SerbiaCommon Heat Treatment Processes for Cold Forming Profile Rolls and Their Functional Effects

Cold forming profile rolls are core forming tools for producing metal profiles, strip steel and thin-walled sections. Long-term continuous cold extrusion, rolling and friction will bring heavy load, surface abrasion and contact fatigue to the rolls. Heat treatment is the key process to adjust the internal metallographic structure of roll blanks, optimize hardness, toughness, wear resistance and fatigue resistance, and extend the service life of forming rolls. Different heat treatment procedures target different performance defects of rolls. This article sorts out the mainstream heat treatment methods for cold forming profile rolls and an alyzes their respective action effects.

1. Annealing

Process flow

The forged roll blank is heated to the specified annealing temperature, held for sufficient time, then cooled slowly inside the furnace. There are full annealing, spheroidizing annealing and stress relief annealing for roll production.

Main effects

1. Eliminate internal forging stress generated during roll blank forging, avoid deformation or cracking of rolls in subsequent machining and quenching;

2. Refine coarse grain structure formed by high-temperature forging, homogenize internal metallographic organization;

3. Reduce the hardness of roll blank, improve cutting performance, lower the loss of turning and milling tools during rough machining;

4. Spheroidizing annealing converts flaky cementite into spherical particles, laying a good organizational foundation for subsequent quenching, effectively reducing quenching cracking risk.Applicable stage: Post-forging pretreatment of all cold forming roll blanks.

2. Normalizing

Process flow

Heat the roll workpiece above the critical transformation temperature, keep warm, then take it out for air cooling. It is often matched with annealing for composite pretreatment.

Main effects

1. Further homogenize the internal structure of large-size heavy rolls, eliminate structural segregation caused by uneven cooling after forging;

2. Improve the grain uniformity of the roll surface and core, reduce the difference in mechanical properties between the surface and the center;

3. Remove network carbide precipitated at grain boundaries of high carbon alloy roll materials, avoid brittle fracture of rolls under rolling load;

4. Properly adjust blank hardness to balance machining efficiency and structural uniformity.Applicable stage: Intermediate treatment of large-diameter cold forming rolls after rough forging.

3. Quenching (Overall quenching & Surface quenching)

Two mainstream quenching modes are adopted for cold forming profile rolls: integral quenching for small light rolls and surface induction quenching for large heavy forming rolls.

Process flow

Heat the roll to quenching temperature, hold heat to complete austenite transformation, then rapidly cool through quenching medium such as water, oil or polymer quenchant. Induction quenching only heats the working surface layer of the roll while the core remains unheated.

Main effects

1. Integral quenching: Obtain martensite structure inside the whole roll, greatly improve the overall hardness and compressive strength of small rolls, suitable for small forming rolls with uniform load on the whole body;

2. Surface induction quenching: Form a high-hardness wear-resistant martensite layer on the roll working surface, while the roll core retains tough tempered sorbite structure. The roll owns hard surface for wear resistance and tough core for impact resistance, which is the most widely used process for large cold forming rolls;

3. Greatly improve surface hardness of the roll forming area, reduce surface scratching, abrasion and indentation during long-term cold forming of metal strips;

4. Enhance the contact fatigue resistance of the roll surface, delay the generation of fatigue pitting and peeling defects under cyclic rolling pressure.

4. Tempering (Low-temperature, Medium-temperature, High-temperature Tempering)

Tempering must be carried out immediately after quenching to eliminate quenching stress, classified by heating temperature.

Low-temperature tempering (180–250℃)

Effects

1. Release most quenching residual stress inside the roll, prevent delayed cracking of quenched rolls during storage and use;

2. Retain high surface hardness of the roll forming area, only slightly reduce internal brittleness;

3. Stabilize the martensite structure, avoid hardness fluctuation and dimensional change during long-term service.Mainly used for cold forming rolls that require high surface wear resistance.

Medium-temperature tempering (350–500℃)

Effects

1. Balance hardness and toughness of rolls, improve the ability to resist impact load;

2. Increase the yield strength of the roll surface, reduce plastic deformation when rolling thick hard strips;Suitable for forming rolls processing thick stainless steel, high-strength carbon steel profiles.

High-temperature tempering (500–650℃)

Effects

1. Obtain tempered sorbite structure with good comprehensive mechanical properties, high toughness and moderate hardness;

2. Completely eliminate forging and quenching composite stress, stabilize the overall size of large rolls;

3. Improve the thermal stability of rolls, reduce softening deformation under continuous rolling heat accumulation;Mostly used for large heavy-duty cold forming main rolls with heavy impact load.

5. Cryogenic Treatment

Process flow

After quenching and before tempering, put the roll into low-temperature equipment at -80℃ ~ -196℃ for heat preservation treatment.

Main effects

1. Convert residual austenite on the roll surface into martensite, further increase surface hardness and wear resistance;

2. Reduce volume instability caused by residual austenite phase transformation during roll service, improve dimensional stability of forming profiles;

3. Refine carbide particles on the roll surface, slow down the generation of fatigue cracks under cyclic cold forming load;Often used for high-precision cold forming rolls with strict dimensional tolerance requirements.

6. Chemical Heat Treatment (Carburizing, Nitriding, Carbonitriding)

1. Gas Nitriding / Ion Nitriding

Effects

1. Form a dense nitride hard layer on the roll surface, significantly improve surface hardness, anti-adhesion and anti-scuffing performance;

2. The nitriding layer has low friction coefficient, effectively avoid metal strip sticking and scratching during cold forming;

3. Introduce surface compressive stress, inhibit the expansion of surface fatigue cracks, greatly extend the service cycle of forming rolls;Suitable for rolls processing thin aluminum strips, stainless steel decorative profiles.

2. Carbonitriding

Effects

Penetrate carbon and nitrogen elements to form a compound hardening layer, with higher hardness and thicker effective layer than single nitriding, low cost, suitable for medium-load general cold forming profile rolls.

7. Composite Heat Treatment Process Matching for Cold Forming Rolls

In actual production, single heat treatment cannot meet the comprehensive performance requirements of forming rolls, and combined processes are commonly matched:

1. Conventional small alloy forming rolls: Spheroidizing annealing → Rough machining → Integral quenching + low-temperature tempering;

2. Large heavy-duty main forming rolls: Forging annealing → Normalizing → Semi-finishing → Surface induction quenching + medium/high temperature tempering;

3. High-precision anti-sticking profile rolls: Induction quenching + low-temperature tempering → Ion nitriding;

4. Ultra-precision thin strip forming rolls: Quenching → Cryogenic treatment → Low-temperature tempering.

Conclusion

The mainstream heat treatment methods for cold forming profile rolls include annealing, normalizing, quenching, tempering, cryogenic treatment and chemical heat treatment such as nitriding. Annealing and normalizing belong to pre-processing heat treatment, which optimize blank structure and eliminate forging stress; quenching and tempering are core procedures to adjust the hardness and toughness matching of rolls; cryogenic treatment improves dimensional stability and surface hardness; nitriding and carbonitriding enhance surface anti-wear and anti-sticking capacity. Reasonable matching of multiple heat treatment processes can solve common roll failure problems such as surface wear, fatigue peeling, impact cracking and dimensional deformation, and meet the long-term stable operation requirements of cold forming profile equipment.