Difference between 303 and 304 Stainless Steel

What is the difference between 303 and 304 stainless?

Despite being one of the most versatile alloys around, the use of grade 304 takes a hit due to the fact that it work hardens rather quickly. This is what the introduction of grade 303 rectified. Hence, grade 303 is referred to as the free-machining grade of 304 stainless steel. Both alloys are classified under the austenitic class of stainless steel and, therefore will exhibit the same face centred cubic crystal microstructure. Though the chemical composition of both alloys is similar to the other, the inclusion of elements like sulfur or selenium to the alloy of grade 303 is what improves its machinability. The inclusion or exclusion of elements in any alloy tends to change the properties of the material as a whole. So the inclusion of either sulfur or selenium in the alloy is known to reduce corrosion resistance properties of grade 303 compared to 304. What gives stainless steel grade 303 excellent toughness properties is its microstructure. However, the addition of sulfur is also what lessens its toughness at a certain level. Grade 304, or as manufacturers and suppliers refer to as 18/8 stainless steel is known to have excellent characteristics, despite being an economical grade. From having higher ductility to moderate tensile strength and adequate resistance to corrosion, the alloy is preferred over several alloys, mostly because the cost makes it a cost-efficient solution across several industries.

How to Identify stainless steel 303 and 304?

The simplest way to identify materials is by conducting an MTR. The MTR is a detailed report on the mechanical, chemical, and physical characteristics of the materials. Aside from procuring a mill test report or material test report or an MTR from the manufacturer, it is possible to identify both the stainless steels by subjecting them to a Sulphur Spot Test. This test is well suited to distinguish various Stainless steels or plain carbon steels that have a minimum of 0.1% of sulfur. This is why it is easy to recognize free-machining grades like grade 303 because the reading obtained from this test is positive for sulfur containing alloys.

303 vs 304 stainless steel machinability

As previously mentioned, it is possible to improve the mechanical characteristics of an alloy, simply by including sulfur or selenium at a higher degree in the austenitic class of stainless steel. Since grade 304 work hardens in a rapid manner, machinability is an issue for this alloy. Contrary to grade 304, the chemical composition of the stainless steel grade 303 has sulfur present in the range of 0.15% to 0.35%, which is a significant increase over the 0.015% in conventional 304 stainless steels.

303 vs 304 stainless steel price

Although the chemical composition of both alloys tends to be similar to each other, the cost of grade 303 stainless steel is higher than grade 304. This is because austenitic stainless steel grade 303 was specifically developed for applications that required machining. This grade is used in those applications that are ok with having a lower resistance to corrosion but demand higher machinability, which is not possible by the use of grade 304 as it is difficult to machine. This increased machinability of the stainless steel grade 303 will often make up for the elevated cost.

303 vs 304 stainless steel yield strength

The yield strength is the highest stress that can be implemented along the materials axis before the alloy initiates a change in shape. The yield strength offset at 0.2% for grade 304 is 290Mpa, whereas, for grade 303, the same value stands at 310 Mpa.

303 vs 304 stainless steel corrosion

In applications where corrosion resistance is of utmost importance, the use of grade 304 stainless steel solves the conundrum. Being a versatile and cost-efficient material, stainless steel type 304 is known to offer good resistance to oxidation and some forms of corrosion. Despite having a similar chemistry base, type 303 stainless steel is still able to exhibit strong corrosion resistance properties. But it is recommended to use type 304 stainless steel for an added boost. This is because the small addition of sulfur in grade 303 is what reduces the corrosion resistance properties of stainless steel, while also improving the machinability of the alloy.

303 Stainless Steel Mechanical Properties

Grade

Tensile Strength (MPa)

Yield Strength 0.2% Proof (MPa)

Elongation (% in 50mm)

Hardness

Rockwell B (HR B)

Brinell (HB)

303

-

-

-

-

262 max

303 Stainless Steel Composition

Grade

C

Mn

Si

P

S

Cr

Mo

Ni

Se

303

min.

max.

-

0.15

-

2.00

-

1.00

-

0.20

0.15

-

17.0

19.0

-

8.0

10.0

-

303Se

min.

max.

-

0.15

-

2.00

-

1.00

-

0.20

0.06

-

17.0

19.0

-

8.0

10.0

0.15

min

303 Stainless Steel Hardness

Type Metric English
Hardness, Rockwell B 96 96
Hardness, Rockwell C 19 19
Hardness, Brinell 228 228
Hardness, Knoop 251 251
Hardness, Vickers 240 240

Stainless Steel 303 ASTM Specification

Trade Name: 303 Se Stainless, 303 Se

  • ASTM A582 (Round Bars) 303 SS Condition B, 303 SS Condition A
  • ASTM A581 (Stainless Steel Wire)
  • ASTM A895 (plate, sheet, and strip)

303 Stainless Steel AMS Specifications

AMS 5640 (plate, sheet, and strip)

SS 303 Price Per Kg In India

    Currency
Type Origin of Material India INR Malaysia Philippines
SS 303 Round Bar India INR 240/ Kg Malaysian Ringgit 13.25 Philippine peso 156.69

SS 303 Density

Type Metric English
Density 8 g/cc 0.289 lb/in³

303 Stainless Steel Thermal Properties

CTE, linear 500°C 18.4 µm/m-°C 10.2 µin/in-°F  at 0-540°C, 18.7 µm/m-C at 0-650°C
CTE, linear 20°C 17.2 µm/m-°C 9.56 µin/in-°F  from from 0-100°C
CTE, linear 250°C 17.8 µm/m-°C 9.89 µin/in-°F  at 0-315°C (32-600°F)
Thermal Conductivity 16.2 W/m-K 112 BTU-in/hr-ft²-°F  at 100°C (212°F), 21.5 W/m-K at 500°C (930°F)
Solidus 1400 °C 2550 °F  
Specific Heat Capacity 0.5 J/g-°C 0.12 BTU/lb-°F  from 0-100°C (32-212°F)
Melting Point 1400 - 1420 °C 2550 - 2590 °F  
Liquidus 1420 °C 2590 °F

303 SS Annealed and Physical Properties

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

303

8027

193

17.3

17.8

18.4

16.3

21.5

500

720

SUS303 Equivalent Material

Grade

UNS No

Old British

Euronorm

Swedish SS

Japanese JIS

BS

En

No

Name

303

S30300

303S31

58M

1.4305

X8CrNiS18-9

2346

SUS 303

303Se

S30323

303S42

-

-

-

-

SUS 303Se

Alternative Grades

Is 303 SS Food Grade?

NO, 304 stainless steel is a food grade

Is SS 303 Magnetic?

No, Its non-magnetic alloy

SUS303 Specific gravity

Grade gravity
SUS303 0.793
SUS303Se 0.793

304 Stainless Steel chemical composition

AISI 304
Ni 8 – 11
Fe Balance
Cr 18 – 20
C 0.08 max
Si 0.75 max
Mn 2 max
P 0.040 max
S 0.030 max
N

AISI 304 Mechanical properties

SS Grade 304
Rockwell B (HR B) max. 92
Brinell (HB) max. 201
Tensile Strength min. (MPa) 515
Yield Stress 0.2% Proof min. (MPa) 205
Elongation min. (% in 50mm) 40
Hardness -

304 Stainless Steel equivalent standard specification

AISI/ SUS JIS UNS WERKSTOFF NR. AFNOR BS GOST EN SS
Grade JAPAN USA GERMAN RUSSIAN BRITISH RUSSIAN EUROPE SWEDISH
SS 304 SUS 304 S30400 1.4301 Z7CN18‐09 304S31 08Х18Н10 X5CrNi18-10 2332

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