Common surface defects of wire rod and steel bar and treatment methods
Common surface defects of wire rod and steel bar
Table of Contents
1.1 defects of raw materials
1.1.1 shrinkage cavity – residual shrinkage cavity in steel and the resulting defects.
(1) shrinkage during pouring.
(2) there are oxides and slag.
1.1.2 lamination — defect of wire rod longitudinally divided into two or more layers.
(1) when pouring ingot, the upper part forms blister or a large number of non-metallic impurities gather, so it can not be welded when rolling billet.
(2) serious segregation of chemical composition.
1.1.3 slag inclusion – the inclusion on the surface of wire rod has refractory inclusion inside.
The reasons are as follows:
(1) the refractory is attached to the surface of ingot and slag is involved in molten steel during casting.
(2) in the process of billet wind heating, refractory materials or other foreign matters on the top of the furnace are rolled on the surface of the wire rod.
1.2.1 longitudinal crack – a relatively deep continuous linear defect along the rolling direction.
The reasons are as follows:
(1) when the billet is heated, micro pores, bubbles and thermal strain aging are formed on the surface.
1.2.2 scaly cracking (overburning) – there are relatively fine cracks on the surface or scaly cracks of adult fish.
(1) billet overburning.
(2) poor composition and poor deoxidation.
1.3 rolling defects
1.3.1 ear – continuous strip like protrusion on the surface of wire rod along the rolling direction.
(1) rolling is caused by overfilling in pass.
(2) the inlet guide wheel is burnt or the opening is too large, and the clamping is unstable, forming inverted steel.
(3) the inlet device deviates from the rolling center line.
1.3.2 folding: the surface of wire rod is straight or curved along the rolling direction, and the cross section is small angle.
(1) caused by the ear of the previous pass.
(2) the deep groove left by improper treatment of defects on the billet may also form folding during rolling.
1.3.3 scratch — scratch caused by poor installation of pass and guide device and the finished product passing through defective equipment.
(1) defects caused by guide device and conveying device.
(2) it is caused when the wire rod passes through the water tank, pinch roll, spinning machine, uncoiling conveyor, coiler and baler.
1.3.4 bump — forming periodic bump along rolling direction.
Cause: the rolling groove burst.
1.3.5 orange peel — the surface of the rolled piece is orange peel shaped and uneven.
Cause: poor pass.
1.4 dimensional defects
1.4.1 smaller transverse and longitudinal ribs – continuous smaller phenomenon along the rolling direction.
Reason: small incoming material and insufficient filling of pass.
1.4.2 horizontal dimension exceeding standard – continuous exceeding standard phenomenon formed along the binding direction.
(1) large amount of materials.
(2) there is steel pouring at the inlet.
1.4.3 the out of roundness does not meet the requirements — the out of roundness size exceeds the standard range.
(1) poor pass design or poor turning.
(2) uneven wear of pass.
How to deal with defective products
2.1 routine inspection items of wire rod
According to the relevant standards and regulations of hot rolling wire rod production in China, the inspection contents are different with different steel grades and uses. However, there are six routine inspection items as follows:
2.1.1 overall dimensions. A 300 mm long sample is taken from each head and tail of the coil, and the label and sequence number are marked to distinguish the head and tail. Then the defects such as ears, folds, surface inclusions, scratches, mechanical scars, pitting, etc. are checked with a low power magnifying glass, and the diameter deviation and out of roundness of the wire are checked.
2.1.2 flattening test. The purpose of flattening test is to check the surface crack of wire rod. The sample for flattening test shall account for more than 25% of the wire rod book, and the wire rod of high grade steel shall be sampled from each disc. If surface cracks are found, take samples at the other end of the wire rod for re inspection. When the defect cannot be determined, the cross-sectional sample should be taken for high-power inspection.
2.1.3 carbon content comparison carbon content comparison is to check whether the carbon content of wire rod is qualified. Take a sample from both ends of each disc of wire rod, and compare the carbon content with the rapid carbon content comparator (the rapid comparator can measure the difference between the sample carbon content and the standard carbon content within ± 0.05%, but can not measure the absolute value of carbon content), and then decide whether to batch. In case of dispute, a rapid analysis is carried out to determine the carbon content.
2.1.4 rapid carbon analysis is determined according to the requirements of the final product. Several samples of each batch of wire rod shall be taken for carbon content inspection, but at least each batch of wire rod shall be sampled at either end of the first three discs and the last three discs for rapid analysis. If the analysis results exceed the specified value, the expanded sampling shall be inspected according to the “dispute settlement inspection rules”. The so-called “dispute settlement inspection rule” refers to a rule used to guide the wire quality inspection when the supplier and the demander dispute the conventional inspection conclusion. Some companies at home and abroad have their own “dispute settlement inspection rules”.
2.1.5 mechanical property test high carbon steel wire rod shall be sampled from at least 20% of coils in each batch for tensile test, and its reduction of area shall be recorded at the same time. Most high carbon steel wire rod for direct drawing shall have the minimum tensile strength corresponding to the actual content of carbon and manganese.
Most mild steel wire rods are required to limit the highest tensile strength. Both high carbon steel and low carbon steel wire rod are expected to have large reduction of area. For some structures, the stress-strain curve should be used to record the stress-strain curve.
2.1.6 whether high magnification inspection is conducted and how many samples are taken from the wire rod end depend on the requirements of the final product. For some steel grades, such as raw materials for nailing, barbed wire, general steel bars, spokes, low-grade steel bars, springs for furniture and other steel wires, generally no more than 20% of the samples are taken for high-power inspection; for wire rods of higher steel grades, such as raw materials for manufacturing high-strength springs and high-strength steel ropes, the samples are generally within 50%; for raw materials for cold heading and cold forging, the wire rods must be 100% sampled for high-power inspection.
According to the product technical requirements, the high-power inspection items include:
- Depth and degree of surface decarburization;
- Length and depth of surface rolling defects;
- Shrinkage cavity;
- Central segregation of carbon and sulfur;
- Distribution state of ferrite;
- Distribution state of pearlite;
- Other microstructure defects;
- Grain size; surface roughness;
- Inclusion content.
2.2 how to deal with defective products
2.2.1 if the defective products are found, the corresponding products shall be inspected separately.
2.2.3 inform the relevant operation desk of the workshop or the on duty dispatcher.
2.2.4 call relevant leaders.
2.2.5 according to the requirements of relevant regulations, the defective products shall be further inspected, the qualified products shall be put into storage, and the unqualified products shall be blocked.
2.2.6 the treatment methods for defective products include: repair, grading and scrap.
Source: Network Arrangement – China Metal Flanges Manufacturer – Yaang Pipe Industry (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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