We shall discuss in this article cast steel production, properties composition and testing in the foundry.
An iron alloy called cast steel has a maximum carbon concentration of 0.75 percent. Solid metal objects called steel castings are created by injecting liquid steel into the mold’s crevices.
Many of the same kinds of carbon and alloy steels as wrought metals can be used to make them. Despite having the same chemical composition as forged steel, cast steel typically has worse mechanical qualities.
This shortcoming is made up of cast steel, which can produce complex shapes in fewer processes. Casting steel in a foundry Steel casting are solid metal objects produced by filling the voids inside the mold with liquid steel. Cast steel properties Different characteristics can be generated in cast steel.
Due to its chemical makeup and heat treatment, cast steel has a range of different physical properties. Choose them based on how well they will perform for the application you have in mind. Hardship The ability of a material to resist wear. The maximum hardness or hardenability that steel can achieve depends on its carbon content.
Strength – strength the force required to change the shape of matter. Higher carbon content and hardness result in higher-strength steel. hammering the capacity of a metal to alter shape when subjected to tension. Steel that is more ductile has a lower carbon content and a lower hardness.
Hardship the capacity to endure pressure. Better toughness is typically correlated with increased ductility. Heat treatment and the addition of metal alloys can be used to modify toughness. abrasion resistance Material resistance to friction and use. Cast steel shows the same wear resistance as wrought steel of the same composition.
Adding alloying elements such as molybdenum and chromium can improve wear resistance. Corrosion resistance Material resistance to oxidation and rust. Cast steel has the same corrosion resistance as forged steel. High alloy steels with high chromium and nickel content are highly resistant to oxidation.
Machine work the ease with which a steel casting can be reshaped by removing material by machining (cutting, grinding, or drilling). Processability is influenced by hardness, strength, thermal conductivity, and thermal expansion. tinning Ability to weld cast steel parts without problems. The chemical make-up and thermal treatment of the steel casting have the most effects on weldability.
High-temperature characteristics Steels operating above ambient temperature can experience reduced mechanical properties and early failure due to oxidation, hydrogen damage, sulfite scaling, and carbide instability. Low-temperature properties the toughness of cast steel decreases drastically at low temperatures.
Alloying and special heat treatment can improve the ability to cast parts to withstand loads and stresses. Chemical composition of cast steel the chemical composition of cast steel has a significant effect on performance characteristics and is often used to classify steel or assign standard designations. Carbon cast steel and alloy cast steel are the two subcategories of cast steel.
Carbon steel casting Like wrought steel, carbon cast steel can also be classified based on its carbon content. Low-carbon cast steel (0.2% carbon) is relatively soft and difficult to heat treat. Medium carbon cast steel (0.2-0.5% carbon) is slightly harder and can be strengthened by heat treatment.
When maximum hardness and wear resistance are required, use high carbon (0.5% carbon) cast steel. Alloy casting steel Alloy casting steel is divided into two categories, low alloy, and high alloy. Low-alloy cast steel (alloy content ≤ 8%) is like ordinary carbon steel but has a higher hardenability. High alloy cast steel (alloy content > 8%) is designed to produce specific properties such as corrosion resistance, heat resistance or wear resistance.
Common high alloy steels are stainless steel (>10.5% Cr) and Hadfield Mn steel (11-15% Mn). The addition of chromium, which forms a passive layer of chromium oxide when exposed to oxygen, gives stainless steel excellent corrosion The manganese. Manganese content in Hadfield steel has high strength and wear resistance.
Cast steel-grades Standard organizations such as ASTM International, the American Iron and Steel Institute, and the Society of Automotive Engineers have developed steel grades to classify steels with specific chemical compositions and physical properties. Foundries can develop their own steel grades to meet user requirements for specific properties or to standardize on specific production grades.
Wrought steel specifications are commonly used to classify various cast alloys based on their principal alloying elements. However, cast steel does not necessarily follow the composition of wrought steel. The silicon and manganese content of cast steel is generally higher than that of wrought steel.
Alloy casting steels, in addition to primarily containing higher levels of silicon and manganese, are oxidized with aluminum, titanium, and zirconium during casting. Aluminum is mainly used as an oxidizer due to its efficiency and relatively low cost. Production of cast steel the method of casting steel dates to the late 1750s, much later than the casting of other metals.
The high melting point of steel and the lack of technology available to melt and process the metal have slowed down the growth of the steel casting industry. Advances in furnace technology have overcome these challenges. A furnace is a refractory vessel that contains the “charge,” the material to be melted, and provides the energy necessary for melting.
Modern steel foundries use two types of furnaces: electric arc furnaces and induction furnaces. Electric arc furnace Electric arc furnaces use an electric arc between graphite electrodes to melt bundles of metal called “hot”. Electrical charges pass directly between the electrodes, exposing them to thermal energy generated by the continuous discharge.
Electric arc furnaces follow a cycle-by-cycle operation: Furnace charging large amounts of scrap and alloys were added to the furnace. melt Steel is melted by supplying energy in a furnace. Electricity is provided by graphite electrodes and is often the largest factor in steelmaking operations.
Chemical energy is provided by oxy-fuel burners and oxygen lances. refinement Oxygen is injected during the melting process to remove impurities and other dissolved gases. slag removal Excess slag, usually containing undesired impurities, is removed from the molten pool before discharge. Deslag can also be carried out in the ladle before pouring.
Induction furnace, Heat treatment of cast steel
At various stages of the process, successive additional steps are usually performed to further deoxidize the steel and remove slag from the metal prior to casting.
The chemical composition of the steel may need to be adjusted to account for alloy losses during long-tapping. Induction Furnace an induction furnace is an electric furnace that transfers heat energy through induction.
A copper coil surrounds the non-conducting charge chamber, and an alternating current is passed through the coil to create an electromagnetic induction within the charge. Induction furnaces can melt most metals and can operate with minimal melt loss. The downside is that there is very little refining of the metal. Unlike electric arc furnaces, steel cannot be converted.
Modern steel foundries often use recycled scrap to reduce the cost and environmental impact of casting production. Used cars, mechanical parts, and similar items are separated, sized, and sent to foundries as scrap. It is combined with internal scrap produced during casting and incorporated with various alloying elements in the furnace.
heat therapy After solidification, casting, and mold cleaning, the physical properties of cast steel are revealed by appropriate heat treatment. baking Steel castings are heated to a certain temperature, held for a certain period, and then slowly cooled. to normalize Similar to annealing, steel castings are cooled in the open air and sometimes fans are used.
This helps the casting to achieve higher strength. turn off Similar to normalizing but uses forced air for faster cooling. Water or oil is used as a quenching medium. mood (or stress reduction) The technology is used to reduce the internal stress of the casting.
These stresses may develop during casting or during hardening or hardening heat treatments, such as normalizing or quenching. Stress relief involves heating the casting to a temperature well below the annealing temperature, holding it at that temperature, and slowly cooling it. Hardness is a measure of casting penetration resistance using the indentation test.
This is a property that expresses the wear and tears resistance of cast steel. Hardness testing can also provide a simple and routine way to test tensile strength indications in a production environment. Hardness scale test results are often closely related to tensile strength properties.
Chemical, Heat, and Product Analysis of Cast Steel
Chemical analysis of cast steel usually uses the wet chemical analysis method or spectrochemical method. Wet chemical analysis is commonly used to determine the composition of small samples or to confirm post-production product analysis.
In contrast, spectrometer analysis is ideal for routine and rapid determination of the chemical composition of larger samples in busy production foundry environments. Foundries can perform chemical analysis at the thermal and product level.
During thermal analysis, a small sample of liquid cast steel is removed from the furnace, allowed to solidify, and then analyzed for chemical composition using spectrochemical analysis. If the composition of the alloying elements is incorrect, quick adjustments can be made in the furnace or ladle before casting.
When the thermal analysis is correct, it is generally considered to be an accurate representation of the thermal component of the entire metal. However, changes in chemical composition are expected due to the separation of alloying elements and the time it takes for the heat to be removed from the steel.
Oxidation of some elements may occur during the casting process. Product analysis is used to confirm the specific chemical analysis because the composition of individual castings cast may not fully conform to applicable specifications.
This happens even if the product is cast from a steel furnace with the correct thermal analysis. Industry standards and procedures allow for differences between thermal analysis and product analysis. By changing the composition and heat treatment of cast steel, different mechanical properties can be obtained for carbon and alloy steel castings.
Foundries use specialized testing methods to check the mechanical properties of the product before finishing. When it comes to testing steel castings, there are two types of testing used in the industry: destructive testing and non-destructive testing.
Destructive testing involves removing test parts to visually determine the internal health of the part. This method only provides information about the condition of the part under test and does not ensure the health of other parts.
NDT is used to check the internal and external health of a mold without damaging the mold itself. Once the casting has passed the test, it can be used for its intended application. The tensile properties of steel castings indicate the casting’s ability to withstand loads under slow loading conditions.
Tensile properties were measured using representative cast specimens with controlled tensile load (tensile force applied at both ends of the tensile rod) until failure. After failure, check the tensile properties.
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