A quench oil is a cooling curve, not a viscosity grade
Quench oil sets how fast a hot steel part cools through the transformation range. Too slow and the hardness is missed. Too fast, or uneven, and the part cracks or distorts. ISO 9950 and ASTM D6200 measure that curve. Fast cold oils, medium oils and hot marquench oils are different products. The bill of materials stays under NDA; the specification does not.
Name the bath before you name the additive
Fast cold oil
Accelerated cooling for leaner steels and parts that must miss pearlite. Higher cooling rate, tighter fire and distortion control.
Medium / normal speed
The general engineering quench. Mineral oil with a modest accelerator, used where the steel has enough hardenability.
Hot oil / marquench
Bath held hot so the part cools fast enough to miss pearlite, then more evenly through martensite. Used to cut distortion on shaped parts.
What it is not
Not a cutting oil, not a rust preventive, and not a hydraulic oil that happened to be in the store. Those fail the cooling curve and the flash-point conversation.
Cutting and drawing fluids sit on the cutting oil and metalworking pages. Quench is its own development.
Flash point, oxidation and drag-out
The bath sits next to steel that was just above the critical temperature. Flash point is a safety limit, not a quality slogan. Oxidation thickens the oil, slows the cooling rate, and raises the fire risk. A quench oil that was fast when new and sluggish after a season has changed its curve — retest D6200 or ISO 9950 on the used bath, do not top up and hope.
Speed improvers, antioxidants and detergents are the additive story. US 3,607,459 (Phillips Petroleum, 1971) is an early public example: a defined calcium petroleum sulfonate, base number under 15, was claimed to raise quench rate and oxidation resistance while limiting stain. Later oils use other accelerators. Citing the patent tells a formulator where the idea came from. It does not transfer the invention, and it is not a Lubechem recipe.
We develop the oil against your probe curve, your steel grades and your bath temperature. We do not sell drums of quench oil from stock.
Standards and prior art
Public patents and papers cited as field references. Lubechem does not own these inventions and this page is not a formula.
- ISO 9950:1995 — cooling characteristics of industrial quenching oils — Nickel-alloy probe, non-agitated oil. A ranking test.
- ASTM D6200 — cooling curve of quench oils — Cooling time versus temperature. Do not interchange results with ISO 9950.
- Thermal Processing — selecting oil quenchants — Practical equivalence window on peak cooling rate and the temperature of that peak.
- US 3,607,459 — quench-rate additive — Phillips Petroleum. Calcium petroleum sulfonate as a historical accelerator. Prior art only.
Quench oil questions
Can hydraulic oil be used as a quench oil?
No. Hydraulic oils are built for pumps and seals, not for a measured cooling curve or for repeated contact with austenitised steel. The flash behaviour and the oxidation life are also wrong.
Which test should the TDS show?
The one your heat-treat customer already uses. Say ISO 9950 or ASTM D6200 by name. A viscosity and a flash point alone do not describe a quench oil.
Do you publish the accelerator treat rate?
No. The page explains the curve and the patent history. The working formula is delivered under NDA with the test report.
Bring the cooling curve you have to hit
Steel grade, section size, bath temperature and the probe method are the brief.
Send a quench-oil brief →