Should I choose Annealed, Hot Rolled or Strain Hardened Condition of Nitronic 50?

Q: What is the difference between Hot Rolled and Strain Hardened Nitronic 50?

Hot Rolled achieves its strength through controlled rolling temperature and dynamic recrystallisation, reaching up to 105ksi (725N/mm2) in smaller sizes. Strain Hardened uses cold drawing through a die at room temperature to reach a minimum yield strength of 125ksi (862N/mm2), at the cost of reduced elongation.

Q: Why is the strain hardened condition mainly used for smaller diameters?

Drawing is practically restricted to bars below about 2 1/2" diameter, because at larger sizes the bar's strength becomes too high to draw further. For smaller diameters, the strain hardened condition also gives more consistent properties and lower hardness variation through the bar than hot rolling.

Q: What is Nitronic 50 High Strength typically used for?

Nitronic 50 High Strength, in either Hot Rolled or Strain Hardened condition, is most commonly used to manufacture valve stems, where its combination of high yield strength, excellent impact toughness and good corrosion resistance is particularly valuable.

Nitronic^® 50 is available in three conditions - Solution Annealed, Hot Rolled and Strain Hardened. The annealed condition machines most easily, while the high-strength hot rolled and strain hardened conditions give progressively higher yield strength. Which to choose depends on the balance you need between machinability, strength and section size.

Nitronic 50 is a higher-performance austenitic stainless steel that provides approximately twice the yield strength of regular 3xx series stainless steels, with improved corrosion performance. It is widely used in a variety of marine and industrial applications.

Solution Annealed

The Solution Annealed condition is the easiest to machine. It is supplied with a minimum yield strength of 55ksi (380N/mm2). It retains its excellent impact toughness and corrosion resistance, but its lower mechanical strength limits some applications. Its ease of machining suits more intricate components, including parts for connectors and pump and valve trim. Sales of Nitronic 50 Annealed are far lower than Nitronic 50 High Strength, because the machinability comes with the compromise of either relative cost or performance (strength, corrosion resistance) versus alternative alloys.

Hot Rolled (High Strength)

Nitronic 50 High Strength is offered in either the Hot Rolled or Strain Hardened condition, depending on the diameter. Larger diameters can attain the higher strength while still falling below the maximum hardness level (HRC<35) specified in NACE MR-1075 (ISO 15156), through hot rolling at lower than normal temperatures to influence the microstructure.

Hot rolling at high temperatures results in dynamic recrystallisation, whereby the microstructure is broken down by the rolling action but recrystallises under the favourable thermodynamic conditions of high temperature. This gives a more refined and uniform microstructure, with good toughness and consistency through the bar. Hot rolling at lower temperatures reduces the extent of recrystallisation, effectively imparting a degree of cold working that increases strength but reduces elongation slightly.

A hot rolled product therefore achieves a minimum yield strength of 60ksi (415N/mm2) above 3" diameter, 75ksi (515N/mm2) below 3" diameter, and 105ksi (725N/mm2) below 2" diameter. Hot rolling at lower temperatures, so-called warm working, achieves 105ksi (725N/mm2) across a wider dimensional range.

Strain Hardened

Strain hardening is a form of cold working, so it greatly increases the strength of the alloy but at the expense of elongation, achieving a minimum yield strength of 125ksi (862N/mm2). It is done by drawing the hot-rolled bars through a die to a smaller diameter at room temperature. Generally, the greater the amount of cold working, the greater the increase in yield strength. Drawing is practically restricted to bars of less than 2 1/2" diameter, as at this size the strength of the bar becomes too high to draw any further. For smaller diameters, we have found the strain hardened condition achieves more consistent properties and lower through-bar hardness.

Thanks to its excellent impact toughness and good corrosion resistance, one of the most common applications for Nitronic 50 High Strength is the manufacture of valve stems.

We carry a comprehensive stock of Fermonic^® 50 (XM-19, UNS S20910, Nitronic 50, 1.3964) in sizes from 3/4" (18.9mm) to 10" (254mm) diameter.

Condition	Size range	Min yield (ksi)	Min yield (N/mm²)
Solution Annealed	All sizes	55	380
Hot Rolled	Above 3"	60	415
Hot Rolled	Below 3"	75	515
Hot Rolled (warm worked)	Below 2"	105	725
Strain Hardened	Below 2 1/2"	125	862

Frequently asked questions

Which condition of Nitronic 50 is easiest to machine?

The Solution Annealed condition is the easiest to machine. It has a minimum yield strength of 55ksi (380N/mm2) and retains excellent impact toughness and corrosion resistance, which suits it to intricate components such as connector parts and pump and valve trim, at the cost of lower strength.

What is the difference between Hot Rolled and Strain Hardened Nitronic 50?

Hot Rolled achieves its strength through controlled rolling temperature and dynamic recrystallisation, reaching up to 105ksi (725N/mm2) in smaller sizes. Strain Hardened uses cold drawing through a die at room temperature to reach a minimum yield strength of 125ksi (862N/mm2), at the cost of reduced elongation.

Why is the strain hardened condition mainly used for smaller diameters?

Drawing is practically restricted to bars below about 2 1/2" diameter, because at larger sizes the bar's strength becomes too high to draw further. For smaller diameters, the strain hardened condition also gives more consistent properties and lower hardness variation through the bar than hot rolling.

What is Nitronic 50 High Strength typically used for?

Nitronic 50 High Strength, in either Hot Rolled or Strain Hardened condition, is most commonly used to manufacture valve stems, where its combination of high yield strength, excellent impact toughness and good corrosion resistance is particularly valuable.

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