Comparision Grade 304 304L 316 316L Corrosion Resistance

As American AISI basic grades, the only practical difference between 304 or 316 and 304L or 316L is carbon content. The carbon ranges are 0.08% maximum for 304 and 316 and 0.030% maximum for the 304L and 316L types. All other element ranges are essentially the same (nickel range for 304 is 8.00-10.50% and for 304L 8.00-12.00%).

There are two European steel of the '304L' type, 1.4306 and 1.4307. The 1.4306 is the variant most commonly offered, outside Germany. The 1.4301 (304) and 1.4306 (304L) have carbon ranges of 0.07% maximum and 0.030% maximum, respectively. The chromium and nickel ranges are similar, nickel for both grades having an 8% minimum. The European grades for the 316 and 316L types, 1.4401 and 1.4404, match on all elements with carbon ranges of 0.07% maximum for 1.4401 and 0.030% maximum for 1.4404.

Effect of carbon on corrosion resistance

The lower carbon 'variants' (316L) were established as alternatives to the 'standards' (316) carbon range grade to overcome the risk of intercystalline corrosion (weld decay), which was identified as a problem in the early days of the application of these stainless steel tube. This can result if the steel is held in a temperature range 450 to 850 for periods of several minutes, depending on the temperature and subsequently exposed to aggressive corrosive environments. Corrosion then takes place next to grain boundaries.

If the carbon level is below 0.030% then this intercrystalline corrosion does not take place following exposure to these temperatures, especially for the sort of time normally experienced in the heat affected zone of welds in 'thick' sections of steel.

Effect of carbon level on weldability

There is a view that the low carbon types are easier to weld than the standard carbon types.

There does not seem to be a clear reason for this and the differences are probably associated with the lower strength of the low carbon type. The low carbon type may be easier to shape and form, which in turn may also affect the levels of residual stress left the steel after is forming and fitting up for welding. This may result in the 'standard' carbon types needing more force to hold them in position once fitted-up for welding, with more of a tendency to spring-back if not properly held in place.

The welding consumables for both types are based on a low carbon composition, to avoid intercrystalline corrosion risk in the solidified weld nugget or from the diffusion of carbon into the parent (surrounding) metal.

Dual-certification of low carbon composition steel

Commercially produced steels, using current steelmaking methods, are often produced as the low carbon type as a matter of course due to the improved control in modern steelmaking. Consequently finished steel products are often offered to the market 'dual certified' to both grade designations as they can then be used for fabrications specifying either grade, within a particular standard.

For example for coil, sheet or plate

304 Types:

BS EN 10088-2 1.4301 / 1.4307 to the European standard.

ASTM A240 304 / 304L OR ASTM A240 / ASME SA240 304 / 304L to the American pressure vessel standards.

316 Types:

BS EN 10088-2 1.4401 / 1.4404 to the European standard.

ASTM A240 316 / 316L OR ASTM A240 / ASME SA240 316 / 316L, to the American pressure vessel standards.

 

What are the different types/grades of stainless steel?

Stainless steel is an alloy that is produced by combining a variety of different base metals to create a new material. Like with other alloys, the final product is considerably stronger than each of the source materials would be on their own.

The History Of Stainless Steel

People have been experimenting with metal alloys for thousands of years. While examples of iron smelting can be found as far back as 1800 B.C., the introduction of crucible steel goes as far back as 300 B.C.

Stainless steel is a very versatile material. Through the years, engineers have experimented with the production of alloys.

By adding and removing certain metals, they were able to produce different types of stainless steel with different characteristics and applications. For example, it is used in everything from the production of kitchen utensils to components for construction projects.

Producing Different Types of Stainless Steel

When producing stainless steel, several different materials can be used to achieve different results. These include:

1.     Carbon
Stainless steel with high carbon content is much more durable and longer-lasting than other alloys. This type of stainless steel is popular for the production of food-grade utensils and cooking implements.

2.     Chromium
Stainless steel made with chromium is much more resistant to corrosion, stains, and tarnishing. One well-known example of this type of stainless in use is the Gateway Arch in St. Louis.

3.     Nickel
Making stainless steel with nickel improves the formability, weldability, and ductility of the material. This also improves its corrosion-resistant properties. Nickel is what allows for stainless steel to be such a versatile alloy.

The Three Primary Types of Stainless Steel

While there are thousands of different types of stainless steel alloy that can be produced, most alloys will fall into one of the following three categories.

1.     Austenitic stainless steel

There are two main characteristics of this type of stainless steel. First, there is a lot of chromium included during the production of austenitic stainless steel. Items produced with this material are more corrosion-resistant. Second, these items tend to be non-magnetic, although they can become magnetic with a cold forming process. These are the most common types of stainless steel alloys.

2.     Ferritic Stainless Steel

This type of stainless steel is the second most common type of alloy and is also magnetic. Items produced with this alloy can be hardened through cold forming and also tend to be less expensive than other types due to the lower nickel content.

3.     Martensitic Stainless Steel

This material is the least common type of stainless steel alloy. Martensitic stainless steel is used in applications where high tensile strength is needed or a lot of impact resistance. In many cases, this material is also combined with a protective polymer coating to improve corrosion-resistance

Different Grades of Stainless Steel Alloys

Within the three primary categories mentioned above, there are also different grades of stainless steel.

Within the austenitic steel types, there are two main grades – grade 304 and grade 316. Grade 304 is known for its high tensile strength of roughly 621 MPa (90 ksi). Grade 316 stainless steel also has a tensile strength of 579 MPs (84 ksi), making the two grades reasonably similar in this regard.

They also both have a high maximum operating temperature. Grade 304 has a maximum temperature of 870°C (1598°F) and Grade 316 has a maximum of 800°C (1472°F).

When comparing 304 vs. 316 stainless steel, one major difference is resistance to chlorides such as salt. Grade 316 is more resistant to the elements, making it a more desirable stainless steel for things like maritime applications.

Ferritic stainless steel also has two main grades – grade 430 and grade 434. Grade 430 stainless steel isn’t as strong as either of the austenitic steels but offers better resistance to nitric acid. It is also still strong enough for most heavy-duty applications.

Grade 434 steel has high tensile strength and maximum operating temperature and is tougher than the 430 grade, including better pitting resistance.

Martensitic stainless steel has only one grade, grade 420. This grade offers slightly less resistance to chemicals than the austenitic and ferritic steels, but it still has good resistance to things such as some alkalis, mild acids, water, and food compounds. It also has great tensile strength and impact resistance. This makes it ideal for producing items like cutlery.

Duplex Stainless Steel

Duplex stainless steel is a family of stainless steel that is made of austenitic steel and ferritic steel in nearly equal proportions. This type of stainless steel is both stronger and more resistant to corrosion than your typical types of stainless steel. Duplex stainless steel is also more ductile than ferritic grades, however, it is not quite as ductile as the austenitic grades.

One of the main differences in the composition is that duplex stainless steel is made with a higher chromium content and a lower nickel content. This not only makes the material stronger, but it also provides cost benefits. For these reasons, duplex stainless steel is often used in applications like pipes and risers in offshore oil rigs.

Grades of Duplex Stainless Steel

Just as with the other types of stainless steel, duplex stainless steel is also broken down into different grades or groups.  The three primary groups are based on the pitting and the corrosion resistance of the material.

• Standard Duplex Steel

Standard duplex steel has a PREN range of 28-38. This is the most typical type of duplex steel used today. It is also sometimes called Grade EN 1.4462 or 2205.

• Super Duplex Steel

With a PREN range of 38-45, super duplex steel was created for use in the oil & gas industry and the chemical industry. This grade of steel is stronger and far more corrosive resistant but is more difficult and more costly to process than standard duplex steel. This is typically grade EN 1.4410.

• Duplex 2507 Stainless Steel

Duplex 2507 stainless steel is another form of super duplex steel. This material is made with 25% chromium, 4% molybdenum, and 7% nickel. This type of stainless steel is known for its resistance to chloride stress corrosion cracking, high thermal conductivity, and a low coefficient of thermal expansion.

• Zeron 100 Stainless Steel

Zeron stainless steel is a super duplex stainless steel that was developed by Rolled Alloys. It contains 25% chromium, 7% nickel, 3.6% molybdenum, along with copper and tungsten additions.

• Lean Duplex Grades

Lean duplex steel has a PREN range of 22-27 and was created for use in less demanding applications such as general building and construction. While the corrosion resistance is going to be similar to standard austenitic steel, it has better strength and mechanical properties.

Applications of Duplex Stainless Steel

Duplex stainless steels are very commonly used in more demanding applications due to their corrosion resistance properties, high mechanical properties, and how strong the material is. This makes the material very popular in a wide variety of industries.

You can find duplex stainless steel used in the oil and gas industry, chemical engineering industry, water and energy industries, architecture industry, and in the construction of things like bridges, seawalls, tunnels, and piers.

18/10 Stainless Steel and Other Types of Stainless Steel

When discussing stainless steel alloys, you’ll typically hear numbers such as 18/10, 18/8, and 18/0 used. These numbers identify the percentage of chromium and nickel that are present in a particular alloy.

For example, 18/8 stainless steel is 18% chromium and 8% nickel; 18/0 stainless steel is 18% chromium and contains roughly .75% nickel, and so on. The chromium-nickel mixture is important to know when deciding on the right alloy for your needs.

For example, if you’re a professional cook, you may have specific requirements for the strength, durability, or heat resistance of various tools and appliances in your kitchen. Understanding the composition of the alloys used in the production of equipment will help choose stronger, longer-lasting products for each application.

The Melting Points for Different Grades of Stainless Steel

One of the more important considerations when choosing the right type of stainless steel for your component or application is the melting point of the specific grade.

One of the reasons stainless steel is chosen over other types of materials, for example, plastic polymers, is its ability to stand up to high-temperatures and still retain its strength and durability.

When comparing the melting points of steel alloys, the number is usually given in a range due to the variations used in the metals used in the production. That number also relates to the metals’ resistance to stress, corrosion, cracking, and other attributes.

As a general rule, metals that have been heat-treated have the following melting points:

• Grade 304: 1400-1450°C (2552-2642°F)
• Grade 316: 1375-1400°C (2507-2552°F)
• Grade 430: 1425-1510°C (2597-2750°F)
• Grade 434: 1426-1510°C (2600-2750°F)
• Grade 410: 1480-1530°C (2696-2786°F)
• Grade 420: 1450-1510°C (2642-2750°F)

It is also important to remember that the maximum use temperatures recommended are usually lower than the maximum number listed in the above chart.

 

Stainless Steel Description

 

201	Chromium nickel manganese steel was developed as a satisfactory alternate for Type 301 for many applications.
301	Chromium nickel steel capable of attaining high tensile strength and ductility by moderate or severe cold working.
302	General purpose chromium nicke stainless steel. Its corrosion resistance is superior to that of Type 301. It can be cold worked to high tensile strengths but with slightly lower ductility than Type 301.
304	Low carbon chromium nickel stainless and heat resisting steel somewhat superior to Type 302 in corrosion resistance.
304L	Very low carbon chromium nickel steel with general corrosion resistance similar to Type 304 but with superior resistance to intergranular corrosion following welding or stress relieving. It is recommended for use in parts which are fabricated by welding and which cannot be subsequently annealed.
305	A high corrosion-resistant alloy with low rate of work hardening, designed for extra deep drawing and spinning.
309	High corrosion-resistant, chromium nickel grade with carbon limited to .08 to reduce carbon precipitation during welding.
310	Similar to 309 with higher resistance to corrosion and oxidation at elevated temperatures.
316	Chromium nickel stainless and heat resisting steel with superior corrosion resistance to other chromium nickel steels when exposed to many types of chemical corrodents; superior creep strength at elevated temperatures.
316L	Low carbon chromium nickel stainless steel with general corrosion resistance similar to Type 316 but with superior resistance to intergranular corrosion following welding or relieving. It is recommended for use in parts which are fabricated by welding and cannot be subsequently annealed.
316TI	Ti stabalized version of 316 with resistance to sensitization. (The formation of grain boundary chromium carbides at evaluated temperatures.)
317L	Similar to 316L but with additional molybdenum to improve corrosion resistance.
321	Chromium nickel steel containing titanium.Recommended for parts fabricated by welding which cannot be subsequently annealed. Also recommended for parts to be used at temperatures between 800°F and 1850°F.
347	Chromium nickel steel containing columbium and tantalum which is recommended for parts fabricated by welding which cannot be subsequently annealed. Also recommended for parts to be used at temperatures between 800°F and 1850°F.
410	General purpose corrosion and heat resisting chromium steel. Good corrosion resistance and fair machining properties. Can be treated to RC35/45.
420	Chromium steel capable of hardening to a maximum of approximately RC53/58.
430	General purpose grade, corrosion-resistant, straight chromium grade, non-heat-treatable.
430LI	Similar to straight 430 in corrosion and mechanical properties. The low interstitials provide improved transverse bending over straight 430.
434	Modification of Grade 430 designed for automotive trim and resistance to atmospheric corrosion.
440A	High carbon grade, high chromium, capable of being heat treated to a hardness range of RC51/62.
444	A low carbon, low nitrogen, ferritic that provides pitting and crevice corrosion resistance superior to most ferritic grades.
A2864	An iron, nickel chromium alloy designed for service up to 1300°F where high strength and corrosion resistance are required.
AM 3508	Similar to 17-7PH. alloy and PH15-7Mo. alloy, but with slightly higher elevated temperature capability.
CARPENTER ® 20 CB3, 10	A highly corrosion-resistant alloy used in the chemical industry for applications where corrosion resistance is extremely critical,superior to the general run of 300 type stainless.
PH15-7Mo®4	Similar to 17-7PH. alloy, but with molybdenum added for higher strength with heat treatment.

Source: https://www.tfgusa.com/types-of-stainless-steel/

Difference between duplex steel S31803 S32205 and 316L

Choose S31803/S32205 and 316L (Urea Grade) be the trial grade, compare each property of duplex stainless steel and austenitic stainless steel. So as to, based on acquaintance of 316L steel, understanding of mechanical properties and corrosion properties of duplex steel.

Since chromium can naturally form a thin protective film of passivation on the surface of stainless steel, stainless steel has corrosion resistance. Molybdenum makes this passivation film stronger and allows it to be rapidly regenerated when the passivation film is destroyed by chloride. An increase in the molybdenum content increases the pitting corrosion resistance and crevice corrosion resistance of the stainless steel.

316L (2% to 3% Mo) is the most widely used molybdenum-containing stainless steel. It is designated as a tank, pipe and heat exchanger material for food processing and pharmaceutical production. Increased molybdenum content enhances resistance to chloride in the air, so Type 316 can be used as a material of choice for offshore and coastal buildings. 316L is used to cover the Canary Wharf building in London and the tallest building in the world - the outer layer of the Petronas Tower in Kuala Lumpur, Malaysia.

S32205 Duplex stainless steel (3.0% to 4.0% Mo) has high strength and excellent resistance to chloride stress corrosion cracking. Multipurpose stainless steel, originally used as a fluid flow tube in the oil and gas industry, is now more used in the chemical processing and petrochemical industries and as a digester in the pulp and paper industry.

ASTM A789 ASTM A790 S32205 Stainless Steel Pipe Composition %:

C	Si	Mn	P	S	Cr	Mo	Ni	N	Cu
max. 0,03	max. 1,00	max. 2,00	max. 0,030	max. 0,020	22,00 - 23,00	3,0 - 3,5	4,5 - 6,50	0,14-0,20	-

 

C	Si	Mn	P	S	Cr	Mo	Ni	N	Cu
max. 0,035	max. 1,00	max. 2,00	max. 0,045	max. 0,040	16,00 - 18,00	2,0 - 3,0	10.0 - 14.0	-	-

2．Mechanical Properties (Tubing and Piping) Table - 2

Grade	Heat Treatment	Tensile Strength (Mpa)	Yield Strength (Mpa)	δ%
S31803(SAF2205)	Solution Annealing 1060 ℃water quenching	655	485	25
TP 316L(UG) （S31603）	Solution Annealing 1050 ℃ water quenching	485	170	35

According to the result, the tensile strength of S32205 is higher than 316L, yield strength near to twice.

3．Macrostructure (Low Power Structure) Table - 3

Grade	Central looseness (Grade)	General looseness (Grade)	Square Looseness (Grade)
S31803(SAF2205)	0.5	0.5	0
TP 316L(UG)	0.5	0.5	0

4．Clearness
According to ASTM E45, Test result as below: Table - 4

Grade	A		B		C		D
	thin	heavy	thin	heavy	thin	heavy	thin	heavy
S31803(SAF2205)	0	0	0.5	0	0	0	1.0	0
	0	0	1.0	0	0	0	1.0	0
TP 316L (UG) (S31603)	0	0	0.5	0.5	0	0	0.5	0
	0	0	0.5	0	0	0	1.0	0

According to Table 3 and Table 4, we found that the macrostructure and clearness of S32205/S31803 and TP 316L is similar.

5．Metallographic Structure Test Result Table - 5

Heat No.	Number		Ferrite (%)
VOD TB02-761	Forging Bar	1	45
		2	46
	Hot Rolled Perforation Pipes	3	47
		4	46

Table 9 dates show the metallographic structure of this heat number steel reasonable. Prove that the steelmaking technology control the chemical analysis very strictly.

6．Intergranular Corrosion Resistance Property

In order to test the intergranular corrosion resistance property of 316L(UG), according to Stamicarbon standard of 316L (UG), do the compare test of S31803/S32205 and 316L(UG). All the trial is solution annealing, Test 5 cycles in the 65 ±0.2% HNO3 boiling solution，every cycle is 48 hours, result show as below:

Table 6

Grade	Cycle, μm/48h					Average μm/48h
	1	2	3	4	5
S31803(SAF2205）	0.8767	0.8110	1.42732	1.35864	1.119585	1.11865
TP 316L (UG) (S31603)	1.88508	0.90842	0.831655	1.71449	1.70169	1.408267

Huey Test is a general way for test corrosion resistance stainless steel for Urea. The weight loss per unit area is measured after each of five 48-hour boils in 65 percent nitric acid. The test results are calculated to and reported as the average corrosive rate of the five boils in inches per month (ipm) corrosion rates. The test is used to determine the suitability of a material for nitric acid service. Since most of the weight loss is due to intergranular attach, the Huey test is commonly used as an indication of the resistance of a stainless steel to intergranular corrosion.

Huey test is very strictly, if the chemical analysis control not very well, steelmaking quality is bad, it is very hard to pass the test. 316L(UG) request 5 cycles average corrosive rate less than ≤ 3.3 μm/48h。According to the test result，S32205/S31803 not only meet the request，But meet the request of 25-22-2（2RE69）austenitic stainless steel average corrosive rate ≤1.5 μm/48h， better than 316L(UG)，special from cycle 5，S32205/S31803 average corrosive rate far lower than 316L (UG)，show the S32205/S31803 chemical analysis is well and steelmaking quality is good.

 

Source: https://tubingchina.com/Difference-Between-S31803-S32205-316L.htm