What Is The Difference Between Austenitic And Martensitic Stainless Steel ?
The martensitic stainless steel is made by creating martensite. Martensite is the formation of body centered crystalized iron which is a cubic form. Most martensitic stainless steels are formed by heating up the austenite and then rapidly cooling to lower temperatures. The process is known as quenching. The rapid cooling of the material prevents cementite formation. The process also eliminates the expelling of excess carbon atoms and traps them unnaturally inside the material.
This provides the martensitic stainless steels very high abrasion resistance and toughness. The microstructure is responsible for the abrasion resistance where the trapped carbon provide high toughness. The corrosion resistance of the martensitic stainless steels is less compared to the austenitic counterparts but the strength, abrasion resistance and toughness are higher. These properties are preferred in applications that need handling of much wear and tear such as platforms, transportation, abrasive surfaces, etc. The toughness of the materials is also important in having structures without deformation with smaller forces excerpted.
Welding of the steels is a necessary process in almost all metallic applications. The welding ease, the welding requirements and the welding speed all depend on the type of material. Austenitic stainless steels are much easier to weld with in comparison to the martensitic ones. The martensitic steels have higher carbon contents than most austenitic counterparts. This reduces the corrosion resistance, increases the toughness and increases the risk of chromium carbide precipitation while welding.
Martensitic steels also have to be preheated to certain temperature before it could be welded correctly. Not all austenitic stainless steels require post weld heat treatments, but the martensitic stainless steels have to be post weld heat treated or annealed to harden them and to avoid embrittlement. The corrosion resistance of the martensitic steels will reduce after welding, but the austenitic stainless steels retain the corrosion resistance even after welding.
The most used welded type of material is the 304 austenitic stainless steel. Most of the austenitic stainless steels have 16% to 26% chromium and up to 22% nickel in their composition with lower carbon contents. This makes them withstand the welding procedure and to retain the corrosion resistance. The martensitic grades have chromium from 12 to 18% and high carbon content. Welding has to be carefully applied in highly thick parts and restrained joints to avoid cracking while welding.
The martensitic steel grades come in the 400 series of stainless steels. They have carbon contents ranging from 0.15 to 0.63%. There are 410, 420, 440A, 420 ultra hone and 410 Cb grades in the martensitic stainless steel. The austenitic stainless steels come in the 200 and 300 series of materials. The nitronic 30, 201, 301, 304, 316, 309 and 316 are some of the austenitic stainless steels. The applications of the martensitic stainless steels are typically in cutlery, surgical instruments, cookware, vehicle stampings, staple guns, springs, scissors, screwdrivers, industrial blades, pliers, etc. The austenitic stainless steels are used in almost all types of domestic, industrial and architectural applications including oil and gas applications as well.
|EURONORM (EN) STANDARD||EN DESIGNATION||AISI GRADE||C||CR||MO||NI||OTHERS|
|1.4305||X8CrNiS18-9 e||303||< 0.10||18||NS||9||0.3|
|1.4541||X6CrNiTi18-10||321||< 0.08||18||NS||10.5||Ti: 5×C ≤ 0.70|
|1.4571||X6CrNiMoTi17-12-2||316Ti||< 0.08||17.5||2.25||12||Ti: 5×C ≤ 0.70|
|EN Steel designation||European EN||AISI||C||Cr||Mo||Others|
|X4CrNiMo16-5-1||1.4418||-||≤ 0.06||16.0||1.10||Ni: 2.00|
|X5CrNiCuNb16-4||1.4542||630 (17/4PH)||≤ 0.07||16.0||-||Ni: 4.00
Nb: 5xC to 0.45
|EN||MININMUM YIELD STRESS, MPA||TENSILE STRENGTH, MPA||MINIMUM ELONGATION, %||HEAT TREATMENT|
|1.4006||450||650 - 850||15||QT650|
|1.4021||600||650 - 850||12||QT800|
|1.4122||550||750 - 950||12||QT750|
|1.4057||700||900 - 1050||12||QT900|
|1.4418||700||840 - 1100||16||QT900|
|1.4542||790||960 - 1160||12||P960|
|300 Series||301 - 302 - 303 - 304/L - 304H - 316/L - 317L - 317LMN - 321 - 321H - 347 - 347H -309 - 309S - 310 - 310S - 310H - 330|