The functionality of the cast piece and the application of the product are important principles in the development of a new component. For this, the following questions must be asked:
- What is the purpose of the product?
- How strong or hard must the product be?
- Will the product have to stand up to extreme temperatures?
- Must the material be able to handle corrosion?
- Which dimensions must be achieved and which dimensions are critical?
- How does the product get built in?
These are important questions for establishing the product’s functionality and for making a casting design on the basis of this. By reasoning from the standpoint of functionality, the best technical products for the most favourable production cost price are realised. With this approach only the functionally needed elements are important. This characterises our specific working method.
functionality of the cast piece
The choice of material is based on a product’s functionality. Every steel alloy has its own specific properties. Based on these properties, the type of steel suitable for a given application is selected. Every product needs to be durable and not break easily. The material’s mechanical properties determine these characteristics. Thermal and chemical properties also play an important role in the selection of the proper material.
Our metallurgical specialists can support you in selecting the most suitable steel alloy for your application.
The elasticity of material indicates how easily its length can change when a force is applied. A material is elastic if it deforms when a force is applied to it. This deformation is a non-permanent deformation. This means that the material returns to its old shape when the force field is removed*. The elasticity of a material is expressed in the elastic modulus (E). This is also called Young’s modulus. The unit of a modulus of elasticity is a force on a surface or N/m2 or Pa. The larger unit of N/mm² = MPa is usually used; for example, steel has an E-modulus of 210,000MPa = 210GPa.
* A good practical example is stretching a rubber band. If a force is exerted on a rubber band its lengths changes. After this force is removed, the rubber band returns to its old shape without having been changed.
It is important to know how much pulling force you can place on a product made of a given material before it breaks. The material deforms elastically up to the point of its elastic limit (Re). After that, the material deforms permanently. This is sometimes called plastic deformation. Tensile strength is the maximum mechanical tension that occurs in the material if it breaks after its plastic deformation.
The tensile strength of steel, for example, is understood to be the largest tensile force in Newton (N) that you can place on a bar of steel with a cross-sectional diameter of 1mm2. If the tensile strength of steel is 360N, for example, then this means that you can pull on a round piece of steel with a diameter of 1mm2, using a force of 360N, without breaking it (or 720 N on a cross-section of 2 mm2). So you can pull with the force of just up to 36 kg on this bar without breaking it.
In practical terms, the elastic limit (0.2%) is more important. Beyond the elastic limit (Re), the material will deform in a plastic fashion. Such a deformation of the material is undesirable because the product’s functionality, power and safety cannot be guaranteed then. The maximum elastic limit is indicated in N/mm². This value indicates how much tension the material can take before plastic deformation begins.
The hardness of the material is the resistance that the material exhibits against permanent mechanical deformation. It therefore determines the extent to which a material can withstand wear. There are various methods for determining hardness. The most customary measurement methods are:
- Brinell (unit: HB)
- Vickers (unit: HV)
- Rockwell (unit: HRB or HRC)
Hardness is measured by pressing a hard point or a ball with standard measurements against a material. A measurement is then made of how large the dent formed in the tested material is. As the measuring point is pressed into the material, the contact surface gradually increases. This causes the pressure to decrease at the point of the material. This continues up to the moment that the point no longer presses into the material. The degree of indentation indicates the value of hardness.
Abrasion-resistant steel is, as the name suggests, a type of steel with a high resistance to wear. A product’s resistance to wear from friction or impact is obtained by hardening the material. A material with high hardness will cause a material with lower hardness to wear. However, hardness alone is not enough. The material must also be tough to provide resistance against direct impact. If the material is not tough, it will tend to break when hit hard.
The brittleness of a material is the property of breaking without much stretching. A brittle break is when little energy is needed to cause a material to break. A brittle material will break immediately with limited tensile force.
The toughness of a given material says something about how it breaks under mechanical loads. Under conditions of increased mechanical tension, tough material will ultimately deform in a plastic way, after which the load can still increase without breakage occurring immediately. A material is tough if it deforms considerably before it breaks. Toughness also indicates the resistance to the propagation of cuts and tears.
In practice, a material’s desired toughness against fractures is indicated by its impact strength. If requirements are placed on the material’s properties, an impact strength value at a given temperature is often requested in addition to the strength requirements. This impact strength value is, in fact, the energy needed to break a bar. So tough materials have a higher impact value than brittle materials.
The measured toughness of a given material is dependent on the material itself but also on the thickness of the piece, the temperature, the speed of the deformation and the presence of cuts or cracks.
Corrosion (better known as “rust”) is the degradation of metals due to environmental influences.
As soon as metals are exposed to air, they will compound chemically with the oxygen in the air. This process is called oxidation. Rust is the red-brown material that is formed when iron reacts with oxygen in the presence of water. Rusting is the commonly used term for a form of corrosion of iron-containing materials, such as steel.
Corrosion results in the loss of strength because the products of corrosion (oxides and salts) are much weaker than the metal. The corrosion products crumble away and the metallic parts become thinner. Holes may even occur in products with rust.
Stainless steel, also called RVS or SS, is a steel alloy that is resistant to corrosion. Stainless steel alloys are comprised of nickel (Ni) and chromium (Cr), among other things. By adding chromium to a steel alloy, a chromium oxide layer is built up on the surface. This makes the surface more resistant to corrosion. CIREX is glad to provide recommendations about the possible applications and properties of stainless steel alloys.
The acid resistance of a material is the maximum acid concentration that a material can absorb without wearing over time. It is the degree to which a material can withstand acidic fluids. Consider, for example, resistance to fluids like hydrochloric acid.
CIREX can advise you as to which materials are suitable for use in an acidic environment. We can also make recommendations about supplemental surface treatments that may also be required.
Just like most other materials, steel expands when it warms up and contracts when it cools off. The degree to which a material contracts or expands is indicated by the thermal coefficient of expansion. The thermal coefficient of expansion is expressed per ˚C.
Most materials will expand when warmed up, which is also called a positive coefficient of expansion. At higher temperatures, molecules vibrate more strongly, causing them to take up more space (the volume becomes greater). The stronger the atoms are bonded to each other, the lower the coefficient of expansion. In general, steel types have a high coefficient of expansion.
We consider heat-resistant material to be the following: the steel alloy retains its mechanical properties under the influence of extremely high temperatures. Heat-resistant types of steel can withstand oxidation as well as the influence of hot gases and combustion products at temperatures above 600°C. These metals retain their form, functionality and dimensions after having come into contact with these extremely high temperatures. Alloying elements that boost heat resistance include nickel (Ni) and chromium (Cr).
Due to the presence of nickel and chrome, most types of stainless steel are heat resistant, but less so then specifically heat-resistant types of steel.