When the measured temperature of molten iron is fully up to specification, yet the liquid metal appears viscous, is difficult to pour, and exhibits extremely poor fluidity, this is known in the foundry industry as the “false cold” (or apparent cold) ظاهرة.
Since temperature has already been ruled out, the core of the problem lies in the alteration of the rheological properties of the molten iron. ببساطة, the internal liquid structure and suspended particles are hindering the free movement of metal atoms. Below is an in-depth analysis and troubleshooting guide for “false cold” caused by non-metallic inclusions, abnormal slag, and trace elements:
أنا. Core Reasons Behind the “False Cold” ظاهرة
1. Excessive Non-Metallic Inclusions (ال “الفرامل” Effect of Suspended Solids)
When large amounts of fine, high-melting-point non-metallic inclusions (مثل آل₂O₃, شافي₂, and composite silicates) exist in the molten iron, they do not easily float to the surface due to the electromagnetic stirring effect of the induction coils. بدلاً من, they remain uniformly suspended.
- Suspension Resistance: These solid or semi-solid inclusions disrupt the continuity of the liquid metal, drastically increasing the apparent viscosity of the molten iron.
- Heterogeneous Nucleation: Excessively fine inclusions act as premature crystallization nuclei during cooling. This causes the molten iron to thicken locally before it even reaches the solidus line.
2. Abnormal Slag (Slag Emulsification and High-Viscosity Entrainment)
The physical and chemical properties of the slag have a direct impact on metal fluidity:
- الخبث “Emulsification”: If the slag has a high melting point and poor fluidity, or if the induction furnace’s electromagnetic stirring is too intense, the slag cannot aggregate effectively on the surface. بدلاً من, it gets “entrained” deep into the melt, forming a problematic slag-liquid mixture.
- Severe Oxidation: Severe rust on the charge or prolonged holding at excessive furnace temperatures leads to severe oxidation. This spikes the الحديد O و شافي₂ levels in the molten iron. The resulting acidic or high-viscosity slag networks directly “lock up” the fluidity of the iron.
3. Increase in Trace Elements (Formation of High-Melting Phases & Altered Surface Tension)
Certain trace elements have very low solubility in molten iron, or they easily react with س, ن, و ج to form high-melting-point interstitial compounds:
- التيتانيوم (ل) and Aluminum (آل): Even trace amounts of ل (>0.04%) easily combine with nitrogen and carbon to form extremely hard, high-melting-point ل(ج, ن) particles. آل generates chain-like or cluster-like Al₂O₃. These are the primary culprits behind the thickening of molten iron.
- الكروم (كر) والفاناديوم (الخامس): These elements hinder carbon diffusion and widen the solidification interval of the molten iron, causing it to prematurely enter a “pasty” or mushy state during pouring.
- Surface Tension Alteration: Certain elements significantly increase the surface tension of the molten iron, preventing it from properly filling the mold cavity, which macroscopically manifests as extremely poor fluidity.
الثاني. On-Site Emergency Treatment and Radical Prevention
لمعالجة هذه القضايا, a combination of “immediate on-site conditioning” و “source control” must be applied:
1. Immediate On-Site Treatment (In-Furnace Measures)
- Deoxidation and Inclusion Modification (علاج الكالسيوم):
Add an appropriate amount of calcium-silicon (نعم) سبيكة أو rare-earth (يكرر) based modifiers to the furnace. Calcium or rare earths convert high-melting-point, stringer-type, or clustered Al₂O₃ and silicates into low-melting-point, easily floatable spherical calcium aluminates (مثل 12 CaO · Al₂O₃), drastically reducing the viscosity of the molten iron.
- Utilize High-Efficiency Slag Coagulants:
Throw high-efficiency slag coagulants or fluxing agents rich in the شافي₂ – آل₂O₃ – F system onto the melt surface to lower the melting point and viscosity of the surface slag. This allows it to fully absorb the fine inclusions suspended in the upper layer of the molten iron. Afterward, completely skim off the slag.
- Balance Static Holding and Electromagnetic Stirring:
After adjusting the furnace composition, reduce the power or turn off the power completely to let the melt sit undisturbed for 2 ل 3 دقائق. This allows the suspended inclusions driven by electromagnetic stirring to float up to the surface using their own buoyancy (enhanced by the calcium treatment). Avoid prolonged, violent, over-powered electromagnetic stirring.
2. Fundamental Preventive Measures (Source Governance)
| البعد التحكم | Specific Control Measures |
| Raw Material Quality Control | * Strictly limit impurity elements like Ti, آل, مثل, and Sb in the pig iron and steel scrap. خاصة, avoid using coated steel sheets (such as aluminized or galvanized sheets) and scrap titanium alloy steels. * Control the ratio of return scrap / عوائد مسبك. Strictly prohibit the use of heavily rusted scrap (which is rich in iron oxides). |
| Melting Process Optimization | * Control the holding time of molten iron at high temperatures to prevent over-oxidation and excessive silicon pickup from the furnace lining materials (like silica sand), which forms micro-inclusions. * Perform proper final deoxidation at the end of the melting cycle. |
| بطانة الفرن & تغطية | * Regularly inspect furnace lining erosion to prevent lining spalling from entering the molten iron and forming exogenous inclusions. * Use high-quality covering agents before tapping to isolate the melt from the air, preventing secondary oxidation in the tapping launder and pouring ladle. |
