Starting from a piece of steel: Sunzo transforms "metallic materials" into the foundational language of elastic technology.

Starting from a piece of steel: Sunzo transforms "metallic materials" into the foundational language of elastic technology.

From a piece of steel to the gentle touch of a disc spring upon the ground.

Many people believe that the manufacturing of disc springs, wave springs, and custom-shaped elastic components relies solely on molds and machine tools.

In reality, what truly determines a product's lifespan is often the step taken beforehand – understanding materials.

Recently, Jiangsu Sunzo Spring Elastic Technology Co., Ltd. organized an internal training session titled "Fundamentals of Metallic Materials" aimed at key personnel from various departments—including Technology, Quality, and Production. The session eschewed flashy PowerPoint slides or superficial discussions about "industry trends"; instead, it offered a rigorous, in-depth review covering topics ranging from carbon content and pig iron to steel, strip steel, hot-rolling and cold-rolling processes, and metallographic examination.

01 Thirty years of frontline experience – shared with you wholeheartedly.

The keynote speaker for this training session is Engineer Huang Yongxiang, a senior industry expert at our company.

Mr.Huang has dedicated over 30 years to the industry, specializing in metal technology research and development, pressure processing, and quality control, and has long been supporting every elastic component manufactured by Sunzo. This time, he has systematically and comprehensively shared his decades of frontline material expertise with key personnel across all departments—including technology, quality, and production.

After the training session, everyone reached a shared understanding—

The competitiveness of elastic components lies not in their spring geometry, but in their iron–carbon phase diagram.

02 Steel and iron – the difference isn't just in their names, but in that mere 0.0001% carbon content.

From the very beginning of the training, the most ambiguous concepts were clearly defined: pure iron, steel, and cast iron – three materials represented by a carbon content spectrum.

Ø Pure iron: with a carbon content below 0.04%, it is soft, tough, and highly conductive, yet it is not the primary material used for structural load-bearing components;

Ø Steel: Primarily composed of iron with a carbon content ranging from approximately 0.04% to 2.11%; it can be forged, rolled, or subjected to heat treatment; it serves as the backbone of the industrial world.

Ø Hard iron: contains 2.1%–4.3% carbon; it is hard and wear-resistant, yet too brittle to be forged; therefore, it is more suitable for machine tool beds, bases, and static castings.

One extra percent carbon yields cast iron; one less percent carbon yields pure iron; only when the carbon content is precisely controlled does one obtain steel.

For Sunzo, this is not textbook knowledge. In nuclear power, aerospace, hydrogen energy, and ultra-high-voltage applications, disc springs must withstand preload, creep, and alternating loads; if the material's "characteristics" are not properly understood, even the most advanced heat treatment will be unable to salvage the component.

03 Steel strip – it's not as simple as just a "slightly narrower large steel plate."

The training devoted considerable time to discussing steel strip – which represents the "early stage" of elastic components.

Steel strip is characterized by its "narrow and long" profile; while it may appear to be merely a variant of flat steel products, it is fundamentally a product driven by downstream market demand: it features high production volume, a wide range of product varieties, high dimensional accuracy, excellent surface quality, is available for roll supply, can be flat-rolled or slit, and can be custom-cut according to specific part layouts and dimensions.

Sunzo manufactures disc springs and waveform springs; this often involves working with the following key parameters:

Ø Thin strip steel / Thick strip steel: the boundary is set at 4 mm;

Ø Narrowband / Broadband: Narrowband is rolled directly on demand; broadband is first rolled into wide strips before being divided into individual strips;

Ø Lengthwise thickness variation: the thickness difference along the longitudinal direction at the front, middle, and rear sections;

Ø Three-point deviation: the deviations to the left, center, and right along the width direction;

Ø Final tolerance: the "quality red line" resulting from the superposition of length and width dimensional errors.

For example, if the ordering requirement is ±0.05 mm, and the actual measured values fall within the ranges of 1.45–1.50,1.47–1.53, or 1.41–1.56, these correspond to "Qualified,"  "High Quality," and "Exceeds Tolerance – Not Acceptable," respectively.

The spring manufacturer purchases not just steel, but an entire set of predictable deformation boundaries.

This is also why Sunzo consistently emphasizes that raw materials are not simply obtained by the procurement department with a click of a mouse; rather, they are the result of a collaborative "review" involving technology, quality, and manufacturing processes.

04 Hot rolling vs. Cold rolling: Temperature – the defining characteristic of the process

There's a clever detail in the training material:

Ø Hot rolling: The material is rolled at temperatures above 900–1200°C, which facilitates deformation and results in a slightly rougher surface; however, this process is well-suited for large-scale forming operations.

Ø Cold rolling: performed at room temperature; results in precise dimensions, excellent surface finish, and high hardness; however, significant work hardening occurs, often requiring subsequent annealing or heat treatment as a final finishing step.

For elastic component manufacturers, deciding whether to use hot-rolled or cold-rolled materials is not about which option is "more advanced," but rather about asking three key questions: Does the part require stamping? Does the surface need to bear loads directly? Where is the optimal window for subsequent heat treatment?

In the Sunzo disc spring manufacturing process chain, annealing, forming, heat treatment, high-pressure pressing, and automatic sorting are not isolated steps; rather, they are closely intertwined with the question of "how this material was originally rolled."

05 Macroscopic inspection reveals "hidden defects"; metallographic inspection uncovers "genetic factors"

The training also provides a thorough explanation of the inspection process – the aspect that matters most to quality professionals:

Ø Low-magnification acid leaching, fracture surface examination, sulfur printing, and tower-shaped inspection: Use the naked eye and a low-magnification magnifying glass to identify shrinkage cavities, cracks, and segregation;

Ø Ultrasonic testing: Detection of internal defects;

Ø Metallographic examination: Using a microscope to inspect decarburization, grain size, network carbides, banded microstructure, liquid segregation, and graphite carbon.

Macroscopic inspection determines whether the material is suitable for use; metallographic inspection determines whether the material will suddenly fracture in the future.

For example, after quenching and tempering, the grain size is reduced to Grade 8–9, while the fracture surface typically falls around Grade 6 – do not underestimate these grades; they represent grain refinement, stress uniformity, and an extended fatigue life.

The reason why Sunzo established a modern testing center to conduct a comprehensive range of tests—including load curves, high-temperature creep, stress relaxation, fatigue cycling, metallographic microstructure analysis, and hydrogen embrittlement testing—is precisely for this reason:

High-end elastic components are sold not for their "ability to deform," but for demonstrating "knowing exactly when they will still dare to deform."

06 The essence of steelmaking: Battling sulfur, phosphorus, shrinkage cavities, and impurities

The most practical and real-world segment of the training focuses on steelmaking.

The blast furnace does not produce steel; it only produces molten iron. Steelmaking is not simply about "heating" iron, but involves decarburization, desulfurization, dephosphorization, removal of impurities, and alloying.

The sulfur and phosphorus content limits have been tightened from the previously lenient standards to 0.025% or even lower; this shift reflects the comprehensive upgrading of the entire mineral processing, smelting, and refining systems.

However, some manufacturers, in pursuit of energy and cost savings, cut corners by omitting certain steps—such as failing to properly trim the ends of steel ingots—and allow shrinkage cavities and impurities present at the riser area of the ingot to remain in the billet. This leads to subsequent issues: when laser cutting is halted, micro-cracks appear in the heat-affected zone; residual shrinkage cavities are not fully removed, resulting in edge cracking in Model 485 products; while the warranty documentation may appear to show no issues, the actual products cannot withstand the operational conditions.

Therefore, at high-end application scenarios, Sunzo will discuss electroslag remelting, single-stage or two-stage remelting processes, and customized processing of special raw materials.

Due to the pre-tightening requirements in nuclear power applications, aerospace flight operations, and the long-term alternating loads experienced by electrolytic cells, a "roughly adequate" approach is not permissible.

07 Sunzo's Strength: Technology, R&D, and Talent – Three Core Competitive Advantages

After discussing the materials, let us now turn to the Threefold Mass itself.

Jiangsu Sunzo Spring Elastic Technology Co., Ltd. conducts R&D in Nanjing and manufacturing in Sihong; its disc springs, wave springs, helical springs, and custom-shaped springs are used in the nuclear power, aviation, aerospace, military industry, hydrogen energy, ultra-high voltage (UHV) power transmission, automotive, wind power, shipbuilding, and construction machinery sectors.

Technical Expertise – End-to-End Control: Sunzo's technical foundation extends beyond spring design to encompass the entire manufacturing chain – from material selection and heat treatment to forming, inspection, and operational application. We have participated in the development and revision of both ISO and national standards for disc springs; we hold certifications under the ISO 9001, IATF 16949, ISO 14001, and ISO 45001 management systems; we maintain an inventory of specialized materials—including refined spring steel, stainless steel, nickel-based alloys, precipitation-hardening stainless steel, and Hastelloy – all of which are processed in-house through annealing, forming, heat treatment, high-pressure forming, and automated sorting processes.

R&D Capability – Turning "invisible reliability" into tangible testing. Our state-of-the-art testing facility is equipped with a comprehensive range of testing services—including load curves, high-temperature creep testing, stress relaxation testing, fatigue cycling testing, metallographic analysis, and hydrogen embrittlement testing—always readily available. Behind every deployment under demanding operating conditions, there is a set of data serving as solid proof.

Talent Strength – A team that understands materials and approaches its work with dedication. The company employs two PhD holders and brings together numerous retired senior industry experts; with key personnel such as Engineer Huang Yongxiang – who has dedicated decades to this field – as its core, the company has built a robust expert team that combines seasoned veterans, mid-career professionals, and young talents. At Sunzo, those with deep expertise in steel materials are not just a few individuals – they form a dedicated team.

Final Note

At the end of that training session, the system was still lagging, and the computer had not yet switched to the retrospective interface for the materials left over from the previous day.

However, no one is in a hurry—because the three-phase approach is inherently structured as follows: first, thoroughly explain the materials; then, ensure the components are properly manufactured; and finally, integrate the failure analysis back into the manufacturing process.

If springs are the "muscles" of industry, then knowledge of metallic materials is the "nerves" of Sunzo Spring Elasticity Technology.

This time, we're sharing it with our engineers; next time, we hope it will become a reliable promise within every disc spring.

Steel has its own unique character, just as humans have their own meticulous nature. Those who don't understand steel cannot manufacture high-quality springs; those who don't recognize defects cannot ensure reliable performance under demanding operating conditions.

Sunzo has always believed that true flexibility is never merely about the flexibility of form—but rather a technical flexibility born from the seamless integration of materials, craftsmanship, and responsibility, one that stands the test of time and load.