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Part one is in this thread:
http://www.bladeforums.com/forums/showthread.php?s=&threadid=202287
Here is part two...
http://www.bladeforums.com/forums/showthread.php?s=&threadid=202287
Here is part two...
The Best All-Purpose Workhorse Stainless? (Part 2)
By Phil Wilson (August issue of Blade Magazine)
In the conclusion of his 2 part story, the author completes his battery of tests on Crucibles new CPM S30V and sees how it stacks up as a blade steel. -- Editor
CPM S30Vs bending strength seems to be excellent. Again, this can be best characterized with a fillet knife.
The 9 test piece was ground pretty flexibly but it took about 10 lbs of force to bend the blade 90 degrees from the original position. The blade was left with a slight permanent bend after the force was released, a force much more than would be needed during a normal fillet operation. The same type of bending takes place on a thin knife edge that's worked hard against the cutting medium. A good steel heat treated correctly will flex and return to the original shape in the same manner that a spring will. If the steel is too soft, it will tend to bend and stay bent. If its too hard, the edge will break before it bends very far. My experience indicates that most stainless steels will perform pretty well under a pure bending situation. I use a lot of ATS-34 and 154CM for fillet knives, and both steels act in a similar way.
Impact Toughness
Impact toughness is the real question. This is the main nemesis of stainless steels used in knife blades. Crucibles aim was to produce a steel with toughness exceeding 440C and D-2. I didnt make a chopping-type knife on which to experiment, but I did chop a Douglas fir 2x4 in half with the fillet knife. It was difficult to put much chopping energy into the task because the knife is so lightweight, yet there was absolutely no damage evident on the thin blade. Did the S30V make the A-2 toughness target I set for it? Ill have to wait for the final data from Crucible to see how close it comes, but I think that, in time, it will be evident that this steel is the toughest true stainless around.
Heat Treating
I was hoping for a material that would be easy to heat treat similar to A-2 or CPM3V. Despite the additional alloys, the objective was met. Again, quoting from the preliminary data sheet, here are the recommendations for heat treating S30V:
"Hardening-Austenize: 1900-2000F. Hold time at temperature 15-30minutes.
Quench: Air or pressure gas quench (two bar minimum) to below 125F, or salt or interrupted oil quench to below 1000F, then air cool to below 125F.
Temper: Double temper at 400-750F. Hold for minimum of 2 hours each temper.
For optimum stress relieving, CPM S30V may be tempered at 1000-1025F. Tempering in this range, a freezing treatment may be used between the first and second tempers. Freezing treatments help to attain maximum hardenability and must always be followed by at least one temper. Aim Hardness: 58-61 Rc.
S30V can be hardened a little higher than 154CM or ATS-34 because of the inherent toughness of the particle-metallurgy structure. Its my opinion that S30V could be used successfully at Rc62 for a high-performance, slicing-type hunting knife. Theres no question that the target was met on ease of heat treating. I was able to get Rc61 on the S30V by using 1970F austenizing and 400F tempering temperatures with an air quench.
The as-quenched hardness was 63Rc. I did a sub-zero quench in liquid nitrogen directly after the air quench down to room temperature. This was followed by two temper cycles at 400F for 2 hours each cycle. I havent tried it yet, but from the data sheet, it looks like a temper of around 1000F would take advantage of the secondary hardening increase typical of alloy steels of this type. It may be possible to end up with a final hardness of Rc62 at the cost of some corrosion resistance.
Wear Resistance
Compared to CPM S90V or CPM 10V, S30V is a pleasure to work. It grinds in the annealed state much like any other stainless steel. It feels a little gummy and gets hot quick if a sharp grinding belt isnt used. If the maker is accustomed to working with non-stainless, then it might seem somewhat tougher to grind. After its hardened to 60/61 Rc, it acts a lot like 3V. As in all CPM steels with a high percentage of vanadium carbide, the final finishing operations take more effort than 154CM or D-2 for example. A hand-rubbed satin finish or a 240-grit belt finish is the best choice for these steel grades. Mirror polishing S30V would take all day, though S30V takes about half the effort to mirror polish that S90V does. In this area, the target also was met high wear resistance at the cutting edge without an inordinate amount of effort for the final finish.
Availability & Cost
Crucible offers a range of rolled sheet stock in various thicknesses that will finish in the dimensions used most often for knife blades. The stock I received from Crucible in November was 0.140 inch thick. This finished after removing the scale to about the 0.125inch range. Reportedly, Crucible plans to stock small quantities of S30V for knife use at its Dallas Texas Service Center. The price varies depending on the amount ordered but it should be about 30% more than 154CM. Availability and cost are important items and it looks like expectations have been met in this area.
Conclusion:
S30V has met all the expectations set forth in my initial introductory article in the April BLADE (Breakthrough! Steel Specifically For Knives). In addition, I can say that its just a very pleasant and forgiving steel to work. In my opinion, its going to end up with the reputation of being the toughest stainless out there, with very good edge-holding and cutting ability.
Crucible Materials Corp has introduced three winning steels in the past 10 years: CPM S90V, CPM 3V, and now CPM S30V. CPM 3V is still the undisputed toughness champ, even surpassing some carbon steels such as A-2. Originally known as CPM420V, S90V was introduced as an upgrade for S60V (originally called CPM 440V), and met all the targets of improved corrosion resistance and toughness. It has the reputation of being hard on heat-treating equipment and is a bear to finish, but is still the best edge-holding stainless steel going. In time, S30V may hold the title of best all-purpose workhorse stainless steel. It could edge out pun intended more widely known stainless steels such as ATS-34, 154CM, BG-42, and 440C. With all these choices available, knife users and knife makers have never had it so good. Theres now one more excellent steel available for that elusive high-performance knife, and its CPM S30V.
Sidebar: Best Grinding Belts
"Ive found that the Norton SG belts in 50 grit are the best for initial grinding of the CPM steels before the heat treat. I then go to a 3M Regalite belt in a 120 grit to take out the deep belt marks and prevent excess stress build-up from deep scratches. After heat treatment, I return the blade to the 120 grit belt and then to a sharp 220 grit. For the final finish, I either leave a 220 grit belt finish or hand rub the blade to a satin finish with wet/dry silicon carbide paper.
Phil Wilson
Dept. BL8
POBox 846
Mt Ranch, CA 95246
(209) 754-1990
seamount@bigplanet.com
