High Tensile Steel

Consider 4130, it is weldable with manageable pre and post weld heat treatment and should be able to be Q&T to reach well over 100KSI in decent section thicknesses. My old EM Jorgensen book from the 1976 shows it topping out at just over 190KSI and 460 Brinnell if the section thickness and tempering time/temp can be met depending on part geometry etc. The chart I'm looking at is for a 1/2" round, normalized at 1600F, quenched from 1575F in water then tempered at 400F to reach it's maximum hardness/strength. Higher Tempering temps (and therefore shorter cycle times) will result in lower strengths, but the same section thickness tempered at 1100F still gives 122.5KSI. This falls off with thickness too, a 4" round tempered at 1100F only gives a yield of 77KSI, a 2" round gives 91.5KSI and a 1" round gives 113KSI. It is through-hardenable in section thicknesses up to about 2" or so (thinner is better in this as shown above). Of course the lower tempering temp you use, the longer you have to keep it in the oven so it can get really cost prohibitive if you shoot for the max. You also start lowering the elongation and reduction in area (and cold toughness) possible with such long tempering times. 900F still gets you over 110KSI yield with good RoD (63%) and elongation (19%) in section diameters up to 2" and a hardness in the 28 HrC/269 Brinell range and an Izod of about 76.

It is a big shaft (diameter 16").

The application is the planetary carrier of a big gear box. The best I could find is 8620 may be normalise after fabrication?

The other (original) option was going for SGI Grade 70 (700 MPa), but the problem is the defects in the supplies that we are recieving.

Seriously consider then a redesign that eliminates the need to weld. (bolted on or shrunk on bits for example).

8620 won't get you anywhere NEAR there. not enough carbon. you'll only get about half the strength of what you need, 4130 would still be better than 8620. Thing about it is that most of your strength will be in the outer third of the shaft where it will be doing the most good. if you can eliminate the need for welding through a redesign 4140, 4340, or 6150 would get you pretty close.

you could consider looking at a precipitation hardening grade, or even a PH type nickel super alloy but they aren't going to be cheap in that size.

bolted on or shrunk on bits was already considered.

Infact like the turbines - we thought about putting HT studs and tensioning. But the gear box is so compact that the bolt head can not be accommodated.

I may be trying out 4130 - since the carbon is just about weldable. Also let me see whether my metallurgist/ R&D persons come up with something better.

Good morning Guest.

Weldability and tensile strength are reverse correlated in steels.

The higher the carbon, the higher the strength; The lower the carbon the easier the welding.

I wrote a blog on this subject here.

You can do the calculation for carbon equivalent for welding using the formulas in my post.

You do not say if you need the tensile strength to be the result of a particular microstructure. We can get to 700Mpa by cold work, martenite, or bainite structures.

Is it possible to use an inertial or friction welding process and avoid the large thermal shocks to the entire assembly? if you are limited to martensite structures this may be a way to join them.

I guess that another question that I have is can another type of mechanical assembly method be used?

Cold drawn (heavily cold worked) 1045 steel will be above 700 Mpa in most sizes below 1-1/2" in my experience. As hot forged if the 1045 steel came from an electric furnace minimill it will be pretty close to that 700 Mpa as forged; 1050 likely would exceed it. Any way to attach such forgings using threads?

There is a bainitic answer if your need is commercial and not hobby use or maintenance small quantity application.

Is your quantity such that you can purchase commercial quantity?

From Japan?

if so this low carbon microalloyed bainitic steel might do the trick

http://www.jfe-steel.co.jp/archives/en/ksc_giho/no.47/e47-035-041.pdf

Yield 680 Mpa, TS 810 Mpa; Excellent toughness, excellent weldability. Go directly to the conclusion on pdf page 6 of 7 to see the answer that you seek.

I do not know a US source.

Good luck.

milo

The situation is a bit complex. The CEq portion I am aware that's why this query here since some out of the box alloy has to suit.

Requirement is a forging with flange (shaft approx 12" to 16" and 16-18" long) one side is a flange 4" thick and 36" diameter). (At this size can not be hobby , it is purely professional) And it is a considerable quantity. may be somewhere around 100-150 pcs per year.

Bainite is a new thread of thought. But availability of this material may be a problem. The organisation/management prefers local suppliers (limited to the country/ may be neighbours at the maximum ) Of course if not available may be forced to go to Japan.

Let me try out 4130 first. Of course some other ideas are there from the metallurgists - to go for some annealed steels, more weldable in that condition, then after welding refine the grains to improve the strength.

We may try out a trial sample for both the models and then finally freeze the WPS/PQR as well as PWHT process, based on the optimum (lowest final cost for the strength) - unless some other ideas come up from here. from our R&D staff.

A few has come up already from them, but none will suit on cost angle, one is for nano and other is for a special steel (these we use for the compressor disks and turbines - weldable - but very high cost may be due to the creep properties, that bonus we don't need in this product)

"to go for some annealed steels, more weldable in that condition, then after welding refine the grains to improve the strength."

I'm not sure that I agree with either premise.

The annealed steel will have less stresses in it so less possible movement upon stress relaxation as the work heats up in welding operation, but i don't know of any other reason that "annealed is more weldable" than as forged or as cold drawn or whatever.

The post weld heat treatment is not to refine the grains per se, it is to 1) relieve stresses created during /from the welding process, 2) possibly help outgas trapped hydrogen, and to 3) temper any martensite that may have been created in the Heat Affected Zone (HAZ). This is why you do it on higher carbon and alloy steels!.

At least, thats my take. The time and temperature for the post weld thermal treatment isn't sufficient to"refine" grain structure; permit grain growth- nor would you want it!.

milo

BTW also here infact 4340 was our first target.

Welding:

Readily welded annealed but avoid when possible if hardened and tempered due to its effect on the mechanical properties. Welding if nitrided, flame or induction hardened is not recommended.

I get it.

When you mean full quench and temper of the entire weldment as PWHT then you will be fine.

I won't argue with your sources (over the annealling preference for welding as opposed to hardened and tempered) if in fact the entire weldment is not going to be re- Q&T as you are describing as your plan. What they are saying is true about affecting mechanical properties of the hardened and tempered material.

However, other conditions that can be welded in my mind are normalised, hot rolled as rolled, and cold drawn, or annealled cold drawn. Plain carbon grades to 0.50 Carbon are often available cold drawn unannealed in North American commercial practice; Alloys typically get the anneal if carbon is above 0.40 wt %. In my experience.

Good luck with your project.

milo