445M2 Stainless Steel – The Ideal Alternative to 316 Stainless Steel – Applications and Properties by Austral Wright Metals

Topics Covered

Background

How Does 445M2 Stainless Steel Differ from 316 Stainless Steel

Benefits of 445M2 Stainless Steel over 316 Stainless Steel

Fabrication of 445M2 Stainless Steel Compared to 316 Stainless Steel

445M2 Stainless Steel

Applications of 445M2 Stainless Steel

Availability of 445M2 Stainless Steel

Fabrication Using 445M2 Stainless Steel

Weldability of 445M2 Stainless Steel

Corrosion Resistance of 445M2 Stainless Steel

Properties of 445M2 Stainless Steel

Chemical Composition of 445M2 Stainless Steel

Typical Mechanical and Physical Properties of 445M2 Stainless Steel

445M2 Stainless Steel Case Studies

Stainless Steel Security Screens

Stainless Steel Walling, Roofing, Guttering and Downpipes

Summary of 445M2 Stainless Steel

Background

Marine grade stainless steel 316 has been around for a long time. Now there’s an alternative, that’s even better – grade 445M2 from Austral Wright Metals. Developed in Japan, with a successful track record in Australasia, 445M2 offers real advantages over 316.

How Does 445M2 Stainless Steel Differ from 316 Stainless Steel

Unlike 316, 445M2 has a ferritic microstructure, and a higher content of the corrosion resisting element, chromium.

Benefits of 445M2 Stainless Steel over 316 Stainless Steel

That gives grade 445M2 some big technical benefits over grade 316 such as:

         Better resistance to atmospheric corrosion & pitting corrosion in water containing chlorides

         Not subject to stress corrosion cracking, or intergranular corrosion when welded properly

         Much better working characteristics – much easier to cut, bend and fold

         Better thermal properties, giving less distortion in welding and requiring less tack welding

         Lower density, covering 3.5% more area at the same weight

Fabrication of 445M2 Stainless Steel Compared to 316 Stainless Steel

Grade 445M2 has excellent punchability, bendability and weldability, making it easy to fabricate. It fabricates like carbon steel, without the strong work hardening of austenitic stainless steels like 316, which make them hard to cut and bend.

445M2 Stainless Steel

Applications of 445M2 Stainless Steel

Typical applications of grade 445M2 are anywhere that 316 is used now.

Grade 445M2 is ideal for:

         Kitchen benchwork

         Food preparation equipment

         Street furniture

         Heat exchangers

         Solar panels

         Roofing

         Walling

         Rainwater goods.

In fact, anywhere that 316 is used for its corrosion resistance, 445M2 will perform better.

Availability of 445M2 Stainless Steel

Marine grade 445M2 is available as coil and sheet 1219 mm wide and 0.55, 0.7, 0.9, 1.2, 1.5, 1.6, 2.0, 2.5 and 3.0 mm thick – all 1219 mm wide. Ask us if you need narrower material. The standard finish is 2B, ask about the non-reflective 2DR finish if you want a lower gloss level for architectural applications.

Fabrication Using 445M2 Stainless Steel

Grade 445M2 is easier to work with than austenitic stainless steels such as 316: the much lower rate of work hardening gives lower forming loads, and less springback. Grade 445M2 also behaves like carbon steel in cutting operations: it gives cleaner cuts, with less distortion, and much better tool life.

These advantages have been crucial for the introduction of the grade to uses like roll formed roofing and cladding, and expanded metal. It is also very useful for perforating into acoustic screens etc.

Weldability of 445M2 Stainless Steel

         445M2 can be spot or seam resistance welded. Post heat treatment of the weld is not required.

         445M2 can be TIG or MIG welded. Pre or post heating or post weld heat treatment are not required.

         445M2 can be welded without filler metal. If filler metal is required, use 316L(Si)

         445M2 can be laser or plasma cut.

After welding, the full corrosion resistance of the surface can be restored by removing any scale and oxide colours mechanically or chemically. Best corrosion resistance is achieved by pickling to ensure the removal of the low chromium layer formed under the high temperature oxide during welding.

Pickling pastes are available: in common with other highly corrosion resistant grades, 445M2 should usually be pickled for a time towards the top of the recommended period.

Corrosion Resistance of 445M2 Stainless Steel

The world class Japanese steel mill, Nisshin Stainless Steel have formulated this grade carefully for good properties. The extra high chromium content (22%) and added molybdenum give excellent corrosion resistance. Then there’s a well balanced addition of small amounts of both niobium and titanium to protect the properties when the steel is welded.

And all heats of 445M2 are made with very low carbon content, well below the 0.03% carbon in the special low carbon 316L used for better welded corrosion resistance.

Corrosion Scientists use PREN (Pitting Resistance Equivalent Number) to compare the resistance of different grades to localised corrosion. With a typical PREN of 26, 445M2 has better corrosion resistance than 316 with a typical PREN of 25.

Figure. Pitting corrosion resistance of stainless steel 445M2 compared to 316 abd 305 stainless steels.

Properties of 445M2 Stainless Steel

Chemical Composition of 445M2 Stainless Steel

Table 1. The chemical composition of 445M2 stainless steel compared to 316 stainless steel.

 

Chromium

Molybdenum

Carbon

Nickel

Others

445M2

22.1%

1.2%

0.01%

-

Nb and Ti

316

18.2%

2.2%

0.5%

10%

-

Typical Mechanical and Physical Properties of 445M2 Stainless Steel

Table 2. The chemical composition of 445M2 stainless steel compared to 316 stainless steel.

Property

Units

445M2

316

Density

kg/m3

7750

7980

Yield stress

MPa

350

315

Tensile strength

MPa

520

560

Youngs Modulus

MPa

199000

193000

Elongation

%

30

55

Hardness

Hv

170

155

Thermal Conductivity

W/m.°C

22.5

13.9

Thermal Expansion

x10-6°C

10.0

16.0

Magnetism

-

Magnetic

Non-Magnetic

445M2 Stainless Steel Case Studies

Stainless Steel Security Screens

Austral Wright Metals worked closely with the Lockers Group to develop expanded metal mesh for security doors and windows. The existing aluminium mesh gave excellent performance inland, but had limited life in the aggressive conditions near the ocean. Lockers turned to stainless steel for a solution.

Figure . A traditional security screen on the left and the 445M2 stainless steel alternative on the right.

But flat panels of mesh were hard to produce in 316, and the tools wore rapidly, causing high downtime for tool sharpening. 445M2 solved both problems and had even better corrosion resistance to cope with the arduous conditions near the ocean.

Manufacturing Director Peter Lowther says “the strong sales growth of the marine grade stainless steel security mesh testifies to the suitability of 445M2 for this application. We provide a superior product for our customers, which uses the strength of the 445M2 to give an unobstructed view from comfort and security. The boys in the tool room love it - they don’t see the tools as often as they used to!”

Stainless Steel Walling, Roofing, Guttering and Downpipes

Glen Roberts, Market Development Manager at Stramit, says “We supply walling, roofing, gutters and downpipes in 445M2. We haven’t had a problem with tea staining, and we have minimal setup time when we run 445M2 on roll formers set up for carbon steel – cleanliness is the key. We always clean the machines down well to remove any carbon steel contamination.

Figure . 445M2 walling and an exploded view of the perforated stainless steel acoustic panel on the right.

We have even had success perforating 445M2 for acoustic screens. When combined with enclosed 50mm acoustic glasswool, Stramit® Acoustic Panels are an effective noise-reduction solution for gymnasiums, factories, public buildings and offices. The wall and ceiling panels add value by providing a “three-in-one” solution that acts as cladding, sound barrier and thermal insulation simultaneously.”

Summary of 445M2 Stainless Steel

1. Features

445M2 is a new generation ferritic stainless steel with better corrosion resistance than 316. It has been used in roofing and facades of buildings, hot water applications, and wherever high resistance to corrosion and staining is needed.

2. Chemical Composition

445M2 contains 22% chromium and 1.2% molybdenum, which give it outstanding corrosion resistance. It does not contain a nickel addition.

3. Microstructure

445M2 is supplied in the annealed condition, with a clean, equiaxed microstructure.

4. Physical Properties

445M2 gives 3.5% more area per kg than an austenitic grade like 316. It also has lower thermal expansion and higher thermal conductivity, so distorts less in welding.

5. Mechanical Properties

The yield strength and hardness of 445M2 are higher than 316. The tensile strength and elongation are lower.

6. Formability

The work hardening coefficient of 445M2 is much lower than 316. It forms in a similar way to carbon steel, and the lower springback and easier shearing give better performance in tools and equipment designed for carbon steel.

7. Corrosion Resistance

 

7.1 Pitting Corrosion

Electrochemical tests in chloride solutions show 445M2 resists pitting corrosion better than 316.

7.2 Crevice Corrosion

Electrochemical tests in chloride solution show 445M2 resists crevice corrosion better than 316 in the as-supplied condition. It is far superior after spot welding.

7.3 Intergranular Corrosion

Very low carbon content and stabilisation with niobium and titanium give 445M2 excellent resistance to intergranular corrosion after sensitising thermal cycles, superior to 316.

7.4 Stress Corrosion Cracking

445M2 is substantially immune from stress corrosion cracking in chloride containing waters, unlike grade 316.

7.5 Rust Resistance

 

7.5.1 Rooftop

In tests simulating an exposed roof in a marine environment, where frequent rain would wash away salt, there was minimal rust staining on 445M2 – much less than 316.

7.5.2 Eaves

Tests simulating an even more severe marine environment – a sheltered area, where salt concentrates – showed minimal rust on 445M2 – much less than 316 which was badly stained.

7.5.3 Atmospheric exposure tests

In atmospheric exposure tests in a severe marine sub-tropical area (equivalent to Fraser Island) 445M2 was almost completely free of rusting (or tea staining) after 2 years exposure. 316 was uniformly tea stained.

7.6 General Corrosion (Acid Resistance)

Sulphuric acid is very aggressive to stainless steels, as it interferes with the formation of the passive surface film. 445M2 has about 1/5 the corrosion rate of 316 in low concentrations of sulphuric acid at elevated temperatures.

8. Weldability

 

8.1 TIG & MIG Weldability

445M2 is easily weldable by TIG or MIG. The steel should be degreased, well shielded with argon and the heat input kept low. 316L(Si) consumables are used.

8.2 Spot & Seam Weldability

445M2 is easily weldable by spot & seam welding.

 

Source: Austral Wright Metals

 

For more information on this source please visit Austral Wright.

 

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