AISI 431 Martensitic Stainless Steel

AISI 431 – Martensitic stainless steel – A combination of corrosion resistance, mechanical properties and machinability. 431 is martensitic stainless steel with chemical composition as C 0,12-0,22 • Cr 15-17 • Ni 1,5-2,5 is a high chromium, low nickel, high hardenability Martensitic stainless steel with high strength and good corrosion resistance, as generally supplied hardened and tempered in the tensile range 850 – 1000 Mpa (condition T), Brinell range 248 – 302. Very good corrosion resistance in general atmospheric corrosive environments, good resistance to mild marine and industrial atmospheres, resistant to many organic materials, nitric acid and petroleum products coupled with high tensile and high yield strength plus excellent toughness in the hardened and tempered condition.  431 is not recommended for use at sub-zero temperatures due to a substantial drop in impact properties consistent with most steels other than the austenitic steel types.

Complies with standards
EN 10088-3 : 1.4057 X17CrNi 16-2 – AISI 431 – JIS SUS 431 – EN10272 : 1.4057

Related Specifications

AustraliaAS 2837-1986 431
GermanyW.Nr 1.4057 X20CrNi17 2
Great BritainBS970 Part3 1991 431S29
BS970 – 1955 EN57
JapanJIS G4303 SuS 431
USAASTM A276-98b 431
SAE 51431 AISI 431
UNS S43100

Grade 431 stainless steels are martensitic, heat-treatable grades with excellent corrosion resistance, torque strength, high toughness and tensile properties. All these properties make them ideal for bolt and shaft applications. These steels, however, cannot be cold-worked owing to their high yield strength, hence they are suitable for operations such as spinning, deep drawing, bending or cold heading.

Characterised by very good corrosion resistance in general atmospheric corrosive environments, good resistance to mild marine and industrial atmospheres, resistant to many organic materials, nitric acid and petroleum products coupled with high tensile and high yield strength plus excellent toughness in the hardened and tempered condition. 

431 due to its excellent hardenability is capable of being through hardened up to Rc44, depending upon carbon content and section size. Small sections can be air cooled and larger sections oil quenched for maximum through hardness.Pre hardened and tempered 431 will also respond readily to nitriding achieving a typical surface hardness of over Rc65. The nitriding process however reduces the corrosion resistance and is therefore not generally recommended except for critical applications where the benefit outweighs all other considerations.

Used extensively for parts requiring a combination of high tensile strength, good toughness and good corrosion resistant properties.

Typical applications are: Aircraft Parts and Components, Bolts and Nuts, Fasteners, Pump Shafts, Propellor Shafts, Studs, Valve Parts etc.

Material magnetic in all conditions.

Corrosion Resistance

Grade 431 stainless steels have considerable resistance to salt water, but they are less resistant to tropical water when compared to that of grade 316 steels. Grade 431 steels have overall corrosion resistance similar to, or slightly lower than, that of grade 304 steels.

Grade 431 steels with a smooth surface finish perform well in tempered and hardened conditions.

Heat Resistance

Grade 431 steels are resistant to scaling at temperatures of 925°C in intermittent conditions, and 870°C during continuous operations. In general, these steels are not to be used at temperatures above standard tempering temperatures, owing to loss of mechanical properties.

Heat Treatment

Full anneal — Full annealing cannot be performed on grade 431 steels. This grade gets hardened even during slow cooling.

Process anneal — Grade 431 steels are heated to 620 to 660°C and then air-cooled.

Grade 431 steels are generally hardened by heating at temperatures from 980 to 1065°C, holding for nearly ½ h, followed by oil or air quenching. Complex or hardened parts of grade 431 steels can be pre-heated to temperatures from 760 to 790°C and tempered, to improve their mechanical properties. Tempering of these steels at 425 to 600°C should be avoided, owing to the loss of impact toughness at this temperature range.

Welding

Welding of grade 431 stainless steels is difficult due to the chances of cracking. It is recommended to pre-heat the materials to 200 – 300°C before welding, and carry out post-weld heat treatment at 650°C. Welding can be performed using grade 410 filler rods, but ductile welds can be achieved using grades 308L, 309 or 310 steels.

Machining

Grade 431 steels can be easily machined in their annealed state. However, it is extremely difficult to machine these steels if they are hardened above 30HRC.

Applications

Typical applications of grade 431 stainless steels include the following:

  • Laboratory equipment
  • Marine systems
  • Beater bars
  • Pump and propeller shafts
  • Nuts and bolts

Fabrication of AISI 431

Fabrication of martensitic steels is generally carried out using techniques that allow hardening and tempering treatments and poor weldability. The corrosion resistance properties of grade 431 steels are lower than that of austenitic grades. The operations of grade 431 are limited by their loss of strength at high temperatures, due to over-tempering, and loss of ductility at negative temperatures.

Mill’s certificate sample of AISI 431 – Martensitic Stainless Steel

Chrome content on AISI 431 vs. 420/410

AISI 431, 420 and 410 are the same type of martensitic stainless steel. A striking difference from AISI 431 compared to AISI 410 and 420 is the chrome (Cr) content of AISI 431 which is higher than AISI 410 and 420. Where, Cr content for AISI 431 is 15-18%, while the content of Cr content in AISI 410 is 11.5- 13.5%. Meanwhile, the content of Cr in AISI 420 is 12-14%.

Here we show the chemical compositions of grades 431, 420 and 410 where all of these grades are classified as martensitic stainless steel. You can compare the elements of Fe, C, Cr, and others.

Grade

Fe

C

Mn

Si

P

S

Cr

Ni

Mo

431

min.

max.

78.2

83.8

0.12

0.20

1

1

0.04

0.03

15

17

1.25

2.50

 

420

min.

max.

83.5

88.4

0.15

0.4

1

1

0.04

0.03

12

14

0.75

 

410

min.

max.

82.3

87.9

0.08

0.15

1

1

0.04

0.03

11.5

13.5

0.75

0

0.5

Martensitic stainless steel types

Type

Description

410

Basic martensitic grade, containing the lowest alloy content of the three basic stainless steels (304, 430, and 410). Low cost, general purpose, heat treatable stainless steel. Used widely where corrosion is not severe (air, water, some chemicals, and food acids. Typical applications include highly stressed parts needing the combination of strength and corrosion resistance such as fasteners.

410S

Contains lower carbon than Type 410, offers improved weldability but lower hardenability. Type 410S is a general purpose corrosion and heat resisting chromium steel recommended for corrosion resisting applications.

414

Has nickel added (2%) for improved corrosion resistance. Typical applications include springs and cutlery.

416

Contains added phosphorus and sulfur for improved machinability. Typical applications include screw machine parts.

420

Contains increased carbon to improve mechanical properties. Typical applications include surgical instruments.

431

Contains increased chromium for greater corrosion resistance and good mechanical properties. Typical applications include high strength parts such as valves and pumps.

440

Further increases chromium and carbon to improve toughness and corrosion resistance. Typical applications include instruments.

References:

  • https://www.azom.com/
  • https://www.makeitfrom.com/
  • htps://www.ugitech.com
  • http://www.interlloy.com.au

SS 316 – Austenitic Stainless Steel Grade

We know the various names of stainless steel that are included in the austenitic grade category, namely: AISI / SUS 201, 202, 301, 302, 303, 304, 305, 309, 310, 316, 317, 327, 347. In this article we will discuss SS 316 and SS 316L and 316H.

Austenitic Stainless Steel

Austenitic stainless steel is a specific type of stainless steel alloy. Stainless steels may be classified by their crystalline structure into four main types: austenitic, ferritic, martensitic and duplex stainless steel.

[1] Austenitic stainless steels possess austenite as their primary crystalline structure (face centered cubic).

This austenite crystalline structure is achieved by sufficient additions of the austenite stabilizing elements nickel, manganese and nitrogen. Due to their crystalline structure, austenitic steels are not hardenable by heat treatment and are essentially non-magnetic.

There are two subgroups of austenitic stainless steel. 300 series stainless steels achieve their austenitic structure primarily by a nickel addition while 200 series stainless steels substitute manganese and nitrogen for nickel, though there is still a small nickel content.

300 series stainless steels are the larger subgroup. The most common austenitic stainless steel and most common of all stainless steel is Type SS 304, also known as 18/8 or A2.

Type SS 304 is extensively used in such items as, cookware, cutlery, and kitchen equipment.

Type SS 316 is the next most common austenitic stainless steel. Some 300 series, such as Type SS 316, also contain some molybdenum to promote resistance to acids and increase resistance to localized attack (e.g. pitting and crevice corrosion). The higher nitrogen addition in 200 series gives them higher mechanical strength than 300 series

Other notable austenitic stainless steels are Type 309 and 310, which are utilized in high temperature applications greater than 800°C.

Alloy 20 (Carpenter 20) is an austenitic stainless steel possessing excellent resistance to hot sulfuric acid and many other aggressive environments which would readily attack type 316 stainless.

This alloy exhibits superior resistance to stress-corrosion cracking in boiling 20–40% sulfuric acid. Alloy 20 has excellent mechanical properties and the presence of niobium in the alloy minimizes the precipitation of carbides during welding.

Austenitic stainless steel can be tested by nondestructive testing using the dye penetrant inspection method but not the magnetic particle inspection method. Eddy-current testing may also be used.

Stainless Steel – Grade SS 316 (UNS S31600)

Austenitic stainless steel – Grade SS 316L

Chemical Formula :
Fe, <0.03% C, 16-18.5% Cr, 10-14% Ni, 2-3% Mo, <2% Mn, <1% Si, <0.045% P, <0.03% S

Grade 316 is the standard molybdenum-bearing grade, second in importance to 304 amongst the austenitic stainless steels.

The molybdenum gives 316 better overall corrosion resistant properties than Grade 304, particularly higher resistance to pitting and crevice corrosion in chloride environments.

It has excellent forming and welding characteristics. It is readily brake or roll formed into a variety of parts for applications in the industrial, architectural, and transportation fields.

Grade 316 also has outstanding welding characteristics. Post-weld annealing is not required when welding thin sections.

What is the difference between 316, 316L and 316H ?

Grade 316L, the low carbon version of 316 ( L=Low Carbon. ) and is immune from sensitisation (grain boundary carbide precipitation).

Thus it is extensively used in heavy gauge welded components (over about 6mm).

Grade 316H, with its higher carbon content has application at elevated temperatures, as does stabilised grade 316Ti.

The austenitic structure also gives these grades excellent toughness, even down to cryogenic temperatures.

Composition ranges for 316 grade of stainless steels.

The following is the chemical composition between SS 316, 316L and 316H

Grade

C

Mn

Si

P

S

Cr

Mo

Ni

N

316

Min

0

16.0

2.00

10.0

Max

0.08

2.0

0.75

0.045

0.03

18.0

3.00

14.0

0.10

316L

Min

16.0

2.00

10.0

Max

0.03

2.0

0.75

0.045

0.03

18.0

3.00

14.0

0.10

316H

Min

0.04

0.04

0

16.0

2.00

10.0

max

0.10

0.10

0.75

0.045

0.03

18.0

3.00

14.0

Mechanical properties of 316 grade stainless steels.

The following are mechanical properties (tensile strength, yield strength, elongation and hardness) of stainless steel SS 316, 316 L and 316 H

Grade

Tensile Str (MPa) min

Yield Str 0.2% Proof (MPa) min

Elong (% in 50 mm) min

Hardness

Rockwell B (HR B) max

Brinell (HB) max

316

515

205

40

95

217

316L

485

170

40

95

217

316H

515

205

40

95

217

Note: 316H also has a requirement for a grain size of ASTM no. 7 or coarser.

 Typical physical properties for 316 grade stainless steels.

Grade

Density(kg/m3)

Elastic Modulus (GPa)

Mean Co-eff of Thermal Expansion (µm/m/°C)

Thermal Conductivity (W/m.K)

Specific Heat 0-100 °C (J/kg.K)

Elec Resistivity (nΩ.m)

0-100 °C

0-315 °C

0-538 °C

At 100 °C

At 500 °C

316/L/H

8000

193

15.9

16.2

17.5

16.3

21.5

500

740

Grade specifications for 316 grade stainless steels.

Grade

UNS No

Old British

Euronorm

Swedish SS

Japanese JIS

BS

En

No

Name

316

S31600

316S31

58H, 58J

1.4401

X5CrNiMo17-12-2

2347

SUS 316

316L

S31603

316S11

1.4404

X2CrNiMo17-12-2

2348

SUS 316L

316H

S31609

316S51

Note: These comparisons are approximate only. The list is intended as a comparison of functionally similar materials not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted.

Possible alternative grades to 316 stainless steel.

Grade

Why it might be chosen instead of 316?

316Ti

Better resistance to temperatures of around 600-900 °C is needed.

316N

Higher strength than standard 316.

317L

Higher resistance to chlorides than 316L, but with similar resistance to stress corrosion cracking.

904L

Much higher resistance to chlorides at elevated temperatures, with good formability

2205

Much higher resistance to chlorides at elevated temperatures, and higher strength than 316

Corrosion Resistance

Excellent in a range of atmospheric environments and many corrosive media – generally more resistant than 304. Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60 °C. Considered resistant to potable water with up to about 1000 mg/L chlorides at ambient temperatures, reducing to about 500 mg/L at 60 °C.

316 is usually regarded as the standard “marine grade stainless steel”, but it is not resistant to warm sea water. In many marine environments 316 does exhibit surface corrosion, usually visible as brown staining. This is particularly associated with crevices and rough surface finish.

Heat Resistance

Good oxidation resistance in intermittent service to 870 °C and in continuous service to 925 °C. Continuous use of 316 in the 425-860 °C range is not recommended if subsequent aqueous corrosion resistance is important. Grade 316L is more resistant to carbide precipitation and can be used in the above temperature range. Grade 316H has higher strength at elevated temperatures and is sometimes used for structural and pressure-containing applications at temperatures above about 500 °C.

Heat Treatment

Solution Treatment (Annealing) – Heat to 1010-1120 °C and cool rapidly. These grades cannot be hardened by thermal treatment.

Welding

Excellent weldability by all standard fusion methods, both with and without filler metals. AS 1554.6 pre-qualifies welding of 316 with Grade 316 and 316L with Grade 316L rods or electrodes (or their high silicon equivalents). Heavy welded sections in Grade 316 require post-weld annealing for maximum corrosion resistance. This is not required for 316L. Grade 316Ti may also be used as an alternative to 316 for heavy section welding.

Machining

A “Ugima” improved machinability version of grade 316 is available in round and hollow bar products. This machines significantly better than standard 316 or 316L, giving higher machining rates and lower tool wear in many operations.

Dual Certification

It is common for 316 and 316L to be stocked in “Dual Certified” form – mainly in plate and pipe. These items have chemical and mechanical properties complying with both 316 and 316L specifications. Such dual certified product does not meet 316H specification and may be unacceptable for high temperature applications.

Applications

  • Food preparation equipment particularly in chloride environments.
  • Laboratory benches & equipment.
  • Coastal architectural panelling, railings & trim.
  • Boat fittings.
  • Chemical containers, including for transport.
  • Heat Exchangers.
  • Woven or welded screens for mining, quarrying & water filtration.
  • Threaded fasteners.
  • Springs.

Typical applications include:

SS 316 Equivalent Grade

316 and 316L round bar equivalent grades

References:

  1.  The International Nickel Company (1974). “Standard Wrought Austenitic Stainless Steels”Nickel Institute.
  2. ^ “Stainless Steel”. Encyclopaedia Britannica.
  3. ^ American Iron and Steel Institute. “Design Guidelines for the Selection and Use of Stainless Steels”Nickel Institute.
  4. Atlas Steels Australia

Martensitic Stainless Steel – Corrodur 4021 / AISI 420

Martensitic stainless steels are widely used in the steam generators, oil and gas esploration, oversea petroleum platforms, pressure valves, mixer blades, cutting tools, and surgical tools and jigs.

Owing to their excellent mechanical properties. In general, these steels are used in quenched and tempered conditions.

Quenching heat treatment is carried out by cooling in oil or air followed by annealing at 980–1100 °C. Tempering is done at the interval of 200 and 700 °C [3].

The annealed Martensitic stainless steels have a microstructure containing spherical carbides in the ferritic matrix.

Since the material is metallurgical complex, the heat treatment must be accurately controlled in order to create a complete martensite structure without forming δ-ferrite and residual austenite.

Stainless steel 1.4021 is a martensitic machining bar with machinability improved with the addition of Sulphur. The Sulphur also lowers weldability, corrosion resistance, and formability to below that of its non-free machining equivalent Grade 410.

Stainless Steel – Martensitic – 1.4021 Bar Properties, Applications and Fabrication

Martensitic stainless steels are designed for high hardness, and other properties are compromised to an extent. Their functional operating temperature range is restricted by their loss of ductility at sub-zero temperatures, and loss of strength by over-tempering at high temperatures.

Alloy designations of 1.4021 is similar, but it may not be a direct equivalent to: 420, UNS42000, 1.4021, 1.4024, 1.4028, 1.4029, 1.4030, and 1.4034. It is supplied in the form of a bar.

Corrosion resistance is lower than the common austenitic grades. It offers resistance to fresh water, dry atmospheres, and mild alkalies and acids; however, the resistant is lower than equivalent non-free-machining grades. High Sulphur content free machining grades – such as 416 – are not suitable for chloride exposure or in marine condition.

Maximum corrosion resistance can be achieved in the hardened condition with a smooth surface finish. The steel has a fair heat resistance to scaling in intermittent service up to 760°C, and up to 675°C in continuous service. It is not recommended for use in temperatures exceeding the relevant tempering temperature.

Chemical Composition

1.4021 SteelEN 10088-3:2005
Chemical Element% Present
Carbon (C)0.16 – 0.25
Chromium (Cr)12.00 – 14.00
Manganese (Mn)0.0 – 1.50
Silicon (Si)0.0 – 1.00
Phosphorous (P)0.0 – 0.04
Sulphur (S)0.0 – 0.03
Iron (Fe)Balance

Properties

Physical PropertyValue
Density7.75 g/cm³
Thermal Expansion10.3 x10^-6 /K
Modulus of Elasticity200 GPa
Thermal Conductivity24.9 W/m.K
Electrical Resistivity0.055 x10^-6 Ω .m
Bar – Up to 160mm Dia/ThicknessEN 10088-3:2005
Mechanical PropertyValue
Proof Stress500 – 600 MPa
Tensile Strength700 – 950 MPa
Elongation A12 – 13 %
 martensitic stainless steel
martensitic stainless steel

Fabrication

Fabrication must be carried out by methods that allow for poor weldability, as well as for a final harden and temper heat treatment.

Cold working – It is not recommended, It is only suitable for minor deformation. Cracking will occur due to severe deformation.

Hot working – Hot working processes should be carried out after uniform heating to 2100-2250°F (1149-1232°C). Hot working below 1700°F (927°C) could result in cracking.

Machinability – Grade 420 offers very good machinability, the highest of any of the commonly available stainless steels. It is achieved best in sub-critical annealed condition.

Weldability – Grade 420 has poor weldability. It can be pre-heated to 150-320°C and post-heated at 610-760°C. Grade 420 coated welding rods can be used for high strength joints, where a post-weld hardening and tempering heat treatment can be carried out. If parts need to used in the “as welded” condition, a ductile joint can be made using Grade 309 filler rod or electrodes.

Applications

The main areas of applications include:

  • Automatic screw machined parts
  • Valve parts
  • Pump shafts
  • Studs
  • Gears
  • Motor shafts
  • Bolts and nuts
  • Shear blades
  • Cutlery blades
  • Surgical Instruments
  • Washing machine parts

Corrodur 4021

Reference:

Reference:

  1. https://www.researchgate.net/publication/283241675_Investigation_of_mechanical_microstructural_and_machining_properties_of_AISI_420_martensitic_stainless_steel_welded_by_laser_welding
  2. https://www.azom.com/article.aspx?ArticleID=972
  3. https://www.azom.com/article.aspx?ArticleID=12574
  4. Deutsche Edelstahlwerke

Duplex Stainless Steel – UNS S31803 / AISI 2205

UNS S31803 / AISI 2205
“Duplex stainless steels” has a two phase micro structure consisting of ferritic and austenitic stainless steel granules. When duplex stainless steel is melted it solidifies from the liquid phase to a completely ferritic structure. As the material cools to room temperature, about half of the ferritic grains transform to austenitic grains. The result is a microstructure of roughly 50% austenite and 50% ferrite.

duplex stainless steel
Duplex stainless steel Microstructure of base metal of the duplex stainless steel, 2205, 250X original magnification. Austenite phases are present as white island in blue sea of ferrite. Duplex stainless steels have a two-phase microstructure of austenite and ferrite grains. The picture shows the yellow austenitic phase as “islands” surrounded by the blue ferritic phase.

Introduction

Stainless steels are high-alloy steels. These steels are available in four groups that include martensitic, austenitic, ferritic and precipitation-hardened steels. These groups are formed based on the crystalline structure of stainless steels.

Stainless steels contain larger amounts of chromium in comparison with other steels and thus have good corrosion resistance. Most of the stainless steels contain about 10% of chromium.

Grade 2205 stainless steel is a duplex stainless steel whose design enables combining improved resistance to pitting, high strength, stress corrosion, crevice corrosion and cracking. Grade 2205 stainless steel resists sulfide stress corrosion and chloride environments.

duplex stainless steel 2205
duplex stainless steel – 2205 grade

The following datasheet provides an overview of grade 2205 duplex stainless steel.
Chemical Composition
The chemical composition of grade 2205 stainless  steel is outlined in the following table.
Table.1
Chemical Composition
Element
Content (%)
Iron, Fe
63.75-71.92
Chromium, Cr
21.0 – 23.0
Nickel, Ni
4.50 – 6.50
Molybdenum, Mo
2.50 – 3.50
Manganese, Mn
2.00
Silicon, Si
1.00
Nitrogen, N
0.080 – 0.20
Carbon, C
0.03
Phosphorous, P
0.03
Sulfur, S
0.02

The duplex structure gives this family of stainless steels a combination of attractive properties:

Strength: Duplex stainless steels are about twice as strong as regular austenitic or ferritic stainless steels.

Toughness and ductility: Duplex stainless steels have significantly better toughness and ductility than ferritic grades; however, they do not reach the excellent values of austenitic grades.

Corrosion resistance: As with all stainless steels, corrosion resistance depends mostly on the composition of the stainless steel. For chloride pitting and crevice corrosion resistance, their chromium, molybdenum and nitrogen content are most important. Duplex stainless steel grades have a range of corrosion resistance, similar to the range for austenitic stainless steels, i.e from Type 304 or 316 (e.g. LDX 2101©) to 6% molybdenum (e.g. SAF 2507©) stainless steels.

Stress corrosion cracking resistance: Duplex stainless steels show very good stress corrosion cracking (SCC) resistance, a property they have “inherited” from the ferritic side. SCC can be a problem under certain circumstances (chlorides, humidity, elevated temperature) for standard austenitics such as Types 304 and 316.

Cost: Duplex stainless steels have lower nickel and molybdenum contents than their austenitic counterparts of similar corrosion resistance. Due to the lower alloying content, duplex stainless steels can be lower in cost, especially in times of high alloy surcharges. Additionally, it may often be possible to reduce the section thickness of duplex stainless steel, due to its increased yield strength compared to austenitic stainless steel. The combination can lead to significant cost and weight savings compared to a solution in austenitic stainless steels.

Mechanical Properties

The mechanical  properties of grade  2205 stainless  steel are displayed  in the following table.

Table 2. Mechanical Properties of Duplex Stainless Steel / UNS S31803 / AISI 2205

Table 2.
Mechanical Properties
Properties
Metric
Imperial
Tensile strength at break
621 MPa
90000 psi
Yield strength (@strain 0.200 %)
448 MPa
65000
psi
Elongation at break (in 50 mm)
25.0%
25.0%
Hardness, Brinell
293
293
Hardness, Rockwell c
31.0
31.0
Other Designations
Equivalent materials to grade 2205 duplex stainless steel are:
  • ASTM A182 Grade F51
  • ASTM A240
  • ASTM A789
  • ASTM A790
  • DIN 1.4462

Applications :

Grade  2205 duplex stainless  steel  is  used  in  the  following applications:
  • Fuel gas filters
  • Chemical tanks
  • Heat exchangers
  • Acetic acid distillation components

References:

  1. https://en.wikipedia.org/wiki/Duplex_stainless_steel
  2. https://www.imoa.info/
  3. https://www.steeltank.com/
  4. http://www.corrosionlab.com/
  5. http://mit.imt.si/Revija/izvodi/mit114/tehovnik.pdf

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