Reasonable carburizing agent was selected to improve the casting tensile strength
The microstructure and properties of cast iron depend on the microstructure and quality of raw materials to a great extent. The use of recarburizer is very important, especially for cylinder block and head castings with high densification requirements.
Choose carburant must choose good quality, nitrogen-containing products. Good recarburizer, sulfur content below 0.5 %, nitrogen content moderate. Nitrogen is not a metal but can be used as an alloy element to improve the strength of castings. Therefore, the suitable carburizing agent for gray iron castings should be limited to a range that can improve the strength of the cast iron without creating nitrogen pores.
CLASSIFICATION OF RECARBURIZING AGENTS FOR CAST IRON
The recarburizing agent for cast oil can be divided into the common recarburizing agent and graphitized recarburizing agent.
Ordinary recarburizer is divided into calcined petroleum coke and calcined coal. Calcined petroleum coke is formed from delayed coke of refinery by calcining at 1400 °C, while calcined coal recarburizer is formed from high-quality anthracite calcined at 1200 °C.
The graphitizing carburizing agent is made of calcined petroleum coke as raw material and graphitized at high temperature.
PERFORMANCE CHARACTERISTICS OF CARBURIZING AGENT
RECARBURIZER is a non-metal material, its melting point is 1200 °C ~ 1300 °C.
Type and composition of recarburizer
| TYPE | Fixed carbon | S | Dust | volatiles | water | granularity | N |
| CF-CA-01 | ≥98﹪ | ＜0.5﹪ | ≤0.5﹪ | ≤0.7﹪ | ＜0.5﹪ | 1-5mm | ≤0.4 |
| CF-CA-02 | ≥98﹪ | ＜0.5﹪ | ≤0.5﹪ | ≤0.7﹪ | ＜0.5﹪ | 0-1mm | ≤0.4 |
| CF-CA-03 | ≥93﹪ | ≤0.3﹪ | ≤6.0﹪ | ≤1.2﹪ | ≤0.5﹪ | 1-3mm | ≤0.4 |
| CF-CA-04 | ≥90﹪ | ≤0.3﹪ | ≤9.0﹪ | ≤1.5﹪ | ≤0.5﹪ | 1-3mm | ≤0.4 |
| CF-CA-05 | ≥98﹪ | ≤0.05﹪ | ≤1.0﹪ | ≤1.0﹪ | ≤0.5﹪ | 1-5mm | ≤0.05 |
THE PRINCIPLE OF CARBURIZING AGENT
Recarburizer plays the role of increasing carbon in steel-making and casting.
When melting cast iron in Cupola, the Molten Iron Liquid passes through the hot bottom coke in the form of liquid droplets, the effect of recarburization is good. Recarburizing agent is necessary for melting cast iron into the induction furnace (scrap + recarburizing agent). Substitution of carburant for pig iron can reduce “harmful heredity” in pig iron and improve metallurgical quality.
According to the different smelting process, recarburizer can increase the mechanical strength of steel, casting. RECARBURIZER can improve the ability of graphite nucleation in molten iron, increase the amount of nodular iron, improve the microstructure of gray iron, and increase the strength of Gray Iron The fine and uniform graphite is obtained to promote the spheroidization and inoculation process.
Particle Size: 0.1-1 mm, 1-5 mm
Packing specification: waterproof bag packing, small bag 25kg packing.
How to use:
- Disperse adding method: According to the carbon content, one layer charge and one layer recarburizing agent are added to the middle and lower part of the electric furnace. We recommend this method of addition.
- Centralized addition method: in the furnace melting or a small amount of molten iron, the carburizing agent will be added all at one time, and immediately covered with charge.
Note: carburant addition method, early and charging at the same time, intermediate charging has been partially melted, molten iron can be added later. However, the amount added should not exceed 0.2% in order to avoid the graphite coarseness.
APPLICATION OF ENHANCED CARBURIZING AGENT IN FOUNDRY
Yunnan Auto Parts Co. , Ltd..
The company mainly produces truck brake drum, using 148 molding machine modeling, used three kinds of carburizing agent. The cylindrical graphite carburizing agent was first used, although there were no nitrogen pores, the tensile strength was relatively low; when the carburizing agent was changed to a certain manufacturer, the tensile strength increased, but the nitrogen pore defect appeared; when the carburizing agent was later used, the tensile strength increased obviously At the same time, the defects of nitrogen pores are avoided.
COMPANY USAGE:
(1)Ingredient ratio
| ITEM | RATIO（%） |
| Iron srap | 45-55 |
| Pig iron | 8-12 |
| Scrap returns | 30-40 |
| Modified silicon carbide | 0.5-0.7 |
| carburant | 1.4-2 |
(2) chemical composition
| composition | C | SI | MN | S | P | Cr | Copper |
| Pre-furnace | 3.32-3.38 | 0.98-1.12 | 0.45-0.55 | 0.06-0.07 | 0.05-0.06 | 0.15-0.2 | 0.11-0.15 |
| After-furnace | 3.32-3.38 | 1.5-1.6 | 0.45-0.55 | 0.06-0.07 | 0.05-0.06 | 0.32-0.4 | 0.22-0.28 |
(3) Mechanical characteristics
| The name of the test bar | Tensile Strength(MPa) | Hardness（HB) |
| Cylinder graphite carburizer bulk test bar | 230-245 | 185-205 |
| Carburizer single cast test bar in a factory | 325-345 | 195-215 |
| A factory carburizer bulk test bar | 260-280 | 190-210 |
| Single cast test bar for casting fu carburetor | 330-350 | 195-215 |
| Castable carbon pick-up agent Bulk Test bar | 270-295 | 185-205 |
(4) air hole data
| TYPE | AIR HOLE | TOTAL PRODUCTION AMOUNT（PCS） | Air hole ratio% | Remarks |
| 1 | 512 | 4950 | 10.3 | A factory carburizer |
| 2 | 5 | 4055 | 0.12 | Castf carburizer |
(5) conclusion:
Using recarburizing agent of cast-fluxes, the high strength under high carbon equivalent was achieved without increasing the alloy, and the tensile strength was improved.
The defects of Nitrogen Pores in brake drum produced by this enterprise are basically eliminated, which proves that the nitrogen content of carburizing agent used by this enterprise is relatively high, which results in the appearance of nitrogen pores. The nitrogen content of castable carburizing agent is suitable, which can improve the casting tensile strength and reduce the nitrogen pore defect.
Recently, the carbon content of brake drum has been raised to 3.4 %, and the content of copper has been reduced to 0.2 %.
