Our Journey, Chapter 1
A sick unit on rented premises
S R Forgings did not begin with a new factory and a business plan. In 2009 I visited a fastener unit in Focal Point, Ludhiana that was up for sale. It was a sick unit, running on rented premises, with machines but no future on its own.
I bought it in partnership with a family member. We kept on the person who had been running it as our manager, because he knew the machines, and in those first months the machines were all we had. S R Forgings started trading on 7 September 2009.
Our first customers, and the first thing we did not know
Our first order came from a forging company here in Ludhiana. Their first condition was that every bolt must pass go/no-go gauging.
We were new, and honestly we did not know what that meant. We learned fast. A go/no-go thread gauge checks a thread against its tolerance limits. The GO ring must screw on fully, which proves the thread is not oversize. The NO-GO ring must not screw on; at most it may start by a turn or two, which proves the thread is not undersize. A bolt that fails either check is rejected, however good it looks.
That first order was for plain bolts, supplied without heat treatment. We passed the gauge check and delivered. Two more Ludhiana companies became customers soon after, and each one added items to our list.
The customer who showed us what a high tensile bolt really is
The major leap came when we started supplying a Ludhiana fastener maker known in the trade for very strict norms. They did not just place orders. They taught us what a high tensile bolt actually is, which material to use for which class, how to gauge, and which parameters to check on every lot.
The most important lesson was the one most people in the trade still miss.
"It's just an EN8D bolt, heat treated to 28–32 HRC."
That is how many people describe an 8.8 bolt. It is not what makes one.
A property class is not a hardness number. Class 8.8 is defined in ISO 898-1 by a full set of mechanical properties that the finished bolt must meet together:
| Property (ISO 898-1, class 8.8) | Up to M16 | Above M16 |
|---|---|---|
| Minimum tensile strength | 800 MPa | 830 MPa |
| Minimum 0.2% proof strength | 640 MPa | 660 MPa |
| Minimum elongation after fracture | 12% | 12% |
| Minimum reduction of area | 52% | 52% |
| Hardness range | 22–32 HRC | 23–34 HRC |
| Heat treatment | Quenched and tempered, minimum tempering temperature 425 °C | |
Hardness is a band, not a target. The steel must also harden through to the core of the threaded section, not just at the surface.
This is why different materials qualify 8.8 at different hardness. A hardness reading is taken at one point. Strength, elongation and toughness belong to the whole cross-section. A plain carbon steel that does not harden through may give a good hardness reading while its core stays soft, so it has to be pushed higher in the band to scrape through the tensile test, and it gives up ductility to get there. An alloy steel such as EN18 hardens through the section and reaches 8.8 at a comfortable point in the band, with elongation to spare.
So the question is never "what hardness?" It is "which steel, which size, and does the finished bolt pass every property?"
What we still do because of it
- Material by class and size. EN18 for 8.8 across the size range; EN18 for 10.9 up to 27 mm and 4140 above 27 mm; 4140 for 12.9. Our article on bolt material grades explains why.
- Through-hardening, not case hardening. Quench and temper in a 2-metre pit furnace, with bolts hanging vertically so long bolts come out straight.
- Gauging on every lot, not just the first sample.
- Testing we can prove. Our heat treatment partner tests two pieces from every lot. We then draw two more at random from the same lot and send them to a NABL-accredited laboratory to verify.
Where it led
Those lessons became our standard, and everything we make now stands on them: high tensile and HSFG bolts in property classes 8.8, 10.9 and 12.9, HSFG bolts to IS 3757, and customised structural bolts up to 75 mm diameter, including HSFG bolts above M36.
It also gave us the confidence to take on a bolt nobody in India was making for our first buyer, with only a drawing to go on. That is Chapter 2.
Have a question about high tensile bolt materials, hardness or gauging?
Ask us on WhatsApp or send your drawing for a quotation.
Next Monday, Chapter 2: How we became tunnel segment bolt manufacturers in India. See all articles on our blog.