The source of steel and components
- Source: put the steelmaking pig iron into the steel furnace melting, and then cast the steel into shape, after cooling, get ingots or continuous casting billet (for re-rolling into a variety of steel) or direct casting into a variety of cast steel parts.
- Composition: carbon content of less than 2% of an iron-carbon alloy. In addition, the content of silicon, manganese, sulfur, phosphorus and other elementsis less than the pig iron.
Steel classification
The method of steel’s classification
- According to the chemical composition of steel: non-alloy steel, low-alloy steel, alloy steel
- According to the main quality of steel grade and the main performance and use characteristics
According to chemical composition classification, limited values for the specified content of elements in each type of steel
| Alloy Elements | Non-alloy steel ＜ | Low-alloy steel | Alloy steels ≥ | |
|---|---|---|---|---|
| ≥ | ＜ | |||
| Al | 0.10 | - | - | 0.10 |
| B | 0.0005 | - | - | 0.0005 |
| Bi | 0.10 | - | - | 0.10 |
| Cr | 0.30 | 0.30 | 0.50 | 0.50 |
| Co | 0.10 | - | - | 0.10 |
| Cu | 0.10 | 0.10 | 0.50 | 0.50 |
| Mn | 1.00 | 1.00 | 1.40 | 1.40 |
| Mo | 0.05 | 0.05 | 0.10 | 0.10 |
| Ni | 0.30 | 0.30 | 0.50 | 0.50 |
| Nb | 0.02 | 0.02 | 0.06 | 0.06 |
| Pb | 0.40 | - | - | 0.40 |
| Se | 0.10 | - | - | 0.10 |
| Si | 0.50 | 0.50 | 0.90 | 0.90 |
| Te | 0.10 | - | - | 0.10 |
| Ti | 0.05 | 0.05 | 0.13 | 0.13 |
| V | 0.04 | 0.04 | 0.12 | 0.12 |
| W | 0.10 | - | - | 0.10 |
| Zr | 0.05 | 0.05 | 0.12 | 0.12 |
The classification of steel by the main quality level and the main performance and use characteristics
（1）Non-alloy steel classification
According to the main quality classification: ordinary quality non-alloy steel, high-quality non-alloy steel, special quality non-alloy steel
- Ordinary quality non-alloy steel, refers towhose production process does not specify the need for special control of quality requirements. This steel shall meet both the following four conditions:
(i) Non-alloyed steel
(ii) Does not specify heat treatment (Note: annealing, normalizing, stress relief and softening treatment, not treated as heat treatment)
(iii) When it comes to product standards or technical conditions, the characteristics of the value should meet the following conditions: ① the highest value of carbon content ≥ 0.10%; ② the highest value of sulfur or phosphorus content ≥ 0.040%; ③ the highest value of nitrogen content ≥ 0.007%; ④ the minimum value of tensile strength ≤ 690N/mm³; ⑤ the minimum value of yield strength ≤ 360N /mm³; ⑥ the minimum value of post-break elongation (Lo = 5.565o) ≤ 33%; ⑦ the minimum diameter value bending center diameter ≥ 0.5 x specimen thickness; ⑧ the minimum value of impact absorption energy (20 ℃, V-notch, longitudinal standard specimens) ≤ 27J; ⑨ the maximum value of hardness (HRC) ≥ 60
(iv) does not specify other quality requirements
- High-quality non-alloy steel, refers to the production process requires special quality control (such as controlgrain size, reduce sulfur&phosphorus content, improve surface quality or increase process control, etc.) to achieve special quality requirements. The requirements are different from ordinary quality non-alloy steel (such as good resistance to brittle fracture, good cold forming, etc.). But the production control of such steel is not as strict as special quality non-alloy steel (such as no control of hardenability). It can also be said that: except for the ordinary quality non-alloy steel and special quality non-alloy steel, others are high-quality non-alloy steel
- Special quality non-alloy steels, are defined as non-alloy steels that require particularly tight control of quality and properties (e.g., control of hardenability and purity) during production. Steel is special quality non-alloy steel if it meets one of the following conditions:
(i) Steel needs to be heat-treated and has at least one of the following special requirements of non-alloy steel (including free-cutting steel and tool steel): ① require the impact performance in the state of quenching and tempering/simulated surface hardening; ② require quenching or quenching&tempering after the depth of the hardened layer or surface hardness; ③ require the restriction of surface defects, more stringent than the provisions of the steel for cold heading and cold extrusion; ④ require the restriction of non-metallic inclusions content and (or) the requirement for internal material uniformity
(ii) Steel, without heat treatment, should have at least one of the following special requirements of non-alloy steel: ① require restrictions on the content of non-metallic inclusions and (or) internal material uniformity, such as steel sheet laminar tear resistance; ② require restrictions on the maximum value of phosphorus content and (or) sulfur content, and comply with the following provisions: melt analysis value ≤ 0.020%; finished analytical value ≤ 0.025%; ③ the melting analysis content of the required residual elements should be limited as follows: copper ≤ 0.10%; cobalt < 0.05%; vanadium ≤ 0.05%.
(iii) Steel with specified conductivity properties (not less than 9s/m) or with specified magnetic properties (except for thin plates and strips for which only the maximum specific total loss and minimum magnetic polarization strength are specified without specifying the magnetic permeability)
(iv) The requirements for surface quality are more stringent than those of GB/T 6478 for cold heading and cold extrusion of the steel.
Classification by principal properties or use characteristics: The principal properties or use characteristics referred to those that are to be given priority in certain cases, for example, in the preparation of systems or in the classification of steels
- Unalloyed steels for which the specified maximum strength (or hardness) is the main characteristic, e.g. thin steel plates for cold forming
- Unalloyed steels with a specified minimum strength as the main characteristic, such as structural steels for shipbuilding, pressure vessels, pipelines, etc.
- Unalloyed steels with restricted carbon content as the main characteristic, such as wire rod, tempered steel, etc.
- Non-alloy free-cutting steel, steel with a minimum value of sulfur content&melting analysis value of not less than 0.070%, and the addition of lead, bismuth, tellurium, selenium, tin, calcium and other elements
- Non-alloy tool steel
- Non-alloy steel with special provisions for magnetic or electrical properties, such as electromagnetism pure iron
- Other non-alloy steel, such as pure iron raw materials, etc.
(2) Low-alloy steel classification
According to the main quality classification: ordinary quality low-alloy steel, high-quality low-alloy steel, special quality low-alloy steel
- Ordinary quality low-alloy steel, refers to the low-alloy steelfor general use whose production process does not require special control of quality requirements. And this steel needs to meet the following conditions:
(i) Low content of alloy
(ii) Does not specify heat treatment (Note: annealing, normalizing, stress relief and softening treatment is not treated as heat treatment)
(iii) When it comes to product standards or technical conditions, the characteristics of the value should meet the following conditions: ① the highest value of the content of the sulfur or phosphorus ≥ 0.040%; ② the minimum value of tensile strength ≤ 690N/mm³; ③ the minimum value of yield strength≤ 360N/mm³; ④ the minimum value of post-break elongation ≤ 26%; ⑤ the minimum value of bending center diameter≥ 2 x the thickness of the test piece
Note: 1. mechanical properties of the specified value refers to the performance the nominal thickness of 3 ~ 16mm steel do the transverse or longitudinal specimens to determine. 2. the specified tensile strength, yield strength or yield strength properties only apply to weldable low-alloy high-strength structural steel
(iv) Does not specify other quality requirements
- High-quality low-alloy steel, refers to the production process requires special quality control (such as reducing sulfur&phosphorus content, control grain size, improve surface quality, increase process control, etc.) to achieve special quality requirements, which is different from ordinary quality low-alloy steel (such as good resistance to brittle fracture, good cold forming, etc.). But the production control and quality requirements of this steelis not as strict as special quality low-alloy steel
- Special quality low-alloy steel, refers tothe low-alloy steel whose production process requires special control of quality and performance (especially strict control of sulfur, phosphorus and other impurity content and purity). Steel meeting one of the following conditions is special quality low-alloy steel:
(i) Specify limits on non-metallic inclusions and/or internal material uniformity, for example, steel sheet resistance to laminar tearing properties
(ii) Specify restrictions on the maximum phosphorus content and/or sulfur content, and comply with the following provisions: melt analysis value ≤ 0.020%, the finished product analysis value ≤ 0.025%
(iii) Specify the limitation of the residual element content and should comply with the following provisions: the maximum content of the copper melting analysis ≤ 0.10%, the maximum content of cobalt melting analysis ≤ 0.05%, the maximum content of vanadium melting analysis ≤ 0.05%
(iv) Specify impact performance of low temperature (below -40 ℃, V-notch)
(v) Steel which can be welded high-strength, the specified minimum value of yield strength ≥ 420N /mm³
Note: Mechanical properties of the specified value refers to the performance the nominal thickness of 3 ~ 16mm steel does the longitudinal or transverse specimens to determine
(vi) Dispersion-reinforced copper, whose specified carbon content of the minimum value of melting analysis is not less than 0.25%, has ferrite/pearlite or other microstructure
(vii) Prestressed steels
(3) Classification of alloy steel
Classified by the main properties or use characteristics
The principal properties or use characteristics referred to in this part are those which, in certain cases, such as in the preparation of systems or classification of steels, are to be given priority
- Weldable low-alloy steels
- Low-alloy weathering steels
- Low-alloy concrete steels and prestressing steels
- Low-alloy steel for railways
- Low alloy steel for mining
- Other low-alloy steels, such as welding steel
According to the main quality classification: high quality alloy steel, special quality alloy steel
- High-quality alloy steel, refers to the production process requires special control of quality and performance (such as toughness, grain size or formability) of the steel, but its production control and quality requirements are not as strict as special quality alloy steel alloy steel. The following steels are high quality alloy steels:
(i) General engineering structural alloy steel, such as steel sheet piles with alloy steel mining alloy steel
(ii) Alloy steel bars
(iii) Electrical alloy steel, mainly containing silicon or silicon&aluminum&other alloying elements, but which is no requirements for magnetic permeability
(iv) Alloy steel for railways, such as GB/T11264 30CuCr
(v) Steel for rock drilling and drilling, such as GB / T101 alloy steel
(vi) The wear-resistant steel whose content of sulfur and phosphorus are greater than 0.035%
- Alloy steelof special quality, refers to that needs to strictly control the chemical composition, specific manufacturing and process conditions. And it ‘s aim is to ensure improved overall performance. And the performance is strictly controlled within the limits. Except for the above-mentioned varieties of high-quality alloy steel, all other alloy steels are special quality alloy steel. The following is the classification of special quality alloy steel according to the main performance and usage characteristics:
(i) Engineering structural alloy steel, including general engineering structural alloy steel, alloy steel for hot-rolled or cold-rolled flat products for cold forming(pressure vessel steel, automotive steel and pipeline steel), prestressing alloy steel, mining alloy steel, high manganese wear-resistant steel, etc.
(ii) Alloy steel for mechanical structures, including quenched alloy structural steel, surface hardening alloy structural steel, cold plastic forming (cold top forging, cold extrusion) alloy structural steel, alloy spring steel, etc., but except stainless, corrosion and heat resistant steel, bearing steel.
(iii) Stainless, corrosion&heat-resistant steels, including stainless steel, acid-resistant steel, oxidation-resistant steel and heat-resistant steel, etc. According to its metallurgical organization, it can be divided into martensitic steel, ferritic steel, austenitic steel, austenitic-ferritic steel, precipitation hardening steel, etc.
(iv) Tool steel, including alloy tool steel, high-speed tool steel. Alloy tool steels are divided into gage tool steel, impact-resistant tool steel, cold work tool steel, hot work tool steel, non-magnetic tool steel, plastic mold steel, etc.; high-speed tool steel is divided into tungsten-molybdenum high-speed tool steel, tungsten high-speed tool steel and cobalt high-speed tool steel
(v) Bearing steel, including high-carbon chromium bearing steel, carburized bearing steel, stainless bearing steel, high-temperature bearing steel, etc.
(vi) Special physical properties of steel, including soft magnetic steel, permanent magnetic steel, non-magnetic steel, and high resistance steel and alloy, etc.
(vii) others, such as welding alloy steel, etc.
