Standard Chemical Composition of Stainless Steel "304" -Part 4

Tables 2 through 6 present the chemical compositions specified for each grade across different standards. Table 1 reveals that ASTM A959-04 includes ten variants of 304 and its derivative grades. The Japanese JIS standard also lists ten, but only six correspond directly to ASTM grades; the remaining four—SUS304J1, SUS304J2, SUS304J3, and SUS304Cu—appear to be unique Japanese developments of 304 derivatives.

From a broader perspective, these derivative grades essentially represent deliberate modifications of the base 304 chemical composition, resulting in variant forms. Consider the following examples:

Carbon Content Modifications: The carbon levels may be lowered or raised depending on the intended properties. For instance, 304L is an extra-low-carbon variant. Its reduced carbon content greatly enhances corrosion resistance—especially intergranular corrosion following welding—making it ideal for large-section welded components where maintaining mechanical strength is critical. Conversely, 304H features elevated carbon (typically 0.04–0.10 %), which increases its strength and stabilizes austenite, making it more suitable than standard 304 for low-temperature applications and non-magnetic components. In fact, 304H’s higher carbon content translates to superior tensile and yield strength in high-temperature environments.

In summary, derivative 304 grades are simply tailored variants of the original 304 alloy—fine-tuned primarily through carbon adjustments to meet specific performance requirements such as enhanced weldability, improved corrosion resistance, or elevated-temperature strength.

The addition of nitrogen and copper elements to 304 Stainless Steel enhances its mechanical properties and corrosion resistance.

Nitrogen Addition:

Nitrogen acts as a solid solution strengthener in austenitic stainless steels. Grades such as 304N (SUS304N1), XM-21 (SUS304N2), and 304LN are nitrogen-enhanced variants of 304 stainless steel. The incorporation of nitrogen increases the yield strength without significantly compromising ductility and toughness. Moreover, nitrogen improves resistance to intergranular corrosion, pitting, and crevice corrosion. For instance, SUS304N2 (XM-21) contains approximately 0.15–0.30% nitrogen, contributing to its enhanced strength and corrosion resistance .

Copper Addition:

Copper is added to certain 304 stainless steel variants to stabilize the austenitic phase, thereby enhancing corrosion resistance, especially in reducing environments like sulfuric acid. However, copper addition may reduce strength and work-hardening tendencies, improving ductility. Grades such as S30430 (06Cr18Ni9Cu3, SUSXM7) and SUS304J3 (06Cr18Ni9Cu2) contain copper to achieve these properties. These steels are suitable for cold heading, extrusion, deep drawing, and stretching applications due to their improved formability .

In the Japanese JIS standard, five 304 stainless steel derivatives contain copper. Among them, SUS304Cu, SUS304J1, and SUS304J2 are designated for sheet and strip products. Notably, SUS304J1 and SUS304J2 have modified chemical compositions compared to standard 304, with reduced chromium (15.00%–18.00%) and nickel (6.00%–9.00%) contents, increased manganese (up to 3.00% or 5.00%), and copper content ranging from 1.00% to 3.00%. These adjustments aim to partially replace nickel with manganese or copper, making these grades suitable for components formed through cold working under general corrosion conditions.

In summary, the strategic addition of nitrogen and copper to 304 stainless steel results in enhanced strength, corrosion resistance, and formability, catering to various industrial applications.