TROJAN (Suzhou) Technology Co., Ltd.
TROJAN (Suzhou) Technology Co., Ltd.
Metallographic preparation report of bolts and nuts
2022-11-14
Bolts and nuts are the most commonly used solid parts. They are tools that use the physical and mathematical principles of the oblique circular rotation and friction of objects to gradually fasten the parts of the utensils.
Bolts and nuts are required to be able to meet high-load and long-term use under alternating stress. The quality of metallographic structure is very important. Generally, good toughness and reasonable hardness are required inside, and high hardness and strong surface are required. Wear and corrosion resistance, different materials and heat treatment systems have different metallographic structures.
01 Equipment and consumables
| Equipment | Trojan TableCUT-200 automatic precision cut-off machine; Trojan FlexPRESS-600 mounting press; Trojan Alpha double disc double control grinder&polisher; Trojan Alpha-600 automatic grinder&polisher; Trojan ThetaMount pressure cold mounting machine; Leica DM2700M metallographic microscope; Hairdryer; |
| Consumables | Alcohol;Degreasing cotton; |
02 Sample preparation process
1-Cutting
Use the TableCUT-200 precision Automatic Cutting Machine to cut the bolt and nut in half (the size is too small or the shape is irregular, a special jig is required).
| Equipment | TableCUT-200automatic precision cut-off machine |
| Consumables | SiC Grinding wheel cutting disc |
| Parameter | RPM:3000rpm,feeding speed:0.2mm/s |
2.1-Hot mounting
Use the FlexPRESS-600 mounting press to mount the cut specimens, and the nuts with smaller diameters can also be mounted directly without cutting.
| Equipment | FlexPRESS-600 mounting press |
| Consumables | TJ2237 edge protection hot mounting compounds |
| Parameter | Pressure:180Bar,temperature:175℃,time:5min,Moderate cooling |
2.2-Cold mounting
Prepare TJ2568AB epoxy resin in proportion to mount samples, place in the ThetaMount pressure cold mounting machine to solidify under pressure after the sample is poured.
| Equipment | ThetaMount pressure cold mounting machine |
| Consumables | TJ2568AB epoxy resin |
| Parameter | Pressure:0.2MPa,time:30min |
3.1.1-automatic grinding and polishing
Grind the specimen with Alpha-600 automatic grinder&polisher.
| Equipment | Alpha-600 automatic grinder&polisher |
| Consumables | SiC abrasive paper:P180;P400;P800;P1200;P2000;P2500 |
| Parameter | Pressure:22N,same direction:200rpm,time:120s |
3.1.2-Polishing(automatic plane polishing)
Polish the specimen with Alpha-600 automatic grinder&polisher, use YS polishing cloth with 3μm polycrystalline diamond suspension,also add PL-W polishing lubricant.
| Equipment | Alpha-600 automatic grinder&polisher |
| Consumables | YS polishing cloth,3μm polycrystalline diamond suspension,PL-W polishing lubricant |
| Parameter | Pressure:25N,same direction:150rpm,300s |
3.1.3-polishing(automatic fine polishing)
Polish the specimen with Alpha-600automatic grinder&polisher,use ET polishing cloth with 0.05μm non-crystallizing silica suspension for fine polishing.
| Equipment | Alpha-600 automatic grinder&polisher |
| Consumables | ET polishing cloth,0.05μm non-crystallizing silica suspension |
| Parameter | Pressure:22N,same direction:120rpm,time:120s |
3.2.1-manual grinding
Grind the specimen with Alpha-202 double disc double control grinder&polisher.
| Equipment | Alpha-202 double disc double control grinder&polisher |
| Consumables | SiC abrasive paper:P180,P400,P800,P1200,P2000,P2500 |
| Parameter | 300rpm |
3.2.2-manual plane polishing
Polish the specimen with Alpha-202 grinder&polisher, use YS polishing cloth with 3μm polycrystalline diamond suspension,add PL-W polishing lubricant.
| Equipment | Alpha-202 double disc double control grinder&polisher |
| Consumables | YS polishing cloth,3μm polycrystalline diamond suspension,PL-W polishing lubricant |
| Parameter | Speed:500rpm,time:5min |
3.2.3-manual fine polishing
Polish the specimen with Alpha-202 grinder&polisher,use ET polishing cloth with 0.05μmnon-crystallizing silica suspension.
| Equipment | Alpha-202 double disc double control grinder&polisher |
| Consumables | ET polishing cloth,0.05μm non-crystallizing silica |
| Parameter | Speed:200rpm,time:2min |
4- Corrosion
The material of the bolt and nut provided by the customer is unknown, and the default is carbon steel or low and medium alloy steel for corrosion. Abrasive with 4% nitric acid.
| Equipment | Formula | Instructions |
| 4% nitrate alcohol | HNO₃ 4ml |
abrasion method |
5-observation
| Equipment | Leica DM2700M metallographic microscope |
| Consumables | |
| Parameter | 50×→500× |
03analysis
hot mounting screw 50×
A large number of sulfide inclusions are visible
hot mounting screw 200×
A large number of sulfide inclusions are visible
hot mounting nut 200×
Visible cracks
hot mounting nut 500×
Visible cracks
Polished 50×
Contains a lot of sulfide inclusions
Figure 1:Corrosive state 50×
Contains a lot of sulfide inclusions
Figure 2:Corrosive state 200×
Contains a lot of sulfide inclusions. The heart is a normalizing organization, and there is Widmandelstein. The surface cools rapidly to form martensite.
Figure 1:Corrosive state 50×
Tempered sorbite with retained martensitic orientation
Figure 2:Corrosive state 200×
Tempered sorbite with retained martensitic orientation
Figure 1:Corrosive state 50×
The tissue is fibrous, with interruptions and turbulence visible on the top of the tooth
Figure 1:Corrosive state 50×
The tissue is fibrous, with interruptions and turbulence visible on the top of the tooth
Figure 1:Corrosive state 100×
Ferrite and tertiary cementite can be seen, and there are infiltrations at the surface grain boundaries
Figure 2:Corrosive state 200×
Ferrite and tertiary cementite can be seen, and there are infiltrations at the surface grain boundaries
Figure 3:Corrosive state 500×
Ferrite and tertiary cementite can be seen, and there are infiltrations at the surface grain boundaries
Available in a wide variety of materials, both bolts and nuts, in different sizes. Special fixtures should be designed for small-sized or special-shaped pieces to hold them during cutting. Of course, some small-sized pieces can also be directly mounted and roughly ground to the middle section.
For coated specimens, edge-preserving hot mounts should be used.
Some thin-walled parts will be deformed when hot-pressed and should be cold-set.
Different grinding and polishing steps are developed for different materials.
