PX5 Steel

PX5 is a 30 HRc, P20-type, pre-hardened steel that can be used for all plastic molding. It is the highest quality P20-type mold steel currently available, and is superior to all other P20-type mold steels in terms of machining, stability, and welding.

Unique Characteristics

  • Exceptionally clean steel with uniform microstructure – no pin holes, inclusions or hard spots.
  • 30-33 HRc hardness.
  • Uniform hardness throughout, even in heavy sections.
  • 75% tougher than typical chrome-moly steels.
  • Patented chemistry suppresses weld cracking and hardness elevation in the heat affected zone, eliminating the need for pre-heating and post-heating in most welding situations.
  • Machines 30-50% faster than any other P20-type steel.
  • Never needs stress relieving, even after heavy machining.

Benefits

Welding

Superior mold quality after welding. Low hardness of heat affected zone eases post-weld cutting and grinding operations and minimizes mold distortion, etch unevenness, and differences in luster upon mirror finishing. Unique composition eliminates weld cracking.

Machining

Rough machines up to 50% faster than P20 (30% overall) to a superior surface with negligible dimensional change. Use of PX5 assures the longest cutting tool life of any 30 HRc, P20-type material. Consistent hardness and microstructure allow dependable, unattended machining.

EDM

EDM surface hardness is about 70% of that produced by typical P20-type steels. Post EDM grinding and polishing operations are simpler and more consistent, and problems such as surface layer cracking or peeling are reduced.

Stability

Uniform hardness and refined grain structure assure the highest level of dimensional stability (after machining) of any P20-type mold steel.

Surface Enhancements

Can be ion-nitrided to produce a surface hardness over 60 HRc with negligible distortion or dimensional change.

Texturing and Polishing

Uniform microstructure and hardness give PX5 the best surface-finish characteristics of any P20-type material. Low chemical segregation eliminates the occurrence of photo etch unevenness.

Toughness

Exceptional toughness reduces cracking problems in molds.

Mechanical Properties

Isotropy and Uniform Strength

PX5’s strength is approximately the same at the center and surface of the material, and that isotropy (T/L) is at least 0.05.

Tensile Properties

PX5 Tensile Properties

When designing deep cavities in molds, PX5’s consistent toughness assures the mold center will have sufficient strength, and cracking problems are dramatically reduced.

Toughness

PX5 Toughness

Physical Properties

Coefficient of thermal expansion (x10-6/F°)
  86-212°F 86-392°F 86-572°F 86-752°F 86-1112°F
PX5 6.6 7.1 7.3 7.5 7.8
Thermal conductivity (btu/ft.·hr.·F°)
  68°F 212°F 392°F 572°F 752°F
PX5 24.53 24.48 24.31 22.67 22.42
Specific heat (btu/lb.·F°)
  68°F 212°F 392°F 572°F 752°F
PX5 0.027 0.028 0.031 0.032 0.036
Young’s modulus (lbs./in²)
  68°F 212°F 392°F 572°F 752°F
PX5 30269 29768 28909 28051 26977

General Design Guidelines

Compressive Strength

Uniform hardness (approximately 32 HRc) from surface to core assures that strength and hardness at the mold center are the same as at the surface. Exceptional toughness reduces cracking problems while increasing flexibility in mold design

PX5 Compressive Strength

Stability

PX5 is substantially more stable than common P20-type steels. Since it has a unique heat treating process, it does not have the stresses inherent in typical quenched and tempered steels. PX5 never needs stress relieving, even after heavy machining. It has excellent dimensional stability and consistency during the machining process, and during the heating and cooling cycles of injection or compression molding.

Processing Guidelines

Machining

Use of PX5 assures the longest cutting tool life of any 30 HRc, P20-type material and an overall 20-30% improvement in machining efficiency.

Note: Positive, effective cutting rake angles are recommended, as are inserts with concave faces and chip breaking edges. TiAlN coatings work well.

PX5 Steel

PX5-Machinability

Machinability

A recent machining test was performed on PX5 material at a mold base manufacturer. Listed below are the tool settings for P20 and the results achieved with PX5.

Tool No. 1
1.250 Diameter DIJET Ballnose Endmill

  P20 PX5
RPM 986 1600
Feed 11.83 27.60
Depth .120 .120

Program time was reduced from 38 minutes to 15.2 minutes

Tool No. 2
1.000 Diameter Waukesha Ballnose Endmill

  P20 PX5
RPM 1600 3000
Feed 16.6 33.0
Depth .6-.180 .160-.180

Program time was reduced from 5.7 minutes to 2.85minutes

Tool No. 3
.750 Sandvik Ballnose Endmill

  P20 PX5
RPM 2660 3000
Feed 18.2 36.0
Depth .160 .160

(Finish cutter) 1.000 Diameter Iscar Ballnose Endmill

Tool No. 4
(Finish cutter) 1.000 Diameter Iscar Ballnose Endmill

  P20 PX5
RPM 2419 3000
Feed 19.35 40.00
Depth .060 .060

Program time was reduced from 10 minutes to 4.85 minutes

There was no noticeable wear in any of the cutting tools using PX5.

Manufacturing Process

A 40″ x 41″ x 87″ block of PX5 was forged and heat treated. The piece was cut through 61″ into the 87″ length. The following hardness readings were taken across the face of the test piece.

PX5-Manufaturing-Process

Inspection Result

Sectional Hardness Rockwell C Scale:

PX5-Inspection-Result

The recast layer from EDM for PX5 is soft, approximately 70% of that produced with typical chrome-moly steels. Because the EDM white layer must be removed, the subsequent stoning or grinding of PX5 is much easier than with other steels. There is also a significant reduction in the incidence of problems involving the hardened layer, such as surface layer cracking or peeling. Consequently, no post EDM stress relieving is needed.

Hardness of EDM Affected Area

PX5 Hardness

PX5 Hardness EDM

Polishing

PX5’s exceptional cleanliness, uniform microstructure, and uniform through hardness facilitate excellent and consistent surface finishing characteristics. PX5 polishes faster and easier to a superior mirror finish than common P20-type steels. PX5 will polish to a 6000-7000 grit finish, while P20 polishes to only a 5000 grit finish.

Mirror Surface

PX5 Mirror Chart

PX5 Mirror Finishing

Photo Etchability

PX5 is an excellent steel for photo etching. Low chemical segregation of the alloying elements results in a clean, homogenous steel. Absolutely no etch unevenness will occur due to chemical segregation. PX5’s uniform hardness and refined grain structure also provide a consistent surface condition for texturing. A reduction in work time and cost can be anticipated due to the elimination of etch unevenness problems.

PX5 chemseg

Ion-Nitriding

Ion-nitriding increases wear resistance and creates a hard surface ideal for slides or molds which will be molding abrasive or mineral-filled thermoplastics. PX5 can be ion-nitrided to produce a surface hardness over 60 HRc without distortion or dimensional changes. This ion-nitrided surface also improves part release and corrosion resistance.

Ion-Nitridingof PX5

Welding

It is essential that no rod other than PX5 should be used in all welding situations. All other rods are incompatible with the base metal chemistry of PX5 and will produce unacceptable results.

In most cases, PX5 can be welded with no pre- or post-heating procedures. However, this is not true in all situations. We suggest that in the event a polished surface must be welded (such as a lens or chrome-plated parts), pre-heat the block to between 650-900°F. Weld with PX5 rod, then post-heat to between 1040-1050°F. Final draw temperature for PX5 mold steel is 1117°F.

DO NOT, under any circumstances, exceed final draw temperature.

On a textured surface, the need to pre- and post-heat is determined by the etching method used by the grain source. If the selected grainer uses the immersion process with a nitric acid-based solution, then there is generally no need for pre- or post-heating procedures. If the grainer uses a ferric chloride flow technique, it is recommended that a full pre- and post-heating procedure be performed prior to texturing as outlined above.

We recognize that many mold welders apply heat locally with torches as a means of pre-heating the welded area. While this is a commonly used procedure, and generally produces acceptable results on non-polished surfaces, it is not recommended for post-heating welded blocks. The result of localized heat of this type is an actual flame-hardening of the weld that will produce an inconsistent increase in hardness by as much as 10-12 points (Rockwell C).

1) Weld Cracking Sensitivity
The compositional balance of PX5 was designed to suppress crack sensitivity. The weld will not shrink and crack at the marriage line, even without pre- and post-heating, as long as basic welding conditions are observed.

Y-Split Cracking Test (determines cracking susceptibility)

Welding method MAG
Filler rod PX5 Weld Rod
Filler rod Diameter 0.047″
Welding Current 280 A
Gas flow rate 25 /min
Pre/post heating None

PX5Y-SlitTest

Results

PX5
PX5 Weld Result

P20
PX5 Weld Results

PX5 exhibits no cracking in either the weld surface or interior.

Weld cracking will not occur as long as basic welding conditions and procedures are observed.

2) Weld Hardness PX5 has the lowest level of hardness in the heat-affected zone of any P20-type mold steel. This relatively low increase in hardness reduces post-weld cutting and grinding times (i.e., high-speed steel end mills can be used)

PX5 y-split weld hardness

Hardness Distribution Around Weld
PX5 Hardness Distribution

3) Photo Etchability
After weld repair, typical P20 will have etch unevenness due to its increased hardness. This requires many hours to correct. PX5’s relatively small increase in hardness in the heat affected zone reduces the incidence of etch unevenness and requires minimal correction work.

Photo Etch Quality Around Weld

PX5 Stees

4) Distortion
Post-weld distortion is the lowest for any P20-type material, due to the relatively
small increase in hardness in the weld area. Post-repair dimensional correction
work is simplified.

Test Conditions
Welding method TIG
Filler rod PX5 Weld Rod
Filler rod Diameter 0.094″
Welding Current 125 A
Gas flow rate 7 /min
Pre/post heating None
Test Method

PX5 Dist-Test Method

Results

5) Undercut Characteristics
While undercutting or “sink” surrounding the weld will always occur to some degree, PX5 has only a small degree of undercutting, dramatically reducing the amount of repair time.

Weld Sink
Test Conditions TIG: 160A, no filler Test piece: 10 degree slant

 PX5 Under Cut

PX5

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