The grade every forging shop already stocks
If there's one alloy steel that PAAPAM-member forging shops along Lahore's GT Road and in Karachi's SITE and Bin Qasim areas keep on hand without being asked, it's 4140. Also known as DIN 1.7225 or 42CrMo4, it's the low-alloy chromium-molybdenum steel behind a large share of Pakistan's auto parts forging output.
What the alloying actually does
4140 runs 0.80 to 1.10% chromium, 0.15 to 0.25% molybdenum, and 0.38 to 0.43% carbon, with manganese in the 0.75 to 1.00% range and silicon between 0.15 and 0.30%. Sulfur and phosphorus are capped low, 0.040% and 0.035% respectively, to keep the steel from becoming brittle at grain boundaries. Chromium and molybdenum together give it hardenability well beyond a plain carbon steel of the same carbon content, meaning it hardens more uniformly through thicker sections, and holds up better under repeated stress cycles. That combination of fatigue strength, abrasion resistance, and toughness is exactly what a forged shaft or gear needs.
Typical published ranges, percent by weight
- Cr0.8 to 1.1%
- Mn0.75 to 1%
- C0.38 to 0.43%
- Si0.15 to 0.3%
- Mo0.15 to 0.25%
- S0.04%
- P0.04%
- Febalance
0%2%
Ranges are typical published values, not guaranteed for a specific batch. Confirm against the mill test certificate.
The numbers that matter for spec sheets
Density sits at 7.85 g/cm³, melting point around 1416°C. Unlike some of the tool steels, 4140's actual mechanical properties (tensile strength, yield strength, hardness) vary a good deal depending on the heat treatment applied after forging, so a mill certificate or a specific temper condition matters more here than a single quoted number. What stays constant is the composition, and that's what a forge shop is really buying: the alloying content that gives them room to heat treat toward whatever strength the finished part calls for.
Where it ends up
Shafts, gears, fasteners, and general automotive and machinery components. It's not a case-hardening steel like 8620, it's typically through-hardened and tempered to the strength level the application calls for, which makes it a flexible stock item for a forge shop serving multiple customers with different strength requirements from the same base material. A single batch of 4140 round bar can end up as a low-strength shaft for one customer and a high-strength fastener for another, purely through different tempering after forging.
The Pakistani forging picture
Closed-die forging shops in Lahore and Karachi, several with in-house CNC gear hobbing and heat treatment lines, are the natural customer base. This isn't a niche import, it's a high-turnover grade that should sit near the top of any Pakistani steel supplier's alloy steel stock list, and it's usually the default answer when a customer asks for "alloy steel" without specifying a grade.
4140 or something else in the family
If the part needs higher core toughness for genuinely high-stress service, landing gear, heavy crankshafts, 4340 is the step up, it adds nickel to the chromium-molybdenum base for better hardenability and toughness at the cost of a more expensive alloy. If the part will be carburized for a hard wear surface over a tough core, gears especially, 8620 is the case-hardening alternative rather than 4140's through-hardening approach, and it's a lower-carbon steel specifically because carburizing adds the surface carbon 4140 already has built in.
Sourcing 4140 for a forging run? Request a quote with your dimensions and quantity.