الفولاذ D2 مقابل 440C: أيهما مناسب لتطبيقك

الوقت المقدر للقراءة: 7 دقائق

فولاذ الأدوات D2 (1.2379) and الفولاذ المقاوم للصدأ 440C are often regarded as highly esteemed yet controversial representatives within the industry. D2’s exceptional wear resistance and high hardness in cold work applications set the benchmark, while 440C remains a common choice for corrosion-resistant cutlery and bearings. This article aims to provide a detailed and objective comparison of these two materials, offering readers the insights needed to make informed decisions. Although both D2 and 440C are high-carbon steels, they exhibit significant differences in corrosion resistance, toughness, and edge retention.

Composition Overview

D2 tool steel:

440C steel:

D2 steel Vs. 440C: Hardness and Wear Resistance

When selecting tool steel and specialty steel grades, hardness and wear resistance are often the two most critical factors for customers. Although both D2 (1.2379) and 440C can achieve extremely high hardness after heat treatment, the mechanisms behind this performance differ, leading to distinct behaviors in practical applications.

Both materials derive their hardness from the precipitation of high-hardness carbide particles within a hardened مارتنسيتي matrix.

D2 mold steel (1.2379) achieves a maximum hardness of 64 HRC after quenching. It is typically recommended for use within the 58-64 HRC range, depending on التلطيف temperature and process. 440C stainless steel is the hardest grade within the 440 series. It can achieve Rockwell C-60 after heat treatment. For applications like bearings, its hardness is typically controlled between 61-64 HRC. Note, however, that to achieve maximum hardness, 440C often requires low-temperature tempering at around 150°C, which demands exact temperature control during heat treatment.

When comparing hardness values alone, the two are evenly matched; however, when it comes to maintaining high hardness while enabling deep machining and impact resistance, D2 offers greater versatility in processing methods.

In many stamping and forming applications, D2 offers a significantly longer service life than 440C due to the type and volume of carbides in its microstructure. Wear resistance depends not only on the matrix hardness but also on the quantity and quality of hard particles in the steel. 

D2 contains a high proportion of extremely hard chromium-rich M₇ج₃ carbides, while the vanadium in its composition forms exceptionally hard VC carbides, further enhancing the material’s resistance to abrasive wear.

The wear resistance of 440C primarily relies on M₂₃ج₆ and M₇ج₃ carbides, which are mainly composed of chromium and iron. While its wear resistance is sufficient for valve components and bearing assemblies, it still falls slightly short of D2 when subjected to high-intensity industrial wear.

 D2 steel Vs. 440C: Toughness and Machinability

We face an inescapable physical law: the higher the hardness, the lower the toughness and machinability tend to be. D2 (1.2379) and 440C are both typical high-carbon, high-alloy steels, each possessing high hardness. For tool and die makers and machining shops, understanding their shortcomings in toughness and machinability is crucial to reducing scrap.

Although D2 is a high-carbon steel with low ductility, exhibiting direct fracture without significant necking during tensile testing, its overall toughness performance is rated as moderately favorable. 440C stainless steel demonstrates comparatively inferior toughness, possessing extremely low ductility, with elongation potentially dropping to as low as 2% after heat treatment. 440C is absolutely unsuitable for high-pressure containers like gas cylinders that require high impact resistance. It is better suited for precision components subjected to static loads, harsh environments, and stringent rust prevention requirements.

Both contain large amounts of hard alloy carbides that enhance wear resistance but also severely wear down your cutting tools, making machining quite difficult. If the machinability of 1% carbon tool steel is set as the baseline at 100 points, D2 scores only 45 points. As a martensitic stainless steel, 440C is equally difficult to machine. Commercially available 440C must be in a fully مُلَدَّن “softened” state to enable forming operations.

D2 steel Vs. 440C: Corrosion Resistance

In the comparison between D2 mold steel and 440C, hardness and wear resistance may be neck-and-neck, but corrosion resistance is the watershed that entirely separates the two.

440C stands as the benchmark among traditional high-carbon martensitic stainless steels. It perfectly combines high hardness with outstanding rust resistance and pitting corrosion resistance. If you require a cutting edge to stay sharp or bearings to operate reliably in humid or corrosive environments, 440C is the unparalleled choice. To achieve high hardness, 440C requires a high carbon content. During heat treatment, chromium combines with carbon to form large chromium-rich carbides. However, as chromium is consumed by carbon to form these hard carbides, the effective chromium content remaining in the steel matrix—which is essential for forming the rust-resistant passivation film—is reduced. This is known as the “chromium depletion” phenomenon. During heat treatment, tempering temperatures must be strictly controlled to ensure the corrosion resistance of 440C steel does not deteriorate. We recommend tempering either below 400°C (750°F) or above 600°C (1100°F), avoiding the intermediate critical zone.

D2 contains as much as 11.5%–12.05% chromium, so why isn’t it considered stainless steel? The primary purpose of chromium in D2 is not rust prevention, but to enhance hardenability and wear resistance. Due to D2’s extremely high carbon content, the vast majority of chromium forms carbides. Consequently, there is almost no free chromium in the matrix to resist corrosion. Therefore, D2 is unsuitable for prolonged exposure to high temperatures or corrosive environments.

D2 Vs. 440C Comparison Table

Applications and Summary

The unique balance of properties dictates the typical use cases for each steel:

Choosing between D2 (1.2379) tool steel and 440C stainless steel is fundamentally not about which is stronger, but which is more suited to the environment.

If your application is in a dry industrial workshop environment, and the goal is wear resistance, dimensional stability, and long service life, D2 is the undisputed best choice.

If your tool must survive in humid, corrosive, or biological environments, D2 will fail due to rust, no matter how hard it is. In this case, 440C is the only option. While maintaining high hardness, 440C offers superior corrosion resistance and rust prevention.

روابط ذات صلة

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