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Stainless Steel - Grade 420 (UNS S42000)

Chemical Formula

Fe, <0.15% C, 12.0-14.0% Cr, <1.0% Mn, <1.0% Si, <0.04% P, >0.03% S

Topics Covered

Background

Key Properties

Composition

Mechanical Properties

Physical Properties

Grade Specification Comparison

Possible Alternative Grades

Corrosion Resistance

Heat Resistance

Heat Treatment

Welding

Machining

Applications

Background

Grade 420 stainless steel is a higher carbon version of 410; like most non-stainless steels it can be hardened by heat treatment. It contains a minimum of 12 per cent chromium, just sufficient to give corrosion resistance properties. It has good ductility in the annealed condition but is capable of being hardened up to Rockwell Hardness 50HRC, the highest hardness of the 12 per cent chromium grades. Its best corrosion resistance is achieved when the metal is hardened and surface ground or polished.

Related grades to 420 are high carbon high hardness martensitic stainless steels such as the 440 series (see Atlas Steels Datasheet on this series of grades) and also variations to 420 containing molybdenum (for increased corrosion resistance), sulphur (for increased machinability) or vanadium (for higher hardness). A slightly higher carbon version of 420 is the non-standard grade 420C.

Martensitic stainless steels are optimised for high hardness, and other properties are to some degree compromised. Fabrication must be by methods that allow for poor weldability and usually also allow for a final harden and temper heat treatment. Corrosion resistance is lower than the common austenitic grades, and their useful operating temperature range is limited by their loss of ductility at sub-zero temperatures and loss of strength by over-tempering at elevated temperatures.

Key Properties

These properties are specified for bar product in ASTM A276. Similar but not necessarily identical properties are specified for other products such as plate and forgings in their respective specifications.

Composition

Typical compositional ranges for grade 420 stainless steels are given in table 1.

Table 1. Composition ranges for 420 grade stainless steel

Grade

C

Mn

Si

P

S

Cr

Mo

Ni

N

420

min.

max.

0.15

-

-

1.00

-

1.00

-

0.040

-

0.030

12.0

14.0

-

-

-

Mechanical Properties

Typical mechanical properties for grade 420 stainless steels are given in table 2.

Table 2. Mechanical properties of 420 grade stainless steel

Tempering Temperature (°C)

Tensile Strength (MPa)

Yield Strength
0.2% Proof (MPa)

Elongation (% in 50mm)

Hardness Brinell (HB)

Impact Charpy V (J)

Annealed *

655

345

25

241 max

-

204

1600

1360

12

444

20

316

1580

1365

14

444

19

427

1620

1420

10

461

#

538

1305

1095

15

375

#

593

1035

810

18

302

22

650

895

680

20

262

42

* Annealed tensile properties are typical for Condition A of ASTM A276; annealed hardness is the specified maximum.

# Due to associated low impact resistance this steel should not be tempered in the range 425-600°C

Physical Properties

Typical physical properties for annealed grade 420 stainless steels are given in table 3.

Table 3. Physical properties of 420 grade stainless steel in the annealed condition

Grade

Density (kg/m3)

Elastic Modulus (GPa)

Mean Coefficient of Thermal Expansion
(
μm/m/°C)

Thermal Conductivity
(W/m.K)

Specific Heat 0-100°C
(J/kg.K)

Electrical Resistivity (nΩ.m)

0-100°C

0-315°C

0-538°C

at 100°C

at 500°C

420

7750

200

10.3

10.8

11.7

24.9

-

460

550

Grade Specification Comparison

Approximate grade comparisons for 420 stainless steels are given in table 4.

Table 4. Grade specifications for 420 grade stainless steel

Grade

UNS No

Old British

Euronorm

Swedish SS

Japanese JIS

BS

En

No

Name

420

S42000

420S37

56C

1.4021

X20Cr13

2303

SUS 420J1

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

Possible alternative grades to grade 420 stainless steels are given in table 5.

Table 5. Possible alternative grades to 420 grade stainless steel

Grade

Why it might be chosen instead of 420

410

Only a lower hardened strength is needed.

416

High machinability is required, and the lower hardened strength and lower corrosion resistance of 416 is acceptable.

440C

A higher hardened strength or hardness than can be obtained from 420 is needed.

"specials"

Variations of 420 are available to special order. These offer higher hardness, corrosion resistance and machinability for particular applications.

Corrosion Resistance

Grade 420 has good resistance in the hardened condition to the atmosphere, foods, fresh water and mild alkalies or acids. Corrosion resistance is lower in the annealed condition.

Performance is best with a smooth surface finish. Less corrosion resistant than the austenitic grades and also less than 17% chromium ferritic alloys such as Grade 430; 420 also has slightly lower resistance than grade 410.

This grade is commonly used for cutlery - particularly blades of table knives and for some carving knives and similar. The corrosion resistance is sufficient to resist attack by food and normal washing methods, but prolonged contact with unwashed food residues can result in pitting.

Heat Resistance

Not recommended for use in temperatures above the relevant tempering temperature, because of reduction in mechanical properties. The scaling temperature is approximately 650°C.

Heat Treatment

Annealing - Full anneal - 840-900°C, slow furnace cool to 600°C and then air cool.

Process Anneal - 735-785°C and air cool.

Hardening - Heat to 980-1035°C, followed by quenching in oil or air. Oil quenching is necessary for heavy sections. Temper at 150-370°C to obtain a wide variety of hardness values and mechanical properties as indicated in the accompanying table.

The tempering range 425-600°C should be avoided.

Welding

Pre-heat to 150-320°C and post-heat at 610-760°C. Grade 420 coated welding rods are recommended for high strength joints, where a post-weld hardening and tempering heat treatment is to be carried out.

If parts are to be used in the "as welded" condition, a ductile joint can be achieved by using Grade 309 filler rod. AS 1554.6 pre-qualifies welding of 420 with Grade 309 rods or electrodes.

Machining

In the annealed condition this grade is relatively easily machined, but if hardened to above 30HRC machining becomes more difficult. Free machining grade 416 is a very readily machined alternative.

Applications

Typical applications include:

         Cutlery

         Knife Blades

         Surgical Instruments

         Needle Valves

         Shear Blades

 

Source: Atlas Steels Australia

 

For more information on this source please visit Atlas Steels Australia

 

Date Added: Oct 23, 2001 | Updated: Jul 12, 2013
Comments
  1. Blu Krome Blu Krome United States says:

    Don't use 309 filler metal to weld onto ferritic steels. The carbon in the ferritic steel will be attracted to the higher chromium content in the 309 and during PWHT and service temps >800F the carbon will diffuse into the 309 and create a carbon-denuded zone at the fusion zone. The differences in the CTE will create a fatigue crack that will propagate along that narrow, carbon-denuded zone. When it breaks, and someday it will break, uninformed observers will swear it was a bad weld because it will look like lack of fusion. Not necessarily so; but definitely a poor choice of filler metal. If you want more ductility in the weld, use 410NiMo filler metal. Avoid austenitic/ferritic joints when possible, and when not possible then try to match the Cr contents and the CTEs. In such cases consider these filler metals: Inco 82/182, Hastelloy W, EPRI P87.

    • Joe McCrink Joe McCrink United States says:

      Will the Carbon migrate during welding as well as during the PWHT that you are discussing above? I regularly weld 410 SS in the hardened condition with 309L and see excessive corrosion in the HAZ about 1cm  away from the weld. Is there any correlation between what I'm seeing and what your discussing. Thanks

  2. Soubhagya Ranjan Soubhagya Ranjan United States says:

    My question is that here the carbon % is 0.15, which is coming under low carbon steel catagory. For this catagory heat treatment is not applicable but in above it is written that this 420-ss material is hardened by heat treatment. So kindly tell me how it is possible.

    Thanks,
    Soubhagya

    • Baljeet Poulastya Baljeet Poulastya India says:

      Mr. Soubhaya only carbon in the steel is not responsible for getting hardened.No doubt it is a low carbon grade but with very specific %age of Cr & Mn i.e. 12-14 & 1 respectively makes it a martensitic stainless steel.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoM.com.
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