Comparison of 65Mn Spring Steel from Different Steel Mill

Silicon (Si): Silicon content is consistent between both steels. Silicon commonly serves as a deoxidizer and strengthening agent, effectively improving steel strength and hardness.

Manganese (Mn): Steel mill A’s steel exhibits slightly higher manganese content. Manganese aids in strengthening ferrite, improves hot working properties, and enhances steel’s strength, hardness, and wear resistance.

Phosphorus (P): Steel mill B’s steel has a slightly higher phosphorus content. Phosphorus is a harmful impurity; excessive amounts significantly reduce steel’s ductility and toughness. It particularly triggers “cold brittleness” at low temperatures, causing a sharp decline in material toughness and increased brittleness, leading to brittle fracture.

Sulfur (S): Steel mill B’s steel exhibits slightly elevated sulfur content. Sulfur typically acts as a harmful impurity, prone to causing “hot brittleness” During high-temperature hot working processes (such as forging or rolling), it can induce cracking or fracture, thereby compromising process feasibility and finished product quality.

Chromium (Cr) and Nitrogen (N): Steel mill A’s steel contains a certain amount of chromium, which enhances hardenability, wear resistance, and corrosion resistance. Steel mill B’s steel steel was found to contain nitrogen. While nitrogen can strengthen steel in appropriate amounts, excessive levels can cause “ageing embrittlement” where the material’s toughness and ductility gradually decrease and brittleness increases after storage or heat treatment.

Comparative Analysis of Mechanical Properties

Strength Performance

The tensile strength of steel mill A’s steel steel exceeds that of steel mill B’s steel, consistent with its higher carbon content and the alloying effect of chromium. Due to differing testing systems employed for yield strength, a direct comparison is currently unfeasible. Overall, however, both products’ strength levels fall within the typical performance range for 65Mn steel.

Ductility Level

Both products exhibit similar elongation values, indicating comparable ductility levels that meet standard application requirements for 65Mn steel.

Surface and Special Properties

Steel mill B’s steel exhibits a distinct decarburization layer (0.08–0.09 mm), significantly higher than steel mill A’s approximately 0.02 mm. If used in applications sensitive to surface hardness (e.g., precision springs, cutting tools), additional processes to remove or repair the decarburized layer are required.

The hardness test results for steel mill A’s steel better reflect its initial surface condition. Given its chromium content, subsequent heat treatment (e.g., quenching + tempering) can further enhance surface hardness and wear resistance, yielding superior performance.

Note: The decarburization layer thickness of 0.08–0.09 mm exceeds most industry strict standards (typically ≤0.05 mm) and is considered relatively high. Without remedial measures (such as carburizing or grinding to remove the decarburized layer), this may lead to reduced surface wear resistance and fatigue strength, shortened service life, or even premature failure. Therefore, in applications demanding high surface performance, strict control of decarburization depth is essential.

Comparative Analysis of Other Factors

According to our company’s research, trace amounts of vanadium (V) and titanium (Ti) elements were detected in manufacturer B’s steel products. Although their concentrations did not reach the standard limits specified in the Material Test Certificate (MTC) and thus were not labeled, these microalloying elements still play a positive role in enhancing steel properties, particularly in improving strength, toughness, and corrosion resistance. Their mechanisms of action are summarized below.

Role of Vanadium (V) in Steel

1) Grain Refinement

Vanadium readily forms uniformly distributed carbonitrides (VC, V(CN)) in steel. These precipitates inhibit the growth of austenite grains during heating, thereby achieving grain refinement. Grain refinement not only enhances steel strength but also improves toughness, representing the primary mechanism by which vanadium strengthens steel properties.

2) Strength Enhancement

Precipitation Hardening: During cooling or aging, fine vanadium carbonitrides precipitate, impeding dislocation movement and significantly increasing yield strength and tensile strength.

Fine-Grain Strengthening: By inhibiting grain growth, strength levels are further elevated.

3) Improved Weldability

Vanadium carbonitrides exhibit high stability and resist complete dissolution in the weld heat-affected zone. This effectively suppresses grain coarsening and reduces crack sensitivity, thereby enhancing weldability. Consequently, vanadium-containing steels are frequently used in welded structural components.

4) Optimized Toughness

The synergistic effect of grain refinement and uniformly distributed precipitates mitigates brittleness tendencies, enhances impact toughness, and maintains good toughness in low-temperature environments.

Role of Titanium (Ti) in Steel

1) Nitrogen and Carbon Fixation, Enhanced Aging Resistance

Titanium exhibits strong affinity for nitrogen and carbon, forming TiN and TiC precipitates. This reduces free nitrogen and carbon content, suppressing embrittlement caused by aging while mitigating carbon’s adverse effects on weldability.

2) Grain Refinement

TiN precipitates resist dissolution during smelting and rolling, acting as pinning sites that effectively inhibit austenite grain coarsening.

For low-carbon steels, titanium’s grain refinement effect is particularly pronounced, improving formability and low-temperature toughness.

3) Enhanced Weldability

Titanium preferentially fixes carbon, reducing carbide precipitation at grain boundaries. This inhibits hardening and embrittlement in the weld heat-affected zone, improving weld reliability. This is especially critical in stainless steels and low-alloy high-strength steels.

4) Improved Corrosion Resistance (in Stainless Steels)

Titanium combines with carbon, reducing Cr₂₃C₆ precipitation and preventing chromium depletion at grain boundaries. This maintains the integrity and stability of the passivation film, significantly enhancing resistance to intergranular corrosion.

5) Improved Plasticity and Formability

Grain refinement enhances the plasticity of steel. For cold-worked materials like automotive sheet steel, titanium-containing steel better accommodates stamping and forming processes.

Comprehensive Evaluation

Both vanadium and titanium enhance steel properties through grain refinement and carbon-nitrogen fixation/precipitation mechanisms, though their primary effects differ:

Vanadium: Primarily achieves precipitation hardening and grain refinement strengthening, significantly boosting strength while optimizing weldability.

Titanium: Focuses on carbon-nitrogen fixation and grain refinement, notably improving aging resistance, weldability, and corrosion resistance.

In practical steel production, vanadium and titanium are often added together to achieve comprehensive optimization of strength, toughness, weldability, and corrosion resistance.

Conclusion

Comparative analysis of material certificates and key performance indicators for 65Mn steel from steel mill A’s steel and steel mill B’s steel yields the following conclusions:

Steel mill A’s steel demonstrates superior strength, resistance to embrittlement, and heat treatment adaptability.

Its elemental composition better ensures stable mechanical properties and greater potential for further strengthening. Overall, steel mill A’s 65Mn steel outperforms steel mill B’s product.

For applications demanding high strength, critical resistance to embrittlement (including heat embrittlement and cold embrittlement), or requiring subsequent heat treatment, steel mill A steel is recommended as its alloy element composition better ensures mechanical property stability and further strengthening potential.

Although trace amounts of rare metal elements (V, Cr, Cu, Ni, Ti) were detected in steel mill B’s steel, their concentrations only marginally exceed standard levels and do not meet the thresholds specified in the material certificates. Therefore, the contribution of these elements to performance improvements (such as enhanced strength or corrosion resistance) during actual heat treatment remains uncertain and requires validation through practical testing.

Disclaimer

The comparative results herein are based on our company’s sampling analysis of material certificates for 65Mn steel from steel mill A and steel mill B. They reflect only the testing outcomes of the sampled products and do not represent the overall quality level of all products from either steel mill. The conclusions and inferences presented are based on the understanding and judgment of our company’s researchers and do not constitute a final determination of the product quality of either steel mill.

To avoid undue impact on the reputation of steel mill A and steel mill B, the names of the steel mills have been withheld in this document. The final product performance should still be determined by actual usage results.

Customers interested in verifying the performance of these two products or conducting trials may contact our sales representatives for further information.