Stainless Steel

Stainless Steel - Grade 444

INTRODUCTION

CS444 is a low carbon, dual stabilised, molybdenum containing ferritic stainless steel with good ductility, toughness and resistance to sensitisation, even in the welds. With 18% chromium and 2% molybdenum, the steel has good pitting resistance and crevice corrosion resistance, similar to CS316 and good general corrosion resistance and oxidation resistance, similar to 316 in most environments. Being a ferritic stainless steel, CS444 is not susceptible to Stress Corrosion Cracking. Annealed CS444 is ductile and can be formed using a wide range of roll forming or mild stretch bending operations as well as the more common drawing and bending operations. CS444 does not harden excessively during cold working.

The steel has limited weldability and should not be used in the as-welded condition for dynamic or impact loaded structures. As with most ferritic stainless steels, CS444 can undergo grain growth in the heat affected zone of weldments, which may adversely affect the mechanical properties in these zones. Applications involving welded CS444 are thus generally limited to a thickness of 2.5mm.

CS444 has good pitting resistance and is thus suitable for roofing and cladding in marine environments, as well as hot water tanks and geysers, heat exchanger tubing and food processing equipment.

SPECIFICATIONS&TOLERANCES

ColumbusStainless(Pty)LtdsuppliesCS444toASTMA240(444)and
EN10088-2(1.4521).

ColumbusStainless(Pty)Ltdnormallysuppliesmaterialtothefollowingtolerances:

HOTROLLED

ASTMA480M
ASMESA480M
EN10051

COLDROLLED

ASTMA480M
ASMESA480M
ENISO9445

Other tolerances may be available on request. Further information is available in the Product Guide, which can be obtained from the Technical Customer Services Department or can be found at www.columbus.co.za

CHEMICAL COMPOSITION

In accordance with ASTM A240 (444) and EN 10088-2(1.4521).

Type

444

1.4521

%C

0.025 max

0.025 max

%Si

1.00 max

1.00 max

%Mn

1.00 max

1.00 max

%P

0.040 max

0.040 max

%S

0.030 max

0.015 max

%Mo

1.75 2.50

1.80 2.50

%Cr

17.50 19.50

17.00 20.00

%Ni

1.00

%Nb

1

2

%Ti

0.20+4(C+N) 0.80

0.15+4(C+N) 0.80

1) Niobium substitution of titanium stabilisation (% by mass) = Ti (% by mass)
2)Niobium substitution of titanium stabilisation (% by mass) = 7/4Ti (% by mass)

MECHANICAL PROPERTIES

In accordance with ASTM A240 (444) and EN 10088-2(1.4521)

Type

444

1.4521

Product Form

C

C

H

P

0.2% Proof Stress (MPa)

275 min

320 min

300 min

300 min

Tensile Strength (MPa)

415 min

420
640

400
600

420
640

Elongation (%)

20 min2

25 min3,4

20 min3,4

20 min3

Brinell Hardness

217 max

PROPERTIES AT ELEVATED TEMPERATURES

The properties quoted below are typical of annealed CS444. These values are given as a guideline only, and should not be used for design purposes

SHORT TIME ELEVATED TEMPERATURE TENSILE STRENGTH

Temperature (°C)

Tensile Strength (MPa)

0.2% Proof Stress (MPA)

% Elongation

100

500

370

30

300

440

310

26

500

380

270

21

700

160

130

22

MAXIMUM RECOMMENDED SERVICE TEMPERATURE
(In oxidising conditions)

Operating Conditions

Continuous

Intermittent

Temperature (°C)

850

950

PHYSICAL PROPERTIES

The values given below are for 20°C, unless otherwise specified.

Density

Modulus of Elasticity in Tension

Modulus of Elasticity in Torsion

Specific Heat Capacity

Thermal Conductivity

Electrical Resistivity

Mean Co-effcient of Thermal Expansior

Melting Range

Relative Permeability

7 750kg/m3

220GPa

65GPa

430J/kg K

@100°C - 26.8W/mK
@500°C - 27.1W/mK

570 ½m

0-100°C - 10.8μm/mK
0-315°C - 11.6μm/mK
0-540°C - 12.0μm/mK
0-700°C - 12.5μm/mK

1 405-1 495°C

Ferromagnetic

THERMAL PROCESSING & FABRICATION

ANNEALING
Annealing is achieved by heating to between 760°C and 830°C for 90 minutes per 25mm followed by air quenching.

STRESS RELIEVING
Stress relieving after welding is not normally required. Should this be necessary, temperatures between 200°C and 300°C are recommended.

HOT WORKING
Uniform heating of the steel in the range of 950°C to 1 050°C is required. The finishing temperature should be below 750°C. Extended holding times above 1 000°C should be avoided as excessive grain growth may occur and ductility may be detrimentally affected. All hot working operations should be followed by annealing and pickling and passivating to restore the mechanical properties and corrosion resistance.

COLD WORKING
CS444 has good formability characteristics with useful mechanical properties. Its good ductility allows it to be readily formed by bending and deep drawing. CS444 does not undergo significant work hardening when cold formed.

WELDING
Being ferritic, CS444 is prone to grain growth in the heat affected zone of weldments. As such, the tensile, fatigue and toughness properties in the welded condition are relatively poor. CS444 should thus not be used for applications where tensile or dynamic loading will be experienced. CS444 is generally limited to a combined thickness of
3 mm in the welded condition, i.e. for lap joints, this is equivalent to
2 x 1,5 mm thickness being welded together. The use of austenitic filler metals such as types 308L, 309L or 316L will improve the ductility of welds to some extent but all welding procedures should nevertheless endeavour to maintain minimum heat inputs. The weld discolouration should be removed by pickling and passivating to restore maximum corrosion resistance.

CORROSION RESISTANCE
CS444 has good resistance to a wide variety of corrosive environments. With 18% chromium and 2% molybdenum the steel has good pitting resistance, better than CS316, good crevice corrosion resistance, similar to CS316 and good general corrosion resistance and oxidation resistance, similar to CS316 in most environments. Atmospheric corrosion resistance is good and similar to CS316. Being a ferritic stainless steel, CS444 is not susceptible to stress corrosion cracking.

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