Yield Strength and Wear Properties of Steel 5

[afarian]

Could someone offer me some advice on the "wear-ability" of steels of varying grades? (i.e. 80ksi vs. 50ksi vs. mild steel) Is there any correlation between yield strength and "wear-ability"? Thank you.

 

[CWIC]

I don't the material properties you've mentioned ("wear" and "yield") are directly related. However, other properties can be correlated with each other such as tensile and yield or wear and abrasion.

 

[metengr]

CWIC is correct. To attempt to generalize wear or "wear -ability" using several material property parameters is an inaccurate approach. First off, you have several different wear mechanisms; such as erosion, erosion/corrosion, abrasion, and sliding damage. Each of these mechanisms has their own set of parameters that directly affects wear rate - material composition, material properties, the medium or environment, the load between two components sliding against each other, velocity etc.

For each wear mechanism, you could probably find information in reference books on Tribology or by using the internet that would descibe what variable(s) have a direct affect on wear rate of materials.

 

[afarian]

Thank you CWIC and metengr for your quick responses. I'm sorry but I guess I left out some details that were pertinent to my question.

The wear I'm talking about is of the "abrasion" and "sliding damage" nature. I am considering changing the material for my application from an 80 ksi yield strength to a 50 ksi yield strength. It was brought to my attention that maybe this wasn't a good idea because this part is continuously rubbing against another, even though there is grease in between the two parts to reduce friction. All our experience has been with the 80 ksi yield strength material so far and I was trying to get a feel for some of the concerns that were raised when I made my suggestion.

metengr, forgive my ignorance and thanks for the tip on Tribology. I will look it up.

 

[CWIC]

Abrasion resistance of steel typically requires one or two
additional processes to achieve this property:
1.) Apply some type of interface between the concerned parts such a abrasion resistant material applied to the base metal by hardfacing (welding, thermal spraying or cladding).

2.) Heat treatment can help but not as much as the previous method. 1045 is not an abrasion resistant material.

If you decide to go with recommendation no:1 above, make sure the hardfacing material is designed for abrasion and not impact. These are often two different materials, but not always. Also, make sure the hardfacing material applied is of the machinable type. There are hardfacing alloys available in for machinable welds and non-machinable welds.

Good luck and let the forum know how you came out with your modification/repair.

 

[EdDanzer]

More information about the application would help. If 2 pieces are sliding, or rotating and there is very little abrasive contamination, hardness or yield strength will have little effect if adequately lubricated.

 

[afarian]

EdDanzer, the application is the lower, front, bottom surface of a semi-trailer which gets bashed by tractors picking up the front of the trailer to engage to it's "kingpin". After picking it up the coupled vehicle goes down the road with a lot of sliding radially on every turn as well as the constant small movements due to the somewhat loose coupling mechanism.

The problem is two-fold: 1) the pick-up interaction between the trailer and the truck, and 2) the slipping and sliding as the coupled vehicle is in operation. Both of the above will try to wear on the interacting surfaces. These days 80ksi yield steel is becoming less available and more expensive, hence the consideration to change to the more abundantly available 50 ksi yield steel.

While I know that the wearing of the surfaces in contact can be minimized by the lubricants present in the joint, I can't count on everyone using their equipment exactly as it was intended. The trucking industry is not so perfect which makes me design with the worst case scenario in mind.

This is my first time on this Web site and I am quite pleased with the speed which with I have received your responses. Thank you all and I hope I can return the favor to some one one day. In addition, I will let the forum know when we finalize this decision.

 

[NickE]

Personally I dont think that a 50ksi yeild will have the hardness required for good performance in the application you describe. I think that you might want to use hardness as a better descriptor of performance in your application.

nick

 

[CWIC]

afarian:
Having being a heavy equipment welder/mechanic in my younger days, this is a problem as old as the industry itself. The entire 5th wheel (kingpin) assembly gets a lot of beating during service and coupling. This application is subject to abrasion, shear, fatigue, tensile and impact loads. I know, I beat up a few moving tractors and trailers to the work area.

If you can develope a system/method to mitigate this problem, you will probably retire early.

 

[afarian]

NickE, I was thinking along the same lines you suggested, looking at hardness, so I looked up various yield strength steels with published hardnesses and ran a quick-and-dirty regression analysis and found a positive slope with a 94% R-squared value. In a round-about way, I ended up answering my original question of the yield strength to wear-ability relationship, provided it is a safe assumption that hardness is directly proportional to wear-ability. IF any one feels this is NOT a good assumption, please let me know.

Now the $64,000 question: Is a lower hardness material high enough for this application? I guess that's why we engineers get the big bucks, right?!?

 

[diamondjim]

Looking at sliding wear on gears,
the charts seem to be related to
hardness. It also seems to be of
some advantage to have the materials
not of the same hardness to reduce
the welding phenomenom. Possibly you
could shot peen the interfaces as
well before assembly ie work handening
these surface. I do not think it would
be that expensive to induction harden
or hard coat the interfaces.

 

[metengr]

Afarian;
We recently had some coal barges that required rub plates to be fabricated to reduce susceptibility to wear damage from impact and abrasion. The following web site is where we had purchased this abrasion resistant plate material. It is made by a Swedish company that provides it in a quenched and tempered condition - hardness with good toughness. It has excellent weldability and formability.

http://www.hardox.com/us/default.asp

 

[stanweld]

Without appropriate surface treatment, the 50 KSI material is expected to have less resistance to wear. Have you thought of using T1 high strength steel for the application or abrasion resistant steels like AR400?

 

[unclesyd]

You might talk to these people about Astralloy V for your application. I don't know if it has been used in this application or not. We have used this material in several applications that required toughness as well as wear resistance.

http://www.astralloy.com/products/av/astralloy-v.asp

 

[NickE]

Guys- not to rain on your excellent suggestions but:

They are currently using a steel w/ a yield of 80ksi. This sounds like an HSLA steel. (IE 980xf for example) If they're having a hard time getting material its cause we all are. The problem is not that their current material is not working well or wearing out quickly. Its that they want to go to the more available and cheaper 50ksi yield grades. (IE 950xf)

I really dont see why they would want to go to a highly alloyed steel from their current material. All they would do is significantly increase cost over the current working material.

If I am way off base here let me know.

[NOMEX suit]
nick

 

[afarian]

Guys, I really do appreciate all the great ideas but NickE actually hit the nail on the head precisely with his analysis of the situation. The problem is price and availability or else I wouldn't be in this situation in the first place.

By the way, metengr, we have looked at some of the higher strength Swedish steels for different applications but that again exposes us to international risks that we are barely exposed to now. That's not to say we never will try them. Another issue is volume. We use a whole lot of steel and I'm not sure how much volume consistently they can support.

Our industry is just not that cutting edge. It's a very mature industry with trailers basically considered as commodities--box-on-wheels. Margins in such a mature industry are VERY tight and that is why I think innovation is squelched. Companies just don't see the payoff in taking the risk because the ones that have tried in the past have had their noses chopped off. I haven't had my nose chopped off but I can imagine that it doesn't feel very good!!

 

[EdDanzer]

Afarian,
The hardness and material of the 5th wheel is something to look at. If cast iron is the mating material, the plate hardness will not matter. The primary concern will be thickness, to thin and it will dent and crack when connecting the trailer. I have seen this plate dented and cracked on some used trailers.

 

[afarian]

EdDanzer, could you please elaborate on the cast iron point you made? Why is this so? Because we do have experience with the current thickness and it hasn't been an issue. I am presuming that the plate is thick enough to avoid the denting and cracking problem you mention.

Based on what I know of our experience with thickness of the plate and the 5th wheel being cast iron, it seems as though I don't have an issue here. Would that be a reasonable conclusion?

 

[EdDanzer]

Afarain,
Higher strength material will spring back in place when deformed with a higher load than a lower strength material. To eliminate the over deformation of the lower strength material it must be thicker.
Cast iron is used in hydraulic cylinders for the head and piston, as well as low speed plain bearings. Cast iron tends to not gall against steel if any lubrication is available. It might help to know the yield strength of the cast iron.

 

[CWIC]

I put another star next to NickE for sticking to the topic. afarian is trying to solve an existing ptobelem using the same materials and is not seeking a replacement or redesign. Many of the parts used for this application are typically cast steel pieces.

The topic of steel availabilty should be affecting any product or service steel-related. It is a good comparison to the price of a gallon of gas. Products which rely on gas to get it to market is also impacted by the price of gas. This is public knowledge. Many manufacturers are now seeking alternative material specifications due to the rising cost and availabilty of metals.

Some of my clients are now looking for alternative materials for the very same reason that afarian is.