If you’ve been sourcing fasteners from China, you’ve probably noticed a pattern: alongside familiar Chinese grades like ML35 and 45#, there’s a Japanese standard that appears everywhere—SWRCH35K. It’s on mill certificates from Baosteel, in specifications for automotive bolts, and quoted by suppliers across the country. In fact, SWRCH35K has become one of the most widely used materials for 8.8-grade fasteners in China. But what exactly is SWRCH35K? How does it compare to Chinese grades? And why is it so popular?
What Does SWRCH35K Mean?
The name follows the Japanese JIS (Japan Industrial Standard) naming convention:
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SWRCH = Steel Wire Rods for Cold Heading (冷镦用碳钢线材)
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35 = Average carbon content in hundredths of a percent (0.35%)
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K = A designation indicating the steel is killed (fully deoxidized)
So SWRCH35K is a killed carbon steel with approximately 0.35% carbon, specifically designed for cold heading applications.
Standards and Equivalents
| Standard | Grade | Notes |
|---|---|---|
| JIS G3507 | SWRCH35K | Original Japanese standard |
| GB/T 6478 | ML35Mn | Chinese equivalent standard |
| Common Usage | SWRCH35K | Most commonly used name in Chinese industry |
In practice, Chinese mills produce SWRCH35K to JIS specifications, and it’s widely accepted as equivalent to Chinese ML35 or ML35Mn.
Chemical Composition
The table below shows the chemical composition requirements for SWRCH35K based on JIS G3507 and actual production values from major Chinese mills.
| Element | JIS G3507 Requirement | Typical Mill Values (Baosteel, etc.) | Notes |
|---|---|---|---|
| Carbon (C) | 0.32 – 0.38% | 0.34 – 0.36% | Core strengthening element |
| Silicon (Si) | 0.10 – 0.35% | 0.15 – 0.25% | Lower silicon improves cold formability |
| Manganese (Mn) | 0.60 – 0.90% | 0.65 – 0.75% | Enhances hardenability |
| Phosphorus (P) | ≤ 0.030% | 0.012 – 0.020% | Impurity; strictly controlled |
| Sulfur (S) | ≤ 0.035% | 0.006 – 0.015% | Impurity; strictly controlled |
| Aluminum (Al) | Not specified | 0.02 – 0.05% (acid soluble) | Al-killed for fine grain structure |
| Chromium (Cr) | ≤ 0.20% (residual) | ≤ 0.10% | Residual element |
| Nickel (Ni) | ≤ 0.20% (residual) | ≤ 0.10% | Residual element |
| Copper (Cu) | ≤ 0.20% (residual) | ≤ 0.15% | Residual element |
Mechanical Properties
As-Rolled Condition (Hot-Rolled Wire Rod)
SWRCH35K is typically supplied as hot-rolled wire rod. In this condition, mechanical properties are not always guaranteed by specification, but typical values are:
| Property | Typical Value | Notes |
|---|---|---|
| Tensile Strength (Rm) | ≤ 620 MPa | Typical range 580-620 MPa |
| Reduction of Area (Z) | ≥ 45% | Indicator of ductility |
| Hardness | 90-95 HRB | Suitable for cold heading |
| Cold Heading Test | 1/2 cold upset (50% reduction) | No cracks |
After Heat Treatment (Quenched and Tempered)
For 8.8-grade fastener production, SWRCH35K is heat-treated to achieve:
| Condition | Typical Value |
|---|---|
| Quenching Temperature | 850-880°C |
| Tempering Temperature | 540-600°C |
| Tensile Strength (after HT) | 800-950 MPa |
| Yield Strength (after HT) | 640-750 MPa |
| Hardness (after HT) | HRC 22-32 |
| Microstructure | Tempered sorbite |
Summary: SWRCH35K at a Glance
| Property | Value |
|---|---|
| Standard | JIS G3507 |
| Chinese Equivalent | ML35 / ML35Mn (GB/T 6478) |
| Carbon Range | 0.32-0.38% |
| Key Feature | Killed steel for cold heading |
| Tensile Strength (as-rolled) | ≤620 MPa |
| After Heat Treatment | Class 8.8 achievable |
| Hardenability | Good for ≤M16; larger sizes need alloy |
| Main Applications | 8.8-grade bolts, nuts, screws |
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