Large rolling dies are the key components for achieving metal deformation during the rolling process. These dies are constantly under high-load conditions and have strict requirements for strength, hardness, and service stability.
Forged large rolling die components are widely used in high-load rolling fields due to their dense internal structure and stable mechanical properties.
This article takes the 30Mn2 alloy forged steel rolling mill rolls as an example, and introduces the material selection, process design, forging process, operation key points, and quality control methods for large-scale rolling mill rolls.
Material Selection for Rolling Rod-Type Forgings
Characteristics of the Forces Acting on Rolling Rods
The working conditions of the rolls are complex and they mainly bear the following loads:
- The roller surface withstands impact and friction.
- The roller neck is subjected to alternating stresses of torsion, bending, and shear.
- The material must possess high strength, high toughness and excellent wear resistance.
Advantages of alloy forged steel rolls
The alloy forged steel rolls have the following characteristics:
- Uniform internal organization.
- Compact structure.
- Good anti-fatigue performance.
- High impact resistance.
Forged steel rolls are suitable for high-load and high-strength rolling conditions.
30Mn2 alloy steel has stable comprehensive performance and is commonly used as the base material for large-sized rolls.
Forging Process Design
- Material Input Specifications and Forging Ratio.
- Design forging ratio: ≥ 3.5.
- Steel ingot weight: Not less than 3.7 tons.
Reasonable forging ratios can effectively improve the internal quality of the forgings.
Hot forging contraction amount and machining allowance
When measuring the dimensions of forgings under high-temperature conditions, the cooling contraction needs to be taken into account:
- The post-pressing contraction rate of 30Mn2 steel: 1.2%.
- Machine processing allowance: Reserved by at least 20 mm.
- This design ensures that the final delivery size is accurate.
Process Flow of Large Rolling Rod Forgings
Rolling Stock Process Flow
3.7 t steel ingot → Grinding→ Heating → Forging blanking→ Removing riser and small head→ Forging to Φ320 mm + 8 mm→ Surface grinding.
Forging forming process flow
Re-heating and holding for insulation
→ Extension
→ Turning and extension
→ Indentation
→ Both ends extension
→ Polishing to Φ165 mm + 5 mm
→ Precision forging
→ Box cooling
→ Heat treatment
→ Precision inspection
→ Cutting off and storage in warehouse
Key Points for Operation Control During the Forging Process
Heating control
- Ensure that the temperature of each surface of the billet is uniform and prevent the occurrence of uneven surfaces.
Cutting heads and measurement control
- Use the three-cut method.
- The length of a single piece does not exceed 2.23 meters.
- After measurement, return to the furnace for heat preservation promptly.
Assembly forging sequence:
- Start by forming a circle from the largest end.
- The middle section retains a diameter of 320 mm and a length of 1940 mm.
- The forging process does not cut through the ribs.
Dimension control and concentricity control
- Strictly control the dimensional tolerances.
- Prevent the forgings from bending.
- Ensure concentricity.
Heat treatment and hardness requirements
- Follow the heat treatment procedure for alloy structural steel.
- The Brinell hardness should be controlled within 207 to 269 HB.
Surface quality control
- Remove surface defects.
- The depth of the defects should not exceed 5 mm.
- The areas exceeding the standard need to be marked and dealt with.
Quality Inspection and Result Analysis
Surface Quality
The surface quality of the forgings complies with the requirements of GB/T 3077—1999.
Mechanical properties and dimensional stability
- The mechanical properties meet the technical specifications.
- The process capability index for dimensions is Cp ≥ 2.0.
- The production in batches has good stability.
- Production practice has shown that the three-step process of roughing, rough forging and fine forging is a reasonable and feasible production method.
- The normal heat treatment system is stable and reliable.
Main technical requirements for the rolls
Strength and toughness
- Strength is the most fundamental technical parameter of the rolling mill rolls.
- The rolls must have sufficient impact resistance.
- The strength level can be determined through material selection and structural size calculation.
Surface Hardness and Wear Resistance
- The hardness of the working surface determines the service life of the rolls.
- The hardness level is controlled by the alloy composition and heat treatment process.Hot-rolled rolls also need to have certain heat resistance.
Stability of Use
- Stable dimensional accuracy.
- Good concentricity.
- Long-term service performance is reliable.
Conclusion
The 30Mn2 alloy forged steel large-sized rolling mill rolls have excellent strength, toughness and wear resistance.
A reasonable forging process and heat treatment regime can ensure the stability of the forging quality.
This process route is suitable for the mass production and engineering application of large-sized rolling mill rolls.
E-mail: cykc@cykcgroup.com.cn