What is Stainlesss Steel? an in depth technical guide



Stainless Steel

An in depth guide

Stainless steel is known for its strength, versatility and smooth surface, it can be used widely across a range of engineering and manufacturing applications due to its corrosion and heat resistant qualities.

Stainless steel was developed by Harry Brearley in Sheffield, England, in 1913. He was trying to develop a new steel alloy for gun barrels when he discovered his new alloy did not rust and was very difficult to etch into. Brearley's first stainless steels contained around 13% chromium. These properties were quickly commercially exploited in the manufacture of cutlery, for which Sheffield become globally renowned.

Worldwide demand for stainless steel is rising by around 5% per year, with current demand reaching around 20 million tonnes per year. Although Stainless grades are more expensive to buy, the strength, corrosion resistance, low maintenance and aesthetic appeal make the long term investment worthwhile.

There are many different types of stainless steel, but they are usually classified into four main types that are identified by their crystalline structure; austenitic, martensitic, duplex, and ferritic. metals4U stock 4 grades of stainless steel; grades 303, 304 and 316 being austenitic and ferritic 430 grade. As the four main types of stainless steel have different properties it is important to ensure you choose the correct type, with the most appropriate properties for your project. Below is a quick overview of the different stainless-steel types.


Austenitic stainless steels from the 300 series contain nickel as their austenite stabilising element. Due to the face-centred cubic crystal structure, austenitic steels maintain their microstructure at all temperatures from the cryogenic temperature region through to the melting point, therefore, they are not able to be hardened by heat treatment. Austenitic stainless steel can be work hardened and are non-magnetic. The 300 series is the largest subgroup of stainless steels; the most common austenitic grade, 304, also known as 18/8 or A2 type steel is in this series which is extensively used in such items as, cookware, cutlery, and kitchen equipment. Grade 316 is the next most common austenitic stainless steel which contains molybdenum to increase resistance to acids, pitting, and crevice corrosion.


Ferritic stainless steel has a ferrite body-centred cubic crystal structure like carbon steel. This microstructure is present at all temperatures due to the addition of chromium, this makes them unable to be hardened by heat treatment and less successfully strengthened by work hardening as austenitic stainless steels. Ferritic stainless-steel grades are tricky to weld as the grain growth in the heat affected zone may result in cracking and reduces ductility. The addition of chromium and molybdenum dramatically increases corrosion resistance and this type of steel is magnetic.


Martensitic stainless steel is produced using a three-phase heat treatment process that changes the microstructure of austenitic steel into martensitic structure. First the steel is heated to between 980°C and 1050°C, depending on the grade, to enter the face centred cubic crystal stage typical of austenitic grades. Secondly, the steel is subjected to a rapid air, water, or oil quench- this changes the austenitic microstructure into a hard, body-centred tetragonal crystal structure known as martensitic. Finally, the steel is tempered by heating through to approximately 500°C, held at a steady temperature and then air cooled. Martensitic stainless steels are magnetic and are not as corrosion resistant as ferritic or austenitic steels, however, their high carbon content makes them able to be hardened through thermal hardening treatments to significantly improve their mechanical properties.


Duplex steels are composed of a microstructure that is part austenitic and part ferrite; this is usually a 50/50 mix; however, some commercial alloys may be split 60/40. Duplex steels have higher molybdenum and chromium and lower nickel than pure austenitic grades, this makes them about twice as strong with a much higher corrosion resistance to chloride stress corrosion cracking.


Stainless steels are suitable for a wide range of applications that require strength and good corrosion resistance, the most common applications are;

Nuts and bolts, gears, bushings, electrical switchgear components, screws, aircraft fixings, beer kegs, flexible metal hose, surgical equipment, shipping drums, still tubes, cooking equipment, sanitary fittings, pharmaceutical & chemical processing equipment, architectural applications, springs, washing machine drums, dishwasher interiors, scientific equipment, refrigerator exteriors, automotive trim, and lashing wires.

Cleaning Stainless Steel

There are many ways to clean stainless steel, however, as with all metals it is important to begin with the least abrasive and work through the techniques in response to the level of staining or damage that needs treating. With stainless steel it is important to avoid the use of harsh abrasives as it can be easily damaged or dulled by using scouring pads and cloths, or cleaning creams and powders. Vinegar, household dishwashing liquid and baking soda can be mixed with warm water and applied using a microfibre cloth in the direction of the metal grain, then dried and finished with a mineral oil to bring back the lustre. Proprietary stainless-steel cleaners are available commercially, it is always advisable to patch test in an inconspicuous area to check for potential damaging effects before placing over a large area.

Corrosion resistance

Stainless steel has good corrosion resistant properties which makes it suitable for recycling as when it needs to be repurposed it will have suffered little degradation. Stainless steel grades can be recycled without losing the integrity of their chemical composition, including the alloying elements of chromium, nickel, and molybdenum.

The use of stainless steels at high temperatures

Stainless steels are used for applications where resistance to aqueous corrosion and high temperatures are necessary but where carbon and other alloyed steels do not provide the same high level of strength and corrosion resistance.

All metals will encounter a change in their metallurgical structure when exposed to elevated temperatures over time; the changes that affect stainless steels are embrittlement, carbide precipitation and softening. Considering that Stainless steel grades are chosen for use in applications such as heat exchangers, aircraft and aerospace applications, superheaters, boilers, feed water heaters, valves, and main steam lines, it is imperative to ensure the correct grade is used to withstand the conditions it will be subjected to.

When using metals at room temperature, the yield and tensile strength, or hardness rating will offer a strong indication of a metal's suitability. Once working at high temperatures, the creep strength becomes an important element. The creep strength of a metal is its ability to resist distortion over prolonged exposure to high temperatures.

Maximum Service Temperatures

Material Intermittent Service Temperature Continuous Service temperature.
Austenitic 304 870°C 925°C
Austenitic 316 870°C 925°C
Ferritic 430 870°C 815°C

When the 300 series stainless steels reach intermittent service temperature, the metal is subjected to 'thermal cycling' caused by the difference in coefficient expansion between the steel and the scale formed under high temperatures, this can cause cracking and spalling; with a continuous high temperature there is less surface deterioration as this thermal cycle does not take place repeatedly. This enables the continuous service temperature to be higher than the intermittent temperature.

With the 400 series of both martensitic and ferritic grades, the intermittent service temperature is higher than the continuous temperature- the reason for this is unknown, but important to remember when selecting a stainless-steel grade suitable for prolonged and continuous high-temperature applications.

303 grade stainless steel does not accommodate the same tolerance for high temperature applications. This is due to the addition of sulphur to increases its machinability rating, however, the sulphur reduces its strength and corrosion resistance compared to other grades of stainless-steel.

Surface finishes

Stainless steel can be polished to a range of finishes; the higher the gloss and smoothness of the polish finish, the more resistant to corrosion the metal will be as the surface will be less pitted. Our range of stainless steel grades can be supplied in a choice of mill, bright, dull, and mirror polish finishes in a wide range of profiles.

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303 grade belongs to the austenitic family of stainless steels. 303 is the most easily machinable grade due to the sulphur content; this does reduce the corrosion resistance and toughness compared to other stainless grades, however, the austenitic qualities still maintain excellent toughness overall.

303 is used in the manufacture of parts that require heavy machining, such as; nuts and bolts, gears, bushings, electrical switchgear components, screws, and aircraft fixings.

Chemical Composition of 303 (weight %)

C Mn Si P S Cr Ni Fe
0.10 max 2.00 max 1.00 max 0.40 max 0.15 max 17.00-19.00 8.00-10.00 Balance

Physical Properties of 303 Grade

Property Value Unit
Density 8030 Kg/m3
Melting point 1455 ° C
Modus of elasticity 193 GPa
Electrical resistance 0.072 µΩm
Thermal conductivity 16.3 W/m°k
Thermal expansion 17.3 µm/m-k
Yield strength 240 N/mm²
0.2% Proof stress 190 min N/mm²
Shear modulus 77.2 GPa
Hardness 167 Vickers - HV
Elongation 35 %
Tensile strength 500-700 N/mm²


303 grade stainless steel has the best machinability of all austenitic stainless steels due to the sulphur in its chemical composition. The metal will work harden so it is recommended to machine at reduced feet per minute and with a heavier feed to prevent glazing at the tool interface. Cutting edges must be sharp as dull edges will cause excessive unwanted work hardening.

The use of chip breakers is recommended to ensure the swarf stays clear of the work.

The low thermal conductivity of austenitic steels causes heat concentration at the cut edge; therefore, coolants and lubricants must be used to reduce work hardening.

Example machining speeds for 303 grade

Process HSS Carbide Depth, width, or diameter of tool (in)
  Metres per Minute in/rev Metres per minute in/rev  
Turning 35 0.0150 114 0.0250 0.005 to 0.200
Reaming 28 0.0050     1/4
End Milling 40 0.0030 91 0.0040 1/2
Drilling 26 0.0100 213 0.0050 1/2
Cut off 90 0.0015 275 0.0020 1/16
Forming 100 0.0020 375 0.0030 1
Tapping and threading 10       7 threads / in


Type 303 has poor formability; some cold working is possible and can be bent with quite a generous bend radius, but a rigorous, sharp bend should not be attempted.


This grade has good ductility; cold working will increase the strength and hardness of 303 but reduce the ductility.


303 can be cut using most standard cutting equipment and techniques such as band saws, bolt cutters, flame cutting, hack saws, and plasma cutting.

If the piece has been treated in a way that may have caused word hardening, hand cutting methods may become difficult, therefore, the use of abrasive disk cutters will often be the best hand tool solution, but this can be slow and messy.


This grade has poor weldability properties; however, it can be welded with some difficulty using alloy 310, 308L, AWS E312 and 309 filler rods or electrodes with minimum heat input; welds must then be annealed to re-dissolve precipitated carbides.


303 requires an annealing temperature of 1010°C to 1120° C and then a rapid cool or water quench.


Stainless steel grade 303 can not be hardened by heat treatments but is easily work hardened.


This grade of steel is not heat treatable.

Corrosion resistance

303 has good corrosion resistance to mildly corrosive environments, but the sulphur content means it is less resistant than 304 grade stainless steel. In most dry environments, it performs as well as other unmodified alloys but should not be used in moist marine environments as rust and pitting corrosion will form. In chloride environments above 60° C it is at a high risk of corrosion cracking.


Hot forging of 303 prevents the work hardening that would occur if cold forged. Working temperatures range between 1149° and 1260° C. The work should be rapidly cooled after hot forging to maintain corrosion resistance. Pieces should be annealed post working to maintain corrosion resistance.


The high sulphur content in 303 grade makes brazing difficult; outgassing and wettability issues make this process 'not recommended'.

Process Rating
Workability - Cold poor to average
Workability- Hot poor to average
Machinability- excellent
Weldability – Gas poor
Weldability – Arc poor
Weldability – Resistance poor
Brazability not recommended
Solderability poor

Grade 303 stainless steel is available in round bar and hexagon profiles, it is supplied in a mill finish.

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This grade is also often referred to as 18-8 stainless due to the 18 % chromium and 8% nickel composition and conforms to EN 1.4301.

304 is the most widely used of the austenitic stainless steels and of all stainless steels generally. 304 grade stainless steel has excellent welding qualities and does not need to be annealed post weld due to the lower carbon content that results in less carbide precipitation in the heat affected zone during welding; this makes it less susceptible to intergranular corrosion. 304 grade has very good drawability and can be severely deep drawn without the need for immediate annealing- making it the dominant grade used for drawn stainless parts, such as sinks, hollow ware and pans.

This grade is commonly used to make beer kegs, flexible metal hose, surgical equipment, shipping drums, still tubes, cooking equipment, sanitary fittings, pharmaceutical & chemical processing equipment, architectural applications, springs, nuts and bolts.

Chemical properties of 304 grade (weight %)

C Cr Mn Si P S Ni Fe
0.07 max 17.50-19.50 2.00 max 1.00 max 0.05 max 0.02 max 8.00-10.50 balance

Physical Properties of 304 Grade

Property Value Unit
Density 8000 Kg/m3
Melting point 1455 ° C
Modus of elasticity 193 GPa
Electrical resistance 0.072 µΩm
Thermal conductivity 16.2 W/m°k
Thermal expansion 17.2 µm/m-k
Yield strength 74-81 N/mm²
0.2% Proof stress 210 min N/mm²
Shear modulus 86 GPa
Hardness 129 Vickers - HV
Elongation 45 min %
Tensile strength 500-700 N/mm²


304 has reasonable to good machinability and will work harden during deformation. The best machining technique is to use slower speeds, heavier feeds, sharp tooling, and generous lubrication. 304 benefits from self-breaking chips which creates an easier machining experience than with some other grades.

Example machining speeds for 304 grade

Process HSS M/minute Carbide M/Minute Metres per minute
Turning (depth 3mm) 20-25 90-100  
Milling (profiling)     12-22
Drilling (6 ø mm) 12-16    
Cutting (depth of cut 6mm) 20-25    


Grade 304 has excellent formability.

Cold forming: Forming processes increase the strength and hardness of 304 through becoming quickly 'work hardened' and may leave it slightly magnetic.

Hot forming: Working temperatures of between 750°C and 1150° C are the recommended optimal temperature for hot working this grade. To maintain maximum corrosion resistance the piece should be annealed, then either water quenched or rapidly cooled by other processes.

304 is excellent for drawing and spinning applications as the low yield strength and high elongation properties make the forming of complex shapes possible, however, 304 will work harden quickly.


304 has 'very good' to 'excellent' ductility making it suitable for forming, drawing, and spinning manufacturing processes.


304 grade can be cut using all main cutting techniques, however, cutting the piece after it has been worked will become increasingly difficult due to the effects of work hardening. Flame and plasma cutting may be the preferred choice as mechanical cutting will work harden the cut edge.


Excellent results are achieved with this grade of stainless steel by using all standard methods of fusion and is possible with and without filler metals. No annealing is necessary post weld on thin weld sections, however, on thicker weld pieces annealing may be necessary.


To anneal this grade, heat evenly to between 1010°C and 1120°C, then quickly water quench or use another preferred rapid cool technique. The rapid cool provides the best post-working corrosion resistance.


This grade does not respond to thermal treatments and will not through harden. The austenitic structure remains uniform throughout all temperatures between cryogenic and liquidus meaning hardness is achieved through work hardening.


304 is not suitable for heat treatments.

Corrosion resistance

304 has very good corrosion resistance to most oxidizing acids and chloride/ salt spray environments. This grade can be prone to pitting and crevice corrosion, and also stress corrosion cracking in warm chloride environments above 60°C.


304 grade is the austenitic stainless steel most commonly used for forging. 304 can be forged under forging dies although this can be a little more difficult with stainless over other steels due to the lower fluidity, but it is an effective method when good strength is required in an application. 304 steel forgings are machinable. The recommended hot forging temperature for initial forging and pressing is 1150°C to 1260°C, with a finishing temperature of between 900°C and 925°C with an air cool. A post forging anneal process will also be necessary which is recommended to be at above 1070°C to ensure the best corrosion resistance.


Excellent results are obtainable with brazing.

Process Rating
Workability - Cold Very good
Workability- Hot Very good
Machinability- Reasonable to good
Weldability – Gas Excellent
Weldability – Arc Excellent
Weldability – Resistance Excellent
Brazability Excellent
Solderability Excellent

304 grade is available in angle, round bar, square bar, flat, box, channel, round tube, threaded bar, and rebar in mill finish.

Pipe and elbow are also available and supplied as nominal bore; the actual dimensions are not stated but the approximate internal dimension for standard wall schedule which relates to wall thickness, these profiles can be supplied in mill, dull/satin or bright polish finish.

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316 grade is an austenitic steel that contains molybdenum to improve corrosion resistance, especially within chloride environments and industrial chemical environments. 316 cannot be hardened by thermal treatments and has very similar mechanical properties to 304 grade stainless steel, however, 316 is stronger when used at elevated temperatures which makes it particularly suitable for the manufacture of parts for furnaces, food preparation equipment, pressure vessels, valves, and pumps.

Chemical properties of 316 grade (weight %)

C Cr Mo Si P S Ni Mn Fe
0.08 max 16.5-18.5 2.00-2.50 1.00 max 0.05 max 0.02 max 10.0-13.0 2.00 max Balance

Physical Properties of 316 Grade

Property Value Unit
Density 8000 Kg/m3
Melting point 1400 ° C
Modus of elasticity 193 GPa
Electrical resistance 0.074 µΩm
Thermal conductivity 16.3 W/m°k
Thermal expansion 15.9 µm/m-k
Yield strength 415 N/mm²
0.2% Proof stress 220 min N/mm²
Shear modulus 74-82 GPa
Hardness 199 Vickers - HV
Elongation 40 min %
Tensile strength 520 -680 W/m°k


This grade has good machinability with a high work hardening rate. It is important to keep work surfaces and tools clean and use tools specifically for stainless steel to avoid cross contamination from easily corroded metals which will discolour the surface of the worked piece.

Chip breakers should be used to keep the swarf free from the cutting edge. The working piece should be machined using rigidly supported sharp tools with the heaviest possible cut to prevent glazing and reduce work hardening through unnecessarily prolonged machining.

Example machining speeds for 316 grade

Process HSS M/minute Carbide M/Minute Metres per minute
Turning (depth 3mm) 18-23 85-95  
Milling     10-20
Drilling (6 ø mm) 12-16    
Cutting (depth of cut 6mm) 18-23    


316 has good formability.

Cold working. 316 can be easily brake or roll formed and is also well suited for drawing, heading, and stamping processes; it is necessary to perform an anneal procedure after cold working to relieve internal stresses. Cold forming will work harden the metal which will increase the strength and hardness of this grade.

Hot working. All common forming processes can be performed on this grade, although hot working below 927°C should be avoided. The optimum temperature for hot work is between 1149°C and 1260°C, as with cold working, a post work annealing is recommended to stress relieve.


Stainless steel grade 316 has very good ductility.


Can be cut using all standard cutting techniques with the use of coolants and liberal lubrication to reduce work hardening on the cut edge. Hand cutting techniques will be more difficult after the piece has been worked because of work hardening.


316 has very good welding properties with most common resistance and fusion techniques, however, oxyacetylene welding is not successful due to the high risk of carbon pickup occurring in the weld zone. Post weld annealing is not usually required on thin weld sections but is recommended on heavy weld sections.


Heat evenly to between 1010°C and 1120° C and then water quench to perform a rapid cool process.


This grade does not respond to thermal treatments and will not be hardened in this way but can work hardened.


Tempering is not a suitable process for 316 grade austenitic stainless steel.

Corrosion resistance

Good corrosion resistance to most chemicals, particularly those used in paper production and reprographics, photographic and textiles industries. 316 has good oxidation resistance at between 870°C and 925°C, however, during fabrication it should not be in continuous use within the 425°C and 860°C range if future aqueous corrosion resistance is important.

316 is often regarded as 'marine grade' stainless steel, but is not recommended within warm sea water environments (above 60°C) as it can be prone to stress crack corrosion and pitting at above 60° C.


316 should not be forged below 930°C and the optimum forging temperature is between 1150°C and 1260°C. The piece should be air cooled after hot forging and then annealed to relieve stress. 316 can be cold forged with very good results, as with hot forging, an annealing cycle is recommended to relieve internal stresses. This grade will also work harden through forging work.


This grade of steel has very good brazing qualities.

Process Rating
Workability - Cold Very good
Workability- Hot Very good
Machinability Very good
Weldability – Gas Not suitable for oxy welding
Weldability – Arc very good
Weldability – Resistance very good
Brazability Very good
Solderability Very good

316 grade is available in angle, round bar, square bar, flat, round tube, threaded bar, and hexagon profiles in mill finish.

Pipe and elbow profiles can be supplied in mill, dull/satin or bright polish finish. These are supplied stating the nominal bore dimensions, not the actual dimensions. This better reflects the approximate internal dimension for the standard wall schedule which relates to wall thickness.

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430 is a non-thermal hardening grade that contains straight chromium to increase its corrosion resistance. This grade belongs to the ferritic family of steels and is therefore ferro-magnetic. 430 has good mechanical properties, is suitable for rigorous cold heading and has good formability. It is resistant to nitric acid, organic acidic conditions and chloride environments which makes it suitable for use in the manufacture of washing machine drums, dishwasher interiors, scientific equipment, refrigerator exteriors, automotive trim, and lashing wires.

Chemical properties of 430 grade (weight %)

C Cr Mn Si p S Fe
0.08 max 16.00-18.00 1.00 max 1.00 max 0.04 max 0.02 max Balance

Physical Properties of 430 Grade

Property Value Unit
Density 7750 Kg/m3
Melting point 1425-1510 ° C
Modus of elasticity 200 GPa
Electrical resistance 0.060 µΩm
Thermal conductivity 23.9 W/m°k
Thermal expansion 10.4 µm/m-k
Yield strength 483 N/mm²
0.2% Proof stress 240 min N/mm²
Shear modulus 75-81 GPa
Hardness 194 Vickers - HV
Elongation 20 %
Tensile strength 450-600 N/mm²


Machinability is classified as good for this grade. It has a low work hardening rate which enables easy bending and forming without the need to frequently anneal the working piece, however, sub-critical intermediate annealing may be required for extreme cold working.

As with many metals that have low work hardening rates, this grade has the possibility of galling, which is a form of severe adhesion between sliding surfaces, especially if there is a large compression force on the components. Galling is caused by friction and can lead to the adhesion of metal from one layer being stuck to the other; this is often also referred to as a friction weld or a cold weld. Liberal use of lubrication while working should help reduce severe galling that can result in the seizing of components.

The use of sharp cutting edges specifically designed for use on steel is recommended to reduce work hardening and galling; cutting should be light but deep enough to reduce work hardening from both the tool riding the surface excessively and possible glazing effects.

Chip breakers should also be used to ensure swarf clears the work.

Example machining speeds for 430 grade

Process HSS M/minute Carbide M/Minute Metres per minute
Turning (depth 3mm) 28    
Reaming 14    
Milling (profiling)     23
Drilling (6 ø mm) 20    
Cutting (depth of cut 6mm)      


This grade has good formability and benefits from lower work hardening rates than many of the other stainless-steel grades.


430 grade has good ductility.


All mechanical, flame and plasma cutting techniques are suitable for this grade. The lower work hardening properties reduce the rate at which mechanically cut edges becoming hardened.


430 grade has limited weldability and welded joints should not be used for applications that are subject to dynamic or impact loading. If performing a welded joint is unavoidable, it is necessary to perform a pre-heat of the pieces to be joined at 150°C to 200°C to reduce the risk of embrittlement; the welded piece must then be post-weld annealed at 790°C- 815°C.


Solution annealing can be completed by heating to 815°C -845°C, then slow cooled in a furnace to 600°C followed by quick air cooling; slow cooling between 540°C and 400°C is likely to cause embrittlement.

Sub-critical annealing can be performed following extreme cold working by heating to 760°C-815°C, followed by water quench or air cooling.


Cannot be hardened through thermal hardening techniques. 430 can be hardened by cold working, typical techniques include bending, forming, and deep drawing.


This is a non-heat treatable grade so tempering is not an appropriate process.

Corrosion resistance

430 has excellent corrosion cracking resistance to many substances, including organic and nitric acid and has good corrosion resistance which can be further enhanced by being well polished or buffed. This grade has similar pitting qualities to 304 stainless steel, but the overall corrosion resistance compared to many other metals is very good to excellent.


To hot work 430 grade, heat through to a uniform temperature of between 816°C and 1038°C. After working, the piece should be air cooled and annealed.

A grain may grow on the surface of metal that is held at forging temperature for prolonged periods of time, this should be avoided as an 'orange peel' texture will form on the surface. This grade is often used for more aesthetic projects so the surface finish is important, excessive grain growth can also reduce the ductility of the metal.


Good results can be achieved by brazing, although the brazed joins may be affected by interfacial corrosion. Low nickel ferritic and martensitic stainless steel are more prone to this type of corrosion than austenitic and duplex; the use of a brazing filler containing a small amount of nickel, such as silver braze 63, will maximise corrosion resistance at the brazed joint.

Process Rating
Workability - Cold Good
Workability- Hot Good
Machinability- Good
Weldability – Gas Poor
Weldability – Arc Poor
Weldability – Resistance Poor
Brazability Good
Solderability Average

430 is available unbreakable mirror which has the same reflection standard as glass mirrors and as magnetic board available in dull polish.

Suggested welding consumables for stainless steel grades

Grade To self Mild steel Copper or Brass Bronze Aluminium
430 If unavoidable to weld- 430, 308L, 309,308.Silverbraze 63 Not suitable Not suitable Not suitable Not suitable
303 With difficulty. 310, 308L, AWS E312, 309 Not recommended Not recommended Not recommended Not recomended
304 Sifmig 308, sifmig 309, sif bronze 2, sifsilver 968 Sifphosphor bronze 8, sifrod stainless 312, sif