What exactly is 303 stainless steel? How does it compare to 304?

Standard Chemical 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	-
Standard Mechanical Property
Grade	Tensile Strength (Mpa)	Yield Stress 0.2%(Mpa)	Elongation (50mm%)	Hardness(Max)
HRB	HB	HV
303	650	300	45	241	262	236
Physical Properties (Annealed Condition)
Grade	Density (Kg/m3)	Elastic Modulus (Gpa)	Average Coefficient of Thermal Expansion	Thermal Conductivity	Specific Heat	Electrical Resistance
0-100°C µm/m/°C	0-315°C µm/m/°C	0-538°C µm/m/°C	100°C (W/mk)	500°C (W/mk)	0-100°C (J/Kg.K)	(nΩ.m)
303	7900	193	17.3	17.8	18.4	16.3	21.5	500	720

303 stainless steel is the most suitable for machining among austenitic stainless steels. It is primarily used in production processes involving a large amount of automatic screw machine cutting. Its machinability rating (compared to B1212) is approximately 78%. There is also a grade called "Ugima" of 303, which offers even better machining performance than the standard 303 grade.

The improvement in machining performance and wear characteristics of 303 stainless steel is due to the addition of sulfur, which also reduces its corrosion resistance below that of 304 stainless steel. Like other austenitic stainless steels, 303 stainless steel has excellent toughness, although sulfur slightly reduces its toughness.

It exhibits good corrosion resistance in mildly corrosive environments, but due to the addition of sulfur, its corrosion resistance, weld ability, and formability are lower than that of 304 stainless steel. Stress corrosion cracking can occur in chloride environments above approximately 50°C; 303 is not suitable for tight radius bending operations; and it cannot be hardened by heat treatment.