When a metal dome fails prematurely or its actuation force drifts between production lots, the root cause is almost always in the material - not the stamping process or the plating. This guide explains why stainless steel grade and temper designation matter for snap dome performance, and how to specify the right material for your application rather than accepting whatever the supplier defaults to.
Figure 1: Stainless steel metal domes - the base material and its temper determine actuation force, fatigue life, and corrosion resistance more than any other design parameter.
Why Material Choice Matters More Than You Think
A metal dome is essentially a precision spring made from ultra-thin stainless steel sheet. Like any spring, its behavior - how much force it takes to snap, how many cycles it survives before weakening, and how well it resists corrosion - is governed almost entirely by the material's mechanical properties. The dome's shape (round, square, four-leg) and dimensions control the exact force value, but the material determines whether that force can be held consistently over a million actuations and across temperature extremes.
In practice, buyers often treat the dome material as a supplier decision and focus instead on dimensions, force, and price. This is a mistake. Two domes that look identical and are stamped to the same drawing can perform very differently if one uses soft temper SUS301 and the other uses full-hard SUS301. The force may measure the same on day one, but after 500,000 actuations the softer material will have lost its snap, while the harder material will still feel crisp.
The Three Stainless Steels Used for Snap Domes
Nearly all commercial metal domes are made from one of three austenitic stainless steel grades. Each has distinct properties that make it suitable for different applications.
SUS301 (17Cr-7Ni) - The Industry Standard
SUS301 is the most widely used material for snap domes by a wide margin. It is a chromium-nickel austenitic stainless steel that can be work-hardened to very high tensile strengths through cold rolling. This work-hardening capability is what makes it ideal for domes: the stamping process itself further work-hardens the material at the bend radii, creating a spring that is both strong and elastic.
- Tensile strength range: 1,000–2,000 MPa depending on temper - far higher than mild steel, which is why a 0.06mm thick SUS301 dome can deliver 200–400g of actuation force.
- Key advantage: Excellent combination of elasticity, fatigue resistance, and corrosion resistance. It snaps cleanly and repeatedly without permanent deformation.
- Typical applications: Consumer electronics, automotive interior controls, medical devices, industrial panels - essentially everything where a standard dome is used.
SUS304 (18Cr-8Ni) - The Economy Choice
SUS304 is the more familiar "18/8" stainless used in cookware and appliances. It has slightly higher nickel content than SUS301 and slightly lower chromium. While it has good corrosion resistance, its work-hardening rate is lower, which means it cannot achieve the same spring properties as SUS301 at equivalent thickness.
- Tensile strength range: 600–1,200 MPa - lower than SUS301 at the same temper, resulting in softer actuation feel and shorter fatigue life.
- Key advantage: Lower raw material cost and excellent corrosion resistance in mild environments.
- Limitation: Domes made from SUS304 tend to have lower tactile ratio (mushier feel) and shorter cycle life. They are suitable only for low-cycle, low-cost applications such as remote controls with infrequent button presses.
- Typical applications: TV remote controls, low-cost keypads, disposable medical devices - applications where cost is critical and cycle life requirements are modest.
SUS316 (17Cr-12Ni-2Mo) - The Corrosion-Resistant Premium
SUS316 adds molybdenum to the chromium-nickel composition, dramatically improving corrosion resistance - particularly against chlorides, salt spray, and chemical exposure. This is the material specified for marine, outdoor, and medical applications where humidity or chemicals would degrade SUS301.
- Tensile strength range: Similar to SUS301 when work-hardened, but at a higher material cost.
- Key advantage: Superior pitting corrosion resistance against salt, sweat, disinfectants, and cleaning agents. Essential for medical-grade domes and outdoor equipment.
- Limitation: 2–3 times the cost of SUS301, with no mechanical advantage for indoor, dry environments.
- Typical applications: Marine electronics, outdoor keypads, medical devices exposed to disinfectants, food processing equipment, and hospital beds.
| Property | SUS301 | SUS304 | SUS316 |
|---|---|---|---|
| Chromium / Nickel | 17% / 7% | 18% / 8% | 17% / 12% |
| Molybdenum | None | None | 2% (added) |
| Max tensile (full hard) | ~2,000 MPa | ~1,200 MPa | ~1,600 MPa |
| Corrosion resistance | Good (indoor) | Good (indoor) | Excellent (salt/chemical) |
| Relative cost | 1.0x (baseline) | 0.8–0.9x | 2.5–3.0x |
| Typical dome life | 1–5 million cycles | 100k–500k cycles | 1–5 million cycles |
Understanding Temper Designations: 1/2H, 3/4H, H, and EH
Within each stainless steel grade, the temper (or hardness) controls how much the material has been cold-worked before stamping. This is the single most important specification for dome performance. A supplier that just says "SUS301" without specifying the temper is leaving a critical variable undefined.
The standard temper designations for austenitic stainless steel strip used in dome manufacturing are:
| Temper | Approx. Tensile Strength | Dome Behavior | Best For |
|---|---|---|---|
| 1/2H (Half Hard) | ~1,000–1,200 MPa | Soft, low force, low tactile ratio, short life | Low-cost remote controls, single-use devices |
| 3/4H (Three-Quarter Hard) | ~1,400–1,600 MPa | Medium force, moderate tactile, good life | General consumer electronics |
| H (Full Hard) | ~1,700–1,900 MPa | High force, crisp tactile, long life | Most applications - automotive, industrial, medical |
| EH (Extra Hard) | ~1,900–2,100 MPa | Very high force, maximum tactile, but brittle - risk of cracking | Heavy-duty industrial panels, high-cycle requirements |
For 90% of applications, SUS301 full hard (H temper) is the correct specification. It balances force, tactile feel, and fatigue life across temperature ranges. Specify EH only if you have a verified need for very high actuation force (above 400g) or ultra-long life (above 5 million cycles), and have discussed the cracking risk with your dome manufacturer.
Figure 2: Automotive-grade dome sheet array - these domes are made from full-hard SUS301 to survive 10+ years of temperature cycling and millions of actuations in steering wheel and center console controls.
Why Suppliers Sometimes Substitute Material
Understanding the supplier's perspective helps buyers avoid material mismatch. There are three common scenarios where a supplier might deviate from the specified material:
1. Substituting SUS304 for SUS301 to save cost. If the buyer does not specify SUS301 explicitly and only says "stainless steel dome," some suppliers will use cheaper SUS304 strip. The dome will pass initial force and dimensional checks, but will fail prematurely in service. Always specify "SUS301 full hard" by name, not just "stainless steel."
2. Using softer temper to hit a low force target. If a buyer requests a very low actuation force (below 100g) for a small dome, the supplier may use softer 1/2H or 3/4H material instead of optimizing the dome geometry. The result is a dome that feels correct initially but has poor tactile ratio and short life. Better to design a larger, thinner dome in full hard material than to use soft material.
3. Mill supply limitations. SUS316 in ultra-thin gauges (0.05–0.08mm) and precise tempers is not always readily available. A supplier may substitute a similar grade or temper. This is acceptable if documented and re-qualified, but it should never happen silently. Ask your supplier for a mill test report (MTR) with every material lot, showing the actual grade, heat number, and hardness.
How Material Affects Other Dome Properties
Temperature Sensitivity
Stainless steel loses tensile strength as temperature rises. SUS301 full hard at +85°C may see 10–15% lower actuation force than at room temperature. At -40°C, force increases by 5–10%. This is normal and predictable, but it matters if your product must operate across a wide temperature range - specify the force at the extreme temperatures, not just room temperature. SUS304 is slightly more temperature-stable but at the cost of lower base strength. SUS316 behaves similarly to SUS301 thermally.
Plating Adhesion
The material surface condition directly affects plating adhesion. SUS301 work-hardened strip has a naturally passivated chromium-rich surface that accepts nickel and gold plating well. However, if the strip has been handled with oil or fingerprints before plating, adhesion fails. This is a process control issue rather than a material grade issue, but it is more noticeable on harder tempers where surface roughness is lower.
Dome Life vs. Material Thickness
For a given dome diameter and force, thicker material in a softer temper will have shorter life than thinner material in a harder temper. This seems counterintuitive but makes sense: the fatigue failure mode is cracking at the bend radius, and a thinner, harder dome has less stress concentration at that radius. When requesting custom dome arrays, ask the supplier to recommend the thinnest gauge that meets your force requirement in full-hard SUS301 rather than defaulting to a thicker, softer gauge.
What to Put in Your RFQ and Purchase Order
To avoid material ambiguity, include these specific items in your dome specification and PO:
- Material grade: "SUS301 full hard" - not just "stainless steel." For corrosion-critical applications: "SUS316 full hard."
- Temper and hardness: Specify both the temper designation (H) and a Rockwell or Vickers hardness range (e.g., HV 550–600). This prevents the supplier from substituting a softer temper.
- Material thickness tolerance: ±10% of nominal thickness. Thickness variation is the largest contributor to force variation between lots.
- Mill test report (MTR): Require MTR with each shipment showing grade, heat number, tensile strength, and hardness. This is your traceability document.
- Acceptable material substitutions: If the supplier needs to substitute (e.g., SUS304L instead of SUS304), require written notification and re-qualification testing - never accept silent substitutions.
For more information on material specifications, plating options, and custom dome design, contact Shanyo's engineering team for a datasheet or sample evaluation.
