Technical Glossary

American Iron and Steel Institute

A widely used American designation system for steel grades (e.g. H13, D2, 4140, 304). AISI designations given as counterparts of EN grades do not always mean exact equivalence; composition ranges may differ.

Aerospace Material Specifications

Aerospace material specifications published by SAE International. They define chemistry, mechanical properties, condition, testing and quality requirements, and are cited with their revision letter (e.g. AMS 4928W).

Annealed / soft annealed

A delivery condition in which the material is held at a set temperature and cooled slowly under control to soften it. It improves machinability and reduces internal stresses. Tool steels are mostly supplied soft annealed; the working hardness is obtained by subsequent heat treatment. EN designation: +A.

ASTM International

An international organisation publishing standards for materials, products and test methods. For example, ASTM B348 covers titanium bars and ASTM A564 covers precipitation-hardening stainless steel bars.

Certificate of Conformity

A statement by the supplier that the delivered product conforms to the order and the specified requirements. It does not replace an MTC with test results and is usually requested together with it.

Electric Arc Furnace

A steelmaking route in which scrap and other charge materials are melted by an electric arc. It is the primary melting step; remelting processes such as ESR or VAR, where required, follow it and ladle metallurgy.

Extra Low Interstitial

A titanium alloy version with lower limits on interstitial elements such as oxygen, nitrogen and carbon, and on iron (e.g. Ti-6Al-4V ELI, Grade 23). Fracture toughness and ductility are the focus; specified for medical and cryogenic applications.

Inspection document standard

The European standard defining the types of inspection documents for metallic products. Document types are 2.1, 2.2, 3.1 and 3.2; the type shows who confirms the results and with what independence.

Inspection certificate 3.1

A document issued by the manufacturer stating the results of specific inspection on the supplied products, validated by the manufacturer’s authorised inspection representative independent of the manufacturing department.

Inspection certificate 3.2

In addition to 3.1, the results are also validated by the purchaser’s authorised representative or the inspector designated by official regulations. The requirement and the validating party should be stated at order stage.

Electroslag Remelting

A process in which a pre-made electrode is remelted through a resistance-heated slag bath and solidified under control. It aims to reduce non-metallic inclusions and segregation, giving a cleaner and more homogeneous internal structure. In tool steels it is relevant to polishability, toughness and die life.

Forging ratio

The ratio of the cross-sectional area before forging to that after forging. It matters for breaking down the cast structure and consolidating the internal structure; some specifications require a minimum forging ratio.

Heat number

The number identifying material produced from the same melt. A match between the marking on the material and the heat number on the certificate is the basis of traceability.

Heat treatment

Controlled heating and cooling operations used to change the microstructure of a material and therefore properties such as hardness, toughness and strength. Annealing, hardening, tempering, quenching and tempering, solution treatment and ageing all fall under this term.

High Speed Steel

Tool steels alloyed with tungsten, molybdenum, vanadium and cobalt that retain their hardness at high temperature (red hardness). Used for cutting tools such as drills, mills, taps and broaches and for some cold-forming tools.

Mill Test Certificate

A manufacturer document showing chemical analysis, mechanical test and other required test results together with the heat number, size, delivery condition and applicable standard. The certificate type is usually stated according to EN 10204 (e.g. 3.1, 3.2).

Precipitation Hardening

A strengthening mechanism in which fine precipitates are formed by an ageing treatment after solution treatment. Stainless steels such as 17-4 PH, 15-5 PH and 13-8 Mo, as well as Alloy 718, are hardened this way; the aged condition (e.g. H900, H1025) determines the properties.

Positive Material Identification

Non-destructive verification of a material’s alloy composition, usually with portable XRF or OES instruments. It is applied at delivery or acceptance to reduce the risk of mixed material; it may not replace a full chemical analysis.

Physical Vapour Deposition

A coating method in which thin, hard layers (e.g. TiN, TiAlN, CrN) are deposited on a surface under vacuum. It is applied to tool and die surfaces to improve wear and friction behaviour; the substrate must have suitable hardness and tempering temperature.

Q&T, +QT · Quenched and tempered

A delivery condition in which the material is hardened and then tempered to balance strength and toughness. Designated +QT in EN standards; mechanical values depend on the section size.

Unified Numbering System

A unified numbering system for metals and alloys administered by ASTM and SAE. It consists of a letter and five digits (e.g. S17400, N07718, R56400) and brings different trade names under one designation.

Ultrasonic Testing

Non-destructive examination of a material for discontinuities such as voids, inclusions and cracks using sound waves. Acceptance criteria depend on the applicable standard and quality class (e.g. EN 10228-3 for steel forgings, AMS 2631 for titanium bar).

Vacuum Arc Remelting

A process in which an electrode is remelted by an electric arc under vacuum. It reduces dissolved gases and inclusions. It is used for titanium alloys, nickel-base superalloys and some special steels; the required melting practice may be stated in the applicable specification.