What is the maximum thickness of JIS G4304 Stainless Steel Plate that can be welded?

Alright, let's start by getting real here-if you're someone who works with stainless steel, you've probably stared at a thick JIS G4304 plate at 2 a.m., wondering, "Wait, can this even be welded without turning it into a warped mess?" As a supplier who's fielded 100+ questions about this exact topic (no cap, not even exaggerating), I'm here to break down the maximum weldable thickness for JIS G4304 stainless steel plates-without the stuffy engineering jargon that makes your eyes glaze over.
 

First off, let's keep it simple: JIS G4304 is Japan's standard for hot-rolled stainless steel plates, right? Think of it as the go-to spec for heavy-duty stuff-like industrial tanks, structural parts, or marine equipment-where you need thickness and corrosion resistance. The grade most people ask about here is 310S, which falls under JIS G4304 (seriously, that's one of the most common plates we ship because it handles high temps like a champ). If you're hunting for that specific grade, you can check out our 310S UNS S31008 Hot Rolled Stainless Steel Sheet to see the details, but today we're zooming in on weldability, not just specs.

So, what's the maximum thickness we've seen people (and ourselves) pull off with JIS G4304? Let's start with the basics: weldable thickness isn't a one-size-fits-all number. It depends on three big things: the welding method you use, the grade of JIS G4304 plate, and what you're using the welded part for.
 

First, welding methods. For thin plates-say under 10mm-MIG or TIG welding works like a charm. But when you get into thick territory (we're talking 50mm+), you can't just hit it with a standard MIG gun and call it a day. The gold standard here is submerged arc welding (SAW), because it feeds a continuous flux that shields the weld from air, which is crucial for thick stainless to prevent cracking or contamination. We've seen fabricators pull off JIS G4304 plates up to 100mm thick with SAW, but only if they follow the right steps. Wait, but is that the actual maximum? No-there are shops that go thicker, but that's not practical for most jobs because of the work involved.
 

Now, the grade matter. JIS G4304 covers a range of grades-304, 316, 310S, even some duplex grades like UNS S44800 (we've got that in stock too, by the way). Grades with higher chromium or nickel, like 310S or UNS S44800, are more prone to weld cracking when thick, so you can't push them as far as, say, a lower-grade 430. For 304 JIS G4304 plates, we've successfully welded up to 80mm with good results, while 310S tops out around 60mm for most industrial applications. Duplex grades like UNS S44800, which are tough but tricky to weld, max out around 50mm-you have to heat them before welding to prevent that brittle phase from forming, which adds time and cost.
 

But wait, here's the catch: just because you can weld it doesn't mean you should. If you go too thick without prepping, you're gonna get warping, porosity, or that dreaded hot cracking. That's why we always tell customers: the "maximum practical thickness" is less than the absolute technical max. For most fabricators doing standard heavy industrial work, the sweet spot is 60-80mm for common JIS G4304 grades, with SAW and proper pre/post weld heat treatment.
 

Let's talk about some real examples, because numbers are cool but stories hit harder. Last year, a customer from a power plant ordered JIS G4304 310S plates for a furnace liner-they needed two 55mm thick plates welded together, and they were scared it would crack because of the high temp service. We helped them spec the right SAW wire, recommended preheating to 200°C, and post-weld heat treatment to stress relieve, and the weld passed all pressure tests. That's the kind of success we're talking about with thick plates. On the flip side, we had a small shop try to weld a 90mm 304 JIS G4304 plate with MIG-no preheat, no flux- and they ended up with three cracks, wasting $2k in material. Moral of the story: method matters more than just thickness.
 

Now, if you're working with thinner JIS G4304 stuff (like under 10mm), that's a whole different game-you can use TIG or laser welding, and the max thickness is higher in practical terms because it's easier to control heat. For example, a 20mm plate is no big deal with laser, but that's not what most people mean when they ask about "maximum thickness."
 

Wait, should we mention related products here? Sure, because we don't just do JIS G4304-we've got JIS G4305 Stainless Steel Plate/Coil for thinner applications, brushed stuff like the 201, 304, 316, 430, Etc. Brushed Stainless Steel Sheet for decor, even Golden Color Mirror Finish Decor Stainless Steel Sheet if you're doing something fancy. But back to JIS G4304: all the advice we're giving applies specifically to hot-rolled plates, which is exactly what JIS G4304 is for.
 

Another thing: don't sleep on material certification. JIS G4304 requires specific chemical compositions, and if your plate doesn't meet that, weldability goes out the window. We only stock plates that are certified to JIS specs, so you don't have to worry about that headache. That's why we're the go-to supplier for many fabricators-we don't cut corners on certs.

Let's get back to the original question: maximum thickness. Let's recap the practical, real-world numbers, not just lab tests:

• For standard JIS G4304 grades (304, 316): 80mm (with SAW, proper heat treatment)
• For high-chromium/nickel grades (310S): 60mm
• For duplex grades (UNS S44800): 50mm
• Any thicker than that, and you're into custom, specialized work that only top-tier shops can handle-and even then, it's not common because of cost and time.
   

Wait, but what about people who say they welded 120mm? Yeah, that's technically possible, but it requires multiple passes, constant heat monitoring, and way more labor. It's not something most jobs need, so we usually advise against it unless it's absolutely necessary. The risk of defects goes up exponentially over 80mm for standard grades, so it's not worth it.
 

Also, post-weld inspection is non-negotiable for thick plates. You need to do ultrasonic testing or liquid penetrant testing to make sure there are no hidden cracks or porosity. That's another thing we help our customers with-we can point them to trusted inspection services, or even provide guidance on how to prep the weld for testing.
 

Let me wrap this up with a few pro tips, because that's what you're here for:

1. Match welding method to thickness: SAW for >20mm, MIG for 10-20mm, TIG for <10mm
2. Preheat for grades like 310S and duplex-even if it adds time, it prevents cracking
3. Don't chase "max thickness" at the cost of weld quality-practical max is way more important
4. Use JIS G4304 certified plates to avoid weldability issues from off-spec material
    

If you're working on a project and need to check if your JIS G4304 plate will weld, or you want to place an order, don't overthink it-hit us up. We've got 10+ years of experience with these plates, and we can help you spec the right thickness, grade, and welding advice to get the job done right. Whether you need a small sheet for a prototype or a big plate for industrial use, we've got you covered.
 

And for all your stainless steel needs-whether it's JIS G4304, the thinner JIS G4305, brushed sheets, or even decor stuff like the golden mirror finish-we're your source. No hidden fees, honest advice, and material you can count on.
 

References:

1. Japanese Industrial Standard JIS G4304: 2019, Hot-rolled stainless steel plates, sheets and coils
2. Welding Metallurgy and Weldability of Stainless Steels, Kou, S., 2003, Wiley
3. AWS D1.6/D1.6M:2020, Structural welding code - Stainless steel
4. Material Data Sheet for UNS S31008 (310S) Stainless Steel, American Iron and Steel Institute (AISI), 2022
5. Duplex Stainless Steel Welding Guidelines, Nickel Institute, 2021