Alloy steel is an iron-carbon alloy formed by adding an appropriate amount of one or more alloying elements to ordinary carbon steel. According to the different added elements and the appropriate processing technology, the alloy steel can obtain high strength, high toughness, wear resistance, corrosion resistance, low-temperature resistance, high-temperature resistance, non-magnetic, and other unique properties. Alloy steel is mainly divided into two categories: low alloy steel and high alloy steel. Investment casting alloy steel is usually low alloy steel.
Common alloyants types in alloy steel
Common alloying agents include manganese (the most common one), nickel, chromium, molybdenum, vanadium, silicon, and boron. Less common alloys include aluminum, cobalt, copper, cerium, niobium, titanium, tungsten, tin, zinc, lead, and zirconium. Strictly speaking, every kind of steel is an alloy, but not all steel is called “alloy steel.” The most uncomplicated steel is an alloy of iron and carbon (about 0.1% to 1%, depending on the type). However, the term “alloy steel” is a standard term that refers to steel with the intentional addition of other alloying elements in addition to carbon.
Alloy Steel Casting Grades
What are the advantages of alloy steel casting？
1. Greater design flexibility
This design has greater freedom in choosing the shape and size of the casting, especially the complicated shape and hollow part. The unique process of core casting can manufacture the alloy steel casting. Easy to shape and change shape, and can quickly produce finished products according to drawings, which can quickly respond and shorten delivery time.
2. Strong flexibility and variability in metallurgical manufacturing
You can choose alloy steel castings with different chemical compositions and organizational structures to meet the needs of different projects. Various heat treatment processes can select mechanical properties and use this property in a wide range and improve solderability and usability.
3. Improve the overall structural strength
Due to the high reliability of the project, coupled with the weight reduction design and short delivery time, alloy steel castings can increase their competitive advantage in terms of price and economy.
4. A wide range of weight changes
Generally, small alloy steel castings may only have 10 grams, while large alloy steel castings can reach several tons, dozens, or even hundreds of tons.
Therefore, when we need high tensile strength or dynamic load components, critical pressure vessel castings, and core components that bear heavy loads at low or high temperatures, in principle, we should give priority to alloy steel castings.
Alloy steel casting production process
The so-called alloy steel casting process uses fusible materials (such as wax or plastic) to make a fusible model (referred to as investment or model).
How are alloy steel castings made?
First, it is coated with several particular refractory paint layers, dried, and hardened to form an integral shell.
Then use steam or hot water to melt the model from the shell, put the shell in the sandbox, and fill it with dry sand.
Next, place the mold into the roasting furnace and burn it at a high temperature (if a high-strength shell is used, the demolded shell can be roasted directly without modeling).
After the mold or shell is fired, molten metal is poured into it to have alloy steel castings.
When pressing an investment mold, a pressing type with a high surface finish of the cavity is usually used. Therefore, the surface finish of the investment mold is relatively high.
In addition, the shell is made of a refractory coating made of a special high-temperature resistant adhesive and refractory material, which is coated on the investment mold, and the inner surface of the cavity in direct contact with the molten metal has a high smoothness.
Therefore, the surface finish of investment castings is higher than that of general castings, generally reaching Ra.1.6~3.2μm.
The dimensional accuracy of alloy steel castings is relatively high, generally up to CT4-6 (sand casting is CT10~13, die casting is CT5~7).
Of course, due to the complex process of alloy steel castings, many factors affect the dimensional accuracy of the castings, such as the shrinkage of the mold material, the deformation of the investment mold, the linear change of the shell in the heating and cooling process, the shrinkage rate of the alloy, and the solidification Deformation of castings in the process, etc.
Therefore, although the dimensional accuracy of ordinary investment castings is relatively high, its consistency still needs to be improved.
Inspection and testing of alloy steel castings
Before using alloy steel castings, we must inspect them in advance to check whether the equipment is suitable for current use and whether it is damaged or not. During testing, we should equip reasonable testing methods and appropriate testing personnel to inspect the quality of finished alloy steel castings.
1. The appearance of alloy steel castings
The comparison samples can judge the surface roughness of alloy steel castings and the micro-cracks on the surface. It can be inspected by the coloring method and magnetic particle method.
2. The internal quality of alloy steel castings.
We usually use audio, ultrasound, eddy current, X-ray, and γ-ray methods for inspection and judgment.
Alloy steel castings should be guaranteed to be free from corrosion and mechanical damage during transportation and storage; It is important to attach a certificate of conformity, indicating that the batch of alloy steel castings meets the requirements of the drawing or contract and relevant technical standards.
The application of alloy steel castings
They are adding alloying elements to alloy steel castings to make the material reach a certain performance. As a guideline, we should add alloying elements in a low proportion (less than 5%) to increase strength or hardenability. And adding a larger proportion (over 5%) to obtain special properties, such as corrosion resistance extreme temperature stability. In the steelmaking process, we should add manganese, silicon, or aluminum to remove dissolved oxygen, sulfur, and phosphorus in the melt.
The following are a series of improved alloy steel castings (compared to carbon steel): strength, hardness, toughness, wear resistance, corrosion resistance, hardenability, and hot hardness. To achieve some of these improved properties, the metal may require heat treatment.
These discoveries are used in exotic and demanding applications, such as turbine blades for jet engines, spacecraft, and nuclear reactors. Due to the ferromagnetic properties of iron, some steel alloys have found critical applications where their response to magnetism is significant, including in motors and transformers. The uses and applications of alloy steel castings cover various industries and casting types.