PX5 Steel

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

Program time was reduced from 38 minutes to 15.2 minutes

Tool No. 2
1.000 Diameter Waukesha Ballnose Endmill

Program time was reduced from 5.7 minutes to 2.85minutes

Tool No. 3
.750 Sandvik Ballnose Endmill

(Finish cutter) 1.000 Diameter Iscar Ballnose Endmill

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

Program time was reduced from 10 minutes to 4.85 minutes

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

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.

Sectional Hardness Rockwell C Scale:

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.

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

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.

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.

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)

Results

PX5

P20

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)

Hardness Distribution Around Weld

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

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

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.