Stainless Steel Castings

Stainless Steel Castings

Stainless alloy castings can be used in a variety of applications where corrosion resistance is required at normal and elevated temperatures, along with reasonable strength, they offer good wear resistance and typical uses range from Flame proof and Explosion proof Enclosures to Valve Control equipment.

For more information please see BS3146 Metals Table 1985 Part 2

BS 3146: (1975) PART 2: ANC 1

Description
13% chromium ferritic-martensitic steel casting. Apart from the very low carbon-content alloys, these steels are capable of being heat-treated by conventional low alloy practice to give a wide spread of mechanical properties ranging from hardness levels of 150 – 500 Brinell. Depending on the particular composition and heat treatment applied, they can be used in a variety of applications where corrosion resistance is required at normal and elevated temperatures, along with reasonable strength, ductility and impact resistance and, at the high carbon levels, good wear resistance. Typical uses range from steam generation equipment to surgical implements.

Additional Information

• Weldability is not considered to be good but where necessary pre-heat and post-weld treatment should be applied. Oxyacetylene gas welding is liable to cause carbon pick-up therefore metal arc or inert gas methods are preferable.
• Machinability – These alloys can be readily softened by conventional annealing practice and machinability is generally good and free-cutting grades are available.

Corrosion resistance – These alloys are virtually rustproof, with good resistance to attack by many organic mediums and environments of an oxidizing nature in relatively mild service.

BS 3146: (1975) PART 2: ANC 2

Description
18% chromium 2% nickel martensitic steel castings. A relatively high tensile stainless steel for general engineering purposes combining improved corrosion resistance over the 13% chromium grades with a strength level of 850N/mm². Typical applications include pump and valve parts in engineering and aircraft service where corrosive conditions do not require an austenitic stainless but where the higher strength is necessary.

Additional Information

• Weldability is poor and welding is not generally recommended
• Machinability is good although tipped tools are necessary to combat the abrasives carbide.

BS 3146: (1975) PART 2: ANC 3

Description
18% chromium 8% nickel austenitic corrosion resistant steel castings for general engineering purposes. The two grades combine moderate strength with excellent resistance to atmospheric and oxidizing media attack along with very good low temperature stability, particularly in the case of Grade A, and reasonable hot strength. Their wide range of applications includes the chemical, pharmaceutical, textile, food- processing and dairy industries.

Additional Information

• Weldability is good although argon arc is preferred to gas methods, in the latter case fluxes are necessary and there is a danger of carbon pick-up.
• Machinability is only fair as the alloys are relatively soft and work hardens rapidly as a result of using blunt tools, low feeds and interrupted cuts. For this reason, high feeds, low speeds and tipped tools are recommended, although for really good machinability a free-cutting grade should be used.

Other Comments
Corrosion resistance – These alloys have excellent resistance to general corrosive attack and specifically to strongly oxidizing media including boiled nitric and sulphuric acid, sulphates and organic acids. The unstabilised grade is liable to suffer severe intergranular attack if used under conditions which cause carbide precipitation or if not solution treated after welding.

Sub-zero Properties – These alloys have very good stability at sub-zero temperatures particularly with the unstabilised grade and can be used at temperatures down to -225°C. For optimum properties the carbon and stabilising additions should be kept at a very low level.

BS 3146: (1975) PART 2: ANC 4

Description
Austenitic chromium-nickel-molybdenum, corrosion resistant steel castings for general engineering purposes. General properties are similar to the 18/8 stainless steel but the addition of molybdenum improves corrosion resistance to reducing media and reduces pitting by chlorides as in sea water. Typical applications include textile, paper and chemical industries and a wide range of marine fittings.

Additional Information

• Weldability is good although inert gas-shielded arc methods are preferred to gas, where fluxes are necessary and there is a danger of carbon pick-up. Within the specified compositional range the alloys can be either fully austenitic and non-magnetic or partially magnetic depending on the amount of delta ferrite present. If acceptable a minimum of 5% delta ferrite is generally recommended for optimum welding characteristics.
• Machinability is only fair as the alloys are relatively soft and work hardens rapidly as a result of using blunt tools, low feeds and interrupted cuts. For this reason high feeds, low speeds and tipped tools are recommended, although for really good machinability a free cutting grade should be used.

Other Comments
Corrosion resistance the addition of molybdenum as compared to the straight 18/8 stainless confers improved corrosion resistance to reducing media, sulphite liquors and chloride which tend to cause pitting as in sea water. Grade A, with the highest molybdenum, nickel and chromium levels has the best properties in this respect, although none of the grades are as resistant to boiling nitric acid as an 18/8 type. Grade C has better resistance to intergranular corrosion from salt solutions and acids at elevated temperatures.

Sub-zero Properties as with the 18/8 stainless these austenitic steels have good stability of properties at sub-zero temperatures, although again the carbon and stabilising element levels should be kept to a minimum for the best results. However, within the ranges of composition specified it is possible for varying amounts of delta ferrite to be present in the steels and as the level of delta ferrite increases the notch toughness at low temperatures is reduced.

BS 3146: (1975) PART 2: ANC 5

Description
Nickel-chromium alloy steel castings resistant to scaling at elevated temperatures. The alloys have good hot strength, hot gas corrosion and carbon penetration resistance and improved resistance to cyclic heating and thermal shock with increasing nickel content. Typical applications cover a wide range of furnace and heat treatment equipment parts where service conditions combine elevated temperatures with corrosive environments. The alloys also have fairly good abrasion resistance, particularly with the high carbon levels.

Additional Information

• Weldability good – gas or electric arc methods are suitable without the necessity for post weld treatment.
• Machinability as with other austenitic alloys is only fair so that it is advisable to use high feeds, low speeds and carbide tipped tools.

Other comments
Corrosion resistance – resistance to corrosion by hot gases is good for all three grades. Grade A has good resistance to attack by all heat treatment salts whereas Grades B and C are not so resistant to neutral salts. Grade C has excellent corrosion resistance to salts in tempering and cyaniding baths. Grades B and C are resistant to molten tin up to 340°C and Grade C to molten lead and vanadium pentoxide.

Elevated Temperature Properties – All grades have good resistance to scaling up to 1050°C, the higher nickel alloys being best in this respect. Maximum service temperatures are 1100° C for Grade A, 1120° for Grade B and 1150° for Grade C. All the alloys have good resistance to carbon penetration in carburising atmosphere, good resistance to cyclic heating, useful creep strength up to 650°C and in the case of Grade C, excellent resistance to thermal shock.

BS 3146: (1975) PART 2: ANC 6

Description
Chromium-nickel alloy steel castings possessing good corrosion and heat resisting properties. The alloys have good hot strength and oxidation resistance and useful creep resistance up to 650°C. Applications include oil refinery, heat treatment equipment, furnace and burner parts as well as welding fixtures.

Additional Information

• Weldability is good, gas or electric arc methods being suitable without the necessity for post-weld treatment. However, it is recommended that castings should be stabilised prior to welding at not less than 950°C.
• Machinability as with other austenitic alloys, is only fair so that it is advisable to use high feeds, low speeds and tipped tools.

Other Comments
Corrosion resistance the alloys are not designed specifically for resistance to corrosion but rather for heat resistance. In comparable corrosive conditions, it is probable that lower alloy content austenitic stainless steels would be adequate at lower temperatures and the high alloy ANC 5 type materials more suitable at higher temperatures.