What Is Thermomechanical Rolling

Release time：

2025-08-05

Thermo-Mechanical Control Process (TMCP) is an advanced metalworking technology that combines temperature control, rolling deformation and cooling processes. It aims to significantly enhance the strength, toughness and weldability of steel by optimizing the microstructure. The core principle is to achieve grain refinement and phase transformation control by precisely regulating the rolling temperature, deformation rate and cooling rate, thereby obtaining high-performance steel without adding excessive alloying elements.

I. Core principle

1. Grain refinement

Rolling is carried out in the non-recrystallization zone of austenite (approximately 800 ° C to 950 ° C) to inhibit the growth of austenite grains and induce the formation of fine ferrite grains during subsequent phase transformation through deformation energy storage.
The final rolling temperature is controlled near the Ar₃ phase transformation point (approximately 700 ° C to 850 ° C) to promote the nucleation of ferrite at the grain boundaries of deformed austenite and further refine the microstructure.

2. Phase change regulation
Immediately after rolling, accelerated cooling (such as water cooling or gas mist cooling) is adopted to rapidly pass through the ferrite-pearlite transformation zone, inhibit the formation of coarse structures, and form strengthening phases such as bainite/martensite.

II. Process flow

TMCP is divided into three stages to synergistically control material properties:
1. Preheating stage
The steel billet is heated to 900℃ to 1200℃ to eliminate internal stress and enhance plasticity, ensuring uniform temperature distribution.

2. Temperature-controlled rolling stage

Rough rolling: Large reduction deformation is carried out above the recrystallization temperature (>950℃) to break the original as-cast structure.
Finishing rolling: Multi-pass temperature-controlled rolling is carried out in the non-recrystallization zone of austenite (800℃ to 950℃) to accumulate deformation energy and prepare for phase transformation.

3. Cooling control stage
After rolling, accelerate the cooling at a rate of 10 ° C /s to 30 ° C /s to the target temperature (e.g., 500 ° C to 600 ° C), lock in the fine-grained structure and inhibit the coarsening of carbides. Tempering may be required after cooling to adjust the residual stress.

III. Differences from traditional hot rolling

Characteristic	Thermal Mechanical Rolling (TMCP)	Traditional Hot Rolling
Rolling Temperature	Staged Precise Control (final rolling in the non-recrystallization zone)	Single High-temperature Range (>1000℃)
Cooling Method	Accelerated Cooling (water cooling/aerosol)	Natural Air Cooling
Grain Size	Ultrafine Grains (≤5μm)	Coarse Grains (20-50μm)
Alloy dependence	Low (carbon equivalent ≤0.45%)	High (strengthening Elements Such As Nb And V Need To Be Added)
Performance Advantages	High Strength and Toughness, Excellent Weldability	Strength And Toughness Are Difficult To Balance

IV. Technical advantages

1. High performance and low cost
Reduce the addition of alloying elements (such as Mn and Mo) to lower production costs while achieving the same strength (e.g., S460 grade yield strength ≥460MPa).

2. Energy conservation and environmental protection
Eliminating heat treatment processes such as normalizing and quenching can reduce energy consumption by 30% to 50% and cut carbon emissions.

3. Enhance weldability
The low-carbon equivalent design (Ceq≤0.45%) reduces the risk of embrittlement in the heat-affected zone of welding and is suitable for welded structures such as ships and Bridges.

4. Adapt to complex cross-sections
The modular cooling systems developed by SMS et al. (such as BeamCool³) can precisely control the cooling uniformity of complex sections of steel sections, solving the problem of uneven performance at corners and webs in traditional processes.

V. typical application fields

High-strength structural steel: Q620M for construction, AH36/DH36 for ships, etc., with a yield strength of up to 620MPa.
Energy equipment: Wind power towers (S355ML), oil and gas pipelines (X80 grade), resistant to low-temperature shock (-50℃).
Transportation and Machinery: Heavy-duty vehicle chassis, port crane boom (S460ML), featuring both lightweight and fatigue resistance.
Section steel products: H-beams, track steel, achieving uniform section performance through TMCP.

VI. Key limitations

Subsequent processing temperature: If the secondary heating exceeds 580℃, it may lead to a decrease in strength (due to tissue recovery).
Process sensitivity: Even minor deviations in temperature and cooling rate may cause performance fluctuations, requiring a high-precision automated control system.

Summary

Thermal mechanical rolling (TMCP) breaks through the traditional metallurgical bottleneck through the synergistic effect of temperature-controlled rolling and accelerated cooling, achieving "fine grain strengthening" and "phase transformation strengthening" of steel, and has become a core technology for the production of high-performance green steel. Its wide application in fields such as ships, Bridges and energy has promoted the development of lightweight, high safety and sustainable manufacturing.

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