Stainless Steel Coil Tube — Quarter Hard (1/4H) Condition

Product Overview

The Stainless Steel Coil Tube in the Quarter Hard (1/4H) temper condition represents a precisely engineered intermediate mechanical state within the cold-worked product spectrum. Supplied by Wenzhou Jixing Metal Materials Co., Ltd, this coil tube is delivered in a light cold-worked condition that achieves an optimal balance between mechanical strength and ductile formability. The 1/4H designation indicates that the material has undergone approximately one-quarter of the total cold reduction typically associated with the fully hard (1/2H) temper, resulting in a material that retains superior bending characteristics while offering enhanced yield strength over the fully annealed (soft) condition.

This product is particularly suited for applications requiring moderate strength combined with excellent secondary forming performance, including deep drawing, tight-radius bending, and complex shaping operations that would be difficult to achieve with harder tempers.

Material & Properties

The Quarter Hard coil tube is manufactured from high-grade austenitic stainless steel, typically from the 300-series (e.g., AISI 304 / 304L or AISI 316 / 316L) or 200-series grades, depending on the specific application requirement. The material undergoes controlled cold working to achieve the designated temper, resulting in the following key mechanical properties:

The unique metallurgical advantage of the 1/4H condition lies in its controlled dislocation density. During cold working, dislocations are introduced into the crystal lattice of the austenitic microstructure, increasing strength through work hardening. However, because the reduction is limited to approximately one-quarter of the full cold work, the material retains sufficient ductile capacity to accommodate further plastic deformation during downstream forming processes.

Specifications

Parameter Specification Notes
Product Name Stainless Steel Coil Tube Supplied in coil form for continuous processing
Temper Condition Quarter Hard (1/4H) Light cold-worked intermediate temper
Vickers Hardness (HV) 180–220 Measured per ASTM E92 / ISO 6507
Elongation (A) ≥30% Measured per ASTM E8 / ISO 6892
Typical Grade AISI 304 / 304L / 316 / 316L / 201 Selectable based on application
Wall Thickness 0.3 mm – 6.0 mm Customizable per project requirements
Outer Diameter 3.0 mm – 150.0 mm Customizable per project requirements
Surface Finish Bright Annealed (BA) / No.4 / Hairline Post-temper surface treatment available
Applicable Standards ASTM A269, ASTM A270, EN 10216-5, GB/T 12771 International and Chinese national standards
Coil Weight Up to 3,000 kg Customizable coil packaging

Manufacturing Process

The production of Quarter Hard stainless steel coil tube follows a multi-stage manufacturing sequence designed to achieve precise mechanical properties while maintaining dimensional accuracy and surface integrity:

  1. Raw Material Selection: High-purity stainless steel strip or wire rod is sourced from certified mills, with strict chemical composition control to ensure compliance with the target grade specification (e.g., ASTM A240, JIS G4304).
  2. Hot Rolling & Annealing: The initial hot-rolled product is subjected to solution annealing at temperatures between 1,050°C and 1,150°C, followed by controlled cooling (air or water quench), to achieve a fully recrystallized, soft annealed microstructure.
  3. Pipe Forming (Seamless or Welded): The annealed strip is formed into tube via seamless piercing or welded processes (ERW, TIG, or MIG), depending on the diameter and wall thickness requirements.
  4. Intermediate Annealing: A controlled annealing cycle is performed to relieve forming stresses and ensure a uniform starting microstructure for the cold work tempering stage.
  5. Controlled Cold Reduction (Quarter Hardening): The tube undergoes a precisely calibrated cold working reduction — approximately 20–30% of the total cold work achievable to reach the fully hard (1/2H) condition. This is achieved through cold drawing, cold rolling, or controlled mechanical sizing. The reduction amount is carefully monitored to achieve the target HV 180–220 hardness range.
  6. Final Inspection & Quality Control: Each coil is subjected to comprehensive mechanical testing (hardness, tensile, elongation), dimensional verification, and surface quality assessment before packaging and shipment.

Applications

The Quarter Hard (1/4H) stainless steel coil tube finds extensive use across multiple industries where a balance of strength and formability is critical:

Quality Certifications

Wenzhou Jixing Metal Materials Co., Ltd maintains a rigorous quality management system ensuring that every batch of Quarter Hard coil tube meets or exceeds international standards. Key certifications and quality assurance measures include:

Unique Selling Points

Optimized Strength-to-Formability Ratio: The Quarter Hard (1/4H) condition uniquely delivers approximately 40–60% higher yield strength compared to the fully annealed (soft) condition, while retaining over 30% elongation — enabling downstream forming operations that would otherwise require intermediate annealing cycles, thereby reducing manufacturing cost and production time.