Generally speaking, the factors affecting the quality of cold heading steel can be summarized as material plasticity, material matrix continuity, material structure continuity and material surface quality, etc. According to the quality inspection of cold heading steel, it was found that the factors affecting the quality of cold heading steel mainly include the following four aspects: chemical composition of steel, surface defects of billet, equipment adjustment, grain size and rolling process parameters.
(1)Influence of chemical composition: Impurity elements such as sulfur and phosphorus in steel directly affect the cold heading performance of cold heading steel. During the smelting process of cold heading steel, corresponding impurities should be removed for different steel types. Certain non-metallic inclusions destroy the continuity of the steel matrix and often become the starting point of cracks in cold heading steel under the action of static and dynamic loads. Therefore, non-metallic inclusions in steel should be reduced as much as possible and treated (such as calcification, etc.) to reduce their harm in steel.
(2) Influence of blank surface defects: Blank surface defects are the source of cracks that cause cold upsetting cracks. The main forms include blank surface heavy skin, cracks, sharp excessiveness, etc. During processing, the presence of cracks causes stress concentration and complex stress states, leading to crack expansion and eventually cold upsetting cracking. Therefore, the selection of high-quality steel billets is a prerequisite for improving the quality of cold heading steel. Severe temperature unevenness during the rolling process can also cause cracking in the product.
(3) The impact of equipment adjustment during the rolling process on the performance of cold heading steel: The formulation of various rolling procedures during the production process is the main factor affecting the cold heading performance of the product, such as the adjustment of reduction, tension, etc., and the production of spare parts. Assembly and adjustment. If the rolling production is improperly adjusted, the product will be folded or scratched during the rolling process, damaging the surface of the product and forming a source of cracks. Therefore, formulating reasonable rolling procedures is the key to improving the quality of cold heading steel.
(4) The influence of grain size: Grain size is one of the standards to measure whether cold heading steel can achieve certain comprehensive properties. The finer the grains, the smaller the chance of cracking caused by stress concentration inside them, which is conducive to the improvement of properties such as cold upsetting. Fine-grained steel can withstand large deformations, has large elongation, area reduction, good plasticity, and high toughness and strength. Therefore, it is required that during the rolling process, the austenitizing temperature should not be too high and the holding time should not be too long.
(5) Influence of rolling process parameters. The structure of cold heading steel is ferrite + pearlite. The key to controlling cooling is to make the austenite decompose at a moderate temperature and make the decomposition and transformation time longer, so as to obtain moderate ferrite grains and a small amount of Pearlite can improve the strength of cold heading steel without reducing the plasticity index, and obtain better comprehensive mechanical properties.

1.Chemical composition
C: The carbon content increases, the steel hardness increases, the plasticity decreases, and the cold heading performance deteriorates. Medium carbon cold heading steel must be annealed.
Si: Steel with high silicon content is not easy to be cold deformed. Low carbon cold heading steel has w[Si] ≤ 0.03%, and medium carbon cold heading steel has w[Si] ≤ 0.20%.
S: Sulfur will deteriorate the thermal processing performance and should be controlled at a low content.
P: Phosphorus causes cold brittleness of steel, increases strength, hardness, and plasticity. The content should be controlled to a low level.
Al: Aluminum refines the grain of steel and improves plasticity. However, if the content is too high, it will easily generate alumina inclusions. It can be controlled at 0.02% to 0.06%.
Cu, Sn: Copper and tin are harmful to cold heading performance.
2. Gases and inclusions in steel
[O] in steel easily forms oxide inclusions, which reduces the plasticity of the steel and becomes the origin of cracks. [H] reduces the plasticity of steel and increases its brittleness. [N] increases the strength of steel, increases hardness, and reduces plasticity and toughness.
The presence of oxide inclusions and sulfide inclusions significantly reduces the deformation ability.
3.Surface quality
Factors affecting surface quality include:
(1) Surface defects and subcutaneous bubbles in the cast slab;
(2) Cracks caused by the rolling process;
(3) Scratches on the surface of rolled materials.

Answers

• 
  What are the differences in thickness and production process between medium and thick steel plates and hot rolled steel plates? 20/12/2024 16:13:18
• 
  What are the differences between PE lining and plastic coating? 04/12/2024 17:18:59
• 
  What are the acceptance criteria for hot-dip galvanized square tubes? 03/12/2024 05:26:54
• 
  How to distinguish between 304 and 201 stainless steel plates? 29/11/2024 17:07:20
• 
  Stainless steel wire rope or galvanized steel wire rope, which one is stronger? 27/11/2024 15:03:48