Processing stainless steel: cutting, bending, welding, polishing
12Х18Н10Т drilling parameters and any other operation on stainless steel run up against three properties of the material: low thermal conductivity, a tendency to work hardening and a passive film that is easy to spoil.
Heat during cutting and drilling goes into the edge, not into the chips, so the tool heats up, the metal hardens under the cutter, and the surface loses its resistance after heating.
This hub is about five operations: cutting, bending and forming, welding, drilling and surface finishing. There is a separate analysis for each of them; here is the overall picture — what is critical and in what order the operations are arranged.
Which operations are needed
The set of operations is determined by three things: the grade, the thickness and the requirements for the edge. Austenitic grades 304 and 316 are ductile and weld well, but tend to work harden and conduct heat away less well. Ferritic 430 is easier to machine but tolerates welding worse. The thicker the metal, the more pronounced the heat input, and the higher the requirements for appearance, the more operations come after welding.
| Operation | When it is needed | What is critical |
|---|---|---|
| Cutting | cutting sheet, pipe, round bar to size | cutting method, edge, heat-affected zone |
| Bending and forming | bent profiles, shells, bends | minimum radius, springback, rolling direction |
| Welding | joining structural elements | consumables, shielding gas, cleaning of the seam |
| Drilling and machining | holes, slots, fits | work hardening, cooling, tool rigidity |
| Surface finishing | appearance and hygiene | abrasive grit, absence of foreign metal |
The order is usually as follows: cutting to size, forming, welding, cleaning and finishing. Cutting and bending can be swapped, but if you weld first and bend afterwards, the seam will end up in the deformation zone and will require separate inspection. For critical structures, the sequence is fixed in the process plan rather than decided on site.
Contamination is a separate topic. Stainless steel must not be processed on the same bench and with the same tools as carbon steel if the surface will later be used in a food or wet environment. Particles of ordinary steel are embedded in the surface and produce ginger spots that are linked neither to the grade nor to the quality of the rolled steel.
Another reference point is the allowance. After thermal cutting, the edge moves away from the cut line by the width of the heat-affected zone, and after bending the part springs back relative to the set angle. That is why the process plan includes a margin for cleaning and fitting, especially for thin sheet, where an error of fractions of a millimetre is visible on the assembled product. If the part goes into a welded structure, the edge is prepared for a specific type of seam: with or without bevelling, with a root face, with backing gas.
Cutting
For stainless steel, laser, plasma, abrasive waterjet and mechanical methods are used: band saw, cutting disc, guillotine. The choice depends on the thickness, the required edge accuracy and the volume. Laser gives a narrow cut and a neat edge, abrasive waterjet does not heat the metal at all, plasma is faster on thick metal but leaves a wider cut and a heat-affected zone.
The main question in cutting is heat input and subsequent cleaning. Thermal methods leave scale and a chromium-depleted layer on the edge. If the edge is later welded or goes into an aggressive environment, this layer is removed mechanically or by pickling, otherwise corrosion starts exactly from it. Laser is used with nitrogen when a clean edge is needed, and with oxygen or air when speed matters more; the colour and condition of the edge depend on the gas.
Mechanical cutting does not heat the metal as much, but it produces a burr and requires separate tooling for stainless steel. A detailed analysis of methods, consumables and typical mistakes is in the article cutting stainless steel.
Cutting pipes and profiles deserves separate mention. A round pipe is more conveniently cut to a template or on a pipe cutter so as not to flatten the wall, a profile pipe — with a mandrel or on a machine that holds the geometry. A guillotine is good for straight cuts of sheet, but on thick austenite it produces a bent edge, which is then removed. For thin-walled pipes, thermal methods require experience: an overheated wall behaves unpredictably during welding.
Bending and forming
Bending stainless steel differs from bending carbon steel in two effects. The first is springback: the elastic return of the metal after the load is removed, so the angle is set with a margin and checked on a sample. The second is work hardening: in the bend zone the metal hardens, becomes noticeably more magnetic and less ductile, and cracks appear if the radius is too small.
| Factor | How it affects | What to do |
|---|---|---|
| Grade | 304 and 316 spring back more, 430 less | select the radius and compensation by grade |
| Thickness | the thicker, the greater the force and springback | check the capabilities of the tooling |
| Rolling direction | bends across and along behave differently | place the bend taking the direction into account |
| Radius | below the minimum the risk of cracks grows | do not reduce the radius to save money |
| Tooling | wear and punch radius determine the result | keep the tooling in order, clean it of foreign metal |
A bent element after forming is more magnetic than the original sheet, and this is not a sign of a defect or of a substituted grade. How to calculate the minimum radius, compensate for springback and not ruin the surface is analysed in the article bending stainless steel.
Forming includes not only bending but also rolling of shells, flanging and drawing. On rolls, it is important to distribute the deformation over several passes: in a single pass the metal work hardens unevenly, and marks remain on the surface that can then only be removed by taking off a layer. After forming, the part is checked against a template, not against the calculated angle, because the actual radius depends on the tooling and the batch of metal.
Welding
Welding stainless steel is the operation most sensitive to mistakes, because the corrosion resistance of the whole assembly depends on it. Thin metal and critical seams are more often welded by the argon-arc method with filler from the same group, thick metal — with electrodes or a semi-automatic welder in shielding gas. Each grade needs its own consumable: 304 must not be welded with filler for carbon steel, the seam will get a different composition and become the weak link.
| Method | Where it is appropriate | What matters |
|---|---|---|
| Manual argon-arc (TIG) | thin metal, critical seams, pipes | filler of the same group, careful gas, clean edge |
| Semi-automatic (MIG) | thicker and faster, production seams | stainless steel wire, argon-based gas |
| Manual arc with electrodes | installation, repair, thick metal | electrodes for the relevant grade, slag removal |
| Welding with backing gas | pipes and vessels where the back bead matters | protection of the seam root from oxidation |
After welding, the seam is cleaned of scale and heat tint and pickled to restore the passive film. If this is not done, corrosion will run along the seam and the heat-affected zone even on 316L. The second risk is hot cracks and intergranular corrosion: against them, low-carbon or titanium-stabilised grades are used. Consumables, gas and parameters — in the article welding stainless steel.
12Х18Н10Т drilling parameters: tools and cooling
Drilling austenitic stainless steel is the operation where both the part and the tool are most often ruined. The reason is work hardening: if the drill slips or the feed is too low, the surface under the edge hardens, and the drill then goes through a hard layer. Hence the rule — do not "stroke" the metal but work with a confident feed and rigid fixation of the part.
| Parameter | Recommendation | Why |
|---|---|---|
| Tool | cobalt or carbide drills | withstand heat and do not sit on the work-hardened layer |
| Speed | lower than for carbon steel | less heat in the edge |
| Feed | do not keep it low, avoid slipping | does not let work hardening develop |
| Cooling | abundant, continuous | heat does not go into the chips |
| Rigidity | jig, vice, short overhang | runout accelerates wear and breaks the drill |
| Centring | centre punch or centring drill | the drill does not slide on a smooth surface |
Exact speeds and feeds are taken from a reference book or from the tool packaging for the specific diameter and grade: there is no universal table that would work the same way for 304, 316L and 201. In practice, a short pass without stopping at the bottom, frequent chip removal and a pause if the part has heated up all help. Reaming and countersinking after drilling are done at a reduced speed, otherwise the hole edge will harden again.
Drilling combined with threading requires separate attention: taps on stainless steel also heat up and break, so the hole is made slightly freer and lubricant is not skimped on. If the part goes into a food environment, after machining the surface is cleaned of chips and traces of lubricant.
Surface finishing
Finishing solves two tasks: appearance and hygiene. The catalogue includes the surfaces 2B, BA, mirror, №4 brushed, brushed, hot-rolled, calibrated and industrial. For interiors and appliances, the uniformity of the pattern matters more; for food equipment, a continuous surface without stagnant zones; for structures, industrial is enough.
| Surface | Appearance | Where it is appropriate |
|---|---|---|
| 2B | matt, even | general engineering, vessels |
| BA | light, smooth | decor, household appliances, medicine |
| №4 brushed | a directional pattern | interiors, cladding, equipment |
| Mirror | polished to a reflective finish | decor, visible elements |
| Hot-rolled | dark, with scale | structures where appearance does not matter |
After welding and cleaning, the surface is returned to its original class: first the scale is removed with a coarse abrasive, then a finer grit is used, and polishing is done with a separate tool. The same disc that was used to clean carbon steel will leave iron particles and ginger spots on the stainless steel. How to arrange the abrasive transitions and how №4 and mirror differ — in the article grinding and polishing of stainless steel.
It is better to state the range of surfaces in the order in the same way as in the certificate: 2B, BA, №4, mirror. Different suppliers put different meanings into everyday names, and "brushed" with one may mean a directional pattern, with another — simply cleaning. If appearance matters, a sample is agreed before ordering the batch.
How to choose a contractor
Look not for "someone who works with metal" but for someone who has a separate zone for stainless steel. A shared area with carbon steel is the main cause of surface contamination and subsequent complaints. The second sign of qualification is a willingness to show a sample after welding and finishing, not just a photo of the finished product.
What to look at when choosing:
- equipment for your thickness and grade, not a "universal" machine;
- separate tools and consumables for stainless steel;
- cleaning and pickling of seams in the process plan, not as an afterthought;
- clear acceptance: by sample, by edge, by surface class;
- willingness to work with low-carbon and stabilised grades.
It is useful to agree on acceptance in advance. It is usually built on three points: incoming inspection of the metal by grade and surface, inspection after welding and cleaning, acceptance of the finished part by sample. If the contractor is not ready to fix these points, a dispute about quality is settled by correspondence rather than by technology.
Ordering rolled steel and ordering processing are two different processes. The GCX exchange matches orders for physical metal: the grade, size, surface and shipment week are fixed in the order. Cutting, bending and welding services are agreed between the parties outside the platform; the exchange does not perform the work and does not assess its quality.
Frequently asked questions
Which operations are needed for processing stainless steel
The basic set: cutting, bending or forming, welding, drilling and surface finishing. The composition of operations depends on the grade, the thickness and the requirements for the edge. For food and wet conditions, cleaning and pickling of seams are added.
12Х18Н10Т drilling parameters — which to use
Exact speeds and feeds are taken for the specific diameter and tool from the manufacturer's reference book. The general rule: speed lower than for carbon steel, a confident feed without slipping, abundant cooling, the part rigidly secured.
What to cut stainless steel with
Laser, plasma, abrasive waterjet or mechanically. Laser gives a neat edge, abrasive waterjet does not heat the metal, plasma is faster on thick metal. After thermal cutting, the edge is cleaned of scale before welding.
Why does stainless steel spring back when bending
Austenitic grades return elastically after the load is removed. The angle is set with a margin, and the compensation is selected on a sample. The thicker the metal and the smaller the radius, the more noticeable the effect.
How does welding affect corrosion resistance
Heating changes the structure of the seam and the heat-affected zone, while scale and heat tint destroy the passive film. That is why the seam is cleaned and pickled, and low-carbon or stabilised grades are used for critical assemblies.
Can stainless steel be processed in a shared area
It is undesirable. Particles of carbon steel that get onto the surface produce ginger spots and trigger corrosion. Separate tools, a bench and abrasives are needed, as well as protection of finished parts from contamination.
What matters more when purchasing: the grade or the surface
It depends on the purpose. For structures, the grade decides; for food and wet conditions, the grade together with the state of the surface. A continuous clean surface without scale and foreign metal is often more important than the alloy number.
What to do next
Sort out the grade and the surface before ordering, so that processing does not reveal a weak point of the metal. Processing requires rolled steel with a clear grade: the GCX exchange offers pipe, sheet, round bar and angle made of AISI 201, 304, 316L and 430. The order fixes the grade, size, surface and shipment week.