Understanding the Art and Science of Identifying Steel
Spark testing is a traditional yet highly effective method for determining the general classification of ferrous materials—metals containing iron. It provides a quick and inexpensive way to distinguish between different grades of steel by observing the sparks produced when a sample is applied to a grinding wheel.
At Roemer’s Grinding Works, spark testing remains a valuable part of our steel identification process, ensuring accuracy and quality in every blade we produce.
What is Spark Testing?
Spark testing involves holding a metal sample—often a small scrap piece—against a rotating grinding wheel. The friction creates sparks whose colour, length, shape, and burst pattern reveal key information about the metal’s carbon content and alloying elements.
While non-ferrous metals such as copper or aluminium do not emit sparks, ferrous materials generate distinctive patterns. These can be compared against known samples or reference charts to determine classification.
Why Use Spark Testing?
Spark testing offers a number of advantages:
Fast and cost-effective — no special sample preparation is required.
Efficient sorting — helps differentiate between steel types before processing.
Practical and accessible — requires only a grinding wheel and a keen eye.
However, spark testing does not provide an exact chemical analysis. For positive identification, a laboratory or spectrographic test may be required. The test also slightly damages the sample surface.
Understanding Spark Characteristics
The spark pattern is determined primarily by carbon content, not hardness.
Low-carbon steels produce long, straight, dull-red sparks with minimal bursting.
High-carbon steels emit short, bright sparks with frequent bursts and branching.
When stainless steel is in question, an acid test can be used—acid will not etch stainless steel, whereas other steels will react. Alternatively, a flame hardening test with a known-hardness file may be performed to check hardenability.
How to Identify Sparks
At Roemer’s Grinding Works, technicians use visual spark identification as part of our internal quality and training programme. Each steel type produces a recognisable pattern:
Type of Steel Spark Description
Air Hardened Steel Short, orange sparks with high bursts and extensive splitting.
High Speed Steel Short, red sparks with few bursts.
Tool Steel Medium to long yellow sparks with moderate bursts.
Stainless Steel Long, light-yellow sparks with large end splits.
Mild Steel Bright, scattered sparks with long terminal splits.
Types of Steel Commonly Used at Roemer’s Grinding Works
1. Air Hardener – 1.2379 (X153CrMoV12 / AISI D2)
A high-carbon, high-chromium tool steel offering excellent wear resistance.
Composition: C 1.55%, Cr 12%, Mo 0.8%, V 0.9%
Specific Gravity: 7.6 g/cm³
Heat Treatment: Harden 1000–1040°C | Quench: gas, air, or oil | Temper: 220–280°C
Working Hardness: 58–62 HRC
Spark Identification: Short, orange sparks with intense bursts and fine splitting.
2. High Speed Steel – 1.3355 (HS18-01 / AISI T1)
A tungsten-based steel with superior hardness, toughness, and heat resistance—ideal for cutting applications.
Composition: C 0.78%, Cr 4%, W 18%, V 1.1%
Specific Gravity: 8.7 g/cm³
Heat Treatment: Harden 1230–1280°C | Quench: gas, oil, or salt bath | Temper: 540–570°C
Working Hardness: 63–66 HRC
Spark Identification: Short, red sparks with few bursts.
3. Tool Steel – 1.2842 (90MnCrV8 / AISI O2)
A tough and versatile steel known for its wear resistance and sharp cutting performance.
Composition: C 0.9%, Mn 2.0%, Cr 0.4%, V 0.1%
Specific Gravity: 7.85 g/cm³
Heat Treatment: Harden 790–820°C | Quench: oil | Temper: 220–260°C
Working Hardness: 58–62 HRC
Spark Identification: Medium to long yellow sparks with moderate bursts.
4. Stainless Steel – 1.4034 (X46Cr13 / AISI 420)
This steel offers high corrosion resistance in water and steam environments, often used for surgical and food-grade blades.
Composition: C 0.45%, Cr 13.5%
Specific Gravity: 7.6 g/cm³
Heat Treatment: Harden 1000–1040°C | Quench: gas or oil | Temper: 180–280°C
Working Hardness: 51–53 HRC
Spark Identification: Long, light-yellow sparks with large end splits.
5. Stainless Steel – 1.4112 (X90CrMoV18 / AISI 440B)
A high-hardness stainless steel offering excellent corrosion resistance across environments.
Composition: C 0.9%, Cr 18.0%, Mo 1.1%, V 0.1%
Specific Gravity: 7.6 g/cm³
Heat Treatment: Harden 1020–1040°C | Quench: gas or oil | Temper: 220–280°C
Working Hardness: 54–57 HRC
Spark Identification: Long yellow sparks with few bursts and distinct splitting.
6. Mild Steel
A low-carbon steel known for its ductility, weldability, and machinability.
Spark Identification: Bright, scattered, long sparks with many terminal splits.
Conclusion
Spark testing continues to play a vital role at Roemer’s Grinding Works—a method where craftsmanship and metallurgical knowledge meet. By observing and understanding spark behaviour, our team ensures each piece of steel is correctly identified before it moves into production or heat treatment.
Though simple in nature, spark testing embodies Roemer’s ongoing commitment to quality, precision, and technical excellence in every operation.
