Questions from the Shop Floor
Materials
No. There is no datasheet for 'armour steel' as such, only trade names such as Armox, Ramor or Secure, where each manufacturer defines composition and hardness itself. What they have in common is that they are low-alloy, quenched-and-tempered martensitic steels with low carbon content that are basically weldable. Basically weldable, however, does not mean weldable however you like — processing follows tight rules.
Look up in the glossary: Manufacturer Qualification (Q1 to Q4)
No. Hardox and similar wear-resistant steels are metallurgically related and in some cases even weldable, but they are not ballistically qualified. Anyone who does not keep this separation clean in storage, at the machine and in the welding procedure specification will fail the technical interview with the accredited body. Armour steel needs its own low-hydrogen filler metals and controlled preheating that, at this level of strictness, is often not customary for wear-resistant steel.
Look up in the glossary: Carbon Equivalent (CET/CEV) · Look up in the glossary: Heat-Affected Zone (HAZ)
Because quenched-and-tempered martensitic steel holds onto a magnetic field once it has been imparted, and susceptibility rises with the hardness of the grade. This residual magnetism causes arc blow during welding: the arc is deflected, and lack of fusion and porosity result, particularly in tack welds and root passes. Residual field should therefore be actively measured at incoming goods and before critical welds, not merely assumed.
Look up in the glossary: Residual Magnetism · Look up in the glossary: Arc Blow
Machining
Because for armour steel, thickness is not just a dimension but a protective property, to which approval and firing test evidence are directly tied. A milled-down plate is not an approved thinner plate; it is a thicker plate with an altered cross-section and no valid evidence. In addition, hardness testing is close to the surface, so anyone who mills it down removes exactly the zone where conformity was verified. Only local machining, for example for fits, is permitted — not reducing the protective thickness over an area.
Look up in the glossary: Thickness Tolerance Class (EN 10029) · Look up in the glossary: Concession and Deviation
Because a magnetic chuck imparts a residual field to the component that later causes arc blow during welding. Armour steel is therefore clamped mechanically, not magnetically. This rule applies to every machining step where the component will still be joined later.
Look up in the glossary: Residual Magnetism · Look up in the glossary: Arc Blow
Qualification
No. EN 1090 governs steel structures as a construction product, with structural design, building authority supervision and CE marking — none of that matters for a vehicle component made of armour steel. What applies instead is DIN 2303 with its four manufacturer qualifications, Q1 to Q4. What does carry over from the EN 1090 world is the EN ISO 3834-2 it requires anyway, which is also needed for DIN 2303.
Look up in the glossary: Manufacturer Qualification (Q1 to Q4)
No, it is not a ladder. Q1 and Q2 are material-related and product-independent, whereas Q3 and Q4 are tied to the function of the component. For a component with an armour function, Q3 applies as a rule, regardless of the fact that the material on its own would also fall under Q2. Q4, moreover, is not a higher Q3 but a separate branch for aerospace with its own standards.
Look up in the glossary: Manufacturer Qualification (Q1 to Q4) · Look up in the glossary: Component Class (BK)
In the documented example of an established German protection equipment supplier, around three years passed from first Q1 approval to Q3 approval for armour steel plate. This figure is a realistic guideline, not a guaranteed value, and depends, among other things, on how quickly personnel qualification and test body manufacture progress. It is a good argument against the expectation that a company could be qualified in six months.
Look up in the glossary: Proof-Firing Test Body · Look up in the glossary: Defense Technology Centre (WTD)
That depends on the component class, not the Q class. For the most demanding component class, BK 1, a welding engineer is generally required; lower levels such as welding specialist or welding foreman are sufficient only for less safety-relevant component classes. In every case, a named deputy is also mandatory, without whom there is no approval.
Look up in the glossary: Welding Engineer (SFI) · Look up in the glossary: Personnel Concept
Then the strictest class, BK 1, applies automatically, with the highest stress level, the highest safety significance and the strictest quality level, B. Anyone who does not document the classification therefore ends up in the toughest regime, even where the component doesn't actually warrant it. A solid classification agreed with the customer is therefore worth it economically.
Closer than many think, but not automatically done. Anyone who properly lives EN ISO 3834-2 and has their welding supervision under control has already built a substantial part of the foundation, because this standard is also the basis for the DIN 2303 requirements. Even so, you need to know where the remaining gaps lie, for example in the company description, the deputy arrangement and material-specific supplementary requirements.
Look up in the glossary: Manufacturer Qualification (Q1 to Q4)
Welding
The practical weldability limit is around 600 HBW. Above this limit, welding is generally no longer used; instead components are bolted, bonded or fitted as add-on panels. For components near this limit it is worth checking early with the material manufacturer, because the filler metal and temperature windows narrow considerably here.
That is typically cold cracking, a hydrogen-induced crack that forms from cooling too quickly, missing preheat, or hydrogen sources such as damp electrodes. Because it appears with a delay, it is easily missed during ongoing production. A damp stock of basic-coated stick electrodes is the most common cause in companies that otherwise do everything right.
Look up in the glossary: Cold Cracking · Look up in the glossary: Carbon Equivalent (CET/CEV)
At least two minutes per 25 millimetres of plate thickness, measured on the thicker plate of the joint. Anyone who measures immediately is only measuring the surface, not the component once it is heated through. The minimum temperature must also be reached across a zone of 75 millimetres on both sides of the weld.
Look up in the glossary: Interpass Temperature · Look up in the glossary: Carbon Equivalent (CET/CEV)
Because too high an interpass temperature softens the heat-affected zone, causing the component to lose exactly the hardness it was bought for. At the same time, sufficient minimum preheat prevents hydrogen cracking, so this is a window with two limits, not a single limit value. The harder the grade, the narrower this window becomes.
Look up in the glossary: Heat-Affected Zone (HAZ) · Look up in the glossary: Interpass Temperature
With a contact thermometer or thermocouple, not with temperature-indicating crayon alone. Heating itself should be as uniform as possible; electric heating mats or induction are clearly superior to a torch. Spot, uneven heating barely slows cooling and creates additional residual stress and distortion.
Because for armour steel, the thermal half of that toolkit falls away — the material must not be heat-treated again after delivery. The core conclusion is that distortion must be avoided, because it can no longer be corrected. Avoiding it starts with weld sequence, joint layout, counter-shrinkage and fixture design, not with rework at the end.
Blasting
No. Armour steel must not be heat-treated again after delivery, because its properties are lost once the material-specific limit temperature is exceeded. That also applies to apparently harmless processes such as powder coating, stove enamelling or nitriding. Depending on the manufacturer, this limit is in the order of around 200 degrees Celsius.
Cutting
Water jet is named in the manuscript as the preferred process, because it works without heat input and therefore without a heat-affected zone. Oxy-fuel cutting is possible but requires a defined preheating regime. Plasma and oxy-fuel cutting additionally need a machining allowance that covers the kerf and the heat-affected zone.
The first milling or grinding pass on a flame-cut edge should go at least 2 millimetres deep, to get safely below the heat-affected zone. In the cutting layout, a corresponding machining allowance is therefore planned on every edge that will later be joined or bent. Narrow offcut strips should be avoided in the process, because they can crack during cutting.
Bending
Because springback increases with the strength of the material, and armour steel is considerably stronger than ordinary mild steel. For armour steel it is the dominant factor in the entire tolerance chain, often larger than plate thickness, cutting and weld distortion combined. Springback also differs by rolling direction and scatters between batches, which is why trial bends are recommended.
Look up in the glossary: Springback · Look up in the glossary: Die Opening Angle
Because tighter bend radii are possible transverse to the rolling direction than along it, with a lower risk of cracking at the same time. For critical radii it is therefore worth planning nesting and cutting so that the future bend line lies transverse. This applies particularly to the higher hardness classes, where the permissible radii become tighter anyway.
Because armour steel fractures in a brittle manner. If a plate breaks during bending or straightening, fragments fly off uncontrolled. Operators and bystanders must therefore stand to the side of the machine — this is not a formality, but the reason inexperienced companies actually cause injuries here.
No. Flame straightening and any form of hot straightening exceed the tempering temperature and destroy hardness and protective performance; they are not permitted for armour steel. The only permitted method is cold straightening in a press or by roller levelling, which nonetheless counts as cold forming and consumes deformation capacity. In most cases, avoiding distortion is more economical than correcting it after the fact.
Look up in the glossary: Cold Straightening · Look up in the glossary: Springback
Testing
For large components made of thick armour steel, EN ISO 13920's tightest class, A, permits values that are practically unattainable, because high heat input brings significant shrinkage with it. In practice, work is therefore mostly done with the mid-range classes B to C for lengths and angles, and F to G for straightness and flatness. Where mating surfaces arise, targeted mechanical rework with an allowance is often more economical than a blanket tight general tolerance class.
Critical, ballistically relevant characteristics are inspected 100 percent as a matter of principle — that is the standard case in defense technology. Sampling under the AQL principle is intended only for non-critical characteristics, and even then must be justified, documented and, where necessary, approved by the customer. 100 percent visual inspection of welds is binding within the scope of DIN 2303 in any case.
Best not as a process description, but on a real part from ongoing production: the 3.1 certificate, the batch transfer during cutting, and the assignment in the inspection report. It should be traceable on a specific component within a few minutes, or not at all. This exact sample check is also recommended as part of your own audit preparation, before the customer asks for it.
Because EN 10029 only governs delivery ex-works, and armour steel, because of its high yield strength, falls under the more tolerant steel type H, whose permissible waviness is twice that of ordinary mild steel. Composite structures and attached parts still have to be fit for installation in the end, so the requirement usually called up on drawings is, in practice, significantly tighter than the pure standard specification. This gap is a manufacturing task, not a purchasing formality.
A concession is prior written customer approval for a departure from the drawing, specification or inspection requirement; it must be applied for before delivery. Applied for after the fact, it is worthless — the route always runs through the customer, never through your own production planning. Rework within the range that is permitted anyway, by contrast, needs no such approval, because it stays within the agreed tolerances.
Market Access
Because a first Q3 application without a nameable order and without a named requiring authority rarely receives consideration at the responsible trials office. Capacity there is limited and is prioritised according to what is actually needed. This reverses the usual order: the need comes first, then the approval built on it — not the other way round.
Look up in the glossary: Defense Technology Centre (WTD) · Look up in the glossary: Proof-Firing Test Body
Usually it is not the manufacturing technology but the rulebook around it: DIN 2303 instead of EN 1090, a welding supervisor with a mandatory named deputy, materials to technical delivery conditions instead of a dealer's datasheet, and the often overlooked question of which requiring authority the parts are actually being made for. These four points frequently decide acceptance or rejection faster than the actual shop-floor competence.
Look up in the glossary: Manufacturer Qualification (Q1 to Q4)
Not the statement that you have a welding specialist, but a name, qualification level, deputy and presence. The buyer wants to know who signs off when the responsible person is on leave. This question cannot be answered in the week before the audit — it needs structure, personnel and time.
Look up in the glossary: Welding Engineer (SFI) · Look up in the glossary: Personnel Concept
Costing
In addition to the ongoing per-unit costs, there are one-off market access costs, order-related start-up costs and contractual risks that hardly play a role in ordinary structural steelwork. These include, for example, approval effort, first article inspection, traceability and concession processes. Anyone who does not cost these layers separately regularly underestimates the actual effort of a defense technology order.
Look up in the glossary: Quality Assurance Requirements (QSB)
The QSB code is the central key referencing the specific quality requirements of an order, for example the submission level required for first article inspection. Only the associated catalogue explains what a code actually demands — the code alone says little. Without resolving it, the actual inspection and documentation effort of an order can hardly be costed seriously.
Look up in the glossary: Quality Assurance Requirements (QSB) · Look up in the glossary: Submission Level
No — that is exactly the expensive mistake many companies make. Before submitting a quote, it is worth an honest check against a fixed set of questions, covering approval level, requiring authority, filler metals and inspection effort, among other things. Anyone who says yes first and then finds out they are not allowed to deliver loses more time and trust than a prior check would have cost.