What are the differences among stainless steel valve 304, 304L, 316 and 316L on the motorized valve（part 1）?

​Valve Science Knowledge

Stainless Steel Valves（part 1）

What exactly are "steel" and "iron", what are their characteristics, what is the relationship, how do the 304, 304L, 316, 316L we usually talk about come from, and what is the difference between them?

They can be used with motorized valve actuators.

Steel: A material with iron as the main element, a carbon content generally below 2%, and other elements. ——GB/T 13304 "Steel Classification"

Iron: A metal element with atomic number 26. Iron materials have strong ferromagnetism and good plasticity and thermal conductivity.

Stainless steel: A type of steel that is resistant to weak corrosive media such as air, steam, and water or has stainless properties. Commonly used steel types are 304, 304L, 316, 316L, which are 300 series steels of austenitic stainless steel.

304 stainless steel performance introduction

304 stainless steel is the most common type of steel. As a widely used steel, it has good corrosion resistance, heat resistance, low temperature strength and mechanical properties; it has good hot processing properties such as stamping and bending, and no heat treatment hardening phenomenon (non-magnetic, use temperature -196℃～800℃).

Scope of application of 304 stainless steel

Household items (1, 2 types of tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs)

Auto parts (windshield wipers, mufflers, molded products)

Medical equipment, building materials, chemistry, food industry, agriculture, ship parts

304L stainless steel (L for low carbon) performance introduction

As a low-carbon 304 steel, its corrosion resistance is similar to that of 304 steel in general state, but after welding or stress relief, its resistance to intergranular corrosion is excellent; it can also maintain good corrosion resistance without heat treatment, and the use temperature is -196℃～800℃.

304L stainless steel application scope

Applicable to outdoor open-air machines in the chemical, coal, and petroleum industries with high requirements for intergranular corrosion resistance, heat-resistant parts of building materials, and parts that are difficult to heat treat.

Introduction to the performance of 316 stainless steel

316 stainless steel has excellent corrosion resistance, atmospheric corrosion resistance, and high-temperature strength due to the addition of molybdenum, and can be used under harsh conditions; excellent work hardening (non-magnetic).

316 stainless steel application scope

Equipment for seawater, chemical, dye, papermaking, oxalic acid, fertilizer and other production equipment; food industry, coastal facilities, ropes, CD rods, bolts, nuts.

316L stainless steel (L for low carbon) performance introduction

As a low-carbon series of 316 steel, in addition to having the same characteristics as 316 steel, it has excellent resistance to intergranular corrosion.

316L stainless steel application scope

Products with special requirements for resistance to intergranular corrosion.

Performance comparison of 316 and 316L stainless steel

Chemical composition

316 and 316L stainless steel are molybdenum-containing stainless steels. The molybdenum content in 316L stainless steel is slightly higher than that in 316 stainless steel. Due to the molybdenum in the steel, the overall performance of this steel is better than that of 310 and 304 stainless steel. Under high temperature conditions, when the concentration of sulfuric acid is lower than 15% and higher than 85%, 316 stainless steel has a wide range of uses. 316 stainless steel also has good resistance to dichloride corrosion, so it is usually used in marine environments. They can be used with motorized valve. actuators.The maximum carbon content of 316L stainless steel is 0.03, which can be used in applications where annealing cannot be performed after welding and maximum corrosion resistance is required.

Corrosion resistance of 316 and 316L stainless steel

The corrosion resistance of 316 stainless steel is better than that of 304 stainless steel, and it has good corrosion resistance in the production process of pulp and papermaking. Moreover, 316 stainless steel is also resistant to corrosion by marine and corrosive industrial atmospheres.

They can be used with motorized valve actuators.

Generally speaking, there is not much difference between 304 stainless steel and 316 stainless steel in terms of chemical corrosion resistance, but there are differences in certain specific media.

The first stainless steel developed was 304, which was sensitive to pitting corrosion under certain circumstances. The addition of 2-3% molybdenum reduced this sensitivity, and thus 316 was born. In addition, this additional molybdenum can also reduce corrosion from certain hot organic acids.

316 stainless steel has become almost a standard material in the food and beverage industry. Due to the shortage of molybdenum worldwide and the higher nickel content in 316 stainless steel, 316 stainless steel is more expensive than 304 stainless steel.

Pitting corrosion is a phenomenon mainly caused by deposit corrosion on the surface of stainless steel, which is due to the lack of oxygen and the inability to form a protective layer of chromium oxide.

Especially in small valves, the possibility of deposits on the valve plate is small, so corrosion rarely occurs.

In various types of aqueous media (distilled water, drinking water, river water, boiler water, seawater, etc.), 304 stainless steel and 316 stainless steel have almost the same corrosion resistance, unless the chloride ion content in the medium is very high, then 316 stainless steel is more suitable.

In most cases, there is not much difference in the corrosion resistance of 304 stainless steel and 316 stainless steel, but in some cases there may be a big difference, which requires specific analysis. Generally speaking, valve users should be aware of this because they will choose the material of the container and pipeline according to the medium. It is not recommended to recommend materials to users.

They can be used with motorized valve actuators.

Tianjin Tianfei High-tech Valve Co., Ltd.

Focusing on the automatic control motorized valve industry for 14 years

Official website: https://www.minimotorizedvalve.com/

Contact number: 022-85685296

Emai：tf.co@tfjt.com