I. Introduction to Steel Ladles
The steel ladle is a critical vessel in the metallurgical industry, used for containing, transporting, refining, and pouring high-temperature molten steel (1500–1700°C). It plays a vital role in transferring molten steel from the steelmaking furnace to the refining station or continuous casting machine, performing secondary refining processes such as argon stirring, alloying, and desulfurization, buffering temperature to maintain the superheat of the steel, and precisely controlling the pouring flow rate via the slide gate mechanism.
Core structure: Outer shell steel plate (supporting the main body—conical or cylindrical)), permanent lining (insulation layer—lightweight refractory bricks/castables), and working lining (directly in contact with molten steel, made of magnesia-carbon bricks/alumina-magnesia-carbon bricks).
II. Common Materials Used for Steel Ladles
Component |
Commonly Used Materials |
Performance Requirements |
Outer shell steel plate |
SA516 Gr70 (American Standard) |
Medium-temperature pressure vessel steel (350°C strength stable) |
Q345R (National Standard) |
Low cost, but requires controlling welding cracks. |
|
Pivot pin |
34Cr2Ni2Mo Forged Steel |
Ultra-high strength (tensile strength ≥800 MPa) |
Breathable brick base |
ZG35Cr24Ni7SiN (Heat-Resistant Cast Steel) |
Thermal Shock Resistance + Oxidation Resistance |
Slag-line area |
304 Stainless Steel Composite Plate |
Preventing slag penetration and corrosion |
Key point: The shell must comply with the ASME Sec. VIII pressure vessel standard, and the lug material must have an impact energy of ≥40 J (-20°C).
III. Selection of Welding Methods
Part |
Welding Process |
Parameter Example |
Outer shell longitudinal/circumferential weld |
Submerged Arc Welding (SAW) |
Current: 600–750 A, Voltage: 32–38 V |
Pivot Shaft and Housing |
Flux-Cored Wire Gas-Shielded Welding (FCAW-G) |
Multi-layer, multi-channel; preheat to 150°C |
Stainless Steel Composite Plate |
Transition Layer: ER309L |
Heat input ≤ 15 kJ/cm (preventing carbon migration) |
。
4. Key Processes in Welding Technology
Pre-weld preparation: Material cutting, forming, and beveling (with precision control).
Strict cleaning: Remove oil, rust, water, oxide scale, and other contaminants from the bevel and surrounding areas on both sides.
Assembly tack welding: Use the same welding materials and processes as for the final welds to ensure high-quality tack welds of appropriate length and spacing. Also, inspect assembly gaps and misalignment.
Preheating (if required): Heat evenly to the specified temperature, and monitor and record accordingly.
Welding process:
Weld strictly according to the WPS and welding sequence.
Control interlayer temperature (monitor and record).
When performing multi-pass, multi-layer welding, carefully clean away interlayer slag and spatter. Ensure proper fusion of the weld beads to prevent defects.
Monitor key parameters (current, voltage, speed, gas flow, etc.).
Key Control Measures
Preheating and Post-Weld Heat Treatment: SA516 Gr70 Steel Plate: Preheat to 120–150°C (for plate thickness >30mm), followed by post-weld heat treatment at 250–300°C for 2 hours to relieve hydrogen.
Deformation Control: The shell joints utilize the "internal welding, external correction" process, with a pre-set counter-deformation allowance of 3–5 mm/m.
Bevel Design: K-Type Bevel (Reduces Residual Stress).
Non-destructive Testing: 100% UT + MT after welding (to detect root cracks).
Composite plate welding: First weld the carbon steel layer → remove root pass → weld the transition layer → apply stainless steel cladding (GTAW for base layer)
Welding Process |
Application Scenarios |
Material preparation process |
Flame cutting (CNC cutting), plasma cutting, laser cutting, shearing, and sawing. High-precision bevel machining (such as edge milling and bevel cutting machines). |
Forming process adopted |
Rolling (cylindrical and conical shapes), bending (using a bending machine), pressure forming (with large-scale presses), and roll forming. |
Assembly and Alignment |
Using large-scale tooling fixtures and platforms—such as welding positioners and roller stands—ensures the precise positioning and dimensions of each component. This is a critical step in quality control. |
Common Welding Methods |
Application Scenarios |
Submerged Arc Welding |
Suitable for long straight welds and circumferential seams (such as longitudinal and circumferential seams of cylindrical shells). |
Gas-shielded welding |
MAG (CO2 or mixed gas), MIG (inert gas). Widely used and highly versatile (manual, semi-automatic, automatic), suitable for various positions and joint types. |
Shielded Metal Arc Welding |
Suitable for positions that are difficult to automate, short welds, and repair welding. It is less efficient and relies heavily on the welder's skill. |
Electroslag Welding |
Vertical welding for extra-thick plates (such as box-beam diaphragms). |
Narrow-Gap Welding |
Designed for butt welding of ultra-thick plates, it offers high efficiency and minimal deformation. |
Post-weld treatment |
|
Stress |
Large components generally require post-weld heat treatment—either overall or localized (typically stress relief annealing)—to remove weld slag and spatter, followed by grinding of the weld seam and its surrounding areas. This process helps relieve residual welding stresses, preventing deformation and cracking while enhancing toughness. |
Orthopedic |
Flame straightening, mechanical straightening (using a press), to control welding deformation. |
Mechanical Processing |
Perform precision machining operations such as milling, boring, and drilling on critical mating surfaces and hole locations. |
We will conduct non-destructive testing, inspection, and testing on the products:
Visual Inspection |
Surface defects (cracks, undercut appearance inspection (VT), porosity, arc craters, etc.). |
Ultrasonic Testing (UT) |
Detecting internal defects (such as lack of fusion, incomplete penetration, slag inclusions, cracks, etc.) is especially critical for thick plates. |
Radiographic Testing (RT) |
Intuitively displays internal defects and is commonly used for critical butt joints. |
Magnetic Particle Testing (MT) |
Detection of Surface and Near-Surface Defects (Ferromagnetic Materials) |
Penetrant Testing (PT) |
Detecting surface opening defects (non-magnetic materials). |
Destructive Testing (Sampling) |
Such as tensile testing, bending tests, impact tests, hardness tests, and metallography (typically conducted during process qualification or random inspections). |
Dimensional Inspection |
Check whether the overall structural dimensions and dimensions of key components meet the drawing requirements. |
Pressure/Leak Test (if required) |
Such as hydraulic tests, pneumatic tests, and air-tightness tests. |
V. Specification Range
Capacity |
The outer shell steel plate is thick. |
Thick work shirt |
Total weight range |
Steel-to-water ratio (self-weight / payload) |
100 tons |
40–50 mm |
150–200 mm |
60 to 80 tons |
0.6~0.8 |
200 tons |
50~60mm |
200–250 mm |
120 to 150 tons |
0.6 to 0.75 |
300 tons |
60~80mm |
250~300mm |
200 to 250 tons |
0.67 to 0.83 |
Please note: The working liner will erode and thin out during use, leaving a residual weight that is 20% to 30% lighter than a new liner—regular maintenance is required!
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Large steel ladle riveted and welded components
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