Stainless Steel & Heat Resistant Alloys
Stainless steel and heat resistant alloys are some of the most versatile materials that we offer, with uses in almost every industry – from aerospace to renewables. Stainless steel investment castings are made from a metal alloy that consists of a blend of at least 50% of iron with a minimum of 10.5% of chromium – the exact percentage of chromium varies, as stainless steel castings can contain up to 30% of this metal, depending on the quality you desire.
WHAT DOES ‘STAINLESS’ MEAN?
A material becomes ‘stainless’ when a chromium-rich oxide film forms on its surface and heals itself continuously when it comes into contact with oxygen. The end result of our stainless steel investment casting process includes:
- Strong mechanical and physical properties
- The ability to last for a very long time
- An aptitude when exposed to increased stress or pressure.
Also, stainless steel contains other elements used to augment its structure and properties – such as nickel, molybdenum, copper, silicon and titanium – which adds strength and durability to this alloy. Carbon is typically present in small amounts, ranging from less than 0.03% to over 1.0% in certain martensitic grades.
Stainless-steel investment casting has a lot of applications, from commercial to industrial, making it an extremely popular option.
WHY CHOOSE STAINLESS STEEL?
When in doubt over whether to choose between stainless steel or any other material we offer, it’s important to consider its features and know whether it’s the right choice for your needs. Many use this material because it’s highly resistant to corrosion and can be used in a variety of environments and settings – this includes investment casting and forging.
TYPES OF STAINLESS STEEL ALLOYS
Selecting the right type of stainless steel casting for your project depends on what the material is going to be used for. Considerations include the temperature of operation, if welding is going to be performed, whether or not the part needs to be magnetic, and the shape of the metal part.
Stainless steel is often classified into five different groups:
Alloys of chromium and carbon that can be hardened by heat treatments and are ferromagnetic. They possess martensitic crystal structure in their hardened condition, although they’re less resistant to corrosion than other grades. The chromium content does not usually exceed 18%, while the carbon content might exceed 1.0%.
Martensitic stainless steels, such as types BS3146 PART 2 1975 ANC1A, B, C and ANC2, are similar in composition to the ferrite group, but contain a balance of C and Ni versus Cr and Mo; hence, austenite at high temperatures transforms to martensite at low temperatures.
Excess carbides may be present to enhance wear resistance or to maintain cutting edges, as is the case with knife blades. They’re commonly used for golf club head and pump and valve parts as well.
UTS 500 – 1000N/mm2. Elongation 8-15%. HB 150-300
These alloys are ferromagnetic, ductile and typically contain less than 30% of chromium in their composition. They possess body-centred cubic (bcc) crystal structures.
This grade has good ductility and formability, but high-temperature mechanical properties are inferior to the austenitic stainless steels. The toughness of the grade is limited at low temperatures and in heavy sections.
Some ferritic stainless steels (such as types 409 and 405) are used, for example, in mufflers, exhaust systems, kitchen counters and sinks, as they are more cost-efficient than other stainless steels. Other more highly alloyed steels low in C and N (such as types 444 and 261) are costlier but are highly resistant to chlorides.
Incredibly easy to weld, austenitic stainless steels are nonmagnetic in the annealed condition and particularly strong at high temperatures. They have a face-centred cubic (FCC) structure. Austenite is formed by using austenising elements like nickel, manganese and nitrogen.
Austenitic stainless steels are the most weldable of the stainless steels and can be divided rather loosely into three groups: common chromium-nickel (300 series), manganese-chromium-nickel-nitrogen (200 series) and speciality alloys.
These alloys can be hardened only by cold working and might present some ferromagnetism due to this cold working or welding. They have good cryogenic properties as well, and chromium content varies between 16% to 26%; the nickel content is commonly below 35%. They are used in industries like chemical, pharmaceutical, firefighting, etc.
UTS 450 – 500N/mm2. Elongation 10-12%. HB 120
These alloys tend to have higher tensile and yield strength, and great stress corrosion cracking resistance that’s better than austenitic alloys. They’re a mixture of bcc ferrite and fcc austenite crystal structures, although most tend to have equal amounts of these phases in the annealed condition.
Duplex stainless steels typically contain approximately 22-25% chromium and 5% nickel with molybdenum and nitrogen. Their main alloying elements are chromium and nickel, and they tend to have poor toughness compared to austenitic stainless steels.
These alloys are made primarily from chromium and nickel and reach high strength by precipitation-hardening of their structure. In the annealed condition, they can be either austenitic or martensitic stainless steels. They’re typically used in the construction industry where resistance to corrosion and high stress is required. They’re also used for surgical instruments and safety fall arrest equipment when working at height.
Precipitation-hardened stainless steels are grouped into three types: martensitic, semi-austenitic and austenitic. The martensitic (such as Type 630, 17-4ph and BS3146 PART 2 1975 ANC22) and semi-austenitic (such as Type 631) can provide higher strength than the austenitic (such as Type 660, also known as A286).
UTS 900 – 1300N/mm2. Elongation 6-8%. HB 270-380 (Approximate Range)
Contact Dean Group for Stainless Steel Castings
If you have any more questions about our stainless steel casting process, contact Dean Group today, we are a family-owned UK foundry with over four decades of casting experience. Contact our expert team today by calling 0161 775 1633.