0
Your Cart
How to Heat treat Damasteel DS93X Stainless Damascus

How to heat treat Damasteel DS93X damascus

Damasteel’s stainless damascus patterned martensitic DS93X steel is a powder-based steel with the two alloys RWL34 and PMC27. Damasteel Solid Steel Technology™, offers steel an exceptional homogeneity and a fine carbide structure resulting in decent corrosion resistance with superior strength/toughness. The metals are equivalent to the non-powered Hitachi ATS-34 and Sanvick 12C27 [5]. You can visit zKnives.com for a graph if you are curious.

Both metals are variations of the martensitic stainless steel 420 type with a minimum of 13% chromium content.

You can also read my guide on heat-treating RWL34.

Damasteel DS93X Chemical Composition (nominal) %:

GradeEtch colorCMnCrMoV
RWL34Bright1,050,501440,2
PMC27Dark0,600,5013

As per Larin’s explanation of carbon migration [1], carbon values will change in the composite steel and influence how it responds to heat treatment. Typical values may resemble the below;

GradeEtch colorCMnCrMoV
RWL34Bright0.95 (-0.1)0,501440,2
PMC27Dark0.70 (+0.1)0,5013
Composite vs individual steels - Damasteel
Damasteel cryo / no cryo versus RWL34 and PMC27 (Knifesteelnerds.com) [4]

Heat Treatment Overview

With steel as “expensive” as Damasteel, any maker would pull out all the tricks at their disposal to ensure a great blade.

According to the Damasteel datasheets [2/3], the steel is capable of 64/63 HRC but for a “balanced” heat treatment with good toughness, most people seem to aim for 61 HRC after tempering depending on the blade’s use.

Melting starts at 1220°C/2230°F which means the material is sensitive to overheating. Damasteel recommends an electric or gas-fired furnace that offers control of the heating temperature over long soaking times.

NB! Long soaking times above 850°C lead to decarburisation and scale formation. It’s important to protect the steel from oxidation and decarburization during hardening. Condursal Z1100, Turco, and ATP-641, (anti-scale compounds) and stainless steel tool wrap (knu-foil), are the best choices.

Thermal cycling / Annealing (optional):

Because of the risk of cracking; no grinding, cutting or machining should be done after hot working until the material is annealed.

Annealing: The recommendation is to have the material fully transformation annealed before hardening. Heat to 910°C (1670°F ), hold 2 hours, slow cool no faster than 25°F (15°C) per hour to 750°C (1380°F), then furnace cool or cool in still air to room temperature.

Austenitizing / Hardening

  • Hardening Temps (Furnace) depending on where you have access to liquid nitrogen or similar:
  • Hold times*: 15 minutes (minimum) up to 30 minutes as thickness increases.
  • No Cryo: 1050°C / 1925°F
  • Cold Treatment (-18°C): 1060°C / 1950°F
  • Cryo (-71°C dry ice slurry “dryo” or colder still with Liquid Nitrogen): 1080°C – 1100°C / 1976°F – 2000°F

* The danger of an insufficient soak is much worse, leading to poor hardness, toughness, and corrosion resistance. While the chances of an overly long soak time are low. The changes to the steel in terms of transformation and carbides dissolving will “level off” after a certain amount of time and then changes are slow after that. So it is recommended that the soak is “long enough”, ie: 15min or longer, rather than trying to make it as short as possible.

Quenching Media

Rapid cooling to room temperature. Damasteel suggests quenching in oil and that the piece reaches room temperature within two (2) min. Apply some pressure on the piece if cooling in air, to avoid warping due to uneven cooling.

  • Recommended: Quenching a medium-speed oil (warm to 125°F / 50°C) can be used until the part is black.
  • Most Popular: Aluminium plates, combined with compressed air, to or below 125°F / 50°C

Cryogenic Treatments

Cryogenic treatment (-196°C) or Deep cooling (-23°C) is recommended to convert retained austenite (RA), which should be done before the first temper cycle (limits the amount of stabilised austenite formed).

Place the blades in the freezer, bath or liquid nitrogen directly after quenching, to maximise the amount of retained austinite that can be converted to martensite or reduce the amounts of retained austinite. RA has some negative effects on the blade when present in higher amounts, softness, deformation of the edge, and feather burrs when sharpening.

You’ll note that I have included a graph for a typical single cryo step and a double cyro, with an additional cryo treatment between the two tempering cycles. With the high amounts of retained austinite (RA) information, the double cryo step may be worthwhile when using higher austenitizing temperatures. Be mindful that converting “all” the RA into martensite will reduce the toughness to a degree.

While liquid nitrogen (-196°C / -320°F) is preferred, a sub-zero bath (dry ice and kerosene/paraffin) (-71°C / -100°F ) or a chest freezer (-18°C / -1°F), will suffice depending on your equipment. Read my article on the cold treatment of knife steels. Submerge in sub-zero treatment for 2 to 6 hours or longer depending on thickness and number of blades. Clamping is recommended to avoid thermal shock-induced warp.

Note: Any cryo treatment (whether between tempers or after the quench, should always be followed by a tempering cycle.

Tempering

As mentioned above, a snap temper is not recommended, however, if you have chosen to austenitize at 1050°C / 1920°F and quenched to room temperature, you can proceed directly to tempering.

To ensure the best corrosion properties are achieved, Damasteel recommends a low tempering temperature.

  • Tempering Temperature Range: The range is between 150°C (minimum) – 300°C (300°F – 570°F)
  • Recommended: Balanced 175 °C – 205 °C ( 350 °F- 400 °F )
  • Times: Two (2) times
  • Duration: Two (2) hours

It is not recommended to temper above 400°C / 750°F. Generally for knifemaking, secondary hardening / high-temperature tempers aren’t recommended and can insight embrittlement, leading to a reduction of toughness and corrosion resistance (should not be used for food handling applications).

*If using a small toaster oven or household kitchen oven for tempering, using a blade holding rack made from kiln furniture, a roasting tray lined with fine sand, or a similar large object will help retain thermal mass to reduce wide swinging temperatures as the device fluctuates trying to maintain temperature.

HRC Summary Table:

damasteel heat treatment chart KSN | Topham Knife Co
Hardening TemperatureTempering temperatureTempering timeHardness RWL34Hardness PMC27Hardness Composite
1050 °C / 1920 F220 °C / 430 °F2 h59 HRC53 HRC59 HRC
1050 °C / 1920 F175 °C / 345 °F2 h62 HRC54 HRC61 HRC
1080 °C / 1980 F220 °C / 430 °F2 h58 HRC56 HRC61 HRC
1080 °C / 1980 F175 °C / 345 °F2 h63 HRC58 HRC63 HRC
1100 °C / 2010 F175 °C / 345 °F2 h64 HRC60 HRC64 HRC

Links / References:

  1. Testing Damasteel – Powder Metallurgy Damascus (Youtube)
  2. Damasteel Datasheet New (pdf)
  3. Damasteel Datasheet old (pdf)
  4. Damasteel Heat Treatment and Properties
  5. Sandvik / Alleima 12c27 datasheet
  6. Purchase: Damasteel (South Africa)
  7. Purchase: Knife Engineering: Steel, Heat Treating, and Geometry By Dr. Larrin Thomas
  8. Purchase: Knu-Foil Stainless Steel Tool Wrap
  9. Purchase: Condursal Z1100

Disclaimer:

Please note that your heat-treating kiln will also differ in its readings compared to mine. As such it’s best to do your own testing (coupons). All information above is from my readings of research papers, forum posts, and discussions with people. I am not a metallurgist; the above is presented here for the benefit of all knifemakers. You do not have to follow the recommendations and I’ll not be held responsible for any loss or damage you may experience.

Please comment below if you have questions, or anything to add to the above.

Leave a Reply

Your email address will not be published. Required fields are marked *