KVA STAINLESS™ - F.A.Q.

• What do the letters "KVA" stand for?
• What does KVA STAINLESS™ do?
• What are martensitic stainless steels?
• Are martensitic stainless steels readily available?
• We considered stainless steels (Nitronic™, dual phase/duplex, Hytens™, etc.) in the past for our applications, it didn't work out. They were too costly, too heavy and too difficult to form.... Why would this be any different?
• My part's design is stiffness-driven.... What good does a higher strength material do if it has the same Modulus of Elasticity as mild steel?
• I am uncomfortable with introducing heat-treating to our fabrication process flow.... Won't heat treating my parts be cost prohibitive and induce an unacceptable amount of distortion?

Q: What do the letters "KVA" stand for?

A: KVA is an acronym for Kilovolt-Ampere. It is equivalent to a kilowatt, a unit of power, commonly used to describe welding power or induction heating power.

Q: What does KVA STAINLESS™ do?

A: KVA STAINLESS™ specializes in developing new technologies, which enable martensitic alloys to be used cost-effectively in novel, high performance structural applications.

Q: What are martensitic stainless steels?

A: Martensitic stainless steels are essentially alloys of chromium and sufficient carbon content that transform into martensite, a distorted body-centered cubic crystal structure, after hardening. They are magnetic, and are formulated to respond well to heat treatment. Similar to non-stainless hardenable steels, the maximum attainable hardness, and strength, is in direct proportion to the amount of carbon present in the alloy. However, the chromium present in the alloy allows for maximum hardness to be reached in all but the thickest sections by austenitizing and quenching in air (air-hardening). Corrosion resistance in mild atmospheric environments is excellent; many times better than mild steel; however common martensitic stainless steels are not as corrosion-free as highly alloyed austenitic stainless grades such as 316L in harsh environments. Martensitic stainless steels are specified when the application requires good tensile strength, creep, and fatigue strength properties, in combination with moderate corrosion resistance and heat resistance up to approx. 1200 °F. Typical (historical) uses of this grade include cutlery, turbine engines, petrochemical equipment, surgical and dental instruments, scissors, valves, gears, cams and ball bearings. Depending on the carbon content, martensitic alloys can be capable of tensile strengths approaching 300 ksi (2000 Mpa). The most common, type 410, can be hardened to approximately 200 ksi (1400 Mpa) in an as quenched-state. However, a tempering operation is usually performed to increase ductility and reduce brittleness.

Q: Are martensitic stainless steels readily available?

A: Martensitic stainless steels are readily available in coil, sheet, strip, plate, wire and bar form from many suppliers, both domestic and international. Numerous standardized grades exist, including those in the UNS, SAE and SUS specifications.

Q: We considered stainless steels (Nitronic™, dual phase/duplex, Hytens™, etc.) in the past for our applications, it didn't work out. They were too costly, too heavy and too difficult to form.... Why would this be any different?

A: There are numerous reasons why martensitic stainless steel could be the optimal solution. One important fact to note is cost: The price per pound for martensitic stainless alloys is typically less than the monthly surcharge alone for austenitic grades. Martensitic stainless steels contain little, if any, nickel, which is an expensive alloying element. Additionally, chromium content is much lower in martensitic stainless grades (11.5-14 wt% for types 410 through 420), unlike many austenitic, ferritic, or duplex grades that can have 20 wt% Cr or more. Additional cost savings are achieved with martensitic stainless grades due to their uniquely high strengths, which can result in mass reductions from 35-50%. These weight savings equate into reduced raw material usage, reduced shipping costs, and reduced handling & fabrication costs. Unlike austenitic stainless grades (and many other high strength steels - HSS), martensitic stainless steels do not rely on work-hardening methods to achieve high strengths. As such, they are easily formed in their annealed state, using low-cost, low-force methods traditionally associated with low strength mild steels. Compounded with the potential down gauge-ing opportunities that would require much lower forming forces, martensitic stainless alloys are very cost effective to implement.

Q: My part's design is stiffness-driven.... What good does a higher strength material do if it has the same Modulus of Elasticity as mild steel?

A: True, many parts are designed to meet certain stiffness requirements, rather than strength requirements. There are two aspects of part design that determine the part's overall stiffness: material stiffness (Young's Modulus, E), and geometrical stiffness (cross-section based moment of inertia). Martensitic stainless steels do have the same Modulus as nearly all steels, 200 GPa (29,000,000 psi), which is nearly triple that of Aluminum alloys and double that of Titanium alloys. Most significant is the fact that martensitic stainless steels do have very high tensile strengths, which allows the designer to expand the outer dimensions of the part (space permitting) while reducing wall thickness, thereby increasing the geometrical stiffness of the part while reducing weight. This approach takes advantage of the fact that the outer fibers of the martensitic stainless part can be stressed to a higher level, while maintaining or increasing part stiffness, part durability and strength.

Q: I am uncomfortable with introducing heat-treating to our fabrication process flow.... Won't heat treating my parts be cost prohibitive and induce an unacceptable amount of distortion?

A: Martensitic stainless steels are unique in that they are considered "air-hardening". Much like high-quality tool steels, they respond to a hardening cycle with a gentle air-quench cooling rate. The air-quench hardening cycle is simple, gentle and low-cost, unlike more rapid quenchants such as water, salts, or oil. The gentle nature of the air-quench serves to limit the thermal shock experienced with other quenching media, resulting in parts with much more uniform residual stress distribution and much less prone to distortion. This enables the use of martensitic stainless steels in lightweight, thin wall sections without concern for thermal processing distortion and variation. Additionally, air-quenching is compatible with the use of continuous thermal treatment methods, which allows for consistent, high throughput and low cost processing.

top