UNS S31803 material is a duplex stainless steel, with about 50% ferrite and 50% austenite organizational structure, combining the advantages of austenitic stainless steel and ferritic stainless steel. Due to its excellent mechanical properties and corrosion resistance, it is widely used in oil and gas, marine engineering, chemical equipment and heat exchangers.

The UNS S31803 (ASTM F51) specification has been largely replaced by UNS S32205 (1.4462, ASTM F60). This reflects their desire to maximize the corrosion properties of the alloy. In addition, it allows influencing the level of nitrogen added, rather than just being present as a background element. As a result, the highest performing duplex grades seek to maximize chromium (Cr), molybdenum (Mo) and nitrogen (N) content.

Chemical Composition

CHEMICAL	LIMITS	C	Mn	P	S	Si	Ni	Cr	Mo	N
UNS S31803	MIN						4.50	21.00	2.50	0.08
	MAX	0.03	2.00	0.030	0.020	1.00	6.50	23.00	3.50	0.20

Key Elements

Chromium (Cr): Provides excellent resistance to oxidation and corrosion, especially pitting and crevice corrosion.

Nickel (Ni): stabilizes the austenite phase, improves plasticity and toughness, and enhances corrosion resistance.

Molybdenum (Mo): Significantly improves resistance to pitting, crevice corrosion and chloride stress corrosion cracking.

Nitrogen (N): enhance austenite stability, improve strength, while further improving the resistance to pitting and crevice corrosion. The addition of nitrogen is one of the keys to the excellent performance of duplex stainless steel.

Carbon (C): is strictly controlled at low levels to avoid the formation of carbides at grain boundaries, thereby reducing susceptibility to intergranular corrosion.

Mechanical Properties

MATERIAL	UNS S31803
T.S (MPA)	620 min
Y.S (MPA)	450 min
EL %	25 min
R/A %	45 min

UNS S31803 has excellent mechanical properties. Its tensile strength at room temperature is typically above 620 MPa, with a yield strength of not less than 450 MPa and an elongation of more than 25%. The high strength enables it to withstand large loads in many structural applications, while the good elongation ensures that the material has a certain degree of plasticity, making it easy to process and mold.

S31803 Equivalent Grades

GB/T	UNS	ID	Trademark	JIS	W.Nr
022Cr22Ni5Mo3N	S31803	F51	AL2205	SUS32953L	1.4462

Corrosion resistance:

Stress Corrosion Cracking (SCC) with Chloride Ions: This is a great advantage of UNS S31803 over austenitic stainless steels. Austenitic stainless steels are highly susceptible to SCC in the presence of chloride ions and at certain temperatures, whereas S31803 is highly resistant to it.

Resistance to pitting and crevice corrosion: In chloride-containing environments, such as seawater, salt water, etc., its resistance to pitting and crevice corrosion is significantly better than ordinary austenitic stainless steel. This is due to its high chromium, molybdenum and nitrogen content, these elements can form a dense passivation film on the material surface, effectively preventing the intrusion of corrosive media.

Welding

UNS S31803 has good welding properties and can be welded by a variety of welding methods, including electric arc welding and tig welding.UNS S31803 (1.4462, F51) has good weldability similar to other stainless steel types. Low thermal expansion reduces residual stresses after welding. To weld UNS S31083, use a duplex electrode similar to the parent steel. The arc welding process is suitable, but oxyacetylene welding is not recommended because of the potential for carbon buildup in the weld area of UNS S31803. Although post-weld annealing is not required for many applications, it will provide optimum corrosion resistance under severe service conditions.

Duplex Stainless Steel S31803 Application

1. Chemical industry: pipelines, pressure vessels and storage tanks, etc.

2. Marine engineering: seawater treatment equipment, ships and offshore platforms, etc.

3.oil and gas industry: oil drilling platforms, natural gas pipelines and oil storage equipment.

4.food processing: food processing equipment and storage tanks.

5. bridges and buildings: building structures, bridges and highway guardrails, etc.

Comparison between UNS S31803 and other stainless steels

1. Performance differences with austenitic stainless steel

Compared with austenitic stainless steel, UNS S31803 has higher strength and better resistance to chloride stress corrosion, but its toughness and welding performance are slightly inferior. Austenitic stainless steel is suitable for occasions with high requirements for toughness and welding performance, while UNS S31803 is suitable for occasions with high requirements for strength and corrosion resistance, such as oil and gas pipelines, marine engineering, etc.

2. Comparison with duplex stainless steel UNS S32205

UNS S31803 and UNS S32205 are both duplex stainless steels. The two have certain similarities in performance, but there are also some differences. UNS S32205 has relatively high chromium, nickel and molybdenum content, so its corrosion resistance is better, especially in high chloride ion environments. However, the cost of UNS S31803 is relatively low, and it has a higher cost-effectiveness in some occasions where corrosion resistance is not particularly high.

You can get an offer for products in below material forms:

-Pipe and Tube (EN 10216-5, ASTM A213, ASTM A249, A312, A790,)

-Forged Fitting and Flange (ASTM A182 , ASTM A105,ASTM B564 )

-Butt Weld Fittings (ASTM A234, ASTM A403,ASTM A815)

-Round bar , Billet (ASTM A276, ASTM A479)

– Plate, Sheet, Strip(ASTM A240, EN 10028-7, A480)

-Bolting, Nuts（ASTM A193, A194, A320）

Conclusion

UNS S31803 is a highly balanced duplex stainless steel that is an important material choice in industry for its high strength, excellent resistance to chloride stress corrosion cracking, excellent pitting and crevice corrosion resistance, and good weldability to meet the needs of a wide range of complex applications. In many applications that require a combination of high strength and harsh corrosive environments, it is an economical and reliable choice, and is often seen as an upgraded alternative to traditional austenitic stainless steels such as 316L.

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