following table.
The mechanical properties of annealed grade 17-4 stainless steel are displayed in the following table.
|Hardness, Knoop (estimated from Rockwell C)
|Hardness, Rockwell C
|Hardness, Vickers (estimated from Rockwell C)
The following table outlines the thermal properties of grade 17-4 stainless steel.
|Thermal expansion co-efficient (@ 21-93°C/69.8-199°F)
|Thermal conductivity ( for condition H 900 at 149ºC. 22.6 W/mK for H 900 at 482ºC)
||124 BTU in/hr.ft².°F
Other designations that are equivalent to grade 17-4 stainless steel are listed in the following table.
||ASTM A693 (630)
||ASTM A705 (630)
||SAE J467 (17-4PH)
|ASTM A564 (630)
Fabrication and Heat Treatment
Grade 17-4 stainless steel can be machined in the annealed condition. This alloy has long and gummy chips. Before final hardening, post machining solution treatment is needed if it is machined in the H1150M condition.
Grade 17-4 stainless steel can be formed mildly.
Grade 17-4 stainless steel can be welded using common fusion and resistance welding methods. Oxyacetylene welding method is not preferred for welding this alloy.
Grade 17-4 stainless steel is soaked at 1038°C (1900°F) for 30 min and cooled below 16°C (60°F) for complete martensite transformation in the condition A. The condition A material is treated at 482°C (900°F) for 1 h followed by cooling. Solution treated material is soaked for 4 h at specific temperature in H925, H1025, H1075, H1100, and H1150 conditions followed by cooling in air.
Solution treated material is soaked at 760°C (1400°F) for 2 h in the H1150M condition followed by cooling. It is again heated at 620°C (1150°F) for 4 h followed by cooling.
Grade 17-4 stainless steel is forged at 1010°C (1850°F). Before performing this process, it is soaked at 1177°C (2150°F). Post-work solution treatment should be performed before final hardening.
Grade 17-4 stainless steel can be hot worked using common processes. It is treated at 1038°C (1900°F). Post-work solution treatment should be performed before final hardening.
Grade 17-4 stainless steel can be cold worked using common techniques in spite of its high initial yield strength.
Grade 17-4 stainless steel is annealed at 1038°C (1900°F) for 0.5 h followed by cooling rapidly.
Grade 17-4 stainless steel has high ductility, and can be formed using all conventional techniques. Powerful equipments are required for forming this alloy because it is stronger than the regular steel. Heavy-duty lubricants are used during cold working.
Grade 17-4 stainless steel is used in the following applications:
- Nuclear reactor
- Aircraft and gas turbines
- Oil field
- Chemical process components
- Paper mill