Super Alloy Marinox 22 (UNS S20910)

Topics Covered

Introduction
Chemical Composition
Physical Properties
Other Designations
Fabrication and Heat Treatment
     Machinability
     Forming
     Forging
     Welding
     Annealing
     Hardening
Applications

Introduction

Super alloy Marinox 22 is an austenitic, nitrogen strengthened steel. Its corrosion resistance matches that of grade 316 stainless steel, but also possesses greater strength.

Marinox 22 can be readily fabricated and remains non-magnetic even after rigorous forming operations. In many cases, Marinox 22 outperforms grades 316 and 317 with nearly double the yield strength.

The following sections will discuss in detail about super alloy Marinox 22.

Chemical Composition

The chemical composition of Marinox 22 is outlined in the following table.

Element Content (%)
Chromium, Cr 20.5 - 23.5
Nickel, Ni 11.5 - 13.5
Manganese, Mn 4-6
Molybdenum, Mo 1.5 - 3
Silicon, Si 1 max
Nitrogen, N 0.2 - 0.4
Niobium, Nb 0.1 - 0.3
Vanadium, V 0.1 - 0.3
Carbon, C 0.06 max
Phosphorus, P 0.04 max
Sulfur, S 0.03 max
Iron, Fe Remainder

Physical Properties

The physical properties of Marinox 22 are tabulated below.

Properties Metric Imperial
Density 7.8 g/cm3 0.283 lb/in3

Other Designations

Equivalent materials to Marinox 22 are tabulated below:

ASTM A193 (B8R, B8RA) ASTM A194 (B8R, B8RA) ASTM A249 (XM-19) ASTM A269 (XM-19) ASTM A276
ASTM A182 (XM-19) ASTM A240 (XM-19) ASTM A312 (XM-19) ASTM A336 (XM-19) ASTM A403 (XM-19)
ASTM A412 (XM-19) ASTM A479 (XM-19) ASTM A580 (XM-19) ASTM A813 (TP XM-19) DIN 1.3964

Fabrication and Heat Treatment

Machinability

Super alloy Marinox 22 can be machined using the common processes. Slow speeds, generous quantity of resulfurized lubricant and constant feeds are essential for machining this alloy. The speeds and feeds can match that of stainless grades 316 or 317. The chips tend be tough and stringy and it is recommended that curlers or breakers are used.

Forming

Super alloy Marinox 22 can be formed using any of the conventional methods. The springback tends to be greater for this alloy than with standard austenitics and hence care should be to provide appropriate forming forces. It is recommended that process annealing be performed to remove stresses caused by this alloys' high work hardening rate. In case of intermediate annealing, this alloy has to be heated to 1065°C (1950°F).

Forging

Forging of super alloy Marinox 22 can be performed by heating to 1093°C (2000°F), soaking to equalize, and then heating to 1176°C (2150°F). This process should be followed by annealing so as to regain optimum corrosion resistance.

Welding

Welding of super alloy Marinox 22 can be performed using all the traditional welding methods such as gas tungsten arc, gas metal arc and submerged arc methods. It is recommended that a filler should have matching chemistry to enhance strength and resistance to intergranular attack. Pre-heating is not required with this material.

Annealing

Annealing of this material can be performed by soaking at 1037-1121°C (1900-2050°F) and then rapidly quenching in air or water.

Hardening

Super alloy Marinox 22 hardens only by cold work.

Applications

Marinox 22 is chiefly used found in applications requiring high strength and corrosion resistance such as fasteners, boat shafting, marine hardware, pumps and valves.

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