Air quenching steel for fine pearlite

[twistedneck]

Seeking high ductility, fatigue and hardness in a spring element. Air quenching is obviously the most efficient and least expensive method.

I'm looking for fine pearlite (ferrite+cementite).

Wondering what size 'fine' really is. i've seen 3microns called fine, 50 microns called 'impossibly fine' etc.

Help needed! thanks.

 

[swall]

I have to question your criteria for a spring element. The usual spring steels, in wire form, have good toughness at high hardness to work as a spring in most situations, and they are martensitic for max strength and resistance to relaxation, i.e. taking a set. What is your configuration and what steel alloys are you considering?

 

[twistedneck]

Swall, usually i would consider standard quench and tempered martensite for a highly stressed spring element. however in applications were there is not a continuous stress (a car spring is ALWAYS under stress) or in situations where there is no change in ride height like a coil spiring slight setting would cause - along with low peak stress.. air quenching is cheap and fine pearlite is proven.. to a point.

I'm considering both micro alloy (1541v) becuase i know that can air harden in still air pretty good (350BHN) but that is a penny more per pound than somehting 1090M or 1090H. Not sure why they would modify 1090 for air quench, but its what i've got so far.

Also, I'm considering 1065. Goal is fine pearlite, good hardness - above 300BHN min, and low loading fatigue performance (100k cycle type).

Thanks for responding!

 

[TVP]

Are you planning to hot wind the spring, and then heat treat afterwards to develop the desired microstructure? Otherwise you could just start with a pearlitic wire which will be essentially free from ferrite and have lamellae thickness < 1 micrometer.

 

[twistedneck]

TVP Wrote: "Are you planning to hot wind the spring, and then heat treat afterwards to develop the desired microstructure? Otherwise you could just start with a pearlitic wire which will be essentially free from ferrite and have lamellae thickness < 1 micrometer."

Hot wind from an open air gas oven, air quench.

Isn't that pearlitic wire the patenting wire? we don't have a chance to deform the long grains with cold working or hot working after

 

[swall]

Patented wire is pearlitic, yes. So are some of the hard drawn high carbon wires.

 

[dbooker630]

Some GM car and light truck stabilizer bars are made from 1090 modified (Mn .80-1.10), microalloyed with vanadium or columbium or a combination of the two. Typically they are controlled air cooled from bending temperature (1600F) to a hardness of 302-363 HB. Microalloying eliminated quench and tempering on this grade, thus reducing distortion as well. A lot of the mini-mills (Macsteel for one) should have this in hot rolled bar form.

 

[twistedneck]

Dbooker, why so much carbon? and why the mod? what do you think of the micro alloy stuff with lower carbon and boron or vanadium?

Also, what are the main concerns with air quench? thanks. TW

 

[twistedneck]

swall, do you think pearlite is a worthy structure even though it can't be elongated and patented (stretched and cold worked)??


Open quesion, what size and structure is 'fine' pearlite?

Seem lamelar spacing of 3microns in some studes.

 

[swall]

A pearlitic structure can be made to work, assuming your design validation is done with this microstructure. Then, you have to establish that your material and processing is robust enough to consistently provide material identical to what you qualified. The definition of "fine pearlite" has to take into consideration the section size. In music wire, you won't be able to resolve the pearlite, even at 1000x. But, with say a .5" dia bar, you won't get pearlite that fine.

 

[dbooker630]

twistedneck,
Basically the modification is to enhance hardenability to maintain the noted hardness range. Many of the components using the 1090 MA were replacements for standard 1070 quench-and tempered.

The biggest concern is that the part should enter the cooling area above the critical temp, fans (or other heat removal system) are working properly, part cooled at the same general rate throughout.

I've seen the lower carbon work on tubular materials, such as 10- or 15B21.