Jiaxing Qunbang (QBH) Reflects on Successful Exhibition at 2026 Shanghai Fastener Show
2026-05-22
With over 10 years of experience in fastener manufacturing, our team specializes in high‑strength bolts, nuts, and custom cold‑headed parts. We manage the entire process from spheroidizing annealing to quenching, tempering, and surface finishing.
IntroductionOn May 20–22, 2026, Jiaxing Qunbang Hardware Co., Ltd. (Qunbang / QBH) exhibited at the 2026 Shanghai International Fastener Show in Shanghai World Expo Exhibition & Convention Center. As the event concluded successfully, we would like to thank all our new and existing customers who visited our booth and engaged in meaningful discussions.
DIN 931 / DIN 933 hex bolts (partial & full thread)
High‑strength nuts (Grade 8, Grade 10)
Custom non‑standard parts (drawn to customer prints)
Quenched & tempered bolts (Grade 8.8, 10.9, 12.9)
Process transparency
In‑house heat treatment line: spheroidizing annealing, quenching, tempering
Controlled atmosphere to minimize decarburization
Material certificates + hardness/metallographic reports per batch
On‑site support
Free selection consulting by our engineering team
Sample display and process parameter explanation
Face‑to‑face cooperation discussions
Why Customers Choose Jiaxing Qunbang (QBH)Full in‑house production – From wire annealing to finished packaging, every step is under our control
International standards – DIN, ISO, GB, ANSI, and custom specifications
Certified quality – ISO 9001:2015 certified with full batch traceability
Responsive service – Direct technical support for selection and problem solving
Gratitude and Next StepsWe deeply appreciate the trust and interest shown by every visitor. If you missed the show or would like to continue a conversation, please reach out:
Email: sales@qbfastener.cn
Website: www.steelbolts.com
We look forward to serving you with high‑quality fasteners and professional heat treatment solutions.
DisclaimerThis article is a post‑event summary from Jiaxing Qunbang. The exhibition dates and venue are based on official organizer information. Jiaxing Qunbang reserves the right of final interpretation.
Jiaxing Qunbang Hardware Co., Ltd. (Qunbang / QBH)Quality Fasteners – Starting from Heat Treatment
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Tempering for Bolts and Nuts – Turning Hardened Steel into Reliable Fasteners
2026-05-08
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If quenching gives bolts their hardness, tempering gives them their usefulness. As‑quenched martensite is hard but brittle – useless for any real application. Tempering transforms that brittle martensite into tempered martensite, the microstructure that delivers the right balance of strength, toughness, and ductility for property classes 8.8, 10.9, and 12.9. In this article, we answer five critical questions about tempering for fasteners, based on our shop floor experience, to help you understand how to achieve consistent, reliable mechanical properties.
What is tempering, and why is it necessary after quenching?
Tempering is a heat treatment process in which hardened (as‑quenched) steel is reheated to a temperature below the lower critical point (typically 400–650°C for most fastener steels), held for a specified time, and then cooled – usually in still air. The purpose is to:
Reduce brittleness – As‑quenched martensite is very hard but extremely brittle; a quenched bolt can snap like glass.
Relieve internal stresses – Rapid cooling during quenching creates high residual stresses that can cause distortion or delayed cracking.
Adjust mechanical properties – By choosing the tempering temperature, we can achieve the exact combination of strength, hardness, and toughness required for a given property class.
The complete quench‑and‑temper (Q&T) sequence for high‑strength fasteners:
Cold‑headed or forged blank → austenitizing (830–880°C) → quench (rapid cool) → as‑quenched martensite (50–55 HRC, brittle) → temper (400–650°C) → tempered martensite (28–44 HRC, tough) → final product.
Real‑world case – the danger of skipping tempering:
A small bolt maker once sent us a sample of “grade 10.9” bolts for testing. When we torqued them to specification, they snapped with a clean, flat fracture. Microstructure revealed untempered martensite – they had skipped tempering to save time. Every bolt was rejected. Tempering is not optional; it transforms a dangerously brittle fastener into a reliable one.
How does tempering change the microstructure and properties? What is the difference between low‑ and high‑temperature tempering?
During tempering, as quenched martensite – a supersaturated solid solution of carbon in iron – decomposes into a mixture of ferrite and fine carbide particles. The higher the temperature, the more the carbides grow and coalesce, reducing strength but increasing ductility and toughness.
Effect of tempering temperature on mechanical properties (typical for 40Cr or SCM435):
Tempering Temperature (°C)
Resulting Microstructure
Hardness (HRC)
Tensile Strength (MPa)
Ductility / Toughness
Typical Fastener Grade
150–200 (low temp)
Tempered martensite (very fine carbides)
50–55
>1800
Very low (brittle)
Not used – too brittle
400–480 (medium temp)
Tempered martensite (fine carbides)
39–44
1200–1400
Moderate
Grade 12.9
500–550 (medium‑high temp)
Tempered martensite (coarser carbides)
32–38
1000–1200
Good
Grade 10.9
550–600 (high temp)
Tempered martensite / tempered sorbité
28–34
800–1000
High
Grade 8.8
650–700 (very high temp)
Tempered sorbité / spheroidized
View More
Annealing Q&A | Spheroidizing Annealing Explained | QBH Fastener
2026-03-31
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IntroductionIn fastener manufacturing, annealing is a heat treatment process that often goes unnoticed but is critically important. Many procurement and quality control professionals focus only on the final hardness and strength, overlooking the decisive role annealing plays in material plasticity, internal structure, and subsequent processability. In this article, we answer five frequently asked questions about bolt and nut annealing from a practical production perspective, helping you understand why high‑quality fasteners depend on a proper annealing process.
What is annealing, and why is it used in bolt and nut production?
Annealing is a heat treatment process in which metal is heated to a certain temperature (usually above the recrystallization temperature), held there for a period, and then slowly cooled. Its main purposes are to reduce hardness, eliminate internal stress, improve structural uniformity, and increase plasticity.
In bolt and nut production, annealing is used in several stages:
Wire annealing before cold heading (spheroidizing annealing)Cold heading requires the wire to have high plasticity. If the wire is too hard, it may crack during cold heading or cause excessive die wear. Spheroidizing annealing makes the carbides inside the wire spheroidal, significantly reducing deformation resistance.
Intermediate annealing after work hardeningFor complex parts that require multiple passes of cold drawing or cold forming (e.g., special‑shaped nuts, long bolts), the material becomes brittle due to work hardening. Intermediate annealing restores plasticity so that forming can continue.
Residual stress reliefAfter cold heading, cold extrusion, or machining, internal residual stresses exist in the part. If not removed, they may cause deformation or cracking during subsequent heat treatment (quenching) or in service.
Real‑world case:
An automotive fastener supplier experienced batch cracking in the heads of M12 flange bolts during cold heading. Analysis showed the wire rod supplied had not been properly spheroidized – the pearlite structure was coarse and lamellar. We recommended adding one cycle of spheroidizing annealing at 740°C. The cracking rate dropped from 12% to 0.3%.
What are the common types of annealing? Which is most often used for bolts and nuts?
Several types of annealing exist. The most common in the fastener industry are:
Annealing Type
Heating Temperature
Cooling Method
Main Purpose
Typical Application
Full annealing
30~50°C above Ac3
Furnace slow cooling
Refine grains, eliminate structural defects
Cast/forged parts, coarse‑grained raw material
Spheroidizing annealing
Near Ac1 (typically 740~760°C)
Isothermal or very slow cooling
Spheroidize carbides, reduce hardness, improve plasticity
Most common for medium‑carbon and alloy steel cold‑heading wire
Stress relief annealing
500~650°C
Air or slow cooling
Remove cold‑working stress, no microstructural change
After cold heading, machining, or cold drawing
Recrystallization annealing
Above recrystallization temp (approx. 650~700°C)
Air cooling
Remove work hardening, restore plasticity
Intermediate treatment for multi‑pass cold drawing or rolling
For bolts and nuts:
Cold‑heading wire (e.g., 10B21, 35K, 40Cr, SCM435) → Spheroidizing annealing is most common. Spheroidization grade ≥ 4 (according to relevant standards) is required.
Intermediate treatment after work hardening → Use recrystallization annealing or stress relief annealing.
How do you judge whether annealing quality is acceptable? What are the inspection criteria?
Annealing quality cannot be judged by hardness alone; microstructure and process parameters must also be considered. Professional suppliers typically check the following three items:
Hardness test
After spheroidizing annealing, wire hardness is typically HRB 70–85 (varies slightly by steel grade).
Too high → insufficient plasticity, risk of cracking during cold heading.
Too low → possible overheating or decarburization.
Spheroidization grade
Evaluated under a metallurgical microscope according to standards such as GB/T 38770 or SEP 1520.
For fastener cold heading, the spheroidization grade is generally required to be at least Grade 4 (out of 6, Grade 4 or above is good).
Reference: spheroidized carbides are uniformly distributed, no coarse lamellar pearlite.
Decarburization depth
If the protective atmosphere is poor during annealing, the surface may decarburize. Decarburization reduces the surface hardness of the finished bolt and can induce fatigue cracks.
Standards require decarburization depth not to exceed 1–2% of the thread height (depending on grade).
Real‑world case:
A batch of Grade 10.9 bolts exhibited thread “peeling" during assembly, and the customer complained of insufficient strength. Our inspection revealed that the raw material had a decarburization depth of 0.15 mm due to poor annealing atmosphere. After switching to QBH wire processed with controlled‑atmosphere spheroidizing annealing, decarburization was kept below 0.03 mm, and the problem was solved.
How do annealing, normalizing, quenching, and tempering differ? What comes after annealing?
Annealing is just one link in the fastener heat treatment chain. The table below clarifies the differences:
Process
Heating Temperature
Cooling Method
Main Purpose
Position in Bolt Production
Annealing
Varies by type (500–900°C)
Slow (furnace or air)
Reduce hardness, improve plasticity, relieve stress
Before cold heading or during intermediate cold working
Normalizing
30–50°C above Ac3
Air cooling
Refine grains, adjust hardness, improve machinability
Optional alternative to annealing for some structural parts
Quenching
Austenitizing temperature (830–880°C)
Rapid (oil/water/polymer)
Obtain martensite, greatly increase strength
After cold heading – first step of quench & temper
Tempering
After quenching (400–650°C)
Air cooling
Remove quenching stress, adjust hardness and toughness
After quenching – to obtain final property class (8.8/10.9/12.9)
What happens after annealing:
Spheroidized wire → pickling & phosphating (scale removal and lubrication) → cold heading → thread rolling → quenching + tempering → surface finishing.
In short: Annealing paves the way for cold heading; quenching & tempering determine the final strength class.
View More
Normalizing for Bolts and Nuts – Purpose, Process, and Key Differences from Annealing
2026-04-07
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Introduction
Normalizing is often overlooked in fastener manufacturing, yet it plays a critical role in refining grain structure, improving consistency, and preparing material for subsequent heat treatment or machining. Many engineers confuse normalizing with annealing, or are unsure when normalizing should be specified. In this article, we answer five common questions about normalizing for bolts and nuts, based on our shop floor experience, to help you make better processing decisions.
What is normalizing, and how is it different from annealing?
Normalizing is a heat treatment process in which steel is heated to a temperature above its upper critical point (Ac3 or Acm), held for sufficient time to achieve full austenitization, and then cooled in still air.
The key differences between normalizing and annealing are:
Feature
Normalizing
Annealing (e.g., full annealing)
Cooling method
Still air (air cooling)
Furnace cooling (slow)
Cooling rate
Faster
Much slower
Resulting structure
Fine pearlite + ferrite (or fine pearlite alone)
Coarse pearlite + ferrite
Hardness
Slightly higher
Lower
Grain size
Refined, uniform
Coarser, less uniform
Cycle time
Shorter (hours)
Longer (often >12 hours)
Main purpose
Refine grains, homogenize structure, improve machinability
Soften material, relieve stress, improve plasticity
Real‑world observation:
In our plant, we once received a batch of 35K steel wire rods with mixed grain sizes (ASTM grain size 3 to 7). Cold heading performance was erratic. A normalizing cycle at 880°C for 40 minutes, followed by air cooling, produced a uniform grain size of ASTM 7–8. The wire drew and headed consistently afterward.
What role does normalizing play in bolt and nut production? Where is it applied?
Normalizing is used at several stages in fastener manufacturing, depending on the material and process route.
Typical applications:
Raw material conditioningFor hot‑rolled wire rods or bars with non‑uniform grain structure or banded ferrite‑pearlite, normalizing homogenizes the microstructure before cold drawing or cold heading.
After forging or hot headingLarge‑diameter bolts or custom‑shaped parts made by hot forging often have coarse grains and decarburized surfaces. Normalizing refines the grain and prepares the part for final quench and temper.
Improving machinabilitySome medium‑carbon and alloy steels (e.g., 40Cr, SCM435) in the as‑rolled condition can be too tough for efficient machining. Normalizing produces a fine pearlitic structure that machines better.
Precursor to carburizingFor case‑hardened bolts (e.g., 10B21 or 20MnTiB used in some high‑strength applications), normalizing after forging ensures uniform case depth during carburizing.
Real‑world case:
A manufacturer of wheel bolts (grade 10.9, material SCM435) experienced inconsistent core hardness after quenching. Investigation revealed banded microstructure in the incoming wire rod. After adding a normalizing step at 860°C before cold heading and final heat treatment, the banding was eliminated, and core hardness variation dropped from ±4 HRC to ±1.5 HRC.
How does normalizing change the microstructure and mechanical properties? How do you inspect normalizing quality?
Microstructural changes:
As‑rolled or as‑forged structures (often coarse pearlite, Widmanstätten ferrite, or mixed grains) transform to fine pearlite + ferrite (hypoeutectoid steels) or fine pearlite + cementite (hypereutectoid steels).
Grain size is refined and homogenized, typically to ASTM 7–9.
Carbides become more uniformly distributed.
Mechanical property changes:
Tensile strength and yield strength increase slightly compared to the annealed condition.
Hardness rises (typically 10–30 HB higher than annealed).
Impact toughness improves due to grain refinement.
Machinability improves (chip formation is more consistent, tool wear reduces).
Inspection methods for normalizing quality:
Inspection item
Method
Acceptance criteria (typical for fastener steels)
Grain size
Optical microscopy (ASTM E112)
ASTM 7 or finer, uniform
Microstructure
Metallographic examination
Fine pearlite + ferrite, no Widmanstätten or coarse ferrite
Hardness
Brinell or Rockwell test
Uniform across section, within specified range (e.g., 160–210 HB for 35K)
Decarburization depth
Microscope on etched cross‑section
≤ 0.05 mm or as per drawing/standard
Real‑world tip:
We once rejected a batch of normalized 40Cr bolts because the core showed mixed grains (ASTM 5–8) while the surface was fine. This indicated inadequate soaking time. After extending the hold time from 30 to 55 minutes, the structure became uniform. Always check both surface and center on a cross‑section.
How does normalizing relate to quenching and tempering? Can normalizing replace annealing?
Normalizing, quenching, tempering, and annealing serve different purposes. They are not interchangeable, but they can be sequenced.
Relationship in bolt production:
Normalizing → often performed before final quench and temper (as a preparatory step) or after hot working (forging/hot heading).
Quenching + Tempering (Q&T) → the final heat treatment that gives bolts their property class (8.8, 10.9, 12.9).
Annealing → typically used before cold heading to soften wire; rarely used as a final treatment for fasteners.
Can normalizing replace annealing?Generally no, for cold heading applications. Annealing (especially spheroidizing annealing) produces a soft, highly plastic structure ideal for cold forming. Normalized wire is harder and less ductile, leading to higher die wear and cracking risk during cold heading.
However, in two cases normalizing may be substituted:
For small‑diameter, low‑carbon steel bolts (e.g., 4.6 or 4.8 grade) where cold heading forces are low and final properties are not demanding.
For hot‑headed bolts that will be machined rather than cold formed – normalized material machines better than annealed.
Flowchart summary:
Hot‑rolled wire → (optional normalizing for structure refinement) → spheroidizing annealing → cold heading → thread rolling → quenching + tempering → finishing.Or: Forged blank → normalizing → machining → Q&T → finishing.
Real‑world caution:
A customer once tried to replace annealing with normalizing for 10B21 M10×1.25 cold‑headed nuts. The normalized wire had a hardness of HRB 92 versus HRB 78 for annealed wire. The forming dies cracked after only 5,000 pieces (normal die life 80,000 pieces). They quickly switched back to spheroidized‑annealed wire.
View More
Quenching for Bolts and Nuts – The Key to High Strength and How to Do It Right
2026-04-17
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IntroductionQuenching is the heart of producing high‑strength bolts and nuts. Without proper quenching, even the best alloy steel cannot reach property classes 8.8, 10.9, or 12.9. Yet quenching is also where many things can go wrong – cracking, distortion, soft spots, and uneven hardness. In this article, we answer five critical questions about quenching for fasteners, based on our shop floor experience, to help you understand what happens inside the furnace and the quench tank.
What is quenching, and why is it necessary for bolts and nuts?
Quenching is the rapid cooling of steel from a temperature above its austenitizing range (typically 830–880°C for most fastener steels) in a liquid or gas medium. The purpose is to transform the austenite into martensite – a hard, metastable microstructure that provides the strength required for high‑grade fasteners.
Without quenching, the steel would cool slowly and form softer structures like pearlite or bainite, which cannot achieve tensile strengths above about 800 MPa (116 ksi). Quenching is the essential first step in the quench‑and‑temper (Q&T) process that produces property classes 8.8, 10.9, and 12.9.
The basic sequence for high‑strength fasteners:
Cold‑headed or hot‑forged blank → austenitizing (heat) → quench (rapid cool) → martensite forms → temper (heat again at lower temperature) → final tempered martensite with specified strength and toughness.
Real‑world case:
A manufacturer of 10.9 grade flange bolts was getting inconsistent proof load results. We discovered that their quenching oil temperature varied from 40°C to 70°C between batches. After stabilizing oil temperature at 50±5°C and ensuring adequate agitation, the hardness variation across batches dropped from ±4 HRC to ±1.5 HRC, and all bolts passed proof load testing.
What are the common quench media for fastener quenching? How do I choose the right one?
The choice of quench medium depends on the steel’s hardenability (how easily it forms martensite), part geometry, and acceptable distortion levels. The table below compares the most common media:
Quench Medium
Cooling Severity (Relative)
Typical Steel Types
Advantages
Disadvantages
Water
Very high
Low‑carbon steels (e.g., 1018, 1022 for low‑grade bolts)
Very cheap, aggressive
High risk of cracking and distortion; not suitable for alloy steels
Polymer (PAG)
Medium to high (adjustable)
Medium‑carbon steels (35K, 40#, 45#)
Adjustable cooling rate; less cracking than water
Requires concentration control; more expensive than water
Quenching Oil (fast)
Medium
Alloy steels (40Cr, SCM435, 42CrMo, 10B21)
Balanced cooling; low distortion risk; good for production
Flammable; produces smoke; requires maintenance
Quenching Oil (martempering)
Low (slow)
Distortion‑sensitive parts (long bolts, thin‑wall nuts)
Minimizes distortion and cracking
Lower hardenability; may not fully harden thick sections
Salt bath (martempering)
Low to medium
Specialty fasteners requiring minimal distortion
Very uniform temperature; no scale
High cost; hazardous; not common for standard fasteners
Selection guidelines for common fastener grades:
Grade 8.8 (medium‑carbon steel, e.g., 35K, 40#): Water or polymer (polymer recommended for better control)
Grade 10.9 (alloy steel, e.g., 40Cr, SCM435): Fast quench oil (or polymer if oil not available)
Grade 12.9 (high‑alloy steel, e.g., SCM435, 42CrMo): Fast quench oil (martempering oil for very thick sections)
Case‑hardened bolts (10B21, 20MnTiB): Water or polymer after carburizing
Real‑world tip:
We once had a customer quenching SCM435 M16 bolts in water because they “wanted faster cooling.” The result: 15% cracked heads. Switching to a high‑speed quench oil (viscosity 22 cSt at 40°C, operating at 60°C) eliminated cracking while still achieving full martensite.
What quenching defects occur in bolts and nuts, and how do you prevent them?
Even with the right quench medium, defects can happen. Here are the most common defects in fastener quenching, their causes, and prevention methods:
Defect
Appearance / Detection
Root Cause
Prevention
Quench cracking
Visible cracks, often longitudinal on head or shank
Too aggressive quench; sharp corners; high carbon content
Use slower quench oil; add radii to design; reduce austenitizing temperature
Soft spots
Localized low hardness (check with Rockwell tester)
Vapor pockets during quenching; uneven agitation; scale on surface
Improve agitator design; increase quenchant flow; clean parts before heating
Distortion (bending)
Bolts are not straight; threads misaligned
Uneven cooling; part loading pattern; residual stresses from cold heading
Use martempering; hang long bolts vertically; normalize before Q&T
Insufficient hardness (core not fully martensitic)
Core hardness below specification
Material hardenability too low for section size; quench too slow
Choose steel with higher hardenability (e.g., SCM440 instead of 40Cr); use faster quench medium
Decarburization
Soft surface layer; lower fatigue life
Poor furnace atmosphere during austenitizing
Use controlled atmosphere (endothermic gas) or vacuum furnace
Quench staining / oxidation
Discolored surface (blue, brown)
Residual water in oil; parts entering quench too hot
Maintain oil quality; control transfer time from furnace to quench
Real‑world case (distortion):
A customer making M20×1.5 wheel nuts (grade 10.9, material SCM440) had 8% rejections due to thread distortion after quenching. The nuts were basket‑quenched (dropped into oil in a wire basket). We switched to single‑piece quenching using a conveyor with individual part drops, and installed a martempering oil at 180°C. Distortion dropped below 1%.
Inspection methods after quenching:
Hardness test: Rockwell C scale (HRC). Typical as‑quenched hardness for martensite: 50–55 HRC for medium‑carbon alloy steels.
Microstructure check: Must be >90% martensite (no pearlite or ferrite) in the core for full hardenability.
Crack detection: Magnetic particle inspection (MPI) or dye penetrant test for critical parts.
Straightness: Roller gauge or optical measurement.
How does quenching relate to tempering? Can I skip tempering after quenching?
No – never skip tempering. As‑quenched martensite is extremely hard but also very brittle. A bolt in the as‑quenched condition would snap under impact or even under high tightening torque. Tempering is a mandatory second step.
The relationship:
Process
Purpose
Typical Temperature
Resulting Structure
Mechanical Properties
Quenching
Form martensite
Rapid cool from 830–880°C
As‑quenched martensite
Very hard (50–55 HRC), zero ductility, high internal stress
Tempering
Reduce brittleness, relieve stress, adjust strength
400–650°C (depending on target grade)
Tempered martensite
Hardness 28–38 HRC (grade 8.8), 32–39 HRC (10.9), 39–44 HRC (12.9) + good toughness
Typical tempering temperatures for common fastener grades (after full quenching):
Property Class
Typical Steel
Tempering Temperature (°C)
Resulting Hardness (HRC)
8.8
35K, 40#, SCM435
550–600
28–34
10.9
40Cr, SCM435
500–550
32–39
12.9
SCM435, 42CrMo
420–480
39–44
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