We use cookies to enhance your experience. By continuing to browse this site you agree to our use of cookies. More info.

Introduction What “L” Grades Are and Why They Are Used What “H” Grades Are and Why They Are Used What the Differences Are      304 and 304L      304 and 304H      316, 316L and 316H      Property Specifications      Dimensional Tolerance Differences Pressure Vessels Alternative Grade Usage      High Temperature Strength Requirements      Tested Carbon Content - L Grades      Tested Carbon Content - H Grades      Dual Certification

The common designations of austenitic grades of stainless steel, such as grades 304 and 316, include sub-grades – L and H variants used for specific applications.

The low carbon “L” grades are used for applications involving welding treatments or high temperature exposure, e.g. welding of heavy or medium sections. The low carbon content of steels prevents carbide precipitation at grain boundaries, which can cause inter-granular corrosion under corrosive operation conditions. Carbide precipitation occurs at temperatures ranging from about 450 to 850°C.

Based on their applications, “L” grade steels are available in the form of pipe, plate and, most commonly, in round bars. The corrosion resistances of standard austenitic and “L” grades are identical in the absence of high temperature exposure or welding treatments.

"H" grades are high carbon stainless steel grades, having improved strength at high temperatures - generally above 500°C. These high carbon grades have high short-term and long-term creep strength. They are usually produced in the form of pipe and plate. Most commonly employed grades are grade 304H and 316H, but ASTM A240/A240M also covers high carbon versions of grade 309, 310, 321, 347 and 348. When used at temperatures of about 450-850°C, these grades are subjected to sensitization which, in turn, causes aqueous corrosion, and reduction in toughness and ductility at ambient temperatures.

Grades 304 and 304L have the same composition limits for all components except carbon. However, neither grade 304 nor grade 304L is specified to have minimum carbon content.

Grade 304H is a high carbon version of grade 304, and it has the same composition specification as that of standard grade 304. Grade 304H does not have the 0.10% nitrogen maximum limit which is applicable to both "L" and standard grades. All austenitic "H" grades should have a grain size of ASTM No 7.

The three grades 316, 316L and 316H are the major counterparts of grade 304. Only the percentage of carbon contents differentiates these grades. The following table provides the carbon content of the alternatives covered under ASTM A240/A240M:

Table 1. Stainless steel carbon contents

NOTE: Specifications for some other products, particularly tube and pipe, have a limit of 0.035% or 0.040% maximum for 304L and 316L, but are otherwise the same.

The table below specifies the differences in mechanical properties of various grades:

Table 2. Stainless steel property specifications

In practice, steel mills generally ensure that the "L" grade heats meet the strength requirements of the standard grades.

There are no dimensional or other differences between standard, "L" and "H" grades.

Pressure vessel codes, such as AS1210, and pressure piping codes, such as AS4041, provide allowable working pressures for each of the stainless steel grades at high temperatures. These codes provide high-pressure ratings for standard stainless steel grades when compared to that of "L" grades at any temperature. The codes avoid utilization of "L" grade steels at temperature of 425 or 525°C.

The codes consist of a clause stating that standard grades, which contain at least 0.04% carbon, must be used at temperatures above 550°C. Therefore, grades 304 or 316, having 0.02% carbon, are not allowed to be used at high temperatures. The pressure vessel codes provide the same allowable pressure rating for "H" grades.

It is possible to use a product labelled as a standard grade instead of "L" or "H" grade, or vice versa, owing to the availability issues. This substitution can be made under the following conditions:

"L" grades can be used as standard grades as long as high temperature strength is not required, and the mechanical properties conform to the standard grade requirements. "L" grades nearly always comply with the standard grade requirements, but this must be investigated on each occasion.

Standard grades can be used as "L" grades if their carbon content meets the "L" grade limits of 0.030 or 0.035% maximum.

Standard grades are often used instead of "H" grades as their carbon contents meet the "H" limits of 0.04 to 0.10%. Additional testing may be required to satisfy the grain size requirement. "H" grades having a maximum 0.10% of nitrogen and 0.08% of carbon are used as standard grades.

It is very common for steel mills to supply "L" heats when standard grades have been ordered. In fact, some of the product and test certificates are marked "304/304L". In some cases the product is marked only as standard, or "L". The details provided on the mill test certificate will show if the alternative grades comply with the standard.

The requirement of an "H" grade for any high temperature application must be specified during the time of order. The required high carbon steel will be supplied, based on availability. The product and its test certificate will confirm grade compliance.

Do you have a review, update or anything you would like to add to this article?

AZoM speaks to Dr. Spence Macdonald from ABOzymes about his discovery of a novel biopolymer, acholetin, synthesized from a bacterial enzyme.

AZoM speaks with Dr. Rajashekar Badam from JAIST about his recently formulated method for anode fabrication that could pave the way to the very fast charging of lithium-ion batteries.

AZoM speaks to Michael Jewett, a researcher at Northwestern University, about a novel process using bacteria to capture CO2 and convert it into the useful commercial chemicals acetone and isopropanol. This could bring us closer to a circular bioeconomy in the chemical sector.

Discover ODIN, a compact deep UV Raman spectrometer by IS-Instruments.

This product profile outlines how the Carousel 12 Plus Reaction Station is used as an effective personal synthesis station.

IKA has released the new reactor system EasySyn which is the only reactor system available on the market where all components are available from a single source.

This article provides an end-of-life assessment of lithium-ion batteries, focusing on the recycling of an ever-growing amount of spent Li-Ion batteries in order to work toward a sustainable and circular approach to battery use and reuse.

This article provides an overview of the materials that are used to produce photovoltaic cells for the production of renewable energy, as well as new research that proposes the use of novel materials.

This article considers laser-based 3D printing, or additive manufacturing, looking at different types of lasers in the fabrication process.

AZoM.com - An AZoNetwork Site

Owned and operated by AZoNetwork, © 2000-2022