20 questions about welding - SSAB

How to weld > 20 questions about welding

20 questions about welding

1. What is welding?

Welding is a family of methods used for joining two workpieces; steel in the case of SSAB. Usually a single heat source, normally an electrical arc, locally melts the two workpieces to form a common liquid pool. When the steel solidifies, the pieces are joined. In many cases, a special steel rod or wire (consumable, filler) is melted into the weld pool to get a good weld joint.

Check now

2. What are the most common welding methods?

The most common welding methods are Shielded Metal Arc Welding (SMAW) more commonly known as MMA or stick welding, Tungsten Inert Gas (TIG), Gas Metal Arc Welding (GMAW) more known as MIG/ MAG welding, submerged arc welding (SAW) and laser welding.

3. Can different welding methods be combined?

Yes. A typical example can be to weld the root pass with TIG and fill passes with MIG/MAG. 

4. Can all steels be welded?

Yes, but it is more challenging to weld some steels than others, depending on alloying and dimensions.

5. How can different steels be welded together?

Welding methods and parameters must be suitable for both steels. Usually, the least weldable steel determines the parameters to be used. 

6. What are the welding consumables?

There is a vast number of consumables. The steelmaker provides advice on these for their different grades. For SSAB steels, see the welding recommendations.

7. How is steel preheated before welding?

Workpieces can be preheated in a furnace with an oxy-fuel flame, with electrical heating mats or with electrical induction. It is crucial not to exceed the maximum temperatures given in the data sheet for the steel grade to be welded. Too high a temperature may negatively affect the properties of the steel.

8. How is welded steel postheated after welding?

Steel workpieces can be preheated in a furnace with an oxy-fuel flame, with electrical heating mats or with electrical induction. It is crucial not to exceed the maximum temperatures given in the data sheet for the steel grade involved. Too high a temperature may negatively affect the properties of the steel.

9. How much hydrogen is allowed in the welded joint?

A rule of thumb is a maximum of 5 ml hydrogen per 100 g weld metal. However, this is in practice not possible to measure. The hydrogen content in solid wires for MAG welding is typically around 1.5-2 ml hydrogen per 100 g weld metal, while cored wires can pick up moisture in the flux which might increase to higher values per 100 g weld metal. Keep all consumables dry and warm, in particular flux-covered and flux-core ones. Packages should be opened shortly before use. 

11. What steels can be welded using hardfacing?

Hardfacing is a procedure where a harder material is welded to the base metal surface to create a protective layer. The method can be applied to all SSAB steels, but for the hardest ones, a soft buffer layer must first be welded on the base plate to reduce the risk of cold cracking into the base plate. All types of conventional welding processes can be used for both the buffer layer and the hardfacing layer.

You will get efficient and thoughtful service from Chuangdi.

12. Can welding be done on the primer?

Yes, it can. However, the primer will increase the porosity in the welded joint. A high-quality weld calls for complete removal of the primer in the welding area. 

13. How much hardness or strength is lost after heating the material?

Hardness deterioration is difficult to control. The maximum heating temperatures stated in the data sheets of the steel should always be respected.

14. What is the heat-affected zone (HAZ) of steel?

The heat-affected zone (HAZ) is close to the welded joint where the temperature has increased temporarily due to the liquid weld pool. HAZ size depends on the heat applied. The mechanical properties of the base steel in the HAZ may change, usually in a negative direction. 

15. How big should the throat thickness be for fillet welds?

The designer has chosen a suitable plate thickness for the expected structural stresses. A rule of thumb is that the throat thickness is equal to the plate thickness for a one-sided fillet weld. For two-sided fillet welds, the throat thickness should be approx. 0.7 times the plate thickness.

16. Why does the plate deform after welding?

Plate shrinkage in the vicinity of the welded joint will vary due to varying peak temperatures and residual stresses of varying sizes will appear. Thin plates will react with deformation and relaxation of the stresses, while the stresses will prevail in thick plates.  

18. What are hydrogen cracks?

Hydrogen cracks in welded joints can form due to the concentration of hydrogen in the material close to the weld, as hydrogen embrittles the material. Hydrogen atoms in a hot welded joint will diffuse and collect at “comfortable” spots, e.g. microdefects in the microstructure. Hydrogen gets trapped when the joint cools. Cracks can initiate from those hydrogen traps after hours or even days. The inevitable residual stresses will elongate the cracks. High hardness and alloying make steels more sensitive to hydrogen cracking. 

19. What can cause a welded joint to fail?

There are many factors that could cause a welded joint to fail. The most common ones are defects in the form of physical discontinuities, poor microstructure, and residual stresses. There are various reasons behind those factors, including choice of design, joint type, joint geometry, welding process, heat input, preheating, and welding consumables. 

Category and tags

How to weld 20 questions about welding

Contact Technical support

For more Welded Mine Screen(ru,fr,rm)information, please contact us. We will provide professional answers.

Hi all:
New to the forum. Looking for some recommendations on what to buy. Would like to be able to weld Metal/Steel, Aluminum and Stainless. Mainly for fixing broken things but also to do some small projects. Don't think I will go past 1/4" thickness very often. Took stick welding (80 hours) and gas welding/cutting torch (80 hours) courses about 40 years ago in Germany but haven't done much welding in the last 10 years. Contemplating if I should go for gas MIG or TIG.
On some other forums I saw the recommendation to get a 240 Volt (or 110/240 Volt) stick/TIG machine. Uncertain if I will use it very often so also looking for low cost of ownership. Don't have any experience how expensive it is to maintain a gas bottle (certifications, etc.). Want to spend as little as possible but willing to spend as much as necessary to get a good solution. Where to go in Calgary for welding machines and supply? Much appreciated!
Thanks,

Gunter

Well there is lots to think about.
I have a Thermal ARC 186 ) ac/dc (Tig and stick with pedal and dial current control on torch ) and a Mig Lincoln 140C (commercial version). Sometimes I wished I had one that did TIG/Mig/Stick as one. The Thermal is 240v hence thicker welding and the Mig is 120v. The 140c has option for spot but they want 400 for a small IC board. I am of the thought to get one with as many options that are available withing your price range. Once you have it and get use to it you will be surprise how often you can use it. You will also find that Oh I should have got that one extra option. Example would be the single pulse option on my TIG or Mig that is not or no longer available. I use the the Mig with gas but also use the flux core if outdoors (use vegatable spray on parts) it a none hazzard way to keep splatter off parts.
So a unit that is both 240 and 120, Tig AC/DC (ac for aluminum). You have to use a stiffer aluminum wire like ER. Just google on how to. I would also suggest that a name brand and at a local store if possible is by far a better option because if say you buy from Princes Auto (nothing against PA) but if it breaks after warrenty forget about getting it serviced. The best piece of welding advice I can give is "practice". I took the full course at a local community college on Sundays. Did all courses in stick (then did MIG) as if I was going to take the test to become certified. I can tell you the only difference between day 1 of the course and day last is burning rods and the teacher showing you "tricks" and "positions" to get better welds. I have a small DC inverter stick from Princess Auto (goes on sale for $99 from time to time.) Great for small jobs. I have a Lincoln 180HD for all other welding (including a spool gun for Aluminum) If I'm telling you mild steel needs practice, Aluminum needs more. A lot more. That metal just wants to MELT! I've actually had more success "brazing" aluminum (with solder and clean aluminum) Tried my hand at "welding" aluminum with my O/A, aluminum tig rods and solder. It wasn't bad. But again... practice and patience! I don't use O/A goggles, just my welding hood.
I believe that a great welding helmet is your best step towards good welding (or brazing).
A great welding hood will not make you a great welder. I am a poor welder with a great welding hood.
My eyes are rather important to me. OK - EXTREMELY IMPORTANT - to me. I want (NEED) the best protection I can get for my eyes!
In my shop, I wear safety glasses. When using the chop saw, bench grinder, or hand disc grinder, I also wear a face shield.
I was a Bronze Medalion lifeguard at age 15.
I was an EMT (Emergency Medical Technician).
I have saved at least 2 lives in my career.
I was the Safety Director and Leader of the Mine Rescue Team at a coal mine.
Safety is in my blood.
I have had 3 Optrel welding hoods. I upgraded as better models came along. They are made in Switzerland.
Optrel is the leader in welding hood technology.
I now have the Optrel Panoramaxx CLT.
The CLT is not just the best welding eye protection you can get (IMO) but the CLT also allows you to see the colours in the puddle. Suttle changes are easy to distinguish. Fantastic for TIG. Also awesome for plasma cutting since the CLT goes to shade level 5. Yes this thread has grown with lots of good comments about welding from several experienced welders (trained & certified not just self-taught hacks like me). IMO moving to tips & tricks section is a good idea. (make it so @Susquatch)

Yes there is an industry standard for the welding hood darkness. Most commonly used shades range from shade 9 to 11 but also go up to shade 13 for the darkest shade. There is likely a chart available somewhere. Auto darkening hoods will automatically switch to the appropriate shade for the optimal protection while maintaining good visibility of the weld puddle. Shade 4 or 5 is common for plasma cutting.
More expensive auto darkening hoods will have lots of control over the parameters like: amount of darkening, sensitivity, initial delay, and how quickly or slowly the darkening turns off. Premium hoods will show colour changes in and around the puddle (which is great for TIG).
Premium hoods also offer a PAPR version (Purified Air Purifying Respirator) which supplies a filter air supply to the hood. The PAPR option is normally about a $ extra. I started with a mig welder, mostly for some stairs and factory-style windows I was doing for a project. I was told TIG was just too slow or difficult.
I hate grinding, even more so with a carbide burr to get a nice architectural finish.
6 years or so I got an Everlast 250ex and have barely touched my mig since, except for a trailer repair, which I could’ve done with TIG anyway.
I’ve done a fair bit of autogenous welding (without filler) and much prefer not grinding. Stainless, aluminum, bronze and even brass. If you can solder you can TIG.
I overheated the torch once (I should’ve used the water cooled torch) bought replacement parts easily in Burlington and had no problems at all with the unit.
Speed is usually not an issue for me, nice looking welds are.
I wouldn’t do a large project with TIG that could be done with MIG, except to get the experience, and to avoid sparks flying everywhere (main reason I like TIG)