quality Steel Nut Bolts & Steel Hex Bolt factory

IntroductionNormalizing 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.

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.

A Complete Guide to the Differences and Applications of DIN 931, DIN 933, and ISO 4014 Author: QBH Fastener Technical Team Background: Our core team members have over 10 years of experience in the fastener industry. We are well‑versed in international standards such as DIN, ISO, ASTM, and GB, and have provided selection support for clients in wind power, rail transportation, heavy machinery, and other sectors. Introduction In mechanical manufacturing, steel structure, and industrial assembly, choosing the right bolt standard is critical. Many buyers and engineers often confuse DIN 931 with DIN 933, or find the relationship between DIN and ISO standards perplexing. In this article, we address these frequently asked questions based on our years of field experience, offering professional and clear answers to help you avoid selection mistakes. What is DIN 931 and where is it mainly used? DIN 931 is officially titled “Hexagon head bolts – Partially threaded.” Its defining characteristic is that the shank is not fully threaded; it consists of a partially threaded section plus a plain shank (unthreaded portion) . Main applications: Connections subject to shear forces: The plain shank helps position the joint and bear transverse shear loads, preventing stress concentration on the threaded portion. Joining thick workpieces: When the total clamping thickness is large and the bolt needs to pass through thick plates, the plain shank provides better guidance. High‑precision mounting: Commonly used for mounting motor bases and positioning heavy machinery. Real‑world case: A port machinery client originally used fully threaded bolts for the slewing mechanism of a quayside crane. Frequent vibrations caused bolt fractures. After an on‑site inspection, we recommended switching to DIN 931 partially threaded bolts. By utilizing the plain shank to absorb shear forces, the failure rate dropped by over 90%. What is the difference between DIN 931 and DIN 933 (fully threaded)? Which one should I choose? This is the most common question. Both are hex head bolts, but they differ fundamentally in design and application.     Feature DIN 931 (Partially Threaded) DIN 933 (Fully Threaded) Thread form Partially threaded (plain shank under the head) Fully threaded (threads from under head to tip) Standard code DIN 931 (corresponds to ISO 4014) DIN 933 (corresponds to ISO 4017) Mechanical performance Plain shank offers higher shear strength, suitable for transverse loads Threaded section is more prone to stress concentration, suitable for pure axial tension Clamping thickness Suitable for applications with varying clamping thickness Suitable for applications with relatively constant clamping thickness Selection advice: If your connection is subject to vibration or shear forces, or requires precise positioning, choose DIN 931. For simple through‑bolting or when space is limited and a nut is required, DIN 933 is the more versatile option. What is the relationship between DIN 931 and ISO 4014? Are they interchangeable? ISO 4014 is the International Organization for Standardization (ISO) equivalent of DIN 931. For most sizes (especially the common range from M1.6 to M39), they are interchangeable in terms of mechanical properties, width across flats, and thread tolerances. However, one important exception: For specific sizes such as M10, M12, M14, and M22, there is a slight difference in the width across flats (wrench size) between the DIN and ISO standards. DIN 931: M10 typically has a width across flats of 17 mm. ISO 4014: M10 typically has a width across flats of 16 mm. The above differences are verified against DIN 931‑1:1987 and ISO 4014:2011. If you need the original standards, please contact us. How do I choose the property class for DIN 931? What’s the difference between 8.8 and 10.9? DIN 931 is commonly available in property classes 8.8, 10.9, and 12.9. Grade 8.8: The entry‑level high‑strength grade. Suitable for general steel structures and ordinary mechanical assembly. It offers the best cost‑effectiveness and is the most widely used. Grade 10.9 / 12.9: Ultra‑high‑strength grades. Suitable for critical applications demanding high preload, such as automotive, heavy machinery, and wind power equipment. Note: High‑strength bolts (grade 10.9 and above) require attention to hydrogen embrittlement prevention during surface finishing (e.g., Dacromet or hot‑dip galvanizing). If your application is in coastal or corrosive environments, please let us know the required salt spray test duration. What surface finishes are available for DIN 931? How do I prevent rust? We recommend the following common surface treatments based on the application environment: Plain / Black oxide: For indoor, dry environments. Low corrosion resistance but the most economical. Usually coated with anti‑rust oil. Zinc plating (blue‑white or yellow): The most common medium‑level corrosion protection. Good appearance and meets standard industrial requirements. Hot‑dip galvanizing: A thick coating with high corrosion resistance, suitable for outdoor use and power transmission towers. Note: Hot‑dip galvanizing can affect thread fit; thread size allowances (e.g., tapping after galvanizing) are typically required. Dacromet (zinc‑aluminum coating): High corrosion resistance (salt spray tests can exceed 1000 hours) with no risk of hydrogen embrittlement. It is the preferred choice for automotive and high‑end equipment. About Us & Quality Assurance QBH Fastener specializes in the R&D and supply of high‑strength fasteners. We are ISO 9001:2015 certified and manufacture products strictly in accordance with DIN, ISO, ASTM, GB, and other standards. Every batch comes with material certificates and inspection reports for full traceability. Technical team: Average 10+ years of industry experience; free selection consulting available Testing capabilities: Equipped with spectrometers, hardness testers, salt spray chambers, and more Success stories: Serving clients in wind power, construction machinery, rail transportation, and beyond

Hot-dip galvanized (HDG) bolts are the most common type of corrosion-protected bolt for one overarching reason: they offer the best balance of high corrosion resistance, durability, and cost-effectiveness for a wide range of applications. Superior Corrosion Protection is the primary reason. The hot-dip process creates a robust, multi-layered coating that is metallurgically bonded to the steel bolt. The zinc coating is significantly thicker (typically 50-100 µm or more) than what is achieved with electroplating (e.g., zinc-plated bolts, which are typically 5-25 µm). More zinc means more sacrificial material to protect the underlying steel. Zinc is more electrochemically active than steel. This means if the coating is scratched or damaged, the surrounding zinc will sacrificially corrode to protect the exposed steel, preventing rust from forming. This is a huge advantage over barrier-only coatings like paint. The hot-dip process creates a coating that is integral to the bolt itself. The outer layer of pure zinc and the inner layers of zinc-iron alloys are extremely hard and durable. They can withstand rough handling, shipping, and installation without the coating being easily chipped or scratched off, which is a common issue with thinner electroplated coatings. During the galvanizing process, the bolt is fully immersed in molten zinc. This ensures complete coverage, including threads, the underside of the head, and any recesses. This is a critical advantage over methods like spray galvanizing, which can miss hidden areas and lead to premature failure. While not the cheapest option (that would be plain or zinc-plated bolts), HDG bolts provide the most protection per dollar for demanding environments. Long Lifecycle: Their long service life (20 to 50+ years in many atmospheres) drastically reduces maintenance, repair, and replacement costs over the lifespan of a structure. They are vastly more affordable than stainless steel bolts for applications where stainless's specific properties (e.g., non-magnetic, high chemical resistance) are not required.

    Hexagonal bolts, also known as hex bolts, are popular due to their unique hexagonal head design. The six-sided shape provides multiple angles from which to apply torque, making them easier to grip and turn during installation or removal. This design also helps prevent slippage and allows for precise tightening.     Hexagonal bolts are known for their durability and strength. Their design allows for even distribution of force, reducing the risk of bolt failure under stress. When paired with the appropriate nut and washer.                                                                                                                                                                                --------- From Jiaxing City Qunbang Hardware Co, Ltd

     In March 2019, our company visited BOSSARD in France after attending the fastener exhibition in Stuttgart, Germany. We were warmly received by the leaders of the company. They introduced BOSSARD's development history, management mode, procurement mode, inspection mode and so on to us. And we visited the company's automated storage, laboratory, office area, sample area and so on. Which lefted us a very deep impact.          We believe that we can bring our company a qualitative leap through the cooperation with the top European fastener enterprises. Not only in the quality of sublimation, but also in the management mode.           Project Name：DIN931 CLASS 6.8  Cr3+ Size:M8X58 Quantity: 2 containers Marking:QBH 6.8 Drawing:                    

Since 2016, we have successively provided DIN557 hot-dip galvanized square nuts for Bangladesh Army factories, which are mainly used in power system. In 2017, we were honored to visit the customer's factory, which laid a solid foundation for future cooperation.   Metric DIN 557 regular pattern square nuts are four sided nuts. Their geometry provides a greater surface area to apply higher torque when tightening and also a greater surface are in contact with the part being fastened, thereby increasing the resistance to loosening.