PM HIP NNS Process for Valve Bodies Made of Garde 91 Material
Shimoda Technical Report E-3 (Dec. 2018)

Shimoda Technical Report E-3-------------------------------------------------------------------------------------------------------------------------------------------PM HIP NNS Process for Valve Bodies Made of Grade 91 Material
Hiroshi URAKAWA*，Mitsuo OKUWAKI***Shimoda Iron Works Co., Ltd.
**Metal Technology Co. Ltd.
Abstract
Shimoda Iron works Co., Ltd. and Metal Technology Co. Ltd. are developing PM HIP
NNS process for pipe fittings made of high grade materials. As a first trial for full scale
manufacturing, valve bodies for thermal power plant made of 9Cr-1Mo material arebeing manufactured. After HIPing and heat treatment some metallurgical andmechanical investigations were made. The results show uniform characteristics andgood strength. This paper introduces an outline of the PM HIP NNS procedure andthe investigation results.

1. Introduction
The PM HIP process (Powder Metallurgy - Hot Isostatic Pressing process) is a state-of-the-art
technology to manufacture metal products made of high grade materials, such as, stainless steels
and super alloys1). This process is not casting nor forging but a kind of powder sintering.
Shimoda Iron Works Co., Ltd. (herein after “Shimoda”) is fundamentally a producer of forged fittings
for piping however Shimoda is now developing a new process to manufacture fittings using this PM
HIP process in collaboration with Metal Technology Co. Ltd. (herein after “MTC”) who specializes inHIP treatment.
As an initial trial of this new process, a type of valve body for thermal power plants was selected tobe manufactured. The material of this product is 9Cr-1Mo also known as “Grade 91” which has highstrength at high temperature condition. In this paper, the trial production and some of the investigationresults of the product will be reported.
2. Outline of HIP treatment
2.1 HIP unit
Figure 1 shows the basic construction of a HIP unit.
There are electric heating coils in a pressure vessel
and high pressure Argon gas is charged in it. The
heating temperature is higher than 1,000℃ and thepressure is more than 100MPa. The gas pressure acts
uniformly in all directions therefore the products canbe pressed isostatically. Owing to this isostaticpressing, the product displays uniform characteristics
throughout.
Figure 1 HIP unit
1PM HIP NNS Process for Valve Bodies Made of Garde 91 Material
Shimoda Technical Report E-3 (Dec. 2018)-------------------------------------------------------------------------------------------------------------------------------------------

2.2 PM HIP NNS process
There are several applications for HIP units, such as, densification of cast parts or 3D printed parts,
diffusion bonding between similar and dissimilar metals, sintering of metal powder to name a few.
Among these applications, PM HIP NNS process will be the focus of this paper. This process is kindof a metal powder sintering process however the special feature of this process is that the metal
powder fills the capsule before HIP treatment. The capsule is prepared depending on the dimensionsof the final product and therefore enabling a Near Net Shape blank to be obtained after HIPing. NNSHIPing reduces both metal powder costs and finish machining costs.
When applying the PM HIP NNS process the design of the capsule and the dimensions are critical.
Since the powder consists of spherical grains, there are some spaces between grains in the capsulebefore HIPing. The density before HIPing is around 65-70%. However HIP treatment increases thedensity up to 100%. This results in more than 30% shrinkage in volume taking place. As aconsequence the capsule designer has to be able to predict the shrinkage cased by HIPing. This is
one of the key points to successfully being able to carry out the PM HIP NNS process.
2.3 Benefits of PM HIP NNS process
The main benefits of the PM HIP NNS process are as follows:
1) Flexibility of chemical composition design, especially alloy contents.
2) Uniform characteristics in the whole section and in all directions.
3) Elimination of welding. It can not only reduce the production cost but also solve the problem ofweak strength performance and corrosion resistance at the welded areas.
4) Reduction of material costs and finish machining costs.
5) Large and more complex shapes can be manufactured.
3. Valve body production
3.1 Product designation
A type of valve body which is designed for thermal power plants was selected for the trial production
by PM HIP NNS process. Conventionally these valve bodies have been manufactured by a forging
process.
3.2 Material
The material of the valve body is UNS K90901 (9Cr-1Mo-0.2V-Nb-N) which is specified in ASTM A989
for HIPed alloy steels2). This material is one grade of so called 9Cr materials which has a high strength
in high temperatures. Since this material is the equivalent to ASTM A182 F91 which is specified forforged products this is called “Grade 91” in this paper.
Table 1 shows the chemical composition of the powder material and Figure 2 shows the SEM
observation of the powder. The grain size is 2-90μm.
Table 1 Chemical composition (wt%)

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PM HIP NNS Process for Valve Bodies Made of Garde 91 Material
Shimoda Technical Report E-3 (Dec. 2018)-------------------------------------------------------------------------------------------------------------------------------------------3.3 Capsule preparation
Figure 3 shows the capsule configuration before and after HIPing. The powder density is predicted
to be 67%. The black square area is a mild steel block which is necessary to fabricate the capsule bywelding. This mild steel block is eliminated by vertical drilling at the post machining stage.

Figure 2 SEM photographof the powder
Figure 3 Capsule design before and after HIP

3.4 HIP treatment
After the capsule filling and de-gassing, the inlet nozzles are sealed. Figure 4 shows the capsule
ready for HIPing. HIP treatment is carried out in the Giga HIP unit at MTC. The Giga HIP is the world’s
largest working zone (2,050mm dia. x 4,200mm height)..
3.5 Removing capsule and heat treatment
After removing the capsule by machining the part then underwent the following heat treatment.
Quenching: 1,050℃ x 3hr → oil quenching
Tempering: 760℃ x 4.5hr → cooling in still air
Figure 5 shows the product after heat treatment.

Figure 4 Before HIPFigure 5 After HIP and heat treatment

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PM HIP NNS Process for Valve Bodies Made of Garde 91 Material
Shimoda Technical Report E-3 (Dec. 2018)-------------------------------------------------------------------------------------------------------------------------------------------4. Investigations and evaluation
4.1 Investigation items
The following investigations were carried out:
1) Tensile tests at room temperature
2) Brinell hardness distribution3) Tensile tests at high temperature up to 700℃
4) Impact tests (Charpy V notch at room temp.)
5) Macrographic observations of the section
6) Micro structures
7) Grain size measurements
8) Non-metallic inclusion
9) Creep tests
4.2 Tensile tests at room temperature
Tensile tests are made at various locations and in every directions. As shown in Figure 6, all theresults show uniformity at all locations and directions.

Sampling location and direction
Figure 6 Tensile test results
4.3 Brinell hardness distribution
Figure 7 shows the Brinell hardness
distribution of the whole section. Hardness
values are uniform (HB200±5) with the
exception of the mild steel area.

Figure 7 Brinell hardness distribution
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PM HIP NNS Process for Valve Bodies Made of Garde 91 Material
Shimoda Technical Report E-3 (Dec. 2018)-------------------------------------------------------------------------------------------------------------------------------------------4.4 Tensile tests at high temperature up to 700℃
The tensile strengths for the high temperature tensile tests from 100℃ to 700℃ are shown in
Figure 8 together with a results for the room temperature (20℃). Reference line in the figure shows
the data of Grade 91 material reported by EPRI3) (Electric Power Research Institute). The results are
greater than this line.
4.5 Impact tests (Charpy V notch at room temp.)
Figure 9 shows the results of the impact tests at room temperature. Firstly there is less variation
between the three individual results at the same condition compared with our usual experiences onforged products. Moreover there is little variation among the average values at any of the locations
and in any direction. This uniformity of impact characteristics is due to the uniformity and the fine grain
size as reported later.

Figure 8 High temperature tensile test results

Figure 9 Impact test results(at room temperature)

4.6 Macro structure
Figure 10 shows the macro structure of the section. It is reasonably uniform, no segregation nor voids.
Needless to say that there no metal flow is observed.
4.7 Micro structure
Every micro structure is almost the same at any location. Figure 11 shows an example of microstructure at the middle of the section.

Figure 10 Macro structure

Figure 11 Micro structure
5PM HIP NNS Process for Valve Bodies Made of Garde 91 Material
Shimoda Technical Report E-3 (Dec. 2018)-------------------------------------------------------------------------------------------------------------------------------------------4.8 Grain size
Grain sizes are measured at 12 points of the section. As shown in Table 2, the grain sizes are
remarkably fine at every location.
Generally speaking, the grain sizes of forged products are much coarser than these results and as aresult the grain sizes of a forged part vary widely depending on the locations. The size in the middle
area is usually coarser than the surface area. In stark contrast the PM HIP part’s most noticeablecharacteristic is the uniformity and fine grain size.
4.8 Non-metallic inclusion
Non-metallic inclusions are investigated at several points of the section. As shown in Table 3, only
D series inclusions (globular oxide) are observed. These results means the material has goodcleanliness.
Table 2 Grain size

Table 3 Non-metallic inclusions

4.9 Creep tests
Creep tests have been made on the test pieces sampled from the product. The results are shown inFigure 12. All specimens were ruptured. The longest test duration is approximately 22,000 hours (2years and 6 months) at 600℃.
The lines in the figure are reference lines reported by NIMS (National Institute for Material Science)
which are showing the conventional test results on existing Grade 91 materials. The solid line means
the average of the conventional data and dotted line means 99% bottom limit respectively. According
to the test results and data by NIMS, it can be concluded that the valve body has the equivalent creep
strength to conventional Grade 91 materials.

Figure 12 Creep test results
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PM HIP NNS Process for Valve Bodies Made of Garde 91 Material
Shimoda Technical Report E-3 (Dec. 2018)-------------------------------------------------------------------------------------------------------------------------------------------5. Finish machining
The blank shown in Figure 5 is finished by Shimoda’smachining factory. The finished valve body is shownin Figure 13. If this valve body is manufactured
through a forging process, it is necessary to forge amono block blank of approximately 900kg. On
contrast, the HIPed NNS blank is only 536kg whichis around 40% less than the forged blank. Also, thefinish machining time of the forged mono block blankis estimated to be around 100 hours. However thefinishing time for the HIPed blank is only 70 hours
which is 30% reduction compared to the forging
process.

Figure 13 Finished valve body

6. Conclusion
1) Valve bodies for a thermal power plant made of Grade 91 material can be successfully
manufactured by the PM HIP NNS process.
2) Due to experienced design of the capsule dimensions, the HIPed product has NNS configuration
for finish machining.
3) Thanks to the NNS configuration, the weight of a blank and the finish machining times are reduced
up to 40% and 30% respectively compared to the forging process.
4) The investigation results show satisfactory characteristics of the HIPed product. The most notablefeature is the uniform characteristics at any location and in any direction.
5) Creep test results have proven that the product has the equivalent creep strength to conventional
Grade 91 material.

References
1)
2)
3)

Introduction to PM HIP Technology, EPMA (European Powder Metallurgy Association) 2011 2ndedition.
ASTM A989/989M Standard Specification for Hot Isostatic Pressed Alloy Steel Flanges, Fittings,
Valves, and Parts for High Temperature Service.
Powder Metallurgy / Hot Isostatic Processing (PM/HIP) Data Package for Grade 91,EPRI

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