Hastelloy®C-22®或Hastelloy®C-276®：哪种适合您的加工环境？

哈氏合金®C-22®与C-276®：均适用于恶劣环境

Here we’ll explore two highly corrosion-resistant alloys -哈氏合金C-22and Hastelloy C-276. These alloys are often used in processing that places heavy demands on equipment –涉及苛刻的化学品，高温，以及需要连续清洁的需求，以确保产品纯度并防止污染。

Sanitary processing, whether it be forfoodandbeverages,个人护理和清洁产品, or药品，完全属于“苛刻”的范畴。它与设备中使用和制造的产品的化学性质，以及用于构建加工系统的材料的化学性质有关。

“哈氏合金” is a trademark name that applies to around 20 high-performance alloys that all have nickel as a primary ingredient.

许多产品对盐酸、硫酸、磷酸、醋酸和甲酸的腐蚀以及氯的腐蚀都有很高的抵抗力，所有这些在卫生处理中都很常见。

The Hastelloys fall into two groups:

• Nickel-molybdenum (Ni-Mo) alloys
• 镍钼铬合金

Both C-22 and C-276 are Ni-Mo-Cr alloys. Let’s first look at the critical role of chromium in enhancing corrosion resistance.

When this protective layer is formed, the alloy surface is referred to as “passive” because it’s unlikely to react chemically or electrochemically with what’s put through the processing equipment.

It is also chemical and electrochemical reactions between processor contents and the equipment construction material that leads to corrosion.

Not only does the passive layer itself not react, but it also acts as a barrier between the contents inside the processor and the system’s underlying metal, preventing it from corroding.钝化可以用强力清洗剂去除还原剂that destroy the protective oxide layer on the metal.

In nominal terms, C-276 is 16% chromium, and C-22 is 22% –a significant difference. 我们将在下面讨论这对它们各自的性能造成的实际差异。

Nickel: strength and stability

Over two-thirds of all the nickel produced goes into making stainless steel, and about three-quarters of all stainless steels, including 304 (about 8% nickel) and 316 (10% nickel), contain it. Nickel lends formability, weldability, and ductility.

It also adds resistance to:

• Reducing acids
• Caustic solutions
• 压力腐蚀裂缝

在某些加工条件下，包括chlorides, the protective chromium passive layer can become chemically reactive and begin to break down, exposing the inside of the system to localized corrosion- 特别是点蚀和缝隙腐蚀。镍在启动该过程中没有作用，但一旦开始，就会减慢进展。它还允许更多的铬掺入合金中，从而提高耐腐蚀性。

Molybdenum: versatility in enhancing alloy qualities

Molybdenum is a key alloying element in high-performance nickel-based alloys that fall into two categories:

• 耐蚀合金
• 需要承受高温条件的合金

在卫生加工，温度通常不超过沸腾（212°F / 100°C），因此耐温质量并不适用。耐腐蚀是卫生处理主要关注的质量。

以下是钼的一些主要防腐优点：

• It resists non-oxidizing conditions (reducing acids where the primary corrodent is the hydrogen ion rather than dissolved oxygen), including hydrochloric and sulfuric acids, common in sanitary processing.
• Molybdenum doesn’t provide corrosion resistance to oxidizing environments - in fact, it typically results in a higher corrosion rate.因此，不建议将含有高水平钼和少量或无铬的镍合金用于氧化酸或含有高水平氧化剂（如氯）的溶液。
• In oxidizing environments, it joins with chromium to protect against localized s such as pitting and crevice corrosion, especially in the presence of chlorides and non-oxidizing acids.
• It dramatically enhances the resistance of nickel to reducing agents such as oxalic acid.

Tungsten

钨的主要优点(increased resistance to oxidation, nitridation, carburization, halogenation, and stress corrosion cracking)适用于高于卫生处理温度的环境。在适用于卫生处理的温度下（通常在室温和沸腾温度之间），它执行许多与钼相同的功能，包括支持冶金稳定性。

Nominal quantities (percent by weight) of Cr, Ni, Mo and W in C-22 and C-276

	Chromium %	Nickel %	Molybdenum %	钨%
C-22	22	56	13	4
C-276	16	57	16	3

氧化和还原:corrosi的基础on

我们之前讨论了铬是如何与氧反应形成保护性钝化层的，之后，铬会趋于稳定并停止与环境中其他元素的反应，从而停止腐蚀。We would think of this as beneficial oxidation, while corrosion is harmful oxidation.为保留被动层的稳定性创造条件是关于为环境选择合适的合金的很多。

When metals react with their environments, two basic electrochemical processes are going on –氧化和减少-导致原子以离子形式离开金属表面，或以溶解金属离子形式留在工艺流中，或与其他物质结合形成累积腐蚀产物。

氧化是一个原子或低价离子放弃一个或多个电子的过程。It will only occur when the electrons from the oxidation reaction can be transferred to another atom or ion by a corresponding reduction reaction. A typical example of this is the corrosion of iron in moist air or a neutral water environment.

在这些条件下，Fe将氧化以形成可溶性Fe2 +离子和两个电子。水中的溶解O2将接受电子并减少以形成OH-离子。对该腐蚀过程的反应总结如下。

Fe = Fe2++ 2e- (oxidation reaction)
O2 + 2H2O + 4e- = 4OH- (reduction reaction)
2Fe+O2+H2O=4OH-+Fe2+（整体腐蚀反应）

When products of this corrosion reaction, OH- and Fe2+, become sufficiently concentrated, they will combine and precipitate out as ferrous hydroxide Fe(OH)2, which in the presence of oxygen will oxidize to Fe(OH)3, which is the final corrosion product known as rust.

接受电子的还原反应中的物种是氧化剂或氧化剂。它正在减少并且变得更加负，因为它接受来自氧化物种的电子。负责腐蚀不锈钢和镍合金的最常见氧化剂是dissolved oxygen in neutral and basic solutions and the H+ ion in acidic solutions.

Comparison of the Aqueous Corrosion Resistances of C-22 and C-276
(in acidified 6 wt.% ferric chloride)

	铬，镍和钼的标称含量（重量％）	Critical Pitting Temp C°/F°	Critical Crevice Temp C°/F°
C-22	22Cr/56Ni/ 13Mo/4W	>150/ >302	176/80
C-276	16Cr/57Ni/16Mo/3W合金	>150/ >302	131/55

The C22 alloy also provides corrosion resistance over a much broader range of oxidizing and reducing environments, and using it to construct your processing system will give you a highly robust system for resisting corrosion in a wide range of chemical environments.