Overview of 303 Stainless Steel | Best Stainless Steel Grades for CNC Machining | CNCLATHING


Stainless steel is a versatile material comes in multiple grades and alloys that differ in properties and characteristics. When manufacturing stainless steel machined parts for different industries, we need to learn about its feature and machining difficulties. In this article, let’s introduce what is 303 stainless steel, SS303 physical and mechanical properties, as well as the best grade of stainless steel for machining.

What is 303 Stainless Steel?

303 Stainless steel, also known as UNS S30300 and SS303, it’s a non-magnetic, austenitic stainless steel. Take a look at the composition of 303 alloy, 17%-19% Cr, 8%-10% Ni, ≤0.15% C, ≤1.00% Si, ≤2.00% Mn, ≤0.20% P, ≥ 0.15% S, and ≤0.6% Mo, which gives stainless steel 303 free machining characteristics, good mechanical and corrosion resistant properties. Similar to other austenitic grades, SS303 also have excellent toughness, while the addition of sulfur does reduce its toughness and corrosion resistance a little, even though it improves machinability as well. In addition, the carbon content makes it also vulnerable to sensitisation. 

Stainless Steel 303 Properties and Uses

Stainless Steel grade 303 has good resistance to mildly corrosive atmospheres (lower than SS304) and good oxidation resistance at temperatures up to 1700°F. Alloy 303 is subject to corrosion cracking in chloride environments above 60℃, and in the humid marine environment, it is easy to suffer from rapid pitting corrosion and easy to form rust film. When it comes to processing, 303 is not suitable for welding but the most readily machineable of all the austenitic grades of stainless steel.


Physical Properties of SS303

Density of 303 Stainless Steel: 8.03 kg/m3 (0.289 lb/in³)

Electrical Resistivity: 0.72 x 10-6 Ω.m

Melting Point: 1400 – 1420 °C

Modulus of Elasticity: 193 GPa (28000 ksi)


Mechanical Properties of SS303

Rockwell C Hardness of 303 Stainless Steel: 19

Vickers Hardness of 303 Stainless Steel: 240

Brinell Hardness of 303 Stainless Steel: 228

Ultimate Tensile Strength of 303 Stainless Steel: 690 MPa (100000 psi)

Yield Tensile Strength of 303 Stainless Steel: 415 MPa (60200 psi)

Elongation at Break: 40%


What are the applications of 303 stainless steel? Based on the properties and features of UNS S30300, the alloy should not be exposed to moist marine environment and it’s not recommended to use it constantly at temperatures above 1400°F, which would cause irregular scaling. As an engineering material, stainless steel 303 is usually made into nuts, bolts, screws, fasteners, shafts, aircraft fittings, electrical components, gears, automotive, aerospace, medical instruments and other parts using CNC machining services, including stainless steel milling, stainless steel turning and stainless steel drilling.

What are the Best Stainless Steel Grades for CNC Machining?

Different composition lead to different stainless steel types suitable for varying processing methods. When you want to choose a stainless steel for cutting with CNC machines, which one is the best choice? 


The first thing we should know is the machinability of various stainless steel alloys. The presence of sulfur and other chemicals can aid the CNC machining process. Check out our metal machinability chart to get more detailed machinability of different grades. 


Most types of stainless steel can be machined on lathes and mills, but it also has challenges, for example, stainless is vulnerable to work hardening. For the best stainless steel grades for machining, alloy 303 is an example of austenitic grades of stainless steel and most free-machining of all chromium-nickel types. Among the ferritic stainless steels, 416 is the most readily machineable due to the addition of sulfur and phosphorus. There are also grade 430 and 410 are highly machinable.