Versatility of Stainless Steel
Since its inception in 1913, stainless steel has evolved into a versatile metal, bridging the gap between heavy industries and everyday applications. It's the invisible hero behind your cooking utensils, automobiles, high-precision electronics, and much more. The demand for stainless steel in India ranks second only to the textile industry, affirming its title as 'the versatile metal' due to its extraordinary properties and myriad applications.
Understanding Stainless Steel
Stainless Steel is not a single material but a diverse family of steels, each containing a minimum of 11% chromium with varying additions of nickel, molybdenum, titanium, and other elements.
Diverse Families of Stainless Steel
The stainless steel varieties fall into three main groups: Austenitic, Ferritic, and Martensitic.
I. Ferritic Stainless Steel
The lack of additional alloying elements classifies ferritic stainless steel as "plain Chromium steels," with a Chromium content typically falling within the 12 to 18% range. Ferritic stainless steel exhibits very low levels of carbon content.
Key Features:
1. Moderate corrosion resistance
2. Magnetic properties
3. Inability to be hardened via heat treatment
4. Usage primarily in the annealed condition
5. Limited weldability for most grades
It has a strong presence in automotive exhaust systems, exemplified by grade 430 and 409 stainless steel.
II. Austenitic Stainless Steel
Adding nickel to stainless steel transforms its microstructure into 'austenite.' Notably, 70% of commercial stainless steel is austenitic, with 304 being its flagship grade, representing over half of global stainless steel consumption. Also known as 18/8, it signifies an average composition of 18% chromium and 8% nickel. This nomenclature is sometimes used interchangeably for other austenitic stainless steel grades, even if their compositions differ significantly.
Key Features:
1. Exceptional corrosion resistance
2. Non-magnetic when annealed
3. Rapid work hardening with cold work
4. Inability to be hardened through heat treatment
5. Ductile and readily formable
6. Excellent weldability
7. Hygienic with exceptional cleanability
8. Outstanding performance at both high and low temperatures
In addition to 304 stainless steel, regular austenitic grades encompass the well-known marine grade, 316 stainless steel, and the versatile machining bar grade, 304 stainless steel.
III. Martensitic Stainless Steel
Martensitic stainless steel, the earliest stainless steel developed for commercial use, found its initial applications in cutlery. Distinguishing themselves from other stainless steel types, martensitic stainless steels boast a relatively higher carbon content ranging from 0.1% to 1.2%. Much like ferritic stainless steel, they are considered plain chromium steels with a chromium content of 12% to 18%.
Key Features:
1. Moderate corrosion resistance
2. Heat treatability
3. Magnetic characteristics
4. Inability to be cold-formed
5. Limited weldability
6. Excellent weldability
7. Hygienic with exceptional cleanability
8. Outstanding performance at both high and low temperatures
Prominent martensitic grades encompass 420 stainless steel, serving construction applications such as shafts, and 440C stainless steel, recognized as the hardest and most abrasion-resistant among all stainless steel varieties.
