normalizing after forging

[thejackal3]

Dear Friends
required ur expect advice, we are OEM manufacturers of axle shafts and earlier we used to follow the same pattern of oem towards our domestic customers, but due to price appreciation and like many other bigs vendors we have to skip one process of Normalizing to save a substantial cost.many big oem vendors are not following normalizing aqfter forging of rear axle shafts for after market sale....my point is

1.is it necessary to do normalizing like we use 1541H steel
2.is there any alternate to normalizing?
3.what will be the effect on durability n strength of rear axle shaft if we skip normalizing....

rgds

 

[racookpe1978]

What does your contract call for?

 

[redpicker]

If you don't normalize after forging, you run the risk of inconsistent heat treat response on quench and tempering. Old school thought was that normalizing is cheap insurance for eliminating a common heat treating problem (which is true).

I have been in working for 4 decades and have only seen a few instances where normalizing was absolutely needed. Usually, cases where consistency of the heat treatment is paramount, such as for sour service steels above 100 KSI SMYS, or cases where (IMO) unnecessarily high Charpy Impact values were specified. I've seen a lot more cases where it (or a second Q&T operation) helped.

There are some issues that occur when the steel is exposed to forging temperatures and has an unpredictable cooling rate, most common is carbon segregation. This is worse with the high manganese steels. With the slow cooling that can occur coming off the forge, you can develop significant banding which can cause problems with your HT response.

One approach I have seen with some success is pseudo-normalizing. That is, austenitize the parts at 1750-1775F (Make sure you have an an aluminum-killed steel, preferably with Cb and or V). The higher austenitizing temperatures are needed as the lean bands are essentially ferrite, which won't austenitize unless you get it above 1670F. Yeah, some say 1750 is high, and it is, but you really have to hit a heavily banded structure hard to get it to transform. After you have a good soak at 1750F, let it cool to 1550 before oil quench. Quenching from 1750 is not advised; this is asking the oil to do more than it has to (remove more heat), which is not your goal. This will take a little more furnace time than a normal Q&T, but it will knock out a lot of the problems that arise when the normalizing operation is skipped.

Mind you, this does not produce the finest GS you could get, but in many cases, it will produce acceptable results.

rp

 

[tbuelna]

thejackal3-

1541H is hot forged at temperatures between 2200 and 1600 degF. The reason for normalizing after hot forging is to provide a controlled and uniform metallurgy in the forging at the start of machining operations. The conventional hot forging process does not allow for controlled cooling of the part. The 1541H blank/preform is simply heated to the required temperature (1600 to 2200 degF), subjected to the forging operation, if necessary reheated and subjected to further forging operations, and finally set aside to air cool.

The typical recommended processing for hot forged 1541H is normalize at 1650degF and air cool, anneal at 1525degF and furnace cool to 1200degF at a rate of 50degF/hr or less, then rough machine. If you want to skip the post-forge normalize operation to save cost, then I'd assume you will skip the post-forge anneal step also, right? Just be aware that by skipping these heat treat operations your finished 1541H component will have lower quality. I've attached some information showing the effect on 1541H metallurgy due to various heat treat conditions.

There are some steel alloys similar to 1541H available that are designed for direct quenching immediately after hot forging. So you might look into using one of them if processing cost is your concern.

Hope that helps.
Terry

 

[dbooker630]

Depending upon section thickness you may have machining issues with turning and drilling/punching holes due to high hardness areas. With this grade I have seen areas of Brinell 270 HB in the sections while the body was only 207 HB. A normalized structure also aids in uniform response to induction hardening although i

 

[weldstan]

Re question 3; the range of predicted failure will be increased.

 

[arunmrao]

In my country, there is a difference between OE supply and after market. In the later, the barrier is lowered a bit. This helps in getting a market friendly price for the spare parts and enables to compete with products from China.

Perhaps, this must have motivated the jackal3's company to suggest avoid normalising for after market parts.I agree with the previous posts of the benefits of normalising a forging.

 

[dbooker630]

At our company we do not have separate specs for OEM and aftermarket. Why should the aftermarket be treated any different, especially with a safety-related component like an axle shaft, where if the shaft breaks someone can get seriously injured if not killed.

 

[TVP]

Good contributions from the others so far. I just wanted to add to dbooker's comments regarding induction hardening. 1541 can be quite banded after hot rolling or hot forging (slow cooling from high temperatures), and will have uneven response to induction hardening, meaning low surface hardness, low case depth, or both. If the microstructure is controlled after forging, then perhaps you can eliminate normalizing, but this is not always the case.

 

[tbuelna]

The subject of cost in an OEM part vs an aftermarket part is interesting. I would think the OEM part would be more cost sensitive than the aftermarket part. OEMs are very good at minimizing component cost by wringing every last bit of performance out of a lower cost material (like 1541H) through optimized manufacturing processes like heat treat cycles.

The material and processing OEMs use for a given component are usually highly optimized for a specific application. If you use the same material for a component, but skip some of the processing steps to save cost, you should not expect to get equivalent performance from the finished component. As others noted, skipping the normalizing step can result in inferior microstructure in the finished component. And this can affect fatigue life of the shaft. Lower overall statistical fatigue life in your aftermarket shaft product can result in higher warranty replacement costs. It would be interesting to see the results of a trade study comparing the cost savings of skipping the normalizing step versus any impact from higher warranty replacement costs due to reduced service life of the shafts.

 

[CoryPad]

Terry,

You are correct, the OEM parts are more cost sensitive and there are more efforts used for cost optimization. Sometimes aftermarket parts are made to lower requirements to increase margin for profitability, especially if the expected lifetime is lower (e.g. only a fraction of the entire vehicle's life).

Cory