Crack Cause Analysis in the Manufacturing of Cr12MoVCo Work Rolls

Published on February 13, 2026Work rolls are the core key components of cold rolling mills, especially the Cr12MoVCo work rolls applied in Sendzimir 20-high rolling mills, which are widely used in the rolling production of stainless steel and silicon steel strips. The manufacturing quality of such work rolls directly determines the production efficiency and product precision of cold-rolled strip steel. In the actual production process, the cracking defect of work rolls will not only cause production interruption and cost loss, but also affect the stability of the whole production line.

Based on the cracking failure of Cr12MoVCo series work rolls in the production process, our R&D team conducted a systematic analysis on the crack causes by means of metallographic microscope, fully automatic hardness tester and direct-reading spectrometer, and put forward targeted improvement measures. The research results provide important theoretical basis and technical guidance for optimizing the manufacturing process of forging work rolls, improving product quality and reducing production defects, and also lay a more solid foundation for the export of our forging products with high quality and high stability.

1. Experimental Instruments and Test Materials

1.1 Experimental Instruments

To ensure the accuracy and reliability of the test results, we selected high-precision professional testing equipment for various performance and structural detection of the cracked work rolls:

Wilson UH4250 Fully Automatic Hardness Tester: For surface hardness detection of work roll samples

DK7750 Wire Cutting Machine: For precision sampling of cracked parts

ZEISS AXIO Observer D1M Inverted Metallographic Microscope: For metallographic structure observation of crack areas

SPECTRO Spark Direct-reading Spectrometer: For chemical composition detection of the material near the cracks

1.2 Test Materials

The Cr12MoVCo work rolls tested are mainly applied to Sendzimir 20-high rolling mills, and the main rolling products are stainless steel and silicon steel strips. Its complete manufacturing process is: Smelting → Forging → Post-forging Heat Treatment → Rough Machining → Quenching → Finish Machining → Finished Product Inspection. The Cr12MoVCo steel is an improved material based on Cr12MoV steel in GB/T 1299-2014 Tool and Die Steels with an appropriate amount of Co element added, which has higher hardness and wear resistance. The chemical composition (mass fraction) of the test material is shown in Table 1.

Table 1 Chemical Composition of Cr12MoVCo Steel (Mass Fraction / %)

The heat treatment quenching process of the work roll is strictly controlled: heating to 1000℃-1050℃ for 2h, oil cooling for 15min-25min, air cooling to 700℃-800℃ for 3h and tempering in time, then air cooling to 400℃-500℃ for 2h, and two times of tempering at 460℃-510℃ for 10h respectively, finally air cooling to room temperature.

2. Test Methods

2.1 Hardness Detection

We cut 15mm×10mm×10mm samples from the cracked part at the roll body end with a wire cutting machine. After sanding and polishing the samples, we detected the surface hardness at the positions 1mm and 2mm above and below the crack with a fully automatic hardness tester, and selected five parallel test points at each position to ensure the accuracy of the hardness data.

2.2 Metallographic Structure Observation

The metallographic samples cut from the roll body end were sanded step by step with 400-mesh, 800-mesh, 1000-mesh and 1500-mesh water sandpaper, then rough polished with 5μm polishing paste and fine polished with 2.5μm polishing paste. The samples were corroded with 4% nitric acid alcohol solution (volume fraction), rinsed with absolute ethanol and dried, and then the metallographic structure observation was carried out with a metallographic microscope.

2.3 Chemical Composition Detection

The SPECTRO spark direct-reading spectrometer was used to detect the chemical composition of the material near the crack of the work roll after finish turning, so as to verify whether the cracking was caused by the non-compliance of the material composition。

3. Test Results and Analysis

3.1 Basic Situation of Cracked Work Rolls

The cracked work roll number is 24#-62#, and a crack was found at the R3 fillet of the roll body after finish turning. The crack is about 5.5mm in length and 2mm in depth, and extends to the end of the roll body. After verification, the implementation of the quenching process, oil temperature and oil cooling time of the work roll are all within the required range, no process operation problems were found, and the surface hardness of the process inspection meets the standard requirements. The ultrasonic flaw detection before quenching is qualified, and no cracks were found before the process flow.

3.2 Hardness Test Results

The average hardness values at the positions 1mm and 2mm above and below the crack were tested by the fully automatic hardness tester, and the specific data are shown in Table 2. The test results show that the hardness at the upper part of the crack is significantly lower than that at the lower part, and the average hardness difference at the position 1mm from the crack reaches 56HV, showing an obvious hardness unevenness.

Table 2 Hardness Test Results of Positions Near the Crack (HV)

3.3 Chemical Composition Detection Results

The chemical composition detection of the crack area by the direct-reading spectrometer shows that the content of each chemical element in the crack area is within the deviation range specified by the national standard, which indicates that the cracking of the work roll is not caused by the unqualified material composition, and the focus of the analysis is further locked on the manufacturing process.

3.4 Metallographic Structure Analysis

After corrosion with 4% nitric acid alcohol solution, the macroscopic morphology observation of the crack area of the roll body found that there is a significant color difference on both sides of the crack: one side is obviously white, and the other side is dark black. The color difference still exists after repeated grinding, polishing and corrosion, which initially indicates that there is decarburization near the crack.

The metallographic structure observation of the crack area shows that the metallographic structure near the crack is all tempered troostite and retained austenite, but the precipitation density of carbides in the upper area of the crack is significantly lower than that in the lower area. The number of carbides in the upper and lower parts at 1mm from the crack is obviously reduced, showing obvious organizational abnormality in the upper part of the crack. Combined with the microhardness test results, it can be comprehensively determined that obvious decarburization occurs in the upper part of the crack.

3.5 Crack Cause Analysis

According to the obvious decarburization phenomenon near the crack, it can be determined that the crack is formed in the forging process rather than the heat treatment quenching process. The main identification basis is that the cracks formed in the heat treatment quenching process have the characteristics of transgranular distribution, wide starting point and slender and tortuous tail, which mostly occur after martensite transformation, so the microstructure around the crack has no significant difference from other areas and no decarburization phenomenon.

The forging cracks of Cr12MoVCo work rolls are mainly formed in the areas with structural defects such as coarse grains and stress concentration, and are accompanied by obvious oxidation and decarburization characteristics. The main causes include:

Improper forging temperature control: Excessively high initial forging temperature or too low final forging temperature will lead to poor plastic deformation of the material and easy to produce cracks.

Unreasonable metal flow during forging: Oxide scale and other defects are involved into the forging to form crevices, or the surface forms an overlapping layer due to unreasonable metal flow, which leads to forging folding and further forms cracks.

Poor surface quality of raw materials: The surface of the raw material has defects such as scratches and unevenness, which easily cause stress concentration during forging and induce crack generation.

4. Improvement Measures for Forging Cracks

Aiming at the causes of forging cracks of Cr12MoVCo work rolls, we put forward the following targeted improvement measures to effectively prevent the generation of forging cracks and improve the manufacturing quality of work rolls:

4.1 Optimize Forging Temperature and Forging Method

Control the initial forging temperature in the austenite single-phase region, and do not exceed the formation temperature of δ-ferrite, at which the material has good toughness and is not easy to produce cracks.

Set the final forging temperature slightly higher than the temperature at which the second phase particles dissolve into the solid solution to ensure the uniform structure of the forging.

For long-time forging operations, if the temperature of the forging decreases, adopt the methods of reheating in the furnace or preheating the mold to maintain the plastic deformation ability of the material and reduce the probability of crack formation.

4.2 Improve the Surface Quality of Raw Materials

Strictly control the surface quality of raw materials, ensure that the surface is clean and flat, and remove defects such as scratches, oxide scale and unevenness on the surface of raw materials in time. For high alloy steels with strong crack sensitivity such as Cr12MoVCo, appropriate surface mechanical processing must be carried out before forging to eliminate surface stress concentration points.

4.3 Select Appropriate Forging Hammer Tonnage

According to the material characteristics and forming requirements of Cr12MoVCo steel, select the matching forging hammer tonnage to ensure the uniform plastic deformation of the forging during the forging process, avoid the generation of internal stress caused by excessive or insufficient forging force, and prevent the formation of cracks.

5. Research Conclusions

Obvious decarburization occurs in the upper part of the crack of the Cr12MoVCo work roll, the number of carbides is significantly reduced, and the average hardness difference at the position 1mm from the crack on both sides of the crack reaches 56HV, which is the key characteristic of the crack defect.

The crack of the Cr12MoVCo work roll is formed in the forging hot working stage rather than the heat treatment quenching process. Forging cracks are usually formed in the areas with structural defects such as coarse grains and stress concentration, and the main causes are excessively high forging temperature or too low final forging temperature.

The generation of forging cracks of Cr12MoVCo work rolls can be effectively prevented by optimizing the forging process parameters such as selecting appropriate forging temperature and forging method, ensuring the clean and flat surface of raw materials, and selecting the matching forging hammer tonnage.

About Our Forging Products Export

We are a professional manufacturer and exporter of high-precision forging products, focusing on the R&D, production and export of various forging work rolls, shaft forgings, cake forgings and other heavy forging products, among which the Cr12MoVCo work roll for cold rolling mills is one of our core export products. We have a complete set of advanced forging production equipment and strict quality control system, and carry out process optimization and defect prevention according to the latest research results to ensure the high quality and high stability of our forging products.

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