HSLA steel
Encyclopedia
High-strength low-alloy steel (HSLA) is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion than carbon steel. HSLA steels vary from other steels in that they are not made to meet a specific chemical composition but rather to specific mechanical properties. They have a carbon content between 0.05–0.25% to retain formability and weldability
. Other alloying elements include up to 2.0% manganese and small quantities of copper
, nickel
, niobium
, nitrogen
, vanadium
, chromium
, molybdenum
, titanium
, calcium
, rare earth elements, or zirconium
. Copper, titanium, vanadium, and niobium are added for strengthening purposes. These elements are intended to alter the microstructure
of carbon steels, which is usually a ferrite
-pearlite
aggregate, to produce a very fine dispersion of alloy carbide
s in an almost pure ferrite matrix. This eliminates the toughness-reducing effect of a pearlitic volume fraction yet maintains and increases the material's strength by refining the grain size, which in the case of ferrite increases yield strength by 50% for every halving of the mean grain diameter. Precipitation strengthening
plays a minor role, too. Their yield strengths can be anywhere between 250 –. Because of their higher strength and toughness HSLA steels usually require 25 to 30% more power to form, as compared to carbon steels.
Copper, silicon, nickel, chromium, and phosphorus are added to increase corrosion resistance. Zirconium, calcium, and rare earth elements are added for sulfide-inclusion shape control which increases formability. These are needed because most HSLA steels have directionally sensitive properties. Formability and impact strength can vary significantly when tested longitudinally and transversely to the grain. Bends that are parallel to the longitudinal grain are more likely to crack around the outer edge because it experiences tensile loads. This directional characteristic is substantially reduced in HSLA steels that have been treated for sulfide shape control.
They are used in cars, trucks, cranes, bridges, roller coasters and other structures that are designed to handle large amounts of stress
or need a good strength-to-weight ratio. HSLA steels are usually 20 to 30% lighter than a carbon steel with the same strength.
HSLA steels are also more resistant to rust
than most carbon steels because of their lack of pearlite – the fine layers of ferrite (almost pure iron) and cementite in pearlite. HSLA steels usually have densities of around 7800 kg/m³.
A common type of micro-alloyed steel is improved-formability HSLA. It has a yield strength up to 80000 psi (551.6 MPa) but only costs 24% more than A36 steel
(36000 psi (248.2 MPa)). One of the disadvantages of this steel is that it is 30 to 40% less ductile. In the U.S., these steels are dictated by the ASTM standards A1008/A1008M and A1011/A1011M for sheet metal and A656/A656M for plates. These steels were developed for the automotive industry to reduce weight without losing strength. Examples of uses include door-intrusion beams, chassis members, reinforcing and mounting brackets, steering and suspension parts, bumpers, and wheels.
Weldability
The weldability, also known as joinability, of a material refers to its ability to be welded. Many metals and thermoplastics can be welded, but some are easier to weld than others...
. Other alloying elements include up to 2.0% manganese and small quantities of copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, niobium
Niobium
Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite...
, nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, vanadium
Vanadium
Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...
, chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
, molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
, titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
, calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
, rare earth elements, or zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
. Copper, titanium, vanadium, and niobium are added for strengthening purposes. These elements are intended to alter the microstructure
Microstructure
Microstructure is defined as the structure of a prepared surface or thin foil of material as revealed by a microscope above 25× magnification...
of carbon steels, which is usually a ferrite
Ferrite (iron)
Ferrite or alpha iron is a materials science term for iron, or a solid solution with iron as the main constituent, with a body centred cubic crystal structure. It is the component which gives steel and cast iron their magnetic properties, and is the classic example of a ferromagnetic material...
-pearlite
Pearlite
Pearlite is often said to be a two-phased, lamellar structure composed of alternating layers of alpha-ferrite and cementite that occurs in some steels and cast irons...
aggregate, to produce a very fine dispersion of alloy carbide
Carbide
In chemistry, a carbide is a compound composed of carbon and a less electronegative element. Carbides can be generally classified by chemical bonding type as follows: salt-like, covalent compounds, interstitial compounds, and "intermediate" transition metal carbides...
s in an almost pure ferrite matrix. This eliminates the toughness-reducing effect of a pearlitic volume fraction yet maintains and increases the material's strength by refining the grain size, which in the case of ferrite increases yield strength by 50% for every halving of the mean grain diameter. Precipitation strengthening
Precipitation strengthening
Precipitation hardening, also called age hardening, is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys of aluminium, magnesium, nickel and titanium, and some stainless steels...
plays a minor role, too. Their yield strengths can be anywhere between 250 –. Because of their higher strength and toughness HSLA steels usually require 25 to 30% more power to form, as compared to carbon steels.
Copper, silicon, nickel, chromium, and phosphorus are added to increase corrosion resistance. Zirconium, calcium, and rare earth elements are added for sulfide-inclusion shape control which increases formability. These are needed because most HSLA steels have directionally sensitive properties. Formability and impact strength can vary significantly when tested longitudinally and transversely to the grain. Bends that are parallel to the longitudinal grain are more likely to crack around the outer edge because it experiences tensile loads. This directional characteristic is substantially reduced in HSLA steels that have been treated for sulfide shape control.
They are used in cars, trucks, cranes, bridges, roller coasters and other structures that are designed to handle large amounts of stress
Stress (physics)
In continuum mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the body on which internal forces act. These internal forces are a reaction to external forces applied on the body...
or need a good strength-to-weight ratio. HSLA steels are usually 20 to 30% lighter than a carbon steel with the same strength.
HSLA steels are also more resistant to rust
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...
than most carbon steels because of their lack of pearlite – the fine layers of ferrite (almost pure iron) and cementite in pearlite. HSLA steels usually have densities of around 7800 kg/m³.
Classifications
- Weathering steels: steels which have better corrosion resistance. A common example is COR-TEN.
- Control-rolled steels: hot rolled steels which have a highly deformed austenite structure that will transform to a very fine equiaxed ferrite structure upon cooling.
- Pearlite-reduced steels: low carbon content steels which lead to little or no pearlite, but rather a very fine grain ferrite matrix. It is strengthened by precipitation hardening.
- Acicular ferriteAcicular ferriteAcicular ferrite is a microstructure of ferrite that is characterised by needle shaped crystallites or grains when viewed in two dimensions. The grains, actually three dimensional in shape, have a thin lenticular shape...
steels: These steels are characterized by a very fine high strength acicular ferrite structure, a very low carbon content, and good hardenabilityHardenabilityThe hardenability of a metal alloy is its capability to be hardened by heat treatment. It should not be confused with hardness, which is a measure of a sample's resistance to indentation or scratching. It is an important property for welding, since it is inversely proportional to weldability,...
. - Dual-phase steelDual-phase steelDual-phase steel is a high-strength steel that has a ferrite and martensitic microstructure. DPA starts as a low or medium carbon steel and is quenched from a temperature above A1 but below A3 on a continuous cooling transformation diagram...
s: These steels have a ferrite microstruture that contain small, uniformly distributed sections of martensite. This microstructure gives the steels a low yield strength, high rate of work hardening, and good formability. - Microalloyed steels: steels which contain very small additions of niobium, vanadium, and/or titanium to obtain a refined grain size and/or precipitation hardening.
A common type of micro-alloyed steel is improved-formability HSLA. It has a yield strength up to 80000 psi (551.6 MPa) but only costs 24% more than A36 steel
A36 steel
A36 steel is a standard steel alloy which is a common structural steel used in the United States.The A36 standard was established by the standards organization ASTM International.- Properties :...
(36000 psi (248.2 MPa)). One of the disadvantages of this steel is that it is 30 to 40% less ductile. In the U.S., these steels are dictated by the ASTM standards A1008/A1008M and A1011/A1011M for sheet metal and A656/A656M for plates. These steels were developed for the automotive industry to reduce weight without losing strength. Examples of uses include door-intrusion beams, chassis members, reinforcing and mounting brackets, steering and suspension parts, bumpers, and wheels.
SAE grades
The Society of Automotive Engineers (SAE) maintains standards for HSLA steel grades because they are often used in automotive applications.| Grade | % Carbon (max) | % Manganese (max) | % Phosphorus (max) | % Sulfur (max) | % Silicon (max) | Notes |
|---|---|---|---|---|---|---|
| 942X | 0.21 | 1.35 | 0.04 | 0.05 | 0.90 | Niobium or vanadium treated |
| 945A | 0.15 | 1.00 | 0.04 | 0.05 | 0.90 | |
| 945C | 0.23 | 1.40 | 0.04 | 0.05 | 0.90 | |
| 945X | 0.22 | 1.35 | 0.04 | 0.05 | 0.90 | Niobium or vanadium treated |
| 950A | 0.15 | 1.30 | 0.04 | 0.05 | 0.90 | |
| 950B | 0.22 | 1.30 | 0.04 | 0.05 | 0.90 | |
| 950C | 0.25 | 1.60 | 0.04 | 0.05 | 0.90 | |
| 950D | 0.15 | 1.00 | 0.15 | 0.05 | 0.90 | |
| 950X | 0.23 | 1.35 | 0.04 | 0.05 | 0.90 | Niobium or vanadium treated |
| 955X | 0.25 | 1.35 | 0.04 | 0.05 | 0.90 | Niobium, vanadium, or nitrogen treated |
| 960X | 0.26 | 1.45 | 0.04 | 0.05 | 0.90 | Niobium, vanadium, or nitrogen treated |
| 965X | 0.26 | 1.45 | 0.04 | 0.05 | 0.90 | Niobium, vanadium, or nitrogen treated |
| 970X | 0.26 | 1.65 | 0.04 | 0.05 | 0.90 | Niobium, vanadium, or nitrogen treated |
| 980X | 0.26 | 1.65 | 0.04 | 0.05 | 0.90 | Niobium, vanadium, or nitrogen treated |
| Grade | Form | Yield strength (min) [psi (MPa)] | Ultimate tensile strength (min) [psi (MPa)] |
|---|---|---|---|
| 942X | Plates, shapes & bars up to 4 in. | 42,000 (290) | 60,000 (414) |
| 945A, C | Sheet & strip | 45,000 (310) | 60,000 (414) |
| Plates, shapes & bars: | |||
| 0–0.5 in. | 45,000 (310) | 65,000 (448) | |
| 0.5–1.5 in. | 42,000 (290) | 62,000 (427) | |
| 1.5–3 in. | 40,000 (276) | 62,000 (427) | |
| 945X | Sheet, strip, plates, shapes & bars up to 1.5 in. | 45,000 (310) | 60,000 (414) |
| 950A, B, C, D | Sheet & strip | 50,000 (345) | 70,000 (483) |
| Plates, shapes & bars: | |||
| 0–0.5 in. | 50,000 (345) | 70,000 (483) | |
| 0.5–1.5 in. | 45,000 (310) | 67,000 (462) | |
| 1.5–3 in. | 42,000 (290) | 63,000 (434) | |
| 950X | Sheet, strip, plates, shapes & bars up to 1.5 in. | 50,000 (345) | 65,000 (448) |
| 955X | Sheet, strip, plates, shapes & bars up to 1.5 in. | 55,000 (379) | 70,000 (483) |
| 960X | Sheet, strip, plates, shapes & bars up to 1.5 in. | 60,000 (414) | 75,000 (517) |
| 965X | Sheet, strip, plates, shapes & bars up to 0.75 in. | 65,000 (448) | 80,000 (552) |
| 970X | Sheet, strip, plates, shapes & bars up to 0.75 in. | 70,000 (483) | 85,000 (586) |
| 980X | Sheet, strip & plates up to 0.375 in. | 80,000 (552) | 95,000 (655) |
| Rank | Weldability | Formability | Toughness |
|---|---|---|---|
| Worst | 980X | 980X | 980X |
| | 970X | 970X | 970X | |
| 965X | 965X | 965X | |
| 960X | 960X | 960X | |
| 955X, 950C, 942X | 955X | 955X | |
| 945C | 950C | 945C, 950C, 942X | |
| 950B, 950X | 950D | 945X, 950X | |
| 945X | 950B, 950X, 942X | 950D | |
| 950D | 945C, 945X | 950B | |
| 950A | 950A | 950A | |
| Best | 945A | 945A | 945A |