Stainless Steel 304/304H

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Stainless Steel 304/304H

304/304H (UNS S30400/S30409) is a modification of the commonly used stainless steel known as "18-8" chromium-nickel austenitic stainless steel. It offers increased strength at temperatures above 800°F (427°C) by controlling the carbon content within the range of 0.04-0.10%. This alloy is known for its versatility, affordability, and corrosion resistance, making it suitable for a wide range of general-purpose applications. It is common for 304H to be dual certified as both 304 and 304H. The high carbon content in 304H allows it to meet the mechanical properties and grain size requirements of 304H, ensuring that it possesses the desired characteristics. Alloy 304/304H exhibits general corrosion resistance similar to that of 304/304L stainless steel. It can withstand atmospheric corrosion and moderately oxidizing and reducing environments. However, due to its high carbon content, carbide precipitation may occur in the heat-affected zone of welds.In the annealed condition, Alloy 304/304H is non-magnetic. However, it may become slightly magnetic as a result of cold working or welding. It can be easily welded and processed using standard shop fabrication practices.

Applications

Chemical and Petrochemical Processing-pressure vessels, tanks, heat exchangers, piping systems, flanges, fittings, valves and pumps Petroleum Refining

Standards

ASTM.......................... A 240
ASME.......................... SA 240
AMS ........................... 5513
QQ-S .......................... 766

Corrosion Resistance

304/304H stainless steel offers good resistance to atmospheric corrosion, as well as to various organic and inorganic chemicals in moderately oxidizing to moderately reducing environments. Its high chromium content provides resistance to oxidizing solutions, including nitric acid up to 55% weight at temperatures up to 176°F (80°C). The alloy also resists moderately aggressive organic acids such as acetic acid. The presence of nickel in the alloy contributes to its resistance to moderately reducing solutions, such as pure phosphoric acid, regardless of the concentration, in both cold and diluted hot solutions. It can also perform well in caustic solutions without chlorides or fluorides at moderate temperatures. However, Alloy 304/304H does not perform well in highly reducing environments containing chlorides and sulfuric acid. In fresh water service with low chloride levels (less than 100ppm).

304/304H performs well. However, at higher chloride levels, it becomes susceptible to crevice corrosion and pitting. In such severe conditions, an alloy with a higher molybdenum content, such as 316/316L, is recommended. 304/304H is not recommended for use in marine environments. In most cases, the corrosion resistance of Alloys 304, 304L, and 304H will be roughly equal in various corrosive environments. However, in environments that can cause intergranular corrosion of welds and heat-affected zones, Alloy 304L should be used due to its low carbon content, which helps mitigate such corrosion.

Lowest Temperature (°F) at Which the Corrosion Rate Exceeds 5mpy

CORROSION ENVIRONMENT	Type 304/304H	Type 316L	2205 (UNS S32205)	2507
0.2% Hydrochloric Acid	>Boiling	>Boiling	>Boiling	>Boiling
1% Hydrochloric Acid	86p	86	185	>Boiling
10% Sulfuric Acid	—	122	140	167
60% Sulfuric Acid	—	<54	<59	<57
96% Sulfuric Acid	—	113	77	86
85% Phosphoric Acid	176	203	194	203
10% Nitric Acid	>Boiling	>Boiling	>Boiling	>Boiling
65% Niitric Acid	212	212	221	230
80% Acetic Acid	212p	>Boiling	>Boiling	>Boiling
50% Formic Acid	≤50	104	194	194
50% Sodium Hydroxide	185	194	194	230
83% Phosphoric Acid + 2% Hydrofluoric Acid	113	149	122	140
60% Nitric Acid + 2% Hydrocloric Acid	>140	>140	>140	>140
50% Acetic Acid + 50% Acetic Anhydride	>Boiling	248	212	230
1% Hydrochloric Acid + 0.3% Ferric Chloride	68p	77p	113ps	203ps
10% Sulfuric Acid + 2000ppm Cl- + N₂	—	77	95	122
10% Sulfuric Acid + 2000ppm Cl- + SO₂	—	<<59p	<59	104
WPA1, High Cl- Content	<<50	≤50	113	203
WPA2, High F- Content	<<50	≤50	140	167

ps = pitting can occur
ps = pitting/crevice corrosion can occur

WPA	P₂O₅	CL^-	F^-	H₂SO₄	Fe₂O₃	Al₂O₃	SiO₂	CaO	MgO
1	54	0.20	0.50	4.0	0.30	0.20	0.10	0.20	0.70
2	54	0.02	2.0	4.0	0.30	0.20	0.10	0.20	0.70

Chemical Analysis

Weight % (all values are maximum unless a range is otherwise indicated)

Element	304	304H
Chromium	18.0 min.-20.0 max.	18.0 min.-20.0 max.
Nickel	8.0 min.-10.5 max.	8.0 min.-10.5 max.
Carbon	0.08	0.04 min-0.10 max.
Manganese	2.00	2.00
Phosphorus	0.045	0.045
Sulfer	0.030	0.030
Silicon	0.75	0.75
Nitrogen	0.10	0.10
Iron	Balance	Balance

Physical Properties

Density

0.285 lbs/in³
7.90 g/cm³

Specific Heat

0.12 BTU/lb-°F (32 – 212°F)
502 J/kg-°K (0 – 100°C)

Modulus of Elasticity

29.0 x 10⁶
200 GPa

Thermal Conductivity 212°F (100°C)

9.4 BTU/hr/ft²/ft/°F
16.3 W/m-°K

Melting Range

2550 – 2590°F
1398 – 1421°C

Electrical Resistivity

29.1 Microhm-in at 68°C
73 Microhm-cm at 20°C

Mean Coefficient of Thermal Expansion

Temperature Range
°F	°C	in/in °F	cm/cm °C
68-212	20-100	9.2 x 10^-6	16.6 x 10^-6
68-932	20-500	10.0 x 10^-6	18.0 x 10^-6
68-1600	20-870	11.0 x 10^-6	19.8 x 10^-6

Mechanical Properties

		ASTM
	Typical*	Type 304	Type 304H
0.2% Offset Yield Strength, ksi	43	30 min.	30 min.
Ultimate Tensile Strength, ksi	91	75 min.	70 min.
Elongation in 2 inches, %	58	40 min.	40 min.
Reduction in Area, %	68	—	—
Hardness, Rockwell B	83	92 max.	92 max.

Fabrication Data

304/304H can be easily welded and processed by standard shop fabrication practices.

Cold Forming

The alloy is quite ductile and forms easily. Cold working operations will increase the strength and hardness of the alloy and might leave it slightly magnetic.

Hot Forming

Working temperatures of 1652–2102°F (750–1150°C) are recommended for most hot working processes. For maximum corrosion resistance, the material should be annealed at 1900°F (1038°C) minimum and water quenched or rapidly cooled by other means after hot working.

Machining

304/304H is subject to work hardening during deformation and is subject to chip breaking. The best machining results are achieved with slower speeds, heavier feeds, excellent lubrication, sharp tooling and powerful rigid equipment.

Operation	Tool	Lubrication	CONDITIONS
			Depth-mm	Depth-in	Feed-mm/t	Feed-in/t	Speed-m/min	Speed-ft/min
Turning	High Speed Steel	Cutting Oil	6	.23	0.5	.019	13-18	42.6-59
Turning	High Speed Steel	Cutting Oil	3	.11	0.4	.016	20-25	65.6-82
Turning	High Speed Steel	Cutting Oil	1	.04	0.2	.008	26-31	85.3-101.7
Turning	Carbide	Dry or Cutting Oil	6	.23	0.5	.019	75-85	246-278.9
Turning	Carbide	Dry or Cutting Oil	3	.11	0.4	.016	90-100	295.3-328.1
Turning	Carbide	Dry or Cutting Oil	1	.04	0.2	.008	110-120	360.8-393.7
			Depth of cut-mm	Depth of cut-in	Feed-mm/t	Feed-in/t	Speed-m/min	Speed-ft/min
Cutting	High Speed Steel	Cutting Oil	1.5	.06	0.03-0.05	.0012-.0020	18-23	59-75.5
Cutting	High Speed Steel	Cutting Oil	3	.11	0.04-0.06	.0016-.0024	19-24	62.3-78.7
Cutting	High Speed Steel	Cutting Oil	6	.23	0.05-0.07	.0020-.0027	20-25	65.6-82
			Drill ø mm	Drill ø in	Feed-mm/t	Feed-in/t	Speed-m/min	Speed-ft/min
Drilling	High Speed Steel	Cutting Oil	1.5	.06	0.02-0.03	.0007-.0012	10-14	32.8-45.9
Drilling	High Speed Steel	Cutting Oil	3	.11	0.05-0.06	.0020-.0024	12-16	39.3-52.5
Drilling	High Speed Steel	Cutting Oil	6	.23	0.08-0.09	.0031-.0035	12-16	39.3-52.5
Drilling	High Speed Steel	Cutting Oil	12	.48	0.09-0.10	.0035-.0039	12-16	39.3-52.5
					Feed-mm/t	Feed-in/t	Speed-m/min	Speed-ft/min
Milling Profiling	High Speed Steel	Cutting Oil			1.05-0.10	.002-.004	12-22	39.4-72.2

Welding

304/304H can be readily welded by most standard processes. After welding Alloy 304/304H it may be necessary to anneal the plate to restore the corrosion resistance lost by sensitization to intergranular corrosion when chromium carbides precipitate in the grain boundaries in the weld heat-affected zone.