17-4 PH stainless steel, also known as SAE Type 630 steel and UNS S17400 steel, is a precipitation-hardened variety of stainless steel that is known for its hardness, durability, corrosion resistance, high tensile and yield mechanical properties and elongation. Barron Industries specializes in 17-4 PH stainless steel, and provides a wide array of services. Read on to learn more about this type of stainless steel, or call us today to learn more about our services.
17-4 PH Stainless Steel Hardness Properties
17-4 PH stainless steel has many unique characteristics. Hardness is one of them. 17-4 PH stainless steel can be age-hardened at temperatures from 900 – 1350 degrees Fahrenheit and achieve hardness levels from 26 to over 40 on the Rockwell “C” scale, with ultimate tensile strength properties ranging from 115,000 – 180,000 PSI. The uses for a corrosion resistant grade of stainless steel that can be hardened to those levels and properties is very broad across the spectrum of defense, aerospace, marine and petrochemical applications where lightweight, high-strength and corrosion resistance is needed.
How We Harden Stainless Steel
Barron Industries achieves varying hardness of 17-4 PH stainless steel using a method called precipitation hardening. This treatment involves heating the stainless steel castings up to 900-1350 degrees Fahrenheit for several hours following its high temperature homogenization or solution heat treat cycle and allowing it to cool to room temperature. This process produces “precipitates” in the metal matrix which stabilizes the steel’s crystalline structure.
The time in which the metal is kept at an elevated temperature is called “aging.” It is crucial that the metal ages for a specific amount of time dependent on the desired hardness and mechanical properties desired.
Equating Hardiness into Mechanical Properties
A steel with a Rockwell level of 20 may have an 80,000 PSI tensile strength, while 17-4 PH stainless steel with a Rockwell level of 40 may have a tensile strength of 180,000 PSI, almost 2 and a half times the strength of regular carbon steel. Tensile properties describe how much force it takes to break the material. Tensile is the force that’s applied at which the material breaks. Yield strength is also important because something will bend or yield before it breaks and that’s typically a lower number. The relationship between the tensile (when it breaks) and the yield ( when it starts to bend ) can be measured in the form of elongation—which is typically between 3 and 30 percent depending upon what grade of steel is used.
Typically the higher the tensile and hardness, the lower the elongation, and the lower the tensile and yield, the higher the elongation. Carbon steels can be bent and molded very easily, with 30-40 percent elongation. A bar of mild steel can be bent 180 degrees around a mandrel, but 17-4 PH hardened would break because it does not possess the same ductility or elongation as mild steel. Engineers choose a material depending on the application and how much ductility and elongation is needed. In the case of 17-4, you can get over 15 percent elongation if you heat treat the part at 1,100 Degrees Fahrenheit or with an H1350M over aging cycle.