Stainless steel is the name used mainly for anti-corrosion properties of high alloy steel. The main feature of the stainless steel family is that at least 10.5% chromium is contained in all of them. This feature allows the steel to resist abrasive atmospheres or corrosive chemical environments. Stainless steel has 60 different types divided into 5 different categories. Stainless steel is a very important part of the world market, although it is expensive from carbon steel and alloy steel and has less use in global markets.
HISTORY OF STAINLESS STEEL
The stainless steel was invented in 1913 by British-born Harry Brearly. During an experiment, it was observed that the resistance to corrosion of the steel increased when the chromium content in the steel was increased to 12% and above. Harry Brearly is known as the person who casts stainless steel bases and has contributed to the development of many types of stainless steel. The development process of stainless steel came to a halt during World War I. By the late 1920s it was understood that martensitic and austenitic stainless steel varieties were the most useful species. Martensitic stainless steels contain between 13 and 18% chromium, while the austenitic paslnamase group contains 18% chromium and 8% nickel. In today’s markets, stainless steel is used in steel with minimum 10,5% chromium content and high corrosion resistance. Chromium forms a self-regenerating layer around the steel, which is the most important factor preventing steel corrosion. The development of stainless steel continues today and is divided into five main groups;
– Ostenitic
– Ferritic
– Martensitic
– Dublex
– Precipitation hardenable alloys
STAINLESS STEEL MAIN CATEGORIES
300 Series Austenitic Alloys: 301, 302, 303, 304, 305, 308, 309, 310, 314, 316, 321 series stainless steels contain chrome and nickel. Heat treatment is not possible and does not hold magnet. Their ability to take shape is high. 300 series or austenitic stainless steels account for about 70% of world stainless steel production. The austenitic structure is formed by the addition of about 8-10% nickel. However, nickel does not form austenitic by itself. Austenitic properties are created by the help of other elements such as manganese, nitrogen, carbon and copper. Molybdenum reinforcement increases corrosion resistance. It is used in decoration, machine manufacturing, white goods, chemical industry and in the production of the sake.
400 Series Ferritic – Alloys: 405, 409, 429, 430, 434, 436, 442 … The stainless steels on this shelf contain chrome. They are magnetizable but not heat treated. Ferritic stainless steels are a stainless steel base that does not contain nickel but contains high chromium (between 12% and 30%), molybdenum, titanium vanadium, carbide builders and ferritic steady breaking alloy elements. In general, the high chromium content of the ferritic material provides a very high corrosion resistance. Ferritic stainless steels, which have mechanical and physical properties close to those of carbon steels, which are more closely related to each other, can not be heat-treated and easily rolled due to their low carbon content, in contrast to austenitics. These steels are the only applicable heat treatment annealing process. They are not suitable to be shaped as austenitics.
| Notation | Symbol | Chemical Composition | |||||||
| C | Si | Mn | P | S | Ni | Cr | Others | ||
| 301 | STS301 | ≤0.15 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 6.00~8.00 | 16.00~18.00 | – |
| 301L | STS301L | ≤0.030 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 6.00~8.00 | 16.00~18.00 | Less than 0.20 N |
| 304 | STS304 | ≤0.08 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 8.00~10.50 | 18.00~20.00 | – |
| 304L | STS304L | ≤0.030 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 9.00~13.00 | 18.00~20.00 | – |
| 304J1 | STS304J1 | ≤0.08 | ≤1.70 | ≤3.00 | ≤0.045 | ≤0.030 | 6.00~9.00 | 15.00~18.00 | Cu 1.00~3.00 |
| 305 | STS305 | ≤0.12 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 10.50~13.00 | 17.00~19.00 | – |
| 316 | STS316 | ≤0.08 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 10.00~14.00 | 16.00~18.00 | Mo 2.00~3.00 |
| 316L | STS316L | ≤0.030 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 12.00~15.00 | 16.00~18.00 | Mo 2.00~3.00 |
| 321 | STS321 | ≤0.08 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 9.00~13.00 | 17.00~19.00 | More than 5×C% Ti |
What is Stainless Steel ?
The four major types of stainless steel are;
- Austenitic
- Ferritic
- Austenitic-Ferritic (Duplex)
- Martensitic
Austenitic is the most widely used type of stainless steel. It has a nickel content of at least of 7%, which makes the steel structure fully austenitic and gives it ductility, a large scale of service temperature, non-magnetic properties and good weldability. The range of applications of austenitic stainless steel includes housewares, containers, industrial piping and vessels, architectural facades and constructional structures.
Ferritic stainless steel has properties similar to mild steel but with the better corrosion resistance. The most common of these steels are 12% and 17% chromium containing steels, with 12% used mostly in structural applications and 17% in housewares, boilers, washing machines and indoor architecture.
Austenitic-Ferritic (Duplex) stainless steel has a ferritic and austenitic lattice structure – hence common name: duplex stainless steel. This steel has some nickel content for a partially austenitic lattice structure. The duplex structure delivers both strength and ductility. Duplex steels are mostly used in petrochemical, paper, pulp and shipbuilding industries. Martensitic stainless steel contains mostly 11 to 13% chromium and is both strong and hard with moderate corrosion resistance. This steel is mostly used in turbine blades and in knives.