Standard Steels  

According to the chemical compositions, standard steels can be classified into three major groups: 

Carbon Steels, Alloy Steels, Stainless Steels

Steels	Compositions
Carbon Steels	Alloying elements do not exceed these limits: 1% carbon, 0.6% copper, 1.65% manganese, 0.4% phosphorus, 0.6% silicon, and 0.05% sulfur.
Alloy Steels	Steels that exceed the element limits for carbon steels. Also includes steels that contain elements not found in carbon steels such as nickel, chromium (up to 3.99%), cobalt, etc.
Stainless Steels	Contains at least 10% chromium, with or without other elements. Based on the structures, stainless steels can be grouped into three grades: Austenitic: Typically contains 18% chromium and 8% nickel and is widely known as 18-8. Nonmagnetic in annealed condition, this grade can only be hardened by cold working. Ferritic: Contains very little nickel and either 17% chromium or 12% chromium with other elements such as aluminum or titanium. Always magnetic, this grade can be hardened only by cold working. Martensitic: Typically contains 12% chromium and no nickel. This grade is magnetic and can be hardened by heat treatment.

Carbon steels are steels whose alloying elements do not exceed the following limits:  C   max.1% Cu  max.0.6% Mn  max.1.65% P  max. 0.4% Si  max.0.6% S   max.0.05%

Designation

Carbon steels are designated by distinct AISI (American Iron and Steel Institute) four-digit numbers. The first two digits indicate the grades of the steels, while the last two digits give the nominal carbon content of the alloy in hundredths of a percent. Here is an example:   XX :0.xx% average carbon content   AISI  10 60       10 >Nonresulfurized  grades 11 >Resulfurized grades 12 >Resulfurized and rephosphorized grades 15 >Nonsulfurized gradesMn content > 1% If a letter L or B shows up between the second and third digits of an AISI number, it means that this grade is either a Leaded steel or a Boron steel; Sometimes a suffix H is attached to a AISI number to indicate that the steel has been produced to prescribed hardenability limits. Examples are: Leaded steels :AISI 12L14, AISI 12L15... Boron steels :AISI 15B48H... H-steels :AISI 1038H, AISI 15B48H...

Alloy steels  comprise a wide variety of steels which have compositions that exceed the limitations of C, Mn, Ni, Mo, Cr, Va, Si, and B which have been set for carbon steels. However, steels containing more than 3.99% chromium are classified differently as stainless  and tool steels.Alloy steels are generally more responsive to heat and mechanical treatments than carbon steels.  AISI Designation Typically, alloy steels are designated by distinct AISI (American Iron and Steel Institute) four-digit numbers. The first two digits indicate the leading alloying elements, while the last two digits give the nominal carbon content of the alloy in hundredths of a percent. Occasionally we see five-digit designations where the last three digits tell that the carbon is actually over 1%. Here is an example:   XXX :x.xx% average carbon content 51 100     13 xx:1.75Mn Manganese 23 xx:3.50Ni Nickel 31 xx:1.25Ni, 0.65-0.80Cr Nickel-Chromium 40 xx:0.20-0.25Mo Molybdenum 44 xx:0.40-0.52Mo 41 xx:0.50-0.95Cr, 0.12-0.30Mo Chromium-Molybdenum 46 xx:0.85-1.82Ni, 0.20-0.25Mo Nickel-Molybdenum 48 xx:3.5Ni, 0.25Mo 50 xx:0.27-0.65Cr Chromium 51 xx:0.80-1.05Cr 50 xxx:0.50Cr, 1.00C 51 xxx:1.02Cr, 1.00C 52 xxx:1.45Cr, 1.00C 61 xx:0.60-0.95Cr, 0.10-0.15V Chromium-Vanadium 92 xx:1.4-2Si, 0.65-0.85Mn, <0.65Cr Silicon-Manganese 43 xx:1.82Ni, 0.50-0.80Cr, 0.25Mo Nickel-Chromium-Molybdenum 47 xx:1.05Ni, 0.45Cr, 0.20-0.35Mo 81 xx:0.30Ni, 0.40Cr, 0.12Mo 86 xx:0.55Ni, 0.50Cr, 0.25Mo 87 xx:0.55Ni, 0.50Cr, 0.25Mo 88 xx:0.55Ni, 0.50Cr, 0.20-0.35Mo 93 xx:3.25Ni, 1.20Cr, 0.12Mo 94 xx:0.45Ni, 0.40Cr, 0.12Mo If a B shows up between the second and third digits of an AISI number, it means that this grade is a Boron steel; Sometimes a suffix H is attached to a AISI number to indicate that the steel has been produced to prescribed hardenability limits.

Stainless steels

Stainless steels are high-alloy steels that have superior corrosion resistance than other steels because they contain large amounts of chromium. Stainless steels can contain anywhere from 4-30 percent chromium, however most contain around 10 percent. Stainless steels can be divided into three basic groups based on their crystalline structure: austenitic, ferritic, and martensitic. Another group of stainless steels known as precipitation-hardened steels are a combination of austenitic and martensitic steels. Below are the general compositional contents of these groups.

Grades

Ferritic grades: Ferritic stainless steels are magnetic non heat-treatable steels that contain chromium but not nickel. They have good heat and corrosion resistance, in particular sea water, and good resistance to stress-corrosion cracking. Their mechanical properties are not as strong as the austenitic grades, however they have better decorative appeal. Martensitic grades: Martensitic grades are magnetic and can be heat-treated by quenching or tempering. They contain chromium but usually contain no nickel, except for 2 grades. Martensitic steels are not as corrosive resistant as austenitic or ferritic grades, but their hardness levels are among the highest of the all the stainless steels. Austenitic grades: Austenitic stainless steels are non-magnetic non heat-treatable steels that are usually annealed and cold worked. Some austenitic steels tend to become slightly magnetic after cold working. Austenitic steels have excellent corrosion and heat resistance with good mechanical properties over a wide range of temperatures. There are two subclasses of austenitic stainless steels: chromium-nickel and chromium-manganese-low nickel steels. Chromium-nickel steels are the most general widely used steels and are also known as 18-8(Cr-Ni) steels. The chromium nickel ratio can be modified to improve formability; carbon content can be reduced to improve intergranular corrosion resistance. Molybdenum can be added to improve corrosion resistance; additionally the Cr-Ni content can be increased.

ANSI  2XX Stainless steel  

ANSI 3XX

ANSI 4XX