Which precision alloys are needed to manufacture electric heaters

Precision alloys possess the needed physical-mechanical characteristics for achieving optimal performance and reliability of electric heaters.

For certain alloys to be usable in producing electric heaters, they must possess a number of specific properties. Such as:

• high heat resistance — electric heaters operate at high temperatures, so alloys must be resistant to oxidation under extreme service conditions;
• high electrical resistance — this makes it possible to effectively concentrate thermal power in a limited volume;
• sufficient creep resistance — alloys must retain their geometry and structure during long service under high-temperature conditions;
• satisfactory ductility in the cold state — this allows manufacturers to create elements of the needed geometry without the need to heat the material.

Among various groups of precision alloys two have found the widest application: iron-chromium-aluminum steels and nichromes. These materials possess the above qualities and are effectively used in electric heaters.

Features of production and quality control of alloys

Alloys for heaters are predominantly released as cold-rolled strip and wire. Heat resistance of these materials is controlled by the service-life test method, i.e. sample service life is determined under cyclic heating and cooling.

Physical and mechanical properties of steels change during holds in certain temperature intervals. For example, Fe-Cr and Fe-Cr-Al alloys after holding at a certain temperature become stronger but less ductile.

Iron-chromium-based alloys when held at 475°C acquire so-called 475-degree embrittlement. However, the embrittlement process is reversible: the required material characteristics can be restored by quenching it in an aqueous medium at 750–860°C.

Fe-Cr-Al alloys and other metals of the ferritic class have low creep resistance at high temperatures (above 1100–1200°C), which in service may lead to sagging of heaters. To prevent this it is recommended to use additional supports along the entire length of heaters. In addition, iron-chromium-aluminum materials react with a number of metals and oxides. This does not allow applying them in combination with any ceramics without an additional insulating layer at contact points of ceramic elements with electric heaters.

Application areas and working temperatures of precision alloys

Eight grades of precision alloys are used in electric heaters, each of which has its purpose and working temperature range.

1. Kh13Yu4 — used in manufacturing rheostats and heating elements of household appliances. The maximum allowable temperature is 1000°C, optimal — 900°C.
2. Kh15N60 — application area similar to the previous steel grade. Optimal service temperature — 950°C, maximum — 1000°C.
3. Kh15N60-N — a precision alloy for industrial and laboratory furnaces, as well as various household appliances with heating elements. Can operate at temperatures up to 1100°C, however the recommended is 1050°C.
4. Kh20N80 — the material is used in producing small-size resistors, rheostats, and household appliances. Optimal working temperature is 1050°C, maximum — 1100°C.
5. Kh20N80-N — used in industrial and laboratory furnaces and household appliances. Can be used at temperatures up to 1200°C; optimal working conditions are considered 1050°C.
6. Kh23Yu5 — used in glow plugs and industrial and laboratory furnaces. Optimal working temperature — 1150°C, maximum — 1200°C.
7. Kh23Yu5A — application area similar to the previous material, but this steel grade can be used in appliances with a longer service life. Maximum allowable temperature is 1200°C, optimal — 1175°C.
8. Kh27Yu5A — considered the most suitable metal for heating elements of high-temperature laboratory and industrial furnaces. Can be used at temperatures up to 1300°C; optimal is considered 1250°C.

Alloys for electric heaters with letters A and N at the end of the marking are high-quality. The required physical-mechanical characteristics are achieved by adding rare-earth and alloying metals that have a substantial effect on oxidation processes at high temperatures.

Precision alloys released by the PZPS plant

Petersburg Plant of Precision Alloys releases steels for producing electric heaters of grades Kh15N60-N, Kh20N80-N, and Kh23Yu5 as cold-rolled strip of thickness from 0.005 to 4.0 mm and width from 3 to 250 mm in accordance with GOST 12766.2. Presence of a modern laboratory complex and modernized production equipment also makes it possible to melt materials to individual customer technical specifications. To learn more about the enterprise’s capabilities and clarify cooperation details, leave a request or call the listed phone number.

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