Difference between nitric acid grade 304L and regular 304L

I may be uninformed; I haven’t heard of nitric acid-grade stainless steel – I only know about urea-grade and nuclear-grade ones. . . . . Stainless steel. As far as I know, at 530°C in a nitrogen atmosphere, the resistance of the three austenitic stainless steels to nitric acid molten salt corrosion is, in order, 316L > 321 > 304.

I also asked this question after seeing the following content: Gang Yimin. Development and Selection of Nitric Acid-Resistant Steels. Chemical Engineering Design, 2004, 14(3):7. 2.2 Nitric acid-grade austenitic stainless steels: To improve resistance to corrosion by dilute nitric acid at high temperatures, “nitric acid-grade” austenitic stainless steels were developed in the 1970s. It is essentially still a modified version of ultra-low carbon stainless steel. The control standards for harmful impurity elements such as carbon, phosphorus, and silicon depend mainly on the level that can be achieved through large-scale production using off-ferrous refining methods; this allows its price to be relatively close to that of conventional types, facilitating widespread adoption. The corresponding steel grades developed by us are: nitric acid grade 00Cr19Ni13 (commercial grade KY701) and nitric acid grade 00Cr25Ni20Nb (grade KY703). The levels of its harmful impurities are kept within the following ranges: ≤0.1020% C, ≤0.1025% P, ≤0.14% Si, etc. Depending on the specific usage requirements and taking cost into account, the internal control standards are determined through negotiation between the supplier and the buyer at the time of signing the contract (the carbon content generally can be kept at ≤0.1015%).

The KY703 grade was discontinued a long time ago

For nitric acid, it is said that C4 steel can be used with stainless steel, but generally aluminum is used!