What is high performance stainless steel?

What is high performance stainless steel?

Due to the progress of modern metallurgical technology, stainless steel products have made a great leap forward. The corrosion resistance of some high-performance stainless steel in a certain environment has been able to replace some high-grade alloys such as nickel base alloy and titanium alloy, reducing the cost of the equipment, and also has superior comprehensive properties.


High performance stainless steel can be divided into three categories: super austenitic stainless steel; super ferritic stainless steel; dual phase steel. Among them, super austenitic stainless steel is represented by AL-6XN, 904L, 33, 20cb-3, 926 alloy, etc.; super ferritic stainless steel is represented by al-29-4c, e-brite26-1, etc.; dual phase steel is represented by 2205, 225, etc.
For stainless steel and other alloys, most of the corrosion damage is still caused by pitting corrosion, crevice corrosion, intergranular corrosion and stress corrosion.

Pitting corrosion

The evaluation of the resistance to pitting corrosion of corrosion-resistant alloys can be measured by the “pitting equivalent” (prEN) of alloy composition. The formula is as follows.

  • PREN=(%Cr)+3.3(%Mo)+30(%N)

This formula is the empirical formula summed up. It can only be used as a reference, not as a basis for material selection. It can be seen from the above formula that N content has an excellent promoting effect on pitting corrosion, followed by molybdenum.

Crevice corrosion

The ability to resist crevice corrosion of corrosion-resistant alloys can be measured by “critical crevice corrosion temperature CCCT”. The critical crevice corrosion temperatures of several alloys in 10% FeCl3 solution are listed in the table below.

Alloy grade

316L

825

317L

904L

2205

Temperature/℃

-3

-3

2

15

20

Alloy grade

E-B26-1

G Alloy

625

AL-6XN

C-276

Temperature/

21

30

38

43

55

Intergranular corrosion

Intergranular corrosion is a kind of local corrosion caused by the precipitation of chromium carbide and intermetallic phase (such as σ phase) at the grain boundary due to improper welding, heat treatment or heat processing of corrosion-resistant alloy,

Stress corrosion

The main form of stress corrosion failure of alloy is stress corrosion fracture, which is caused by the corrosion and tensile stress in a certain direction. The methods to prevent stress corrosion are as follows: stress relieving heat treatment, structural design improvement, stress concentration avoidance, surface shot peening to produce compressive stress, etc
The following two tables summarize the comparison of stainless steel grades commonly used in China and other countries in the world.
Comparison table of standard steel grades of stainless steel at home and abroad

China
GB1220-92[84]
GB3220-92[84]

Japan
JIS

USA
AISI
UNS

United Kingdom
BS 970 Part4
BS 1449 Part2

Germany
DIN 17440
DIN 17224

France
NFA35-572
NFA35-576~582
NFA35-584

SUS410S

410S

0Cr13

 

S41000

X7Cr13

Z6C13

1Cr13

SUS410

410

410S21

X10Cr13

Z12Cr13

2Cr13

SUS420J1

420

420S29

X20Cr13

Z20Cr13

S4200

420S27

3Cr13

SUS420J2

420S45

3Cr13Mo

3Cr16

SUS429J1

1Cr17Ni2

SUS431

431

431S29

X22CrNi17

Z15CN-02

S43100

7Cr17

SUS440A

440A

S44002

11Cr17

SUS440C

440C

S44004

8Cr17

SUS44013

44013

S44003

1Cr12

4Cr13

SUS420J2

X4DCr13

Z40C13

9Cr18

SUS440C

440C

X105CrMo17

Z100CD17

9Cr18Mo

SUS440C

440C

9Cr18MoV

SUS440B

440B

X90CrMoV18

Z6CN17.12

0Cr17Ni4Cu4Nb

SUS630

630

S17400

Z6CNU17.04

0Cr17Ni7Al

SUS631

631

S17700

X7CrNiAl177

Z8CNA17.7

0Cr15Ni7Mo2Al

632

S15700

Z8CND15.7

00Cr12

SUS410

0Cr13Al[00Cr13Al]

SUS405

405

S40500

405S17

X7CrAl13

Z6CA13

1Cr15

SUS429

429

S42900

1Cr17

SUS430

430

S43000

430S15

X8Cr17

Z8C17

[Y1Cr17]

SUS430F

430F

S43020

X12CrMoS17

Z10CF17

00Cr17

SUS430LX

1Cr17Mo

SUS434

434

S43400

434S19

X6CrMo17

Z8CD17.01

00Cr17Mo

SUS436L

00Cr18Mo2

SUS444

00Cr27Mo

SUSXM27

XM27

S44625

Z01CD26.1

00Cr30Mo2

SUS447J1

1Cr17Mn6Ni5N

SUS201

201

S20100

1Cr18Mn8Ni5N

SUS202

202

S20200

284S16

2Cr13Mn9Ni4

1Cr17Ni7

SUS301

301

S30100

301S21

X12CrNi177

Z12CN17.07

1Cr17Ni8

SUS301J1

X12CrNi177

1Cr18Ni9

SUS302

302

302S25

X12CrNi188

Z10CN18.09

S30200

1Cr18Ni9Si3

SUS302B

302B

S30215

Y1Cr18Ni9

SUS303

303

303S21

X12CrNiS188

Z10CNF18.09

S30300

Y1Cr18Ni9Se

SUS303Se

303Se

303S41

S30323

0Cr18Ni9

SUS304

304

304S15

X2CrNi89

Z6CN18.09

S30400

00Cr19Ni10

SUS304L

304L

304S12

X2CrNi189

Z2CN18.09

S30403

0Cr19Ni9N

SUS304N1

304N

Z5CN18.09A2

S30451

00Cr19Ni10NbN

SUS304N

XM21

S30452

00Cr18Ni10N

SUS304LN

X2CrNiN1810

Z2CN18.10N

305

1Cr18Ni12

SUS305

S30500

305S19

X5CrNi1911

Z8CN18.12

[0Cr20Ni10]

SUS308

308

S30800

0Cr23Ni13

SUS309S

309S

S30908

0Cr25Ni20

SUS310S

310S

S31008

0Cr17Ni12Mo2

SUS316

316

316S16

X5CrNiMo1812

Z6CND17.12

S31600

00Cr17Ni14Mo2

SUS316L

316L

316S12

X2CrNiMo1812

Z2CND17.12

S31603

0Cr17Ni12Mo2N

SUS316N

316N

S31651

00Cr17Ni13Mo2N

SUS316LN

X2CrNiMoN1812

Z2CND17.12N

0Cr18Ni12Mo2Ti

320S17

X10CrNiMo1810

Z6CND17.12

0Cr18Ni14Mo2Cu2

SUS316J1

00Cr18Ni14Mo2Cu2

SUS316J1L

0Cr18Ni12Mo3Ti

1Cr18Ni12Mo3Ti

0Cr19Ni13Mo3

SUS317

317

317S16

S31700

00Cr19Ni13Mo3

SUS317L

317L

317S12

X2CrNiMo1816

S31703

0Cr18Ni16Mo5

SUS317J1

0Cr18Ni11Ti

SUS321

321

X10CrNiTi189

Z6CNT18.10

S32100

1Cr18Ni9Ti

0Cr18Ni11Nb

SUS347

347

347S17

X10CrNiNb189

Z6CNNb18.10

S34700

0Cr18Ni13Si4

SUSXM15J1

XM15

S38100

0Cr18Ni9Cu3

SUSXM7

XM7

Z6CNU18.10

1Cr18Mn10NiMo3N

1Cr18Ni12Mo2Ti

320S17

X10CrNiMoTi1810

Z8CND17.12

00Cr18Ni5Mo3Si2

S31500

3RE60(Sweden)

0Cr26Ni5Mo2

SUS329J1

1Cr18Ni11Si4AlTi

1Cr21Ni5Ti

Comparison of stainless steel nonstandard grades used in China with foreign grades

China

Japan

U.S.A

Sweden

France

Germany

00Cr25Ni4Mo4

UNS S44635

Avesta Monit

00Cr29Ni2Mo4

UNS S44800

00Cr22Ni5Mo2N

329J2L

UNS S31803

SS 2377

DZN 1.4462

DP8

SAF 2205

Uranus 45N

AF22

00Cr21Ni7Mo2N

UNS S32404

Uranus 50

00Cr25Ni7Mo3N

SAF 2507

00Cr25Ni6Mo2CuN

UNS S32550

Frralium 255

0Cr25Ni5Mo2Cu3

CD4MCu

00Cr25Ni7Mo3WCuN

DP3

UNS S31260

00Cr26Ni6Ti

IN744

00Cr26Ni7Mo2Ti

Z3CN2304 AZ

00Cr23Ni4MoN

UNS S32304

SAF 2304

UR 35N

00Cr25Ni22Mo2N

2RE69

X2CrNiMoN2522

00Cr20Ni25Mo4.5Cu

904L

2RK65

UNS N08904

SS 2562

UB-6

X2CrNiMoCu25205

0Cr20Ni29Mo3Cu4

Carpenter 20

0Cr20Ni30Mo3Cu4Nb

Carpenter 20Cb

0Cr27Ni31Mo3Cu

UNS N08082

Sanicro 28

DIN 1.4563

SS 2504

X1NiCrMoCuN31274

00Cr20Ni18Mo6CuN

254 SMO

UNS S31254

SS 2378

00Cr24Ni22Mo7Mn3CuN

UNS S32654

654 SMO

00Cr25Ni20Mo6CuN

X1NiCrMoCuN25206

00Cr17Ni14Si4Nb

NAR-SN-1

00Cr18Ni20Si6MoCu

Sandvik SX

00Cr13Ni4Mo

Z5CND13-04

0Cr12Ni5Ti

AM363

0Cr13Ni8Mo2Al

PH13-8Mo

0Cr13Ni5Cu3Nb

15-5 PH

0Cr16Ni6MoCuNb

Custom 450

00Cr12Ni10AlTi

Unimar CR-1

0Cr17Ti

ZBCT17

X8CrTi17

00Cr17Ti

X8CrTi17

1Cr28

X8CrMoTi17

Several typical advanced stainless steels are introduced to help understand their basic properties.

AL-6XN super austenitic stainless steel

AL-6XN is a low-carbon, high-purity nitrogen super austenitic stainless steel produced by Allegheny Ludlum company of the United States. It has excellent resistance to pitting corrosion, crevice corrosion and stress corrosion of chloride ions, and its own properties make it perform well in acid or alkaline environment. Its main applications are as follows.

  • 1. Chemical tanks and pipelines;
  • 2. Offshore oil and gas field platform;
  • 3. Keywords seawater condenser, heat exchanger and pipeline; crude oil pipeline;
  • 4. Filter, barrel and pressure roller in bleaching process;
  • 5. Power station flue gas scour environment;
  • 6. Desalination equipment and pumps;
  • 7. Water supply pipeline system of nuclear power plant;
  • 8. Transformer enclosure in marine environment;
  • 9. High purity pharmaceutical production equipment.

Chemical composition

Chemical composition of AL-6XN

Chemical element

Content,Wt.%

 

Typical AL-6XN

ASTM standard

C

0.02

0.03max

Mn

0.40

2.00max

P

0.020

0.040max

S

0.001

0.030max

Si

0.40

1.00max

Cr

20.5

20.00/22.00

Ni

24.0

23.50/25.50

Mo

6.2

6.00/7.00

N

0.22

0.18/0.25

Cu

0.2

0.75max

Fe

Allowance

Allowance

Material standard of AL-6XN

ASME and ASTM standards for AL-6XN materials are shown in the table below.

Product form

ASME

ASTM

Plate and strip

SB688

B688

Bars and wires

SB691

B691

Welded pipe

SB675

B675

Welded pipe fittings

SB676

B676

Seamless pipes and fittings

SB690

B690

Spindle

B472

Forged pipe flange and joint

SB462

B462

Malleable weldment

SB366

B366

Forging

SB564

B564

Filler metal welded pipe

B804

Casting

A743/A744

Corrosion resistance of AL-6XN

The important decision of design choice is often based on the results of laboratory and field coupon tests. To predict the corrosion resistance of metal in a certain environment, the characteristics of metal itself and environmental factors should be considered.
Generally speaking, the most common failure mode of stainless steel is local corrosion caused by pitting corrosion, crevice corrosion and stress corrosion fracture of chloride ion.
One of the important characteristics of stainless steel used in seawater and flue gas system is its good resistance to pitting and crevice corrosion. AL-6XN contains high levels of Cr, Mo and Ni, of which Mo content reaches 6-7%, which makes AL-6XN have excellent resistance to pitting and crevice corrosion. The following table is the corrosion resistance test results of several alloys according to ASTM standards.

Alloy

ComponentWt.%

PREN1

CCCT2  

CPT3    ℃

CPT4    ℃

 

Cr

Mo

N

 

 

 

 

304

18.0

0.06

19.8

-2.5

316

16.5

2.1

0.05

24.9

-2.5

15

317

18.5

3.1

0.06

30.5

1.7

19

25

904L

20.5

4.5

0.05

36.9

20

40

45

AL-6XN

20.5

6.5

0.22

47.6

43

80

78

  • PrEN = Cr + 3.3 (% Mo) + 30 (% n) “pitting equivalent”
  • Based on ASTM g-48b standard (6% FeCl 372 hours, with cracks), “critical crevice corrosion temperature”
  • Based on ASTM g-48a standard (6% FeCl 372 hours) “critical pitting temperature”
  • Test solution: 4% NaCl + 1% Fe2 (SO4) 3 + 0.001 M HCl “critical pitting temperature”

In AL-6XN, Cr is the main element to resist neutral and oxidizing environment corrosion. Cr, Mo and N increase the resistance of AL-6XN to pitting and crevice corrosion, Ni and Mo increase the resistance of materials to chloride ion stress corrosion and crevice corrosion, and also make the alloy have good corrosion resistance (such as dilute sulfuric acid) in reducing environment.
The following table shows the corrosion performance test results under different corrosion environments.

Test environment (boiling)

Corrosion rate mm/a

 

316

Al-6XN

 

Basic sample

Welding sample (self melting)

Basic sample

Welding sample (self melting)

20% acetic acid

0.01

0.01

0.01

0.01

45% formic acid

0.28

0.26

0.06

0.07

10% oxalic acid

1.02

0.99

0.19

0.23

20% phosphoric acid

0.18

0.16

0.01

0.01

10% sulfamic acid

1.62

1.58

0.24

0.27

10% sulphuric acid

9.44

9.44

1.83

1.94

10% sodium bisulfate

1.06

1.06

0.12

0.17

50% sodium hydroxide

3.12

3.45

0.29

0.28

65% nitric acid

0.87

0.74

0.66

0.66

1% hydrochloric acid

5.33

5.49

5.16

5.16

The following table shows the corrosion Comparison of different alloys in chemical environment.

Test solution and temperature ℃

Corrosion rate mm/a

 

304

316

20 alloy

C-276

Al-6XN

0.1% hydrochloric acid           90

 

 

 

 

0.01

0.2% hydrochloric acid           70

0.46

 

 

 

0.01

60% sulphuric acid          50

 

 

0.10

 

0.12

95% sulphuric acid           30

0.28

 

 

 

0.01

85% phosphoric acid           70

 

0.06

 

 

0.01

10% nitric acid           90

 

 

 

0.22

0.01

65% nitric acid          116

0.21

0.87

0.23

23.1

0.66

65% nitric acid + 2% hydrochloric acid   50

 

 

 

0.28

0.21

10% nitric acid + 3% hydrofluoric acid 70

157

64.4

7.64

6.70

2.62

80% acetic acid          103

0.13

 

 

 

0.01

50% formic acid         105

 

0.46

 

 

0.06

The laboratory has simulated the high acid environment scoured by the flue gas of the power station. The experimental results of sulfuric acid, hydrochloric acid and chloride solution on the sample are shown in the table below. (the sample is in the welding state)

Simulated scour solution

H2SO4-7VOL%

HCL-3VOL%

CuCl2-1Wt%

FeCl3-1Wt%

50

Base metal

Filler metal

Weight loss (mg/cm2)

Pitting area

317L(4.2%Mo)

Matching

26.9

Weld line

317L(4.2%Mo)

Alloy

22.1

Base material, weld line

317L(4.2%Mo)

625Covering electrode)

18.6

Fusion line, base material

904L

G Alloy

22.5

Base material, weld line

904L

625

23.3

Weld line

AL-6XN

625

2.2

Weld line

Pitting corrosion of AL-6XN

AL-6XN has excellent resistance to pitting and crevice corrosion of chloride ions. In the United States, there are more than 300000000 ft thin-walled tubes that have been used in heat exchangers of seawater and brine projects. Some of them have been used for more than 10 years, but they are still intact without pitting and crevice corrosion.
The following table is the test of crevice corrosion of four metals in 10% FeCl3 solution according to ASTM g48b standard.

Alloy

Crevice corrosion temperature()

304

-2.5

316

-2.5

AL-6XN

45

Inconel625

45

Of course, the temperature of crevice corrosion is related to many factors, such as the geometry and size of crevice, the surface finish of crevice, etc. So the data of this experiment has its typicality and universality.
It has been proved that AL-6XN has good corrosion resistance to pulp bleaching solution (containing chloride ion or chloride oxide ion). AL-6XN can also be used when 317L cannot be used, so AL-6XN is often used to repair or upgrade low alloy stainless steel equipment.

Stress corrosion of AL-6XN

The stress corrosion cracking of stainless steel materials against chloride ions mainly depends on the nickel composition in the alloy. The results show that when the nickel content in the alloy exceeds 12%, it has obvious resistance to stress corrosion of chloride ions. The content of nickel in AL-6XN is about 24%. It has good stress corrosion resistance in the boiling MgCl2 solution. Similarly, when the Mo content in the alloy is more than 3%, the material has a good resistance to chloride stress corrosion. The Mo content of AL-6XN is about 6%, which should be relatively large, and also increases its resistance to stress corrosion. The stress corrosion resistance of AL-6XN to chloride ion is much better than that of alloy 304, 316 and 20 due to the high content of Ni and mo.

Erosion corrosion of AL-6XN

AL-6XN is not like copper base alloy, it will not increase the corrosion rate in the high scour environment.

Intergranular corrosion of AL-6XN

AL-6XN is smelted by advanced AOD Process, in which n is added, but because of its very low carbon content, it also has good intergranular corrosion resistance.
The following table is typical intergranular corrosion test data of AL-6XN.

Test method

Basic materials

Welding specimen

ASTM A262A   (Electrolytic etching solution)

Adopt

Adopt

ASTM A262B(G28A) (Fe2(SO4)3-50%H2SO4)

0.39mm/a

0.372mm/a

ASTM A262E        (Cu-CuSO4-16%H2SO4)

No crack passing

No crack passing

ASTM A262F         (Cu-CuSO4-50%H2SO4)

0.577mm/a

0.599mm/a

Physical property of AL-6XN

  • Density: 8.06g/cm3
  • Melting point range: 1320-1400 ℃
  • Permeability: 1.0028 (magnetic strength 200)
  • Heat conductivity: 20-100 ℃ 13.7w/m-k
  • Specific heat: 500J / kg-k

Dynamic modulus of elasticity

Temperature

Modulus of elasticity

oF

106psi

GPa

75

24

28.3

195

200

93

27.4

189

400

204

26.1

180

600

316

24.8

171

800

427

23.4

161

1000

538

22.1

152

Coefficient of linear thermal expansion

Temperature range

Coefficient of linear thermal expansion

oF

10-6/ oF

10-6/ oC

68-212

20-100

8.5

15.3

68-392

20-200

8.6

15.5

68-572

20-300

8.8

15.7

68-752

20-400

8.9

16.0

68-932

20-500

9.1

16.4

68-1112

20-600

9.3

16.7

68-1292

20-700

9.5

17.1

68-1472

20-800

9.8

17.6

Mechanical property of AL-6XN

Mechanical properties at room temperature

The existence of N in AL-6XN makes it have higher strength than other austenitic stainless steels. At the same time, it has a stable austenite structure, even in the case of extreme deformation will not be transformed into martensite. Of course, AL-6XN also has certain ductility and formability.
Typical mechanical properties of annealed plates are listed below:
Yield strength: 380MPa
Tensile strength: 760mpa
Extended chlorine: 45%
Reduction of area: 60%
Hardness:

  • RB 90
  • BHN 185
  • R30T 72

Tensile properties at high temperature

Test temperature          ()

0.2% yield strength     (MPa)

Tensile strength         (MPa)

Elongation rate δ5          (%)

21

365

770

50

93

325

725

45

149

290

670

45

204

270

640

45

260

255

620

45

316

235

605

45

371

230

595

45

427

230

585

45

482

220

580

44

538

215

560

42

Impact resistance of AL-6XN

AL-6XN material in annealed state has good toughness, especially excellent impact resistance under zero degree. The following table shows the results of Charpy V-groove impact test specimen (the specimen is kept at the test temperature for 1 hour).
Manufacture
Cold forming
The cold forming process of ordinary austenitic stainless steel is also suitable for AL-6XN. Due to the higher strength of AL-6XN, the deformation processing needs to have a larger load.
Thermoforming
The hot working temperature of AL-6XN should be between 1000-1260 ℃. At this temperature, the strength of AL-6XN is between ordinary 300 series stainless steel and nickel base alloy, such as 625 and 276 alloy.
After hot working, in order to obtain better corrosion resistance, the whole annealing and quenching heat treatment should be carried out after descaling and pickling.
Machining
Like other austenitic stainless steels, AL-6XN is difficult to machine, because of its high strength and work hardening tendency, so large cutting force should be used in machining. Machining speed is generally 2 / 3 of 304 stainless steel.

Welding of AL-6XN

In the welding process of AL-6XN and itself, in order to make the weld have good corrosion resistance, the welding wire of higher grade such as 625, 112 and 276 can be selected. The weld with high alloy filler has ductility.
However, the matching filler metal and self fusion welding are generally not used because the corrosion resistance of the weld cannot be guaranteed. The corrosion resistance of the weld can be improved by annealing at 1107 ℃ and rapid cooling. In order to protect the weld from corrosion environment, ordinary austenitic filler metal can be used.
To avoid hot cracks, avoid contact with copper and brass before welding and annealing.
* welding of pipe and tube plate
Automatic welding and manual welding equipment can be used for sealing welding of AL-6XN pipes and tubesheets. Self fusion welding or suitable anti-corrosion material filler metal can be used for welding. If the tube sheet material is a typical 316 or high-grade alloy, self fusion welding can be used for welding. Special corrosion environment can change the choice of tube sheet material. The welding test shows that the welding seam and heat affected zone of AL-6XN tube and tube sheet will not cause the corrosion resistance to decline greatly because of the intermediate phase.

Heat treatment of AL-6XN

AL-6XN should be annealed between 1107-1232 ℃ and cooled rapidly. The relatively slow cooling rate will increase the generation of mesophase, resulting in the decrease of corrosion resistance. The addition of N delayed the formation of mesophase at 540-1040 ℃, but did not prevent it.
When AL-6XN is annealed in air or oxidizing gas, Cr rich oxides will be produced. Like other high molybdenum alloys, the machining process (such as long-time annealing) that may cause a large loss of Mo should be avoided. If it cannot be avoided, pitting will easily occur on the surface of the material.
Once the oxide rich in CR is formed, the surface of the material will also produce the phenomenon of Cr deficiency. Therefore, after annealing, the CR poor surface must be removed mechanically and then pickled in the mixture of nitric acid and hydrofluoric acid. However, AL-6XN is difficult to be pickled due to its strong corrosion resistance. High acid concentration, high temperature and long time immersion are necessary to achieve the pickling effect.

AL-6XN + reinforced new material

AL-6XN + is an upgraded material based on AL-6XN. It fully conforms to the United States UNS N08367 standard, but has higher content of Cr, Mo, n alloy elements to improve the corrosion resistance. The following table shows the composition comparison and pitting equivalent (prEN) comparison of AL-6XN and AL-6XN +.

Composition comparison table

Element

AL-6XN

AL-6XN+

C

0.02

0.02

Mn

0.40

0.35

P

0.020

0.020

S

<0.001

<0.001

Si

0.40

0.35

Cr

20.5

21.8

Ni

24.0

25.3

Mo

6.2

6.7

N

0.22

0.24

Cu

0.2

0.2

Fe

Allowance

Allowance

PREN

47.5

50.0(min)

The following table is the test comparison of critical pitting temperature and critical crevice corrosion temperature.
Corrosion contrast test

Test method

Test solution

Test surface

AL-6XN

AL-6XN+

ASTM G48    PracticeB

Acid FeCl3 solution

Smooth pickling surface

CCCT=43

CCCT=55

ASTM G48    PracticeC

Acid FeCl3 solution

Smooth pickling surface

CPT=75

CPT=90

ASTM G48    PracticeD

Acid FeCl3 solution

Smooth pickling surface

CCCT=35

CCCT=45

ASTM G150

1M NaCl

Ordinary surface

ECPT=78

ECPT=90

  • CCCT = critical crevice corrosion temperature
  • CPT = critical pitting temperature
  • Ecpt = electrochemical critical pitting temperature

Mechanical property of AL-6XN

As the chemical composition of AL-6XN + is within the range specified in UNS N08367 standard, its mechanical properties are basically the same as that of AL-6XN. Refer to the mechanical properties of AL-6XN.

904L austenitic stainless steel

904L is a kind of austenitic stainless steel which can be used for medium and high level corrosion. It has a high content of Cr and Ni. At the same time, a certain amount of Mo and Cu are added to it to increase the corrosion resistance. This alloy has a very low carbon content and can be used in various corrosion environments under welding conditions.
The high content of Ni and Mo in 904L makes the alloy have good resistance to chloride ion stress corrosion cracking. Although it can not completely resist the corrosion of boiling MgCl2 solution, it is still a good corrosion-resistant material. Cr, Mo and Ni in 904L make it have better corrosion resistance than typical 316 and 317 in many uniform corrosion and chloride ion pitting environments. The addition of copper in the alloy makes the alloy have better corrosion resistance in reducing environment such as hot phosphoric acid and dilute sulfuric acid.
904L alloy has consistent instructions in ASTM and ASME standards for reference. There are many kinds of products, which will be described in detail later.

Chemical composition of 904L

The following table specifies the chemical composition of 904L in ASTM standard
Chemical composition

Element

Typical components

ASTM standardN08904

C

0.015

0.020max

Mn

1.60

2.00max

P

0.035

0.045max

S

0.003

0.035max

Si

0.50

1.00max

Cr

20.50

19.00-23.00

Ni

24.5

23.00-28.00

Mo

4.50

4.00-5.00

Cu

1.50

1.00-2.00

Fe

Allowance

Allowance

Corrosion resistance of 904L

The following table shows the corrosion resistance comparison test of 904L and typical 316 stainless steel.

Boiling solution

Corrosion rate (mm/a)

 

Typical 316

904L

20% acetic acid

<0.01

0.02

45% formic acid

0.28

0.20

1% hydrochloric acid

>5

0.55

10% oxalic acid

1.02

0.69

20% phosphoric acid

0.18

0.01

10% sodium bisulfate

1.06

0.23

50% sodium hydroxide

>2.5

0.24

10% sulfamic acid

1.62

0.23

10% sulphuric acid

>5

2.57

Pitting corrosion of 904L

The high content of Cr and Mo in 904L makes it have better resistance to chloride ion pitting and crevice corrosion than the typical 316 stainless steel. The end use of 904L has always been considered as the equipment of tube sheet and bleaching system of pulp and paper industry of seawater heat exchanger, because in such a highly corrosive environment with chloride ions, 904L has stronger corrosion resistance than the typical 316. However, 904L is not fully competent in the aerated seawater environment.
The following table lists the test conditions of several alloys in ASTM g48 standard. In this experiment, the temperature of crevice corrosion is called crevice corrosion temperature, which is also one of the parameters to measure the corrosion resistance of materials.
Temperature test results of crevice corrosion

Alloy

Crevice corrosion temperature ()

Typical 315

-3

Typical 317

2

904L

18

AL-6XN

45

Inconel625

45

AL-29-4C

52

  • ASTM G-48 = 6% FeCl3 solution

Chloride stress corrosion cracking of 904L

Ni is the main alloy element to resist chloride ion stress corrosion fracture. 904L with 25% Ni content has obvious advantages over 304 stainless steel.
The corrosion resistance of 904L is also suitable for the content of 4.5% Mo, but 904L can not resist the corrosion of boiling MgCl2 solution in the laboratory. The specific comparison test results are shown in the table below.
Chloride ion stress corrosion test results

U-bend specimens – test time 1000 hours

Boiling solution

Typical 316

904L

Alloy 20

42%MgCl2

Fail

Fail

Fail

33%LiCl

Fail

Adopt

Adopt

26%NaCl

Fail

Adopt

Adopt

Galvanic corrosion of 904L

In fact, 904L can be regarded as precious metal, even if it is used as tube sheet and used with better corrosion-resistant alloy tube, 904L has enough corrosion resistance to galvanic corrosion.

Intergranular corrosion of 904L

The low carbon content of 904L makes it difficult to produce intergranular corrosion even when it is used in welding state. ASTM a708 or a262 practice e intergranular corrosion test method is suitable for 904L. The following table shows the test results.
Intergranular corrosion test

Intergranular corrosion test method

Corrosion rate (mm/a)

 

Typical 315

904L

Cu-CuSO4-16%H2SO4       (ASTM A262 Practice E)       Bending specimen

No cracking

No cracking

Fe2(SO4)3-H2SO4              (ASTM A262 Practice B)

0.90

0.36

65%HNO3                      (ASTM A262 Practice C)

0.87

0.39

Physical property of 904L

  • Density: 7.95g/cm3
  • Average thermal expansion coefficient: 15.3 × 10-6 / ℃ (20-100 ℃)
  • 16.5×10-6/℃  (20-400℃)
  • 18.2×10-6/℃  (20-800℃)
  • Heat conductivity: 20 ℃ 11.5w/m-k
  • 100℃  12.9 W/m-k
  • 200℃  15.2 W/m-k
  • Permeability: < 1.02
  • Modulus of elasticity: 190gpa

The thermal conductivity of 904L is a typical high alloy austenitic stainless steel. Due to the high content of Ni in the alloy, there is no formation of ferrite phase. At the same time, the permeability is very low even in the case of strong cold deformation.

Mechanical property of 904L

Material standard

Product form

ASTM standard

ASME standard

Plate and strip

B625

SB625

Welded pipe

B673

SB673

Welded pipe fittings

B674

SB674

Seamless pipe

B677

SB677

Sticks, wire

B649

SB649

Typical mechanical properties of solution treated materials

Project

Typical data

ASTM and ASME requirements

Yield strength

270Gpa

220 Gpa min

Tensile strength

605Gpa

490Gpa min

Elongation rate δ5%

50

36 min

Reduction of area %

55

Brinell hardness
Rockwell hardness

150

79

 

70-90*

*This hardness value is for reference only
The allowable stress of 904L is specified in Section VIII of ASME Boiler and pressure vessel standard as follows. The material standard is UNS N08904. For welded pipes and fittings, the weld coefficient is 0.85.
Allowable stress

Maximum temperature of material ()

Maximum allowable stress (MPa)

38

123

93

115

149

104

204

95

260

88

316

83

371

79

Impact resistance

The annealed 904L shows the typical properties of austenitic stainless steel, and has good toughness even below zero.

Formability

904L can be processed and shaped like standard austenitic stainless steel, but its strength is slightly higher than that of typical 304 and 316, so higher forming load is required.
Welding
In 904L welding, in order to ensure the corrosion resistance of the weld, it is recommended to use the matching metal or high-grade alloy material for the filler metal. High grade welding filler metal is mainly used in the manufacturing of erosion resistant components. For high alloy filler metals, the weld can be ductile.
For 904L with moderate corrosion environment, the matching filler metal can be competent.
Heat treatment
904L should be annealed (solution treatment) between 1050-1090 ℃ and cooled rapidly.

Al 29-4c super ferritic stainless steel

The application of ferritic stainless steel is relatively less, so we will not give a detailed introduction here, but only introduce the relevant key points.

UNS

Main characteristics and application of alloy

Product form and corresponding ASTM standards

Chemical composition                            wt%

Tensile strength     σb  MPa

Yield strength     σ0.2  MPa

Tensile strength     δ  %

Supply status

Hardness

AL 29-4C

UNS S44735

 The alloy is a patented product of Allegheny company. It is a high-grade super ferritic stainless steel, which has a wide range of resistance to chloride pitting, crevice corrosion and stress corrosion. It has a better ability to resist uniform corrosion in oxidizing environment and medium reducing environment, and the alloy cost is low.
Allegheny’s al 29-4c pipe has been used for more than 2000 miles in condensers and heat exchangers in power plants and in brine cooling units.
Main uses: condenser and heat exchanger of power plant; chemical treatment equipment, such as brine cooling and treatment tower liner; petroleum refining equipment, such as desalination device, ammonia separation device, overhead fractionation condenser; CO2 precooler; household heating equipment, etc.

    

Plates, sheets and strips
A176
Plates, sheets and strips
A240
General seamless and welded pipe
(tubing):A268
Tubing:
A511

Element

ASTM standard

Typical components

ASTM standard (strip)

Annealing

C

0.030

0.02

550

415

18

 

Mn

1.00

0.30

ASTM standard (pipe)

P

0.040

0.03

515

415

18

S

0.030

0.01

Typical mechanical properties (strip)

Si

1.00

0.35

620

500

22

Cr

28.0-30.0

29.00

Typical mechanical properties (pipe)

Ni

1.00

0.30

620

515

25

Mo

3.60-4.20

3.80

Proportion

N

0.045

0.02

7.66g/cm3

Ti

 

0.30

 

Nb

 

0.30

Nb+Ti

0.20-1.00

 

Co

 

0.03

Fe

Allowance

Allowance

Al 29-4-2 super ferritic stainless steel

UNS

Main characteristics and application of alloy

Product form and corresponding ASTM standards

Chemical composition                             wt%

Tensile strength     σb  MPa

Yield strength     σ0.2  MPa

Tensile strength    δ  %

Supply status

Hardness

AL 29-4-2

UNS S44800

  High purity super ferritic stainless steel. The alloy composition is designed on the basis of Al 29-4c and many corrosion problems. It not only has good resistance to chloride pitting, crevice corrosion and stress corrosion cracking, but also has significant homogeneous corrosion under many harsh external conditions, such as sea water, salt water, dilute sulfuric acid, nitric acid, caustic soda, organic acid, etc.; at the same time, the alloy has good plasticity, toughness and processing characteristics. Because of its good cost performance, the alloy can replace the expensive titanium alloy, high nickel and nickel base alloy in many harsh environments.
Main uses: steam, sea water, acid, alkali, salt and other chemical processing equipment; environmental processing equipment; food, power generation, oil refining and other engineering equipment.

    

Plates, sheets and strips
A176
Plates, sheets and strips
A240
General seamless and welded pipe
(tubing):A268
Bars and sections: a276
Forging billets and bars:
A314
Bars and sections: A479
Seamless and welded pipes:
A731

 

 

Element

ASTM standard

Typical components

ASTM standard (strip)

Annealing

C

0.010

0.003

550

415

20

Rc20

Mn

0.30

0.05

ASTM standard (pipe)

Annealing

P

0.025

0.02

550

415

20

RB100

S

0.020

0.01

Typical mechanical properties (strip)

Annealing

Si

0.20

0.10

655

515

25

RB92

Cr

28.0-30.0

29.00

Typical mechanical properties (pipe)

Annealing

Ni

2.0-2.5

2.10

690

550

25

RB95

Mo

3.5-4.2

4.00

Proportion

 

Cu

0.15

0.06

7.70g/cm3

N

0.020

0.015

 

C+N

0.025

0.018

Fe

Allowance

Allowance

 

E-brite26-1 high purity ferritic stainless steel

UNS

Main characteristics and application of alloy

Product form and corresponding ASTM standards

Chemical composition                             wt%

Tensile strength     σb  MPa

Yield strength     σ0.2  MPa

Tensile strength     δ  %

Supply status

Hardness

E-BRITE26-1

UNS S448627

  High purity ferritic stainless steel. It has excellent resistance to stress corrosion, pitting corrosion, crevice corrosion and intergranular corrosion, which is superior to the traditional Ferritic and austenitic stainless steel, and has the advantage of low cost. The alloy has good plasticity and processing properties.
Main uses: chemical plant and chemical treatment equipment; alkali evaporation equipment; food processing equipment; high temperature resistance, oxidation resistance and sulfuration environment; related equipment of refinery.

Plates, sheets and strips
A176
Plates, sheets and strips
A240
General seamless and welded pipe
(tubing):A268
Bars and sections: a276
Forging billets and bars:
A314
Bars and sections: A479
Seamless and welded pipes:
A731

 

 

Element

ASTM standard

Typical components

ASTM standard (strip)

Annealing

C

0.010

0.002

450

275

22

RB90

Mn

0.40

0.05

ASTM standard (pipe)

Annealing

P

0.02

0.01

450

275

20

RB90

S

0.02

0.01

Typical mechanical properties (strip)

Annealing

Si

0.40

0.20

485

345

30

Rb83

Cr

25.0-27.5

26.0

Typical mechanical properties (pipe)

Annealing

Ni

0.50

0.15

515

415

25

RB88

Mo

0.75-1.5

1.0

Proportion

 

Cu

0.20

0.02

7.66g/cm3

N

0.015

0.010

 

Nb

0.05-0.20

0.10

Fe

Allowance

Allowance

 

Source: China Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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what is high performance stainless steel - What is high performance stainless steel?
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What is high performance stainless steel?
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Due to the progress of modern metallurgical technology, stainless steel products have made a great leap forward. The corrosion resistance of some high-performance stainless steel in a certain environment has been able to replace some high-grade alloys such as nickel base alloy and titanium alloy, reducing the cost of the equipment, and also has superior comprehensive properties.
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