Is steel an alloy?

Materials science metal / iron and steel / standards and alloys


There is an almost unmanageable number of types and alloys of steel and iron. To keep track of things, were Norms introduced. But there are many standards co-existing and no one can know them all - but there are books for that.

With industrialization, a standardization of technology became necessary, and the results were recorded in standards. The data range from definitions to extensive data sets in tabular form. They are based on long experience, complicated calculations and sometimes arbitrariness. Standards represent a consensus reached by a wide variety of interest groups (industry, trade, research, authorities and consumers). Their purpose is economy, rationalization and understanding, as well as the regulation of quality, safety and environmental protection. Various organizations at national and international level are responsible for creating and maintaining the standards.

  • DIN stands for German Institute for Standard e.V. The association is responsible for standardization in Germany and participates in the development of international standards.
    • The Association of German Engineers (VDI) has created a set of 1,700 valid standards for mechanical engineering.
    • The Technical Monitoring Association (TÜV) is commissioned by the authorities to check compliance with standards and legal regulations.
  • As European standard (EN) are standards that arise in cooperation with several European institutes or through the unification of national standards.
  • The International Organization for Standardization (ISO) carries out this activity internationally for more than 100 member states. The organization abbreviation would not be appropriate because of the differences in translation. ISO is therefore from the Greek word isos derived and stands for equal.
  • Among many others, the American ANSI standard and the Japanese JIS standard are also important.

Examples

  • DIN standards are indicated with DIN, followed by the number of the standard.
  • International standards that come into force directly with us bear the abbreviation of their organization.
  • If necessary, DIN adopts international standards and incorporates them into its set of rules. They are then referred to as DIN EN, DIN ISO or DIN EN ISO.

Definition of terms (according to DIN EN 10020) [edit]

In this standard, steel is an iron-carbon alloy with a C content of at most 2.06%. Iron materials with more than 2.06% C are considered cast materials. Steel is divided into three classes here:

Unalloyed steels

Steels for which none of the limit values ​​below are reached.

Stainless steels

Steels with

  • Chromium ≥ 10.5%
  • Carbon ≤ 1.2%
Other alloy steels

Steels for which at least one of the limit values ​​below is reached, but which are not classified as stainless steels

AlB.BiCoCrCuLaMnMonNb NiPbSeSiTeTiV.W.Zr
0,30,00080,10,30,30,40,11,650,080,06 0,30,40,10,60,10,050,10,30,05%
  • The class of Basic steels was abolished with the new version of the standard in July 2000.
    These were steels that - apart from their relatively low strength - were not subject to any requirements.
  • Both unalloyed and alloyed steels (not stainless) are divided into quality and stainless steels:
    • For Quality steels Specified requirements apply, such as toughness, weldability and formability.
      However, they are not suitable for targeted heat treatment (tempering, hardening). The steel gets its quality from a fine-grain structure and the required purity of max.0.045% phosphorus and sulfur.
    • At Stainless steels the specified requirements are higher than those for quality steels.
      They achieve higher strength values ​​and are suitable for targeted heat treatment (especially hardening and tempering). The quality of the further improved purity is achieved through special manufacturing processes such as the electroslag remelting process. Slag inclusions are largely removed; the sulfur and phosphorus content must not exceed 0.025%.
    • Alloy steels are further used in low- and high-alloy steels assigned. As soon as the salary one Alloy element over 5 % the steel is high-alloyed. This limit was set relatively arbitrarily and "only" serves to ensure good legibility in the material designation.
  • Stainless steels are by the high Chromium content passivated - that is, particularly inert and corrosion-resistant.
    Depending on the alloying elements, they have different structural shapes:
    • Austenitic steels - They are by far the most widely used stainless steels.
      The best known representative is X5CrNi18-10, also known as V2A. Austenitic steels are not magnetic, difficult to machine, but easy to form and are suitable for welding. They are very soft and not curable.
      (V2A is often used under the designation 18/10 for saucepans and cutlery, but never for knives)
    • Ferritic steels - Are magnetizable, difficult to machine and suitable for welding. Their heat resistance is of great importance.
    • Martensitic steels - They have the highest strength among stainless steels and can reach the greatest hardness. They are used, among other things, for knives and other cutting tools in the food industry. They are magnetizable and easy to machine, but are difficult to weld.
Stainless steel ≠ rustproof

The term becomes colloquial stainless steel Equated with stainless steel, especially with the special alloys V2A and V4A (Nirosta, Inox). The word noble is associated with the immortality of precious metals such as gold and platinum.

When it comes to steel noble but for particularly small amounts or mass fractions of defined steel contaminants. Unalloyed stainless steel can rust through very quickly.

Classification according to purpose [edit]

Structural steel

Construction materials for steel and machine components.

  • Carbon content: 0.05-0.6%
  • In general, toughness and good machinability are in the foreground
Tool steel

Materials for making tools.

  • Carbon content: 0.6 - 1.7% (max. 2.1%)
  • First and foremost, they must be wear-resistant, i.e. have a high degree of hardness and strength.
General structural steel
with a C content of 0.15-0.5%.
For components with normal temperature stress.
Inexpensive material for general constructions.
Weldable fine-grain structural steel
Like general structural steel, but with additives to refine the grain. Improved toughness and strength.
Case-hardening steel
0.05-0.2% -C; partially alloyed with Cr, Mn, Mg, Ni.
Not hardenable per se. With case hardening, the surface is specifically enriched with carbon and hardened, the core remains tough.
Use for shafts, gears, cams, chain links
Quenched and tempered steel
0.22 - 0.6% -C, partially alloyed with Cr, Ni, Mo, V.
Materials that are intended for quenching and tempering. The steel is hardened and tempered - that is, the stresses in the steel are partially relieved again. Very high strength with good toughness. A special feature is the depth of remuneration, i.e. how far the remuneration extends below the surface.
Drive and gear shafts, bolts, wheel tires (rail)
Nitriding steel
0.31 - 0.41% -C, alloyed with the nitride formers Al, Cr, Ti.
During nitriding, the surface is treated with nitrogen; extremely hard nitrides are formed, which make the surface wear-resistant.
For gears, cams, valves (motor head)
Free cutting steel
By adding lead or sulfur to the alloy, the steel is optimized for machining on machine tools and machining centers. Tool wear and cutting forces are reduced, chips are broken at short intervals. The formation of long flowing chips, which "clog" the machines, is prevented.
For machined parts in mass production.
Stainless steels
see above
Bright steel
no own class according to the composition.
Bright drawn parts show increased strength due to cold forming and have smooth surfaces with high dimensional accuracy
Cost-reduced production of machine parts without further surface processing.
Unalloyed tool steels
Hardenability and strength are essentially determined by the carbon content. The hardening depth is only small and at temperatures above 200 ° C there is a significant drop in hardness.
Use for punches and cutting inserts of punches (not to be confused with indexable inserts for lathes), as well as for bending and drawing tools.
Alloyed cold work steels
Alloy additives such as Cr, V, W and Si increase toughness, compressive strength and wear resistance. In addition, the hardening delay is reduced. Here, too, the working temperature is limited to a maximum of 200 ° C.
Use for pliers, spanners, punches and other hand tools.
Alloyed hot work steels
Additionally alloyed with Co, Mo and Ni, the working temperature is increased to max. 400 ° C.
Use for forging dies and injection molds
High speed steel
The name HSS is derived from the English "High Speed ​​Steel", which is often translated as high-performance high-speed steel. They are extremely wear-resistant and resilient, even when used at high temperatures. In addition, they are less sensitive to temperature changes. They are used for drills, milling cutters and turning tools in machining. A clear improvement in the cutting performance and stability of the tool is achieved by coating with hard metal. Titanium nitrite (TiN, recognizable by its golden color) or titanium carbide (TiC) is used particularly frequently for this purpose.


Other cutting materials


In addition to HSS, manufacturing technology knows many other cutting materials that are more wear-resistant and allow higher cutting speeds. However, they cannot exceed the toughness of HSS. For example, Schneid achievedceramic very high cutting speeds, but breaks very quickly in rough conditions (e.g. interrupted cut) due to its brittleness. The “ideal” cutting material, both stable and tough, does not (yet) exist.

Short names (according to DIN EN 10027-1) [edit]

Designation according to purpose and yield point [edit]

The designation consists of the following sections:

  • Area of ​​application (table 1)
  • Minimum yield strength Re
  • Notched impact strength (Table 2)
  • After a plus sign, various additional properties, if applicable (Tables 3, 4)

example

  • S = steels for steel construction
  • 235 = minimum yield strength 235 N / mm²
  • JR = 27J notched impact strength + 20 °
  • + C = cold formable

(Table 1)

Code numberscope of application
D.cold formable steels
E.Engineering steels
HHigh strength flat products
L.Steels for line pipes and other types of pipes
PSteels for pressure vessels
R.Rail steels
S.Steels for steel construction

(Table 2)

+200-20-30-40-50-60
JRJ0J2J3J4J5J627 y
KRK0K2K3K4K5K640 y
LRL0L2L3L4L5L660 y

(Table 3)

M.thermomechanically rolled
Nnormalized
Qhardened and tempered
Gother features with 1 or more digits

(Table 4)

C.cold formable
L.for low temperatures
Hfor higher temperatures
W.Weatherproof

Unalloyed steels [edit]

The standard-compliant designation begins with C (chemical symbol for carbon), followed by a number indicating the carbon content and then the special symbols (see table).

In addition, every unalloyed steel according to this standard has a manganese content <1% (except for free-cutting steels).

Additional symbolimportance
E.Maximum sulfur content
R.Range of sulfur content
C.Good for cold forming NMBV
GSpecial features
S.for springs
Ufor tools
W.for welding wire
D.for wire drawing

example

C80U

C80 = carbon content of 0.8%
U = for tools

Low-alloy steels [edit]

Low-alloy steels can be recognized by the fact that they begin with the specification of the carbon content as a two-digit number. (e.g. 17Cr3 = 0.17% carbon). Then come the alloy elements (see example below). Their share is determined by a factor dividedwhich can be found in the table. If not stated, the proportion is insignificant, but still important for the properties of the alloy.

All alloying elements are indicated in their chemical symbols

Alloy elementDivision factor
Cr, Co, Mn, Ni, Si, W4
Al, Cu, Mo, V, Pb, Nb, Ti, Ta, Zr, Be10
C, Ce, N, P, S100
B.1000


Example:

32CrMoV5-3

32/100% C = 0.32% carbon

5/4% Cr = 1.25% chromium

3/10% Mo = 0.3% molybdenum

V = low proportion of vanadium (less than 1%)

important NOTE: In the case of high-alloy steels, the proportion of alloying elements is directly in% specified.

High-alloy steels [edit]

You can recognize a high-alloy steel by the fact that its first character is an X. It is also often marked with a Y abroad. The proportion of alloying elements is given without a factor. The exception is the carbon content: Its percentage is given with a factor of 100.

Example:

X38CrMoV5-3

X = high-alloy steel

38/100% C = 0.38% carbon

5 Cr = 5% chromium

3 Mo = 3% molybdenum

V = low proportion of vanadium (less than 1%)

High speed steels [edit]

The standard-compliant designation begins with the letters HS followed by the alloy metals in percentages in a specific order (W, Mo, V, Co)

example

HS 10-4-3-10

HS = high speed steel

10 = 10% tungsten

4 = 4% molybdenum

3 = 3% vanadium

10 = 10% cobalt

11 hydrobel axide

Iron cast materials

EN-GJS-350-22

EN = European norm
G = cast ...
J = ... iron
S = spherical
(Structure

EN-GJL = cast iron with lamellar graphite | M || tempered carbon
L.Lamellar
S.Spherical
A.Austenite
F.ferrite
PPerlite
W.decarburized annealed

)

350 = minimum tensile strength (Rm in N / mm²) or chemical composition
22 = elongation at break A in% (S cast separately, C taken from the workpiece)

Additional requirement (always added)

H = heat treated
W = suitable for welding

Material numbers [edit]

The material numbers are a system with which all materials - whether metallic or not - can be sorted. The seven-digit material number is also suitable for electronic data processing. It is made up of the main material group (digit 1), the type number (digits 2 to 5) as well as the 1st appendix number and the 2nd appendix number (digits 6 and 7). The type number is divided into the type class (digits 2 and 3) and the counting number (digits 4 and 5)

Key figures of the main groups

  • 0: Pig iron, ferro-alloys, cast iron
  • 1: steel, cast steel
  • 2: heavy metals except Fe (iron)
  • 3: light metals
  • 4 to 8: Non-metallic materials
  • 9: Not assigned, therefore free for internal use

Systematics of main group 1: steel [edit]

The material number of a steel looks like this: 1.SSZZ.AA. The first number (6th position) indicates the steelmaking process. The second appendix number (7th position) the treatment status.

Meaning of the variety numbers (digits 2 and 3)

  • Bulk and quality steels
    • 00: Commercial and basic grades
    • 01 ... 02: general structural steels, unalloyed
    • 03 ... 07: Quality steels, unalloyed
    • 08 ... 09: Quality steels, alloyed
    • 90: Special grades, commercial and basic grades
    • 91 ... 99: other special varieties
  • Unalloyed stainless steels
    • 10: Steels with special physical properties
    • 11 ... 12: Structural steels
    • 15 ... 18: Tool steels
  • Alloyed stainless steels
    • 20 ... 28: Tool steels
    • 32 ... 33: High speed steels
    • 34: wear-resistant steels
    • 35: Rolling bearing steels
    • 36 ... 39: Ferrous materials with special physical properties
    • 40 ... 45: Stainless steels
    • 47 ... 48: Heat-resistant steels
    • 49: High temperature materials
    • 50 ... 84: Structural steels
    • 85: nitriding steels
    • 88: hard alloys

Meanings of the 1st number of annexes (6th position)

Steelmaking process

  • 0: indefinite or irrelevant
  • 1: unquenched Thomasstahl
  • 2: calmed Thomasstahl
  • 3: other type of melting, unsettled
  • 4: other type of melting, calmed down
  • 5: unquenched Siemens-Martin steel
  • 6: calmed Siemens-Martin steel
  • 7: unkilled oxygen blow-off steel
  • 8: killed oxygen inflation steel
  • 9: electric steel

Meaning of the 2nd number of annexes (7th position)

Condition of treatment

  • 0: no treatment or any treatment
  • 1: normalized
  • 2: soft annealed
  • 3: heat-treated for good machinability
  • 4: toughened and tempered
  • 5: remunerated
  • 6: hard-coated
  • 7: cold worked
  • 8: cold-worked as hard as a spring
  • 9: treated according to special information

Molybdenum:

improves the wear resistance of steel, so it is often used in shafts and gears with high loads.

Lead:

Used almost only for free-cutting steels that are suitable for turning in order to obtain a better surface.

Sulfur:

It is often used in free-cutting steels because of its short-breaking chips. However, sulfur leads to poor formability.

Chrome:

Often used for highly stressed parts but also as improved corrosion protection and heat resistance.

Manganese:

Increases the tensile strength and thus also the resilience. It is often used in free-cutting steels and in plastic presses.

Tungsten:

Very heat-resistant (melting point at 3422 ° C), mostly in tool steels, often hot-work steels (high density 19.25 kg / dm3)

Nickel:

High strength and heat resistance, is often used in highly stressed steel. But it is also used in chemical tanks.

Vanadium:

Very hard, very heat resistant. Mostly used in tool steels.

Carbon-rich alloys that exceed the limit of 2.06% can still be considered steels. (they are often used in the event of sudden pressure loads, e.g. punching and pressing tools)

The reason lies in the high Chromium content: Chromium binds a lot of carbon in Chromium carbide, an extremely hard and resistant connection. This carbon is no longer available for the formation of Iron carbide (Fe3C) available. This is how the formation of Ledeburit prevents the structural component that makes cast iron.