VACUUM HEAT TREATING OF D2 TOOL STEEL

D2 material and equivalents

AISI	DIN	JIS	BS	THYSSEN	ASSAB
D2	1.2379	SKD11	BD2	Thyrodur 2379	XW-41

DAIDO	HITACHI	PHILIPS	BOHLER	LEONG JIN	ROCHLING
DC11/53	YSS-SLD	N1019	K110	LEO 364	RCC SUPRA

Composition of D2 and equivalent tool steels

Steels	Composition
	C	Cr	Mo	V	Si	Mn	S max	P max
D2	1.5	12.0	1.0	1.0	-	-	-	-
1.2379	1.55	11.75	0.75	0.95	0.3	0.35	0.005	0.020
XW-41	1.55	12.0	0.8	0.8	0.3	0.3	-	-
XW-42	1.42	11.2	0.8	0.2	0.3	0.4	-	-

Process requirements

Hardening

Pre-heating Temperature:

• Heat very slowly and preheat between 600° - 815°C

Austenite Temperature:

• Temperature between 980°- 1050°C
• Hold the temperature 15 minutes for small tool to 45 minutes for large tools

Quenching:

• For oil quenching, the temperature should be between 65° - 90°C. Parts are then taken out from bath and air cooled.
• For gas quenching up to 6 bars, lower pressure can be used for small parts that have thickness less than 50-60mm to minimize excessive distortion.
• For salt bath quenching, parts should be quench in salt bath at 540°C, hold only long enough to equalize temperature, cool in air

Tempering

• Choose the tempering temperature according to the hardness required by reference to the tempering graph as shown below.
• Normally, parts should be tempered immediate at 205° to 540°C after it has cooled to about 50° to 66°C.
• For double temper, allow the tool to cool to room temperature before second temper.
• Minimum holding time is 2 hours.

Stabilizing

• It is an optional stage.
• For intricate shapes having abrupt changes in section size, stress relieve temper at 150° to 160°C briefly before refrigerating at -85°C or less.
• Temper immediately after part reaches room temperature

The typical heat treating process is shown in Fig.1.

Operation procedures for vacuum heat treating

Heat treating procedure

• Rough pump down to 100 micro vacuum and start flow 75 scfh nitrogen partial pressure.
• Ramp at 30°F per minute to 1500°F ±50ºF.
• Hold at 1500°F for two hours (work thermocouple)
• Ramp 30°F per minute to 1775°F ±25°F
• Hold at 1775°F ±25°F for one hour and 45 minutes (work thermocouple)
• Ramp 30°F per minute to 1875°F -25°F +0°F
• Hold at 1875°F -25°F +0°F for 20 minutes (work thermocouple).
• Nitrogen quench to room temperature between 2-6 bars.
• Deep freeze -100°F immediately and leave in 12 hours
• Air warm to room temperature
• Record as-quenched hardness.
• Air temper 300°F for one hour minimum (work thermocouple)
• Record resultant hardness on all three sizes.

Key points

• Not advisable to run all different sizes of material in one heat as the smaller size may get over-soaked
• Gas quenching must be done with nitrogen gas or inert gas.
• Parts with smaller diameter and mass rounds quenched faster. The larger and heavier parts will be quenched at a slower rate.
• Primary heating and soak times should be controlled to ensure full soak of the material.
• Experiment had showed that -100°F deep freeze immediately following the austenitizing is desirable to provide maximum metallurgical transformation and improved hardness results.
• Vacuum furnace is able to protected against decarburization and oxidation during heat treatment.
• Surface cooling rates are considerable faster.
• Heating rates for vacuum are slower as compared to salt bath heat treatment.
• Hardness fall off on oversoak time at temperature.

Distortion

After quenching, the steel has a microstructure consisting of retained austenite and martensite with carbide. Therefore, the formation of undesirable components like bainite or ferrite/pearlite must be avoided. Thus, a slow quenching rate is recommended to minimize distortion because it results in lower temperature differences between the surface and the core of the heat treated material.

Applications

Application	Working Hardness HRC
Flat and circular shear blades for cutting sheets up to about 4mm thickness	58-60
High efficient blanking and stamping dies (material to be cut up to 6mm thickness)	58-62
Thread-rolling dies and jaws	58-62
Highly-stressed woodworking tools	58-62
Shearing knives for the manufacture of screws and nuts	60-62
Perforating dies at high stressings and hobbing punches	58-62
Roller segments for the cutlery industry	56-60
Coining dies	56-60
Cold heading dies	56-60
Punches in the tube presses	58-62
Glasses forming tools	58-62
Crushing Hammers	56-60
Swaging blocks	56-60
Gauges, Measuring tools, Guide rails, brushes, sleeves; Knurling tools; Sandblast nozzles	58-62
Tube- and section forming tools; plain rolls	58-62
Ejector bushings	58-62
Center punches	58-60