{"id":180557,"date":"2026-01-19T11:26:57","date_gmt":"2026-01-19T11:26:57","guid":{"rendered":"https:\/\/stalesia.com\/knowledge-base\/how-to-tell-316-from-304-stainless-steel\/"},"modified":"2026-01-19T11:26:57","modified_gmt":"2026-01-19T11:26:57","slug":"how-to-tell-316-from-304-stainless-steel","status":"publish","type":"post","link":"https:\/\/stalesia.com\/en\/knowledge-base\/how-to-tell-316-from-304-stainless-steel\/","title":{"rendered":"Acid-resistant steel vs ordinary stainless \u2013 how to tell 316 from 304"},"content":{"rendered":"\n

In a stockyard, two pipes can look identical: the same shine, the same diameter, almost the same price per metre. One is grade 1.4301, the other 1.4404. You cannot see the difference with the naked eye, yet it can decide whether an installation lasts for years or starts to corrode after its first season in contact with brine. So how do you tell “acid-resistant” steel from ordinary stainless?<\/p>\n\n\n\n

First, a word about names<\/h2>\n\n\n\n

Formally, both are stainless steels \u2013 EN 10088 does not recognise “acid-resistant steel” as a term. In Poland, though, the trade commonly splits stainless into two groups, and we explain where that comes from in Stainless or acid-resistant steel?<\/a> In workshop and trade usage, “ordinary stainless” usually means chromium-nickel steel of the 304 type (1.4301<\/a>, 1.4307<\/a>), and “acid-resistant” means molybdenum-bearing steel of the 316 type (1.4401<\/a>, 1.4404<\/a>, 1.4571<\/a>). That is the convention used in the rest of this article.<\/p>\n\n\n\n

What really separates them \u2013 molybdenum<\/h2>\n\n\n\n

The difference comes down mainly to one element. According to EN 10088, grade 1.4301 contains 17.5\u201319.5% chromium and 8\u201310.5% nickel, and no molybdenum at all. Grade 1.4404 has slightly less chromium (16.5\u201318.5%), more nickel (10\u201313%) and 2\u20132.5% molybdenum.<\/p>\n\n\n\n

Molybdenum strengthens the passive layer where it is most vulnerable \u2013 in the presence of chlorides. That is why 316-type steel copes much better with seawater, road salt, pool water, chlorine-based disinfectants and many of the acids used in the food and chemical industries. The PREN, used to compare resistance to pitting corrosion, shows this clearly.<\/p>\n\n\n\n

Property<\/th>1.4301 (304)<\/th>1.4404 (316L)<\/th>1.4571 (316Ti)<\/th><\/tr><\/thead>
Chromium<\/td>17.5\u201319.5%<\/td>16.5\u201318.5%<\/td>16.5\u201318.5%<\/td><\/tr>
Nickel<\/td>8\u201310.5%<\/td>10\u201313%<\/td>10.5\u201313.5%<\/td><\/tr>
Molybdenum<\/td>\u2013<\/td>2\u20132.5%<\/td>2\u20132.5%<\/td><\/tr>
Carbon (max.)<\/td>0.07%<\/td>0.03%<\/td>0.08%<\/td><\/tr>
Stabilising addition<\/td>\u2013<\/td>\u2013<\/td>titanium<\/td><\/tr>
PREN (approx.)<\/td>18\u201320<\/td>23\u201328<\/td>23\u201327<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

What you cannot see with the naked eye<\/h2>\n\n\n\n

The surface tells you nothing about the grade. Shine, grit finish and tone depend on the finish \u2013 2B, BA, K240 grinding \u2013 not on the chemical composition. Weight won’t help either: the densities of the two steels differ by about 1%, which you cannot feel in a stockyard.<\/p>\n\n\n\n

The magnet test \u2013 what it shows and what it doesn’t<\/h2>\n\n\n\n

The popular magnet test separates austenitic steels from ferritic and martensitic ones, but it does not separate 304 from 316. Both 1.4301 and 1.4404 are practically non-magnetic in the solution-annealed condition. A magnet will, however, attract ferritic steels such as 1.4016<\/a> and martensitic steels such as 1.4021<\/a>.<\/p>\n\n\n\n

There is a catch. After cold forming \u2013 bending, drawing, rolling \u2013 grade 1.4301 can become slightly magnetic, because part of the austenite transforms into strain-induced martensite. Grade 1.4404 has a more stable structure and is less affected. So a slight pull on an elbow or a drawn tube does not mean it is “ordinary steel” or a fake.<\/p>\n\n\n\n

The molybdenum spot test<\/h2>\n\n\n\n

The simplest workshop method is a molybdenum detection reagent. A drop of reagent is applied to a cleaned surface \u2013 some kits assist the reaction with a small electric current \u2013 and a colour change indicates molybdenum. The test is cheap and fast, but it has its limits: it tells steel with molybdenum from steel without it, it does not give the content, and it cannot tell 1.4401, 1.4404 and 1.4571 apart.<\/p>\n\n\n\n

XRF analysers and spectrometers \u2013 a definite answer<\/h2>\n\n\n\n

Plants and laboratories use handheld X-ray fluorescence (XRF) analysers for PMI (Positive Material Identification<\/em>). In a few seconds, and without damaging the part, they show the content of chromium, nickel, molybdenum or titanium, so they easily tell 1.4301 from 1.4404 and 1.4571.<\/p>\n\n\n\n

XRF does not measure carbon, however. To tell a low-carbon version (1.4404, 316L) from a standard one (1.4401, 316), you need an optical emission spectrometer (OES) or a laboratory analysis. This matters above all in welding \u2013 see our guide to welding stainless steel<\/a>.<\/p>\n\n\n\n

The most reliable source: marking and inspection certificate<\/h2>\n\n\n\n

Before reaching for reagents, check the markings and the paperwork. Mill pipes, bars and sheets are usually marked \u2013 the print or stamp gives the grade, standard, size and heat number. The heat number links the item to a 3.1 inspection certificate to EN 10204, in which the producer states the actual chemical composition and mechanical properties of the batch.<\/p>\n\n\n\n

If the material is going somewhere the grade matters \u2013 the food, pharmaceutical or chemical industries, or structures by the sea \u2013 it is worth ordering the 3.1 certificate straight away. In our shop it can be added to an order as a paid extra. Also look out for multi-grade designations such as “1.4401 \/ 1.4404 \/ 316 \/ 316L” \u2013 we explain them in which grade do you actually get?<\/a><\/p>\n\n\n\n

When do you need 316, and when is 304 enough?<\/h2>\n\n\n\n