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Views: 0 Author: Helen Shao Publish Time: 2026-03-31 Origin: Analysis of the Damage Reason of the High Speed Steel Roll Collar and Its Countermeasures Zhang Zhongfeng, Wang Pingji, Yin Daiyong, Li Junfang, Kong Fangang Published in Steel Rolling, March
High-Speed Steel (HSS) rolls are widely used in hot rolling mills because of their excellent wear resistance, long service life, and strong cost-performance ratio. In the production of ribbed steel bars, HSS rolls can deliver much higher rolling output than many conventional roll materials. However, in actual mill operation, the final performance of HSS rolls depends not only on the material itself, but also on groove design, cooling conditions, repair practice, and operating control.
A practical case from ribbed bar production showed that two common failure modes may occur during HSS roll service: roll collar breakage between adjacent grooves, and groove spalling or shelling at the groove bottom. These problems can directly affect product quality, reduce roll service life, and in severe cases even cause rolling accidents or unexpected downtime. According to the paper, such defects once created a significant hidden risk in production and led to an average annual defective-product rate of around 0.02%.
From the technical point of view, this type of damage is essentially a fatigue failure process. During rolling, the grooves are subjected to complex working conditions, including rolling force, impact load, repeated thermal stress caused by hot material and cooling water, as well as axial compressive stress. Under these combined and fluctuating loads, micro-cracks may initiate and gradually propagate until visible fracture, shelling, or local spalling appears.
The paper identifies several major reasons behind the damage. One key factor was insufficient roll collar strength. In practice, higher hardness improves wear resistance, but it also reduces toughness, which makes the collar area more vulnerable to breakage. Traditional design experience was no longer sufficient under the actual rolling conditions. Another important factor was poor cooling performance. Blue discoloration at the groove edge and surface temperatures above 80°C indicated that the cooling effect was inadequate, which promoted crack formation. In addition, if the groove repair allowance was too small, micro-cracks could remain after turning and then grow rapidly when the roll was put back into service. The paper also notes that excessive K2 pass width and improper operation, such as abnormal guide contact or roll wrapping, could further accelerate groove damage.
To solve these problems, several practical measures were implemented. First, the groove center distance was increased and the roll collar width was enlarged to improve collar strength. At the same time, the groove fillet radius was enlarged to reduce stress concentration. Second, the cooling system was upgraded. A new medium-pressure recirculating water system was introduced, and the roll cooling device was optimized several times to improve cooling efficiency. During production, cooling water pressure was maintained above 0.5 MPa, and after rolling stopped, groove surface temperature was controlled below 35°C. Third, the repair allowance was increased to ensure that all cracks at the groove bottom and groove edge were completely removed before the roll returned to service. Finally, tighter control was applied to pass design and mill operation in order to avoid overloading and accidental mechanical damage.
The improvement results were very clear. After these corrective actions were applied, the plant no longer experienced repeated roll collar breakage or groove spalling in ribbed bar production. For 12 mm ribbed bar rolling, the average output per groove reached about 350 tons, which was around 230 tons higher than that of bainitic rolls. With longer groove life and reduced roll change frequency, production efficiency improved significantly. The paper reports that the plant’s operating rate increased by an average of 2.08%, while annual output increased by about 15,000 tons, creating considerable economic benefit.
This case once again shows that the successful application of HSS rolls is not determined by material quality alone. Proper groove design, sufficient cooling, complete crack removal during repair, and disciplined operating practice are all essential to achieving stable performance and maximum roll life. For steel mills aiming to improve rolling efficiency and reduce total roll cost, these details are just as important as the roll material itself.
